Journal articles on the topic 'Airborne Eddy Covariance'
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1
Lloyd, J., O. Kolle, H. Fritsch, S. R. de Freitas, M. A. F. Silva Dias, P. Artaxo, A. D. Nobre, et al. "An airborne regional carbon balance for Central Amazonia." Biogeosciences 4, no. 5 (September 14, 2007): 759–68. http://dx.doi.org/10.5194/bg-4-759-2007.
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Abstract. We obtained regional estimates of surface CO2 exchange rates using atmospheric boundary layer budgeting techniques above tropical forest near Manaus, Brazil. Comparisons were made with simultaneous measurements from two eddy covariance towers below. Although there was good agreement for daytime measurements, large differences emerged for integrating periods dominated by the night-time fluxes. These results suggest that a systematic underestimation of night time respiratory effluxes may be responsible for the high Amazonian carbon sink suggested by several previous eddy covariance studies. Large CO2 fluxes from riverine sources or high respiratory losses from recently disturbed forests do not need to be invoked in order to balance the carbon budget of the Amazon. Our results do not, however, discount some contribution of these processes to the overall Amazon carbon budget.
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Lloyd, J., O. Kolle, H. Fritsch, S. R. de Freitas, M. A. F. Silva Dias, P. Artaxo, A. D. Nobre, et al. "An airborne regional carbon balance for Central Amazonia." Biogeosciences Discussions 4, no. 1 (January 24, 2007): 99–123. http://dx.doi.org/10.5194/bgd-4-99-2007.
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Abstract. We obtained regional estimates of surface CO2 exchange rates using atmospheric boundary layer budgeting techniques above tropical forest near Manaus, Brazil. Comparisons were made with simultaneous measurements from two eddy covariance towers below. Although there was good agreement for daytime measurements, large differences emerged for integrating periods dominated by the night-time fluxes. These results suggest that a systematic underestimation of night time respiratory effluxes may be responsible for the high Amazonian carbon sink suggested by several previous eddy covariance studies. Large CO2 fluxes from riverine sources or high respiratory losses from recently disturbed forests do not need to be invoked in order to balance the carbon budget of the Amazon. Our results do not, however, discount some contribution of these processes to the overall Amazon carbon budget.
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Ellsäßer, Florian, Christian Stiegler, Alexander Röll, Tania June, Alexander Knohl, and Dirk Hölscher. "Predicting evapotranspiration from drone-based thermography – a method comparison in a tropical oil palm plantation." Biogeosciences 18, no. 3 (February 5, 2021): 861–72. http://dx.doi.org/10.5194/bg-18-861-2021.
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Abstract. For the assessment of evapotranspiration, near-surface airborne thermography offers new opportunities for studies with high numbers of spatial replicates and in a fine spatial resolution. We tested drone-based thermography and the subsequent application of the DATTUTDUT energy balance model using the widely accepted eddy covariance technique as a reference method. The study site was a mature oil palm plantation in lowland Sumatra, Indonesia. For the 61 flight missions, latent heat flux estimates of the DATTUTDUT (Deriving Atmosphere Turbulent Transport Useful To Dummies Using Temperature) model with measured net radiation agreed well with eddy covariance measurements (r2 = 0.85; MAE = 47; RMSE = 60) across variable weather conditions and times of day. Confidence intervals for slope and intercept of a model II Deming regression suggest no difference between drone-based and eddy covariance methods, thus indicating interchangeability. The DATTUTDUT model is sensitive to the configuration of the net radiation assessment. Overall, we conclude that drone-based thermography with energy balance modeling is a reliable method complementing available methods for evapotranspiration studies. It offers promising, additional opportunities for fine grain and spatially explicit studies.
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Karl, T., P. K. Misztal, H. H. Jonsson, S. Shertz, A. H. Goldstein, and A. B. Guenther. "Airborne Flux Measurements of BVOCs above Californian Oak Forests: Experimental Investigation of Surface and Entrainment Fluxes, OH Densities, and Damköhler Numbers." Journal of the Atmospheric Sciences 70, no. 10 (October 1, 2013): 3277–87. http://dx.doi.org/10.1175/jas-d-13-054.1.
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Abstract Airborne flux measurements of isoprene were performed over the Californian oak belts surrounding the Central Valley. The authors demonstrate for the first time 1) the feasibility of airborne eddy covariance measurements of reactive biogenic volatile organic compounds; 2) the effect of chemistry on the vertical transport of reactive species, such as isoprene; and 3) the applicability of wavelet analysis to estimate regional fluxes of biogenic volatile organic compounds. These flux measurements demonstrate that instrumentation operating at slower response times (e.g., 1–5 s) can still be used to determine eddy covariance fluxes in the mixed layer above land, where typical length scales of 0.5–3 km were observed. Flux divergence of isoprene measured in the planetary boundary layer (PBL) is indicative of OH densities in the range of 4–7 × 106 molecules per cubic centimeter and allows extrapolation of airborne fluxes to the surface with Damköhler numbers (ratio between the mixing time scale and the chemical time scale) in the range of 0.3–0.9. Most of the isoprene is oxidized in the PBL with entrainment fluxes of about 10% compared to the corresponding surface fluxes. Entrainment velocities of 1–10 cm s−1 were measured. The authors present implications for parameterizing PBL schemes of reactive species in regional and global models.
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Witt, Felix, Javis Nwaboh, Henning Bohlius, Astrid Lampert, and Volker Ebert. "Towards a Fast, Open-Path Laser Hygrometer for Airborne Eddy Covariance Measurements." Applied Sciences 11, no. 11 (June 3, 2021): 5189. http://dx.doi.org/10.3390/app11115189.
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Water vapor fluxes play a key role in the energy budget of the atmosphere, and better flux measurements are needed to improve our understanding of the formation of clouds and storms. Large-scale measurements of these fluxes are possible by employing the eddy correlation (EC) method from an aircraft. A hygrometer used for such measurements needs to deliver a temporal resolution of at least 10 Hz while reliably operating in the harsh conditions on the exterior of an aircraft. Here, we present a design concept for a calibration-free, first-principles, open-path dTDLAS hygrometer with a planar, circular and rotationally symmetric multipass cell with new, angled coupling optics. From our measurements, the uncertainty of the instrument is estimated to be below 4.5% (coverage factor k = 1). A static intercomparison between a dTDLAS prototype of the new optics setup and a traceable dew point mirror hygrometer was conducted and showed a systematic relative deviation of 2.6% with a maximal relative error of 2.2%. Combined with a precision of around 1 ppm H2O at tropospheric conditions, the newly designed setup fulfills the static precision and accuracy requirements of the proposed airborne EC hygrometer.
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Miglietta, F., B. Gioli, Y. Brunet, R. W. A. Hutjes, A. Matese, C. Sarrat, and A. Zaldei. "Sensible and latent heat flux from radiometric surface temperatures at the regional scale: methodology and validation." Biogeosciences Discussions 6, no. 1 (February 10, 2009): 1945–78. http://dx.doi.org/10.5194/bgd-6-1945-2009.
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Abstract. The CarboEurope Regional Experiment Strategy (CERES) was designed to develop and test a range of methodologies to assess regional surface energy and mass exchange of a large study area in the south-western part of France. This paper describes a methodology to estimate sensible and latent heat fluxes on the basis of net radiation, surface radiometric temperature measurements and information obtained from available products derived from the Meteosat Second Generation (MSG) geostationary meteorological satellite, weather stations and ground-based eddy covariance towers. It is based on a simplified bulk formulation of sensible heat flux that considers the degree of coupling between the vegetation and the atmosphere and estimates latent heat as the residual term of net radiation. Estimates of regional energy fluxes obtained in this way are validated at the regional scale by means of a comparison with direct flux measurements made by airborne eddy-covariance. The results show an overall good matching between airborne fluxes and estimates of sensible and latent heat flux obtained from radiometric surface temperatures that holds for different weather conditions and different land use types. The overall applicability of the proposed methodology to regional studies is discussed.
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Miglietta, F., B. Gioli, Y. Brunet, R. W. A. Hutjes, A. Matese, C. Sarrat, and A. Zaldei. "Sensible and latent heat flux from radiometric surface temperatures at the regional scale: methodology and evaluation." Biogeosciences 6, no. 10 (October 2, 2009): 1975–86. http://dx.doi.org/10.5194/bg-6-1975-2009.
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Abstract. The CarboEurope Regional Experiment Strategy (CERES) was designed to develop and test a range of methodologies to assess regional surface energy and mass exchange of a large study area in the South-Western part of France. This paper describes a methodology to estimate sensible and latent heat fluxes on the basis of net radiation, surface radiometric temperature measurements and information obtained from available products derived from the Meteosat Second Generation (MSG) geostationary meteorological satellite, weather stations and ground-based eddy covariance towers. It is based on a simplified bulk formulation of sensible heat flux that considers the degree of coupling between the vegetation and the atmosphere and estimates latent heat as the residual term of net radiation. Estimates of regional energy fluxes obtained in this way are validated at the regional scale by means of a comparison with direct flux measurements made by airborne eddy-covariance. The results show an overall good matching between airborne fluxes and estimates of sensible and latent heat flux obtained from radiometric surface temperatures that holds for different weather conditions and different land use types. The overall applicability of the proposed methodology to regional studies is discussed.
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Ammann, C., V. Wolff, O. Marx, C. Brümmer, and A. Neftel. "Measuring the biosphere-atmosphere exchange of total reactive nitrogen by eddy covariance." Biogeosciences Discussions 9, no. 6 (June 13, 2012): 6857–98. http://dx.doi.org/10.5194/bgd-9-6857-2012.
