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Protat, Alain, Valentin Louf, Joshua Soderholm, Jordan Brook e William Ponsonby. "Three-way calibration checks using ground-based, ship-based, and spaceborne radars". Atmospheric Measurement Techniques 15, n.º 4 (21 de fevereiro de 2022): 915–26. http://dx.doi.org/10.5194/amt-15-915-2022.
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Abstract. This study uses ship-based weather radar observations collected from research vessel Investigator to evaluate the Australian weather radar network calibration monitoring technique that uses spaceborne radar observations from the NASA Global Precipitation Mission (GPM). Quantitative operational applications such as rainfall and hail nowcasting require a calibration accuracy of ±1 dB for radars of the Australian network covering capital cities. Seven ground-based radars along the western coast of Australia and the ship-based OceanPOL radar are first calibrated independently using GPM radar overpasses over a 3-month period. The calibration difference between the OceanPOL radar (used as a moving reference for the second step of the study) and each of the seven operational radars is then estimated using collocated, gridded, radar observations to quantify the accuracy of the GPM technique. For all seven radars the calibration difference with the ship radar lies within ±0.5 dB, therefore fulfilling the 1 dB requirement. This result validates the concept of using the GPM spaceborne radar observations to calibrate national weather radar networks (provided that the spaceborne radar maintains a high calibration accuracy). The analysis of the day-to-day and hourly variability of calibration differences between the OceanPOL and Darwin (Berrimah) radars also demonstrates that quantitative comparisons of gridded radar observations can accurately track daily and hourly calibration differences between pairs of operational radars with overlapping coverage (daily and hourly standard deviations of ∼ 0.3 and ∼ 1 dB, respectively).
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Elachi, Charles. "Spaceborne imaging radars". International Journal of Imaging Systems and Technology 3, n.º 2 (1991): 167–85. http://dx.doi.org/10.1002/ima.1850030212.
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Fall, Veronica M., Qing Cao e Yang Hong. "Intercomparison of Vertical Structure of Storms Revealed by Ground-Based (NMQ) and Spaceborne Radars (CloudSat-CPR and TRMM-PR)". Scientific World Journal 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/270726.
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Spaceborne radars provide great opportunities to investigate the vertical structure of clouds and precipitation. Two typical spaceborne radars for such a study are the W-band Cloud Profiling Radar (CPR) and Ku-band Precipitation Radar (PR), which are onboard NASA’s CloudSat and TRMM satellites, respectively. Compared to S-band ground-based radars, they have distinct scattering characteristics for different hydrometeors in clouds and precipitation. The combination of spaceborne and ground-based radar observations can help in the identification of hydrometeors and improve the radar-based quantitative precipitation estimation (QPE). This study analyzes the vertical structure of the 18 January, 2009 storm using data from the CloudSat CPR, TRMM PR, and a NEXRAD-based National Mosaic and Multisensor QPE (NMQ) system. Microphysics above, within, and below the melting layer are studied through an intercomparison of multifrequency measurements. Hydrometeors’ type and their radar scattering characteristics are analyzed. Additionally, the study of the vertical profile of reflectivity (VPR) reveals the brightband properties in the cold-season precipitation and its effect on the radar-based QPE. In all, the joint analysis of spaceborne and ground-based radar data increases the understanding of the vertical structure of storm systems and provides a good insight into the microphysical modeling for weather forecasts.
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Pfitzenmaier, Lukas, Alessandro Battaglia e Pavlos Kollias. "The Impact of the Radar-Sampling Volume on Multiwavelength Spaceborne Radar Measurements Using Airborne Radar Observations". Remote Sensing 11, n.º 19 (28 de setembro de 2019): 2263. http://dx.doi.org/10.3390/rs11192263.
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Multiwavelength radar observations have demonstrated great potential in improving microphysical retrievals of cloud properties especially in ice and snow precipitation systems. Advancements in spaceborne radar technology have already fostered the launch in 2014 of the first multiwavelength radar system in space, while several future spaceborne multiwavelength radar concepts are under consideration. However, due to antenna size limitations, the sampling volume of spaceborne radars is considerably larger than those achieved by surface- and airborne-based radars. Here, the impact of these large sampling volumes in the information content of the Dual-Wavelength Ratio estimates at Ka-W, Ku-Ka is investigated. High-resolution airborne multiwavelength radar observations during the Olympic Mountain Experiment (OLYMPEx) are used to perform retrievals of ice/snow characteristic particle size, such as mass-weighted particle diameter. To mimic the different satellite sampling volumes, a moving average is applied to the airborne measurements. The radar-observed variables (reflectivity and dual-wavelength ratios) and retrieved microphysical properties at the coarser resolution are compared against those at the original resolution. Our analysis indicates that future Ka-W spaceborne radar missions should take into account the impact of the radar resolution volume on the retrieval of microphysical properties and avoid footprints larger than 2–3 km.
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Battaglia, Alessandro, Filippo Emilio Scarsi, Kamil Mroz e Anthony Illingworth. "In-orbit cross-calibration of millimeter conically scanning spaceborne radars". Atmospheric Measurement Techniques 16, n.º 12 (29 de junho de 2023): 3283–97. http://dx.doi.org/10.5194/amt-16-3283-2023.
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Abstract. The planned and potential introduction in global satellite observing systems of conically scanning Ka- and W-band atmospheric radars (e.g., the radars in the Tomorrow.IO constellation, https://www.tomorrow.io/space/, last access: 1 June 2022, and the Wivern (WInd VElocity Radar Nephoscope) radar, https://www.wivern.polito.it, last access: 1 July 2022) calls for the development of methodologies for calibrating and cross-calibrating these systems. Traditional calibration techniques pointing at the sea surface at about 11∘ incidence angle are in fact unfeasible for such fast rotating systems. This study proposes a cross-calibration method for conically scanning spaceborne radars based on ice cloud reflectivity probability distribution functions (PDFs) provided by reference radars like the Global Precipitation Measurement (GPM) Ka-band radar or the W-band radars planned for the ESA-JAXA EarthCARE or for the NASA Atmosphere Observing System missions. In order to establish the accuracy of the methodology, radar antenna boresight positions are propagated based on four configurations of expected satellite orbits so that the ground-track intersections can be calculated for different intersection criteria, defined by cross-over instrument footprints within a certain time and a given distance. The climatology of the calibrating clouds, derived from the W-band CloudSat and Ka-band GPM reflectivity records, can be used to compute the number and the spatial distribution of calibration points. Finally, the mean number of days required to achieve a given calibration accuracy is computed based on the number of calibration points needed to distinguish a biased reflectivity PDF from the sampling-induced noisiness of the reflectivity PDF itself. Findings demonstrate that it will be possible to cross-calibrate, within 1 dB, a Ka-band (W-band) conically scanning radar like that envisaged for the Tomorrow.io constellation (Wivern mission) every few days (a week). Such uncertainties are generally meeting the mission requirements and the standards currently achieved with absolute calibration accuracies.
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Friedt, Jean-Michel, Éric Bernard e Madeleine Griselin. "Ground-Based Oblique-View Photogrammetry and Sentinel-1 Spaceborne RADAR Reflectivity Snow Melt Processes Assessment on an Arctic Glacier". Remote Sensing 15, n.º 7 (30 de março de 2023): 1858. http://dx.doi.org/10.3390/rs15071858.
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The snowpack evolution during the melt season on an Arctic glacier is assessed using ground-based oblique-view cameras, spaceborne imaging and spaceborne RADAR. The repeated and systematic Synthetic Aperture RADAR (SAR) imaging by the European Space Agency’s Sentinel-1 spaceborne RADARs allows for all-weather, all-illumination condition monitoring of the snow-covered fraction of the glacier and hence assessing its water production potential. A comparison of the RADAR reflectivity with optical and multispectral imaging highlights the difference between the observed quantities—water content in the former, albedo in the latter—and the complementarity for understanding the snow melt processes. This work highlights the temporal inertia between the visible spring melting of the snowpack and the snow metamorphism. It was found that the snowpack exhibits that approximately 30 days before it starts to fade.
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Kulie, Mark S., e Ralf Bennartz. "Utilizing Spaceborne Radars to Retrieve Dry Snowfall". Journal of Applied Meteorology and Climatology 48, n.º 12 (1 de dezembro de 2009): 2564–80. http://dx.doi.org/10.1175/2009jamc2193.1.
