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Ad Stoffelen - One of the best experts on this subject based on the ideXlab platform.
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ERAstar: A High-Resolution Ocean Forcing Product
'Institute of Electrical and Electronics Engineers (IEEE)', 2020Co-Authors: Trindade Ana, Portabella Marcos, Lin Wenming, Ad Stoffelen, Verhoef AntonAbstract:11 pages, 6 figures, 2 tables.-- © 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksTo address the growing demand for accurate high-resolution ocean wind forcing from the ocean modeling community, we develop a new forcing product, ERA*, by means of a geolocated scatterometer-based correction applied to the European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis or ERA-interim (hereafter referred to as ERAi). This method successfully corrects for local wind vector biases present in the ERAi output globally. Several configurations of the ERA* are tested using complementary scatterometer data [advanced scatterometer (ASCAT)-A/B and oceansat-2 scatterometer (OSCAT)] accumulated over different temporal windows, verified against independent scatterometer data [HY-2A scatterometer (HSCAT)], and evaluated through spectral analysis to assess the geophysical consistency of the new stress equivalent wind fields (U10S). Due to the high quality of the scatterometer U10S, ERA* contains some of the physical processes missing or misrepresented in ERAi. Although the method is highly dependent on sampling, it shows potential, notably in the tropics. Short temporal windows are preferred, to avoid oversmoothing of the U10S fields. Thus, corrections based on increased scatterometer sampling (use of multiple Scatterometers) are required to capture the detailed forcing errors. When verified against HSCAT, the ERA* configurations based on multiple Scatterometers reduce the vector root-mean-square difference about 10% with respect to that of ERAi. ERA* also shows a significant increase in small-scale true wind variability, observed in the U10S spectral slopes. In particular, the ERA* spectral slopes consistently lay between those of HSCAT and ERAi, but closer to HSCAT, suggesting that ERA* effectively adds spatial scales of about 50 km, substantially smaller than those resolved by global numerical weather prediction (NWP) output over the open ocean (about 150 km)The work was supported by the Spanish Research and Development Plan under the FPI grant (BES-2013-064521) from the project MIDAS-7 (reference AYA2012-39356-C05-03) and the R&D project L-BAND (reference ESP2017-89463-C3-2-R
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Development of an ASCAT coastal wind product
'European Space Agency', 2020Co-Authors: Portabella Marcos, Ad Stoffelen, Verhoef Anton, Vogelzang J.Abstract:Second EPS/MetOp RAO Workshop, 20-22 May 2009 Barcelona, Spain.-- 6 pages, 4 figures, 3 tablesThe Advanced scatterometer, ASCAT, on MetOp-A was launched on 19 October 2006 as the third wind scatterometer currently in space joining up with the ERS-2 and the SeaWinds Scatterometers. Scatterometers measure the radar backscatter from wind-generated cm-size gravity-capillary waves and provide high-resolution wind vector fields over the sea with high quality. In this paper we show progress in high resolution processing and its verification, and in processing closer to the coast
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Improvement of the ERA* high-resolution forcing product: benefits from the scatterometer constellation
'European Space Agency', 2020Co-Authors: Portabella Marcos, Ad Stoffelen, Verhoef Anton, Trindade Ana, Vall-llossera MercèAbstract:2019 Living Planet Symposium, 13-17 May 2019, Milan, ItalyHigh-resolution satellite derived sea surface wind data, such as those from Scatterometers, are increasingly required for operational monitoring and forecasting of the ocean. We present an improved version of ERA*, an ocean forcing product which keeps the time and space coverage of atmospheric model fields, but adds the accurately observed local mean and variability of wind Scatterometers, to make these datasets suitable for, among others, high-resolution ocean model forcing. Recent attempts of combining scatterometer data and numerical weather prediction (NWP) outputs, i.e., blended ocean forcing products, allows for an increased temporal resolution (e.g., daily) but generally only resolves NWP spatial scales of about 100-150 km. Therefore, information on the wind-current interaction, the diurnal wind cycle and the wind variability in moist convection areas is lost in such products. Moreover, known systematic NWP model (parameterization) errors are in fact propagated at times and locations where no scatterometer winds are available. The alternative, direct forcing from NWP