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Abstract. The (net) exchange of reactive nitrogen (Nr) with the atmosphere is an important driver for ecosystem productivity and greenhouse gas exchange. The exchange of airborne Nr includes various trace compounds that usually require different specific measurement techniques, and up to now fast response instruments suitable for eddy covariance measurements are only available for few of these compounds. Here we present eddy covariance flux measurements with a recently introduced converter (TRANC) for the sum of all Nr compounds (∑Nr). Measurements were performed over a managed grassland field with phases of net emission and net deposition of ∑Nr and alternating dominance of oxidized (NOx) and reduced species (NH3). Spectral analysis of the eddy covariance data exhibited the existence of covariance function peaks at a reasonable time lag related to the sampling tube residence time under stationary conditions. Using ogive analysis, the high-frequency damping was quantified to 19–26% for a low measurement height of 1.2 m and to about 10% for 4.8 m measurement height. ∑Nr concentrations and fluxes were compared to parallel NO and NO2 measurements by dynamic chambers and NH3 measurements by the aerodynamic gradient technique. The average concentration results indicate that close-to-full conversion of the main compounds NO2 and NH3 was generally obtained by the TRANC system. With an optimised sample inlet also the fluxes of these compounds were recovered fairly including net deposition and net emission phases. The study shows that the TRANC system is suitable for fast response measurements of oxidized and reduced nitrogen compounds and can be used for continuous eddy covariance flux measurements of total reactive nitrogen.
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Ammann, C., V. Wolff, O. Marx, C. Brümmer, and A. Neftel. "Measuring the biosphere-atmosphere exchange of total reactive nitrogen by eddy covariance." Biogeosciences 9, no. 11 (November 2, 2012): 4247–61. http://dx.doi.org/10.5194/bg-9-4247-2012.
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Abstract. The (net) exchange of reactive nitrogen (Nr) with the atmosphere is an important driver for ecosystem productivity and greenhouse gas exchange. The exchange of airborne Nr includes various trace compounds that usually require different specific measurement techniques, and up to now fast response instruments suitable for eddy covariance measurements are only available for few of these compounds. Here we present eddy covariance flux measurements with a recently introduced converter (TRANC) for the sum of all Nr compounds (∑Nr). Measurements were performed over a managed grassland field with phases of net emission and net deposition of ∑Nr and alternating dominance of oxidized (NOX) and reduced species (NH3). Spectral analysis of the eddy covariance data exhibited the existence of covariance function peaks at a reasonable time lag related to the sampling tube residence time under stationary conditions. Using ogive analysis, the high-frequency damping was quantified to 19%–26% for a low measurement height of 1.2 m and to about 10% for 4.8 m measurement height. ∑Nr concentrations and fluxes were compared to parallel NO and NO2 measurements by dynamic chambers and NH3 measurements by the aerodynamic gradient technique. The average concentration results indicate that the main compounds NO2 and NH3 were converted by the TRANC system with an efficiency of near 100%. With an optimised sample inlet also the fluxes of these compounds were recovered reasonably well including net deposition and net emission phases. The study shows that the TRANC system is suitable for fast response measurements of oxidized and reduced nitrogen compounds and can be used for continuous eddy covariance flux measurements of total reactive nitrogen.
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Serafimovich, Andrei, Stefan Metzger, Jörg Hartmann, Katrin Kohnert, Donatella Zona, and Torsten Sachs. "Upscaling surface energy fluxes over the North Slope of Alaska using airborne eddy-covariance measurements and environmental response functions." Atmospheric Chemistry and Physics 18, no. 13 (July 13, 2018): 10007–23. http://dx.doi.org/10.5194/acp-18-10007-2018.
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Abstract. The objective of this study was to upscale airborne flux measurements of sensible heat and latent heat and to develop high-resolution flux maps. In order to support the evaluation of coupled atmospheric–land-surface models we investigated spatial patterns of energy fluxes in relation to land-surface properties. We used airborne eddy-covariance measurements acquired by the Polar 5 research aircraft in June–July 2012 to analyze surface fluxes. Footprint-weighted surface properties were then related to 21 529 sensible heat flux observations and 25 608 latent heat flux observations using both remote sensing and modeled data. A boosted regression tree technique was used to estimate environmental response functions between spatially and temporally resolved flux observations and corresponding biophysical and meteorological drivers. In order to improve the spatial coverage and spatial representativeness of energy fluxes we used relationships extracted across heterogeneous Arctic landscapes to infer high-resolution surface energy flux maps, thus directly upscaling the observational data. These maps of projected sensible heat and latent heat fluxes were used to assess energy partitioning in northern ecosystems and to determine the dominant energy exchange processes in permafrost areas. This allowed us to estimate energy fluxes for specific types of land cover, taking into account meteorological conditions. Airborne and modeled fluxes were then compared with measurements from an eddy-covariance tower near Atqasuk. Our results are an important contribution for the advanced, scale-dependent quantification of surface energy fluxes and they provide new insights into the processes affecting these fluxes for the main vegetation types in high-latitude permafrost areas.
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Metzger, S., W. Junkermann, M. Mauder, F. Beyrich, K. Butterbach-Bahl, H. P. Schmid, and T. Foken. "Eddy Covariance flux measurements with a weight-shift microlight aircraft." Atmospheric Measurement Techniques Discussions 5, no. 2 (March 30, 2012): 2591–643. http://dx.doi.org/10.5194/amtd-5-2591-2012.
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Abstract. The objective of this study is to assess the feasibility and quality of Eddy-Covariance flux measurements from a weight-shift microlight aircraft (WSMA). Firstly we investigate the precision of the wind measurement (σu,v≤ 0.09 m s−1, σw = 0.04 m s−1), the lynchpin of flux calculations from aircraft. From here the smallest resolvable changes in friction velocity (0.02 m s−1), and sensible- (5 W m−2) and latent (3 W m−2) heat flux are estimated. Secondly a seven-day flight campaign was performed near Lindenberg (Germany). Here we compare measurements of wind, temperature, humidity and respective fluxes between a tall tower and the WSMA. The maximum likelihood functional relationship (MLFR) between tower and WSMA measurements considers the random error in the data, and shows very good agreement of the scalar averages. The MLFRs for standard deviations (SDs, 2–34%) and fluxes (17–21%) indicate higher estimates of the airborne measurements compared to the tower. Considering the 99.5% confidence intervals the observed differences are not significant, with exception of the temperature SD. The comparison with a large-aperture scintillometer reveals lower sensible heat flux estimates at both, tower (−40–−25%) and WSMA (−25–0%). We relate the observed differences to (i) inconsistencies in the temperature and wind measurement at the tower and (ii) the measurement platforms differing abilities to capture contributions from non-propagating eddies. These findings encourage the use of WSMA as a low price and highly versatile flux measurement platform.
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Vaughan, Adam R., James D. Lee, Marvin D. Shaw, Pawel K. Misztal, Stefan Metzger, Massimo Vieno, Brian Davison, et al. "VOC emission rates over London and South East England obtained by airborne eddy covariance." Faraday Discussions 200 (2017): 599–620. http://dx.doi.org/10.1039/c7fd00002b.
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Volatile organic compounds (VOCs) originate from a variety of sources, and play an intrinsic role in influencing air quality. Some VOCs, including benzene, are carcinogens and so directly affect human health, while others, such as isoprene, are very reactive in the atmosphere and play an important role in the formation of secondary pollutants such as ozone and particles. Here we report spatially-resolved measurements of the surface-to-atmosphere fluxes of VOCs across London and SE England made in 2013 and 2014. High-frequency 3-D wind velocities and VOC volume mixing ratios (made by proton transfer reaction – mass spectrometry) were obtained from a low-flying aircraft and used to calculate fluxes using the technique of eddy covariance. A footprint model was then used to quantify the flux contribution from the ground surface at spatial resolution of 100 m, averaged to 1 km. Measured fluxes of benzene over Greater London showed positive agreement with the UK’s National Atmospheric Emissions Inventory, with the highest fluxes originating from central London. Comparison of MTBE and toluene fluxes suggest that petroleum evaporation is an important emission source of toluene in central London. Outside London, increased isoprene emissions were observed over wooded areas, at rates greater than those predicted by a UK regional application of the European Monitoring and Evaluation Programme model (EMEP4UK). This work demonstrates the applicability of the airborne eddy covariance method to the determination of anthropogenic and biogenic VOC fluxes and the possibility of validating emission inventories through measurements.
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Metzger, S., W. Junkermann, M. Mauder, F. Beyrich, K. Butterbach-Bahl, H. P. Schmid, and T. Foken. "Eddy-covariance flux measurements with a weight-shift microlight aircraft." Atmospheric Measurement Techniques 5, no. 7 (July 19, 2012): 1699–717. http://dx.doi.org/10.5194/amt-5-1699-2012.
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Abstract. The objective of this study is to assess the feasibility and quality of eddy-covariance flux measurements from a weight-shift microlight aircraft (WSMA). Firstly, we investigate the precision of the wind measurement (σu,v ≤ 0.09 m s−1, σw = 0.04 m s−1), the lynchpin of flux calculations from aircraft. From here, the smallest resolvable changes in friction velocity (0.02 m s−1), and sensible- (5 W m−2) and latent (3 W m−2) heat flux are estimated. Secondly, a seven-day flight campaign was performed near Lindenberg (Germany). Here we compare measurements of wind, temperature, humidity and respective fluxes between a tall tower and the WSMA. The maximum likelihood functional relationship (MLFR) between tower and WSMA measurements considers the random error in the data, and shows very good agreement of the scalar averages. The MLFRs for standard deviations (SDs, 2–34%) and fluxes (17–21%) indicate higher estimates of the airborne measurements compared to the tower. Considering the 99.5% confidence intervals, the observed differences are not significant, with exception of the temperature SD. The comparison with a large-aperture scintillometer reveals lower sensible heat flux estimates at both tower (−40 to −25%) and WSMA (−25–0%). We relate the observed differences to (i) inconsistencies in the temperature and wind measurement at the tower and (ii) the measurement platforms' differing abilities to capture contributions from non-propagating eddies. These findings encourage the use of WSMA as a low cost and highly versatile flux measurement platform.
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Misztal, P. K., T. Karl, R. Weber, H. H. Jonsson, A. B. Guenther, and A. H. Goldstein. "Airborne flux measurements of biogenic volatile organic compounds over California." Atmospheric Chemistry and Physics Discussions 14, no. 6 (March 24, 2014): 7965–8013. http://dx.doi.org/10.5194/acpd-14-7965-2014.