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Abstract A dataset consisting of one year of CloudSat Cloud Profiling Radar (CPR) near-surface radar reflectivity Z associated with dry snowfall is examined in this study. The CPR observations are converted to snowfall rates S using derived Ze–S relationships, which were created from backscatter cross sections of various nonspherical and spherical ice particle models. The CPR reflectivity histograms show that the dominant mode of global near-surface dry snowfall has extremely light reflectivity values (∼3–4 dBZe), and an estimated 94% of all CPR dry snowfall observations are less than 10 dBZe. The average conditional global snowfall rate is calculated to be about 0.28 mm h−1, but is regionally highly variable as well as strongly sensitive to the ice particle model chosen. Further, ground clutter contamination is found in regions of complex terrain even when a vertical reflectivity continuity threshold is utilized. The potential of future multifrequency spaceborne radars is evaluated using proxy 35–13.6-GHz reflectivities and sensor specifications of the proposed Global Precipitation Measurement dual-frequency precipitation radar (DPR). It is estimated that because of its higher detectability threshold, only about 7%–1% of the near-surface radar reflectivity values and about 17%–4% of the total accumulation associated with global dry snowfall would be detected by a DPR-like instrument, but these results are very sensitive to the chosen ice particle model. These potential detection shortcomings can be partially mitigated by using snowfall-rate distributions derived by the CPR or other similar high-frequency active sensors.
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Meneghini, Robert, e Liang Liao. "On the Equivalence of Dual-Wavelength and Dual-Polarization Equations for Estimation of the Raindrop Size Distribution". Journal of Atmospheric and Oceanic Technology 24, n.º 5 (1 de maio de 2007): 806–20. http://dx.doi.org/10.1175/jtech2005.1.
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Abstract For air- and spaceborne weather radars, which typically operate at frequencies of 10 GHz and above, attenuation correction is usually an essential part of any rain estimation procedure. For ground-based radars, where the maximum range within the precipitation is usually much greater than that from air- or spaceborne radars, attenuation correction becomes increasingly important at frequencies above about 5 GHz. Although dual-polarization radar algorithms rely on the correlation between raindrop shape and size, while dual-wavelength weather radar algorithms rely primarily on non-Rayleigh scattering at the shorter wavelength, the equations for estimating parameters of the drop size distribution (DSD) are nearly identical in the presence of attenuation. Many of the attenuation correction methods that have been proposed can be classified as one of two types: those that employ a kZ (specific attenuation–radar reflectivity factor) relation, and those that use an integral equation formalism where the attenuation is obtained from the DSD parameters at prior gates, either stepping outward from the radar or inward toward the radar from some final range gate. The similarity is shown between the dual-polarization and dual-wavelength equations when either the kZ or the integral equation formulation is used. Differences between the two attenuation correction procedures are illustrated for simulated measurements from an X-band dual-polarization radar.
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Durden, S. L., M. A. Fischman, R. A. Johnson, A. J. Chu, M. N. Jourdan e S. Tanelli. "An FPGA-Based Doppler Processor for a Spaceborne Precipitation Radar". Journal of Atmospheric and Oceanic Technology 24, n.º 10 (1 de outubro de 2007): 1811–15. http://dx.doi.org/10.1175/jtech2086.1.
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Abstract Measurement of precipitation Doppler velocity by spaceborne radar is complicated by the large velocity of the satellite platform. Even if successive pulses are well correlated, the velocity measurement may be biased if the precipitation target does not uniformly fill the radar footprint. It has been previously shown that the bias in such situations can be reduced if full spectral processing is used. The authors present a processor based on field-programmable gate array (FPGA) technology that can be used for spectral processing of data acquired by future spaceborne precipitation radars. The requirements for and design of the Doppler processor are addressed. Simulation and laboratory test results show that the processor can meet real-time constraints while easily fitting in a single FPGA.
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Leinonen, Jussi, Dmitri Moisseev, Matti Leskinen e Walter A. Petersen. "A Climatology of Disdrometer Measurements of Rainfall in Finland over Five Years with Implications for Global Radar Observations". Journal of Applied Meteorology and Climatology 51, n.º 2 (fevereiro de 2012): 392–404. http://dx.doi.org/10.1175/jamc-d-11-056.1.
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AbstractTo improve the understanding of high-latitude rain microphysics and its implications for the remote sensing of rainfall by ground-based and spaceborne radars, raindrop size measurements have been analyzed that were collected over five years with a Joss–Waldvogel disdrometer located in Järvenpää, Finland. The analysis shows that the regional climate is characterized by light rain and small drop size with narrow size distributions and that the mutual relations of drop size distribution parameters differ from those reported at lower latitudes. Radar parameters computed from the distributions demonstrate that the high latitudes are a challenging target for weather radar observations, particularly those employing polarimetric and dual-frequency techniques. Nevertheless, the findings imply that polarimetric ground radars can produce reliable “ground truth” estimates for space observations and identify dual-frequency radars utilizing a W-band channel as promising tools for observing rainfall in the high-latitude climate.
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Wang, Wen-Qin. "Detecting and Mitigating Wind Turbine Clutter for Airspace Radar Systems". Scientific World Journal 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/385182.
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It is well recognized that a wind turbine has a large radar cross-section (RCS) and, due to the movement of the blades, the wind turbine will generate a Doppler frequency shift. This scattering behavior may cause severe interferences on existing radar systems including static ground-based radars and spaceborne or airborne radars. To resolve this problem, efficient techniques or algorithms should be developed to mitigate the effects of wind farms on radars. Herein, one transponder-based mitigation technique is presented. The transponder is not a new concept, which has been proposed for calibrating high-resolution imaging radars. It modulates the radar signal in a manner that the retransmitted signals can be separated from the scene echoes. As wind farms often occupy only a small area, mitigation processing in the whole radar operation will be redundant and cost inefficient. Hence, this paper uses a transponder to determine whether the radar is impacted by the wind farms. If so, the effects of wind farms are then mitigated with subsequent Kalman filtering or plot target extraction algorithms. Taking airborne synthetic aperture radar (SAR) and pulse Doppler radar as the examples, this paper provides the corresponding system configuration and processing algorithms. The effectiveness of the mitigation technique is validated by numerical simulation results.
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Battaglia, Alessandro, Pavlos Kollias, Ranvir Dhillon, Katia Lamer, Marat Khairoutdinov e Daniel Watters. "Mind the gap – Part 2: Improving quantitative estimates of cloud and rain water path in oceanic warm rain using spaceborne radars". Atmospheric Measurement Techniques 13, n.º 9 (15 de setembro de 2020): 4865–83. http://dx.doi.org/10.5194/amt-13-4865-2020.
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Abstract. The intrinsic small spatial scales and low-reflectivity structure of oceanic warm precipitating clouds suggest that millimeter spaceborne radars are best suited to providing quantitative estimates of cloud and rain liquid water paths (LWPs). This assertion is based on their smaller horizontal footprint; high sensitivities; and a wide dynamic range of path-integrated attenuations associated with warm-rain cells across the millimeter wavelength spectrum, with diverse spectral responses to rain and cloud partitioning. State-of-the-art single-frequency radar profiling algorithms of warm rain seem to be inadequate because of their dependence on uncertain assumptions about the rain–cloud partitioning and because of the rain microphysics. Here, high-resolution cloud-resolving model simulations for the Rain in Cumulus over the Ocean field study and a spaceborne forward radar simulator are exploited to assess the potential of existing and future spaceborne radar systems for quantitative warm-rain microphysical retrievals. Specifically, the detrimental effects of nonuniform beam filling on estimates of path-integrated attenuation (PIA), the added value of brightness temperature (TB) derived adopting radiometric radar modes, and the performances of multifrequency PIA and/or TB combinations when retrieving liquid water paths partitioned into cloud (c-LWPs) and rain (r-LWPs) are assessed. Results show that (1) Ka- and W-band TB values add useful constraints and are effective at lower LWPs than the same-frequency PIAs; (2) matched-beam combined TB values and PIAs from single-frequency or multifrequency radars can significantly narrow down uncertainties in retrieved cloud and rain liquid water paths; and (3) the configuration including PIAs, TB values and near-surface reflectivities for the Ka-band–W-band pairs in our synthetic retrieval can achieve an RMSE of better than 30 % for c-LWPs and r-LWPs exceeding 100 g m−2.
