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Sergey Y. Matrosov - One of the best experts on this subject based on the ideXlab platform.
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observations of wintertime u s west coast precipitating systems with w band Satellite radar and other spaceborne instruments
Journal of Hydrometeorology, 2012Co-Authors: Sergey Y. MatrosovAbstract:The potentialofCloudSatW-bandradarfor observingwintertime storms affecting the West Coast ofNorth 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 overocean andland.These retrievalspresentquasi-instantaneousverticalcross sectionsofprecipitating 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 rainwereobservedwithabout26%,24%,and50%frequency.Stratiformregionsgenerallyhadhigherrainrates. Significant correlation (;0.72) between mean values of IWP and rain rate was observed for stratiform rainfall.
Sarah T. Gille - One of the best experts on this subject based on the ideXlab platform.
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Mean sea surface height of the Antarctic circumpolar current from Geosat data : method and application
Journal of Geophysical Research, 1994Co-Authors: Sarah T. GilleAbstract:The mean sea surface height across the Antarctic Circumpolar Current has been reconstructed from height variability measured by the Geosat altimeter without assuming prior knowledge of the geoid. For this study, an automated technique has been developed to estimate mean sea surface height for each Satellite Ground Track using a meandering Gaussian jet model, and errors have been estimated using Monte Carlo simulation. The results are objectively mapped to produce a picture of the mean Subantarctic and Polar Fronts, which together comprise the major components of the Antarctic Circumpolar Current. The meandering jet model explains between 40% and 70% of the height variance along the jet axes. The results show that the fronts are substantially steered by topography and that the jets have an average Gaussian width of about 44 km in the meridional direction and meander about 75 km to either side of their mean locations. The average height difference across the Subantarctic Front (SAF) is 0.7 m and across the Polar Front (PF) 0.6 m. The mean widths of the fronts are correlated with the size of the baroclinic Rossby radius.
Noel Gourmelen - One of the best experts on this subject based on the ideXlab platform.
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cryosat 2 swath interferometric altimetry for mapping ice elevation and elevation change
Advances in Space Research, 2017Co-Authors: Noel Gourmelen, Mariajose Escorihuela, Andrew Shepherd, Luca Foresta, Alan Muir, Albert Garciamondejar, Monica Roca, Steven Baker, M R DrinkwaterAbstract:Abstract For more than 25 years, Satellite radar altimetry has provided continuous information on the state of the cryosphere and on its contribution to global sea-level rise. The technique typically delivers maps of ice-sheet elevation and elevation change with 3–10 km spatial resolution and seasonal to monthly temporal resolution. Here we show how the interferometric mode of CryoSat-2 can be used to map broad (5 km-wide) swaths of surface elevation with fine (500 m) spatial resolution from each Satellite pass, providing a step-change in the capability of Satellite altimetry for glaciology. These swaths of elevation data contain up to two orders of magnitude more surface elevation measurements than standard altimeter products, which provide single elevation measurements based on the range to the Point-Of-Closest-Approach (POCA) in the vicinity of the sub-Satellite Ground Track. The swath elevations allow a more dense, statistically robust time series of elevation change to be formed with temporal resolution of a factor 5 higher than for POCA. The mean differences between airborne altimeter and CryoSat-2 derived ice sheet elevations and elevation rates range from −0.93 ± 1.17 m and 0.29 ± 1.25 m a−1, respectively, at the POCA, to −1.50 ± 1.73 m and 0.04 ± 1.04 m a−1, respectively, across the entire swath. We demonstrate the potential of these data by creating and evaluating elevation models of: (i) the Austfonna Ice Cap (Svalbard), (ii) western Greenland, and (iii) Law Dome (East Antarctica); and maps of ice elevation change of: (iv) the Amundsen Sea sector (West Antarctica), (v) Icelandic ice caps, and (vi) above an active subglacial lake system at Thwaites Glacier (Antarctica), each at 500 m spatial posting – around 10 times finer than possible using traditional approaches based on standard altimetry products.
