Soil Moisture Active Passive (SMAP) Soil Moisture Active Passive (SMAP) About Mission Objectives
Launched on 31 January 2015, the NASA Soil Moisture Active Passive (SMAP) mission is designed to principally measure soil moisture and freeze/thaw state from space for all non-liquid water surfaces globally within the top layer of the Earth. The mission additionally provides a value-added Level 4 terrestrial carbon dataset derived from SMAP observations.
SMAP is now also building upon the legacy of Aquarius/SAC-D mission in delivering both soil moisture and derived sea surface salinity (SSS) observations for the world’s oceans. With the loss of the Aquarius mission on 7 June 2015 it became critical also to continue the time series of global salinity observations important to studies of the Earth’s water cycle. Because both Aquarius and SMAP shared a L-band feed-horn configuration, lessons learned from the algorithm development under the Aquarius mission could be applied to SMAP to retrieve SSS via SMAP. However, because of the larger swath coverage, spatial resolutions under SMAP are approximately 40 km instead of 100 km with Aquarius. The increased spatial coverage provides opportunities for applying SMAP data for higher resolution studies than Aquarius. With the initiation of SMAP science operations and data flows in April of 2015, the approximate 3-month overlap period between SMAP and Aquarius also allows for inter-calibration and comparative studies.
The primary SMAP salinity datasets include a Level 2 orbital dataset, in which data granules contain both the ascending and descending arcs of the orbit, and two Level 3 gridded datasets: an 8-day running average (linked to the day repeat cycle of SMAP) and monthly average. SMAP SSS data are archived and distributed via the PO.DAAC. SMAP soil moisture and L4 carbon datasets are available from the National Snow and Ice Data Center (NSIDC), with Level 1 SMAP radar data distributed by the Alaska Satellite Facility (ASF). These DAACs are the official NASA repositories for SMAP mission data.
Instruments
Radiometer – L-band microwave radiometer to measure the brightness temperature of microwave emissions from the ocean surface with a center frequency of 1.41 GHz.Radar – L-band (1.26 GHz) radar to measure the echoes of very short radio frequency (RF) pulses that bounce ("backscatter") off the Earth's surface. The radar uses a special technique known as "synthetic aperture" to resolve the RF backscatter over much smaller surface areas that would otherwise be possible.
Documentation
Current Dataset Versions
Prior Dataset Versions
Other Technical Documents
Known Issues
Related Links
References
Brown, D., R. Gran, A. Buis, 2015. International Spacecraft Carrying NASA’s Aquarius Instrument Ends Operations. NASA press release 15-126, June 17, 2015. http://www.nasa.gov/press-release/international-spacecraft-carrying-nasa...
Meissner, T, FJ Wentz, D LeVine, J. Scott, 2014a, Aquarius Salinity Retrieval Algorithm Theoretical Basis Document (ATBD) , Addendum 3, report number 060414, Remote Sensing Systems, Santa Rosa, CA, 24 pp.
Meissner, T, FJ Wentz, L Ricciardulli, 2014b, The emission and scattering of L-band microwave radiation from rough ocean surfaces and wind speed measurements from Aquarius , Journal of Geophysical Research: Oceans, 119, doi:10.1002/2014JC009837.
Piepmeier, J. R., P. N. Mohammed, J. Peng, E. J. Kim, G. De Amici, and C. Ruf, 2015. SMAP L1B Radiometer Half-Orbit Time-Ordered Brightness Temperatures. [data used: antenna temperatures after RFI mitigation]. Boulder, Colorado USA: NASA National Snow and Ice Data Center Distributed Active Archive Center. http://dx.doi.org/10.5067/1V33MVRRLCCT .
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