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Berg, Wesley, Tristan L’Ecuyer e John M. Haynes. "The Distribution of Rainfall over Oceans from Spaceborne Radars". Journal of Applied Meteorology and Climatology 49, n.º 3 (1 de março de 2010): 535–43. http://dx.doi.org/10.1175/2009jamc2330.1.
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Abstract A combination of rainfall estimates from the 13.8-GHz Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) and the 94-GHz CloudSat Cloud Profiling Radar (CPR) is used to assess the distribution of rainfall intensity over tropical and subtropical oceans. These two spaceborne radars provide highly complementary information: the PR provides the best information on the total rain volume because of its ability to estimate the intensity of all but the lightest rain rates while the CPR’s higher sensitivity provides superior rainfall detection as well as estimates of drizzle and light rain. Over the TRMM region between 35°S and 35°N, rainfall frequency from the CPR is around 9%, approximately 2.5 times that detected by the PR, and the CPR estimates indicate a contribution by light rain that is undetected by the PR of around 10% of the total. Stratifying the results by total precipitable water (TPW) as a proxy for rainfall regime indicates dramatic differences over stratus-dominated subsidence regions, with nearly 20% of the total rain occurring as light rain. Over moist tropical regions, the CPR substantially underestimates rain from intense convective storms because of large attenuation and multiple-scattering effects while the PR misses very little of the total rain volume because of a lower relative contribution from light rain. Over low-TPW regions, however, inconsistencies between estimates from the PR and the CPR point to uncertainties in the algorithm assumptions that remain to be understood and addressed.
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Crisologo, Irene, e Maik Heistermann. "Using ground radar overlaps to verify the retrieval of calibration bias estimates from spaceborne platforms". Atmospheric Measurement Techniques 13, n.º 2 (11 de fevereiro de 2020): 645–59. http://dx.doi.org/10.5194/amt-13-645-2020.
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Abstract. Many institutions struggle to tap into the potential of their large archives of radar reflectivity: these data are often affected by miscalibration, yet the bias is typically unknown and temporally volatile. Still, relative calibration techniques can be used to correct the measurements a posteriori. For that purpose, the usage of spaceborne reflectivity observations from the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Measurement (GPM) platforms has become increasingly popular: the calibration bias of a ground radar (GR) is estimated from its average reflectivity difference to the spaceborne radar (SR). Recently, Crisologo et al. (2018) introduced a formal procedure to enhance the reliability of such estimates: each match between SR and GR observations is assigned a quality index, and the calibration bias is inferred as a quality-weighted average of the differences between SR and GR. The relevance of quality was exemplified for the Subic S-band radar in the Philippines, which is greatly affected by partial beam blockage. The present study extends the concept of quality-weighted averaging by accounting for path-integrated attenuation (PIA) in addition to beam blockage. This extension becomes vital for radars that operate at the C or X band. Correspondingly, the study setup includes a C-band radar that substantially overlaps with the S-band radar. Based on the extended quality-weighting approach, we retrieve, for each of the two ground radars, a time series of calibration bias estimates from suitable SR overpasses. As a result of applying these estimates to correct the ground radar observations, the consistency between the ground radars in the region of overlap increased substantially. Furthermore, we investigated if the bias estimates can be interpolated in time, so that ground radar observations can be corrected even in the absence of prompt SR overpasses. We found that a moving average approach was most suitable for that purpose, although limited by the absence of explicit records of radar maintenance operations.
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Ryzhkov, Alexander, Pengfei Zhang, Heather Reeves, Matthew Kumjian, Timo Tschallener, Silke Trömel e Clemens Simmer. "Quasi-Vertical Profiles—A New Way to Look at Polarimetric Radar Data". Journal of Atmospheric and Oceanic Technology 33, n.º 3 (março de 2016): 551–62. http://dx.doi.org/10.1175/jtech-d-15-0020.1.
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AbstractA novel methodology is introduced for processing and presenting polarimetric data collected by weather surveillance radars. It involves azimuthal averaging of radar reflectivity Z, differential reflectivity ZDR, cross-correlation coefficient ρhv, and differential phase ΦDP at high antenna elevation, and presenting resulting quasi-vertical profiles (QVPs) in a height-versus-time format. Multiple examples of QVPs retrieved from the data collected by S-, C-, and X-band dual-polarization radars at elevations ranging from 6.4° to 28° illustrate advantages of the QVP technique. The benefits include an ability to examine the temporal evolution of microphysical processes governing precipitation production and to compare polarimetric data obtained from the scanning surveillance weather radars with observations made by vertically looking remote sensors, such as wind profilers, lidars, radiometers, cloud radars, and radars operating on spaceborne and airborne platforms. Continuous monitoring of the melting layer and the layer of dendritic growth with high vertical resolution, and the possible opportunity to discriminate between the processes of snow aggregation and riming, constitute other potential benefits of the suggested methodology.
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Battaglia, Alessandro, Satoru Kobayashi, Simone Tanelli, Clemens Simmer e Eastwood Im. "Multiple Scattering Effects in Pulsed Radar Systems: An Intercomparison Study". Journal of Atmospheric and Oceanic Technology 25, n.º 9 (1 de setembro de 2008): 1556–67. http://dx.doi.org/10.1175/2008jtecha1023.1.
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Abstract In this paper, two different numerical methods capable of computing multiple scattering effects in pulsed-radar systems are compared. Both methods are based on the solution of the time-dependent vectorial form of the radiative transfer equation: one exploits the successive order of scattering approximation, the other a forward Monte Carlo technique. Different benchmark results are presented (including layers of monodisperse spherical water and ice particles), which are of specific interest for W-band spaceborne cloud radars such as CloudSat’s or EarthCARE’s cloud profiling radars. Results demonstrate a good agreement between the two methods. The pros and cons of the two models are discussed, with a particular focus on the validity of the second order of scattering approximation.
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Bouniol, Dominique, Alain Protat, Artemio Plana-Fattori, Manuel Giraud, Jean-Paul Vinson e Noël Grand. "Comparison of Airborne and Spaceborne 95-GHz Radar Reflectivities and Evaluation of Multiple Scattering Effects in Spaceborne Measurements". Journal of Atmospheric and Oceanic Technology 25, n.º 11 (1 de novembro de 2008): 1983–95. http://dx.doi.org/10.1175/2008jtecha1011.1.
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Abstract This paper provides an evaluation of the level 1 (reflectivity) CloudSat products by making use of coincident measurements collected by an airborne 95-GHz radar during the African Monsoon Multidisciplinary Analysis (AMMA) experiment that took place in summer 2006 over West Africa. In a first step the airborne radar calibration is assessed. Collocated measurements of the spaceborne and airborne radars within the ice anvil of a mesoscale convective system are then compared. Several aspects are interesting in this comparison: First, both instruments exhibit attenuation within the ice part of the convective system, which suggests either the presence of a significant amount of supercooled liquid water above the melting layer or the presence of wet and very dense ice. Second, from the differences in the observed reflectivity values, a multiple scattering enhancement of at least 2.5 dB in the CloudSat reflectivities at flight altitude is estimated. The main conclusion of this paper is that in such thick anvils of mesoscale convective systems the CloudSat measurements have to be corrected for this effect, if one wants to derive accurate level 2 products such as the ice water content from radar reflectivity. This effect is expected to be much smaller in nonprecipitating clouds though.
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Li, Fuk-kwok, Daniel Held, John Curlander e Chialin Wu. "Doppler Parameter Estimation for Spaceborne Synthetic-Aperture Radars". IEEE Transactions on Geoscience and Remote Sensing GE-23, n.º 1 (janeiro de 1985): 47–56. http://dx.doi.org/10.1109/tgrs.1985.289499.
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Li, F. K., e R. M. Goldstein. "Studies of multibaseline spaceborne interferometric synthetic aperture radars". IEEE Transactions on Geoscience and Remote Sensing 28, n.º 1 (1990): 88–97. http://dx.doi.org/10.1109/36.45749.
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Kidd, Chris, Edward Graham, Tim Smyth e Michael Gill. "Assessing the Impact of Light/Shallow Precipitation Retrievals from Satellite-Based Observations Using Surface Radar and Micro Rain Radar Observations". Remote Sensing 13, n.º 9 (28 de abril de 2021): 1708. http://dx.doi.org/10.3390/rs13091708.
