Abstract
Due to the larger orbital arc and longer synthetic aperture time in medium Earth orbit (MEO) synthetic aperture radar (SAR), it is difficult for conventional SAR imaging algorithms to achieve a good imaging result. An improved higher order nonlinear chirp scaling (NLCS) algorithm is presented for MEO SAR imaging. First, the point target spectrum of the modified equivalent squint range model-based signal is derived, where a concise expression is obtained by the method of series reversion. Second, the well-known NLCS algorithm is modified according to the new spectrum and an improved algorithm is developed. The range dependence of the two-dimensional point target reference spectrum is removed by improved CS processing, and accurate focusing is realized through range-matched filter and range-dependent azimuth-matched filter. Simulations are performed to validate the presented algorithm.
Highlights
Synthetic aperture radar (SAR) is a well-established remote sensing technique, capable of acquiring images of Earth’s surface independent of weather conditions and sunlight illumination.[1]
Extensive simulations are performed to show the significantly improved imaging result
The spaceborne synthetic aperture radar (SAR) geometry in Earth-centered rotating coordinates is illustrated in Fig. 1, where the actual path is represented by the black solid line, and the paths based on hyperbolic range equation model (HREM) and modified equivalent squint range model (MESRM) are denoted by the blue dotted line and red dashed lines, respectively
Summary
Synthetic aperture radar (SAR) is a well-established remote sensing technique, capable of acquiring images of Earth’s surface independent of weather conditions and sunlight illumination.[1]. The chirp scaling (CS) algorithm is a common approach adopted for the processing of spaceborne SAR data due to its good phase preservation and high efficiency properties.[13] the traditional CS algorithm was derived based on HREM and cannot be directly applied to our MESRM. We derive the point target spectrum (PTS) of the MESRM-based signal, and develop an improved higher order nonlinear chirp scaling (NLCS) algorithm for MEO SAR imaging where the improved CS processing is applied to remove the range dependence of a twodimensional (2-D) point target reference spectrum (PTRS), and the higher order phase compensation, range-matched filter, and range-dependent azimuth filter are used to realize accurate focusing.
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