Estimating the Hotspot Area Observed by Earth Imaging Satellite via ISAR Image Sequence

Compared with directly estimating the stable attitude of space targets, estimating the hotspot area observed by an Earth imaging satellite using inverse synthetic aperture radar (ISAR) imaging is a more practical and challenging task. In this article, by parameterizing the time-varying attitude of an Earth imaging satellite in spotlight mode into a fixed hotspot area location in the geodetic coordinates, a novel method is proposed. First, the migrations of the scatterers on the rotating component with respect to reference scatterers on the satellite body in the range and Doppler dimensions (MRCRSRDs) are analyzed, which are used for recognizing the scatterers on the rotating component. Next, it is proven that for the same scatterer on the rotating component, the vector difference sequences of the projection vectors normalized using the range and Doppler coordinates are orthogonal to the position vector of the scatterer. Based on this characteristic, an objective function for estimating the hotspot area is constructed. Then, based on the error principle, expressions of the estimated hotspot area longitude and latitude are derived, along with expressions of the estimation accuracy. Finally, the effects of different factors on the MRCRSRD are analyzed by traversal, under the assumption that the scatterer coordinates obtained by radar are error-free, the feasibility of the proposed method is validated and the estimation error caused by the grid quantization is evaluated, and then the robustness of the proposed method is validated by comparative experiments using parameter search method (PSM) and indirect adjustment method (IAM) under different Gaussian noise conditions.