星载微光成像仪CCD像元异常响应动态检测与校正

Dynamic Detection and Correction for Abnormal Response of CCD Pixels in Spaceborne Low-Light Imager

地球的夜间微光信号强度是白天反射的可见光强度的百万分之一,星载微光CCD成像载荷像元响应特性的微小变化将显著影响成像质量。针对CCD推扫式载荷在轨响应特性的分析表明,异常响应导致微光图像中出现多条强弱不一的沿轨亮线,且具有数量时变性、位置随机性和响应非线性的特征。针对异常响应校正中无统一参考目标以及像元响应差异的非线性问题,提出了一种空间域松弛匹配而辐射域严格映射的修正方法。通过计算沿轨方向像元辐射均值的相对偏差,利用直方图分析确定亮线检测阈值并实现自动检测。在此基础上,针对每一条亮线采取先建立参考辐射值、后排序映射的方法实现亮线校正。为验证算法效果,分别选取包含海表、沙漠、湖冰、大雾和冰川等5种典型均匀场景的微光观测数据进行测试。测试结果表明,校正处理后图像中亮线基本消失,整体非均匀性相对改进44%、强亮线非均匀性相对改进60%,典型暗背景图像的信噪比由2提升至4.2。该方法具有逐像元实时检测与校正的特点,适用于无星上定标装置的推扫式CCD光学遥感卫星业务化辐射校正处理。

The signal intensity of the earth at night is one-millionth of the reflected visible light intensity during the day.Small changes in the pixel response characteristics of the spaceborne low-light CCD imaging payload will significantly affect the imaging quality.The analysis of the on-orbit response characteristics of the CCD push-broom load shows that the abnormal response results in multiple bright lines along the track with different intensities in the low-light image,which have the characteristics of time-varying quantity,random position and nonlinear response.A correction method is proposed in which the spatial domain is loosely matched and the radiation domain is strictly mapped.By calculating the relative deviation of the mean radiation value of the pixels along the track,the bright line detection threshold is determined by histogram analysis and automatic detection is realized.On this basis,for each bright line,the method of establishing reference radiation value first and then sorting mapping is adopted to achieve bright line correction.In order to verify the effect of the algorithm,the low-light observation data of five typical uniform scenes including sea surface,desert,lake ice,fog and glacier,are selected for testing.The test results show that after correction,bright lines in the images disappear.The overall non-uniformity is improved by 44%,the non-uniformity of strong bright lines is relatively improved by 60%,and the signal-to-noise ratio of the typical dark background image is improved from 2to 4.2.The method has the characteristics of real-time detection and correction pixel by pixel and is suitable for the operational radiometric correction of push-broom CCD on optical remote sensing satellites without on-board calibration devices.