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Abstract. Biogenic Volatile Organic Compound (BVOC) fluxes were measured onboard the CIRPAS Twin Otter aircraft as part of the California Airborne BVOC Emission Research in Natural Ecosystem Transects (CABERNET) campaign during June 2011. The airborne virtual disjunct eddy covariance (AvDEC) approach used measurements from a PTR-MS and a wind radome probe to directly determine fluxes of isoprene, MVK + MAC, methanol, monoterpenes, and MBO over ∼10 000 km of flight paths focusing on areas of California predicted to have the largest emissions of isoprene. The Fast Fourier Transform (FFT) approach was used to calculate fluxes over long transects of more than 15 km, most commonly between 50 and 150 km. The Continuous Wavelet Transformation (CWT) approach was used over the same transects to also calculate "instantaneous" fluxes with localization of both frequency and time independent of non-stationarities. Vertical flux divergence of isoprene is expected due to its relatively short lifetime and was measured directly using "racetrack" profiles at multiple altitudes. It was found to be linear and in the range 5% to 30% depending on the ratio of aircraft altitude to PBL height (z / zi). Fluxes were generally measured by flying consistently at 400 ± 50 m (a.g.l.) altitude, and extrapolated to the surface according to the determined flux divergence. The wavelet-derived surface fluxes of isoprene averaged to 2 km spatial resolution showed good correspondence to Basal Emission Factor (BEF) landcover datasets used to drive biogenic VOC (BVOC) emission models. The surface flux of isoprene was close to zero over Central Valley crops and desert shrublands, but was very high (up to 15 mg m−2 h−1) above oak woodlands, with clear dependence of emissions on temperature and oak density. Isoprene concentrations of up to 8 ppb were observed at aircraft height on the hottest days and over the dominant source regions. While isoprene emissions from agricultural crop regions, shrublands, and coniferous forests were extremely low, high concentrations of methanol and monoterpenes were found above some of these regions. These observations demonstrate the ability to measure fluxes from specific sources by eddy covariance from an aircraft, and suggest the utility of measurements using fast response chemical sensors to constrain emission inventories and map out source distributions for a much broader array of trace gases than was observed in this study. This paper reports the first regional direct eddy covariance fluxes of isoprene. The emissions of VOCs measured from aircraft with 2 km spatial resolution can quantify the distribution of major sources providing the observations required for testing statewide emission inventories of these important trace gases. These measurements will be used in a future study to assess BVOC emission models and their driving variable datasets.
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Karl, T., E. Apel, A. Hodzic, D. Riemer, D. Blake, and C. Wiedinmyer. "Emissions of volatile organic compounds inferred from airborne flux measurements over a megacity." Atmospheric Chemistry and Physics Discussions 8, no. 4 (July 25, 2008): 14273–309. http://dx.doi.org/10.5194/acpd-8-14273-2008.
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Abstract. Toluene and benzene are used for assessing the ability to measure disjunct eddy covariance (DEC) fluxes of Volatile Organic Compounds (VOC) using Proton Transfer Reaction Mass Spectrometry (PTR-MS) on aircraft. Statistically significant correlation between vertical wind speed and mixing ratios suggests that airborne VOC eddy covariance (EC) flux measurements using PTR-MS are feasible. City-average midday toluene and benzene fluxes are calculated to be on the order of 15.5±4.0 mg/m2/h and 4.7±2.3 mg/m2/h respectively. These values argue for an underestimation of toluene and benzene emissions in current inventories used for the Mexico City Metropolitan Area (MCMA). Wavelet analysis of instantaneous toluene and benzene measurements during city overpasses is tested as a tool to assess surface emission heterogeneity. High toluene to benzene flux ratios above an industrial district (e.g. 10–15) including the International airport (e.g. 3–5) and a mean flux (concentration) ratio of 3.2±0.5 (3.9±0.3) across Mexico City indicate that evaporative fuel and industrial emissions play an important role for the prevalence of aromatic compounds. Based on a tracer model, which was constrained by BTEX (Benzene/Toluene/Ethylbenzene/m,p,o-Xylenes) compound concentration ratios, the fuel marker methyl-tertiary-butyl-ether (MTBE) and the biomass burning marker acetonitrile (CH3CN), we show that a combination of industrial, evaporative fuel, and exhaust emissions account for >90% of all BTEX sources. Our observations suggest that biomass burning emissions play a minor role for the abundance of BTEX compounds (0–10%) in the MCMA.
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Karl, T., E. Apel, A. Hodzic, D. D. Riemer, D. R. Blake, and C. Wiedinmyer. "Emissions of volatile organic compounds inferred from airborne flux measurements over a megacity." Atmospheric Chemistry and Physics 9, no. 1 (January 14, 2009): 271–85. http://dx.doi.org/10.5194/acp-9-271-2009.
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Abstract. Toluene and benzene are used for assessing the ability to measure disjunct eddy covariance (DEC) fluxes of Volatile Organic Compounds (VOC) using Proton Transfer Reaction Mass Spectrometry (PTR-MS) on aircraft. Statistically significant correlation between vertical wind speed and mixing ratios suggests that airborne VOC eddy covariance (EC) flux measurements using PTR-MS are feasible. City-median midday toluene and benzene fluxes are calculated to be on the order of 14.1±4.0 mg/m2/h and 4.7±2.3 mg/m2/h, respectively. For comparison the adjusted CAM2004 emission inventory estimates toluene fluxes of 10 mg/m2/h along the footprint of the flight-track. Wavelet analysis of instantaneous toluene and benzene measurements during city overpasses is tested as a tool to assess surface emission heterogeneity. High toluene to benzene flux ratios above an industrial district (e.g. 10–15 g/g) including the International airport (e.g. 3–5 g/g) and a mean flux (concentration) ratio of 3.2±0.5 g/g (3.9±0.3 g/g) across Mexico City indicate that evaporative fuel and industrial emissions play an important role for the prevalence of aromatic compounds. Based on a tracer model, which was constrained by BTEX (BTEX– Benzene/Toluene/Ethylbenzene/m, p, o-Xylenes) compound concentration ratios, the fuel marker methyl-tertiary-butyl-ether (MTBE) and the biomass burning marker acetonitrile (CH3CN), we show that a combination of industrial, evaporative fuel, and exhaust emissions account for >87% of all BTEX sources. Our observations suggest that biomass burning emissions play a minor role for the abundance of BTEX compounds in the MCMA (2–13%).
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Wilkerson, Jordan, Ronald Dobosy, David S. Sayres, Claire Healy, Edward Dumas, Bruce Baker, and James G. Anderson. "Permafrost nitrous oxide emissions observed on a landscape scale using the airborne eddy-covariance method." Atmospheric Chemistry and Physics 19, no. 7 (April 3, 2019): 4257–68. http://dx.doi.org/10.5194/acp-19-4257-2019.
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Abstract. The microbial by-product nitrous oxide (N2O), a potent greenhouse gas and ozone depleting substance, has conventionally been assumed to have minimal emissions in permafrost regions. This assumption has been questioned by recent in situ studies which have demonstrated that some geologic features in permafrost may, in fact, have elevated emissions comparable to those of tropical soils. However, these recent studies, along with every known in situ study focused on permafrost N2O fluxes, have used chambers to examine small areas (<50 m2). In late August 2013, we used the airborne eddy-covariance technique to make in situ N2O flux measurements over the North Slope of Alaska from a low-flying aircraft spanning a much larger area: around 310 km2. We observed large variability of N2O fluxes with many areas exhibiting negligible emissions. Still, the daily mean averaged over our flight campaign was 3.8 (2.2–4.7) mg N2O m−2 d−1 with the 90 % confidence interval shown in parentheses. If these measurements are representative of the whole month, then the permafrost areas we observed emitted a total of around 0.04–0.09 g m−2 for August, which is comparable to what is typically assumed to be the upper limit of yearly emissions for these regions.
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Vaughan, Adam R., James D. Lee, Stefan Metzger, David Durden, Alastair C. Lewis, Marvin D. Shaw, Will S. Drysdale, Ruth M. Purvis, Brian Davison, and C. Nicholas Hewitt. "Spatially and temporally resolved measurements of NO<sub><i>x</i></sub> fluxes by airborne eddy covariance over Greater London." Atmospheric Chemistry and Physics 21, no. 19 (October 14, 2021): 15283–98. http://dx.doi.org/10.5194/acp-21-15283-2021.
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Abstract. Flux measurements of nitrogen oxides (NOx) were made over London using airborne eddy covariance from a low-flying aircraft. Seven low-altitude flights were conducted over Greater London, performing multiple overpasses across the city during eight days in July 2014. NOx fluxes across the Greater London region (GLR) exhibited high heterogeneity and strong diurnal variability, with central areas responsible for the highest emission rates (20–30 mg m−2 h−1). Other high-emission areas included the M25 orbital motorway. The complexity of London's emission characteristics makes it challenging to pinpoint single emissions sources definitively using airborne measurements. Multiple sources, including road transport and residential, commercial and industrial combustion sources, are all likely to contribute to measured fluxes. Measured flux estimates were compared to scaled National Atmospheric Emissions Inventory (NAEI) estimates, accounting for monthly, daily and hourly variability. Significant differences were found between the flux-driven emissions and the NAEI estimates across Greater London, with measured values up to 2 times higher in Central London than those predicted by the inventory. To overcome the limitations of using the national inventory to contextualise measured fluxes, we used physics-guided flux data fusion to train environmental response functions (ERFs) between measured flux and environmental drivers (meteorological and surface). The aim was to generate time-of-day emission surfaces using calculated ERF relationships for the entire GLR; 98 % spatial coverage was achieved across the GLR at 400 m2 spatial resolution. All flight leg projections showed substantial heterogeneity across the domain, with high emissions emanating from Central London and major road infrastructure. The diurnal emission structure of the GLR was also investigated, through ERF, with the morning rush hour distinguished from lower emissions during the early afternoon. Overall, the integration of airborne fluxes with an ERF-driven strategy enabled the first independent generation of surface NOx emissions, at high resolution using an eddy-covariance approach, for an entire city region.