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The accurate representation of precipitation across the Earth’s surface is crucial to furthering our knowledge and understanding of the Earth System and its component processes. Precipitation poses a number of challenges, particularly due to the variability of precipitation over time and space and whether it falls as snow or rain. While conventional measures of precipitation are reasonably good at the location of their measurement, their distribution across the Earth’s surface is uneven with some regions having no surface measurements. Spaceborne sensors have the capability of providing regular observations across the Earth’s surface that can provide estimates of precipitation. However, the estimation of precipitation from satellite observations is not necessarily straightforward. Visible and/or infrared techniques rely upon imprecise cloud-top to surface precipitation relationships, while the sensitivity of passive microwave techniques to different precipitation types is not consistent. Active microwave (radar) observations provide the most direct satellite measurements of precipitation but cannot provide estimates close to the surface and are generally not sufficiently sensitive to resolve light precipitation. This is particularly problematic at mid to high latitudes, where light and/or shallow precipitation dominates. This paper compares measurements made by ground-based weather radars, Micro Rain Radars and the spaceborne Dual-frequency Precipitation Radar to study both light precipitation intensity and shallow precipitation occurrence and to assess their impact on satellites retrievals of precipitation at the mid to high latitudes.
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Ji, Lei, Weixin Xu, Haonan Chen e Nana Liu. "Consistency of Vertical Reflectivity Profiles and Echo-Top Heights between Spaceborne Radars Onboard TRMM and GPM". Remote Sensing 14, n.º 9 (21 de abril de 2022): 1987. http://dx.doi.org/10.3390/rs14091987.
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Globally consistent long-term radar measurements are imperative for understanding the global climatology and potential trends of convection. This study investigates the consistency of vertical profiles of reflectivity (VPR) and 20-dBZ echo-top height (Topht20) between the two precipitation radars onboard the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Measurement (GPM) satellites. Results show that VPR coincidently observed by the TRMM’s and GPM’s Ku-band radar agree well for both convective and stratiform precipitation, although certain discrepancies exist in the VPR of weak convection. Topht20s of the TRMM and GPM are consistent either for coincident events, or latitudinal mean during the 7-month common period, all with biases within the radar range resolution (0.1–0.2 km). The largest difference in the Topht20 between the TRMM’s and GPM’s Ku-band radar occurs in shallow precipitation. Possible reasons for this discrepancy are discussed, including sidelobe clutter, beam-mismatch, non-uniform beam filling, and insufficient sampling. Finally, a 23-year (1998–2020) climatology of Topht20 has been constructed from the two spaceborne radars, and the global mean Topht20 time series shows no significant trend in convective depth during the last two decades.
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Matrosov, Sergey Y., Matthew D. Shupe e Irina V. Djalalova. "Snowfall Retrievals Using Millimeter-Wavelength Cloud Radars". Journal of Applied Meteorology and Climatology 47, n.º 3 (1 de março de 2008): 769–77. http://dx.doi.org/10.1175/2007jamc1768.1.
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Abstract It is demonstrated that millimeter-wavelength radars that are designed primarily for cloud studies can be also used effectively for snowfall retrievals. Radar reflectivity–liquid equivalent snowfall rate (Ze–S) relations specifically tuned for Ka- and W-band radar frequencies are applied to measurements taken by vertically pointing ground-based 8-mm cloud radars (MMCR) that are designed for the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Program and by the nadir-pointing spaceborne 94-GHz CloudSat radar. Comparisons of the MMCR-based snowfall accumulations estimated during experimental events with no significant snowflake riming and controlled gauge measurements indicated an 87% standard deviation between radar and gauge data that is consistent with the uncertainties in the coefficients of the Ze–S relations resulting from variability in snowflake microphysical properties. Comparisons of CloudSat-based snowfall-rate retrievals in heavy snowfall were consistent with estimates from surface S-band precipitation surveillance radars made using algorithms that were specifically designed for use with these radars. A typical difference between the CloudSat and the S-band precipitation radar estimates of snowfall rate for approximately collocated resolution pixels was within a factor of 2, which is of the order of the uncertainty of each estimate. The results of this study suggest that the ground-based and satellite-borne radars operating at Ka and W bands can provide valuable retrieval information on vertical profiles of snowfall, which is an important component of the global water cycle. This information is particularly important in Arctic regions where precipitation information from other sources is scarce.
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Louf, Valentin, Alain Protat, Robert A. Warren, Scott M. Collis, David B. Wolff, Surendra Raunyiar, Christian Jakob e Walter A. Petersen. "An Integrated Approach to Weather Radar Calibration and Monitoring Using Ground Clutter and Satellite Comparisons". Journal of Atmospheric and Oceanic Technology 36, n.º 1 (janeiro de 2019): 17–39. http://dx.doi.org/10.1175/jtech-d-18-0007.1.
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AbstractThe stability and accuracy of weather radar reflectivity calibration are imperative for quantitative applications, such as rainfall estimation, severe weather monitoring and nowcasting, and assimilation in numerical weather prediction models. Various radar calibration and monitoring techniques have been developed, but only recently have integrated approaches been proposed, that is, using different calibration techniques in combination. In this paper the following three techniques are used: 1) ground clutter monitoring, 2) comparisons with spaceborne radars, and 3) the self-consistency of polarimetric variables. These techniques are applied to a C-band polarimetric radar (CPOL) located in the Australian tropics since 1998. The ground clutter monitoring technique is applied to each radar volumetric scan and provides a means to reliably detect changes in calibration, relative to a baseline. It is remarkably stable to within a standard deviation of 0.1 dB. To obtain an absolute calibration value, CPOL observations are compared to spaceborne radars on board TRMM and GPM using a volume-matching technique. Using an iterative procedure and stable calibration periods identified by the ground echoes technique, we improve the accuracy of this technique to about 1 dB. Finally, we review the self-consistency technique and constrain its assumptions using results from the hybrid TRMM–GPM and ground echo technique. Small changes in the self-consistency parameterization can lead to 5 dB of variation in the reflectivity calibration. We find that the drop-shape model of Brandes et al. with a standard deviation of the canting angle of 12° best matches our dataset.
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Li, Bo, Defeng Chen, Huawei Cao, Junling Wang, Haiguang Li, Tuo Fu, Shuo Zhang e Lizhi Zhao. "Estimating the Observation Area of a Stripmap SAR via an ISAR Image Sequence". Remote Sensing 15, n.º 23 (24 de novembro de 2023): 5484. http://dx.doi.org/10.3390/rs15235484.
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The stripmap mode is a basic and important mode for spaceborne synthetic aperture radars (SARs). Estimating the time-varying area observed by spaceborne SARs operating in stripmap mode is a practical but challenging field of research. In this article, we propose a novel method that parameterizes the time-varying area observed by the spaceborne SAR operating in the boresight stripmap mode into a fixed antenna attitude. Based on the principle of minimizing the dihedral angle between the plane containing the ideal estimated scatterers and the plane containing the actual parabolic antenna edge of a spaceborne SAR, an objective function is established for estimating the area observed by a spaceborne SAR operating in the boresight stripmap mode. Then, simulation experiments are designed to validate the feasibility and the robustness of the proposed method. The experimental simulation results show that the proposed method is feasible, and even under low signal-to-noise ratio (SNR) conditions of 10 dB, the proposed method still has good robustness.
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Protat, A., D. Bouniol, E. J. O’Connor, H. Klein Baltink, J. Verlinde e K. Widener. "CloudSat as a Global Radar Calibrator". Journal of Atmospheric and Oceanic Technology 28, n.º 3 (1 de março de 2011): 445–52. http://dx.doi.org/10.1175/2010jtecha1443.1.
