Improved Limb Atmospheric Spectrometer (ILAS) developed by the Environment Agency of Japan is a sensor to monitor the polar stratospheric ozone. The object of ILAS is to monitor and study changes in the stratosphere which are triggered by emissions of Chloro Fluoro Carbons (CFC), and to check the effectiveness of world-wide emission controls of CFCs. ILAS is a spectrometer which observes the atmospheric limb absorption spectrum from the upper troposphere to the stratosphere using sunlight (solar occultation technique). This covers the infrared region (850-1610cm-1) and the near visible region (753 to 781nm). ILAS is designed based on LAS (Limb Atmospheric infrared Spectrometer), which was aboard EXOS-C (Ohzora, ISAS). It was developed to improve observation accuracy and also to detect minor constituents related to ozone hole chemistry. ILAS's observations are focused on the high latitude regions because of the geometrical relation of the solar occultation events with the sun-synchronous orbit. From these spectral observations, ILAS can measure the vertical profile of ozone hole related components: ozone (O3), nitrogen dioxide (NO2), aerosols, water vapor (H2O), CFC11, methane (CH4), nitrous oxide (N2O), temperature, and pressure. This dataset covers the key physical and chemical parameters which characterize ozone hold events: the cooling at the polar lower stratosphere, PSC formation, the removal of nitrogen reservoirs, and the ozone reduction by activated chemical chain reactions.ILAS will continue to contribute to research into stratospheric ozone changes into the late 1990's.

Spectral Coverage	Ir(850-1610cm-1,6.21-11.77m),Visible(753-7784mm)
Spectrometer	Gratung Spectrometers with Lonear Linear Array Detector
Spectral Data Sampling Rate	12Hz
IFOV	2km Vertical * 13km Horizontal
Observation Parameters	O3,NHO3,N2O,H2O,CFC11,CH4,Areosols,Pressure,and Temperature
Observation Rgion	N57-70 deg. S60-85deg.
Weight	140kg
Power	100W or less
Size	800*1600*550

ILAS measures the sequence of the limb atmospheric absorption spectrum which pass the various tangent heights, in 12Hz. The absorption (concentration) of each layer is derived from this spectral data stream. ILAS tracks the radiometric center of the solar disk. ILAS also has an IFOV position sensor which measues the angle between IFOV and the top edge of the sun.