Journal articles on the topic 'Observations par satellite'
To see the other types of publications on this topic, follow the link: Observations par satellite.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Observations par satellite.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Joiner, Joanna, Yasuko Yoshida, Philipp Köehler, Petya Campbell, Christian Frankenberg, Christiaan van der Tol, Peiqi Yang, Nicholas Parazoo, Luis Guanter, and Ying Sun. "Systematic Orbital Geometry-Dependent Variations in Satellite Solar-Induced Fluorescence (SIF) Retrievals." Remote Sensing 12, no. 15 (July 22, 2020): 2346. http://dx.doi.org/10.3390/rs12152346.
Abstract:
While solar-induced fluorescence (SIF) shows promise as a remotely-sensed measurement directly related to photosynthesis, interpretation and validation of satellite-based SIF retrievals remains a challenge. SIF is influenced by the fraction of absorbed photosynthetically-active radiation at the canopy level that depends upon illumination geometry as well as the escape of SIF through the canopy that depends upon the viewing geometry. Several approaches to estimate the effects of sun-sensor geometry on satellite-based SIF have been proposed, and some have been implemented, most relying upon satellite reflectance measurements and/or other ancillary data sets. These approaches, designed to ultimately estimate intrinsic or physiological components of SIF related to photosynthesis, have not generally been applied globally to satellite measurements. Here, we examine in detail how SIF and related reflectance-based indices from wide swath polar orbiting satellites in low Earth orbit vary systematically due to the host satellite orbital characteristics. We compare SIF and reflectance-based parameters from the Global Ozone Mapping Experiment 2 (GOME-2) on the MetOp-B platform and from the TROPOspheric Monitoring Instrument (TROPOMI) on the Sentinel 5 Precursor satellite with a focus on high northern latitudes in summer where observations at similar geometries and local times occur. We show that GOME-2 and TROPOMI SIF observations agree nearly to within estimated uncertainties when they are compared at similar observing geometries. We show that the cross-track dependence of SIF normalized by PAR and related reflectance-based indices are highly correlated for dense canopies, but diverge substantially as the vegetation within a field-of-view becomes more sparse. This has implications for approaches that utilize reflectance measurements to help account for SIF geometrical dependences in satellite measurements. To further help interpret the GOME-2 and TROPOMI SIF observations, we simulated cross-track dependences of PAR normalized SIF and reflectance-based indices with the one dimensional Soil-Canopy Observation Photosynthesis and Energy fluxes (SCOPE) canopy radiative transfer model at sun–satellite geometries that occur across the wide swaths of these instruments and examine the geometrical dependencies of the various components (e.g., fraction of absorbed PAR, SIF yield, and escape of SIF from the canopy) of the observed SIF signal. The simulations show that most of the cross-track variations in SIF result from the escape of SIF through the scattering canopy and not the illumination.
2
Frouin, Robert, and Rachel T. Pinker. "Estimating Photosynthetically Active Radiation (PAR) at the earth's surface from satellite observations." Remote Sensing of Environment 51, no. 1 (January 1995): 98–107. http://dx.doi.org/10.1016/0034-4257(94)00068-x.
3
Dorf, M., H. Bösch, A. Butz, C. Camy-Peyret, M. P. Chipperfield, A. Engel, F. Goutail, et al. "Balloon-borne stratospheric BrO measurements: comparison with Envisat/SCIAMACHY BrO limb profiles." Atmospheric Chemistry and Physics 6, no. 9 (June 29, 2006): 2483–501. http://dx.doi.org/10.5194/acp-6-2483-2006.
Abstract:
Abstract. For the first time, results of four stratospheric BrO profiling instruments, are presented and compared with reference to the SLIMCAT 3-dimensional chemical transport model (3-D CTM). Model calculations are used to infer a BrO profile validation set, measured by 3 different balloon sensors, for the new Envisat/SCIAMACHY (ENVIronment SATellite/SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) satellite instrument. The balloon observations include (a) balloon-borne in situ resonance fluorescence detection of BrO (Triple), (b) balloon-borne solar occultation DOAS measurements (Differential Optical Absorption Spectroscopy) of BrO in the UV, and (c) BrO profiling from the solar occultation SAOZ (Systeme d'Analyse par Observation Zenithale) balloon instrument. Since stratospheric BrO is subject to considerable diurnal variation and none of the measurements are performed close enough in time and space for a direct comparison, all balloon observations are considered with reference to outputs from the 3-D CTM. The referencing is performed by forward and backward air mass trajectory calculations to match the balloon with the satellite observations. The diurnal variation of BrO is considered by 1-D photochemical model calculation along the trajectories. The 1-D photochemical model is initialised with output data of the 3-D model with additional constraints on the vertical transport, the total amount and photochemistry of stratospheric bromine as given by the various balloon observations. Total [Bry]=(20.1±2.5) pptv obtained from DOAS BrO observations at mid-latitudes in 2003, serves as an upper limit of the comparison. Most of the balloon observations agree with the photochemical model predictions within their given error estimates. First retrieval exercises of BrO limb profiling from the SCIAMACHY satellite instrument on average agree to around 20% with the photochemically-corrected balloon observations of the remote sensing instruments (SAOZ and DOAS). An exception is the in situ Triple profile, in which the balloon and satellite data mostly does not agree within the given errors. In general, the satellite measurements show systematically higher values below 25 km than the balloon data and a change in profile shape above about 25 km.
4
Dorf, M., H. Bösch, A. Butz, C. Camy-Peyret, M. P. Chipperfield, A. Engel, F. Goutail, et al. "Balloon-borne stratospheric BrO measurements: comparison with Envisat/SCIAMACHY BrO limb profiles." Atmospheric Chemistry and Physics Discussions 5, no. 6 (December 19, 2005): 13011–52. http://dx.doi.org/10.5194/acpd-5-13011-2005.
Abstract:
Abstract. For the first time, results of all four existing stratospheric BrO profiling instruments, are presented and compared with reference to the SLIMCAT 3-dimensional chemical transport model (3-D CTM). Model calculations are used to infer a BrO profile validation set, measured by 3 different balloon sensors, for the new Envisat/SCIAMACHY (ENVIronment SATellite/SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) satellite instrument. The balloon observations include (a) balloon-borne in situ resonance fluorescence detection of BrO, (b) balloon-borne solar occultation DOAS measurements (Differential Optical Absorption Spectroscopy) of BrO in the UV, and (c) BrO profiling from the solar occultation SAOZ (Systeme d'Analyse par Observation Zenithale) balloon instrument. Since stratospheric BrO is subject to considerable diurnal variation and none of the measurements are performed close enough in time and space for a direct comparison, all balloon observations are considered with reference to outputs from the 3-D CTM. The referencing is performed by forward and backward air mass trajectory calculations to match the balloon with the satellite observations. The diurnal variation of BrO is considered by 1-D photochemical model calculation along the trajectories. The 1-D photochemical model is initialised with output data of the 3-D model with additional constraints on the vertical transport, the total amount and photochemistry of stratospheric bromine as given by the various balloon observations. Total [Bry]=(20.1±2.8)pptv obtained from DOAS BrO observations at mid-latitudes in 2003, serves as an upper limit of the comparison. Most of the balloon observations agree with the photochemical model predictions within their given error estimates. First retrieval exercises of BrO limb profiling from the SCIAMACHY satellite instrument agree to <±50% with the photochemically-corrected balloon observations, and tend to show less agreement below 20 km.
5
Singh, Rakesh Kumar, Anna Vader, Christopher J. Mundy, Janne E. Søreide, Katrin Iken, Kenneth H. Dunton, Laura Castro de la Guardia, Mikael K. Sejr, and Simon Bélanger. "Satellite-Derived Photosynthetically Available Radiation at the Coastal Arctic Seafloor." Remote Sensing 14, no. 20 (October 17, 2022): 5180. http://dx.doi.org/10.3390/rs14205180.
Abstract:
Climate change has affected the Arctic Ocean (AO) and its marginal seas significantly. The reduction of sea ice in the Arctic region has altered the magnitude of photosynthetically available radiation (PAR) entering the water column, impacting primary productivity. Increasing cloudiness in the atmosphere and rising turbidity in the coastal waters of the Arctic region are considered as the major factors that counteract the effect of reduced sea ice on underwater PAR. Additionally, extreme solar zenith angles and sea-ice cover in the AO increase the complexity of retrieving PAR. In this study, a PAR algorithm based on radiative transfer in the atmosphere and satellite observations is implemented to evaluate the effect of these factors on PAR in the coastal AO. To improve the performance of the algorithm, a flag is defined to identify pixels containing open-water, sea-ice or cloud. The use of flag enabled selective application of algorithms to compute the input parameters for the PAR algorithm. The PAR algorithm is validated using in situ measurements from various coastal sites in the Arctic and sub-Arctic seas. The algorithm estimated daily integrated PAR above the sea surface with an uncertainty of 19% in summer. The uncertainty increased to 24% when the algorithm was applied year-round. The PAR values at the seafloor were estimated with an uncertainty of 76%, with 36% of the samples under sea ice and/or cloud cover. The robust performance of the PAR algorithm in the pan-Arctic region throughout the year will help to effectively study the temporal and spatial variability of PAR in the Arctic coastal waters. The calculated PAR data are used to quantify the changing trend in PAR at the seafloor in the coastal AO with depth < 100 m using MODIS-Aqua data from 2003 to 2020. The general trends calculated using the pixels with average PAR > 0.415 mol m−2day−1 at the seafloor during summer indicate that the annual average of PAR entering the water column in the coastal AO between 2003 and 2020 increased by 23%. Concurrently, due to increased turbidity, the attenuation in the water column increased by 22%. The surge in incident PAR in the water column due to retreating sea ice first led to increased PAR observed at the seafloor (∼12% between 2003 and 2014). However, in the last decade, the rapid increase in light attenuation of the water column has restricted the increase in average annual PAR reaching the bottom in the coastal AO.
6
Wang, Dongdong, Shunlin Liang, Ronggao Liu, and Tao Zheng. "Estimation of daily-integrated PAR from sparse satellite observations: comparison of temporal scaling methods." International Journal of Remote Sensing 31, no. 6 (March 26, 2010): 1661–77. http://dx.doi.org/10.1080/01431160903475407.
7
Lange, Johannes U., Frank C. van den Bosch, Andrew R. Zentner, Kuan Wang, and Antonio S. Villarreal. "Updated results on the galaxy–halo connection from satellite kinematics in SDSS." Monthly Notices of the Royal Astronomical Society 487, no. 3 (June 7, 2019): 3112–29. http://dx.doi.org/10.1093/mnras/stz1466.
Abstract:
ABSTRACT We present new results on the relationship between central galaxies and dark matter haloes inferred from observations of galaxy abundances and satellite kinematics in the Sloan Digital Sky Survey (SDSS) DR7. We employ an updated analysis framework that includes detailed mock catalogues to model observational effects in SDSS. Our results constrain the colour-dependent conditional luminosity function of dark matter haloes, as well as the radial profile of satellite galaxies. Confirming previous results, we find that red central galaxies live in more massive haloes than blue galaxies at a fixed luminosity. Additionally, our results suggest that satellite galaxies have a radial profile less centrally concentrated than dark matter but not as cored as resolved subhaloes in dark-matter-only simulations. Compared to previous works using satellite kinematics by More et al., we find much more competitive constraints on the galaxy–halo connection, on par with those derived from a combination of galaxy clustering and galaxy–galaxy lensing. This improvement stems from also modelling the abundance of galaxies as well as a larger sample size and more realistic observational uncertainties. We compare our results on the galaxy–halo connection to other studies using galaxy clustering and group catalogues, showing a reasonable agreement between these different techniques. We discuss future applications of satellite kinematics in the context of constraining cosmology and the relationship between galaxies and dark matter haloes.
8
Zheng, Tao, Shunlin Liang, and Kaicun Wang. "Estimation of Incident Photosynthetically Active Radiation from GOES Visible Imagery." Journal of Applied Meteorology and Climatology 47, no. 3 (March 1, 2008): 853–68. http://dx.doi.org/10.1175/2007jamc1475.1.