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Abstract The calibration of the CloudSat spaceborne cloud radar has been thoroughly assessed using very accurate internal link budgets before launch, comparisons with predicted ocean surface backscatter at 94 GHz, direct comparisons with airborne cloud radars, and statistical comparisons with ground-based cloud radars at different locations of the world. It is believed that the calibration of CloudSat is accurate to within 0.5–1 dB. In the present paper it is shown that an approach similar to that used for the statistical comparisons with ground-based radars can now be adopted the other way around to calibrate other ground-based or airborne radars against CloudSat and/or to detect anomalies in long time series of ground-based radar measurements, provided that the calibration of CloudSat is followed up closely (which is the case). The power of using CloudSat as a global radar calibrator is demonstrated using the Atmospheric Radiation Measurement cloud radar data taken at Barrow, Alaska, the cloud radar data from the Cabauw site, Netherlands, and airborne Doppler cloud radar measurements taken along the CloudSat track in the Arctic by the Radar System Airborne (RASTA) cloud radar installed in the French ATR-42 aircraft for the first time. It is found that the Barrow radar data in 2008 are calibrated too high by 9.8 dB, while the Cabauw radar data in 2008 are calibrated too low by 8.0 dB. The calibration of the RASTA airborne cloud radar using direct comparisons with CloudSat agrees well with the expected gains and losses resulting from the change in configuration that required verification of the RASTA calibration.
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Carter, D. J. Q., D. L. Hurd e R. A. Cordey. "Calibration and characterisation of spaceborne Synthetic Aperture Radars (SAR)". Advances in Space Research 19, n.º 9 (janeiro de 1997): 1415–23. http://dx.doi.org/10.1016/s0273-1177(97)00255-x.
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Schutgens, N. A. J. "Simulating Range Oversampled Doppler Radar Profiles of Inhomogeneous Targets". Journal of Atmospheric and Oceanic Technology 25, n.º 9 (1 de setembro de 2008): 1514–28. http://dx.doi.org/10.1175/2007jtecha1026.1.
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Abstract A new technique for generating range oversampled profiles of Doppler radar signals that have been backscattered by distributed targets is presented in this paper. The technique was developed for spaceborne cloud radars, but it can just as well be used for ground-based precipitation or wind-profiling radars. The technique is more versatile than the traditional inverse FFT technique and faster than the individual hydrometeor simulation (Monte Carlo) technique. Doppler radar signals from backscattering hydrometeors are essentially correlated stochastic variables. The technique uses an accurate description of covariances between voltages measured for different pulses and at different positions (range gates) along a profile. A matrix formalism is developed to subsequently transform uncorrelated Gaussian noise into correlated receiver voltages with the appropriate covariances. In particular, the new technique deals with target variability in a physically consistent manner, accounting for the effects of inhomogeneity both within the instantaneous field of view and between subsequent pulses. The new technique is showcased with examples of simulated 95-GHz Doppler radar observations by the Earth Clouds, Aerosols and Radiation Explorer (EarthCARE) space mission.
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Schutgens, N. A. J. "Simulated Doppler Radar Observations of Inhomogeneous Clouds: Application to the EarthCARE Space Mission". Journal of Atmospheric and Oceanic Technology 25, n.º 1 (1 de janeiro de 2008): 26–42. http://dx.doi.org/10.1175/2007jtecha956.1.
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Abstract A new simulation technique for spaceborne Doppler radar observations that was developed specifically for inhomogeneous targets is presented. Cloud inhomogeneity affects Doppler observations in two ways. First, line-of-sight velocities within the instantaneous field of view are unequally weighted. As the large forward motion of a spaceborne radar contributes to these line-of-sight velocities this causes biases in observed Doppler speeds. Second, receiver voltages now have time-varying stochastical properties, increasing the inaccuracy of Doppler observations. The new technique predicts larger inaccuracies of observed Doppler speeds than the traditional random signal simulations based on the inverse Fourier transform. The accuracy of Doppler speed observations by a spaceborne 95-GHz radar [as part of the proposed European Space Agency (ESA)/Japan Aerospace Exploration Agency (JAXA)/National Institute for Information and Communications Technology (NICT) EarthCARE mission] is assessed through simulations for realistic cloud scenes based on observations made by ground-based cloud-profiling radars. Close to lateral cloud boundary biases as large as several meters per second occur. For half of the cloud scenes investigated, the distribution of the in-cloud bias has an rms of 0.5 m s−1, implying that a bias in excess of 0.5 m s−1 will not be uncommon. An algorithm to correct the bias in observed Doppler observations, based on the observed gradient of reflectivity along track, is suggested and shown to be effective; that is, the aforementioned rms bias reduces to 0.14 m s−1.
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Kollias, Pavlos, Bernat Puigdomènech Treserras e Alain Protat. "Calibration of the 2007–2017 record of Atmospheric Radiation Measurements cloud radar observations using CloudSat". Atmospheric Measurement Techniques 12, n.º 9 (12 de setembro de 2019): 4949–64. http://dx.doi.org/10.5194/amt-12-4949-2019.
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Abstract. The U.S. Department of Energy (DOE) Atmospheric Radiation Measurements (ARM) facility has been at the forefront of millimeter-wavelength radar development and operations since the late 1990s. The operational performance of the ARM cloud radar network is very high; however, the calibration of the historical record is not well established. Here, a well-characterized spaceborne 94 GHz cloud profiling radar (CloudSat) is used to characterize the calibration of the ARM cloud radars. The calibration extends from 2007 to 2017 and includes both fixed and mobile deployments. Collectively, over 43 years of ARM profiling cloud radar observations are compared to CloudSat and the calibration offsets are reported as a function of time using a sliding window of 6 months. The study also provides the calibration offsets for each operating mode of the ARM cloud radars. Overall, significant calibration offsets are found that exceed the uncertainty of the technique (1–2 dB). The findings of this study are critical to past, ongoing, and planned studies of cloud and precipitation and should assist the DOE ARM to build a legacy decadal ground-based cloud radar dataset for global climate model validation.
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Li, Lihua, Gerald M. Heymsfield, Lin Tian e Paul E. Racette. "Measurements of Ocean Surface Backscattering Using an Airborne 94-GHz Cloud Radar—Implication for Calibration of Airborne and Spaceborne W-Band Radars". Journal of Atmospheric and Oceanic Technology 22, n.º 7 (1 de julho de 2005): 1033–45. http://dx.doi.org/10.1175/jtech1722.1.
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Abstract Backscattering properties of the ocean surface have been widely used as a calibration reference for airborne and spaceborne microwave sensors. However, at millimeter-wave frequencies, the ocean surface backscattering mechanism is still not well understood, in part, due to the lack of experimental measurements. During the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE), measurements of ocean surface backscattering were made using a 94-GHz (W band) cloud radar on board a NASA ER-2 high-altitude aircraft. This unprecedented dataset enhances our knowledge about the ocean surface scattering mechanism at 94 GHz. The measurement set includes the normalized ocean surface cross section over a range of the incidence angles under a variety of wind conditions. It was confirmed that even at 94 GHz, the normalized ocean surface radar cross section, σo, is insensitive to surface wind conditions near a 10° incidence angle, a finding similar to what has been found in the literature for lower frequencies. Analysis of the radar measurements also shows good agreement with a quasi-specular scattering model at low incidence angles. The results of this work support the proposition of using the ocean surface as a calibration reference for airborne millimeter-wave cloud radars and for the ongoing NASA CloudSat mission, which will use a 94-GHz spaceborne cloud radar for global cloud measurements.
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Battaglia, Alessandro, Simone Tanelli e Pavlos Kollias. "Polarization Diversity for Millimeter Spaceborne Doppler Radars: An Answer for Observing Deep Convection?" Journal of Atmospheric and Oceanic Technology 30, n.º 12 (1 de dezembro de 2013): 2768–87. http://dx.doi.org/10.1175/jtech-d-13-00085.1.
