A MULTI-SPECTRAL CAMERA FOR SMALL MULTI-MISSION SATELLITE (SMMS)

摘要

One of the main missions of the Small Multi-Mission Satellite (SMMS) project, which is planned to be implemented with the cooperation of Asia-Pacific countries, is on remote sensing. Therefore, the multi-spectral CCD camera is an important part of the payload of SMMS. The SMMS satellite payload includes two sets of multi-spectral CCD cameras with a swath width of 700 Km (360 Km for each one) and the Attitude of satellite is 650 Km. The camera scanning system is push broom with a ground resolution of 30 meters which operates in three visible and one near IR spectral bands. Because of the limited weight of the camera (25 Kg one set), the multi-spectral camera consists of only one single optical system and we have to choose a F-number as large as possible. The single lens system covers a wide spectral range from 430-900 nm. The optical system has to acquire images of the earth in four different spectral bandwidths simultaneously. The four images have to be of the same ground scene with a small error out of that area and every bandwidth should have exactly the same focal length. To measure the radiation reflected from the earth surface a linear CCD array will be used which has more than 12000 pixels with a square pixel elements of 10 * 10 microns (can be adjusted), so it is equivalent to 360 Km in cross track direction and 30 m in along track direction on the ground. In order to meet the high quality and proper MTF demands, special optical glasses with large Abbe number are needed. Precise design, calculation and processing are made and special instruments are required for the assembly of optical pieces and optical alignment adjustment.