空间相机在轨成像模式的建立

Establishment of image model for on-board space camera

提出空间相机在轨成像模式的概念,研究了建立空间相机成像模式的方法。首先,根据太阳高角和地物反射率,使用MODTRAN软件计算相机入瞳前的辐射亮度,分析相机的辐射定标数据,包括每种成像模式的响应度、辐射亮度范围,积分时间关系等。然后,分析相机测摆成像与平飞成像时的积分时间关系,获得相机在各侧摆角下,每种成像模式的辐射亮度范围。最后,依据成像模式的辐射亮度范围和各太阳高角下景物的辐射亮度范围,建立了太阳高角和相机侧摆角组合下的成像模式表。空间相机成像时,依据成像模式表查找对应的成像模式,即可按该模式成像。该方法已多次应用于遥感相机成像实验中,获得了较好的成像效果,图像质量的满意度由65%提高到99.9%。结果表明:依据该方法建立的空间相机成像模式,获得图像效果较好,图像既包含全部景物信息又具有丰富的图像层次。

The concept of on-board imaging model for a space camera was proposed, and the method to establish the imaging model of the space camera was researched. On the basis of the solar elevation angle and the reflection of earth surface, the radiance at the entrance pupil of space camera was calculated using the MODTRAN software. Then the radiometric calibration data were analyzed and the re sponsibility, radiance range and the integration time for each image model were acquired. Meanwhile, the relation between the responsibility and the integration time was obtained for scroll image and standard image and the radiance ranges at each image model was calculated at every scroll angle. Finally, according to the radiance range at each image model and the maximum objective at sensor radiance from the earth surface, an imaging model table was established under the scroll angle and solar elevation angle. When the space camera worked on board, one could choose a corresponding imaging model by looking up the table and could achieve better images. The method has been used in space camera imaging for several times, high quality remote images have been acquired. The image satisfaction improves from 65% to 99.9%. According to the method, the remote imagers quality has been improved obviously. The image not only includes all scene information, but also has abundant levels.