results in even more extensive physical drawbacks. We propose to maintain the increased temporal coverage in a gridded wind and stress product (ERA*), but also to maintain the most beneficial physical qualities of the scatterometer winds, i.e., 25-km spatial resolution, wind-current interaction, variability due to moist convection, etc., and, at the same time correct the large-scale NWP parameterization and dynamical errors. Additionally, we correct these winds for the effects of atmospheric stability and mass density, using stress equivalent 10 m winds, U10S. A scatterometer-based correction, using accurate, unbiased, high spatial resolution ocean vector winds from several Scatterometers, i.e., the Advanced Scatterometers (ASCATs) on board Metop satellites and the OSCAT scatterometer onboard Oceansat-2, is proposed as a new angle to tackle this problem, i.e., to reduce NWP local wind biases accounting for satellite sampling characteristics (note that the scatterometer temporal sampling is latitudinal dependent and rather poor in the tropics). The correction consists of geolocated (i.e., at every ocean grid point), temporally - averaged differences between the scatterometer and the collocated NWP reanalysis (ERA-interim) U10S. Since ERA local biases are relatively persistent over time but such persistence is regionally dependent (e.g., such persistence is longer in the tropics than in the extratropics), we test different configurations of ERA*, i.e., with different temporal windows (from 1 to 5 days) and varying number of Scatterometers (i.e., different combinations of the above mentioned scatterometer systems) in order to find the best quality forcing product. The new ERA* gridded ocean forcing product is validated against independent scatterometer data, i.e., the 25-km HSCAT (onboard HY-2A) wind product. HSCAT is a good wind reference since the orbit pass (6am/6pm) is very different from that of ASCAT-A/B (9:30am/9:30pm) and OSCAT (12:00am/12:00pm). Globally, there is a reduction of the vector root-mean-square error in ERA* w.r.t. ERA interim of more than 10%. Overall, the 1-day temporal window and the multiple scatterometer correction lead to the best quality ERA* global wind product, although such wind quality depends on the region. In particular, this ERA* product outperforms ERA in the tropics, where moist convection and wind-current interaction are not well resolved by the latter. Scores of the bias and standard deviation error support the above statements. Moreover, in contrast with ERA, ERA* is able to resolve eddy scales similar to those resolved by Scatterometers, as shown by wind spectral analysi
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Advancements in Scatterometer Wind Processing
EUMETSAT, 2020Co-Authors: Ad Stoffelen, Portabella Marcos, Verhoef Anton, Verspeek Jeroen, Vogelzang J.Abstract:Ninth International Winds Workshop, Annapolis, Maryland, USA, 14-18 April 2008.-- 8 pages, 7 figures, 1 tableThe EUMETSAT Advanced Scatterometer ASCAT on MetOp-A was launched on 19 October 2006 as the third wind scatterometer currently in space joining up with the ESA ERS-2 and the NASA SeaWinds Scatterometers. Scatterometers measure the radar backscatter from wind generated cm-size gravity-capillary waves and provide high-resolution wind vector fields over the sea. Wind speed and wind direction are provided with high quality and uniquely define the mesoscale wind vector field at the sea surface. The all-weather ERS scatterometer observations have proven important for the forecasting of dynamical and severe weather. Oceanographic applications have been initiated using winds from SeaWinds on QuikScat, since Scatterometers provide unique forcing information on the ocean eddy scale. Together, ERS-2, ASCAT and SeaWinds provide good coverage over the oceans and are now used routinely in marine and weather forecasting. In this paper we show progress in high resolution processing and its verification, in providing gridded winds with mesoscale detail, and in processing closer to the coast with improved geophysical interpretatio
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ERA*: Towards an eddy resolving ocean forcing
