A Novel High-Order Range Model and Imaging Approach for High-Resolution LEO SAR

High-resolution spaceborne synthetic aperture radar (SAR) mainly poses two challenges to signal processing. The first challenge involves the signal model, where a precise range equation of spaceborne SAR should be considered as the conventional hyperbolic range equation fails to precisely describe the range history in the high-resolution case. The second challenge is an efficient focusing algorithm since the existing SAR processors are inaccurate or inefficient for high-resolution spaceborne SAR. Therefore, in this paper, a novel fourth-order polynomial range equation based on Doppler parameters is proposed, and the method for parameter determination is also addressed. Compared with conventional range equations, the presented one is more accurate and concise for low-earth-orbit SAR so that a higher azimuth resolution can be achieved. Based on the range model, a 2-D spectrum is derived, and an extended range Doppler domain algorithm for SAR image formation in the sliding spotlight mode is also developed. Additionally, we carried out several simulations to validate the presented approach. Results demonstrate high performances of the focusing algorithm as well as the range equation.