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Vaughan, Adam R., James D. Lee, Stefan Metzger, David Durden, Alastair C. Lewis, Marvin D. Shaw, Will S. Drysdale, Ruth M. Purvis, Brian Davison, and C. Nicholas Hewitt. "Spatially and temporally resolved measurements of NO<sub><i>x</i></sub> fluxes by airborne eddy covariance over Greater London." Atmospheric Chemistry and Physics 21, no. 19 (October 14, 2021): 15283–98. http://dx.doi.org/10.5194/acp-21-15283-2021.
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Abstract. Flux measurements of nitrogen oxides (NOx) were made over London using airborne eddy covariance from a low-flying aircraft. Seven low-altitude flights were conducted over Greater London, performing multiple overpasses across the city during eight days in July 2014. NOx fluxes across the Greater London region (GLR) exhibited high heterogeneity and strong diurnal variability, with central areas responsible for the highest emission rates (20–30 mg m−2 h−1). Other high-emission areas included the M25 orbital motorway. The complexity of London's emission characteristics makes it challenging to pinpoint single emissions sources definitively using airborne measurements. Multiple sources, including road transport and residential, commercial and industrial combustion sources, are all likely to contribute to measured fluxes. Measured flux estimates were compared to scaled National Atmospheric Emissions Inventory (NAEI) estimates, accounting for monthly, daily and hourly variability. Significant differences were found between the flux-driven emissions and the NAEI estimates across Greater London, with measured values up to 2 times higher in Central London than those predicted by the inventory. To overcome the limitations of using the national inventory to contextualise measured fluxes, we used physics-guided flux data fusion to train environmental response functions (ERFs) between measured flux and environmental drivers (meteorological and surface). The aim was to generate time-of-day emission surfaces using calculated ERF relationships for the entire GLR; 98 % spatial coverage was achieved across the GLR at 400 m2 spatial resolution. All flight leg projections showed substantial heterogeneity across the domain, with high emissions emanating from Central London and major road infrastructure. The diurnal emission structure of the GLR was also investigated, through ERF, with the morning rush hour distinguished from lower emissions during the early afternoon. Overall, the integration of airborne fluxes with an ERF-driven strategy enabled the first independent generation of surface NOx emissions, at high resolution using an eddy-covariance approach, for an entire city region.
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MIGLIETTA, F., B. GIOLI, R. W. A. HUTJES, and M. REICHSTEIN. "Net regional ecosystem CO2exchange from airborne and ground-based eddy covariance, land-use maps and weather observations." Global Change Biology 13, no. 3 (March 2007): 548–60. http://dx.doi.org/10.1111/j.1365-2486.2006.01219.x.
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Font, A., C. S. B. Grimmond, S. Kotthaus, J. A. Morguí, C. Stockdale, E. O'Connor, M. Priestman, and B. Barratt. "Daytime CO2 urban surface fluxes from airborne measurements, eddy-covariance observations and emissions inventory in Greater London." Environmental Pollution 196 (January 2015): 98–106. http://dx.doi.org/10.1016/j.envpol.2014.10.001.
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Misztal, P. K., T. Karl, R. Weber, H. H. Jonsson, A. B. Guenther, and A. H. Goldstein. "Airborne flux measurements of biogenic isoprene over California." Atmospheric Chemistry and Physics 14, no. 19 (October 10, 2014): 10631–47. http://dx.doi.org/10.5194/acp-14-10631-2014.
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Abstract. Biogenic isoprene fluxes were measured onboard the CIRPAS Twin Otter aircraft as part of the California Airborne Biogenic volatile organic compound (BVOC) Emission Research in Natural Ecosystem Transects (CABERNET) campaign during June 2011. The airborne virtual disjunct eddy covariance (AvDEC) approach used measurements from a proton transfer reaction mass spectrometer (PTR–MS) and a wind radome probe to directly determine fluxes of isoprene over 7400 km of flight paths focusing on areas of California predicted to have the largest emissions. The fast Fourier transform (FFT) approach was used to calculate fluxes of isoprene over long transects of more than 15 km, most commonly between 50 and 150 km. The continuous wavelet transformation (CWT) approach was used over the same transects to also calculate instantaneous isoprene fluxes with localization of both frequency and time independent of non-stationarities. Fluxes were generally measured by flying consistently at 400 m ± 50 m (a.g.l.) altitude, and extrapolated to the surface according to the determined flux divergence determined in the racetrack-stacked profiles. The wavelet-derived surface fluxes of isoprene averaged to 2 km spatial resolution showed good correspondence to basal emission factor (BEF) land-cover data sets used to drive BVOC emission models. The surface flux of isoprene was close to zero over Central Valley crops and desert shrublands, but was very high (up to 15 mg m−2 h−1) above oak woodlands, with clear dependence of emissions on temperature and oak density. Isoprene concentrations of up to 8 ppb were observed at aircraft height on the hottest days and over the dominant source regions. Even though the isoprene emissions from agricultural crop regions, shrublands, and coniferous forests were extremely low, observations at the Walnut Grove tower south of Sacramento demonstrate that isoprene oxidation products from the high emitting regions in the surrounding oak woodlands accumulate at night in the residual layer above the valley and mix down into the valley in the morning. Thus, the isoprene emissions surrounding the valley have relevance for the regional photochemistry that is not immediately apparent solely from the direct emission flux distribution. This paper reports the first regional observations of fluxes from specific sources by eddy covariance from an aircraft which can finally constrain statewide isoprene emission inventories used for ozone simulations by state agencies. While previously there was no available means to constrain the biogenic models, our results provide a good understanding of what the major sources of isoprene are in California, their magnitude, and how they are distributed. This data set on isoprene fluxes will be particularly useful for evaluating potential model alternatives which will be dealt with in a separate paper to assess isoprene emission models and their driving variable data sets.
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Chávez, JoséL, Christopher M. U. Neale, Lawrence E. Hipps, John H. Prueger, and William P. Kustas. "Comparing Aircraft-Based Remotely Sensed Energy Balance Fluxes with Eddy Covariance Tower Data Using Heat Flux Source Area Functions." Journal of Hydrometeorology 6, no. 6 (December 1, 2005): 923–40. http://dx.doi.org/10.1175/jhm467.1.
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Abstract In an effort to better evaluate distributed airborne remotely sensed sensible and latent heat flux estimates, two heat flux source area (footprint) models were applied to the imagery, and their pixel weighting/integrating functionality was investigated through statistical analysis. Soil heat flux and sensible heat flux models were calibrated. The latent heat flux was determined as a residual from the energy balance equation. The resulting raster images were integrated using the 2D footprints and were compared to eddy covariance energy balance flux measurements. The results show latent heat flux estimates (adjusted for closure) with errors of (mean ± std dev) −9.2 ± 39.4 W m−2, sensible heat flux estimate errors of 9.4 ± 28.3 W m−2, net radiation error of −4.8 ± 20.7 W m−2, and soil heat flux error of −0.5 ± 24.5 W m−2. This good agreement with measured values indicates that the adopted methodology for estimating the energy balance components, using high-resolution airborne multispectral imagery, is appropriate for modeling latent heat fluxes. The method worked well for the unstable atmospheric conditions of the study. The footprint weighting/integration models tested indicate that they perform better than simple pixel averages upwind from the flux stations. In particular the flux source area model (footprint) seemed to better integrate the resulting heat flux image pixels. It is suggested that future studies test the methodology for heterogeneous surfaces under stable atmospheric conditions.
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Hopkinson, C., L. Chasmer, A. G. Barr, N. Kljun, T. A. Black, and J. H. McCaughey. "Monitoring boreal forest biomass and carbon storage change by integrating airborne laser scanning, biometry and eddy covariance data." Remote Sensing of Environment 181 (August 2016): 82–95. http://dx.doi.org/10.1016/j.rse.2016.04.010.
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Hacker, Jorg M., Deli Chen, Mei Bai, Caecilia Ewenz, Wolfgang Junkermann, Wolfgang Lieff, Barry McManus, et al. "Using airborne technology to quantify and apportion emissions of CH4 and NH3 from feedlots." Animal Production Science 56, no. 3 (2016): 190. http://dx.doi.org/10.1071/an15513.
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A novel airborne approach using the latest technology in concentration measurements of methane (CH4) and ammonia (NH3), with quantum cascade laser gas analysers (QCLAs) and high-resolution wind, turbulence and other atmospheric parameters integrated into a low- and slow-flying modern airborne platform, was tested at a 17 000 head feedlot near Charlton, Victoria, Australia, in early 2015. Aircraft flights on 7 days aimed to define the lateral and vertical dimensions of the gas plume above and downwind of the feedlot and the gas concentrations within the plume, allowing emission rates of the target gases to be calculated. The airborne methodology, in the first instance, allowed the emissions to be qualitatively apportioned to individual rows of cattle pens, effluent ponds and manure piles. During each flight, independent measurements of emissions were conducted by ground-based inverse-dispersion and eddy covariance techniques, simultaneously. The aircraft measurements showed good agreement with earlier studies using more traditional approaches and the concurrent ground-based measurements. It is envisaged to use the aircraft technology for determining emissions from large-scale open grazing farms with low cattle densities. Our results suggested that this technique is able to quantify emissions from various sources within a feedlot (pens, manure piles and ponds), as well as the whole feedlot. Furthermore, the airborne technique enables tracing emissions for considerable distances downwind. In the current case, it was possible to detect elevated CH4 to at least 25 km and NH3 at least 7 km downwind of the feedlot.
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Wolfe, Glenn M., S. Randy Kawa, Thomas F. Hanisco, Reem A. Hannun, Paul A. Newman, Andrew Swanson, Steve Bailey, et al. "The NASA Carbon Airborne Flux Experiment (CARAFE): instrumentation and methodology." Atmospheric Measurement Techniques 11, no. 3 (March 28, 2018): 1757–76. http://dx.doi.org/10.5194/amt-11-1757-2018.