European Geosciences Union, 2020Co-Authors: Trindade Ana, Portabella Marcos, Ad Stoffelen, Verhoef Anton, Vall-llossera MercèAbstract:European Geosciences Union (EGU) General Assembly, 7-12 April 2019, Vienna, Austria.-- 1 pageHigh-resolution satellite derived sea surface wind data, such as those from Scatterometers, are increasing lyrequired for operational monitoring and forecasting of the ocean. We present an improved version of ERA*, an ocean forcing product which keeps the time and space coverage of atmospheric model fields, but adds the accurately observed local mean and variability of wind Scatterometers, to make these datasets suitable for, among others, high-resolution ocean forcing. Recent attempts of combining scatterometer data and numerical weather prediction (NWP) outputs, i.e. blended ocean forcing products, allows for an increased temporal resolution (e.g., daily) but generally only resolves NWP spatial scales of about 100-150 km. Therefore, information on the wind-current interaction, the diurnal wind cycle and the wind variability in moist convection areas is lost in such products. Moreover, known systematic NWP model (parameterization) errors are in fact propagated at times and locations where no scatterometer winds are available. The alternative, direct forcing from NWP results in even more extensive physical drawbacks. We propose to maintain the increased temporal coverage in a gridded wind and stress product (ERA*), but also to maintain the most beneficial physical qualities of the scatterometer winds, i.e. 25-km spatial resolution, wind-current interaction, variability due to moist convection, etc., and, at the same time correct the large-scale NWP parameterization and dynamical errors. Additionally, we correct these winds for the effects of atmospheric stability and mass density, using stress equivalent 10 m winds, U10S. A scatterometer-based correction, using accurate, unbiased, high spatial resolution ocean vector winds from several Scatterometers, i.e. the Advanced Scatterometers (ASCATs) on board Metop satellites and the OSCAT scatterometer onboard Oceansat-2, is proposed as a new angle to tackle this problem, i.e. to reduce NWP local wind biases accounting for satellite sampling characteristics. Since ERA local biases are relatively persistent over time but such persistence is regionally dependent (e.g., persistency is longer in the tropics than in the extratropics), we test different configurations of ERA*, i.e. with different temporal windows (from 1 to 5 days) and varying number of Scatterometers (i.e. different combinations of the above mentioned scatterometer systems) to find the best quality forcing product. The new ERA* gridded ocean forcing product is validated against independent scatterometer data, i.e. the 25-km HSCAT (onboard HY-2A) wind product. HSCAT is a good wind reference since the orbit pass (6am/6pm) is very different from that of ASCAT-A/B (9:30am/9:30pm) and OSCAT (12:00am/12:00pm). Globally, there is a reduction of the vector root-mean-square error in ERA* w.r.t. ERA interim of more than 10%. Overall, the 1-day temporal window and the multiple scatterometer correction lead to the best quality ERA* global wind product, although such wind quality depends on the region. In particular, this ERA* product outperforms ERA in the tropics, where moist convection and wind-current interaction are not well resolved by the latter. Scores of the bias and standard deviation error support the above statements. Moreover, in contrast with ERA, ERA* is able to resolve eddy scales similar to those resolved by Scatterometers, as shown by wind spectral analysi
D G Long - One of the best experts on this subject based on the ideXlab platform.
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high resolution measurements with a spaceborne pencil beam scatterometer using combined range doppler discrimination techniques
IEEE Transactions on Geoscience and Remote Sensing, 2003Co-Authors: M W Spencer, Wuyang Tsai, D G LongAbstract:Conically scanning pencil-beam scatterometer systems, such as the SeaWinds radar, constitute an important class of instruments for spaceborne climate observation. In addition to ocean winds, scatterometer data are being applied to a wide range of land and cryospheric applications. A key issue for future scatterometer missions is improved spatial resolution. Pencil-beam Scatterometers to date have been real-aperture systems where only range discrimination is used, resulting in a relatively coarse resolution of approximately 25 km. In this paper, the addition of Doppler discrimination techniques is proposed to meet the need for higher resolution. The unique issues associated with the simultaneous application of range and Doppler processing to a conically scanning radar are addressed, and expressions for the theoretical measurement performance of such a system are derived. Important differences with side-looking imaging radars, which also may employ Doppler techniques, are highlighted. Conceptual design examples based on scatterometer missions of current interest are provided to illustrate this new high-resolution scatterometer approach. It is shown that spatial resolution of pencil-beam scatterometer systems can be improved by an order of magnitude by utilizing combined range/Doppler discrimination techniques, while maintaining the wide-swath and constant incidence angle needed for many geophysical measurements.
