An analytic method for precisely determining the revisit time of SAR satellites and optimizing RGT orbit design

Abstract

This paper addresses a particular analytic method for calculating the revisit time (RT) of Synthetic Aperture Radar (SAR) satellites in the circular repeating ground track orbit (RGTO) and its application to optimizing the orbital elements according to the payload characteristics. The most critical aspect of SAR payloads is sun-independent, allowing photos to be collected from ascending and descending phases (both-phase). Different from the traditional methods only considering single-phase, the proposed method is mapping every pass into its ascending and descending points on the Equator. A new concept of half-subcycle is presented in this paper to determine the distribution of the ascending and descending points. Through the combination of subcycle and half-subcycle, the both-phase ground track sequences can be fully obtained without resorting to complex computer programs. The minimum, maximum, and average RT, considered at the Equator, can be computed fast by establishing and analyzing the revisiting tracks in the both-side non-nadir instantaneous access area of the SAR payload. The step value of the RT can be a half-day instead of a full day as in previous researches. By studying both-phase acquisition and both-side non-nadir looking, the obtained results reflect better the actual characteristics of SAR payloads, comparing to traditional approaches. The method is also applied in studying SAR satellite’s orbital design process. With mission requirements and payload characteristics provided as inputs, the optimal orbit is rapidly determined.