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Abstract Spaceborne Doppler radars have the potential to provide key missing observations of convective vertical air motions especially over the tropical oceans. Such measurements can improve understanding of the role of tropical convection in vertical energy transport and its interaction with the environment. Several millimeter wavelength Doppler radar concepts have been proposed since the 1990s. The Earth Clouds, Aerosols, and Radiation Explorer (EarthCARE) Cloud Profiling Radar (CPR) will be the first Dopplerized atmospheric radar in space but has not been optimized for Doppler measurements in deep convective clouds. The key challenge that constrains the CPR performance in convective clouds is the range–Doppler dilemma. Polarization diversity (PD) offers a solution to this constraint by decoupling the coherency (Doppler) requirement from the unambiguous range requirement. Careful modeling of the radar signal depolarization and its impact on radar receiver channel cross talk is needed to accurately assess the performance of the PD approach. The end-to-end simulator presented in this work allows reproduction of the signal sensed by a Doppler radar equipped with polarization diversity when overpassing realistic three-dimensional convective cells, with all relevant cross-talk sources accounted for. The notional study highlights that multiple scattering is the primary source of cross talk, highly detrimental for millimeter Doppler velocity accuracy. The ambitious scientific requirement of 1 m s−1 accuracy at 500-m integration for reflectivities above −15 dBZ are within reach for a W-band radar with a 2.5-m antenna with optimal values of the pulse-pair interval between 20 and 30 μs but only once multiple scattering and ghost-contaminated regions are screened out. The identification of such areas is key for Doppler accuracies and can be achieved by employing an interlaced pulse-pair mode that measures the cross and the copolar reflectivities. To mitigate the impact of attenuation and multiple scattering, the Ka band has been considered as either alternative or additional to the W band. However, a Ka system produces worse Doppler performances than a W-band system with the same 2.5-m antenna size. Furthermore, in deep convection it results in similar levels of multiple scattering and therefore it does not increase significantly the depth of penetration. In addition, the larger footprint causes stronger nonuniform beam-filling effects. One advantage of the Ka-band option is the larger Nyquist velocity that tends to reduce the Doppler accuracies. More significant benefits are derived from the Ka band when observing precipitation not as intense as the deep convection is considered here. This study demonstrates that polarization diversity indeed represents a very promising methodology capable of significantly reducing aliasing and Doppler moment estimate errors, two main error sources for Doppler velocity estimates in deep convective systems and a key step to achieving typical mission requirements for convection-oriented millimeter radar-based spaceborne missions.
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Matrosov, Sergey Y. "Observations of Wintertime U.S. West Coast Precipitating Systems with W-Band Satellite Radar and Other Spaceborne Instruments". Journal of Hydrometeorology 13, n.º 1 (1 de fevereiro de 2012): 223–38. http://dx.doi.org/10.1175/jhm-d-10-05025.1.
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Abstract The potential of CloudSat W-band radar for observing wintertime storms affecting the West Coast of North America is evaluated. Storms having high hydrological impact often result from landfalls of “atmospheric rivers” (“ARs”), which are the narrow elongated regions of water vapor transport from the tropics. CloudSat measurements are used for retrievals of rain rate R and cloud ice water path (IWP) along the satellite ground track over ocean and land. These retrievals present quasi-instantaneous vertical cross sections of precipitating systems with high-resolution information about hydrometeors. This information is valuable in coastal areas with complex terrain where observations with existing instrumentation, including ground-based radars, are limited. CloudSat reflectivity enhancements [i.e., bright band (BB)] present a way to estimate freezing levels, indicating transitions between rainfall and snowfall. CloudSat estimates of these levels were validated using data from radiosonde soundings and compared to model and microwave sounder data. Comparisons of CloudSat retrievals of rain rates with estimates from ground-based radars in the areas where measurements from these radars were available indicated an agreement within retrieval uncertainties, which were around 50%. The utility of CloudSat was illustrated for case studies of pronounced AR events at landfall and over ocean. Initial analysis of CloudSat crossings of ARs during the 2006/07 season were used for rainfall regime prevalence assessment. It indicated that stratiform rain, which often had BB features, warm rain, and mixed rain were observed with about 26%, 24%, and 50% frequency. Stratiform regions generally had higher rain rates. Significant correlation (~0.72) between mean values of IWP and rain rate was observed for stratiform rainfall.
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Yeh, H.-Y. M., N. Prasad, R. Meneghini, W.-K. Tao, J. A. Jones e R. F. Adler. "Cloud Model-Based Simulation of Spaceborne Radar Observations". Journal of Applied Meteorology 34, n.º 1 (1 de janeiro de 1995): 175–97. http://dx.doi.org/10.1175/1520-0450-34.1.175.
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Abstract Simulations of observations from potential spaceborne radars are made based on storm structure generated from the three-dimensional (3D) Goddard cumulus ensemble model simulation of an intense overland convective system. Five frequencies of 3, 10, 14, 35, and 95 GHz are discussed, but the Tropical Rainfall Measuring Mission precipitation radar sensor frequency ( 14 GHz) is the focus of this study. Radar reflectivities and their attenuation in various atmospheric conditions are studied in this simulation. With the attenuation from cloud and precipitation in the estimation of reflectivity factor (dBZ), the reflectivities in the lower atmosphere in the convective coresare significantly reduced. With spatial resolution of 4 km X 4 km, attenuation at 14 GHz may cause as large as a 20-dBZ difference between the simulated measurements of the peak (Zmp) and near-surface reflectivity (Zmp) in the most intense convective region. The Zmp occurs at various altitudes depending on the hydrometeor concentrations and their vertical distribution. Despite the significant attenuation in the intense cores, the presence of the rain maximum is easily detected by using information of Zmp. In the stratiform region, the attenuation is quite limited (usually less than 5 dBZ), and the reduction of reflectivity is mostly related to the actual vertical structure of cloud distribution. Since Zmp suffers severe attenuation and tends to underestimate surface rainfall intensity in convective regions, Zmp can be more representative for rainfall retrieval in the lower atmosphere in these regions. In the stratiform region where attenuation is negligible, however, Zmp tends to overestimate surface rainfall and Zmp is more appropriate for rainfall retrieval. A hybrid technique using a weight between the two rain intensities is testedand found potentially useful for future applications. The estimated surface rain-rate map based on this hybrid approach captures many of the details of the cloud model rain field but still slightly underestimates the rain-rate maximum.
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Qi, Youcun, Jian Zhang, Qing Cao, Yang Hong e Xiao-Ming Hu. "Correction of Radar QPE Errors for Nonuniform VPRs in Mesoscale Convective Systems Using TRMM Observations". Journal of Hydrometeorology 14, n.º 5 (1 de outubro de 2013): 1672–82. http://dx.doi.org/10.1175/jhm-d-12-0165.1.
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Abstract Mesoscale convective systems (MCSs) contain both regions of convective and stratiform precipitation, and a bright band (BB) is often found in the stratiform region. Inflated reflectivity intensities in the BB often cause positive biases in radar quantitative precipitation estimation (QPE). A vertical profile of reflectivity (VPR) correction is necessary to reduce such biases. However, existing VPR correction methods for ground-based radars often perform poorly for MCSs owing to their coarse resolution and poor coverage in the vertical direction, especially at far ranges. Spaceborne radars such as the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR), on the other hand, can provide high resolution VPRs. The current study explores a new approach of incorporating the TRMM VPRs into the VPR correction for the Weather Surveillance Radar-1988 Doppler (WSR-88D) radar QPE. High-resolution VPRs derived from the Ku-band TRMM PR data are converted into equivalent S-band VPRs using an empirical technique. The equivalent S-band TRMM VPRs are resampled according to the WSR-88D beam resolution, and the resampled (apparent) VPRs are then used to correct for BB effects in the WSR-88D QPE when the ground radar VPR cannot accurately capture the BB bottom. The new scheme was tested on six MCSs from different regions in the United States and it was shown to provide effective mitigation of the radar QPE errors due to BB contamination.
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Matrosov, Sergey Y. "Comparative Evaluation of Snowfall Retrievals from the CloudSat W-band Radar Using Ground-Based Weather Radars". Journal of Atmospheric and Oceanic Technology 36, n.º 1 (janeiro de 2019): 101–11. http://dx.doi.org/10.1175/jtech-d-18-0069.1.
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AbstractInstantaneous liquid-equivalent snowfall rates S retrieved from CloudSat W-band cloud radar reflectivity Ze measurements are compared to estimates of S from operational Weather Surveillance Radar-1988 Doppler (WSR-88D) systems when the CloudSat satellite overflew the ground-based radar sites during spatially extensive nimbostratus snowfall events. For these comparisons, the ground-based radar measurements are interpolated to closely match in space and time spaceborne radar resolution volumes above ground clutter, thus avoiding uncertainties in deriving near-surface snowfall rates from measurements aloft by both radar types. Although typical uncertainties of both ground-based and spaceborne snowfall-rate retrieval approaches are quite high, the results from the standard optimal estimation CloudSat 2C-SNOW-PROFILE algorithm are on average in good agreement with the WSR-88D default snowfall algorithm results with correlation coefficients being around 0.8–0.85. The CloudSat standard optimal estimation snowfall-rate products are also shown to be in satisfactory agreement with retrievals from several simple W-band Ze–S relations suggested earlier. The snowfall rate and snow/ice water content (IWC) parameters from the CloudSat 2C-SNOW-PROFILE algorithm are highly interdependent. A tight relation between S and IWC is apparently introduced through the ice particle fall velocity assumption that is made in the reflectivity-based snowfall retrieval algorithm. This suggests that ice sedimentation rate estimates can also be deduced from applications of numerous empirical IWC–reflectivity relations derived previously for different cloud conditions when appropriate assumptions about fall velocities are made. Intercomparisons between different CloudSat snow/ice water content products indicated significant discrepancies in IWC values from different standard CloudSat retrieval algorithms.