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multi spectral analysis of the amazon basin using seawinds ers seasat Scatterometers trmm pr and ssm i
International Geoscience and Remote Sensing Symposium, 2002Co-Authors: Haroon Stephen, D G LongAbstract:The Amazon basin represents a vast geographical zone containing large proportion of global biomass. We use the SeaWinds scatterometer (QSCAT), ERS-1/-2 scatterometer (ESCAT), NASA scatterometer (NSCAT) Seasat scatterometer (SASS), Tropical Rain Measuring Mission Precipitation Radar (TRMM-PR) and Special Sensor Microwave/Imager (SSM/I) data to study the multi-spectral microwave response of Amazon vegetation. Incidence angle signatures of combined backscatter measurements (/spl sigma//sup o/) from the Scatterometers and precipitation radar indicate a good inter-calibration of the sensors. The multi-frequency signatures of both /spl sigma//sup o/ and radiometric temperature measurements (T/sub b/) from SSM/I are also studied. Temporal variability of the Amazon basin is studied using C-band ERS data and a Ku-band time series formed by SASS, NSCAT and QSCAT data. ESCAT data reveals a possible mismatch in the calibration of Scatterometers between ERS-1 and ERS-2. Although the central Amazon forest represents an area of very stable radar backscatter measurements, portions of the southern region exhibit backscatter changes over the past two decades.
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radar backscatter measurement accuracy for a spaceborne pencil beam wind scatterometer with transmit modulation
IEEE Transactions on Geoscience and Remote Sensing, 1997Co-Authors: D G Long, M SpencerAbstract:Scatterometers are remote sensing radars designed to measure near-surface winds over the ocean. The difficulties of accommodating traditional fan-beam Scatterometers on spacecraft has lead to the development of a scanning pencil-beam instrument known as SeaWinds. SeaWinds will be part of the Japanese Advanced Earth Observing Satellite II (ADEOS-II) to be launched in 1999. To analyze the performance of the SeaWinds design, a new expression for the measurement accuracy of a pencil-beam system is required. In this paper the authors derive a general expression for the backscatter measurement accuracy for a pencil-beam scatterometer which includes the effects of transmit signal modulation with simple power detection. Both separate and simultaneous signal+noise and noise-only measurements are considered. The utility of the new expression for scatterometer design tradeoffs is demonstrated using a simplified geometry. A separate paper, ibid., 1997, describes detailed tradeoffs made to develop the SeaWinds design.
