February 7, 2024


Credits: Elodie Bransolle - CNES / Prodigima 2023.


Science issues

Besides the first priority of providing continuity in infrared spectra measurements but with improved radiometric and spectral performance to get more precise information on atmospheric structures for numerical weather prediction (NWP), the science objectives are focused on one side on essential climate variables (ECVs), including atmospheric profiles, clouds, aerosols, greenhouse gases and ozone, and on atmospheric composition to gain a better understanding of dynamic/chemical processes in the atmosphere, to support air quality monitoring and alerting extreme events (volcanic eruptions, fires, etc.).

IASI has huge potential for these applications.

Geophysics Products derived from IASI on METOP
Geophysics products derived from IASI on MetOp

Short studies have already been completed to demonstrate the extra potential of IASI-NG. A first report by LMD is available.

IASI-NG channels sensitivities and radiometric noise computed for the brightness temperature IASI channels sensitivities and radiometric noise computed for the brightness temperature
IASI-NG (left) and IASI (right) channels sensitivities
and radiometric noise computed for the brightness temperature
(mean for tropical atmospheres TIGR).

IASI-NG (left) and IASI (right) Temperature Jacoblans
IASI-NG (left) and IASI (right) Temperature Jacoblans
for the 2200-2220 cm-1 spectral band channels

Mission Objectives

The mission rationale for IASI-NG is derived from the CNES/EUMETSAT Mission Rationale and requirement Document.


The IASI-NG system, like the IASI series flying on MetOp satellite, aims at observing and measuring twice a day the spectrum of infrared radiation emitted by the Earth, from a low altitude sun-synchronous orbit, over a swath of 2,000 km. These measurements are compatible in terms of sampling, resolution, accuracy and overall performance with the mission objectives. IASI-NG is designed to provide invaluable information for numerical weather prediction (NWP) as well as for climate monitoring, atmospheric chemistry and, to a lesser extent, oceanography and hydrology.

The IASI-NG mission draws directly on the heritage of EPS IASI (Infrared Atmospheric Sounding Interferometer). The main IASI mission rationale is the measurement of temperature and moisture profiles in clear or partly cloudy scenes at high accuracy (1 K and 5%, respectively) at a vertical resolution in the lower troposphere of 1 km. The requirements are user-driven, but also take into account the heritage from similar missions such as IASI.

As a baseline, the minimum expected performance of the IASI-NG mission is that of the IASI mission.

The primary objective of the IASI mission was to support numerical weather prediction at regional and global scales, through the provision of level 1 radiances and:

  • 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 parameters
  • A number of atmospheric trace gases

Infrared soundings with high vertical, horizontal, vertical/spectral resolution greatly enhance the ability of National Meteorological Services (NMS) to initialize global and regional NWP models with realistic information on temperature and moisture.
The frequent availability of detailed temperature and moisture soundings would also help to fulfil other key requirements common to now-casting and very short-range forecast (VSRF) at regional scales:

  • Monitoring of instability, for early warning of convective intensity
  • Early warning for CAPE/convective instability
  • DCAPE (down draught intensity), for early warning of risks by downburst and severe outflow gusts
  • Cloud microphysical structure

The extent of wich these objectives are met will depend strongly on the space-time resolution of the IASI-NG mission, and is particularly critical at high latitudes where information from geostationary spacecraft is scarce or even totally lacking.

The secondary objective of the IASI-NG mission is to support pollution monitoring and air quality forecasting at global and regional scales with further trace gas measurements and the assessment of composition - climate interaction.

The IASI-NG mission also provides support to climate monitoring due to the importance of spectrally resolved infrared observations in the field of inter-sensor calibration and spectral corrections of irradiances.

The main users of the IASI-NG mission will be the WMO real-time users, i.e. NWP centres at National Meteorological Services and ECMWF. Operational now casting services of National Meteorological Services may also be users of the IRS mission. The IASI-NG mission is also relevant to non-real-time users, such as for climate monitoring and atmospheric chemistry.

