Exploring the performances of SAR altimetry and improvements offered by fully focused SAR

Abstract

With the development of the altimetry techniques, the measurement principle has been changed from the conventional pulse-limited principle to the delay-Doppler principle since CryoSat-2. The delay-Doppler altimetry presents scientists with the chance to develop new processing schemes and improve products that maximize the benefits of the measurements. Nevertheless, one of the challenges for delay-Doppler Altimetry lies in the complexity of the post-processing, especially the Delay-Doppler processing. The focus of this thesis is to better understand delay-Doppler and fully focused SAR altimetry. This thesis compares the retrieved waveforms and resultant water level time series with different altimetry principles, processing options and retracking methods. By using platform SARvatore for delay-Doppler altimetry and SMAP for fully focused SAR altimetry, different processing options (data posting rate, Hamming window and zero padding) and different retrackers (SAMOSA family for SARvatore, PTR for SMAP) can be applied and compared. Our results reveal that the waveforms generated by different configurations have different peaks for SARvatore. For SMAP, with or without zero padding or Hamming window had very little impact, with more differences mainly coming from the different retracking methods. Our results also show that fully focused SAR does not bring a significant improvement when applied to Sentinel-3 data. In summary, different configurations and retracking methods can significantly affect the shape of waveforms and their derived ranges. According to this thesis's experiments, the configuration with 80 Hz data posting rate, Hamming window, zero padding, extended receiving window and retracker SAMOSA++ offers the best performance.