Calibration of SIMO Formations with Azimuth Ambiguities

Formations of small satellites are gaining momentum as an alternative to single synthetic aperture radar (SAR) systems, allowing them to improve performance and reduce costs. Each sensor operates with a low pulse repetition frequency (PRF), so swath size can be kept large, and the strong azimuth ambiguities are later resolved by combining acquisitions from multiple satellites. For proper imaging to be successful, careful calibration of the system and geometric parameters is performed based on the single-channel images. However, ambiguities jeopardize the retrieval of parameters from data; therefore, it is crucial to identify those areas that are inherently ambiguity-free. This article handles acquisitions that are highly affected by azimuth ambiguities, as in the case of the formation. First, we model the replica's structure in the focused image and then propose an effective yet simple method to detect such disturbances. Finally, we demonstrate an improved approach for estimating the along-track baseline by incorporating the aforementioned ambiguity detection scheme. The proposed analysis is validated with simulated data, considering a realistic reflectivity map derived from a COSMO-SkyMed stack.