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1. Introduction
The Improved Limb Atmospheric Spectrometer (ILAS) is a solar-occultation satellite sensor developed by the Environment Agency of Japan (EA) for studying the stratospheric ozone layer environment [Sasano et al., 1997; Sasano et al., 1999a]. ILAS onboard the Advanced Earth Observing Satellite (ADEOS) was launched on August 17, 1996 from Tanegashima Space Center of the National Space Development Agency of Japan (NASDA).
After the launch and checkout period of ADEOS, ILAS started its normal operation from November 1, 1996. From then, ILAS has been working successfully and gathered about 6700 occultation measurements for 8 months until ADEOS lost its function in June 30, 1997.
ILAS measured O3, HNO3, NO2, N2O, CH4, H2O, and aerosol extinction coefficients in both Arctic and Antarctic polar stratosphere. Validations of ILAS measurements (Version 3.10 products) were done for O3 with ozonesondes [Sasano et al., 1999b] and with other satellite measurements [Lee et al., 1999], HNO3 with several balloon measurements [Koike et al., 2000], and aerosol extinction coefficients with SAGE II measurements [Burton et al., 1999]. Validations of other species and later versions were underway, but preliminary comparison shows very good agreement of each species with other correlative measurements. Here we used the latest Version 5.10/5.11 products for our current analysis.