Abstract:
Abstract Incident photosynthetically active radiation (PAR) is an important parameter for terrestrial ecosystem models. Because of its high temporal resolution, the Geostationary Operational Environmental Satellite (GOES) observations are very suited to catch the diurnal variation of PAR. In this paper, a new method is developed to derive PAR using GOES data. What makes this new method distinct from the existing method is that it does not need external knowledge of atmospheric conditions. The new method retrieves both atmospheric and surface conditions using only at-sensor radiance through interpolation of time series of observations. Validations against ground measurement are carried out at four “FLUXNET” sites. The values of RMSE of estimated and ground-measured instantaneous PAR at the four sites are 130.71, 131.44, 141.16, and 190.22 μmol m−2 s−1, respectively. At the four validation sites, the RMSE as the percentage of estimated mean PAR value are 9.52%, 13.01%, 13.92%, and 24.09%, respectively; the biases are −101.54, 16.56, 11.09, and 53.64 μmol m−2 s−1, respectively. The independence of external atmospheric information enables this method to be applicable to many situations in which external atmospheric information is not available. In addition, topographic impacts on surface PAR are examined at the 1-km resolution at which PAR is retrieved using the GOES visible band data.
9
Hendrick, F., B. Barret, M. Van Roozendael, H. Boesch, A. Butz, M. De Mazière, F. Goutail, et al. "Retrieval of nitrogen dioxide stratospheric profiles from ground-based zenith-sky UV-visible observations: validation of the technique through correlative comparisons." Atmospheric Chemistry and Physics Discussions 4, no. 3 (May 25, 2004): 2867–904. http://dx.doi.org/10.5194/acpd-4-2867-2004.
Abstract:
Abstract. A retrieval algorithm based on the Optimal Estimation Method (OEM) has been developed in order to provide vertical distributions of NO2 in the stratosphere from ground-based (GB) zenith-sky UV-visible observations. It has been applied to observational data sets from the NDSC (Network for Detection of Stratospheric Change) stations of Harestua (60° N, 10° E) and Andøya (69.3° N, 16.1° E) in Norway. The information content and retrieval errors have been analyzed following a formalism used for characterizing ozone profiles retrieved from solar infrared absorption spectra. In order to validate the technique, the retrieved NO2 vertical profiles and columns have been compared to correlative balloon and satellite observations. Such extensive validation of the profile and column retrievals was not reported in previously published work on the profiling from GB UV-visible measurements. A good agreement – generally better than 25% – has been found with the SAOZ (Système d'Analyse par Observations Zénithales) and DOAS (Differential Optical Absorption Spectroscopy) balloon data. A similar agreement has been reached with correlative satellite data from HALogen Occultation Experiment (HALOE) and Polar Ozone and Aerosol Measurement (POAM) III instruments above 25 km of altitude. Below 25 km, a systematic overestimation of our retrieved profiles – by up to 50% in some cases – has been observed by both HALOE and POAM III, pointing out the limitation of the satellite solar occultation technique at these altitudes. We have concluded that our study strengthens our confidence in the reliability of the retrieval of vertical distribution information from GB UV-visible observations and offers new perspectives in the use of GB UV-visible network data for validation purposes.
10
Hendrick, F., B. Barret, M. Van Roozendael, H. Boesch, A. Butz, M. De Mazière, F. Goutail, et al. "Retrieval of nitrogen dioxide stratospheric profiles from ground-based zenith-sky UV-visible observations: validation of the technique through correlative comparisons." Atmospheric Chemistry and Physics 4, no. 8 (October 21, 2004): 2091–106. http://dx.doi.org/10.5194/acp-4-2091-2004.
Abstract:
Abstract. A retrieval algorithm based on the Optimal Estimation Method (OEM) has been developed in order to provide vertical distributions of NO2 in the stratosphere from ground-based (GB) zenith-sky UV-visible observations. It has been applied to observational data sets from the NDSC (Network for Detection of Stratospheric Change) stations of Harestua (60° N, 10° E) and Andøya (69° N, 16° E) in Norway. The information content and retrieval errors have been analyzed following a formalism used for characterizing ozone profiles retrieved from solar infrared absorption spectra. In order to validate the technique, the retrieved NO2 vertical profiles and columns have been compared to correlative balloon and satellite observations. Such extensive validation of the profile and column retrievals was not reported in previously published work on the profiling from GB UV-visible measurements. A good agreement - generally better than 25% - has been found with the SAOZ (Système d'Analyse par Observations Zénithales) and DOAS (Differential Optical Absorption Spectroscopy) balloons. A similar agreement has been reached with correlative satellite data from the HALogen Occultation Experiment (HALOE) and Polar Ozone and Aerosol Measurement (POAM) III instruments above 25km of altitude. Below 25km, a systematic underestimation - by up to 40% in some cases - of both HALOE and POAM III profiles by our GB profile retrievals has been observed, pointing out more likely a limitation of both satellite instruments at these altitudes. We have concluded that our study strengthens our confidence in the reliability of the retrieval of vertical distribution information from GB UV-visible observations and offers new perspectives in the use of GB UV-visible network data for validation purposes.
11
Brown, Meredith G. L., Sergii Skakun, Tao He, and Shunlin Liang. "Intercomparison of Machine-Learning Methods for Estimating Surface Shortwave and Photosynthetically Active Radiation." Remote Sensing 12, no. 3 (January 23, 2020): 372. http://dx.doi.org/10.3390/rs12030372.
Abstract:
Satellite-derived estimates of downward surface shortwave radiation (SSR) and photosynthetically active radiation (PAR) are a part of the surface radiation budget, an essential climate variable (ECV) required by climate and vegetation models. Ground measurements are insufficient for generating long-term, global measurements of surface radiation, primarily due to spatial limitations; however, remotely sensed Earth observations offer freely available, multi-day, global coverage of radiance that can be used to derive SSR and PAR estimates. Satellite-derived SSR and PAR estimates are generated by computing the radiative transfer inversion of top-of-atmosphere (TOA) measurements, and require ancillary data on the atmospheric condition. To reduce computational costs, often the radiative transfer calculations are done offline and large look-up tables (LUTs) are generated to derive estimates more quickly. Recently studies have begun exploring the use of machine-learning techniques, such as neural networks, to try to improve computational efficiency. Here, nine machine-learning methods were tested to model SSR and PAR using minimal input data from the Moderate Resolution Imaging Spectrometer (MODIS) observations at 1 km spatial resolution. The aim was to reduce the input data requirements to create the most robust model possible. The bootstrap aggregated decision tree (Bagged Tree), Gaussian Process Regression, and Neural Network yielded the best results with minimal training data requirements: an R 2 of 0.77, 0.78, and 0.78 respectively, a bias of 0 ± 6, 0 ± 6, and 0 ± 5 W / m 2 , and an RMSE of 140 ± 7, 135 ± 8, and 138 ± 7 W / m 2 , respectively, for all-sky condition total surface shortwave radiation and viewing angles less than 55°. Viewing angles above 55° were excluded because the residual analysis showed exponential error growth above 55°. A simple, robust model for estimating SSR and PAR using machine-learning methods is useful for a variety of climate system studies. Future studies may focus on developing high temporal resolution direct and diffuse estimates of SSR and PAR as most current models estimate only total SSR or PAR.
12
Tang, Wenjun, Jun Qin, Kun Yang, Yaozhi Jiang, and Weihao Pan. "Mapping long-term and high-resolution global gridded photosynthetically active radiation using the ISCCP H-series cloud product and reanalysis data." Earth System Science Data 14, no. 4 (April 27, 2022): 2007–19. http://dx.doi.org/10.5194/essd-14-2007-2022.
Abstract:
Abstract. Photosynthetically active radiation (PAR) is a fundamental physiological variable for research in the ecological, agricultural, and global change fields. In this study, we produced a 35-year (1984–2018) high-resolution (3 h, 10 km) global gridded PAR dataset using an effective physical-based model. The main inputs of the model were the latest International Satellite Cloud Climatology Project (ISCCP) H-series cloud products, MERRA-2 aerosol data, ERA5 surface routine variables, and MODIS and CLARRA-2 albedo products. Our gridded PAR product was evaluated against surface observations measured at 7 experimental stations of the SURFace RADiation budget network (SURFRAD), 42 experimental stations of the National Ecological Observatory Network (NEON), and 38 experimental stations of the Chinese Ecosystem Research Network (CERN). Instantaneous PAR was validated against SURFRAD and NEON data; mean bias errors (MBE) and root mean square errors (RMSE) were, on average 5.8 and 44.9 W m−2, respectively, and the correlation coefficient (R) was 0.94 at the 10 km scale. When upscaled to 30 km, the errors were markedly reduced. Daily PAR was validated against SURFRAD, NEON, and CERN data, and the RMSEs were 13.2, 13.1, and 19.6 W m−2, respectively, at the 10 km scale. The RMSEs were slightly reduced when upscaled to 30 km. Compared with the well-known global satellite-based PAR product of the Earth's Radiant Energy System (CERES), our PAR product was found to be a more accurate dataset with higher resolution. This new dataset is now available at https://doi.org/10.11888/RemoteSen.tpdc.271909 (Tang, 2021).
13
Scheibenreif, L., M. Mommert, and D. Borth. "CONTRASTIVE SELF-SUPERVISED DATA FUSION FOR SATELLITE IMAGERY." ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences V-3-2022 (May 17, 2022): 705–11. http://dx.doi.org/10.5194/isprs-annals-v-3-2022-705-2022.
Abstract:
Abstract. Self-supervised learning has great potential for the remote sensing domain, where unlabelled observations are abundant, but labels are hard to obtain. This work leverages unlabelled multi-modal remote sensing data for augmentation-free contrastive self-supervised learning. Deep neural network models are trained to maximize the similarity of latent representations obtained with different sensing techniques from the same location, while distinguishing them from other locations. We showcase this idea with two self-supervised data fusion methods and compare against standard supervised and self-supervised learning approaches on a land-cover classification task. Our results show that contrastive data fusion is a powerful self-supervised technique to train image encoders that are capable of producing meaningful representations: Simple linear probing performs on par with fully supervised approaches and fine-tuning with as little as 10% of the labelled data results in higher accuracy than supervised training on the entire dataset.
14
Pagán, Brianna, Wouter Maes, Pierre Gentine, Brecht Martens, and Diego Miralles. "Exploring the Potential of Satellite Solar-Induced Fluorescence to Constrain Global Transpiration Estimates." Remote Sensing 11, no. 4 (February 18, 2019): 413. http://dx.doi.org/10.3390/rs11040413.
Abstract:
The opening and closing of plant stomata regulates the global water, carbon and energy cycles. Biophysical feedbacks on climate are highly dependent on transpiration, which is mediated by vegetation phenology and plant responses to stress conditions. Here, we explore the potential of satellite observations of solar-induced chlorophyll fluorescence (SIF)—normalized by photosynthetically-active radiation (PAR)—to diagnose the ratio of transpiration to potential evaporation (‘transpiration efficiency’, τ). This potential is validated at 25 eddy-covariance sites from seven biomes worldwide. The skill of the state-of-the-art land surface models (LSMs) from the eartH2Observe project to estimate τ is also contrasted against eddy-covariance data. Despite its relatively coarse (0.5°) resolution, SIF/PAR estimates, based on data from the Global Ozone Monitoring Experiment 2 (GOME-2) and the Clouds and Earth’s Radiant Energy System (CERES), correlate to the in situ τ significantly (average inter-site correlation of 0.59), with higher correlations during growing seasons (0.64) compared to decaying periods (0.53). In addition, the skill to diagnose the variability of in situ τ demonstrated by all LSMs is on average lower, indicating the potential of SIF data to constrain the formulations of transpiration in global models via, e.g., data assimilation. Overall, SIF/PAR estimates successfully capture the effect of phenological changes and environmental stress on natural ecosystem transpiration, adequately reflecting the timing of this variability without complex parameterizations.
