IASI

The main goal of the IASI mission is to provide temperature and humidity profiles for use in the understanding and making atmospheric forecasts.

IASI image, from CNES, large

IASI is the main payload instrument for the purpose of supporting Numerical Weather prediction. It provides information on the vertical structure of the atmospheric temperature and humidity in an unprecedented accuracy of 1 K and a vertical resolution of 1 km, which is needed to decisively improve NWP. The use of Metop data in NWP accounts for 40% of the impact of all space based observations in NWP forecasts.

Dieter Klaes, EPS Programme Scientist at EUMETSAT, explains: "When first launched on Metop-A, in 2006, IASI was a world-leading instrument. It was the first polar-orbiting interferometer providing huge amounts of operational data. The impact on NWP was enormous, much higher than anticipated."

What is IASI?

IASI measures in the infrared part of the electromagnetic spectrum at a horizontal resolution of 12 km over a swath width of about 2,200 km. With 14 orbits in a sun-synchronous mid-morning orbit (9:30 Local Solar Time equator crossing, descending node) global observations can be provided twice a day.

Technical details

IASI Summmary Budget

A graphic showing the field of view of IASI

The temperature of the troposphere and lower stratosphere is measured under cloud-free conditions with a vertical resolution of 1 km in the lower troposphere; a horizontal resolution of 25 km, and an accuracy of 1 kelvin.

The humidity of the troposphere is measured under cloud-free conditions, with a vertical resolution of 1–2 km in the lower troposphere; a horizontal resolution of 25 km, with an accuracy of 10%.

IASI also measures the fractional cloud cover and cloud top temperature and pressure.

The total amount of ozone under cloud-free conditions is measured with a horizontal resolution of 25 km and an accuracy of 5%, and total column-integrated content of CO, CH4 and N2O with an accuracy of 10% and a horizontal resolution of 100 km.

Why is IASI so important?

The IASI instrument has led to an increase in knowledge of atmospheric composition monitoring, as well as volcanic ash detection. It was observed that during volcanic eruptions SO2, values exceeded initial expectations.

Cathy Clerbaux, from the SAF on Ozone and Atmospheric Chemistry Monitoring, said: "IASI has provided unprecedented atmospheric chemistry data, allowing near-real-time mapping of chemical species and aerosols, contributing to air traffic safety and to our understanding of atmospheric transport processes.

"Observations from IASI have unexpectedly allowed the detection from space of volatile chemical species, providing an ability to map sources and sinks of gases, such as ammonia. It has already been shown that IASI exhibits sensitivity to the change in quantities of greenhouse gases, can be used to study cloud and aerosol properties, and will provide information on a range of other climate variables."

Global ammonia distribution derived from infrared satellite observations (Nature)

Dieter Klaes explains: "Additional products derived from IASI include Sea Surface Temperature (SST) at a high accuracy, and Surface Emissivity, the latter still a matter of further research and improvement. The continuity provided by Metop-B, for the coming years (its nominal life time is five years), means we can continue the valuable service to our users and continue to develop more products for and with our users. For weather forecasters worldwide the data IASI on Metop-B will provide, along with similar data from the new CrIS (Cross-track Infrared Sounder) instrument on Suomi-NPP — in cooperation with our partner NOAA — will be invaluable."

The IASI programme is led by CNES in association with EUMETSAT. Alcatel Alenia Space is the instrument Prime Contractor. For more in-depth information, see the IASI Level 1 Product Guide (PDF, 3 MB).

IASI Summary Budgets
Scan Rate 8 secs
Scan Type Step and dwell
Pixel IFOV 0.8225°
IFOV size at Nadir S12 km
Sampling at Nadir 18 km
Earth View Pixels/Scan Two rows of 60 pixels each
Swath ± 48.98°
Swath ± 1066 km
Spectral Range 645 to 2760 cm-1
Spectral Sampling 0.25 cm-1
Lifetime Five years
Power 210 W
Size 1.2 m x 1.1 m x 1.3 m
Mass 236 kg
Data rate 1.5 Mbps