IASI-NG is with the Microwave sounder and the imager the core of the EPS-SG mission. Use of the data from these instruments is important for meteorological and scientific applications. Some IASI-NG's features are compatible with other meteorological instruments. This refers to the simultaneous operation and identical geographical coverage for all instruments and co-registration between them.

Furthermore, co-registration better than 1 km is required between the IASI-NG sounder and the METImage imager.

The currently defined target life time for IASI-NG is seven years.

Under nominal conditions starting with the pre-operational assessment phase, the IASI-NG system, composed of the IASI-NG instrument and its ground segment, should allow a daily permanent coverage of at least 95% of the Earth without any significant systematic gap in coverage.

Over the Atlantic Ocean, Europe and the Mediterranean Sea, the objective is to reach 99% daily coverage.


Priority of Requirements

  1. Spectral and radiometric resolution shall have priority over spatial sampling distance, as long as the spatial sample equivalent diameter is less than the specified threshold value.
  2. Spectral resolution shall have priority over radiometric resolution for the atmospheric chemistry application, as long as the threshold values are not exceeded.
  3. Radiometric resolution shall have priority over spectral resolution for the NWP application.

Spectral Requirements

The IASI-NG shall cover the spectral range from 645 cm-1 to 2760 cm-1 (i.e. 3.62 µm to 15.5 µm). The IASI-NG band characteristics and priorities are listed in Table 1 and Table 2

Table 1: IASI band characteristics and priorities for NWP

Range (cm-1)
PurposePrioritySpectral Resolution
Radiometric Resolution
(NET@280 K)
IASI-1645 - 770Temperature profile10.35/0.175/0.0780.3/0.2/0.1
IASI-2770 - 1000Temperature and water-vapour profiles, SST, surfaces and cloud properties10.35/0.175/0.0780.15/0.1/0.05
IASI-31000 - 1070O3 column20.35/0.2/0.10.3/0.2/0.15
IASI-41070 - 1150Surfaces and cloud properties20.5/0.3/0.20.35/0.15/0.05
IASI-51150 - 1650Water vapour profile10.5/0.25/0.10.15/0.075/0.05
IASI-61650 - 2100Water-vapour profile10.5/0.25/0.10.6/0.3/0.1
IASI-82160 - 2250Temperature profile,20.5/0.3/0.10.3/0.2/0.1
IASI-92250 - 2420Temperature profile10.5/0.3/0.10.3/0.2/0.1
IASI-102420 – 2700SST, surfaces and cloud properties20.5/0.3/0.10.3/0.2/0.1
O: Objective, B: Breakthrough, T: Threshold

Table 2: IASI band characteristics and priorities for Atmospheric Chemistry

Range (cm-1)
PurposePrioritySpectral Resolution
Radiometric Resolution
(NET@280 K)
IASI-2a650 - 750C2H2, HCN30.3/0.225/0.150.25/0.14/0.07
IASI-2b750 - 850PAN30.3/0.225/0.150.25/0.14/0.07
IASI-2c850 - 920HNO320.3/0.15/0.0750.25/0.14/0.07
IASI-2d920 - 980NH3, C2H430.3/0.15/0.0750.25/0.14/0.07
IASI-3a1030 - 1080O3 profile10.3/0.15/0.0750.25/0.14/0.07
IASI-3b980 - 1080CH3OH30.3/0.15/0.0750.25/0.14/0.07
IASI-4a1080 - 1130HCOOH30.3/0.225/0.150.25/0.14/0.07
IASI-4b1120 - 1160Volcanic SO230.3/0.225/0.150.25/0.14/0.07
IASI-4c1130 - 1200PAN, NH330.3/0.225/0.150.25/0.14/0.07
IASI-5a1200 - 1360Temperature profile, and N2O, CH4 columns20.3/0.225/0.150.25/0.14/0.07
IASI-5b1340 - 1400Volcanic SO220.3/0.225/0.150.25/0.14/0.07
IASI-7a2140 - 2180CO profile10.3/0.15/0.0750.25/0.14/0.07
IASI-112700 - 2760CH4 column30.3/0.225/0.150.3/0.25/0.1