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Abstract. The exchange of trace gases between the Earth's surface and atmosphere strongly influences atmospheric composition. Airborne eddy covariance can quantify surface fluxes at local to regional scales (1–1000 km), potentially helping to bridge gaps between top-down and bottom-up flux estimates and offering novel insights into biophysical and biogeochemical processes. The NASA Carbon Airborne Flux Experiment (CARAFE) utilizes the NASA C-23 Sherpa aircraft with a suite of commercial and custom instrumentation to acquire fluxes of carbon dioxide, methane, sensible heat, and latent heat at high spatial resolution. Key components of the CARAFE payload are described, including the meteorological, greenhouse gas, water vapor, and surface imaging systems. Continuous wavelet transforms deliver spatially resolved fluxes along aircraft flight tracks. Flux analysis methodology is discussed in depth, with special emphasis on quantification of uncertainties. Typical uncertainties in derived surface fluxes are 40–90 % for a nominal resolution of 2 km or 16–35 % when averaged over a full leg (typically 30–40 km). CARAFE has successfully flown two missions in the eastern US in 2016 and 2017, quantifying fluxes over forest, cropland, wetlands, and water. Preliminary results from these campaigns are presented to highlight the performance of this system.
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Mauder, Matthias, Thomas Foken, and Joan Cuxart. "Surface-Energy-Balance Closure over Land: A Review." Boundary-Layer Meteorology 177, no. 2-3 (May 30, 2020): 395–426. http://dx.doi.org/10.1007/s10546-020-00529-6.
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Abstract Quantitative knowledge of the surface energy balance is essential for the prediction of weather and climate. However, a multitude of studies from around the world indicate that the turbulent heat fluxes are generally underestimated using eddy-covariance measurements, and hence, the energy balance is not closed. This energy-balance-closure problem, which has been heavily covered in the literature for more than 25 years, is the topic of the present review, in which we provide an overview of the potential reason for the lack of closure. We demonstrate the effects of the diurnal cycle on the energy balance closure, and address questions with regard to the partitioning of the energy balance residual between the sensible and the latent fluxes, and whether the magnitude of the flux underestimation can be predicted based on other variables typically measured at micrometeorological stations. Remaining open questions are discussed and potential avenues for future research on this topic are laid out. Integrated studies, combining multi-tower experiments and scale-crossing, spatially-resolving lidar and airborne measurements with high-resolution large-eddy simulations, are considered to be of critical importance for enhancing our understanding of the underlying transport processes in the atmospheric boundary layer.
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Hannun, Reem A., Glenn M. Wolfe, S. Randy Kawa, Thomas F. Hanisco, Paul A. Newman, Joseph G. Alfieri, John Barrick, et al. "Spatial heterogeneity in CO2, CH4, and energy fluxes: insights from airborne eddy covariance measurements over the Mid-Atlantic region." Environmental Research Letters 15, no. 3 (March 6, 2020): 035008. http://dx.doi.org/10.1088/1748-9326/ab7391.
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Sun, Yibo, Junyong Ma, Bilige Sude, Xingwen Lin, Haolu Shang, Bing Geng, Zhaoyan Diao, Jiaqiang Du, and Zhanjun Quan. "A UAV-Based Eddy Covariance System for Measurement of Mass and Energy Exchange of the Ecosystem: Preliminary Results." Sensors 21, no. 2 (January 8, 2021): 403. http://dx.doi.org/10.3390/s21020403.
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Airborne eddy covariance (EC) measurement is one of the most effective methods to directly measure the surface mass and energy fluxes at the regional scale. It offers the possibility to bridge the scale gap between local- and global-scale measurements by ground-based sites and remote-sensing instrumentations, and to validate the surface fluxes estimated by satellite products or process-based models. In this study, we developed an unmanned aerial vehicle (UAV)-based EC system that can be operated to measure the turbulent fluxes in carbon dioxides, momentum, latent and sensible heat, as well as net radiation and photosynthetically active radiation. Flight tests of the developed UAV-based EC system over land were conducted in October 2020 in Inner Mongolia, China. The in-flight calibration was firstly conducted to correct the mounting error. Then, three flight comparison tests were performed, and we compared the measurement with those from a ground tower. The results, along with power spectral comparison and consideration of the differing measurement strategies indicate that the system can resolve the turbulent fluxes in the encountered measurement condition. Lastly, the challenges of the UAV-based EC method were discussed, and potential improvements with further development were explored. The results of this paper reveal the considerable potential of the UAV-based EC method for land surface process studies.
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Sun, Yibo, Junyong Ma, Bilige Sude, Xingwen Lin, Haolu Shang, Bing Geng, Zhaoyan Diao, Jiaqiang Du, and Zhanjun Quan. "A UAV-Based Eddy Covariance System for Measurement of Mass and Energy Exchange of the Ecosystem: Preliminary Results." Sensors 21, no. 2 (January 8, 2021): 403. http://dx.doi.org/10.3390/s21020403.
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Airborne eddy covariance (EC) measurement is one of the most effective methods to directly measure the surface mass and energy fluxes at the regional scale. It offers the possibility to bridge the scale gap between local- and global-scale measurements by ground-based sites and remote-sensing instrumentations, and to validate the surface fluxes estimated by satellite products or process-based models. In this study, we developed an unmanned aerial vehicle (UAV)-based EC system that can be operated to measure the turbulent fluxes in carbon dioxides, momentum, latent and sensible heat, as well as net radiation and photosynthetically active radiation. Flight tests of the developed UAV-based EC system over land were conducted in October 2020 in Inner Mongolia, China. The in-flight calibration was firstly conducted to correct the mounting error. Then, three flight comparison tests were performed, and we compared the measurement with those from a ground tower. The results, along with power spectral comparison and consideration of the differing measurement strategies indicate that the system can resolve the turbulent fluxes in the encountered measurement condition. Lastly, the challenges of the UAV-based EC method were discussed, and potential improvements with further development were explored. The results of this paper reveal the considerable potential of the UAV-based EC method for land surface process studies.
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Baghi, R., P. Durand, C. Jambert, C. Jarnot, C. Delon, D. Serça, N. Striebig, M. Ferlicoq, and P. Keravec. "A new disjunct eddy-covariance system for BVOC flux measurements – validation on CO<sub>2</sub> and H<sub>2</sub>O fluxes." Atmospheric Measurement Techniques Discussions 5, no. 3 (June 13, 2012): 4157–93. http://dx.doi.org/10.5194/amtd-5-4157-2012.
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Abstract. The disjunct eddy covariance (DEC) method is an interesting alternative to the conventional eddy covariance (EC) method, because it allows the estimation of turbulent fluxes of species for which fast sensors are not available. A new disjunct sampling system (called MEDEE) was developed and validated. This system was built with chemically inert materials. Air samples are grabbed quickly and alternately in two cylindrical reservoirs, whose internal pressures are regulated by a moving piston. It was designed to be operated either on ground or aboard an airplane (the French ATR-42 research aircraft). It is also compatible with most analysers since it transfers the air samples at a regulated pressure. For validating the system, DEC and EC measurements of CO2 and latent heat fluxes were performed concurrently during a field campaign. EC fluxes were first compared to simulated DEC (SDEC) fluxes and then to actual DEC fluxes. The EC fluxes were in agreement with both the simulated and actual DEC fluxes. The EC fluxes compare well to SDEC fluxes (R2 = 0.92 and 0.68 for latent heat and CO2 fluxes, respectively) and to actual DEC fluxes (R2 = 0.91 and 0.67 for latent heat and CO2 fluxes, respectively), in spite of low fluxes experienced during the campaign. This good agreement between the two techniques demonstrates that MEDEE is suitable for DEC measurements and highlights the DEC method as a reliable alternative to EC for slower sensors. A first field campaign focused on biogenic volatile organic compound (BVOC) emissions was done to measure isoprene fluxes above a downy oak (Quercus Pubescens) forest in the southeast of France. The measured emission rates were in good agreement with the values reported in earlier studies. Further analysis will be conducted from ground-based and airborne campaigns in the forthcoming years.
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Baghi, R., P. Durand, C. Jambert, C. Jarnot, C. Delon, D. Serça, N. Striebig, M. Ferlicoq, and P. Keravec. "A new disjunct eddy-covariance system for BVOC flux measurements – validation on CO<sub>2</sub> and H<sub>2</sub>O fluxes." Atmospheric Measurement Techniques 5, no. 12 (December 21, 2012): 3119–32. http://dx.doi.org/10.5194/amt-5-3119-2012.
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Abstract. The disjunct eddy covariance (DEC) method is an interesting alternative to the conventional eddy covariance (EC) method because it allows the estimation of turbulent fluxes of species for which fast sensors are not available. We have developed and validated a new disjunct sampling system (called MEDEE). This system is built with chemically inert materials. Air samples are taken quickly and alternately in two cylindrical reservoirs, the internal pressures of which are regulated by a moving piston. The MEDEE system was designed to be operated either on the ground or aboard an aircraft. It is also compatible with most analysers since it transfers the air samples at a regulated pressure. To validate the system, DEC and EC measurements of CO2 and latent heat fluxes were performed concurrently during a field campaign. EC fluxes were first compared to simulated DEC (SDEC) fluxes and then to actual DEC fluxes. Both the simulated and actual DEC fluxes showed a good agreement with EC fluxes in terms of correlation. The determination coefficients (R2) were 0.93 and 0.91 for DEC and SDEC latent heat fluxes, respectively. For DEC and SDEC CO2 fluxes R2 was 0.69 in both cases. The conditions of low fluxes experienced during the campaign impaired the comparison of the different techniques especially for CO2 flux measurements. Linear regression analysis showed an 14% underestimation of DEC fluxes for both CO2 and latent heat compared to EC fluxes. A first field campaign, focusing on biogenic volatile organic compound (BVOC) emissions, was carried out to measure isoprene fluxes above a downy oak (Quercus Pubescens) forest in the south-east of France. The measured standard emission rate was in the lower range of reported values in earlier studies. Further analysis will be conducted through ground-based and airborne campaigns in the coming years.
