Data-Driven Phase Synchronization of Harmony’s Ocean Surface Topography Product

The Harmony mission features two bistatic synthetic-aperture radar (SAR) companions of Sentinel-1. As with any multistatic system, frequency deviations among the oscillators of the receivers cause a phase error in the phase of the demodulated SAR signal. Given that interferometry will be used to retrieve geophysical parameters from Harmony’s radar instruments, an erroneous phase difference between the SAR signals of the two companions will bias the retrieval. The companions will use a global-navigation system (GNSS)-based method to synchronize the phase of the signals. The residual phase that remains after the synchronization is significant enough to make the retrieval of relative sea-surface height (RSSH) impossible. In this paper, we present Multisquint with Overlaps (MuSO), a data-driven algorithm to remove the synchronization residual. The algorithm uses the multisquint processing approach, together with the overlap regions of the TOPSAR acquisition mode, to estimate the derivative of the residual. After running the algorithm, simulations suggest that the error signal reduces from a standard deviation of 4° to 0.01°, allowing the retrieval of RSSH from Harmony data.