大视场多光谱空间相机在轨自动相对辐射校正研究

Research on on-orbit automatic relative radiometric correction of multi-spectral space camera with large field of view

大视场多光谱空间遥感相机获取的图像直接合成彩色图像后存在严重的色带,且不同片探测器获取的图像存在较大的颜色偏差。随着分辨率、视场角和光谱谱段数量的增加,在地面进行相对辐射校正时数据处理量大且耗时长。提出了一种大视场多光谱遥感相机的在轨自动相对辐射校正方法,通过最小二乘法拟合得到绝对辐射定标系数,计算得到能够消除片间颜色偏差的相对辐射校正系数。在成像控制FPGA中原始图像和从BLOCK RAM中读取的校正系数,依次经过13 b有符号加法器、17 b无符号乘法器和四舍五入模块,自动完成每个像元图像数据的实时相对辐射校正。实验室均匀辐射背景成像实验和仿真结果表明,自动相对辐射校正的结果和在地面进行相对辐射校正的结果一致,校正误差在0.5个DN(digital number)值以内,校正后的图像滞后原始图像6个系统时钟,可以满足实时性要求。在轨成像实验结果表明,经过自动相对辐射校正后直接合成的彩色图像去除了色带和片间色差,使得对感兴趣目标分辨和识别更加快速及时。

Severe color strips exist in the color images directly synthesized from the images obtained from multi-spectral space camera with large field of view. In addition the color image from one piece of sensor differs from that of another in color greatly. With the increasing of resolution, angle of field of view and number of spectral coverage, more data should be processed and much time would be consumed in relative radiometric correction on the ground. An on-orbit automatic relative radiometric correction method was put forward to solve this problem. Least squares fitting method is used to obtain the absolute radiometric correction coefficients; through calculation the relative radiometric correction coefficients are obtained, which could be used to eliminate the color difference between the images from different pieces of sensors. The original images in the imaging control FPGA and the correction coefficients read from Block RAM are sent to 13 b signed adder, 17 b unsigned multiplier and round-off module in sequence, and the real-time rel- ative radiometric correction of each pixel is accomplished automatically. Results of imaging experiments under uniform radiometrie background in laboratory and simulation indicate that the results of automatic relative radiometric correction coincide with those of the relative radiometric correction performed on the ground. The correction errors are within 0.5 DN（digital number）. The corrected image lags behind the original image by 6 system clocks, which meets the real- time requirement of the system. Results of on-orbit imaging experiments indicate that color strips and color difference between the images from different pieces of sensors are removed in the color images directly synthesized after automatic relative radiometrie correction, and the interested targets could be distinguished and recognized more rapidly.