Formation Design for Single-Pass GEO InSAR Considering Earth Rotation Based on Coordinate Rotational Transformation

Abstract

The single-pass geosynchronous synthetic aperture radar interferometry (GEO InSAR) adopts the formation of a slave satellite accompanying the master satellite, which can reduce the temporal decorrelation caused by atmospheric disturbance and observation time gap between repeated tracks. Current formation design methods for spaceborne SAR are based on the Relative Motion Equation (RME) in the Earth-Centered-Inertial (ECI) coordinate system (referred to as ECI-RME). Since the Earth rotation is not taken into account, the methods will lead to a significant error for the baseline calculation while applied to formation design for GEO InSAR. In this paper, a formation design method for single-pass GEO InSAR based on Coordinate Rotational Transformation (CRT) is proposed. Through CRT, the RME in Earth-Centered-Earth-Fixed (ECEF) coordinate system (referred to as ECEF-RME) is derived. The ECEF-RME can be used to describe the accurate baseline of close-flying satellites for different orbital altitudes, but not limited to geosynchronous orbit. Aiming at the problem that ECEF-RME does not have a regular geometry as ECI-RME does, a numerical formation design method based on the minimum baseline error criterion is proposed. Then, an analytical formation design method is proposed for GEO InSAR, based on the Minimum Along-track Baseline Criterion (MABC) subject to a fixed root mean square of the perpendicular baseline. Simulation results verify the validity of the ECEF-RME and the analytical formation design method. The simulation results also show that the proposed method can help alleviate the atmospheric phase impacts and improve the retrieval accuracy of the digital elevation model (DEM) compared with the ECI-RME-based approach.The performance of InSAR and TomoSAR based on monostatic GEO SAR significantly degrades due to temporal decorrelation (caused by the scene scattering fluctuation during the observation time gap between repeated tracks) and atmospheric disturbance. Similar to LEO SAR [8], we can use the formation GEO SAR to form a real-time baseline to improve interferometry performance [9,10], realizing single-pass GEO InSAR. Additionally, multiple phase centers can be generated in GEO SAR formation, and a flexible baseline configuration can enrich the functions.The primary task of SAR formation is to design the satellite orbital elements to obtain a reasonable formation configuration and then meet the application performance requirements. The formation design of LEO SAR has been adequately studied, and a very mature solution has been found. A very typical method is to describe the geometry of the formation using the Relative Motion Equation (RME) based on the difference between the master satellite's and slave satellite's orbital elements, and combining the mission requirements to design the satellite's orbital elements [11].The theoretical study of the Relative Motion Equation has gone through three stages. The earliest form of RME, which was used to complete spacecraft rendezvous and docking tasks [12], was obtain...

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