Research On Imaging Uniformity And Real-time Automatic Exposure Of Remote Sensing Camera

With the development of space remote sensing technology, demands on imagequality are becoming higher. With high sensitivity and highsignal–noise-ratio(SNR), time-delay-integration charge-coupled-device (TDICCD) isthe most widely used sensor in the space optical remote sensing field. Forhigh-resolution multi-TDICCD mosaic camera, automatic exposuremethod, multi-channel imaging uniformity design, non-uniformity correction andtheir implementation on FPGA have been researched in this paper.The structure and working principle of TDICCD were introduced. The mosaicmethod and components of multi-TDICCD mosaic remote sensing camera weredescribed. Then two key points affecting the veracity of automatic exposure wereindicated, including low noise and imaging uniformity. Whereafter, the main noisesource and noise reducing method in camera were analyzed.It was proposed that the uniformity design was the basic preconditionof multi-imaging-unit's imaging uniformity. First of all, from hardware point, eachprocess affecting uniform imaging was discussed, including filtration of device,design of power, key signals transmission and PCB design etc. Afterward, severalsoftware design details were dicussed, concerning multi-FPGA identity decoding,synchronous clock, reset design and high-precision adaptive CDS design. Non-uniformity correction was used to correct theresidual imaging non-uniformity after imaging uniformity design. By analyzingcommon non-uniformity correction methods based on calibration and scene, asynthesized non-uniformity correction algorithm with high reliability and real-timeability was presented, using the two-point correction method in a single channel, gainaveraging method among channels and scene-adaptive correction method amongTDICCDs. Simulation results show that this algorithm has impressive correctioneffect.Given uniform imaging, automatic exposure algorithm was studyed formulti-TDICCD mosaic camera. For TDICCD camera, an automatic exposure methodwas proposed, taking integral stages and gain as parameters, combining withimage-stretch. Afterward, effects of the automatic exposure parameters on SNRand modulation transfer function(MTF) were analyzed, then MTF degradation indifferent integral stages was used as one of the constraints of integral stages'improvment. At last, through judging statistics of4key image exposure characteristic,the detailed automatic exposure algorithm was illustrated.Finally, hardware implementation based on FPGA of thenon-uniformity correction algorithm and the automatic exposure algorithm wasdiscussed. The experimental results indicate that the imaging non-uniformity can bedecreased from4.82%to0.27%for a single TDICCD, and to0.44%for a3-TDICCD mosaic camera, the automatic exposure algorithm can achieveexpectation under underexposure and overexposure, both real-time performance andresource utilization meet the requirements. Moreover, reliability and safety designmethod was applied in FPGAs' software, supporting the above algorithms in spaceengineering.