Calibration of the shuttle radar topography mission X-SAR instrument using a synthetic altimetry data model

Satellite radar altimetry (RA) can provide highly accurate measurements of the sea surface height (SSH). The SSH is used for the calibration and as a ground truth for the shuttle radar topography mission (SRTM) X-band synthetic aperture radar (X-SAR) instrument. Since altimeter missions and the SRTM fly with different ground patterns, a composite "synthetic" altimetry data (SAD) model is developed to provide the instantaneous SSH at the time and position of the SRTM X-SAR data takes. The SAD model is composed of a static and a time-variable part of the SSH. The static part consists of a mean SSH model, which is calculated from the RA data. The time-variable part is reconstructed from models. Since the accuracy of the SAD model is strongly dependent on the location, a static mean error model is estimated which is based on the comparison of independent RA along-track measurements and the SAD model. The error model confirms the accuracy of the SAD model at most locations and helps to identify the areas where the stipulated X-SAR calibration requirement of 1 m cannot be fulfilled.