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Buzorius, G. "Technical Note: In-situ quantification of aerosol sources and sinks over regional geographical scales." Atmospheric Chemistry and Physics 9, no. 14 (July 22, 2009): 4869–78. http://dx.doi.org/10.5194/acp-9-4869-2009.
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Abstract. In order to obtain the source/sink functions for atmospheric particulates located on the planetary surface or elevated in the atmosphere; direct aerosol emission measurements are required. For this purpose, the performance of an airborne aerosol flux measurement system with an improved 3-kilometer (km) spatial resolution is evaluated in this study. Eddy covariance method was used in flux calculations. A footprint for airborne flux sampling with the increased resolution becomes comparable in area to the footprint for tower sampling (with the footprint length being 2 to 10 km). The improvement in spatial resolution allows the quantification of emission rates from individual sources located several kilometers apart such as highway segments, city blocks, and remote and industrial areas. The advantage is a moving platform that allows scanning of aerosol emissions or depositions over regional geographic scales. Airborne flux measurements with the improved spatial resolution were conducted in various environments ranging from clean to partly polluted marine to polluted continental environment with low (<500 m) mixed boundary layer heights. The upward and downward fluxes from the clean marine environment were smaller than 0.5×106 particles m−2 s−1 in absolute value. The effective emissions measured from a ship plume ranged from 2×108 to 3×108 m−2 s−1, and effective fluxes measured crossing cities plumes with populations of 10 000 to 12 000 inhabitants were in the range of 2×108 to 3×108 m−2 s−1. Correlations between heat and aerosol fluxes are evaluated.
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Sun, Yibo, Li Jia, Qiting Chen, and Chaolei Zheng. "Optimizing Window Length for Turbulent Heat Flux Calculations from Airborne Eddy Covariance Measurements under Near Neutral to Unstable Atmospheric Stability Conditions." Remote Sensing 10, no. 5 (April 25, 2018): 670. http://dx.doi.org/10.3390/rs10050670.
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Chasmer, L., A. Barr, C. Hopkinson, H. McCaughey, P. Treitz, A. Black, and A. Shashkov. "Scaling and assessment of GPP from MODIS using a combination of airborne lidar and eddy covariance measurements over jack pine forests." Remote Sensing of Environment 113, no. 1 (January 2009): 82–93. http://dx.doi.org/10.1016/j.rse.2008.08.009.
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El-Madany, T., H. Geiß, A. Schmidt, and O. Klemm. "Regionalization of turbulent fluxes by combining aircraft measurements with footprint analysis." Biogeosciences Discussions 6, no. 4 (July 14, 2009): 7017–51. http://dx.doi.org/10.5194/bgd-6-7017-2009.
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Abstract. This paper presents a method for the regionalization of turbulent fluxes by combining airborne flux measurements and footprint analysis. Eddy covariance measurements were performed with a small environmental research aircraft in May 2008 over the "Münsterland" region in northwest Germany. This region is dominated by agricultural patches that are typically a few hectares in size. An analytic footprint model was tested and applied to relate the fluxes, as measured on the aircraft during day time conditions, to different vegetation types on the ground. The geo referenced footprint areas were merged with high resolution land use data (30×30 m), resulting in a quantification of different land use types inside the respective footprints. The fluxes of the sampled area in the Münsterland of 1510 km2 were scaled up to the area of the "Westfälische Bucht" (6054 km2), since the land use composition are comparable to a large extent. The mean fluxes calculated of 99 flight segments and used for the regionalization were found −0.69 mg m−2 s−1 for carbon dioxide and +0.17 g m−2 s−1 for water vapor.
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Metzger, S., W. Junkermann, M. Mauder, K. Butterbach-Bahl, B. Trancón y Widemann, F. Neidl, K. Schäfer, et al. "Spatially explicit regionalization of airborne flux measurements using environmental response functions." Biogeosciences 10, no. 4 (April 3, 2013): 2193–217. http://dx.doi.org/10.5194/bg-10-2193-2013.
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Abstract. The goal of this study is to characterize the sensible (H) and latent (LE) heat exchange for different land covers in the heterogeneous steppe landscape of the Xilin River catchment, Inner Mongolia, China. Eddy-covariance flux measurements at 50–100 m above ground were conducted in July 2009 using a weight-shift microlight aircraft. Wavelet decomposition of the turbulence data enables a spatial discretization of 90 m of the flux measurements. For a total of 8446 flux observations during 12 flights, MODIS land surface temperature (LST) and enhanced vegetation index (EVI) in each flux footprint are determined. Boosted regression trees are then used to infer an environmental response function (ERF) between all flux observations (H, LE) and biophysical (LST, EVI) and meteorological drivers. Numerical tests show that ERF predictions covering the entire Xilin River catchment (&approx;3670 km2) are accurate to ≤18% (1 σ). The predictions are then summarized for each land cover type, providing individual estimates of source strength (36 W m−2 < H < 364 W m−2, 46 W m−2 < LE < 425 W m−2) and spatial variability (11 W m−2 < σH < 169 W m−2, 14 W m−2 < σLE < 152 W m−2) to a precision of ≤5%. Lastly, ERF predictions of land cover specific Bowen ratios are compared between subsequent flights at different locations in the Xilin River catchment. Agreement of the land cover specific Bowen ratios to within 12 &pm; 9% emphasizes the robustness of the presented approach. This study indicates the potential of ERFs for (i) extending airborne flux measurements to the catchment scale, (ii) assessing the spatial representativeness of long-term tower flux measurements, and (iii) designing, constraining and evaluating flux algorithms for remote sensing and numerical modelling applications.
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Buzorius, G. "Technical Note: In-situ quantification of aerosol sources and sinks over regional geographical scales." Atmospheric Chemistry and Physics Discussions 9, no. 1 (January 15, 2009): 1301–28. http://dx.doi.org/10.5194/acpd-9-1301-2009.
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Abstract. In order to obtain the source/sink functions for atmospheric particulates located on the planetary surface or elevated in the atmosphere; direct aerosol emission measurements are required. For this purpose, the performance of an airborne aerosol flux measurement system with an improved 3-km spatial resolution is evaluated in this study. Eddy covariance method was used in flux calculations. A footprint for airborne flux sampling with the increased resolution becomes comparable in area to the footprint for tower sampling (with the footprint length being 2 to 10 km). The improvement in spatial resolution allows quantification of emission rates from individual sources located several kilometers apart. Locally measured aerosol flux provides useful information about aerosol sources and sinks located below or aloft of measurement altitude. The advantage is a moving platform that allows scanning of aerosol emissions or depositions over practically unlimited geographic scales. The technique delivers effective emission rates of atmospheric particulates from specific sources such as highway segments, city blocks, and remote and industrial areas. The improved spatial resolution airborne flux measurements were conducted in ambient conditions with low (<500 m) mixed boundary layer heights. Measurement results are reported from clean and partly polluted marine environments, and heavily polluted continental environments. The upward and downward fluxes from the clean marine environment were smaller than 0.5×106 particles m−2 s−1 in absolute value. The effective emissions measured from a ship plume ranged from 2×108 to 3×108 m−2 s−1, and effective fluxes measured crossing cities plumes with populations of 10 000 to 12 000 inhabitants were in the range of 2×108 to 3×108 m−2 s−1. Correlations between heat and aerosol fluxes are evaluated.
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O'Shea, S. J., G. Allen, M. W. Gallagher, K. Bower, S. M. Illingworth, J. B. A. Muller, B. Jones, et al. "Methane and carbon dioxide fluxes and their regional scalability for the European Arctic wetlands during the MAMM project in summer 2012." Atmospheric Chemistry and Physics Discussions 14, no. 6 (March 31, 2014): 8455–94. http://dx.doi.org/10.5194/acpd-14-8455-2014.
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Abstract. Airborne and ground-based measurements of methane (CH4), carbon dioxide (CO2) and boundary layer thermodynamics were recorded over the Fennoscandian wetlands in July 2012 as part of the MAMM (Methane and other greenhouse gases in the Arctic – Measurements, process studies and Modelling) field campaign. Employing these airborne measurements and a~simple boundary layer box model, net regional scale (~100 km) fluxes were calculated to be 1.2 ± 0.5 mg CH4 h−1 m−2 and −350 ± 143 mg CO2 h−1 m−2. These airborne fluxes were found to be relatively consistent with seasonally-averaged surface chamber (1.3 ± 1.0 mg CH4 h−1 m−2) and eddy covariance (1.3 ± 0.3 mg CH4 h−1 m−2 and −309 ± 306 mg CO2 h−1 m−2) flux measurements in the local area. The internal consistency of the aircraft-derived fluxes across a wide swath of Fennoscandia coupled with an excellent statistical comparison with local seasonally-averaged ground-based measurements demonstrates the potential scalability of such localised measurements to regional scale representivity. Comparisons were also made to longer term regional CH4 climatologies from the JULES (Joint UK Land Environment Simulator) and Hybrid8 land surface models within the area of the MAMM campaign. The average hourly emission flux output for the summer period (July–August) across the years 1980 to 2010 was 0.054 mg CH4 h−1 m−2 (minimum 0.0 and maximum 0.38 mg CH4 h−1 m−2) for the JULES model and 0.073 mg CH4 h−1 m−2 (minimum −0.0018 and maximum 4.62 mg CH4 h−1 m−2) for Hybrid8. Based on these observations both models were found to significantly underestimate the CH4 emission flux in this region, which was linked to the under prediction of the wetland extents generated by the models.
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O'Shea, S. J., G. Allen, M. W. Gallagher, K. Bower, S. M. Illingworth, J. B. A. Muller, B. T. Jones, et al. "Methane and carbon dioxide fluxes and their regional scalability for the European Arctic wetlands during the MAMM project in summer 2012." Atmospheric Chemistry and Physics 14, no. 23 (December 10, 2014): 13159–74. http://dx.doi.org/10.5194/acp-14-13159-2014.
