非匀速弹道SAR成像方法研究

The SAR Imaging Method of the Non-Uniform Straight Line Trajectory

非匀速直线弹道成像是弹载SAR领域的核心问题之一。首先构建三维空间中的非匀直弹道模型,通过泰勒近似公式分析运动偏差的来源,并将运动偏差分解成方位偏移、地距偏移和俯仰偏移等三个部分。推导了横向运动和俯冲运动分别引起的地距偏移和俯仰偏移函数,从而得到了对应的运动补偿函数。方位偏移表现为SAR平台在方位向作变速直线运动,回波的数据格式可看成空间非均匀采样的结果。为此,提出了一种利用空间非均匀采样模型替代时域变多普勒模型的成像方法。该算法将变速运动等间隔时间采样的回波数据等效为匀速运动中非等间隔时间采样数据,然后通过方位向非均匀离散傅立叶变换将数据变换到均匀频率域,再完成其它后续的成像操作。完整地推导了非匀直弹道SAR成像的全过程,点目标仿真结果清晰可见,表明了算法的有效性。

Ballistic imaging of non-uniform linear is one of the core issues of missile-borne SAR. At first the non- uniform straight line trajectory model in the three dimensional space is constructed and the Taylor approximate formula is used to analyze the sources of motion deviation, which can further be decomposed into three parts of azimuth, ground distance and pitch deviation. The functions of the ground distance deviation caused by diving motion and the pitch deviation caused by yaw motion are derived respectively, so the motion compensation functions are obtained. The SAR platform＇ s performance of the azimuth derivation is the variable motion in the azimuth position, and echo data format can be seen as the result of non-uniform sampling in the azimuth position. Therefore, a method based on the space non-uniform sampling model to replace the time domain varying-Doppler model is proposed to resolve the problem in this paper. The scene of invariable motion and non-uniform interval sample time is constructed to equivalent to the scene of variable motion and uniform interval sample time. Then the data from the non-uniform space domain is transformed into the uniform frequency domain by using the non-uniform discrete Fourier transform so as to complete the other imaging operation. The whole SAR imaging process of non-uniform straight trajectory is derived completely. Point target simulation results are clearly visible, and the validity of the algorithm is verified.