TDI CCD相机大姿态角推扫成像行频精确匹配

针对大视场TDI CCD相机大姿态角推扫成像过程中像面上像点像速差异较大,行频匹配精度不高引起的相机传函下降等问题,提出一种可支持粗调和精调的高精度行频匹配方法。首先,阐述了大视场遥感相机像速场的主要特点及像速匹配的关键问题;其次,深入分析了大视场TDI CCD相机大角度侧摆和前后摆推扫成像的像速场特性;然后,根据像速场特性制定同速匹配模式和异速匹配模式,分析传函特性,确定各自模式的使用条件;最后,提出了一种可支持粗调和精调的高精度行频匹配方法,并分析已实现行频匹配方法的精度,最终满足给定行频匹配精度要求。实验结果表明:在积分级数为96级,粗调方法使行频精度达到0.999 425,精调方法使行频精度达到0.999 928,2种方法均能使相机传函MTF优于0.998,从而实现大视场TDI CCD相机在各种大姿态角推扫成像条件下高质量成像。

超宽幅遥感转扫成像分析

空间遥感成像正朝着小型化、大幅宽和高分辨率的方向发展。区别于常用的沿轨推扫成像方法,本文提出采用反射镜转扫成像的新方法,实现了垂轨千公里级成像。结合卫星运动模型,本文分析了该系统中转扫行频、分辨率以及成像幅宽等计算方法。基于实际的设计参数,文中仿真分析了卫星轨道变化对成像系统的影响。轨道越高,分辨率越低,成像幅宽越大,渡越时间越大,行频越低,对后端读出系统设计要求越低。相反,轨道越低,分辨率越高,成像幅宽越小,渡越时间越小,行频越高,对后端读出系统设计要求越高。

Single-Frequency Matching Pursuits Based Time-of-Flight Measurement in Viscoacoustic Medium

Broadband ultrasound signals will produce distortion in viscoacoustic medium, which may influence the accuracy of time-of-flight (TOF) measurement. Under the condition of single-frequency acoustic source, the wave propagation process in viscoacoustic medium was analyzed and an approximate solution of the wave propagation was given. Instances of broadband ultrasound were analyzed and simulated based on the single-frequency results. A single-frequency matching pursuits (SFMP) algorithm was then introduced to solve the waveform distortion problem. Time-frequency decomposition was applied to extracting the single-frequency compositions from broadband ultrasound signals, and then these compositions were sent to the matching pursuits (MP) algorithm for calculating the TOF parameters. Compared with the broadband signals, the shapes of extracted single-frequency signals change more slightly as distance and attenuation coefficient increase. The residuals of SFMP were far less than those of MP algorithm. Experimental results show that the SFMP algorithm is able to eliminate waveform distortion of broadband ultrasound in viscoacoustic medium, which helps improve the accuracy of TOF measurement.