【作者】 王俊；

【导师】 毛示艺； 刘祥林；

【作者基本信息】 北京航空航天大学 ， 信号与信息处理， 2001， 博士

【摘要】 近年来随着DSP技术的飞速发展,加之高分辨率SAR实时成像技术在军事、国民经济和科学研究方面的有着重要地位,SAR实时处理机因而受到各国的重视。本研究组研制的基于CS算法的全数字式高分辨率SAR实时处理机可以在前斜视和正侧视模式下进行高分辨率条带式实时成像处理。本文的研究工作属于该处理机研制的一部分。在文中讨论了处理机设计中信号处理能力、数据通信等难点问题。对以下方面问题进行了研究:对SAR实时处理机的结构、组成、各处理模块的功能分配;矢量处理模块的设计,及其完成CS处理中FFT和复乘的方法,矢量处理模块的处理精度处理、处理速度;标量处理模块的并行处理时的任务分配;CORDIC处理模块在处理机中的应用;处理机的性能指标;并且对聚束式SAR的实时处理和SAR图像后处理问题进行了研究。利用高性能DSP(如ADSP2106x、BDSP9124/9320)和自定义多总线的模块化处理机结构,从而很好地解决了SAR实时处理中对处理速度和数据传输速度的要求。在处理算法上采用适合于并行或专用DSP完成的高精度CS算法,因而可以满足正侧视和前斜视成像处理的要求。矢量处理模块的主要处理芯片组为BDSP9124/9320,其处理速度和数据传输速度均优于通用DSP,可以进行CS成像算法中的FFT和复乘处理。矢量处理模块采用大容量、高速SARM进行数据存储,可以对1M点以内的复数数据进行处理。由i386Ex和FPGA对矢量处理模块上的资源进行控制,其编程比较方便。而且可以通过多模块扩展来提高处理性能。在对矢量处理模块处理性能和速度分析的基础上,进行CS成像处理时利用大基底两维FFT处理,从而提高了处理速度、节省了BDSP9124/9320的控制代码。分析了标量处理模块在进行计算时的性能指标和并行编程方法。在课题组各位成员的努力下,完成了处理机的设计工作,并给出了实时处理机的性能指标。由CORDIC可以快速进行极坐标和直角坐标之间的变换,我们利用FPGA完成了一个流水线结构的CORDIC处理模块。它可以用来完成标量处理中相位因子极坐标表示到直角坐标之间的转换,可以提高实时处理机的性能。最后对聚束式SAR实时处理问题和斑点噪声消除进行了一些研究更多还原

【Abstract】 High and super-high resolution airborne Synthetic Aperture Radar (SAR) is an important research orientation. Currently, the advanced countries are trying their best to develop high-resolution airborne SAR systems. The research work of this paper goes with the development of real time SAR processor in our research group. A study of the special characteristics in the real time SAR processor is presented.I/Q error is the first problem faced to the SAR signal. I/Q amplitude and phase error can create an image response at the negative frequency, which cause serious disturbance to signal detection. The SAR echo studied here, the imaging algorithm is adopted to compress pulses, which is a two dimension matched filter. When the I/Q error is constant in an aperture, it will do nothing to the signal after the pulse compression. Considering the real time computation, in this SAR processor the I/Q correction is not considered.Motion compensation is an inseparable part to SAR. Combined with the real time SAR processor, a motion compensation realization is introduced in this paper. That includes the first order motion compensation, which is important and necessary, the second order motion compensation, whose phase is miner and has a large computation, in real time SAR processor, it is not be considered, autofocus is obtained by plug in. Furthermore, autofocus only can solve defocus problem, this paper introduces an idea to correct the image geometric distortion, this method uses the result of PGA, by which a phase multiplication corrects the geometry distortion. When the motion error of phase center passes over a range bin, resample should be taken into consideration, the resample inaccuracy within one range bin does not have impact on azimuth focus, but to the signal amplitude.This real time SAR processor has side-looking and squint modes. Two approaches are proposed to use the side-looking raw data to squint imaging. The first one is the direct transformation, which uses the data with a wide beam angle. The maximum of the E-SAR raw data squint angle is 7°. The second one is the indirect transformation, which is carried out by adding a platform velocity along slant range according to the required squint angle. Then the squint data is determined by the angle between the new forward velocity and LOS direction. The drift angle is less than 15°, the indirect transformation is showed acceptable.Squint imaging has some specialties, which are different under squint condition, compared four mainly squint imaging algorithms, a new extend Chirp-scaling algorithm is presented to eliminate the cubic phase error due to the slant range expanding to the cubic term under high squint angle.更多还原