Improved Limb Atmospheric Spectrometer-II (ILAS-II), Version 2

The Improved Limb Atmospheric Spectrometer (ILAS)-II is a satellite-borne sensor that measures ozone and its related chemical species in the high-latitude stratosphere on the basis of the solar occultation technique. There are approximately 14 measurements a day for each of the hemispheres, at sunrise seen from the satellite in the Northern Hemisphere and at sunset seen from the satellite in the Southern Hemisphere.
The retrieval algorithm is based on an onion-peeling method that uses a nonlinear least squares fitting for observed and theoretically calculated transmittance spectra (spectral fitting) at every 1 km downward from an altitude of 70 km to ~10 km to determine the volume mixing ratios of ten different trace gases (O3, HNO3, NO2, N2O, CH4, H2O, CFC-11, CFC-12, ClONO2, and N2O5). In practice, the sunset and sunrise data are retrieved by the version 2.0 and 2.1 algorithms, respectively, but this data set is distributed as the version 2.