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Warren, Robert A., Alain Protat, Steven T. Siems, Hamish A. Ramsay, Valentin Louf, Michael J. Manton e Thomas A. Kane. "Calibrating Ground-Based Radars against TRMM and GPM". Journal of Atmospheric and Oceanic Technology 35, n.º 2 (fevereiro de 2018): 323–46. http://dx.doi.org/10.1175/jtech-d-17-0128.1.
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AbstractCalibration error represents a significant source of uncertainty in quantitative applications of ground-based radar (GR) reflectivity data. Correcting it requires knowledge of the true reflectivity at well-defined locations and times during a volume scan. Previous work has demonstrated that observations from certain spaceborne radar (SR) platforms may be suitable for this purpose. Specifically, the Ku-band precipitation radars on board the Tropical Rainfall Measuring Mission (TRMM) satellite and its successor, the Global Precipitation Measurement (GPM) mission Core Observatory satellite together provide nearly two decades of well-calibrated reflectivity measurements over low-latitude regions (±35°). However, when comparing SR and GR reflectivities, great care must be taken to account for differences in instrument sensitivity and frequency, and to ensure that the observations are spatially and temporally coincident. Here, a volume-matching method, developed as part of the ground validation network for GPM, is adapted and used to quantify historical calibration errors for three S-band radars in the vicinity of Sydney, Australia. Volume-matched GR–SR sample pairs are identified over a 7-yr period and carefully filtered to isolate reflectivity differences associated with GR calibration error. These are then used in combination with radar engineering work records to derive a piecewise-constant time series of calibration error for each site. The efficacy of this approach is verified through comparisons between GR reflectivities in regions of overlapping coverage, with improved agreement when the estimated errors are removed.
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Matrosov, Sergey Y. "Intercomparisons of CloudSat and Ground-Based Radar Retrievals of Rain Rate over Land". Journal of Applied Meteorology and Climatology 53, n.º 10 (outubro de 2014): 2360–70. http://dx.doi.org/10.1175/jamc-d-14-0055.1.
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AbstractExperimental retrievals of rain rates using the CloudSat spaceborne 94-GHz radar reflectivity gradient method over land were evaluated by comparing them with standard estimates from ground-based operational S-band radar measurements, which are widely used for quantitative precipitation estimations. The comparisons were performed for predominantly stratiform precipitation events that occurred in the vicinity of the Weather Surveillance Radar-1988 Doppler (WSR-88D) KGWX and KSHV radars during the CloudSat overpasses in the vicinity of these ground radar sites. The standard reflectivity-based WSR-88D rain-rate retrievals used in operational practice were utilized as a reference for the CloudSat retrieval evaluation. Spaceborne and ground-based radar rain-rate estimates that were closely collocated in space and time were generally well correlated. The correlation coefficients were approximately 0.65 on average, and the mean relative biases were usually within ±35% for the whole dataset and for individual events with typical rain rates exceeding ~2 mm h−1. For events with lighter rainfall, higher biases and lower correlations were often present. The normalized mean absolute differences between satellite- and ground-based radar retrievals were on average ~60%, with an increasing trend for lighter rainfall. Such mean differences are comparable to combined retrieval errors from both ground-based and satellite radar remote sensing approaches. Evaluation of potential effects of partial beam blockage on the ground-based radar measurements was performed, and the influence of the choice of relation between WSR-88D reflectivity and rain rate that was utilized in the ground-based rain-rate retrievals was assessed.
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Bentz, Cristina Maria, e Josemá Oliveira de Barros. "A MULTI-SENSOR APPROACH FOR OIL SPILL AND SEA SURFACE MONITORING, IN SOUTHEASTERN BRAZIL". International Oil Spill Conference Proceedings 2005, n.º 1 (1 de maio de 2005): 703–6. http://dx.doi.org/10.7901/2169-3358-2005-1-703.
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ABSTRACT Since May 2001 PETROBRAS is using spaceborne multi-sensor remote sensing for its sea surface monitoring program at the Campos, Santos and Espirito Santo Basins, southeastern Brazilian coast. This area is presently responsible for about 80% of all the Brazilian oil and gas production. Ocean color (SeaWiFS and MODIS), thermal infrared (NOAA/AVHRR), scatterometer (QuikSCAT) and Synthetic Aperture Radar (RADARSAT-1 and ENVISAT) data were integrated in order to detect and characterize different sorts of marine pollution and meteo-oceanographic phenomena. The near real time processing and delivery of the SAR data allowed the timely in-situ verification and sampling of the remotely detected events. Satellite sensors operating in the visible part of the spectrum are used to monitor ocean color variations and associated biomass changes. Thermal infrared radiometers are ideal to monitor features like oceanic fronts and upwelling plumes. However, the major limitation for both types of sensors is the extensive and persistent presence of clouds in the monitored area. Fortunately, microwave sensors such imaging spaceborne Synthetic Aperture Radars (SAR) permit the acquisition of oceanic scenes, regardless cloud coverage. With the spaceborne SAR systems available it is possible to have almost a daily synoptic view of large areas with suitable spatial resolution for the detection of different natural and men-made events. The integrated analysis of these dataset presents an important decision tool for emergencies, as well for the elaboration of contingency plans and evaluation of the oil industry activity impacts.
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Durden, S. L., P. R. Siqueira e S. Tanelli. "On the Use of Multiantenna Radars for Spaceborne Doppler Precipitation Measurements". IEEE Geoscience and Remote Sensing Letters 4, n.º 1 (janeiro de 2007): 181–83. http://dx.doi.org/10.1109/lgrs.2006.887136.
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Astin, I., e L. Di Girolamo. "Minimizing Systematic Errors in Cloud Fraction Estimates from Spaceborne Cloud Radars". Journal of Atmospheric and Oceanic Technology 20, n.º 5 (maio de 2003): 707–16. http://dx.doi.org/10.1175/1520-0426(2003)20<707:mseicf>2.0.co;2.
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Rignot, E. J., R. Zimmermann e J. J. van Zyl. "Spaceborne applications of P band imaging radars for measuring forest biomass". IEEE Transactions on Geoscience and Remote Sensing 33, n.º 5 (1995): 1162–69. http://dx.doi.org/10.1109/36.469480.
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Matrosov, Sergey Y. "Modeling Backscatter Properties of Snowfall at Millimeter Wavelengths". Journal of the Atmospheric Sciences 64, n.º 5 (1 de maio de 2007): 1727–36. http://dx.doi.org/10.1175/jas3904.1.
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Abstract Ground-based vertically pointing and airborne/spaceborne nadir-pointing millimeter-wavelength radars are being increasingly used worldwide. Though such radars are primarily designed for cloud remote sensing, they can also be used for precipitation measurements including snowfall estimates. In this study, modeling of snowfall radar properties is performed for the common frequencies of millimeter-wavelength radars such as those used by the U.S. Department of Energy’s Atmospheric Radiation Measurement Program (Ka and W bands) and the CloudSat mission (W band). Realistic snowflake models including aggregates and single dendrite crystals were used. The model input included appropriate mass–size and terminal fall velocity–size relations and snowflake orientation and shape assumptions. It was shown that unlike in the Rayleigh scattering regime, which is often applicable for longer radar wavelengths, the spherical model does not generally satisfactorily describe scattering of larger snowflakes at millimeter wavelengths. This is especially true when, due to aerodynamic forcing, these snowflakes are oriented primarily with their major dimensions in the horizontal plane and the zenith/nadir radar pointing geometry is used. As a result of modeling using the experimental snowflake size distributions, radar reflectivity–liquid equivalent snowfall rates (Ze–S) relations are suggested for “dry” snowfalls that consist of mostly unrimed snowflakes containing negligible amounts of liquid water. Owing to uncertainties in the model assumptions, these relations, which are derived for the common Ka- and W-band radar frequencies, have significant variability in their coefficients that can exceed a factor of 2 or so. Modeling snowfall attenuation suggests that the attenuation effects in “dry” snowfall can be neglected at the Ka band for most practical cases, while at the W band attenuation may need to be accounted for in heavier snowfalls observed at longer ranges.
