In-orbit straylight characterization and correction of optical radiometer using the moon image

Abstract

The moon images have been in recent years employed as a referential light source for in-orbit radiometric characterization of on-board radiometer in spacecraft. The irradiance obtained by the integration of the radiance of moon pixels is compared to the referential irradiance that derives from the astrophysical model, and the comparison result includes the gain characteristics of radiometer. In addition to this radiometric purpose, the limb between moon disk and deep space is also an ideal edge in optical aspect. The edge response of radiometer obtained in the limb includes the characteristics of MTF (modulation transfer function) and straylight. In this paper, in-orbit straylight characterization and correction of SGLI (Second Generation Global Imager) radiometer that is flying on JAXA's remote sensing satellite "SHIKISAI" is reported. It is shown that LSF (line spread function) measured in the moon limb is effective trend monitor of radiometer's geometric property in orbit and is also a key to verify the validity of straylight correction model implemented in the ground data processing system. This paper proposes the methodology that constructs PSF (point spread function) by LSFs in two orthogonal direction and corrects straylight of not only the Moon but the earth image by using the constructed PSF.