15
Plana-Fattori, Artemio, Gérard Brogniez, Patrick Chervet, Martial Haeffelin, Olga Lado-Bordowsky, Yohann Morille, Frédéric Parol, et al. "Comparison of High-Cloud Characteristics as Estimated by Selected Spaceborne Observations and Ground-Based Lidar Datasets." Journal of Applied Meteorology and Climatology 48, no. 6 (June 1, 2009): 1142–60. http://dx.doi.org/10.1175/2009jamc1964.1.
Abstract:
Abstract The characterization of high clouds as performed from selected spaceborne observations is assessed in this article by employing a number of worldwide ground-based lidar multiyear datasets as reference. Among the latter, the ground lidar observations conducted at Lannion, Bretagne (48.7°N, 3.5°W), and Palaiseau, near Paris [the Site Instrumental de Recherche par Télédétection Atmosphérique (SIRTA) observatory: 48.7°N, 2.2°E], both in France, are discussed in detail. High-cloud altitude statistics at these two sites were found to be similar. Optical thicknesses disagree, and possible reasons were analyzed. Despite the variety of instruments, observation strategies, and methods of analysis employed by different lidar groups, high-cloud optical thicknesses from the Geoscience Laser Altimeter System (GLAS) on board the Ice, Cloud and land Elevation Satellite (ICESat) were found to be consistent on the latitude band 40°–60°N. Respective high-cloud altitudes agree within 1 km with respect to those from ground lidars at Lannion and Palaiseau; such a finding remains to be verified under other synoptic regimes. Mean altitudes of high clouds from Lannion and Palaiseau ground lidars were compared with altitudes of thin cirrus from the Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS) Path-B 8-yr climatology for a common range of optical thicknesses (0.1–1.4). Over both sites, the annual altitude distribution of thin high clouds from TOVS Path-B is asymmetric, with a peak around 8–9.5 km, whereas the distribution of high clouds retrieved from ground lidars seems symmetric with a peak around 9.5–11.5 km. Additional efforts in standardizing ground lidar observation and processing methods, and in merging high-cloud statistics from complementary measuring platforms, are recommended.
16
Pastel, M., J. P. Pommereau, F. Goutail, A. Richter, A. Pazmiño, and D. Ionov. "Comparison of long term series of total ozone and NO<sub>2</sub> column measurements in the southern tropics by SAOZ/NDACC UV-Vis spectrometers and satellites." Atmospheric Measurement Techniques Discussions 6, no. 3 (May 31, 2013): 4851–93. http://dx.doi.org/10.5194/amtd-6-4851-2013.
Abstract:
Abstract. Long series of ozone and NO2 total column measurements at the Southern tropics are available from two ground-based SAOZ (Système d'Analyse par Observation Zenithale) UV-visible spectrometers operated within the NDACC (Network for the Detection of Amtospheric Composition Change) deployed in Bauru in S-E Brazil and Reunion Island in the S-W Indian Ocean in 1995 and 1993 respectively. Although at the same latitude, the data show larger columns of both species above the South American continent than above the Indian Ocean. For verifying the reliability of these data before carrying out trend analysis, they have been compared to satellites observations available during the same period. However, since no single satellite was operating from 1995 until present, the comparison requires the building of a composite, called merged satellites series. As systematic differences exist between the individual data sets because of the many differences between instruments, spectral ranges, absorption cross-sections, and retrieval procedures used, the building of such a composite requires thorough evaluation and normalisation of each. From comparisons with SAOZ, the merged satellite data set build with EP-TOMS from 1995 to 2004 and OMI-TOMS from 2005 to 2012 are found best for ozone in the Southern tropics. After correction for biases with SAOZ, both are confirming the larger ozone columns reported by SAOZ above South America compared to the Indian Ocean shown to origin from ozone production by lightning NOx (LNOx) over the continent in the summer and the advection from Africa of ozone produced by biomass burning emissions in the winter. For NO2, best matching the SAOZ is a combination of GOME GDP4 1996–2003 and SCIAMACHY 2003–2012 products, after correction for the photochemical diurnal change of the concentration of the species between the SAOZ twilight observations and the time of satellites overpasses. The merged data series built from the data of these two satellites fully confirms the larger NO2 column reported by SAOZ above the South American continent as well as and its seasonality. The 35% larger column above Brazil in the summer is shown to be due to the NOx production in the upper troposphere by the frequent lightning during the thunderstorm season, whereas the winter maximum is shown to come from the larger exchange of NOx rich air with mid-latitudes in the lower stratosphere due to the more equatorial latitude of the subtropical jet above South America compared to the Indian Ocean.
17
Castro-Arvizu, Juan Manuel, Daniel Medina, Ralf Ziebold, Jordi Vilà-Valls, Eric Chaumette, and Pau Closas. "Precision-Aided Partial Ambiguity Resolution Scheme for Instantaneous RTK Positioning." Remote Sensing 13, no. 15 (July 23, 2021): 2904. http://dx.doi.org/10.3390/rs13152904.
Abstract:
The use of carrier phase data is the main driver for high-precision Global Navigation Satellite Systems (GNSS) positioning solutions, such as Real-Time Kinematic (RTK). However, carrier phase observations are ambiguous by an unknown number of cycles, and their use in RTK relies on the process of mapping real-valued ambiguities to integer ones, so-called Integer Ambiguity Resolution (IAR). The main goal of IAR is to enhance the position solution by virtue of its correlation with the estimated integer ambiguities. With the deployment of new GNSS constellations and frequencies, a large number of observations is available. While this is generally positive, positioning in medium and long baselines is challenging due to the atmospheric residuals. In this context, the process of solving the complete set of ambiguities, so-called Full Ambiguity Resolution (FAR), is limiting and may lead to a decreased availability of precise positioning. Alternatively, Partial Ambiguity Resolution (PAR) relaxes the condition of estimating the complete vector of ambiguities and, instead, finds a subset of them to maximize the availability. This article reviews the state-of-the-art PAR schemes, addresses the analytical performance of a PAR estimator following a generalization of the Cramér–Rao Bound (CRB) for the RTK problem, and introduces Precision-Driven PAR (PD-PAR). The latter constitutes a new PAR scheme which employs the formal precision of the (potentially fixed) positioning solution as selection criteria for the subset of ambiguities to fix. Numerical simulations are used to showcase the performance of conventional FAR and FAR approaches, and the proposed PD-PAR against the generalized CRB associated with PAR problems. Real-data experimental analysis for a medium baseline complements the synthetic scenario. The results demonstrate that (i) the generalization for the RTK CRB constitutes a valid lower bound to assess the asymptotic behavior of PAR estimators, and (ii) the proposed PD-PAR technique outperforms existing FAR and PAR solutions as a non-recursive estimator for medium and long baselines.
18
Carella, Giulia, Mathieu Vrac, Hélène Brogniez, Pascal Yiou, and Hélène Chepfer. "Statistical downscaling of water vapour satellite measurements from profiles of tropical ice clouds." Earth System Science Data 12, no. 1 (January 3, 2020): 1–20. http://dx.doi.org/10.5194/essd-12-1-2020.
Abstract:
Abstract. Multi-scale interactions between the main players of the atmospheric water cycle are poorly understood, even in the present-day climate, and represent one of the main sources of uncertainty among future climate projections. Here, we present a method to downscale observations of relative humidity available from the Sondeur Atmosphérique du Profil d'Humidité Intertropical par Radiométrie (SAPHIR) passive microwave sounder at a nominal horizontal resolution of 10 km to the finer resolution of 90 m using scattering ratio profiles from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar. With the scattering ratio profiles as covariates, an iterative approach applied to a non-parametric regression model based on a quantile random forest is used. This allows us to effectively incorporate into the predicted relative humidity structure the high-resolution variability from cloud profiles. The finer-scale water vapour structure is hereby deduced from the indirect physical correlation between relative humidity and the lidar observations. Results are presented for tropical ice clouds over the ocean: based on the coefficient of determination (with respect to the observed relative humidity) and the continuous rank probability skill score (with respect to the climatology), we conclude that we are able to successfully predict, at the resolution of cloud measurements, the relative humidity along the whole troposphere, yet ensure the best possible coherence with the values observed by SAPHIR. By providing a method to generate pseudo-observations of relative humidity (at high spatial resolution) from simultaneous co-located cloud profiles, this work will help revisit some of the current key barriers in atmospheric science. A sample dataset of simultaneous co-located scattering ratio profiles of tropical ice clouds and observations of relative humidity downscaled at the resolution of cloud measurements is available at https://doi.org/10.14768/20181022001.1 (Carella et al., 2019).
19
Chen, Zichong, Junjie Liu, Daven K. Henze, Deborah N. Huntzinger, Kelley C. Wells, Stephen Sitch, Pierre Friedlingstein, et al. "Linking global terrestrial CO<sub>2</sub> fluxes and environmental drivers: inferences from the Orbiting Carbon Observatory 2 satellite and terrestrial biospheric models." Atmospheric Chemistry and Physics 21, no. 9 (May 4, 2021): 6663–80. http://dx.doi.org/10.5194/acp-21-6663-2021.
Abstract:
Abstract. Observations from the Orbiting Carbon Observatory 2 (OCO-2) satellite have been used to estimate CO2 fluxes in many regions of the globe and provide new insight into the global carbon cycle. The objective of this study is to infer the relationships between patterns in OCO-2 observations and environmental drivers (e.g., temperature, precipitation) and therefore inform a process understanding of carbon fluxes using OCO-2. We use a multiple regression and inverse model, and the regression coefficients quantify the relationships between observations from OCO-2 and environmental driver datasets within individual years for 2015–2018 and within seven global biomes. We subsequently compare these inferences to the relationships estimated from 15 terrestrial biosphere models (TBMs) that participated in the TRENDY model inter-comparison. Using OCO-2, we are able to quantify only a limited number of relationships between patterns in atmospheric CO2 observations and patterns in environmental driver datasets (i.e., 10 out of the 42 relationships examined). We further find that the ensemble of TBMs exhibits a large spread in the relationships with these key environmental driver datasets. The largest uncertainty in the models is in the relationship with precipitation, particularly in the tropics, with smaller uncertainties for temperature and photosynthetically active radiation (PAR). Using observations from OCO-2, we find that precipitation is associated with increased CO2 uptake in all tropical biomes, a result that agrees with half of the TBMs. By contrast, the relationships that we infer from OCO-2 for temperature and PAR are similar to the ensemble mean of the TBMs, though the results differ from many individual TBMs. These results point to the limitations of current space-based observations for inferring environmental relationships but also indicate the potential to help inform key relationships that are very uncertain in state-of-the-art TBMs.
20
Brogniez, Hélène, Renaud Fallourd, Cécile Mallet, Ramsès Sivira, and Christophe Dufour. "Estimating Confidence Intervals around Relative Humidity Profiles from Satellite Observations: Application to the SAPHIR Sounder." Journal of Atmospheric and Oceanic Technology 33, no. 5 (May 2016): 1005–22. http://dx.doi.org/10.1175/jtech-d-15-0237.1.
Abstract:
AbstractA novel scheme for the estimation of layer-averaged relative humidity (RH) profiles from spaceborne observations in the 183.31-GHz line is presented. Named atmospheric relative humidity profiles including analysis of confidence intervals (ARPIA), it provides for each vector of observations the parameters of the distribution of the RH instead of its expectation, as is usually done by the current methods. The profiles are composed of six layers distributed between 100 and 950 hPa. The approach combines the six channels of the Sondeur Atmosphérique du Profil d’Humidité Intertropical par Radiométrie (SAPHIR) instrument on board the Megha-Tropiques satellite and the generalized additive model for location, scale and shape (GAMLSS) method to infer the parametric distributions, assuming that they follow a Gaussian law. The knowledge of the conditional uncertainty is an asset in the evaluation using radiosounding profiles of RH with a dedicated Bayesian method. Taking the uncertainties into account in both the ARPIA estimates and the in situ measurements yields biases, root-mean-square, and correlation coefficients in the range of −0.56% to 9.79%, 1.58% to 13.32%, and 0.55 to 0.98, respectively, with the largest biases being obtained over the continent, in the midtropospheric layers.
