Soil Moisture Active Passive

Soil Moisture Active Passive
Soil Moisture Active Passive illustration (15-180, cropped).jpg
An artist rendering of the Soil Moisture Active Passive spacecraft.
Mission typeEarth observation
COSPAR ID2015-003A
SATCAT no.40376
Mission duration3 years (nominal) [1]
Elapsed: 6 years, 7 months, 19 days
Spacecraft properties
ManufacturerJet Propulsion Laboratory
Launch mass944 kg
Payload mass79 kg
Dimensions1.5 x 0.9 x 0.9 m
Power1450 watts
Start of mission
Launch date31 January 2015, 14:22 (2015-01-31UTC14:22) UTC [2]
RocketDelta II 7320-10C [3]
Launch siteVandenberg, SLC-2W
ContractorUnited Launch Alliance
Entered serviceAugust 2015
Orbital parameters
Reference systemGeocentric
Perigee altitude680.9 km
Apogee altitude683.5 km
Period98.5 minutes
Epoch15 October 2019, 23:39:39 UTC[4]
An animation of SMAP's trajectory around Earth from 31 January 2015 to 19 August 2015:
  SMAP ·   Earth

Soil Moisture Active Passive (SMAP) is a NASA environmental monitoring satellite launched on 31 January 2015.[2] It was one of the first Earth observation satellites developed by NASA in response to the National Research Council's Decadal Survey.[5][6]

NASA's investment is of US$916 million (design, development, launch, and operations).[7]

Mission overview[]

SMAP provides measurements of the land surface soil moisture and freeze-thaw state with near-global revisit coverage in 2-3 days. SMAP surface measurements are coupled with hydrologic models to infer soil moisture conditions in the root zone. These measurements enable science applications users to:

  1. Understand processes that link the terrestrial water, energy, and carbon cycles.
  2. Estimate global water and energy fluxes at the land surface.
  3. Quantify net carbon flux in boreal landscapes.
  4. Enhance weather and climate forecast skill.
  5. Develop improved flood prediction and drought monitoring capability.

SMAP observations are acquired for a period of at least three years after launch, and the 81 kg of propellant that it carries should allow the mission to operate well beyond its design lifetime. A comprehensive validation, science, and the application program are implemented, and all data are publicly available through the NASA archive centers.

Measurement concept[]

The SMAP observatory includes a dedicated spacecraft and instrument suite in a near-polar, Sun-synchronous orbit. The SMAP measurement system consists of a radiometer (passive) instrument and a synthetic-aperture radar (active) instrument operating with multiple polarizations in the L-band range. The combined active and passive measurement approach takes advantage of the spatial resolution of the radar and the sensing accuracy of the radiometer.[8]

The active and passive sensors provide coincident measurements of the surface-emission and backscatter. The instruments sense conditions in the top 5 cm of soil through moderate vegetation cover to yield globally mapped estimates of soil moisture and its freeze-thaw state.

The spacecraft orbits Earth once every 98.5 minutes and repeats the same ground track every eight days.[7]

Scientific payload[]

The satellite carries two scientific instruments: a radar and a radiometer, that share a single feed and deployable 6 m reflector antenna system, built by Northrop Grumman,[9] that rotates around the nadir axis making conical scans of the surface. The wide swath provides near-global revisit every 2-3 days.

SMAP system characteristics[]

Characteristic Radar Radiometer
Frequency 1.2 GHz 1.41 GHz
Polarizations VV, HH, HV V, H, U
Resolution 1-3 km[a] 40 km
Antenna diameter 6 m
Rotation rate 14,6 rpm
Incidence angle 40°
Swath width 1000 km
Orbit Near Polar, Sun-synchronous
Local time des. node 06:00 
Local time asc. node 06:00 
Altitude 685 km

Auxiliary Payloads[]

Educational Launch of Nanosatellite X (ELaNa X), consisting of three Poly Picosatellite Orbital Deployers containing four CubeSats (three CubeSat missions), mounted on the second stage of the Delta II launch vehicle:[7]

The CubeSat projects are deployed at a minimum of 2,896 seconds after the separation of the Soil Moisture Active Passive observatory, into a 440 x 670 km, 99.12° inclination orbit.[7]

Program description[]

SMAP is a directed mission of the National Aeronautics and Space Administration. The SMAP project is managed for NASA by the Jet Propulsion Laboratory, with participation by the Goddard Space Flight Center. SMAP builds on the heritage and risk reduction activities of NASA's cancelled ESSP Hydros Mission.[10]

Science and applications[]

SMAP observations are used to characterize hydrologic and ecosystem processes including land-atmosphere exchanges of water, energy, and carbon. Among the users of SMAP data are hydrologists, weather forecasters, climate scientists and agricultural and water resource managers.[11] Additional users include fire hazard and flood disaster managers, disease control and prevention managers, emergency planners and policy makers.[11] SMAP soil moisture and freeze-thaw information directly benefit several societal applications areas, including:

Weather and climate forecasting[]

Initialization of numerical weather prediction models and seasonal climate models with accurate soil moisture information extend forecast lead times and enhance prediction skill.