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calibration of spaceborne Scatterometers using the amazon tropical rainforest
Proceedings of SPIE, 1993Co-Authors: D G Long, G.b. SkousonAbstract:Spaceborne Scatterometers are radar systems designed specifically to measure the normalized radar backscatter coefficient ((sigma) 0) of the ocean's surface in order to determine the near-surface wind vector. Precise calibration of the instrument sensor is required to determine (sigma) 0 accurately (of the order of a few tenths of a dB). Although careful calibration of the instrument is performed before launch, a post-launch calibration must also be performed. Post-launch calibration may be performed using ground stations and/or extended-area natural targets. The most commonly used extended area target has been the Amazon tropical rainforest which exhibits a remarkably high degree of homogeneity in its radar response over a very large area. However, the rainforest does exhibit some spatial and temporal variability. In this paper we present a simple technique for post-launch calibration of spaceborne scatterometer data using tropical rainforests which accounts for the temporal and spatial variability of the forest response. We first illustrate the technique with Seasat scatterometer (SASS) data then apply the technique to ERS-1 Active Microwave Instrument (AMI) scatterometer data. Gains corrections of up to several tenths of a dB are estimated for SASS. ERS-1 data was found to be well calibrated so that no corrections are required.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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spaceborne radar measurement of wind velocity over the ocean an overview of the nscat scatterometer system
Proceedings of the IEEE, 1991Co-Authors: F M Naderi, Michael H Freilich, D G LongAbstract:Scatterometry and scatterometer design issues are reviewed. The design of the NASA Scatterometer (NSCAT) to be flown on the Japanese ADEOS mission is presented. Building on Seasat experience, the NSCAT system includes several enhancements, such as three antenna azimuths in each of two swaths, and an onboard digital Doppler processor to allow backscatter measurements to be colocated everywhere within the orbit. These enhancements will greatly increase the quality of the NSCAT wind data. The ground processing of data is discussed, and Scatterometers of the next decade are briefly described. >
Klaus Scipal - One of the best experts on this subject based on the ideXlab platform.
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initial soil moisture retrievals from the metop a advanced scatterometer ascat
Geophysical Research Letters, 2007Co-Authors: Zoltan Bartalis, Hans Bonekamp, Vahid Naeimi, Stefan Hasenauer, Josep Figa, Klaus Scipal, Wolfgang Wagner, Craig AndersonAbstract:[1] This article presents first results of deriving relative surface soil moisture from the METOP-A Advanced Scatterometer. Retrieval is based on a change detection approach which has originally been developed for the Active MicrowaveInstrument flownonboardtheEuropeansatellites ERS-1 and ERS-2. Using model parameters derived from eight years of ERS scatterometer data, first global soil moisture maps have been produced from ASCAT data. The ASCAT data were distributed by EUMETSAT for validation purposes during the ASCAT product commissioning activities. Several recent cases of drought and excessive rainfall are clearly visible in the soil moisture data. The results confirm that seamless soil moisture time series can be expected from the series of two ERS and three METOP Scatterometers, providing global coverage on decadal time scales (from 1991 to about 2021). Thereby, operational, nearreal-time ASCAT soil moisture products will become available for weather prediction and hydrometeorological applications. Citation: Bartalis, Z., W. Wagner, V. Naeimi, S. Hasenauer, K. Scipal, H. Bonekamp, J. Figa, and C. Anderson (2007), Initial soil moisture retrievals from the METOP-A Advanced Scatterometer (ASCAT), Geophys. Res. Lett., 34, L20401, doi:10.1029/2007GL031088.
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Azimuthal anisotropy of scatterometer measurements over land
IEEE Transactions on Geoscience and Remote Sensing, 2006Co-Authors: Zoltan Bartalis, Klaus Scipal, Wolfgang WagnerAbstract:Studies of the Earth's land surface involving Scatterometers are becoming an increasingly important application field of microwave remote sensing. Similarly to scatterometer observations of ocean waves, the backscattering coefficient (sigma0) response of land surfaces depends on both the incidence and azimuth angle under which the observations are made. In order to retrieve geophysical parameters from scatterometer data, it is necessary to account for azimuthal-modulation effects of the backscattered signal. In the present study, this paper localizes the regions affected by a strong azimuthal signal dependence when observed with the European Remote Sensing Satellite Scatterometer