21
Toihir, A. M., H. Bencherif, V. Sivakumar, L. El Amraoui, T. Portafaix, and N. Mbatha. "Comparison of total column ozone obtained by the IASI-MetOp satellite with ground-based and OMI satellite observations in the southern tropics and subtropics." Annales Geophysicae 33, no. 9 (September 16, 2015): 1135–46. http://dx.doi.org/10.5194/angeo-33-1135-2015.
Abstract:
Abstract. This paper presents comparison results of the total column ozone (TCO) data product over 13 southern tropical and subtropical sites recorded from the Infrared Atmospheric Sounder Interferometer (IASI) onboard the EUMETSAT (European organization for the exploitation of METeorological SATellite) MetOp (Meteorological Operational satellite program) satellite. TCO monthly averages obtained from IASI between June 2008 and December 2012 are compared with collocated TCO measurements from the Ozone Monitoring Instrument (OMI) on the OMI/Aura satellite and the Dobson and SAOZ (Système d'Analyse par Observation Zénithale) ground-based instruments. The results show that IASI displays a positive bias with an average less than 2 % with respect to OMI and Dobson observations, but exhibits a negative bias compared to SAOZ over Bauru with a bias around 2.63 %. There is a good agreement between IASI and the other instruments, especially from 15° S southward where a correlation coefficient higher than 0.87 is found. IASI exhibits a seasonal dependence, with an upward trend in autumn and a downward trend during spring, especially before September 2010. After September 2010, the autumn seasonal bias is considerably reduced due to changes made to the retrieval algorithm of the IASI level 2 (L2) product. The L2 product released after August (L2 O3 version 5 (v5)) matches TCO from the other instruments better compared to version 4 (v4), which was released between June 2008 and August 2010. IASI bias error recorded from September 2010 is estimated to be at 1.5 % with respect to OMI and less than ±1 % with respect to the other ground-based instruments. Thus, the improvement made by O3 L2 version 5 (v5) product compared with version 4 (v4), allows IASI TCO products to be used with confidence to study the distribution and interannual variability of total ozone in the southern tropics and subtropics.
22
Fragkos, Konstantinos, Ilias Fountoulakis, Georgia Charalampous, Kyriakoula Papachristopoulou, Argyro Nisantzi, Diofantos Hadjimitsis, and Stelios Kazadzis. "Twenty-Year Climatology of Solar UV and PAR in Cyprus: Integrating Satellite Earth Observations with Radiative Transfer Modeling." Remote Sensing 16, no. 11 (May 24, 2024): 1878. http://dx.doi.org/10.3390/rs16111878.
Abstract:
In this study, we present comprehensive climatologies of effective ultraviolet (UV) quantities and photosynthetically active radiation (PAR) over Cyprus for the period 2004 to 2023, leveraging the synergy of earth observation (EO) data and radiative transfer model simulations. The EO dataset, encompassing satellite and reanalysis data for aerosols, total ozone column, and water vapor, alongside cloud modification factors, captures the nuanced dynamics of Cyprus’s atmospheric conditions. With a temporal resolution of 15 min and a spatial of 0.05° × 0.05°, these climatologies undergo rigorous validation against established satellite datasets and are further evaluated through comparisons with ground-based global horizontal irradiance measurements provided by the Meteorological Office of Cyprus. This dual-method validation approach not only underscores the models’ accuracy but also highlights its proficiency in capturing intra-daily cloud coverage variations. Our analysis extends to investigating the long-term trends of these solar radiation quantities, examining their interplay with changes in cloud attenuation, aerosol optical depth (AOD), and total ozone column (TOC). Significant decreasing trends in the noon ultraviolet index (UVI), ranging from −2 to −4% per decade, have been found in autumn, especially marked in the island’s northeastern part, mainly originating from the (significant) positive trends in TOC. The significant decreasing trends in TOC, of −2 to −3% per decade, which were found in spring, do not result in correspondingly significant positive trends in the noon UVI since variations in cloudiness and aerosols also have a strong impact on the UVI in this season. The seasonal trends in the day light integral (DLI) were generally not significant. These insights provide a valuable foundation for further studies aimed at developing public health strategies and enhancing agricultural productivity, highlighting the critical importance of accurate and high-resolution climatological data.
23
Demidov, Andrey B., Tatiana A. Belevich, and Sergey V. Sheberstov. "Optimal Assimilation Number of Phytoplankton in the Siberian Seas: Spatiotemporal Variability, Environmental Control and Estimation using a Region-Specific Model." Journal of Marine Science and Engineering 11, no. 3 (February 27, 2023): 522. http://dx.doi.org/10.3390/jmse11030522.
Abstract:
The maximal value of the chlorophyll-specific carbon fixation rate in the water column or the optimal assimilation number (Pbopt) is an important parameter used to estimate water column integrated primary production (IPP) using models and satellite-derived data. The spatiotemporal variability in the Pbopt of the total and size-fractionated phytoplankton in the Siberian Seas (SSs) and its links with environmental factors were studied based on long-term (1993–2020) field and satellite-derived (MODIS-Aqua) observations. The average value of Pbopt in the SSs was equal to 1.38 ± 0.76 mgC (mg Chl a)–1 h–1. The monthly average values of Pbopt decreased during the growing season from 1.95 mgC (mg Chl a)–1 h–1 in July to 0.64 mgC (mg Chl a)–1 h–1 in October. The average value of Pbopt for small (<3 μm) phytoplankton 1.6-fold exceeded that for large (>3 μm) phytoplankton. The values of Pbopt depend mainly on incident photosynthetically available radiation (PAR). Based on the relationship between Pbopt and PAR, the empirical region-specific algorithm (E0reg) was developed. The E0reg algorithm performed better than commonly used temperature-based models. The application of E0reg for the calculation of Pbopt will make it possible to more precisely estimate IPP in the SSs.
24
Jones, Erin E., Kevin Garrett, and Sid-Ahmed Boukabara. "Assimilation of Megha-Tropiques SAPHIR Observations in the NOAA Global Model." Monthly Weather Review 145, no. 9 (September 2017): 3725–44. http://dx.doi.org/10.1175/mwr-d-16-0148.1.
Abstract:
The National Oceanic and Atmospheric Administration (NOAA) Global Data Assimilation System/Global Forecast System (GDAS/GFS) was extended to assimilate brightness temperatures from the Sondeur Atmosphérique du Profil d’Humidité Intertropicale par Radiométrie (SAPHIR) passive microwave water vapor sounder on board the Megha-Tropiques satellite. Quality control procedures were developed to assess the SAPHIR data quality for assimilating clear-sky observations over ocean surfaces, and to characterize observation biases and errors. A 6-week impact experiment was performed using the GDAS/GFS data assimilation system. The addition of SAPHIR observations on top of the current global observing system improved analysis and forecast humidity root-mean-square error (RMSE) results at the upper levels of the troposphere by about 6%, mostly at 100 hPa, when verified against European Centre for Medium-Range Weather Forecasts (ECMWF) analysis, though some degradation to the forecast humidity was seen at 150–200 hPa. The forecast impacts were predominant at earlier lead times between 24 and 96 h. Verification using global radiosonde observations also showed a reduction of the humidity RMSE from 4% to 6% between 500 hPa and the surface when assimilating SAPHIR, while temperature and wind speed RMSEs were reduced by up to 9% and 7% near the tropical tropopause, respectively. Other conventional forecast skill parameters including the 500-hPa geopotential height anomaly correlation showed neutral impact when assimilating SAPHIR.
25
Du, Shanshan, Liangyun Liu, Xinjie Liu, Jian Guo, Jiaochan Hu, Shaoqiang Wang, and Yongguang Zhang. "SIFSpec: Measuring Solar-Induced Chlorophyll Fluorescence Observations for Remote Sensing of Photosynthesis." Sensors 19, no. 13 (July 8, 2019): 3009. http://dx.doi.org/10.3390/s19133009.
Abstract:
Solar-induced chlorophyll fluorescence (SIF) is regarded as a proxy for photosynthesis in terrestrial vegetation. Tower-based long-term observations of SIF are very important for gaining further insight into the ecosystem-specific seasonal dynamics of photosynthetic activity, including gross primary production (GPP). Here, we present the design and operation of the tower-based automated SIF measurement (SIFSpec) system. This system was developed with the aim of obtaining synchronous SIF observations and flux measurements across different terrestrial ecosystems, as well as to validate the increasing number of satellite SIF products using in situ measurements. Details of the system components, instrument installation, calibration, data collection, and processing are introduced. Atmospheric correction is also included in the data processing chain, which is important, but usually ignored for tower-based SIF measurements. Continuous measurements made across two growing cycles over maize at a Daman (DM) flux site (in Gansu province, China) demonstrate the reliable performance of SIF as an indicator for tracking the diurnal variations in photosynthetically active radiation (PAR) and seasonal variations in GPP. For the O2–A band in particular, a high correlation coefficient value of 0.81 is found between the SIF and seasonal variations of GPP. It is thus concluded that, in coordination with continuous eddy covariance (EC) flux measurements, automated and continuous SIF observations can provide a reliable approach for understanding the photosynthetic activity of the terrestrial ecosystem, and are also able to bridge the link between ground-based optical measurements and airborne or satellite remote sensing data.
26
Peres, Lucas Vaz, Damaris Kirsh Pinheiro, Hassan Bencherif, Nelson Begue, José Valentin Bageston, Gabriela Dorneles Bittencourt, Thierry Portafaix, et al. "Observations, Remote Sensing, and Model Simulation to Analyze Southern Brazil Antarctic Ozone Hole Influence." Remote Sensing 16, no. 11 (June 4, 2024): 2017. http://dx.doi.org/10.3390/rs16112017.
Abstract:
This paper presents the observational, remote sensing, and model simulation used to analyze southern Brazil Antarctic ozone hole influence (SBAOHI) events that occurred between 2005 and 2014. To analyze it, we use total ozone column (TOC) data provided by a Brewer spectrophotometer (BS) and the OMI (Ozone Monitoring Instrument). In addition to the AURA/MLS (Microwave Limb Sounder) instrument, satellite ozone profiles were utilized with DYBAL (Dynamical Barrier Localization) code in the MIMOSA (Modélisation Isentrope du Transport Mésoéchelle de l’Ozone Stratosphérique par Advection) model Potential Vorticity (PV) fields. TOC has 7.0 ± 2.9 DU reductions average in 62 events. October has more events (30.7%). Polar tongue events are 19.3% in total, being more frequently observed in October (50% of cases), with medium intensity (58.2%), and in the stratosphere medium levels (55.0%). Already, polar filament events (80.7%) are more frequent in September (32.0%), with medium intensity (42.0%), and stratosphere medium levels (40.7%).
27
Hendrick, F., J. P. Pommereau, F. Goutail, R. D. Evans, D. Ionov, A. Pazmino, E. Kyrö, et al. "NDACC/SAOZ UV-visible total ozone measurements: improved retrieval and comparison with correlative ground-based and satellite observations." Atmospheric Chemistry and Physics 11, no. 12 (June 24, 2011): 5975–95. http://dx.doi.org/10.5194/acp-11-5975-2011.
