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

This paper addresses the critical issue of phase synchronization in multistatic SAR. We present the experimental validation of a 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 master oscillator, and radar synchronization is achieved through post-processing of carrier phase data from the GNSS receiver and precise baseline determination outputs. The paper 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 lab environment relative synchronization errors below 515 fs (1 σ), or 1 degree for a 5.4 GHz radar system, in a zero-baseline scenario, and below 1.5 degrees at 5.4 GHz in a short baseline scenario, in which the systems are physically separated.