and the SeaWinds Scatterometer on QuikSCAT (QSCAT). The possible physical reasons for the azimuthal effects, relating the very detailed QSCAT azimuthal response to the spatial orientation of special topographic features and land cover within the sensor footprint, were then discussed. Different methods for normalizing the backscattering coefficient with respect of observation azimuth angle were also proposed and evaluated. First, the mean local incidence angle of the sensor footprint using the shuttle radar topography mission digital elevation model (DEM) were modeled and concluded that the resolution of the DEM is too coarse to characterize most of the observed azimuthal effects. A more effective way of normalizing the backscatter with respect to azimuth is then found to be by using historical backscatter observations to statistically determine the expected backscatter at each observation azimuth and incidence angle as well as time of the year. The efficiency of this method is limited to the availability of past measurements for each location on the Earth
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Soil moisture-runoff relation at the catchment scale as observed with coarse resolution microwave remote sensing
Hydrology and Earth System Sciences Discussions, 2005Co-Authors: Klaus Scipal, C. Scheffler, W. WagnerAbstract:Microwave remote sensing offers emerging capabilities to monitor global hydrological processes. Instruments like the two dedicated soil moisture missions SMOS and HYDROS or the Advanced Scatterometer onboard METOP will provide a flow of coarse resolution microwave data, suited for macro-scale applications. Only recently, the scatterometer onboard of the European Remote Sensing Satellite, which is the precursor instrument of the Advanced Scatterometer, has been used successfully to derive soil moisture information at global scale with a spatial resolution of 50 km. Concepts of how to integrate macro-scale soil moisture data in hydrologic models are however still vague. In fact, the coarse resolution of the data provided by microwave radiometers and Scatterometers is often considered to impede hydrological applications. Nevertheless, even if most hydrologic models are run at much finer scales, radiometers and Scatterometers allow monitoring of atmosphere-induced changes in regional soil moisture patterns. This may prove to be valuable information for modelling hydrological processes in large river basins (>10 000 km2. In this paper, ERS scatterometer derived soil moisture products are compared to measured runoff of the Zambezi River in south-eastern Africa for several years (1992?2000). This comparison serves as one of the first demonstrations that there is hydrologic relevant information in coarse resolution satellite data. The observed high correlations between basin-averaged soil moisture and runoff time series (R2>0.85) demonstrate that the seasonal change from low runoff during the dry season to high runoff during the wet season is well captured by the ERS scatterometer. It can be expected that the high correlations are to a certain degree predetermined by the pronounced inter-annual cycle observed in the discharge behaviour of the Zambezi. To quantify this effect, time series of anomalies have been compared. This analysis showed that differences in runoff from year to year could, to some extent, be explained by soil moisture anomalies.
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Soil moisture-runoff relation at the catchment scale as observed with coarse resolution microwave remote sensing
Hydrology and Earth System Sciences Discussions, 2005Co-Authors: Klaus Scipal, C. Scheffler, W. WagnerAbstract:Microwave remote sensing offers emerging capabilities to monitor global hydrological processes. Instruments like the two dedicated soil moisture missions SMOS and HYDROS or the Advanced Scatterometer (ASCAT) onboard METOP will provide a flow of coarse resolution microwave data, suited for macro-scale applications. Only recently, the ERS scatterometer, which is the precursor instrument of ASCAT, has been used successfully to derive soil moisture information at global scale with a spatial resolution of 50 km. Concepts of how to integrate macro-scale soil moisture data in hydrologic models are however still vague. In fact, the coarse resolution of the data provided by microwave radiometers and Scatterometers is often considered to impede hydrological applications. Nevertheless, even if most hydrologic models are run at much finer scales, radiometers and scatterometer allow monitoring of atmosphere-induced changes in regional soil moisture patterns. This may prove to be valuable information for modelling hydrological processes in large river basins (0.85) clearly demonstrate that the seasonal change from low runoff during the dry season to high runoff during the wet season is well captured by the ERS scatterometer. Additionally, differences in runoff from year to year could be to some extend, explained by soil moisture anomalies.
