| | IASI overview
The Infrared Atmospheric Sounding Interferometer (IASI) consists of a Fourier Transform Spectrometer based on a Michelson Interferometer, coupled to an integrated imaging system which allows characterisation of cloudiness inside the spectrometer field of view. The instrument provides spectra of high radiometric quality at
0.5 cm-1 resolution, from 645 to 2760 cm-1. Data samples are taken at intervals of 25 km along and across track (nadir), each sample having a maximum diameter of about 12 km.
The scan duration of eight seconds and the horizontal spacing of the full Earth views are identical to those of the AMSU-A instrument. This facilitates synergistic use of the two instruments.
The imager of the IASI samples the sounder pixels with a kilometric spatial resolution. This enables registration with the AVHRR/3 instrument.
IASI measurements
The IASI system aims at observing and measuring the infrared spectrum emitted by the earth. These measurements are compatible in terms of sampling, resolution, accuracy and overall performances with the mission objectives of providing information on:
- the profile of temperature in the troposphere and lower stratosphere with an accuracy of 1K, a vertical resolution of 1 km in the low troposphere and an horizontal sampling of 25 km
- the profiles of water vapour in the troposphere with an accuracy of 10% on relative humidity, a vertical resolution of 1 km in the lower troposphere and an horizontal sampling of 25 km
- the total amount of ozone with an accuracy of 5% and an horizontal sampling of typically 25 km, possibly also ozone vertical distribution with an accuracy of 10% and a vertical resolution providing two or three pieces of independent information
- fractional cloud cover and cloud top temperature/pressure
- sea and land surface temperatures
In addition, IASI has the ability to measure the total column content of the main greenhouse gas. It will supply valuable data for scientific studies to achieve a closer understanding of climate processes and to represent them better in global models.
| Geophysical variables | Vertical resolution | Horizontal resolution | Accuracy | | Temperature profile | 1 Km
(low Troposphere) | 25 Km
(cloud free) | 1K
(cloud free) | | Humidity profile | 1-2 Km
(low Troposphere) | 25 Km
(cloud free) | 10%
(cloud free) | | Ozone total amount | Integrated content | 25 Km
(cloud free) | 5%
(cloud free) | | CO, CH4, N2O | Integrated content | 100 Km | 10%
(cloud free) |
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IASI fields of View
Interferometer
The IASI interferometer field of view is square, seen under an angle of 3.33 x 3.33°. Information matrix of 2 x 2 circular pixels seen under an angle of 1.25°. The overall swath is ± 48.3° with respect to the nadir direction, corresponding to 30 mirror positions.
Imager
The IASI imager field of view is based on an array matrix, analysing a square field that is slightly larger than the interferometer one.
Last update: 23 December 2005 | |
