With the spectral resolutions specified above IASI shall measure equivalent temperatures in the range 180 K to 315 K. The quality of the measurement is determined in particular by the radiometric noise and radiometric calibration accuracy.
Radiometric noise is specified in terms of the noise equivalent temperature difference, NEDT, for a given reference temperature of 280 K. The NEDT requirements are defined for a bandwith of 0.5 cm¹.
The radiometric specifications are given in figure 2.
These include all noise contributions (detectors, amplifiers, A/D converters, processing) and all errors sources which do not result in a bias (e.g., errors due to field-of-view motion, fluctuations of wavelength calibration, knowledge of the spectral response function, fluctuations of the radiometric calibration).
The specifications for the on-board radiometric calibration are as follows:
- The absolute accuracy is < 0.5 K.
- The stability is < 0.3 K.
- The relative accuracy between bands, different scan angles and different ground pixels for targets at the same equivalent temperature is < 0.2 K.
The specifications for the spectral calibration are:
- The relative accuracy better than 2.10-4
- The stability better than 10-6 relative error in any 5 min period