W. Wagner - One of the best experts on this subject based on the ideXlab platform.
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Soil moisture-runoff relation at the catchment scale as observed with coarse resolution microwave remote sensing
Hydrology and Earth System Sciences Discussions, 2005Co-Authors: Klaus Scipal, C. Scheffler, W. WagnerAbstract:Microwave remote sensing offers emerging capabilities to monitor global hydrological processes. Instruments like the two dedicated soil moisture missions SMOS and HYDROS or the Advanced Scatterometer onboard METOP will provide a flow of coarse resolution microwave data, suited for macro-scale applications. Only recently, the scatterometer onboard of the European Remote Sensing Satellite, which is the precursor instrument of the Advanced Scatterometer, has been used successfully to derive soil moisture information at global scale with a spatial resolution of 50 km. Concepts of how to integrate macro-scale soil moisture data in hydrologic models are however still vague. In fact, the coarse resolution of the data provided by microwave radiometers and Scatterometers is often considered to impede hydrological applications. Nevertheless, even if most hydrologic models are run at much finer scales, radiometers and Scatterometers allow monitoring of atmosphere-induced changes in regional soil moisture patterns. This may prove to be valuable information for modelling hydrological processes in large river basins (>10 000 km2. In this paper, ERS scatterometer derived soil moisture products are compared to measured runoff of the Zambezi River in south-eastern Africa for several years (1992?2000). This comparison serves as one of the first demonstrations that there is hydrologic relevant information in coarse resolution satellite data. The observed high correlations between basin-averaged soil moisture and runoff time series (R2>0.85) demonstrate that the seasonal change from low runoff during the dry season to high runoff during the wet season is well captured by the ERS scatterometer. It can be expected that the high correlations are to a certain degree predetermined by the pronounced inter-annual cycle observed in the discharge behaviour of the Zambezi. To quantify this effect, time series of anomalies have been compared. This analysis showed that differences in runoff from year to year could, to some extent, be explained by soil moisture anomalies.
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Soil moisture-runoff relation at the catchment scale as observed with coarse resolution microwave remote sensing
Hydrology and Earth System Sciences Discussions, 2005Co-Authors: Klaus Scipal, C. Scheffler, W. WagnerAbstract:Microwave remote sensing offers emerging capabilities to monitor global hydrological processes. Instruments like the two dedicated soil moisture missions SMOS and HYDROS or the Advanced Scatterometer (ASCAT) onboard METOP will provide a flow of coarse resolution microwave data, suited for macro-scale applications. Only recently, the ERS scatterometer, which is the precursor instrument of ASCAT, has been used successfully to derive soil moisture information at global scale with a spatial resolution of 50 km. Concepts of how to integrate macro-scale soil moisture data in hydrologic models are however still vague. In fact, the coarse resolution of the data provided by microwave radiometers and Scatterometers is often considered to impede hydrological applications. Nevertheless, even if most hydrologic models are run at much finer scales, radiometers and scatterometer allow monitoring of atmosphere-induced changes in regional soil moisture patterns. This may prove to be valuable information for modelling hydrological processes in large river basins (0.85) clearly demonstrate that the seasonal change from low runoff during the dry season to high runoff during the wet season is well captured by the ERS scatterometer. Additionally, differences in runoff from year to year could be to some extend, explained by soil moisture anomalies.
David G. Long - One of the best experts on this subject based on the ideXlab platform.
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Ultrahigh Resolution Scatterometer Winds near Hawaii
Remote Sensing, 2020Co-Authors: Nolan Hutchings, Thomas Kilpatrick, David G. LongAbstract:Hawaii regional climate model (HRCM), QuikSCAT, and ASCAT wind estimates are compared in the lee of Hawaii’s Big Island with the goal of understanding ultrahigh resolution (UHR) scatterometer wind retrieval capabilities in this area, which includes a reverse-flow toward the island in the lee of the predominate flow. A comparison of scatterometer measured σ 0 and model predicted σ 0 suggests that Scatterometers can detect the reverse flow in the lee of the island; however, neither QuikSCAT- nor ASCAT-estimated winds consistently report this flow. Furthermore, the scatterometer UHR winds do not resolve the wind direction features predicted by the HRCM. Differences between scatterometer measured σ 0 and HRCM predicted σ 0 indicate possible error in the placement of key reverse flow features predicted by the HRCM. We find that coarse initialization fields and a large size median filter windows used in ambiguity selection can impede the accuracy of the UHR wind direction retrieval in this area, suggesting the need for further development of improved near-coastal ambiguity selection algorithms.
