September 12, 2014

Spectral Resolution

© CNES

The IASI instrument covers the spectral range from the edge of the thermal infrared at 3.62 µm (2760 cm-¹) where solar backscatter begins to contribute up to 15.5 µm (645 cm-¹) covering the peak of the thermal infrared and particularly the CO2 band with Q branch around 666 cm-¹. Inside this range the following primary regions contain most of information required:

650 to 770 cm-¹Temperature sounding (CO2 band)
770 to 980 cm-¹Surface and cloud properties
1000 to 1070 cm-¹O3 sounding
1080 to 1150 cm-¹Surface and cloud properties
1210 to 1650 cm-¹Water vapour sounding; N2O, CH4 and SO2
2100 to 2150 cm-¹CO column amount
2150 to 2250 cm-¹Temperature sounding; N2O column amount
2350 to 2420 cm-¹Temperature sounding
2420 to 2700 cm-¹Surface and cloud properties
2700 to 2760 cm-¹CH4 column amount

To optimise the performance of the IASI instrument the full spectral range has been subdivised into three spectral bands. The boundaries for these bands are given in Table 1. IASI has a constant spectral sampling interval of 0.25 cm-¹.

Band 1 is mainly contributing to retrievals of temperature profiles and ozone, band 2 to retrievals of humidity and some trace gases and band 3 to retrievals of temperature and some trace gases.

BandRange (cm-¹)Range (µm)
1645 to 121015.5 to 8.26
21210 to 20008.26 to 5
32000 to 27605 to 3.62
Table 1 : IASI Spectral Bands

Overall the IASI mission objectives are deemed compatible with a spectral resolution of 0.35 to 0.50 cm-¹ depending on wavelength.