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-¹||Temperature sounding (CO2 band)|
|770 to 980 cm-¹||Surface and cloud properties|
|1000 to 1070 cm-¹||O3 sounding|
|1080 to 1150 cm-¹||Surface and cloud properties|
|1210 to 1650 cm-¹||Water vapour sounding; N2O, CH4 and SO2|
|2100 to 2150 cm-¹||CO column amount|
|2150 to 2250 cm-¹||Temperature sounding; N2O column amount|
|2350 to 2420 cm-¹||Temperature sounding|
|2420 to 2700 cm-¹||Surface and cloud properties|
|2700 to 2760 cm-¹||CH4 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.
|Band||Range (cm-¹)||Range (µm)|
|1||645 to 1210||15.5 to 8.26|
|2||1210 to 2000||8.26 to 5|
|3||2000 to 2760||5 to 3.62|
Overall the IASI mission objectives are deemed compatible with a spectral resolution of 0.35 to 0.50 cm-¹ depending on wavelength.