基于月球定标的双相机辐射一致性校正

Radiation Consistency Correction of Dual Cameras Based on Lunar Calibration

针对吉林一号光谱星双相机辐射响应不一致的现象,提出基于月球定标的双相机辐射一致性校正方法。利用卫星敏捷成像特性获取双相机对月成像观测数据,解算待定标传感器月球圆盘光谱辐照度,比对Robotic Lunar Observatory(ROLO)辐照度模型,选取双相机辐射响应一致且衰减较小的谱段作为基准谱段,通过计算相对于基准谱段的辐照度比值,核算各个谱段的辐射衰减量,从而校正双相机辐射一致性。对吉林一号光谱02星进行了测试,实验结果表明,双相机辐射在各个谱段有不同程度的衰减,最大衰减量超过30%,所提方法能够有效改善图像目视效果,提高传感器辐射质量。

Objective Due to the influence of the external environment and system aging,the radiation characteristics of the camera will change after launch.It is of great importance to carry out on-orbit radiometric calibration,which converts the image grayscale value of the sensor response into spectral radiance or top of atmosphere reflectance,for remote sensing data quantitative application.Common methods of on-orbit radiometric calibration can be divided into four categories:on-board calibration,site calibration,cross calibration,and scene calibration.As a long-term stable natural celestial body in the universe,the moon has very high surface reflectivity stability.It can be used as a calibration source to avoid interference from complex atmospheres and as a supplement to the on-board calibration.At present,the internationally representative lunar radiation models are the Robotic Lunar Observatory(ROLO)model and the Miller-Turner 2009(MT2009)model.The spectral coverage of the ROLO model used in this study is 300-2550 nm,and the model uncertainty is 5%-10%.Although the ROLO model has larger uncertainty than the site calibration or on-board calibration,its relative stability can reach 1%-2%,which can be used as a normalized reference to monitor the attenuation of sensors.Many scholars use the lunar irradiance model as the basis to carry out radiometric calibration or monitor the stability of the satellite sensor by comparing the data of different months and different moon phases.However,these studies only focus on multi-temporal tracking of the on-orbit radiation performance of sensors and do not consider the consistency correction of radiation performance between different sensors and different spectral bands.In the present study,we propose a radiation consistency correction method based on lunar calibration.We hope that method can help the inconsistent radiation response of dual cameras installed on the Jilin-1 GP satellite.Methods We propose a radiation consistency correction method for dual cameras equipped with Jilin-1 GP satellite by lunar calibration based on the stable radiation response characteristics of the moon.Firstly,the lunar imaging data of the two cameras are obtained successively by adjusting the satellite attitude.Then,the lunar spectral irradiances of different spectral channels of the two sensors are calculated based on the image data.The calculation results are compared with the ROLO lunar irradiance model and the spectral band with small irradiance change and close irradiance response of the two cameras is selected as the reference band.At last,the ratio irradiance of each band to the reference band is calculated to correct the attenuation of each band,to achieve dual-camera radiometric consistency correction of Jilin-1 GP satellite.Results and Discussions The correction value of the absolute radiometric calibration coefficient of each spectral band indicates that after the satellite has been on orbit for a period of time,certain fluctuations have occurred in each band,and some spectral bands even have an attenuation of more than 30%(Table 3).Four sets of data from different imaging scene types are selected for testing,of which the red,green,and blue spectral bands are combined into true color images.Visually,the corrected dual-camera images have better color consistency(Figs.7 and 8).Relative average spectral error(RASE)and relative global dimensional synthesis error(ERGAS)are adopted to evaluate the spectral consistency of the entire image and lap region imaged by both cameras before and after correction.Compared with the calculation results of the indicators before and after the correction,the calculation results of RASE and ERGAS between the two cameras after the correction are better than those before the correction,whether it is the entire area or the overlapping area(Table 5).Experimental results show that our dual-camera radiometric consistency correction method significantly improves the radiometric consistency,especially in the overlapping area.Conclusions In the present study,based on the imaging data of the simultaneous observation of the moon by two cameras of the Jilin-1 GP02 satellite,we propose a dual-camera radiation consistency correction method based on lunar calibration.Firstly,based on acquired observation data of the moon,the consistency of the single spectral band radiation reference of the two cameras is determined by selecting the spectral band with the closest lunar irradiance results of the two cameras as the benchmark for the correction between the respective bands.Furthermore,the relative relationship between each spectral band in the ROLO model is used as a reference,and all bands of the two cameras are corrected relatively to realize the consistency of the remaining spectral bands of the dual cameras to the consistency of the reference band.The test results show that some spectral bands of the Jilin-1 GP02 satellite have obvious attenuation.After compensating for the attenuation,the visual effect of the true color images taken by the two cameras of the Jilin-1 GP02 satellite is more consistent,and the relative average spectral error and the relative adimensional global error in synthesis of the overlapping area of the dual camera are also significantly smaller.