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Abstract. Airborne and ground-based measurements of methane (CH4), carbon dioxide (CO2) and boundary layer thermodynamics were recorded over the Fennoscandian landscape (67–69.5° N, 20–28° E) in July 2012 as part of the MAMM (Methane and other greenhouse gases in the Arctic: Measurements, process studies and Modelling) field campaign. Employing these airborne measurements and a simple boundary layer box model, net regional-scale (~ 100 km) fluxes were calculated to be 1.2 ± 0.5 mg CH4 h−1 m−2 and −350 ± 143 mg CO2 h−1 m−2. These airborne fluxes were found to be relatively consistent with seasonally averaged surface chamber (1.3 ± 1.0 mg CH4 h−1 m−2) and eddy covariance (1.3 ± 0.3 mg CH4 h−1 m−2 and −309 ± 306 mg CO2 h−1 m−2) flux measurements in the local area. The internal consistency of the aircraft-derived fluxes across a wide swath of Fennoscandia coupled with an excellent statistical comparison with local seasonally averaged ground-based measurements demonstrates the potential scalability of such localised measurements to regional-scale representativeness. Comparisons were also made to longer-term regional CH4 climatologies from the JULES (Joint UK Land Environment Simulator) and HYBRID8 land surface models within the area of the MAMM campaign. The average hourly emission flux output for the summer period (July–August) for the year 2012 was 0.084 mg CH4 h−1 m−2 (minimum 0.0 and maximum 0.21 mg CH4 h−1 m−2) for the JULES model and 0.088 mg CH4 h−1 m−2 (minimum 0.0008 and maximum 1.53 mg CH4 h−1 m−2) for HYBRID8. Based on these observations both models were found to significantly underestimate the CH4 emission flux in this region, which was linked to the under-prediction of the wetland extents generated by the models.
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Ma, Jingyong, Tianshan Zha, Xin Jia, Steve Sargent, Rex Burgon, Charles P. A. Bourque, Xinhua Zhou, Peng Liu, Yujie Bai, and Yajuan Wu. "An eddy-covariance system with an innovative vortex intake for measuring carbon dioxide and water fluxes of ecosystems." Atmospheric Measurement Techniques 10, no. 3 (March 30, 2017): 1259–67. http://dx.doi.org/10.5194/amt-10-1259-2017.
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Abstract. Closed-path eddy-covariance (EC) systems are used to monitor exchanges of trace gases (e.g., carbon dioxide [CO2], water vapor [H2O], nitrous oxide and methane) between the atmosphere and biosphere. Traditional EC-intake systems are equipped with inline filters to prevent airborne dust particulate from contaminating the optical windows of the sample cell which causes measurement degradation. The inline filter should have a fine pore size (1 to 20 µm is common) to adequately protect the optics and a large filtration surface area to extend the time before it clogs. However, the filter must also have minimal internal volume to preserve good frequency response. This paper reports test results of the field performance of an EC system (EC155, Campbell Scientific, Inc., Logan Utah, USA) with a prototype vortex intake replacing the inline filter of a traditional EC system. The vortex-intake design is based on fluid dynamics theory. An air sample is drawn into the vortex chamber, where it spins in a vortex flow. The initially homogenous flow is separated when particle momentum forces heavier particles to the periphery of the chamber, leaving a much cleaner airstream at the center. Clean air (75 % of total flow) is drawn from the center of the vortex chamber, through a tube, to the sample cell where it is exposed to the optical windows of the gas analyzer. The remaining 25 % of the flow carries the heavier dust particles away through a separate bypass tube. An EC155 system measured CO2 and H2O fluxes in two urban-forest ecosystems in the megalopolis of Beijing, China. These sites present a challenge for EC measurements because of the generally poor air quality which has high concentrations of suspended particulate. The closed-path EC system with vortex intake significantly reduced maintenance requirements by preserving optical signal strength and sample-cell pressure within acceptable ranges for much longer periods. The system with vortex intake also maintained an excellent frequency response. For example, at the Badaling site, the amount of system downtime attributed solely to clogged filters was reduced from 26 % with traditional inline filters to 0 % with the prototype vortex intake. The use of a vortex intake could extend the geographical applicability of the EC technique in ecology and allow investigators to acquire more accurate and continuous measurements of trace-gas fluxes in a wider range of ecosystems.
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Metzger, S., W. Junkermann, M. Mauder, K. Butterbach-Bahl, B. Trancón y Widemann, F. Neidl, K. Schäfer, et al. "Spatial resolution and regionalization of airborne flux measurements using environmental response functions." Biogeosciences Discussions 9, no. 11 (November 14, 2012): 15937–6003. http://dx.doi.org/10.5194/bgd-9-15937-2012.
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Abstract. The goal of this study is to characterize the sensible (H) and latent (LE) heat exchange for different land covers in the heterogeneous steppe landscape of the Xilin River Catchment, Inner Mongolia, China. Eddy-covariance flux measurements at 50–100 m above ground were conducted in July 2009 using a weight-shift microlight aircraft. Wavelet decomposition of the turbulence data enables a spatial discretization of 90 m of the flux measurements. For a total of 8446 flux observations during 12 flights, MODIS land surface temperature (LST) and enhanced vegetation index (EVI) in each flux footprint are determined. Boosted regression trees are then used to infer an environmental response function (ERF) between all flux observations (H, LE) and biophysical- (LST, EVI) and meteorological drivers. Numerical tests show that ERF predictions covering the entire Xilin River Catchment (&approx; 3670 km2) are accurate to ≤ 18%. The predictions are then summarized for each land cover type, providing individual estimates of source strength (36 W m−2 < H < 364 W m−2, 46 W m−2 < LE < 425 W m−2) and spatial variability (11 W m−2 < σH < 169 W m−2, 14 W m−2 < σLE < 152 W m−2) to a precision of ≤ 5%. Lastly, ERF predictions of land cover specific Bowen ratios are compared between subsequent flights at different locations in the Xilin River Catchment. Agreement of the land cover specific Bowen ratios to within 12 ± 9% emphasizes the robustness of the presented approach. This study indicates the potential of ERFs for (i) extending airborne flux measurements to the catchment scale, (ii) assessing the spatial representativeness of long-term tower flux measurements, and (iii) designing, constraining and evaluating flux algorithms for remote sensing and numerical modelling applications.
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Dobosy, Ronald, David Sayres, Claire Healy, Edward Dumas, Mark Heuer, John Kochendorfer, Bruce Baker, and James Anderson. "Estimating Random Uncertainty in Airborne Flux Measurements over Alaskan Tundra: Update on the Flux Fragment Method." Journal of Atmospheric and Oceanic Technology 34, no. 8 (August 2017): 1807–22. http://dx.doi.org/10.1175/jtech-d-16-0187.1.
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AbstractAirborne turbulence measurement gives a spatial distribution of air–surface fluxes that networks of fixed surface sites typically cannot capture. Much work has improved the accuracy of such measurements and the estimation of the uncertainty peculiar to streams of turbulence data measured from the air. A particularly significant challenge and opportunity is to distinguish fluxes from different surface types, especially those occurring in patches smaller than the necessary averaging length. The flux fragment method (FFM), a conditional-sampling variant of eddy covariance in the space–time domain, was presented in 2008. It was shown capable of segregating the mean flux density (CO2, H2O, sensible heat) in maize from that in soybeans over the patchwork farmlands of Illinois. This was, however, an ideal surface for the method, and the random-error estimate used a relatively rudimentary bootstrap resampling. The present paper describes an upgraded random-error estimate that accounts for the serial correlation of the time/space series and the heterogeneity of the signal. Results are presented from the Alaskan tundra. Though recognized as important, systematic error estimates are not covered in this paper. Some discussion is offered on the relation of the FFM to other approaches similarly motivated, particularly those using wavelets. Successful measurement of the variation of air–surface exchange over heterogeneous surfaces has value for developing and improving process models relating surface flux to remotely sensible quantities, such as the vegetative land-cover type and its condition.
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Sakowska, Karolina, Alasdair MacArthur, Damiano Gianelle, Michele Dalponte, Giorgio Alberti, Beniamino Gioli, Franco Miglietta, et al. "Assessing Across-Scale Optical Diversity and Productivity Relationships in Grasslands of the Italian Alps." Remote Sensing 11, no. 6 (March 13, 2019): 614. http://dx.doi.org/10.3390/rs11060614.
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The linearity and scale-dependency of ecosystem biodiversity and productivity relationships (BPRs) have been under intense debate. In a changing climate, monitoring BPRs within and across different ecosystem types is crucial, and novel remote sensing tools such as the Sentinel-2 (S2) may be adopted to retrieve ecosystem diversity information and to investigate optical diversity and productivity patterns. But are the S2 spectral and spatial resolutions suitable to detect relationships between optical diversity and productivity? In this study, we implemented an integrated analysis of spatial patterns of grassland productivity and optical diversity using optical remote sensing and Eddy Covariance data. Across-scale optical diversity and ecosystem productivity patterns were analyzed for different grassland associations with a wide range of productivity. Using airborne optical data to simulate S2, we provided empirical evidence that the best optical proxies of ecosystem productivity were linearly correlated with optical diversity. Correlation analysis at increasing pixel sizes proved an evident scale-dependency of the relationships between optical diversity and productivity. The results indicate the strong potential of S2 for future large-scale assessment of across-ecosystem dynamics at upper levels of observation.
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El Bahlouli, Asmae, Daniel Leukauf, Andreas Platis, Kjell zum Berge, Jens Bange, and Hermann Knaus. "Validating CFD Predictions of Flow over an Escarpment Using Ground-Based and Airborne Measurement Devices." Energies 13, no. 18 (September 9, 2020): 4688. http://dx.doi.org/10.3390/en13184688.
