<title>Improved limb atmospheric spectrometer (ILAS) project: ILAS instrument, performance, and validation plan</title>

Ozone layer observation will be conducted with the solar occultation sensor ILAS (improved limb atmospheric spectrometer) on board the ADEOS (Advanced Earth Observing Satellite; to be launched in August 1996) to provide vertical profiles of ozone, methane, water vapor, nitrogen dioxide, nitric acid, and nitrous oxide from absorption measurements in the infrared region, and temperature and pressure profiles from measurements of absorption due to oxygen molecules in the visible region. Optical properties of stratospheric aerosol and polar stratospheric clouds (PSCs) are also derived from visible and infrared extinction measurements. Using the ILAS flight model, optical performance data was obtained from the experiments with a gas cell and a black body light source. Field experiments have been planned for the post-launch validation, which includes field campaigns using large balloons at Kiruna (Sweden) and ground-based remote sensors at Kiruna, Alaska, Syowa Station and other locations. This paper briefly describes the ILAS instrument, its performance evaluation, laboratory experiments to determine the instrument function, data processing algorithms and validation plans.