WRAL WeatherCenter Blog

Launch delayed for soil monitoring station

Posted January 28, 2015
Updated January 29, 2015

SMAP's antenna spins every four seconds providing overlapping loops 1,000 km wide making a complete moisture map of the Earth's surface every 2-3 days.

The Thursday morning launch of a the Soil Moisture Active Passive (SMAP) observatory from the Vandenberg Air Force Base was delayed by bad weather.

NASA said it would plan to try again Friday to get the Delta II 7320-10C rocket to push the satellite into a near-polar, sun-synchronous orbit providing complete coverage of the Earth's surface and ensuring the sun is at the same angle each time the observatory passes over a particular point.

SMAP will monitor soil moisture and its freeze/thaw state. This may seem like a mundane thing to measure so closely, but the ground’s water content is a critical part of our climate. Evaporation is the predominant way that land sheds the solar energy it receives every day. Because of the large amount of heat exchanged as water changes phase from solid to liquid to gas, the water cycle is fundamental to the Earth’s energy cycle. As the universal solvent, water is also central to the nitrogen, carbon, methane and other biogeochemical cycles.

Soil moisture has been a part of weather forecasting models for years, but data has been spotty at best. While precipitation and temperatures change from day to day and hour to hour, soil moisture is much more long lived. SMAP will provide global data that will better quantify energy exchange between the land and atmosphere. This is a key input to weather and climate models. Additional users of the data from this mission include those managing fire hazards, flood disasters, disease control and prevention and emergency planners.

The “Active Passive” portion of the title comes from the instrument that actively emit signals in the microwave frequency range and measures backscatter. A passive radiometer also measures the Earth’s own naturally emitted microwave signals. Variations in these signals provide insight into changes in soil moisture. Data will be downlinked to tracking stations in Alaska, Norway, Antarctica and Wallops Island, Va.

SMAP draws from previous work on the Hydrosphere State Mission (Hydros) mission which was canceled in 2005 amid budget cuts. Algorithms and instruments developed for Hydros gave Jet Propulsion Laboratory (JPL) scientists a head start in developing SMAP. Data from the satellite will be made available publicly through the National Snow and Ice Data Center in Boulder, Colo., and an Alaska Satellite Facility in Fairbanks.

The spacecraft includes a unique 19.7-foot (6-meter) scanning reflector antenna made of a lightweight mesh that will be unfurled in orbit. The antenna will scan a width of about 620 miles (1,000 km) of the Earth’s surface every four seconds. Higher latitudes will be mapped by the observatory every two days and equatorial regions every three days.

The launch also includes a trio of nano-satellites developed by students. A California Polytechnic State University-designed space weather satellite measuring about 3x3x12 inches will measure hydrogen, oxygen, helium and nitrogen in the Earth’s upper atmosphere. A similarly sized satellite developed by the University of Michigan’s Exploration Laboratory will measure pollution in the upper atmosphere, paving the way for the future larger scale Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission. And a 6x4x4-inch Firebird-II cubesat developed by the University of New Hampshire and Montana State University will study electron bursts in the Van Allen radiation belts surrounding Earth.

Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and software engineer at Cisco Systems. You can follow him on twitter @rtphokie.


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  • Tony Rice Jan 30, 2015
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    New launch time is 6:20 am PST (9:20 am EST) Check NASATV for coverage of the launch

  • Tony Rice Jan 29, 2015
    user avatar

    Upper level winds have forced a scrub for today. They'll try again tomorrow