SMOS

SMOS (Soil Moisture and Ocean Salinity) is an ESA Earth Explorer mission launched on 2 November 2009 from Plesetsk Cosmodrome, Russia, aboard a Rockot/Breeze-KM vehicle ^[1]. It is the second ESA Earth Explorer Opportunity mission (EE-2) ^[1]. ESA describes MIRAS as the first satellite instrument to carry a 2D interferometric synthetic-aperture radiometer in orbit ^[1]. The spacecraft is built on the Proteus bus developed by Thales Alenia Space and CNES, with a total launch mass of 658 kg ^[1].

The sole instrument is MIRAS (Microwave Imaging Radiometer using Aperture Synthesis), a Y-shaped interferometric array built by a consortium of more than 20 European companies led by EADS CASA Espacio (Spain). MIRAS carries 69 L-band receivers distributed across three arms and a central hub, operating at 1.413 GHz (21 cm wavelength) ^[1]. Aperture synthesis combines signals across the array to reconstruct brightness temperature images with a spatial resolution of 35 to 50 km over a swath of approximately 1050 km ^[1]. Global coverage repeats on a 3-day sub-cycle within a 23-day exact repeat orbit ^[1].

SMOS flies in a sun-synchronous dusk-dawn orbit at a mean altitude of 758 km, with a 98.44 degree inclination and a 06:00 ascending node ^[1]. Primary science products include Level-2 and Level-3 surface soil moisture (0-5 cm depth) at 35 to 50 km resolution, Level-2 and Level-3 sea surface salinity, a Level-3 soil freeze-thaw state product, sea ice thickness estimates, and ocean surface wind speed ^[2]. Near-real-time products are available for operational users ^[2]. Data are distributed through the ESA SMOS Online Dissemination service and the Copernicus Data Space Ecosystem ^[2].

Designed for a five-year mission (three-year nominal plus a two-year extension) ^[1], SMOS has operated significantly beyond its design life and continues to return science data as of June 2026 ^[3]. ESA has extended the mission multiple times; a new Level-3 soil freeze-thaw product was published in June 2025, confirming continued operations ^[3]. ESA is the mission operator.