基于光照条件的空间相机增益在轨自动调整  

Automatic on-Orbit Adjusting Gains of Space Camera Based on Lighting Conditions

作　　者：武星星[1] 刘金国[1] 周怀得[1] 张博研[1] 

机构地区：[1]中国科学院长春光学精密机械与物理研究所,吉林长春130033

出　　处：《光学学报》2014年第3期275-281,共7页Acta Optica Sinica

基　　金：国家自然科学基金(61108066);吉林省科技发展计划(20130101028jc)

摘　　要：空间相机摄影过程中,通常采用较小的固定增益以避免图像饱和,导致获取的图像存在整体偏暗、图像层次不丰富等问题。提出一种基于光照条件的空间相机增益在轨自动调整方法,根据当前的航天器位置和时间等实时计算星下点处的太阳天顶角,通过非线性拟合建立太阳天顶角与对目标最大反射率对应的地物成像时相机入瞳辐亮度之间的函数关系,进而完成对增益的实时计算和调整。与卫星工具包(STK)仿真和MODTRAN计算结果的对比实验表明,在太阳天顶角取[20°,70°]时辐亮度拟合误差小于等于0.3 W/(m2·sr),相对误差小于等于2.2%。计算和仿真得到太阳天顶角之差约为0.39°(3σ)。在轨成像实验结果表明,太阳天顶角为62.5°时增益调整后图像灰度层次从98提高到183,信息熵提高约19.2%,图像灰度层次更加丰富,使目标更容易辨识。During the imaging process of space camera, small fixed gains are often used to avoid image saturation. As a result, obtained images have problems such as dark as a whole, short of digital number levels. An automatic on- orbit adjusting gains method of space camera based on lighting conditions is put forward. In this method sun zenith angle at substellar point is calculated in real time according to current position of spacecraft and time. Function relationship between sun zenith angle and radiance at entrance pupil of space camera corresponding to maximum reflection index of targets is established by non-linear curve fitting. In this way real-time calculation and adjustment of gains are realized. Results of contrastive experiment with results of simulation by satellite tool kit （STK） and computation by MODTRAN indicate that radiance fitting errors are no more than 0.3 W/（m2 ·sr） as sun zenith angle belongs to [20°, 70°]. Relative errors are no more than 2.2 %. Difference error between calculated sun zenith angles and those simulated is about 0.39° （3σ）. Results of on-orbit imaging experiments indicate that digital number levels are improved from 98 to 183 and entropies are improved about 19.2 % after adjusting of gains as sun zenith angle is 62.5°. Targets will be easier to be recognized as more digital number levels can be obtained.

关 键 词：遥感 空间相机 增益 太阳天顶角 

分 类 号：V445.8[航空宇航科学与技术—飞行器设计]