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Yin, Mengtao, e Cheng Yuan. "Assessing Snow Water Retrievals over Ocean from Coincident Spaceborne Radar Measurements". Remote Sensing 15, n.º 4 (19 de fevereiro de 2023): 1140. http://dx.doi.org/10.3390/rs15041140.
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Spaceborne snow water retrievals over oceans are assessed using a multiyear coincident dataset of CloudSat Cloud Profiling Radar (CPR) and Global Precipitation Mission (GPM) Dual-frequency Precipitation Radar (DPR). Various factors contributing to differences in snow water retrievals between CPR and DPR are carefully considered. A set of relationships between radar reflectivity (Ze) and snow water content (SWC) at Ku- and W-bands is developed using the same microphysical assumptions. It is found that surface snow water contents from CPR are much larger than those from DPR at latitudes above 60°, while surface snow water contents from DPR slightly exceed those from CPR at latitudes below 50°. Coincident snow water content profiles between CPR and DPR are further divided into two conditions. One is that only CPR detects the falling snow. Another is that both CPR and DPR detect the falling snow. The results indicate that about 88% of all snow water content profiles are under the first condition and usually associated with light snowfall events. The remaining snow water content profiles are generally associated with moderate and heavy snowfall events. Moreover, CPR surface snow water contents are larger than DPR ones at high latitudes because most light snowfall events are misdetected by DPR due to its low sensitivity. DPR surface snow water contents exceed CPR ones at low latitudes because CPR may experience a significant reduction in backscattering efficiency of large particles and attenuation in heavy snowfall events. The low sensitivity of DPR also causes a noticeable decrease in detected snow layer depth. The results presented here can help in developing global snowfall retrieval algorithms using multi-radars.
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Lamer, Katia, Pavlos Kollias, Alessandro Battaglia e Simon Preval. "Mind the gap – Part 1: Accurately locating warm marine boundary layer clouds and precipitation using spaceborne radars". Atmospheric Measurement Techniques 13, n.º 5 (14 de maio de 2020): 2363–79. http://dx.doi.org/10.5194/amt-13-2363-2020.
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Abstract. Ground-based radar observations show that, over the eastern North Atlantic, 50 % of warm marine boundary layer (WMBL) hydrometeors occur below 1.2 km and have reflectivities of < −17 dBZ, thus making their detection from space susceptible to the extent of surface clutter and radar sensitivity. Surface clutter limits the ability of the CloudSat cloud profiling radar (CPR) to observe the true cloud base in ∼52 % of the cloudy columns it detects and true virga base in ∼80 %, meaning the CloudSat CPR often provides an incomplete view of even the clouds it does detect. Using forward simulations, we determine that a 250 m resolution radar would most accurately capture the boundaries of WMBL clouds and precipitation; that being said, because of sensitivity limitations, such a radar would suffer from cloud cover biases similar to those of the CloudSat CPR. Observations and forward simulations indicate that the CloudSat CPR fails to detect 29 %–43 % of the cloudy columns detected by ground-based sensors. Out of all configurations tested, the 7 dB more sensitive EarthCARE CPR performs best (only missing 9.0 % of cloudy columns) indicating that improving radar sensitivity is more important than decreasing the vertical extent of surface clutter for measuring cloud cover. However, because 50 % of WMBL systems are thinner than 400 m, they tend to be artificially stretched by long sensitive radar pulses, hence the EarthCARE CPR overestimation of cloud top height and hydrometeor fraction. Thus, it is recommended that the next generation of space-borne radars targeting WMBL science should operate interlaced pulse modes including both a highly sensitive long-pulse mode and a less sensitive but clutter-limiting short-pulse mode.
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Yin, Yan, Jinghai Sun, Lijia Huang, Peng Jiang, Xiaochen Wang e Chibiao Ding. "Moon Imaging Performance of FAST Radio Telescope in Bistatic Configuration with Other Radars". Remote Sensing 15, n.º 16 (16 de agosto de 2023): 4045. http://dx.doi.org/10.3390/rs15164045.
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Ground-based radar has been used for Moon imaging for more than 60 years. Five-hundred-meter Aperture Spherical radio Telescope (FAST), as the largest radio telescope on Earth, holds significant potential for celestial imaging missions with its exceptional sensitivity. A bistatic Synthetic Aperture Radar (SAR) Moon imaging model that incorporates FAST and other transmitting radars is presented. The objective of this paper is to design the imaging parameters of this bistatic configuration based on the required resolution, and to estimate the resolution performance based on a given bistatic system capability. Considering the ultra-far range and the ultra-long observation time between the radars and the Moon, the geometric relationship involved in this bistatic configuration is significantly distinct from the bistatic configuration of airborne and spaceborne radars. Therefore, this paper accurately derives the two-dimensional resolution on the Moon’s surface. First of all, the models of the Earth’s surface and the Moon’s surface, and the celestial motion of the Earth and Moon are established using WGS-84 and JPL-DE421, given by STK. Secondly, the bistatic range history within the observation time is calculated in terms of continuous celestial motion instead of the popular ‘stop-and-go’ assumption. Thirdly, no approximation is used in the resolution derivation process, and, in addition to the two-dimensional resolutions, the incident angle and the included angle are also given to describe the imaging performance. This method can also be extended to other bistatic-station and single-station celestial imaging, providing support for radar location and parameters design, for observation time span selection, for observation area selection, and for imaging performance estimation. The echo generation and imaging for point targets set on the Moon are shown. The simulation results prove the validity and accuracy of the proposed method in the paper.
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Kobayashi, Satoru, e Hiroshi Kumagai. "Doppler Velocity from Sea Surface on the Spaceborne and Airborne Weather Radars". Journal of Atmospheric and Oceanic Technology 20, n.º 3 (março de 2003): 372–81. http://dx.doi.org/10.1175/1520-0426(2003)020<0372:dvfsso>2.0.co;2.
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Jameson, A. R. "The Estimation of Rainfall Parameters Using Spaceborne and Airborne Nadir-Pointing Radars". Journal of Applied Meteorology 33, n.º 2 (fevereiro de 1994): 230–44. http://dx.doi.org/10.1175/1520-0450(1994)033<0230:teorpu>2.0.co;2.
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Kalmykov, A. I., S. A. Velichko, V. N. Tsymbal, Yu A. Kuleshov, J. A. Weinman e I. Jurkevich. "Observations of the marine environment from spaceborne side-looking real aperture radars". Remote Sensing of Environment 45, n.º 2 (agosto de 1993): 193–208. http://dx.doi.org/10.1016/0034-4257(93)90042-v.
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Dong, Xiang, Zhigang Yuan, Qinglin Zhu, Haining Wang, Fang Sun, Jiawei Zhu, Yi Liu e Chen Zhou. "Computerized Ionospheric Tomography Based on the ADS-B System". Atmosphere 14, n.º 7 (29 de junho de 2023): 1091. http://dx.doi.org/10.3390/atmos14071091.
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The broadcast automatic dependent surveillance (ADS-B) system is a new-generation air traffic control system designed to avoid the waste of resources in secondary radars. The establishment of the spaceborne ADS-B system provides a broad prospect for ionospheric tomography. In this paper, the external observation information of the ionosphere is obtained by measuring the Faraday rotation angle, that is, the total electron content (TEC). Tomography research can be carried out all over the world to conduct large-scale ionospheric electron density research. The experiment selected two different regions and had a time resolution of two hours, a height resolution of 200 km, a latitude resolution of 2°, and a longitude resolution of 5°. Based on the simulated spaceborne ADS-B signal to invert the regional ionospheric electron density, the latitude, longitude, and height distributions of inversion result are basically consistent with those of the actual ionospheric electron density.
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Gabella, Marco, David Duque e Riccardo Notarpietro. "Comparing meteorological spaceborne and ground-based radars: optimal satellite overpass distance from a ground-based radar site". International Journal of Remote Sensing 33, n.º 1 (18 de agosto de 2011): 322–30. http://dx.doi.org/10.1080/01431161.2011.599347.
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