Abstract:
Abstract. Accurate long-term monitoring of total ozone is one of the most important requirements for identifying possible natural or anthropogenic changes in the composition of the stratosphere. For this purpose, the NDACC (Network for the Detection of Atmospheric Composition Change) UV-visible Working Group has made recommendations for improving and homogenizing the retrieval of total ozone columns from twilight zenith-sky visible spectrometers. These instruments, deployed all over the world in about 35 stations, allow measuring total ozone twice daily with limited sensitivity to stratospheric temperature and cloud cover. The NDACC recommendations address both the DOAS spectral parameters and the calculation of air mass factors (AMF) needed for the conversion of O3 slant column densities into vertical column amounts. The most important improvement is the use of O3 AMF look-up tables calculated using the TOMS V8 (TV8) O3 profile climatology, that allows accounting for the dependence of the O3 AMF on the seasonal and latitudinal variations of the O3 vertical distribution. To investigate their impact on the retrieved ozone columns, the recommendations have been applied to measurements from the NDACC/SAOZ (Système d'Analyse par Observation Zénithale) network. The revised SAOZ ozone data from eight stations deployed at all latitudes have been compared to TOMS, GOME-GDP4, SCIAMACHY-TOSOMI, SCIAMACHY-OL3, OMI-TOMS, and OMI-DOAS satellite overpass observations, as well as to those of collocated Dobson and Brewer instruments at Observatoire de Haute Provence (44° N, 5.5° E) and Sodankyla (67° N, 27° E), respectively. A significantly better agreement is obtained between SAOZ and correlative reference ground-based measurements after applying the new O3 AMFs. However, systematic seasonal differences between SAOZ and satellite instruments remain. These are shown to mainly originate from (i) a possible problem in the satellite retrieval algorithms in dealing with the temperature dependence of the ozone cross-sections in the UV and the solar zenith angle (SZA) dependence, (ii) zonal modulations and seasonal variations of tropospheric ozone columns not accounted for in the TV8 profile climatology, and (iii) uncertainty on the stratospheric ozone profiles at high latitude in the winter in the TV8 climatology. For those measurements mostly sensitive to stratospheric temperature like TOMS, OMI-TOMS, Dobson and Brewer, or to SZA like SCIAMACHY-TOSOMI, the application of temperature and SZA corrections results in the almost complete removal of the seasonal difference with SAOZ, improving significantly the consistency between all ground-based and satellite total ozone observations.
28
Trisolino, Pamela, Alcide di Sarra, Fabrizio Anello, Carlo Bommarito, Tatiana Di Iorio, Daniela Meloni, Francesco Monteleone, Giandomenico Pace, Salvatore Piacentino, and Damiano Sferlazzo. "A long-term time series of global and diffuse photosynthetically active radiation in the Mediterranean: interannual variability and cloud effects." Atmospheric Chemistry and Physics 18, no. 11 (June 7, 2018): 7985–8000. http://dx.doi.org/10.5194/acp-18-7985-2018.
Abstract:
Abstract. Measurements of global and diffuse photosynthetically active radiation (PAR) have been carried out on the island of Lampedusa, in the central Mediterranean Sea, since 2002. PAR is derived from observations made with multi-filter rotating shadowband radiometers (MFRSRs) by comparison with a freshly calibrated PAR sensor and by relying on the on-site Langley plots. In this way, a long-term calibrated record covering the period 2002–2016 is obtained and is presented in this work. The monthly mean global PAR peaks in June, with about 160 W m−2, while the diffuse PAR reaches 60 W m−2 in spring or summer. The global PAR displays a clear annual cycle with a semi amplitude of about 52 W m−2. The diffuse PAR annual cycle has a semi amplitude of about 12 W m−2. A simple method to retrieve the cloud-free PAR global and diffuse irradiances in days characterized by partly cloudy conditions has been implemented and applied to the dataset. This method allows retrieval of the cloud-free evolution of PAR and calculation of the cloud radiative effect, CRE, for downwelling PAR. The cloud-free monthly mean global PAR reaches 175 W m−2 in summer, while the diffuse PAR peaks at about 40 W m−2. The cloud radiative effect, CRE, on global and diffuse PAR is calculated as the difference between all-sky and cloud-free measurements. The annual average CRE is about −14.7 W m−2 for the global PAR and +8.1 W m−2 for the diffuse PAR. The smallest CRE is observed in July, due to the high cloud-free condition frequency. Maxima (negative for the global, and positive for the diffuse component) occur in March–April and in October, due to the combination of elevated PAR irradiances and high occurrence of cloudy conditions. Summer clouds appear to be characterized by a low frequency of occurrence, low altitude, and low optical thickness, possibly linked to the peculiar marine boundary layer structure. These properties also contribute to produce small radiative effects on PAR in summer. The cloud radiative effect has been deseasonalized to remove the influence of annual irradiance variations. The monthly mean normalized CRE for global PAR can be well represented by a multi-linear regression with respect to monthly cloud fraction, cloud top pressure, and cloud optical thickness, as determined from satellite MODIS observations. The behaviour of the normalized CRE for diffuse PAR can not be satisfactorily described by a simple multi-linear model with respect to the cloud properties, due to its non-linear dependency, in particular on the cloud optical depth. The analysis suggests that about 77 % of the global PAR interannual variability may be ascribed to cloud variability in winter.
29
Walther, Sophia, Luis Guanter, Birgit Heim, Martin Jung, Gregory Duveiller, Aleksandra Wolanin, and Torsten Sachs. "Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis." Biogeosciences 15, no. 20 (October 26, 2018): 6221–56. http://dx.doi.org/10.5194/bg-15-6221-2018.
Abstract:
Abstract. High-latitude treeless ecosystems represent spatially highly heterogeneous landscapes with small net carbon fluxes and a short growing season. Reliable observations and process understanding are critical for projections of the carbon balance of the climate-sensitive tundra. Space-borne remote sensing is the only tool to obtain spatially continuous and temporally resolved information on vegetation greenness and activity in remote circumpolar areas. However, confounding effects from persistent clouds, low sun elevation angles, numerous lakes, widespread surface inundation, and the sparseness of the vegetation render it highly challenging. Here, we conduct an extensive analysis of the timing of peak vegetation productivity as shown by satellite observations of complementary indicators of plant greenness and photosynthesis. We choose to focus on productivity during the peak of the growing season, as it importantly affects the total annual carbon uptake. The suite of indicators are as follows: (1) MODIS-based vegetation indices (VIs) as proxies for the fraction of incident photosynthetically active radiation (PAR) that is absorbed (fPAR), (2) VIs combined with estimates of PAR as a proxy of the total absorbed radiation (APAR), (3) sun-induced chlorophyll fluorescence (SIF) serving as a proxy for photosynthesis, (4) vegetation optical depth (VOD), indicative of total water content and (5) empirically upscaled modelled gross primary productivity (GPP). Averaged over the pan-Arctic we find a clear order of the annual peak as APAR ≦ GPP<SIF<VIs/VOD. SIF as an indicator of photosynthesis is maximised around the time of highest annual temperatures. The modelled GPP peaks at a similar time to APAR. The time lag of the annual peak between APAR and instantaneous SIF fluxes indicates that the SIF data do contain information on light-use efficiency of tundra vegetation, but further detailed studies are necessary to verify this. Delayed peak greenness compared to peak photosynthesis is consistently found across years and land-cover classes. A particularly late peak of the normalised difference vegetation index (NDVI) in regions with very small seasonality in greenness and a high amount of lakes probably originates from artefacts. Given the very short growing season in circumpolar areas, the average time difference in maximum annual photosynthetic activity and greenness or growth of 3 to 25 days (depending on the data sets chosen) is important and needs to be considered when using satellite observations as drivers in vegetation models.
30
Hendrick, F., J. P. Pommereau, F. Goutail, R. D. Evans, D. Ionov, A. Pazmino, E. Kyrö, et al. "NDACC UV-visible total ozone measurements: improved retrieval and comparison with correlative satellite and ground-based observations." Atmospheric Chemistry and Physics Discussions 10, no. 8 (August 27, 2010): 20405–60. http://dx.doi.org/10.5194/acpd-10-20405-2010.
Abstract:
Abstract. Accurate long-term monitoring of total ozone is one of the most important requirements for identifying possible natural or anthropogenic changes in the composition of the stratosphere. For this purpose, the NDACC (Network for the Detection of Atmospheric Composition Change) UV-visible Working Group has made recommendations for improving and homogenizing the retrieval of total ozone columns from twilight zenith-sky visible spectrometers. These instruments, deployed all over the world in about 35 stations, allow measurements of total ozone twice daily with little sensitivity to stratospheric temperature and cloud cover. The NDACC recommendations address both the DOAS retrieval parameters and the calculation of air mass factors (AMF) needed for the conversion of O3 slant column densities into vertical column amounts. The most important improvement is the use of O3 AMF look-up tables calculated using the TOMS V8 O3 profile climatology, that allows accounting for the dependence of the O3 AMF on the seasonal and latitudinal variations of the O3 vertical distribution. To investigate their impact on the retrieved ozone columns, the recommendations have been applied to measurements from the NDACC/SAOZ (Système d'Analyse par Observation Zénithale) network. The revised SAOZ ozone data from eight stations covering all latitude regions have been compared to TOMS, GOME-GDP4, SCIAMACHY-TOSOMI, OMI-TOMS, and OMI-DOAS satellite overpass observations, as well as to those of collocated Dobson and Brewer instruments. A significant improvement is obtained after applying the new O3 AMFs, although systematic seasonal differences between SAOZ and all other instruments remain. These are shown to mainly originate from i) the temperature dependence of the ozone absorption cross sections in the UV being not or improperly corrected by some retrieval algorithms, and ii) the longitudinal differences in tropospheric ozone column being ignored by zonal climatologies. For those measurements sensitive to stratospheric temperature like TOMS, OMI-TOMS, Dobson and Brewer, the application of a temperature correction results in the almost complete removal of the seasonal difference with SAOZ, improving significantly the consistency between all ground-based and satellite total ozone observations.
31
Gaudel, Audrey, Owen R. Cooper, Kai-Lan Chang, Claire Granier, Valérie Thouret, Philippe Nédélec, Romain Blot, et al. "Augmentation d'ozone troposphérique dans l'hémisphère Nord observée grâce aux mesures Iagos." La Météorologie, no. 116 (2022): 017. http://dx.doi.org/10.37053/lameteorologie-2022-0010.
Abstract:
L'ozone troposphérique est un gaz à effet de serre, nocif pour la santé humaine, les cultures et la productivité des écosystèmes. Il contrôle la capacité oxydante de la troposphère. Du fait de sa grande variabilité spatiale et temporelle et d'observations en nombre limité, il n'avait pas encore été possible de quantifier les tendances de l'ozone troposphérique dans l'hémisphère Nord sur des échelles de temps de deux décennies. Cette étude montre, grâce à l'infrastructure de recherche Iagos installée à bord d'avions commerciaux, que l'ozone troposphérique a augmenté au-dessus de onze régions de l'hémisphère Nord depuis le milieu des années 1990. Ces observations sont cohérentes avec les observations effectuées par l'instrument OMI/MLS embarqué sur satellite. La modification de la répartition spatiale des émissions anthropiques de précurseurs d'ozone, comme les oxydes d'azote (NOx), a conduit à une augmentation de l'ozone et du forçage radiatif associé au-dessus des 11 régions d'étude, malgré les réductions des émissions de NOx aux latitudes moyennes. Tropospheric ozone is an important greenhouse gas, is detrimental to human health and crop and ecosystem productivity, and controls the oxidizing capacity of the troposphere. Because of its high spatial and temporal variability and limited observations, quantifying net tropospheric ozone changes across the Northern Hemisphere on time scales of two decades had not been possible. Here, we show, using 2 decades of observations from the IAGOS Research Infrastructure using commercial aircraft, that tropospheric ozone has increased above 11 regions of the Northern Hemisphere since the mid-1990s, consistent with the OMI/MLS satellite product. The net result of shifting anthropogenic ozone precursor emissions has led to an increase of ozone and its radiative forcing above all 11 study regions of the Northern Hemisphere, despite nitrogen oxides emission reductions at midlatitudes.
32
Cervantes-Duarte, Rafael, Eduardo González-Rodríguez, René Funes-Rodríguez, Alejandro Ramos-Rodríguez , María Yesenia Torres-Hernández, and Fernando Aguirre-Bahena. "Variability of Net Primary Productivity and Associated Biophysical Drivers in Bahía de La Paz (Mexico)." Remote Sensing 13, no. 9 (April 23, 2021): 1644. http://dx.doi.org/10.3390/rs13091644.
