四阶模型方位NCS高分辨SAR成像

针对长积累时间SAR回波耦合性强,聚焦困难的问题,从提高成像模型近似精度和距离徙动校正精度两方面开展了SAR成像研究,推导了一种考虑方位非线性调频变标(NCS)的四阶近似成像模型。首先,为了提高模型近似度,将斜距展开到四次项;然后,为了将距离向和方位向进行初步解耦,在时域进行走动补偿,但是带来了聚焦深度问题,高分辨成像时,这种现象更明显;为此,二维频域解耦后又在方位向采用二阶非线性变标方法解决这一问题。仿真结果表明,从主观分析和量化指标两方面来讲,该算法优于传统的高分辨斜视SAR成像算法。

An Algorithm of Azimuth NCS Based on Fourth-Model for High Resolution SAR Imaging

To eliminate the serious coupling between azimuth and range for high resolution SAR in large squint mode, a new forth model imaging algorithm based on 2-order azimuth nonlinear chirp scaling（NCS） is proposed, which can improve the precision of SAR imaging model and RCMC. First, the range expression is expanded to its Taylor series and approximate to 4-order. Secondly, considering the instability, large range walk is corrected, which will produced a problem of the limit of focus depth. Then, based on series rever- sion, small range curvature is compensated in 2-D frequency. At last, 2-order azimuth nonlinear chirp scaling operation was adopted to compensate the azimuth-dependent chirp rate. Meanwhile the improved algorithm was simulated. Simulation results illustrate that during 4-order imaging model the phase error can be neglect, and 2-order azimuth NCS efficiently compensates the azimuth-dependent chirp rate, also the method posses- ses high precision and satisfies the imaging quality of SAR in high resolution mode.