SMAP

SMAP (Soil Moisture Active Passive) is a NASA Earth science mission launched on 31 January 2015 from Vandenberg Space Force Base aboard a Delta II 7320-10C rocket ^[1]. The spacecraft, built jointly by JPL (bus) and NASA Goddard Space Flight Center (radiometer instrument), flies in a sun-synchronous dusk-dawn orbit at 685 km altitude with an 18:00 local solar time ascending node, completing a full ground-track repeat every eight days (117 orbits) while achieving near-global coverage in approximately three days ^[2].

The mission carries two L-band instruments sharing a 6 m diameter rotating reflector antenna that spins at 14.6 rpm to produce a 1000 km conical swath ^[2]. The L-band radiometer operates at 1.41 GHz and measures brightness temperatures; surface soil moisture is retrieved at 36 km resolution, with an enhanced algorithm producing estimates at 9 km ^[2]. Historically, the mission also carried an L-band radar operating at 1.26 GHz, designed to retrieve soil moisture at 3 km resolution; that instrument suffered a power supply failure in July 2015 after collecting approximately three months of science data and has not operated since ^[3]. The radiometer remains the sole operational science instrument as of June 2026 ^[2].

SMAP's primary data products include Level-2 surface soil moisture at 36 km and 9 km (radiometer-only retrievals), Level-3 daily composite soil moisture maps, a Level-3 freeze-thaw state product at 36 km, Level-4 root-zone soil moisture derived by model assimilation, and a Level-4 carbon net ecosystem exchange product ^[1]. A combined SMAP and Sentinel-1 product (L2_SM_SP) provides soil moisture at 3 km by fusing SMAP brightness temperatures with Sentinel-1 C-band radar backscatter ^[1]. Data are distributed through the NASA National Snow and Ice Data Center with a near-real-time latency of approximately three hours ^[1].

eoPortal reports a spacecraft dry mass of 686 kg and a total launch mass of 944 kg ^[4]. The three-year prime mission concluded in summer 2018; extended operations have continued since, reviewed on a three-year cycle ^[3]. NASA is the mission operator.