SMAP Satellite

NASA Soil Moisture Mission Begins Science Operations

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High-resolution global soil moisture map from SMAP’s combined radar and radiometer instruments Southern U.S. SMAP soil moisture retrievals from April 27, 2015 High-resolution global soil moisture map from SMAP’s combined radar and radiometer instruments, acquired between May 4 and May 11, 2015 during SMAP’s commissioning phase. The map has a resolution of 5.6 miles (9 kilometers). The data gap is due to turning the instruments on and off during testing. Image Credit: NASA/JPL-Caltech/GSFC

NASA’s new Soil Moisture Active Passive (SMAP) mission to map global soil moisture and detect whether soils are frozen or thawed has begun science operations.
Launched Jan. 31 on a minimum three-year mission, SMAP will help scientists understand links among Earth’s water, energy and carbon cycles; reduce uncertainties in predicting climate; and enhance our ability to monitor and predict natural hazards like floods and droughts. SMAP data have additional practical applications, including improved weather forecasting and crop yield predictions.

A first global view of SMAP’s flagship product, a combined active-passive soil moisture map with a spatial resolution of 5.6 miles (9 kilometers), is available at:

During SMAP’s first three months in orbit, referred to as SMAP’s “commissioning” phase, the observatory was first exposed to the space environment, its solar array and reflector boom assembly containing SMAP’s 20-foot (6-meter) reflector antenna were deployed, and the antenna and instruments were spun up to their full speed, enabling global measurements every two to three days.

The commissioning phase also was used to ensure that SMAP science data reliably flow from its instruments to science data processing facilities at NASA’s Jet Propulsion Laboratory in Pasadena, California, and the agency’s Goddard Space Flight Center in Greenbelt, Maryland.

“Fourteen years after the concept for a NASA mission to map global soil moisture was first proposed, SMAP now has formally transitioned to routine science operations,” said Kent Kellogg, SMAP project manager at JPL. “SMAP’s science team can now begin the important task of calibrating the observatory’s science data products to ensure SMAP is meeting its requirements for measurement accuracy.”

Together, SMAP’s two instruments, which share a common antenna, produce the highest-resolution, most accurate soil moisture maps ever obtained from space. The spacecraft’s radar transmits microwave pulses to the ground and measures the strength of the signals that bounce back from Earth, whereas its radiometer measures microwaves that are naturally emitted from Earth’s surface.

“SMAP data will eventually reveal how soil moisture conditions are changing over time in response to climate and

Southern U.S. SMAP soil moisture retrievals from April 27, 2015, when severe storms were affecting Texas. Top: radiometer data alone. Bottom: combined radar and radiometer data with a resolution of 5.6 miles (9 kilometers). The combined product reveals more detailed surface soil moisture features.

how this impacts regional water availability,” said Dara Entekhabi, SMAP science team leader at the Massachusetts Institute of Technology in Cambridge. “SMAP data will be combined with data from other missions like NASA’s Global Precipitation Measurement, Aquarius and Gravity Recovery and Climate Experiment to reveal deeper insights into how the water cycle is evolving at global and regional scales.”

The new global image shows dry conditions in the southwestern United States and in Australia’s interior. Moist soil conditions are evident in the U.S. Midwest and in eastern regions of the United States, Europe and Asia. The far northern regions depicted in these SMAP maps do not indicate soil moisture measurements because the ground there was frozen.

Zooming in on the data allows a closer look at the benefits of combining SMAP’s radar and radiometer data. A segment of a SMAP orbit covering the central and southern United States on April 27 is available at:

The upper part of the image shows the radiometer-based estimate of soil moisture at a spatial resolution of 22.5 miles (36 kilometers). The lower part of the image shows the active-passive, or merged high-resolution (5.6 miles, or 9 kilometers), radar- and radiometer-derived soil moisture product.

In the days prior to this data collection, intense rainstorms pounded northern Texas. The areas affected by the storm in northern Texas and the Gulf Coast are visible in much greater detail. Such detail can be used to improve local weather forecasts, assist in monitoring drought in smaller watersheds, and forecast floods.

Over the next year, SMAP data will be calibrated and validated by comparing it against ground measurements of soil moisture and freeze/thaw state around the world at sites representing a broad spectrum of soil types, topography, vegetation and ground cover. SMAP data also will be compared with soil moisture data from existing aircraft-mounted instruments and other satellites.

Preliminary calibrated data will be available in August at designated public-access data archives, including the National Snow and Ice Data Center in Boulder, Colorado, and Alaska Satellite Facility in Fairbanks. Preliminary soil moisture and freeze/thaw products will be available in November, with validated measurements scheduled to be available for use by the general science community in the summer of 2016.

NASA uses the vantage point of space to increase our understanding of our home planet, improve lives and safeguard our future. NASA develops new ways to observe and study Earth’s interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing.

For more information on SMAP, visit:

For more information about NASA’s Earth science activities, visit:

NASA SMAP Observatory Ready for Launch

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PRESS RELEASE (JPL) – The launch of NASA’s Soil Moisture Active Passive (SMAP) mission at Vandenberg Air Force Base (VAFB) in California is scheduled for Thursday, Jan. 29. Liftoff from Space Launch Complex 2 aboard a United Launch Alliance Delta II rocket is targeted for 6:20:42 a.m. PST (9:20:42 a.m. EST) at the opening of a three-minute launch window. If needed, a backup launch opportunity is available on the Western Range on Jan. 30 with the same launch window.

