The SMOS mission was born from the conjonction of new technological developments (ASTRIUM/MMS-DASA, CASA) and the modelling needs for meteorological prediction.
The instrument is based on a L-band interferometric radiometer (passive microwave, 1.4GHz) with an average spatial resolution of 43 km (30 to 50 depending on the view angle) and a repetition of 3 days at the equator (only ascending orbits).
The instrument concept is very original (VLBI, used by astrophysicists) and it benefits from the experience acquired during the development of an airplane- mounted version : MIRAS (for the preparation of the ESA mission). The instrument can be placed on a PROTEUS-type mini-satelllite platform.
SMOS is the first mission that observe the land surface with multi-angular measurementsin L-band.
Currently two projects are selected by NASA:
- 1. Aquarius measure ocean salinity with a precision of 0.2 PSU over a surface of 200X200 km2 every 10 days (the satellite repetition is 8 days with a long track of 300 km and a spatial resolution of 100 km). Aquarius has been launched in june 2011.
- 2. SMAP will provide a capability for global mapping of soil moisture and freeze/thaw state. The SMAP instrument includes a radiometer and a synthetic aperture radar operating at L-band (1.20-1.41 GHz). The instrument is designed to make coincident measurements of surface emission and backscatter, with the ability to sense the soil conditions through moderate vegetation cover. The instrument measurements will be analyzed to yield estimates of soil moisture and freeze/thaw state. The measurement swath width is 1000 km, providing global coverage within 3 days at the equator and 2 days at boreal latitudes (>45 degrees N).
These two projects are based on L-band radiometers.
In comparison, SMOS will provide both the ocean surface salinity (0.1 PSU over 200x 200 km2 every 10 days), and the superficial humidity (4% vol every3 days with an average spatial resolution of 43 km). The originality of SMOS comes from directional measurements used in order to determine the vegetation water content.