Improved Limb Atmospheric Spectrometer (ILAS)

Observation Cencept

ILAS Observation Concept

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.

ILAS Main Characteristics

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.

ILAS Overview