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Architectures for Earth-observing CubeSat Scatterometers
CubeSats and NanoSats for Remote Sensing II, 2018Co-Authors: M. Patrick Walton, David G. LongAbstract:Earth-observing satellite Scatterometers are important instruments capable of measuring a variety of geophysical properties. Historically, the scatterometer design space has revolved around two main architectures: the fan beam and the scanning pencil beam. Since the implementation of these architectures, developments in satellite- relevant technology, spacecraft standards, and engineering practice have expanded the potential design space for Earth-observing scatterometer systems. This expanded design space is investigated and example designs are presented that utilize the expanded design space to improve performance and reduce cost.
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Polar Applications of Spaceborne Scatterometers
IEEE journal of selected topics in applied earth observations and remote sensing, 2016Co-Authors: David G. LongAbstract:Wind Scatterometers were originally developed for observation of near-surface winds over the ocean. They retrieve wind indirectly by measuring the normalized radar cross section ( $\sigma ^o$ ) of the surface, and estimating the wind via a geophysical model function relating $\sigma ^o$ to the vector wind. The $\sigma ^o$ measurements have proven to be remarkably capable in studies of the polar regions where they can map snow cover; detect the freeze/thaw state of forest, tundra, and ice; map and classify sea ice; and track icebergs. Further, a long time series of scatterometer $\sigma ^o$ observations is available to support climate studies. In addition to fundamental scientific research, scatterometer data are operationally used for sea-ice mapping to support navigation. Scatterometers are, thus, invaluable tools for monitoring the polar regions. In this paper, a brief review of some of the polar applications of spaceborne wind scatterometer data is provided. The paper considers both C-band and Ku-band Scatterometers, and the relative merits of fan-beam and pencil-beam Scatterometers in polar remote sensing are discussed.
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Global ice and land climate studies using scatterometer image data
Eos Transactions American Geophysical Union, 2001Co-Authors: David G. Long, Mark R. Drinkwater, Benjamin Holt, Sasan S. Saatchi, Cheryl BertoiaAbstract:Scatterometers have provided continuous synoptic microwave radar coverage of the Earth from space for nearly a decade. NASA launched three Scatterometers: the current SeaWinds scatterometer onboard QuikSCAT (QSCAT, 13.4 GHz) launched in 1999; the NASA scatterometer (NSCAT, 14.0 GHz), which flew on the Japanese Space Agency's ADEOS-1 platform during 1996–1997; and the Seasat-A scatterometer system (SASS, 14.6 GHz), which flew in 1978. The European Space Agency's (ESA) 5.3-GHz scatterometer (ESCAT) has been carried onboard both the ERS-1 and ERS-2 satellites since 1991. properties, including the phase state, of a particular surface type. Varying response from the surface also results from different polarizations, viewing angles and orientations, and radar frequencies. The wide swath of Scatterometers provides near daily global coverage at intrinsic sensor resolutions that are generally between 25–50 km.
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Status of the SeaWinds scatterometer on QuikScat
Earth Observing Systems IV, 1999Co-Authors: David G. LongAbstract:The QuikScat satellite carrying the SeaWinds Scatterometer was developed as a replacement mission for the aborted Japanese Advanced Earth Observation System-I (ADEOS-I) mission carrying the NASA Scatterometer. Like NSCAT, SeaWinds is an active microwave remote sensor designed to measure winds over the ocean from space. SeaWinds can measure vector winds over 95 percent of the Earth's ice-free oceans every day, a significant improvement over previous Scatterometers. Such data is expected to have a significant impact on weather forecasting and will support air-sea interaction studies. SeaWinds will also fly aboard ADEOS-I sensor scheduled for launch in Nov. 2000. QuikScat was successfully launched on June 19, 1999, though as of this writing the instrument has not ben turned on. This paper provides a brief overview of the SeaWinds instrument and discussed new applications of scatterometer data for the study of land and ice.
