Abstract
This article presents a modified Omega-K algorithm for circular trajectory scanning synthetic aperture radar (CTSSAR) imaging. Due to the curvature of circular trajectory, it is difficult to have access to the two-dimensional frequency spectrum for CTSSAR via the principle of stationary phase (POSP), as conventional SAR imaging methods RD and CS. Herein, the analytic point target spectrum is first derived by series reversion and the POSP, based on which a modified Omega-K algorithm is developed to focus data accurately. The accuracy can be controlled by keeping enough terms in the two series expansions so that a well-focused image can be achieved with a proper range approximation. After detailed analyses and experiments, the fourth-order approximation is proved to be the best choice. Furthermore, the computational efficiency is evaluated by comparing the given method with the back projection algorithm and other methods with different approximated orders. The proposed algorithm is verified to be the best one in terms of computational burden. A well-focused image is obtained by simulations, validating the feasibility of the proposed algorithm.
Highlights
Due to its capability of working day/night and all weather conditions, synthetic aperture radar (SAR) has widely been applied to the military and civilian practical uses
An imaging mode called circular SAR (CSAR), whose radar system moves along a circular trajectory, gradually became one of the hotspots in the field of radar signal processing [5]
We can get a conclusion that the back projection (BP) algorithm is too slow for imaging, the quadratic method cannot reach our imaging standard, and the higher-order method needs a little more time compared with the proposed method without any improvement for the imaging
Summary
Due to its capability of working day/night and all weather conditions, synthetic aperture radar (SAR) has widely been applied to the military and civilian practical uses. From (9), it can be noticed that there are trigonometric functions in both numerator and denominator of the azimuth Doppler frequency, which will make the deduction of η by (9) very hard to carry out and further put a huge obstacle in the way of deriving the accurate 2D spectrum This problem is caused by the curvature of the circular trajectory in CTSSAR. Sun et al [16] proposed a quadratic approximation method to make the spectrum expression similar to that of the traditional straight line stripmap mode This approach ignores the curvature of the circular trajectory and the parabolic approximation is introduced, making the spectrum derivation relatively easy to implement. The imaging algorithm for CTSSAR will be given based on the 2D spectrum derived by the above analysis
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