Abstract:
The use of information of net primary productivity (NPP) from remote ocean color sensors is increasingly common in marine sciences. The resulting information has been used to explain variations in productivity at different spatio-temporal scales and in the presence of climate phenomena, such as the El Niño Southern Oscillation, and global warming. Satellite remote sensing data were analyzed in Bahía de La Paz (BLP), Mexico, to determine the spatio-temporal variation in NPP. In addition, in situ hydrographic data were obtained to characterize the water properties in the bay. The satellite data agree with in situ measurements, validating the satellite observations over this region. The NPP generally presented seasonal variation with maximum values in winter-spring and minimum values in summer–autumn. The variance explained by NPP from the measured variables was ranked as Chl-a < DEN < SST < PAR < WSC. The highest NPP values generally occurred when subtropical subsurface (SsStW) water was relatively shallow. Due to divergence and mixing processes, this water provided nutrients to the euphotic zone, and consequently an increase in NPP and changes in plankton biomass were observed. The annual trends of the variation in hydrographic data with respect to that of remote sensing data were similar; however, it is necessary to increase the number of data validation studies. The remote sensing and in situ measurements allowed for the main biophysical variables that modulate NPP in different time scales to be identified. The satellite-derived NPP data classifies the BLP as a high productivity zone with 432 g C m−2 year−1. The use of satellite NPP data is satisfactory and should be incorporated into marine primary productivity studies.
33
Henrion-Dourcy, Isabelle. "Une rupture dans l’air." Anthropologie et Sociétés 36, no. 1-2 (August 10, 2012): 139–59. http://dx.doi.org/10.7202/1011721ar.
Abstract:
La plupart des études des diasporas soulignent le rôle de cohésion culturelle, sociale et souvent politique joué par les médias au sein de ces groupes établis à travers plusieurs espaces nationaux. Mais tous les médias dans la langue du groupe sont-ils pour autant des vecteurs de cohésion ? Le cas de la télévision satellite dans la communauté tibétaine de Dharamsala (Himachal Pradesh, Inde), où cette enquête ethnographique a été menée, est particulier, du fait que les Tibétains ont accès, depuis à peine une dizaine d’années, à une offre télévisuelle aussi foisonnante qu’idéologiquement variée. À la soixantaine de chaînes du bouquet de STAR, G et Sony TV s’ajoutent des médias diasporiques (deux programmes en tibétain réalisés soit à Dharamsala, soit à Washington) et des médias transnationaux (trois chaînes en tibétain et trois autres en chinois diffusées depuis le Tibet). Les observations révèlent que la consommation différentielle de ces médias met en lumière les fractures internes de la communauté, non seulement selon l’âge, mais aussi et surtout selon le parcours migratoire, plus ou moins ancien en Inde, des téléspectateurs. Par ailleurs, l’impact d’une exposition continue des exilés, très politisés, aux médias chinois est soit passé sous silence par les autorités, soit démenti par les spectateurs, au nom d’une rhétorique qui survalorise les contenus discursifs à la fois de l’identité tibétaine et du langage télévisuel. Or, celui-ci n’est pas qu’outil pédagogique, il est aussi machine à créer du désir, consommatoire ou affectif, deux dimensions pour l’instant négligées localement.
34
Chokmani, Karem, Monique Bernier, and Michel Slivitzky. "Suivi spatio-temporel du couvert nival du Québec à l’aide des données NOAA-AVHRR." Revue des sciences de l'eau 19, no. 3 (September 13, 2006): 163–79. http://dx.doi.org/10.7202/013536ar.
Abstract:
Résumé L’imagerie satellitaire dans le visible et l’infrarouge permet de cartographier le couvert nival à grande échelle, ce qui n’est pas facilement réalisable à partir des observations locales conventionnelles. Cependant, en raison de leur résolution spatiale inadéquate ou de la faible durée de leurs séries d’observations, les produits satellitaires actuellement disponibles sont inutilisables pour l’étude à long terme du couvert nival. Par conséquent, l’objectif de la présente étude a été de développer un algorithme opérationnel de cartographie de la neige à l’aide des données du capteur AVHRR (Advanced Very High Resolution Radiometer) embarqué à bord du satellite NOAA. Cette procédure doit permettre de suivre l’évolution spatio-temporelle de la neige au sol sur une longue période de temps et avec une bonne résolution spatiale. Les résultats de la cartographie ont été validés par rapport aux observations de l’occurrence et de l’épaisseur de la neige au sol. L’algorithme a été appliqué au territoire du Québec sur trois périodes spécifiques : 1998-1999, 1991-1992 et 1986-1987. L’algorithme a réussi à identifier la catégorie de surface (neige/non-neige) avec un taux de succès global moyen de 87 %. Les performances de l’algorithme ont été supérieures dans la détection de la neige (90 %) qu’elles l’ont été pour les surfaces sans neige (82 %). Également, l’algorithme a permis de situer le début des périodes de formation et de fonte de la neige, et ce tant au niveau local qu’à l’échelle du bassin versant.
35
Dumain, C., G. Padern, J. Broner, E. Arnaud, M. Fantone, G. Chastellan, M. Biurrarena, R. Najjari, and R. Goulabchand. "Deux observations originales d’hypercalcémie médiée par le calcitriol, quand le granulome satellite d’une pneumocystose est au cœur de la réflexion médicale." La Revue de Médecine Interne 44 (December 2023): A480—A481. http://dx.doi.org/10.1016/j.revmed.2023.10.383.
36
Hao, Dalei, Ghassem R. Asrar, Yelu Zeng, Qing Zhu, Jianguang Wen, Qing Xiao, and Min Chen. "DSCOVR/EPIC-derived global hourly and daily downward shortwave and photosynthetically active radiation data at 0.1° × 0.1° resolution." Earth System Science Data 12, no. 3 (September 15, 2020): 2209–21. http://dx.doi.org/10.5194/essd-12-2209-2020.
Abstract:
Abstract. Downward shortwave radiation (SW) and photosynthetically active radiation (PAR) play crucial roles in Earth system dynamics. Spaceborne remote sensing techniques provide a unique means for mapping accurate spatiotemporally continuous SW–PAR, globally. However, any individual polar-orbiting or geostationary satellite cannot satisfy the desired high temporal resolution (sub-daily) and global coverage simultaneously, while integrating and fusing multisource data from complementary satellites/sensors is challenging because of co-registration, intercalibration, near real-time data delivery and the effects of discrepancies in orbital geometry. The Earth Polychromatic Imaging Camera (EPIC) on board the Deep Space Climate Observatory (DSCOVR), launched in February 2015, offers an unprecedented possibility to bridge the gap between high temporal resolution and global coverage and characterize the diurnal cycles of SW–PAR globally. In this study, we adopted a suite of well-validated data-driven machine-learning models to generate the first global land products of SW–PAR, from June 2015 to June 2019, based on DSCOVR/EPIC data. The derived products have high temporal resolution (hourly) and medium spatial resolution (0.1∘×0.1∘), and they include estimates of the direct and diffuse components of SW–PAR. We used independently widely distributed ground station data from the Baseline Surface Radiation Network (BSRN), the Surface Radiation Budget Network (SURFRAD), NOAA's Global Monitoring Division and the U.S. Department of Energy's Atmospheric System Research (ASR) program to evaluate the performance of our products, and we further analyzed and compared the spatiotemporal characteristics of the derived products with the benchmarking Clouds and the Earth's Radiant Energy System Synoptic (CERES) data. We found both the hourly and daily products to be consistent with ground-based observations (e.g., hourly and daily total SWs have low biases of −3.96 and −0.71 W m−2 and root-mean-square errors (RMSEs) of 103.50 and 35.40 W m−2, respectively). The developed products capture the complex spatiotemporal patterns well and accurately track substantial diurnal, monthly, and seasonal variations in SW–PAR when compared to CERES data. They provide a reliable and valuable alternative for solar photovoltaic applications worldwide and can be used to improve our understanding of the diurnal and seasonal variabilities of the terrestrial water, carbon and energy fluxes at various spatial scales. The products are freely available at https://doi.org/10.25584/1595069 (Hao et al., 2020).
37
Cheng, Xiangfen, Yu Zhou, Meijun Hu, Feng Wang, Hui Huang, and Jinsong Zhang. "The Links between Canopy Solar-Induced Chlorophyll Fluorescence and Gross Primary Production Responses to Meteorological Factors in the Growing Season in Deciduous Broadleaf Forest." Remote Sensing 13, no. 12 (June 17, 2021): 2363. http://dx.doi.org/10.3390/rs13122363.
Abstract:
Solar-induced chlorophyll fluorescence (SIF) is a hopeful indicator, which along with remote sensing, is used to measure the photosynthetic efficiency and gross primary production (GPP) of vegetation in regional terrestrial ecosystems. Studies have found a significant linear correlation between SIF and GPP in a variety of ecosystems. However, this relationship has mainly been established using SIF and GPP data derived from satellite remote sensing and continuous ground-based observations, respectively, which are difficult to accurately match. To overcome this, some studies have begun to use tower-based automatic observation instruments to study the changes of near-surface SIF and GPP. This study conducts continuous simultaneous observation of SIF, carbon flux, and meteorological factors on the forest canopy of a cork oak plantation during the growing season to explore how meteorological factors impact on canopy SIF and its relationship with GPP. This research found that the canopy SIF has obvious diurnal and day-to-day variations during the growing season but overall is relatively stable. Furthermore, SIF is greatly affected by incident radiation in different weather conditions and can change daily. Meteorological factors have a major role in the relationship between SIF and GPP; overall, the relationship shows a significant linear regression on the 30 min scale, but weakens when aggregating to the diurnal scale. Photosynthetically active radiation (PAR) drives SIF on a daily basis and changes the relationship between SIF and GPP on a seasonal timescale. As PAR increases, the daily slopes of the linear regressions between SIF and GPP decrease. On the 30 min timescale, both SIF and GPP increase with PAR until it reaches 1250 μmol·m−2·s−1; subsequently, SIF continues to increase while GPP decreases and they show opposite trends. Soil moisture and vapor pressure deficit influence SIF and GPP, respectively. Our findings demonstrate that meteorological factors affect the relationship between SIF and GPP, thereby enhancing the understanding of the mechanistic link between chlorophyll fluorescence and photosynthesis.
38
Fetanat, Gholamreza, Abdollah Homaifar, and Kenneth R. Knapp. "Objective Tropical Cyclone Intensity Estimation Using Analogs of Spatial Features in Satellite Data." Weather and Forecasting 28, no. 6 (December 1, 2013): 1446–59. http://dx.doi.org/10.1175/waf-d-13-00006.1.
Abstract:
Abstract An objective method for estimating tropical cyclone (TC) intensity using historical hurricane satellite data (HURSAT) is developed and tested. This new method, referred to as feature analogs in satellite imagery (FASI), requires a TC's center location to extract azimuthal brightness temperature (BT) profiles from current imagery as well as BT profiles from imagery 6, 12, and 24 h prior. Instead of using regression techniques, the estimated TC intensity is determined from the 10 closest analogs to this TC based on the BT profiles using a k-nearest-neighbor algorithm. The FASI technique was trained and validated using intensity data from aircraft reconnaissance in the North Atlantic Ocean, where the data were restricted to include storms that are over water and south of 45°N. This subset comprised 2016 observations from 165 storms during 1988–2006. Several tests were implemented to statistically justify the FASI algorithm using n-fold cross validation. The resulting average mean absolute intensity error was 10.9 kt (50% of estimates are within 10 kt, 1 kt = 0.51 m s−1) or 8.4 mb (50% of estimates are within 8 mb); its accuracy is on par with other objective techniques. This approach has the potential to provide global TC intensity estimates that could augment intensity estimates made by other objective techniques.
39
Clain, G., H. Brogniez, V. H. Payne, V. O. John, and M. Luo. "An Assessment of SAPHIR Calibration Using Quality Tropical Soundings." Journal of Atmospheric and Oceanic Technology 32, no. 1 (January 2015): 61–78. http://dx.doi.org/10.1175/jtech-d-14-00054.1.
