Abstract
Geosynchronous Orbit Synthetic Aperture Radar (GEO SAR) has recently received increasing attention due to its ability of performing staring observations of ground targets. However, GEO SAR staring observation has an ultra-long integration time that conventional frequency domain algorithms cannot handle because of the inaccurately assumed slant range model and existing azimuth aliasing. To overcome this problem, this paper proposes an improved chirp-scaling algorithm that uses a fifth-order slant range model where considering the impact of the “stop and go” assumption to overcome the inaccuracy of the conventional slant model and a two-step processing method to remove azimuth aliasing. Furthermore, the expression of two-dimensional spectrum is deduced based on a series of reversion methods, leading to an improved chirp-scaling algorithm including a high-order-phase coupling function compensation, range and azimuth compression. The important innovations of this algorithm are implementation of a fifth-order order slant range model and removal of azimuth aliasing for GEO SAR staring observations. A simulation of an L-band GEO SAR with 1800 s integration time is used to demonstrate the validity and accuracy of this algorithm.
Highlights
Owing to its ability of all-weather and all-day Earth observation, synthetic aperture radar (SAR)has been widely applied in a variety of microwave remote sensing fields, such as disaster monitoring [1], topographic mapping [2], soil moisture estimation [3], oil spill observation [4], crop growth monitoring [5], forest cover measurement [6], wetland mapping [7], maritime surveillance [8,9,10], and so on
It can be clearly seen that all clearly seen that all the point targets are severely defocused in the scene
The improved scaling imaging algorithm based on the slantslant model is used for imaging imaging algorithm based on fifth-order the fifth-order model is used for imaging processing
Summary
Owing to its ability of all-weather and all-day Earth observation, synthetic aperture radar (SAR)has been widely applied in a variety of microwave remote sensing fields, such as disaster monitoring [1], topographic mapping [2], soil moisture estimation [3], oil spill observation [4], crop growth monitoring [5], forest cover measurement [6], wetland mapping [7], maritime surveillance [8,9,10], and so on. With increasing demands of wider imaging swath and shorter revisit period, it is difficult for low Earth orbit (LEO) SAR to satisfy the application requirements. To solve this problem, the Geosynchronous Orbit SAR (GEO SAR) concept has been put forward. Compared with LEO SAR, GEO SAR has more advantages, such as wider swath, and shorter revisiting period [11,12,13,14,15,16], but it can realize long time observation of ground targets even with staring, which will be beneficial to its applications in microwave remote sensing fields. GEO SAR’s staring observation can be obtained using a certain beam forming strategy that could be implemented by adjusting the antenna beam direction, or through satellite attitude steering [18]
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