A Two-dimensional Attitude Steering Method to Compensate for the Doppler Centroid in Moon-based SAR

Abstract

The rising attention to Moon-based Earth observation provides a new way to monitor Earth. Among Moon-based detectors, the SAR method has the advantage of long-term, stable, unique observations compared to space-borne SAR. Unlike space-borne SAR, however, the complicated relative motion of a Moon-based sensor makes its Doppler centroid estimation more difficult. This paper proposes a method for two-dimensional attitude steering to compensate for the Doppler centroid of Moon-based SAR. In the periodic movement between Earth and the Moon, the track speed of sites distributed around the near side of the Moon are almost perpendicular to vectors from the sites to the Earth centroid. This situation indicates the feasibility of attitude steering to guide antennas into a zero Doppler plane intersecting Earth’s surface. Therefore, this paper proposes a method for two-dimensional attitude steering to compensate the Doppler centroid to zero. In this method, the Moon is no longer deemed as a point but a natural celestial body with an average radius. Sites distributed around the hemisphere of the near side are also considered separately because of differences in spatial position and speed. Through the proposed method, the pointing of SAR antennas will be steered to a place on Earth where the Doppler centroid is compensated to zero. The JPL DE430 and EOP data are closer to reality and are used for accurate simulation. In this paper, the twodimensional attitude steering method is compared with no attitude steering and a onedimensional attitude steering method, and the results show its effectiveness.