Correction of the Phase Bias in the Sentinel-1 Generated Interferograms

With the advent of the European Commission’s Copernicus two-satellite Sentinel-1 constellation, operated by ESA, space-borne Synthetic Aperture Radar (SAR) Interferometry (InSAR) has become a key geophysical tool for surface deformation studies. Since the completion of the constellation in 2016, data are acquired globally with a typical revisit period of 12 days, and every 6 days in Europe. The relatively short revisit time (compared to 35-days of previous ESA SAR satellites) is a significant advance because interferograms spanning a short interval maintain better coherence and allow a more accurate estimate of rapid deformation. The short revisit time also leads to a greater number of acquisitions, which is useful for statistical reduction of the noise contribution (e.g., due to atmospheric phase delay) in InSAR time series analyses.
Despite the clear benefits, it has recently been shown that using the shorter-interval, multilooked interferograms can introduce a bias in the interferometric phase, which, in turn, biases the estimated velocities. This poses a dilemma – we would like to include all short-interval interferograms and to carry out multilooking because this improves coherence and hugely improves coverage, but the velocities obtained from using these interferograms alone are not reliable.  
The purpose of this proposal is twofold. Firstly, we aim at exploring the characteristics of the phase bias by investigating its temporal and spatial behaviour. This will help better understand how the bias varies throughout the year in different land cover classes. Secondly, we propose implementation and generalization of an empirical mitigation strategy we have recently developed, which can correct short-term interferograms for any bias. 
We aim to develop a set of codes that can be plugged into any processing chain and to correct short-term interferograms for the phase bias. We will use the COMET-LiCSAR system as a demonstrator.

Impact

Correction of the short-term interferograms for the phase bias is of great importance, particularly for InSAR processing systems aimed at studying geohazards over vast areas, including the COMET LiCSAR system, ESA’s Geohazard Exploitation Platform (GEP), NASA’s Advanced Rapid Imaging and Analysis (ARIA) system  or Alaska Satellite Facility (ASF), which automatically (or on-demand) produce a subset of short-term interferograms and carry out the time-series analysis using small baseline algorithms. Our proposed strategy can operationally be a part of any time-series analysis package. 

Publications and outputs

Maghsoudi, A. J. Hooper and T. J. Wright, M. Lazecky and H. Ansari, Characterizing and correcting phase biases in short-term, multilooked interferograms, Remote Sensing of Environment, Volume 275, 2022, 113022, ISSN 0034-4257