Infrared Atmospheric Sounding Interferometer - New Generation (IASI-NG) is a passive infrared sounder which has the capability to measure the temperature and water vapour profiles of the Earth’s atmosphere.

Last Updated

20 June 2022

Published on

19 May 2020

EPS-SG IASI-NG Instrument
Figure 1: Illustration of the IASI-NG instrument (Credit: Airbus DS)

In addition to this, IASI-NG has a huge potential to measure greenhouse gases, clouds, aerosols, ozone and trace gases.

IASI-NG has a direct heritage from the IASI (InfraRed Atmospheric Sounding Interferometer) instrument on board EUMETSAT Polar System (EPS) satellites. IASI-NG will ensure continuity to EPS-IAS, with improved spectral and radiometric performances.

The primary objective of the IAS (Infra-red Atmospheric Sounding) mission is to support numerical weather prediction (NWP) at regional and global scales, through the provision of infrared radiance spectra measurements with information on:

  • Atmospheric temperature profiles at high vertical resolution in clear and partly cloudy air.
  • Atmospheric water vapour profiles at high vertical resolution in clear and partly cloudy air.
  • Surface temperature over sea, ice, and land surfaces.
  • Cloud variables.
  • A number of atmospheric trace gases like ozone, carbon dioxide, carbon monoxide, sulphur dioxide, methane, nitric acid, ammonia, and nitrogen dioxide.

On a regional scale, IASI-NG with its high resolution temperature and moisture sounding, will be able to improve nowcasting and very short-range forecasts, through the provision of monitoring of atmospheric instability and cloud microphysical structure. This will particularly be useful for high latitudes where geostationary satellites have only sparse coverage.

The secondary objectives of the IAS mission are to support air quality monitoring at global and regional scales by observation of pollutants in the free troposphere, and the assessment of composition – climate interaction by the observation of greenhouse gases.

Furthermore, IASI-NG will support climate monitoring by providing well calibrated radiance spectra.

IASI-NG spectral characteristics

IASI-NG is a Fourier transform spectrometer, with 16921 spectral samples between 645 and 2760cm-1. The table shows the spectral bands of IASI-NG. The spectral resolution of IASI-NG is 0.25cm-1 after apodisation (0.5cm-1 for IASI) and spectral sampling is 0.125cm-1 (0.25cm-1 for IASI). The reduction in radiometric noise is expected to be at least a factor of two, compared to IASI. The increase in spectral resolution of IASI-NG will result in a better vertical resolution and the reduced and radiometric noise will result in an improvement in the accuracy of the IASI-NG products.

Spectral Band Wavenumber or Wavenumber Range Purpose Radiometric Resolution (*NEΔT@280 K) apodised (K)
IAS-1 645cm-1
Temperature profile Acetylene (C2H2), Hydrogen cyanide (HCN) 0.39
IAS-2 690–770cm-1 Temperature profile C2H2, HCN 0.130
IAS-3 770–1000cm-1 Temperature and water vapour profiles, Sea Surface Temperature (SST), surface and cloud properties. peroxyacetylnitrate (PAN), Nitric acid (HNO3), Ethylene (C2H4) 0.130
IAS-4 1000–1070cm-1 Ozone (O3) Column, O3 profile, Methyl alcohol (CH3OH) 0.195
IAS-5 1070–1150cm-1 Surface and cloud properties, Formic acid (HCOOH), volcanic sulfur dioxide (SO2) 0.195
IAS-6 1150–1650cm-1 Water vapour profile, PAN, Ammonia (NH3), Nitrous oxide (N2O), Methane (CH4), volcanic SO2 0.130
IAS-7 1650–2100cm-1 Water vapour profile 0.449
IAS-8 2100–2180cm-1 Temperature profile, carbon monoxide (CO) profile 0.156
IAS-9 2180–2250cm-1 Temperature profile 0.26
IAS-10 2250–2420cm-1 Temperature profile 0.26
IAS-11 2420cm-1
Sea surface temperature, surface and cloud properties 0.26
IAS-12 2700cm-1
CH4 1.138

*NEΔT — Noise Equivalent Temperature change

IASI-NG scanning geometry

IASI-NG scans across the track in a step and scare mode, with each scan cycle consisting of 14 earth views, one cold space view and one black body view. The duration of a scan cycle is 15.6 seconds and the swath width is 2000km.

The scan pattern is such that on either side of the nadir, seven Earth views or Field of Regards (FOR) are placed symmetrically. The instrument scans left to right according to in-flight direction (Sunward). Each FOR contains 4×4 fields of view (FOV), which implies 14 X 16 FOVS per scan line. Each FOV has a 12km ground resolution corresponding to a satellite altitude range of 823–848km (dependent on latitudes). Detailed scanning characteristics of IASI-NG is shown in the figure.

IASI-NG scan pattern
Figure 2: IASI-NG scan pattern

Improvements in IASI-NG compared to IASI characteristics

Characteristics IASI-NG IASI
No. of spectral samples 16921 8461
Spectral resolution 0.25cm-1 0.50cm-1
Spectral Sampling 0.125cm-1 0.25cm-1