Experimental Validation and Calibration of GNSS-Based Phase Synchronization for Bistatic and Multistatic SAR Missions

This article addresses the critical issue of phase synchronization in multistatic synthetic aperture radar (SAR). We present the experimental validation of a global navigation satellite system (GNSS)-based synchronization technique planned for use in ESA’s upcoming Earth Explorer mission, Harmony. In this technique, the radar payload and GNSS receiver utilize the same main oscillator, and radar synchronization is achieved through the postprocessing of carrier phase data from the GNSS receiver and precise baseline determination (PBD) outputs. This article presents an experimental procedure that serves as a general proof of concept of the technique, a method for assessing the achievable synchronization accuracy for a given GNSS receiver, and a method to estimate the covariance matrix to optimize the weighting between the various carrier phase observables. We present point-to-point estimation and smoothing approaches. The technique achieved in a laboratory environment relative synchronization errors below 515 fs ( $1\sigma $ ), or 1° for a 5.4-GHz radar system, in a zero-baseline scenario, and below 1.5° at 5.4 GHz in a short-baseline scenario, in which the systems are physically separated.