Sentinel-1 TOPS co-registration over low-coherence areas and its application to velocity estimation using the all pairs shortest path algorithm

Abstract

The C-band Sentinel-1 A/B satellites in TOPS mode provide unprecedented opportunities for continuous radar mapping of the earth with enhanced revisit frequency. The reliability for routine operational services relies on a very stringent azimuth co-registration accuracy. However, while the enhanced spectral diversity (ESD) technique achieves a co-registration accuracy of better than 0.001 pixels, the accuracy might still be degraded over low-coherence areas due to fast decorrelation. When TOPS time series data are available, the abrupt loss of coherence further affects the estimation accuracy of the network ESD. I integrate a double sample over the burst overlap region with an ESD estimator to reduce the ESD phase error and simultaneously mitigate the abrupt loss of coherence in the time series using the all pairs shortest path algorithm. I further use this algorithm to create a spatio-temporal network of co-registered Sentinel-1 SAR stacks for line-of-sight (LOS) velocity estimation over low-coherence areas. I perform InSAR time series analysis and evaluate the effectiveness of the proposed method using data acquired from descending tracks over representative low-coherence regions in south-western China. For those images suffering from significant low coherence, this method can achieve a better co-registration accuracy than those obtained from the previous network ESD method. By cross-validating descending COSMO-SkyMed data, a 39% uncertainty reduction in the estimated LOS velocity can be achieved when applying a co-registered Sentinel-1 stack with high accuracy and spatio-temporal network evolution.