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LAPAN-A3 satellite brings a multispectral imager as main payload which has four color channel, i.e.: red, green, blue and near-infrared. The imager optics system uses beam-splitter mechanism, which divides the incoming light passing lens system into each color channel detector. Since each channel detector has different position and orientation with respect to lens center, then images produced by each channel detector will have different image focus quality. Such factor could reduce the quality of image produced. This research aims to improve the composite image quality of LAPAN-A3 satellite multispectral imager by ensuring that every channel detector will have uniform focus setting. The method used in this research consists of taking series of observation of object with zebra-cross pattern, then processed them by using Imatest software. The determination of the quality of each image focus are based on Modulation Transfer Function (MTF) calculation in particular spatial frequency. After several observations and calculation, image focus level of each channel detector can be successfully uniformed by controlling the distance of each detector to the center of lens. Furthermore, the experiment also able to reduce distortion caused by channel co-registration in horizontal axes. As a result, image quality of LAPAN-A3 satellite multispectral imager can be improved significantly. These results can be used as reference on the actual LAPAN-A3 sattelite ground station operation, and to support the development of experimental multispectral imager that is prepared for the next LAPAN-A4 sattelite.

PENINGKATAN KUALITAS FOKUS CITRA IMAGER MULTISPEKTRAL SATELIT LAPAN-A3 (IMAGE-FOCUSING QUALITY IMPROVEMENT ON LAPAN-A3 SATELLITE MULTISPECTRAL IMAGER)