Abstract:
AbstractThe Sondeur Atmosphérique du Profil d’Humidité Intertropicale par Radiométrie (SAPHIR) instrument on board the Megha-Tropiques (MT) platform is a cross-track, multichannel microwave humidity sounder with six channels near the 183.31-GHz water vapor absorption line, a maximum scan angle of 42.96° (resulting in a maximum incidence angle of 50.7°), a 1700-km-wide swath, and a footprint resolution of 10 km at nadir. SAPHIR L1A2 brightness temperature (BT) observations have been compared to BTs simulated by the radiative transfer model (RTM) Radiative Transfer for the Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder (RTTOV-10), using in situ measurements from radiosondes as input. Selected radiosonde humidity observations from the Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year (CINDY)–Dynamics of the Madden–Julian Oscillation (DYNAMO) campaign (September 2011–March 2012) were spatiotemporally collocated with MT overpasses. Although several sonde systems were used during the campaign, all of the sites selected for this study used the Vaisala RS92-SGPD system and were chosen in order to avoid discrepancies in data quality and biases.To interpret the results of the comparison between the sensor data and the RTM simulations, uncertainties associated with the data processing must be propagated throughout the evaluation. The magnitude of the bias was found to be dependent on the observing channel, increasing from 0.18 K for the 183.31 ± 0.2-GHz channel to 2.3 K for the 183.31 ± 11-GHz channel. Uncertainties and errors that could impact the BT biases were investigated. These can be linked to the RTM input and design, the radiosonde observations, the chosen methodology of comparison, and the SAPHIR instrument itself.
40
Chiriaco, M., H. Chepfer, P. Minnis, M. Haeffelin, S. Platnick, D. Baumgardner, P. Dubuisson, et al. "Comparison of CALIPSO-Like, LaRC, and MODIS Retrievals of Ice-Cloud Properties over SIRTA in France and Florida during CRYSTAL-FACE." Journal of Applied Meteorology and Climatology 46, no. 3 (March 1, 2007): 249–72. http://dx.doi.org/10.1175/jam2435.1.
Abstract:
Abstract This study compares cirrus-cloud properties and, in particular, particle effective radius retrieved by a Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)-like method with two similar methods using Moderate-Resolution Imaging Spectroradiometer (MODIS), MODIS Airborne Simulator (MAS), and Geostationary Operational Environmental Satellite imagery. The CALIPSO-like method uses lidar measurements coupled with the split-window technique that uses the infrared spectral information contained at the 8.65-, 11.15-, and 12.05-μm bands to infer the microphysical properties of cirrus clouds. The two other methods, using passive remote sensing at visible and infrared wavelengths, are the operational MODIS cloud products (using 20 spectral bands from visible to infrared, referred to by its archival product identifier MOD06 for MODIS Terra) and MODIS retrievals performed by the Clouds and the Earth’s Radiant Energy System (CERES) team at Langley Research Center (LaRC) in support of CERES algorithms (using 0.65-, 3.75-, 10.8-, and 12.05-μm bands); the two algorithms will be referred to as the MOD06 and LaRC methods, respectively. The three techniques are compared at two different latitudes. The midlatitude ice-clouds study uses 16 days of observations at the Palaiseau ground-based site in France [Site Instrumental de Recherche par Télédétection Atmosphérique (SIRTA)], including a ground-based 532-nm lidar and the MODIS overpasses on the Terra platform. The tropical ice-clouds study uses 14 different flight legs of observations collected in Florida during the intensive field experiment known as the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL-FACE), including the airborne cloud-physics lidar and the MAS. The comparison of the three methods gives consistent results for the particle effective radius and the optical thickness but discrepancies in cloud detection and altitudes. The study confirms the value of an active remote sensing method (CALIPSO like) for the study of subvisible ice clouds, in both the midlatitudes and Tropics. Nevertheless, this method is not reliable in optically very thick tropical ice clouds, because of their particular microphysical properties.
41
Hilton, T. W., K. J. Davis, K. Keller, and N. M. Urban. "Improving terrestrial CO<sub>2</sub> flux diagnosis using spatial structure in land surface model residuals." Biogeosciences Discussions 9, no. 6 (June 15, 2012): 7073–116. http://dx.doi.org/10.5194/bgd-9-7073-2012.
Abstract:
Abstract. We evaluate spatial structure in North American CO2 flux observations using a simple diagnostic land surface model. The Vegetation Photosynthesis Respiration Model (VPRM) calculates net ecosystem exchange (NEE) using locally observed temperature and photosynthetically active radiation (PAR) along with satellite-derived phenology and moisture. We use observed NEE from a group of 65 North American eddy covariance tower sites spanning North America to estimate VPRM parameters for these sites. We investigate spatial coherence in regional CO2 fluxes at several different time scales by using geostatistical methods to examine the spatial structure of model data-model residuals. We find that persistent spatial structure does exist in the data-model residuals at a length scale of approximately 1000 km. This spatial structure defines a flux-tower-based VPRM residual covariance matrix. The residual covariance matrix is useful in constructing prior fluxes for atmospheric CO2 concentration inversion calculations, as well as for constructing a VPRM North American CO2 flux map optimized to eddy covariance observations. Finally, the estimated VPRM parameter values do not separate clearly by plant functional type (PFT). This calls into question whether PFTs partition ecosystems by carbon cycle participation when the viewing lens is a simple model.
42
Zhang, Y., F. Zhu, and X. Zhang. "IMPROVING GNSS POSITIONING RELIABILITY AND ACCURACY BASED ON FACTOR GRAPH OPTIMIZATION IN URBAN ENVIRONMENT." International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLVIII-1/W2-2023 (December 13, 2023): 1179–84. http://dx.doi.org/10.5194/isprs-archives-xlviii-1-w2-2023-1179-2023.
Abstract:
Abstract. Global navigation satellite system (GNSS) can provide global, precise, and continuous positioning in open-sky environments. However, urban environments with frequent outliers and cycle slips degrade the traditional Extended Kalman Filter (EKF) positioning performance. The susceptibility of EKF to outliers is attributed to its inherent structure. To mitigate, the GNSS positioning based on the Factor Graph Optimization (FGO) structure is adopted. FGO can enhance time correlation among observations and enable the updating of historical information, thereby improving resistance against outliers. In this study, we proposed a single-differenced GNSS-FGO model instead of the double-differenced model to preserve the sparsity of FGO, and outlier detection and PAR methods are employed to ensure urban positioning performance. To evaluate the proposed structure, experiments are conducted in both urban and open-sky environments. The results demonstrate the improvement of positioning accuracy and reliability, compared to EKF.
43
Hong, Zhongkun, Di Long, Xingdong Li, Yiming Wang, Jianmin Zhang, Mohamed A. Hamouda, and Mohamed M. Mohamed. "A global daily gap-filled chlorophyll-a dataset in open oceans during 2001–2021 from multisource information using convolutional neural networks." Earth System Science Data 15, no. 12 (November 29, 2023): 5281–300. http://dx.doi.org/10.5194/essd-15-5281-2023.
Abstract:
Abstract. Ocean color data are essential for developing our understanding of biological and ecological phenomena and processes and also of important sources of input for physical and biogeochemical ocean models. Chlorophyll-a (Chl-a) is a critical variable of ocean color in the marine environment. Quantitative retrieval from satellite remote sensing is a main way to obtain large-scale oceanic Chl-a. However, missing data are a major limitation in satellite remote-sensing-based Chl-a products due mostly to the influence of cloud, sun glint contamination, and high satellite viewing angles. The common methods to reconstruct (gap fill) missing data often consider spatiotemporal information of initial images alone, such as Data Interpolating Empirical Orthogonal Functions, optimal interpolation, Kriging interpolation, and the extended Kalman filter. However, these methods do not perform well in the presence of large-scale missing values in the image and overlook the valuable information available from other datasets for data reconstruction. Here, we developed a convolutional neural network (CNN) named Ocean Chlorophyll-a concentration reconstruction by convolutional neural NETwork (OCNET) for Chl-a concentration data reconstruction in open-ocean areas, considering environmental variables that are associated with ocean phytoplankton growth and distribution. Sea surface temperature (SST), salinity (SAL), photosynthetically active radiation (PAR), and sea surface pressure (SSP) from reanalysis data and satellite observations were selected as the input of OCNET to correlate with the environment and phytoplankton biomass. The developed OCNET model achieves good performance in the reconstruction of global open ocean Chl-a concentration data and captures spatiotemporal variations of these features. The reconstructed Chl-a data are available online at https://doi.org/10.5281/zenodo.10011908 (Hong et al., 2023). This study also shows the potential of machine learning in large-scale ocean color data reconstruction and offers the possibility of predicting Chl-a concentration trends in a changing environment.
44
Lin, S., J. Li, and Q. Liu. "ESTIMATING GROSS PRIMARY PRODUCTION IN CROPLAND WITH HIGH SPATIAL AND TEMPORAL SCALE REMOTE SENSING DATA." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-3 (April 30, 2018): 1009–14. http://dx.doi.org/10.5194/isprs-archives-xlii-3-1009-2018.
Abstract:
Satellite remote sensing data provide spatially continuous and temporally repetitive observations of land surfaces, and they have become increasingly important for monitoring large region of vegetation photosynthetic dynamic. But remote sensing data have their limitation on spatial and temporal scale, for example, higher spatial resolution data as Landsat data have 30-m spatial resolution but 16&thinsp;days revisit period, while high temporal scale data such as geostationary data have 30-minute imaging period, which has lower spatial resolution (&gt;&thinsp;1&thinsp;km). The objective of this study is to investigate whether combining high spatial and temporal resolution remote sensing data can improve the gross primary production (GPP) estimation accuracy in cropland. For this analysis we used three years (from 2010 to 2012) Landsat based NDVI data, MOD13 vegetation index product and Geostationary Operational Environmental Satellite (GOES) geostationary data as input parameters to estimate GPP in a small region cropland of Nebraska, US. Then we validated the remote sensing based GPP with the in-situ measurement carbon flux data. Results showed that: 1) the overall correlation between GOES visible band and in-situ measurement photosynthesis active radiation (PAR) is about 50&thinsp;% (R<sup>2</sup>&thinsp;=&thinsp;0.52) and the European Center for Medium-Range Weather Forecasts ERA-Interim reanalysis data can explain 64&thinsp;% of PAR variance (R<sup>2</sup>&thinsp;=&thinsp;0.64); 2) estimating GPP with Landsat 30-m spatial resolution data and ERA daily meteorology data has the highest accuracy(R<sup>2</sup>&thinsp;=&thinsp;0.85, RMSE &lt;&thinsp;3&thinsp;gC/m<sup>2</sup>/day), which has better performance than using MODIS 1-km NDVI/EVI product import; 3) using daily meteorology data as input for GPP estimation in high spatial resolution data would have higher relevance than 8-day and 16-day input. Generally speaking, using the high spatial resolution and high frequency satellite based remote sensing data can improve GPP estimation accuracy in cropland.
45
Lamy, Kévin, Thierry Portafaix, Colette Brogniez, Sophie Godin-Beekmann, Hassan Bencherif, Béatrice Morel, Andrea Pazmino, et al. "Ultraviolet radiation modelling from ground-based and satellite measurements on Reunion Island, southern tropics." Atmospheric Chemistry and Physics 18, no. 1 (January 9, 2018): 227–46. http://dx.doi.org/10.5194/acp-18-227-2018.
