On the performance of CryoSat-2 SAR and LR mode over inland water bodies

Shirzad Roohi (Universität Stuttgart, Geodätisches Institut, Germany)


Nico Sneeuw ( Universität Stuttgart, Geodätisches Institut , Germany )

Event: 2014 Ocean Surface Topography Science Team Meeting

Session: Instrument Processing: Measurement and retracking (SAR and LRM)

Presentation type: Type Poster

The CryoSat-2 satellite altimetry mission was originally designed to study the fluctuations in Earth's land and marine ice fields due to climate change. The radar instrument of this mission, SIRAL, operates in low resolution mode (LRM) over the open ocean, land and flat ice sheets. It uses synthetic aperture radar mode (SAR) over sea-ice and coastal zones, and SAR interferometry mode (SIN) over mountain glaciers. In LRM, CryoSat-2 acts like a pulse-limited altimeter but because of the SAR and SIN this mission is able to outperform pulse-limited altimeters. A special radar configuration system due to SAR technology provides independent multi-looked observations and smaller footprint size that leads to better resolution. Due to these characteristics CryoSat-2 can be used for hydrological purposes. Generally the LRM covers many inland water bodies. Real data of SAR mode shows very good SAR coverage over the coastal zones and a number of land areas.
Even though the footprint of SIRAL is small, particularly for SAR mode, returned waveforms from the area inside the footprint can be corrupted and can deviate from the Brown model waveform due to environmental effects. If these contaminated waveforms are used in range measurements to determine water level changes, we will not get realistic result. Retracking of the corrupted waveform is necessary to improve the accuracy of the range measurements and to obtain robust water level determination.
In this study we use LRM and SAR data for the time period of October 2010 - 2014 and perform waveform retracking. We analyze the performance of CryoSat-2 in the monitoring of water level variations over three test areas. The largest salt lake in the Middle East, Urmia, and the largest freshwater lake in China, Qinghai, have been selected for LRM mode. Lough Neagh in Northern Ireland is the area of studying SAR data analysis. We apply full and sub-waveform analysis using different retracking algorithms to retrack water level variations. The retracked water level variations will be validated against in-situ gauge and other satellite altimetry data to find the optimize retracker algorithm and to assess the accuracy of CryoSat-2 measurements for monitoring inland water bodies.
Shirzad Roohi
Universität Stuttgart, Geodätisches Institut