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Micrometeorological observations from a tower, an eddy-covariance (EC) station and an unmanned aircraft system (UAS) at the WINSENT test-site are used to validate a computational fluid dynamics (CFD) model, driven by a mesoscale model. The observation site is characterised by a forested escarpment in a complex terrain. A two-day measurement campaign with a flow almost perpendicular to the escarpment is analysed. The first day is dominated by high wind speeds, while, on the second one, calm wind conditions are present. Despite some minor differences, the flow structure, analysed in terms of horizontal wind speeds, wind direction and inclination angles shows similarities for both days. A real-time strategy is used for the CFD validation with the UAS measurement, where the model follows spatially and temporally the aircraft. This strategy has proved to be successful. Stability indices such as the potential temperature and the bulk Richardson number are calculated to diagnose atmospheric boundary layer (ABL) characteristics up to the highest flight level. The calculated bulk Richardson values indicate a dynamically unstable region behind the escarpment and near the ground for both days. At higher altitudes, the ABL is returning to a near neutral state. The same characteristics are found in the model but only for the first day. The second day, where shear instabilities are more dominant, is not well simulated. UAS proves its great value for sensing the flow over complex terrains at high altitudes and we demonstrate the usefulness of UAS for validating and improving models.
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Mauder, Matthias, R. L. Desjardins, Steven P. Oncley, and Ian MacPherson. "Atmospheric Response to a Partial Solar Eclipse over a Cotton Field in Central California." Journal of Applied Meteorology and Climatology 46, no. 11 (November 1, 2007): 1792–803. http://dx.doi.org/10.1175/2007jamc1495.1.
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Abstract The partial solar eclipse on 11 July 1991 in central California, with 58.3% maximum coverage, provided an exceptional opportunity to study the temporal response of processes in the atmospheric boundary layer to an abrupt change in solar radiation. Almost laboratory-like conditions were met over a cotton field, since no clouds disturbed the course of the eclipse. Tower-based and complementing aircraft-based systems monitored the micrometeorological conditions over the site. Temperature profile measurements indicated neutral stratification during the maximum eclipse in contrast to the unstable conditions before and after the eclipse. Accordingly, the sensible heat exchange completely stopped, as a wavelet analysis of the tower measurements and airborne eddy-covariance measurements showed. Turbulent fluxes of water vapor, carbon dioxide, and ozone were reduced by approximately ⅔ at the peak of the eclipse. Wavelet analysis further indicated that the same eddies contributed to the turbulent transport of water vapor and carbon dioxide, whereas sensible heat was transported by different ones. An analysis of the decay of turbulent kinetic energy followed a power law of time with an exponent of −1.25. The response of the sensible heat flux was 8–13 min delayed relative to the solar forcing, whereas no significant time lag could be detected for the turbulent fluxes of air constituents.
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Chasmer, L., N. Kljun, A. Barr, A. Black, C. Hopkinson, H. McCaughey, and P. Treitz. "Influences of vegetation structure and elevation on CO2 uptake in a mature jack pine forest in Saskatchewan, Canada." Canadian Journal of Forest Research 38, no. 11 (November 2008): 2746–61. http://dx.doi.org/10.1139/x08-121.
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Carbon dioxide, water vapour, and energy fluxes vary spatially and temporally within forested environments. However, it is not clear to what extent they vary as a result of variability in the spatial distribution of biomass and elevation. The following study presents a new methodology for extracting changes in the structural characteristics of vegetation and elevation within footprint areas, for direct comparison with eddy covariance (EC) CO2 flux concentrations. The purpose was to determine whether within-site canopy structure and local elevation influenced CO2 fluxes in a mature jack pine ( Pinus banksiana Lamb.) forest located in Saskatchewan, Canada. Airborne light detection and ranging (lidar) was used to extract tree height, canopy depth, foliage cover, and elevation within 30 min flux footprints. Within-footprint mean structural components and elevation were related to 30 min mean net ecosystem productivity (NEP) and gross ecosystem production (GEP). NEP and GEP were modeled using multiple regression, and when compared with measured fluxes, almost all periods showed improvements in the prediction of flux concentration when canopy structure and elevation were included. Increased biomass was related to increased NEP and GEP in June and August when the ecosystem was not limited by soil moisture. On a daily basis, fractional cover and elevation had varying but significant influences on CO2 fluxes.
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Metzger, Stefan, David Durden, Sreenath Paleri, Matthias Sühring, Brian J. Butterworth, Christopher Florian, Matthias Mauder, et al. "Novel approach to observing system simulation experiments improves information gain of surface–atmosphere field measurements." Atmospheric Measurement Techniques 14, no. 11 (November 1, 2021): 6929–54. http://dx.doi.org/10.5194/amt-14-6929-2021.
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Abstract. The observing system design of multidisciplinary field measurements involves a variety of considerations on logistics, safety, and science objectives. Typically, this is done based on investigator intuition and designs of prior field measurements. However, there is potential for considerable increases in efficiency, safety, and scientific success by integrating numerical simulations in the design process. Here, we present a novel numerical simulation–environmental response function (NS–ERF) approach to observing system simulation experiments that aids surface–atmosphere synthesis at the interface of mesoscale and microscale meteorology. In a case study we demonstrate application of the NS–ERF approach to optimize the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors 2019 (CHEESEHEAD19). During CHEESEHEAD19 pre-field simulation experiments, we considered the placement of 20 eddy covariance flux towers, operations for 72 h of low-altitude flux aircraft measurements, and integration of various remote sensing data products. A 2 h high-resolution large eddy simulation created a cloud-free virtual atmosphere for surface and meteorological conditions characteristic of the field campaign domain and period. To explore two specific design hypotheses we super-sampled this virtual atmosphere as observed by 13 different yet simultaneous observing system designs consisting of virtual ground, airborne, and satellite observations. We then analyzed these virtual observations through ERFs to yield an optimal aircraft flight strategy for augmenting a stratified random flux tower network in combination with satellite retrievals. We demonstrate how the novel NS–ERF approach doubled CHEESEHEAD19's potential to explore energy balance closure and spatial patterning science objectives while substantially simplifying logistics. Owing to its modular extensibility, NS–ERF lends itself to optimizing observing system designs also for natural climate solutions, emission inventory validation, urban air quality, industry leak detection, and multi-species applications, among other use cases.
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Kiemle, C., G. Ehret, A. Fix, M. Wirth, G. Poberaj, W. A. Brewer, R. M. Hardesty, C. Senff, and M. A. LeMone. "Latent Heat Flux Profiles from Collocated Airborne Water Vapor and Wind Lidars during IHOP_2002." Journal of Atmospheric and Oceanic Technology 24, no. 4 (April 1, 2007): 627–39. http://dx.doi.org/10.1175/jtech1997.1.
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Abstract Latent heat flux profiles in the convective boundary layer (CBL) are obtained for the first time with the combination of the Deutsches Zentrum für Luft- und Raumfahrt (DLR) water vapor differential absorption lidar (DIAL) and the NOAA high resolution Doppler wind lidar (HRDL). Both instruments were integrated nadir viewing on board the DLR Falcon research aircraft during the International H2O Project (IHOP_2002) over the U.S. Southern Great Plains. Flux profiles from 300 to 2500 m AGL are computed from high spatial resolution (150 m horizontal and vertical) two-dimensional water vapor and vertical velocity lidar cross sections using the eddy covariance technique. Three flight segments on 7 June 2002 between 1000 and 1300 LT over western Oklahoma and southwestern Kansas are analyzed. On two segments with strong convection, the latent heat flux peaks at (700 ± 200) W m−2 in the entrainment zone and decreases linearly to (200 ± 100) W m−2 in the lower CBL. A water vapor budget analysis reveals that this flux divergence [(0.9 ± 0.4) g kg−1 h−1] plus the advection (0.3 g kg−1 h−1) are nearly balanced by substantial CBL drying [(1.5 ± 0.2) g kg−1 h−1] observed by airborne and surface in situ instruments, within the limits of the overall budget rms error of 0.5 g kg−1 h−1. Entrainment of dry air from aloft and net upward humidity transport caused the CBL drying and finally inhibited the initiation of deep convection. All cospectra show significant contributions to the flux between 1- and 10-km wavelength, with peaks between 2 and 6 km, originating from large eddies. The main flux uncertainty is due to low sampling (55% rmse at mid-CBL), while instrument noise (15%) and systematic errors (7%) play a minor role. The combination of a water vapor and a wind lidar on an aircraft appears as an attractive new tool that allows measuring latent heat flux profiles from a single overflight of the investigated area.
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Font, A., C. S. B. Grimmond, J. A. Morguí, S. Kotthaus, M. Priestman, and B. Barratt. "Cross-validation of inferred daytime airborne CO<sub>2</sub> urban-regional scale surface fluxes with eddy-covariance observations and emissions inventories in Greater London." Atmospheric Chemistry and Physics Discussions 13, no. 5 (May 22, 2013): 13465–93. http://dx.doi.org/10.5194/acpd-13-13465-2013.
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Abstract. Data obtained from eleven flight surveys on six days during October 2011 were used to characterize the urban CO2 dome in Greater London (GL) and to calculate CO2 fluxes at the city scale. Flights crossed GL along two transects (SW-NE and SSE-NNW) at an altitude of 360 m. Increments as high as 23 ppmv were measured. The maximum CO2 mixing ratios were localized over GL under low wind speeds, whereas a displacement of the urban plume downwind from the centre of the urban area occurred during high wind speeds. The urban-regional surface CO2 flux was calculated for four days by the Integrative Mass Boundary Layer (IMBL) method. The diurnal CO2 flux in GL obtained from the aircraft observations ranged from 46 to 104 μmol CO2 m−2 s−1 during the day time. The mean CO2 fluxes estimated from the IMBL method were statistically similar to those observed by eddy-covariance systems located in central London and a spatially integrated emissions inventory for GL. This study provides an important cross-validation of two independent measurement-based methods to infer the contribution of urban areas to climate change in terms of CO2 surface fluxes, both of which complement bottom-up emissions inventories. The uncertainties of fluxes estimated by the IMBL method are considered and the limits of implementation of atmospheric methods to infer city-scale fluxes are discussed.