Improved Limb Atmospheric Spectrometer (ILAS), Version 6.1

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The Improved Limb Atmospheric Spectrometer (ILAS) 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).


Release date
Temporal coverage
1996/09/18 - 1997/06/29
Data provider
Email: cgerdb_admin(at)
File format
Data volume
64.1 MiB
V6.1 (Last updated: 2005/11/01)

Data Set

O3, HNO3, NO2, N2O, CH4, H2O, ClONO2, CFC-12, and other data
Observation period
From September 1996 to June 1997 (Ended)
Spatial coverage
[Northern Hemisphere] Latitude: 57°~ 73°, Longitude: -180°~ 180°
[Southern Hemisphere] Latitude: -64°~ -88°, Longitude: -180°~ 180°
Vertical: ~10 km - 70 km
Time resolution
1 profile per ~100 min in each hemisphere
Spatial resolution
Latitude: Depends on season
Longitude: ~25 degrees
Vertical: 1.9-3.5 km at tangent heights of 15-55 km
Depends on species and altitude
Measurement method
ILAS was a satellite-borne solar-occultation sensor on board the satellite ADEOS. ILAS consisted of two spectrometers: an infrared spectrometer (between 6.21 µm to 11.77 µm) and a visible spectrometer (between 753 nm and 784 nm).
Calculation method
Vertical profiles of gases were retrieved by applying both the onion-peeling method and the non-linear least-squares fitting method.
Earth observation satellites > ADEOS > ADEOS-I
Atmosphere > Atmospheric Chemistry > Trace gases/Trace species
[Free keywords]
Stratosphere, Ozone, O3, Nitric Acid, HNO3, Nitrogen Dioxide, NO2, Nitrous Oxide, N2O, Methane, CH4, Water Vapor, H2O, Chlorine Nitrate, ClONO2, CFC-12, CC BY
Update history
All Version 6.1 data are released. V6.1.


Readme file
Sugita, T., T. Yokota, H. Nakajima, S. Oshchepkov, Y. Sasano, H. Irie, N. Saitoh, M. K. Ejiri, H. Kanzawa, Y. Itou, H. Saeki, H. Matsuda, and M. Kaji (2005), Assessment of Improved Limb Atmospheric Spectrometer (ILAS) Version 6 data quality: measurements of stratospheric O3, HNO3, NO2, N2O, CH4, H2O, and aerosol extinction coefficient, ILAS project report No. 1.
Nakajima, H., et al. (2006), Measurements of ClONO2 by the Improved Limb Atmospheric Spectrometer (ILAS) in high-latitude stratosphere: New products using version 6.1 data processing algorithm, J. Geophys. Res., 111, D11S09, doi:10.1029/2005JD006441.
Yokota, T., H. Nakajima, T. Sugita, H. Tsubaki, Y. Itou, M. Kaji, M. Suzuki, H. Kanzawa, J. H. Park, and Y. Sasano (2002), Improved Limb Atmospheric Spectrometer (ILAS) data retrieval algorithm for Version 5.20 gas profile products, J. Geophys. Res., 107, D24, 8216, doi:10.1029/2001JD000628.
Nakajima, H., M. Suzuki, A. Matsuzaki, T. Ishigaki, K. Waragai, Y. Mogi, N. Kimura, N. Araki, T. Yokota, H. Kanzawa, T. Sugita, and Y. Sasano (2002), Characteristics and performance of the Improved Limb Atmospheric Spectrometer (ILAS) in orbit, J. Geophys. Res., 107(D24), 8213, doi:10.1029/2001JD001439.
Other publications

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Citation format
When this data set is referred to in publications, it should be cited in the following format.
Sugita, T., H. Nakajima, and T. Yokota (2018), Improved Limb Atmospheric Spectrometer (ILAS), Version 6.1, Center for Global Environmental Research, NIES, DOI:10.17595/20180628.001. (Reference date*: YYYY/MM/DD)
*As the reference date, please indicate the date you downloaded the files.

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