SMAP is the first U.S. Earth-observing satellite designed to collect global observations of surface soil moisture and its freeze/thaw state. High-resolution space-based measurements of soil moisture and whether the soil is frozen or thawed will give scientists a new capability to better predict natural hazards of extreme weather, climate change, floods and droughts, and will help reduce uncertainties in our understanding of Earth’s water, energy and carbon cycles.

The mission will provide the most accurate and highest-resolution maps of soil moisture ever obtained, mapping the globe every two to three days from space for a least three years. The spacecraft’s final circular polar orbit will be 426 miles (685 kilometers) at an inclination of 98.1 degrees. The spacecraft will orbit Earth once every 98.5 minutes and will repeat the same ground track every eight days.

Technology Innovations Spin NASA’s SMAP into Space

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It’s active. It’s passive. And it’s got a big, spinning lasso.

Scheduled for launch on Jan. 29, 2015, NASA’s Soil Moisture Active Passive (SMAP) instrument will measure the moisture lodged in Earth’s soils with an unprecedented accuracy and resolution. The instrument’s three main parts are a radar, a radiometer and the largest rotating mesh antenna ever deployed in space.

Remote sensing instruments are called “active” when they emit their own signals and “passive” when they record signals that already exist. The mission’s science instrument ropes together a sensor of each type to corral the highest-resolution, most accurate measurements ever made of soil moisture — a tiny fraction of Earth’s water that has a disproportionately large effect on weather and agriculture.

To enable the mission to meet its accuracy needs while covering the globe every three days or less, SMAP engineers at NASA’s Jet Propulsion Laboratory in Pasadena, California, designed and built the largest rotating antenna that could be stowed into a space of only one foot by four feet (30 by 120 centimeters) for launch. The dish is 19.7 feet (6 meters) in diameter.

“We call it the spinning lasso,” said Wendy Edelstein of NASA’s Jet Propulsion Laboratory, Pasadena, California, the SMAP instrument manager.

Like the cowboy’s lariat, the antenna is attached on one side to an arm with a crook in its elbow. It spins around the arm at about 14 revolutions per minute (one complete rotation every four seconds). The antenna dish was provided by Northrop Grumman Astro Aerospace in Carpinteria, California. The motor that spins the antenna was provided by the Boeing Company in El Segundo, California.

“The antenna caused us a lot of angst, no doubt about it,” Edelstein noted. Although the antenna must fit during launch into a space not much bigger than a tall kitchen trash can, it must unfold so precisely that the surface shape of the mesh is accurate within about an eighth of an inch (a few millimeters).

The mesh dish is edged with a ring of lightweight graphite supports that stretch apart like a baby gate when a single cable is pulled, drawing the mesh outward. “Making sure we don’t have snags, that the mesh doesn’t hang up on the supports and tear when it’s deploying — all of that requires very careful engineering,” Edelstein said. “We test, and we test, and we test some more. We have a very stable and robust system now.”

SMAP’s radar, developed and built at JPL, uses the antenna to transmit microwaves toward Earth and receive the signals that bounce back, called backscatter. The microwaves penetrate a few inches or more into the soil before they rebound. Changes in the electrical properties of the returning microwaves indicate changes in soil moisture, and also tell whether or not the soil is frozen. Using a complex technique called synthetic aperture radar processing, the radar can produce ultra-sharp images with a resolution of about half a mile to a mile and a half (one to three kilometers).

SMAP’s radiometer detects differences in Earth’s natural emissions of microwaves that are caused by water in soil. To address a problem that has seriously hampered earlier missions using this kind of instrument to study soil moisture, the radiometer designers at NASA’s Goddard Space Flight Center, Greenbelt, Maryland, developed and built one of the most sophisticated signal-processing systems ever created for such a scientific instrument.

The problem is radio frequency interference. The microwave wavelengths that SMAP uses are officially reserved for scientific use, but signals at nearby wavelengths that are used for air traffic control, cell phones and other purposes spill over into SMAP’s wavelengths unpredictably. Conventional signal processing averages data over a long time period, which means that even a short burst of interference skews the record for that whole period. The Goddard engineers devised a new way to delete only the small segments of actual interference, leaving much more of the observations untouched.

Combining the radar and radiometer signals allows scientists to take advantage of the strengths of both technologies while working around their weaknesses. “The radiometer provides more accurate soil moisture but a coarse resolution of about 40 kilometers [25 miles] across,” said JPL’s Eni Njoku, a research scientist with SMAP. “With the radar, you can create very high resolution, but it’s less accurate. To get both an accurate and a high-resolution measurement, we process the two signals together.”

SMAP will be the fifth NASA Earth science mission launched within the last 12 months.

For more about the SMAP mission, visit:

NASA monitors Earth’s vital signs from space, air and land with a fleet of satellites and ambitious airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth’s interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.

For more information about NASA’s Earth science activities this year, visit:

Media Contact

Alan Buis
Jet Propulsion Laboratory, Pasadena, California

Written by Carol Rasmussen
NASA Earth Science News Team