Characteristics and performance of the Improved Limb Atmospheric Spectrometer‐II (ILAS‐II) on board the ADEOS‐II satellite

[1] The Improved Limb Atmospheric Spectrometer-II (ILAS-II) monitored components associated with Polar ozone depletion. ILAS-II was on board the Advanced Earth Observing Satellite-II (ADEOS-II, “Midori-II”), which was successfully launched on 14 December 2002 from the Tanegashima Space Center of the Japan Aerospace Exploration Agency (JAXA). ILAS-II used a solar occultation technique to measure vertical profiles of ozone (O3), nitric acid (HNO3), nitrogen dioxide (NO2), nitrous oxide (N2O), methane (CH4), water vapor (H2O), chlorine nitrate (ClONO2), dinitrogen pentoxide (N2O5), CFC-11, CFC-12 and aerosol extinction coefficients at high latitudes in both the Northern and Southern hemispheres. ILAS-II included Sun-tracking optics and four spectrometers, a Sun-edge sensor, and electronics. The four spectrometers measured in the infrared (channel 1) between 6.21 and 11.76 μm, in the midinfrared (channel 2) between 3.0 and 5.7 μm, at high resolution in the infrared (channel 3) between 12.78 and 12.85 μm, and in the visible (channel 4) between 753 and 784 nm. The vertical height of the entrance slit was 1 km at the tangent point. A Sun-edge sensor accurately registered tangent height. After an initial check of the instruments, ILAS-II recorded routine measurements for about 7 months, from 2 April 2003 to 24 October 2003, a period that included the formation and collapse of an Antarctic ozone hole in 2003 that was one of the largest in history. All of the ILAS-II data were processed using the version 1.4 data-processing algorithm. Validation analyses show promising results for some ILAS-II measurement species, which can be used to elucidate mechanisms of Polar ozone depletion. Studies are ongoing on ozone depletion, on the formation mechanisms of Polar stratospheric clouds, on denitrification, and on air mass descent. A state-of-the-art data retrieval algorithm that is currently being developed will yield more sophisticated data sets from the ILAS-II data in the near future.