Peter Bauergottwein - One of the best experts on this subject based on the ideXlab platform.
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operational reservoir inflow forecasting with radar altimetry the zambezi case study
Hydrology and Earth System Sciences, 2014Co-Authors: Claire Irene B Michailovsky, Peter BauergottweinAbstract:Abstract. River basin management can greatly benefit from short-term river discharge predictions. In order to improve model produced discharge forecasts, data assimilation allows for the integration of current observations of the hydrological system to produce improved forecasts and reduce prediction uncertainty. Data assimilation is widely used in operational applications to update hydrological models with in situ discharge or level measurements. In areas where timely access to in situ data is not possible, remote sensing data products can be used in assimilation schemes. While river discharge itself cannot be measured from space, radar altimetry can Track surface water level variations at crossing locations between the Satellite Ground Track and the river system called virtual stations (VS). Use of radar altimetry versus traditional monitoring in operational settings is complicated by the low temporal resolution of the data (between 10 and 35 days revisit time at a VS depending on the Satellite) as well as the fact that the location of the measurements is not necessarily at the point of interest. However, combining radar altimetry from multiple VS with hydrological models can help overcome these limitations. In this study, a rainfall runoff model of the Zambezi River basin is built using remote sensing data sets and used to drive a routing scheme coupled to a simple floodplain model. The extended Kalman filter is used to update the states in the routing model with data from 9 Envisat VS. Model fit was improved through assimilation with the Nash–Sutcliffe model efficiencies increasing from 0.19 to 0.62 and from 0.82 to 0.88 at the outlets of two distinct watersheds, the initial NSE (Nash–Sutcliffe efficiency) being low at one outlet due to large errors in the precipitation data set. However, model reliability was poor in one watershed with only 58 and 44% of observations falling in the 90% confidence bounds, for the open loop and assimilation runs respectively, pointing to problems with the simple approach used to represent model error.
M R Drinkwater - One of the best experts on this subject based on the ideXlab platform.
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cryosat 2 swath interferometric altimetry for mapping ice elevation and elevation change
Advances in Space Research, 2017Co-Authors: Noel Gourmelen, Mariajose Escorihuela, Andrew Shepherd, Luca Foresta, Alan Muir, Albert Garciamondejar, Monica Roca, Steven Baker, M R DrinkwaterAbstract:Abstract For more than 25 years, Satellite radar altimetry has provided continuous information on the state of the cryosphere and on its contribution to global sea-level rise. The technique typically delivers maps of ice-sheet elevation and elevation change with 3–10 km spatial resolution and seasonal to monthly temporal resolution. Here we show how the interferometric mode of CryoSat-2 can be used to map broad (5 km-wide) swaths of surface elevation with fine (500 m) spatial resolution from each Satellite pass, providing a step-change in the capability of Satellite altimetry for glaciology. These swaths of elevation data contain up to two orders of magnitude more surface elevation measurements than standard altimeter products, which provide single elevation measurements based on the range to the Point-Of-Closest-Approach (POCA) in the vicinity of the sub-Satellite Ground Track. The swath elevations allow a more dense, statistically robust time series of elevation change to be formed with temporal resolution of a factor 5 higher than for POCA. The mean differences between airborne altimeter and CryoSat-2 derived ice sheet elevations and elevation rates range from −0.93 ± 1.17 m and 0.29 ± 1.25 m a−1, respectively, at the POCA, to −1.50 ± 1.73 m and 0.04 ± 1.04 m a−1, respectively, across the entire swath. We demonstrate the potential of these data by creating and evaluating elevation models of: (i) the Austfonna Ice Cap (Svalbard), (ii) western Greenland, and (iii) Law Dome (East Antarctica); and maps of ice elevation change of: (iv) the Amundsen Sea sector (West Antarctica), (v) Icelandic ice caps, and (vi) above an active subglacial lake system at Thwaites Glacier (Antarctica), each at 500 m spatial posting – around 10 times finer than possible using traditional approaches based on standard altimetry products.