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-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.