SMAP soil moisture information improves the monitoring and forecasting of drought conditions, enabling new capabilities for mitigating drought impacts.

Floods and landslides[]

Hydrologic forecast systems calibrated and initialized with high-resolution soil moisture fields lead to improved flood forecasts and provide essential information on the potential for landslides.

Agricultural productivity[]

Soil moisture observations from SMAP lead to improvements in crop yield forecasts and enhance the capabilities of crop water stress decision support systems for agricultural productivity.[11]

Human health[]

Improved seasonal soil moisture forecasts directly benefit famine early warning systems. Benefits also are realized through improved predictions of heat stress and virus spread rates, and improved disaster preparation and response.


In August 2015, scientists completed their initial calibration of the two instruments on board, however, SMAP's radar stopped transmitting 7 July due to an anomaly that was investigated by a team at JPL.[12] The team identified the anomaly to the power supply for the radar's high-power amplifier.[13][14] On 2 September 2015, NASA announced that the amplifier failure meant that the radar could no longer return data. The science mission continues with data being returned only by the radiometer instrument.[15] SMAP's prime mission ended in June 2018. The 2017 Earth Science senior review endorsed the SMAP mission for continued operations through 2020, and preliminarily, through 2023.[16]

See also[]


  1. ^ Over outer 70% of swath


  1. ^
  2. ^ a b "NASA SMAP "Here I go!!!!"". NASA/Jet Propulsion Laboratory. 31 January 2015. Retrieved 31 January 2015.
  3. ^ Ray, Justin (16 July 2012). "NASA gives the Delta 2 rocket a new lease on life". Spaceflight Now. Retrieved 17 July 2012.
  4. ^ "SMAP - Orbit". Heavens-Above. 15 October 2019. Retrieved 16 October 2019.
  5. ^ O'Neill, Peggy; et al. (2010). The NASA Soil Moisture Active Passive (SMAP) Mission: Overview. 30th IEEE International Geoscience and Remote Sensing Symposium. 25-30 July 2010. Honolulu, Hawaii. NASA. hdl:2060/20110015242.
  6. ^ "Decadal Survey". NASA. Archived from the original on 25 August 2009.
  7. ^ a b c d e f g "Soil Moisture Active Passive Launch" (PDF). January 2015. Retrieved 20 February 2020. Public Domain This article incorporates text from this source, which is in the public domain.
  8. ^ "Instrument". Soil Moisture Active Passive. NASA/Jet Propulsion Laboratory. Retrieved 19 April 2015.
  9. ^
  10. ^ Bélair, Stéphane; et al. Science Plan and Possible Canadian Contributions to the Soil Moisture Active and Passive (SMAP) Mission (PDF). International Workshop on Microwave Remote Sensing for Land Hydrology: Research and Applications. 20-22 October 2008. Oxnard, California. Canadian Space Agency. Archived from the original (PDF) on 13 April 2009. As SMAP was emerging from the ashes of HYDROS in 2007, CSA exchanged with NASA on the possibility of renewing their partnership. CSA, in collaboration with other Canadian Government Departments, is currently developing plans regarding possible scientific and technical contributions to the new mission. The scientific activities would include both government and academic partners.
  11. ^ a b c Buis, Alan (15 October 2014). "NASA Soil Moisture Mapper Arrives at Launch Site". NASA/Jet Propulsion Laboratory. Retrieved 24 October 2014.
  12. ^ Buis, Alan (5 August 2015). "NASA's SMAP Releases First Calibrated Data". NASA/Jet Propulsion Laboratory. Retrieved 10 August 2015.
  13. ^ Buis, Alan (5 August 2015). "SMAP Team Investigating Radar Instrument Anomaly". NASA/Jet Propulsion Laboratory. Retrieved 11 August 2015.
  14. ^ Clark, Stephen (10 August 2015). "NASA troubleshoots radar outage on new SMAP satellite". Spaceflight Now. Retrieved 11 August 2015.
  15. ^ Cole, Steve & Buis, Alan (2 September 2015). "NASA Soil Moisture Radar Ends Operations, Mission Science Continues". NASA. Retrieved 2 September 2015.
  16. ^

External links[]