Study Of Geosynchronous Synthetic Aperture Radar Imaging Algorithm

Since geosynchronous synthetic aperture radar(GEO SAR) runs on an orbit height of 36000 km, it is provided with the capacity of high revisiting and large scene observation. However, this orbit mode is equipped with low bandwidth product and high squint imaging problems. Aiming at these problems, this paper provided a deep research on the nonlinear time frequency relationship caused by low bandwidth product and two dimensional space variant caused by high squint in the GEO SAR.Firstly, since the traditional slant range model is not suitable for the slant range history under the condition of long synthetic aperture time and curve trajectory in GEO SAR, a high order polynomial slant range model by Taylor expansion is proposed to describe this. What’s more, a two dimensional frequency domain expression is solved by the series reversion based on the polynomial slant range model. Simulation results are performed to verify the correctness of this slant range model and corresponding two dimensional frequency domain expressions.Secondly, since the Doppler time frequency relationship is nonlinear and RCM doesn’t match with Doppler frequency on the low bandwidth product orbit position in GEO SAR., an optimal quadratic factor compensation algorithm is proposed to transform the nonlinear Doppler time frequency relationship into linear and to reduce the azimuth variety. Then, a two dimensional nonlinear chirps scaling manipulation is performed to do the imaging process. A large scene size simulation result is performed to verify the validity of the proposed algorithm.Lastly, the Doppler time frequency relationship and the two dimensional variety of the focus parameters under the high squint model in GEO SAR are analyzed. This paper also proposed an optimal time compensation method to realize the range walk correction and reduce the azimuth variety, which could also reduce the nonlinear part of the original Doppler time frequency to better complete the frequency domain imaging process. A large scene size computer simulation under high ground squint angle is provided in order to verify the validity of the proposed algorithm.