Assessment Of SAR Signal Penetration Effect On TanDEM-X Elevations In Antarctica With Laser Altimetry And GNSS Measurements

Synthetic Aperture Radar(SAR)has been widely used in many different fields,such as geoscience,climate monitoring,security-related applications.It is able to provide high-resolution,weather independent,cloud independent and day-and-night images which make it has the advantages of polar region observation.The Digital Elevation Model(DEM)plays an important role in terrain-related applications and there are variety methods for obtaining elevation data used to generate DEMs,such as Real Time Kinematic(RTK)GPS,Lidar and SAR interferometry.However,over natural terrain the radar signal has the ability to penetrate the ground surface which will cause the bias in the elevation measurements.The aim of the proposed investigations is to assess the SAR signal penetration effect on the TanDEM-X absolute elevation over ice and snow covered areas.Using the bistatic SAR satellite data from TanDEM-X,DEMs of two areas of interest located in Antarctica were generated with the Integrated TanDEM-X Processor(ITP).For one of the sites,the Recovery Ice Stream-located in the interior of the ice sheet-a time series of DEMs could be generated.The oldest one(acquired in 2013)was corrected with IceBridge ATM laser altimetry elevations and used as the reference.This was possible because no elevation changes were found from the time series of ATM data in this area without melt and low accumulation.The absolute elevations from TanDEM-X were validated with the laser altimetry over ice free areas.Also the backscattering coefficient of the same areas was analysed to interpret the conditions at the glacier surface.The second site is located in East Antarctica close to the margin(in the vicinity of the Schirmacher Oasis)and covers slow moving glaciers and two ice shelves.Here we compare the surface elevations over blue ice and snow measured by TanDEM-X with elevations obtained from kinematic GPS.From the difference in the elevations the penetration depth of SAR signal can be assessed.The third site is on Brunt Ice Shelf fringing the east coast of Weddell Sea.The elevation difference between the WorldView DEM and TanDEM-X DEM with ice motion correction is available and has been compared with the backscattering coefficient to assess the X-band SAR signal penetration effect.For all areas,the elevation difference between TanDEM-X and the other sources and the SAR backscattering coefficients of the active TanDEM-X channel were analysed along the paths covered by ATM and the kinematic GPS,respectively.The aim was to find relationships between the SAR backscattering and the elevation differences associated with the SAR signal penetration depth in these ice-covered areas.