Abstract:
Abstract. Surface ultraviolet radiation (SUR) is not an increasing concern after the implementation of the Montreal Protocol and the recovery of the ozone layer (Morgenstern et al., 2008). However, large uncertainties remain in the prediction of future changes of SUR (Bais et al., 2015). Several studies pointed out that UV-B impacts the biosphere (Erickson et al., 2015), especially the aquatic system, which plays a central part in the biogeochemical cycle (Hader et al., 2007). It can affect phytoplankton productivity (Smith and Cullen, 1995). This influence can result in either positive or negative feedback on climate (Zepp et al., 2007). Global circulation model simulations predict an acceleration of the Brewer-Dobson circulation over the next century (Butchart, 2014), which would lead to a decrease in ozone levels in the tropics and an enhancement at higher latitudes (Hegglin and Shepherd, 2009). Reunion Island is located in the tropics (21° S, 55° E), in a part of the world where the amount of ozone in the ozone column is naturally low. In addition, this island is mountainous and the marine atmosphere is often clean with low aerosol concentrations. Thus, measurements show much higher SUR than at other sites at the same latitude or at midlatitudes. Ground-based measurements of SUR have been taken on Reunion Island by a Bentham DTMc300 spectroradiometer since 2009. This instrument is affiliated with the Network for the Detection of Atmospheric Composition Change (NDACC). In order to quantify the future evolution of SUR in the tropics, it is necessary to validate a model against present observations. This study is designed to be a preliminary parametric and sensitivity study of SUR modelling in the tropics. We developed a local parameterisation using the Tropospheric Ultraviolet and Visible Model (TUV; Madronich, 1993) and compared the output of TUV to multiple years of Bentham spectral measurements. This comparison started in early 2009 and continued until 2016. Only clear-sky SUR was modelled, so we needed to sort out the clear-sky measurements. We used two methods to detect cloudy conditions: the first was based on an observer's hourly report on the sky cover, while the second was based on applying Long and Ackerman (2000)'s algorithm to broadband pyranometer data to obtain the cloud fraction and then discriminating clear-sky windows on SUR measurements. Long et al. (2006)'s algorithm, with the co-located pyranometer data, gave better results for clear-sky filtering than the observer's report. Multiple model inputs were tested to evaluate the model sensitivity to different parameters such as total ozone column, aerosol optical properties, extraterrestrial spectrum or ozone cross section. For total column ozone, we used ground-based measurements from the SAOZ (Système d'Analyse par Observation Zénithale) spectrometer and satellite measurements from the OMI and SBUV instruments, while ozone profiles were derived from radio-soundings and the MLS ozone product. Aerosol optical properties came from a local aerosol climatology established using a Cimel photometer. Since the mean difference between various inputs of total ozone column was small, the corresponding response on UVI modelling was also quite small, at about 1 %. The radiative amplification factor of total ozone column on UVI was also compared for observations and the model. Finally, we were able to estimate UVI on Reunion Island with, at best, a mean relative difference of about 0.5 %, compared to clear-sky observations.
46
Meyssignac, Benoît, Jonathan Chenal, Robin Guillaume-Castel, Alejandro Blazquez, and Sébastien Fourest. "Mesurer le déséquilibre énergétique de la planète pour évaluer la sensibilité du climat aux émissions de gaz à effet de serre." La Météorologie, no. 122 (2023): 023. http://dx.doi.org/10.37053/lameteorologie-2023-0069.
Abstract:
La sensibilité climatique à l'équilibre (SCE) est définie comme le réchauffement de la surface terrestre en réponse à un doublement de la concentration du CO2 dans l'atmosphère par rapport au climat préindustriel. Estimer la SCE revient à estimer au premier ordre la réponse du bilan d'énergie de la planète aux émissions de gaz à effet de serre, ce qui permet ensuite de caractériser le changement climatique actuel. Pour cette raison, l'évaluation de la SCE est devenue depuis 40 ans un des objectifs majeurs de la recherche sur le climat. Face à un tel enjeu, il est apparu nécessaire d'utiliser les observations actuelles du bilan d'énergie pour contraindre de manière indépendante les estimations de la SCE qui jusqu'à récemment étaient essentiellement tirées des simulations des modèles de climat et des observations paléoclimatiques. Nous retraçons ici les progrès récents qui permettent désormais de déterminer la SCE grâce aux observations du bilan d'énergie de la Terre du réseau de profileurs océaniques Argo, l'altimétrie satellitaire et la gravimétrie spatiale. The equilibrium climate sensitivity (ECS) is defined as the equilibrium annual global mean temperature response to a doubling of atmospheric CO2 from preindustrial level. Estimating the ECS amounts to estimating the first-order response of the global energy balance to greenhouse gases emissions, which characterizes current climate change. For this reason, the assessment of the ECS has become one of the major objectives of climate research over the last 40 years. Faced with such a challenge, it appeared necessary to use current energy balance observations to independently constrain ECS estimates, which until recently were mainly derived from climate model simulations and paleoclimate observations. We trace here the recent progress which now makes it possible to determine the SCE thanks to the observations of the Earth energy imbalance with Argo oceanic profilers, satellite altimetry and space gravimetry.
47
Boynard, Anne, Daniel Hurtmans, Mariliza E. Koukouli, Florence Goutail, Jérôme Bureau, Sarah Safieddine, Christophe Lerot, et al. "Seven years of IASI ozone retrievals from FORLI: validation with independent total column and vertical profile measurements." Atmospheric Measurement Techniques 9, no. 9 (September 6, 2016): 4327–53. http://dx.doi.org/10.5194/amt-9-4327-2016.
Abstract:
Abstract. This paper presents an extensive intercomparison and validation for the ozone (O3) product measured by the two Infrared Atmospheric Sounding Interferometers (IASIs) launched on board the MetOp-A and MetOp-B satellites in 2006 and in 2012 respectively. IASI O3 total columns and vertical profiles obtained from Fast Optimal Retrievals on Layers for IASI (FORLI) v20140922 software (running up until recently) are validated against independent observations during the period 2008–2014 on a global scale. On average for the period 2013–2014, IASI-A and IASI-B total ozone columns (TOCs) retrieved using FORLI are consistent, with IASI-B providing slightly lower values with a global difference of only 0.2 ± 0.8 %. The comparison between IASI-A and IASI-B O3 vertical profiles shows differences within ± 2 % over the entire altitude range. Global validation results for 7 years of IASI TOCs from FORLI against the Global Ozone Monitoring Experiment-2 (GOME-2) launched on board MetOp-A and Brewer–Dobson data show that, on average, IASI overestimates the ultraviolet (UV) data by 5–6 % with the largest differences found in the southern high latitudes. The comparison with UV–visible SAOZ (Système d'Analyse par Observation Zénithale) measurements shows a mean bias between IASI and SAOZ TOCs of 2–4 % in the midlatitudes and tropics and 7 % at the polar circle. Part of the discrepancies found at high latitudes can be attributed to the limited information content in the observations due to low brightness temperatures. The comparison with ozonesonde vertical profiles (limited to 30 km) shows that on average IASI with FORLI processing underestimates O3 by ∼ 5–15 % in the troposphere while it overestimates O3 by ∼ 10–40 % in the stratosphere, depending on the latitude. The largest relative differences are found in the tropical tropopause region; this can be explained by the low O3 amounts leading to large relative errors. In this study, we also evaluate an updated version of FORLI-O3 retrieval software (v20151001), using look-up tables recalculated to cover a larger spectral range using the latest HITRAN spectroscopic database (HITRAN 2012) and implementing numerical corrections. The assessment of the new O3 product with the same set of observations as that used for the validation exercise shows a correction of ∼ 4 % for the TOC positive bias when compared to the UV ground-based and satellite observations, bringing the overall global comparison to ∼ 1–2 % on average. This improvement is mainly associated with a decrease in the retrieved O3 concentration in the middle stratosphere (above 30 hPa/25 km) as shown by the comparison with ozonesonde data.
48
Hilton, T. W., K. J. Davis, K. Keller, and N. M. Urban. "Improving North American terrestrial CO<sub>2</sub> flux diagnosis using spatial structure in land surface model residuals." Biogeosciences 10, no. 7 (July 11, 2013): 4607–25. http://dx.doi.org/10.5194/bg-10-4607-2013.
Abstract:
Abstract. We evaluate spatial structure in North American CO2 flux observations using a simple diagnostic land surface model. The vegetation photosynthesis respiration model (VPRM) calculates net ecosystem exchange (NEE) using locally observed temperature and photosynthetically active radiation (PAR) along with satellite-derived phenology and moisture. We use observed NEE from a group of 65 North American eddy covariance tower sites spanning North America to estimate VPRM parameters for these sites. We investigate spatial coherence in regional CO2 fluxes at several different time scales by using geostatistical methods to examine the spatial structure of model–data residuals. We find that persistent spatial structure does exist in the model–data residuals at a length scale of approximately 400 km (median 402 km, mean 712 km, standard deviation 931 km). This spatial structure defines a flux-tower-based VPRM residual covariance matrix. The residual covariance matrix is useful in constructing prior fluxes for atmospheric CO2 concentration inversion calculations, as well as for constructing a VPRM North American CO2 flux map optimized to eddy covariance observations. Finally (and secondarily), the estimated VPRM parameter values do not separate clearly by plant functional type (PFT). This calls into question whether PFTs can successfully partition ecosystems' fundamental ecological drivers when the viewing lens is a simple model.
49
Pastel, M., J. P. Pommereau, F. Goutail, A. Richter, A. Pazmiño, D. Ionov, and T. Portafaix. "Construction of merged satellite total O<sub>3</sub> and NO<sub>2</sub> time series in the tropics for trend studies and evaluation by comparison to NDACC SAOZ measurements." Atmospheric Measurement Techniques 7, no. 10 (October 7, 2014): 3337–54. http://dx.doi.org/10.5194/amt-7-3337-2014.
Abstract:
Abstract. Long time series of ozone and NO2 total column measurements in the southern tropics are available from two ground-based SAOZ (Système d'Analyse par Observation Zénithale) UV-visible spectrometers operated within the Network for the Detection of Atmospheric Composition Change (NDACC) in Bauru (22° S, 49° W) in S-E Brazil since 1995 and Reunion Island (21° S, 55° E) in the S-W Indian Ocean since 1993. Although the stations are located at the same latitude, significant differences are observed in the columns of both species, attributed to differences in tropospheric content and equivalent latitude in the lower stratosphere. These data are used to identify which satellites operating during the same period, are capturing the same features and are thus best suited for building reliable merged time series for trend studies. For ozone, the satellites series best matching SAOZ observations are EP-TOMS (1995–2004) and OMI-TOMS (2005–2011), whereas for NO2, best results are obtained by combining GOME version GDP5 (1996–2003) and SCIAMACHY – IUP (2003–2011), displaying lower noise and seasonality in reference to SAOZ. Both merged data sets are fully consistent with the larger columns of the two species above South America and the seasonality of the differences between the two stations, reported by SAOZ, providing reliable time series for further trend analyses and identification of sources of interannual variability in the future analysis.
50
Rajani Kanta, Mishra, Jena Babula, Narayana Pillai Anilkumar, Naik Ravidas Krishna, Parli Venkateswaran Bhaskar, and Soares Melena A. "Variability of chlorophyll-a and diatoms in the frontal ecosystem of Indian Ocean sector of the Southern Ocean." Polish Polar Research 38, no. 3 (September 1, 2017): 375–92. http://dx.doi.org/10.1515/popore-2017-0014.
Abstract:
Abstract Phytoplankton composition plays a major role in biogeochemical cycles of the ocean. The intensity of carbon fixation and export is strongly dependent on the phytoplankton community. Yet, the contribution of different types of phytoplankton to the total production on various communities is still poorly understood in the Indian Ocean sector of Southern Ocean (SO). Therefore the variability of chlorophyll-a (Chl-a) and diatoms in the frontal ecosystems of the Indian sector of SO have been investigated along with the sea surface temperature (SST), sea surface wind (SSW), photosynthetically active radiation (PAR), and nutrients datasets for the period of 1998–2012. Combined analysis of in-situ, model and satellite observations indicate that the variability of Chl-a and diatoms were primarily influenced by light and wind. The Chl-a was higher at the sub-Antarctic front (SAF) followed by the sub-tropical front (STF) and the polar front (PF). The diatom concentration was higher at the SAF followed by the PF and STF. Maximum concentration of Chl-a and diatoms commonly observed at the SAF region are probably due to the moderate PAR, SST and wind. Dominance of diatoms at the PF may be attributed to their adaptability for low light conditions. The results from this study in the frontal ecosystems would help to understand the biogeochemical cycle of the Indian sector of the SO.