NASA SMAP.Satellite's Spinning Lasso to Map Soil Moisture

The SMAP Spacecraft and Antenna

Daily Satellite News - NASA...How Does A Satellite's Spinning Lasso Determine The Moisture In The Soil? With An Extraordinary Antenna
[SatNews]

Launching in January 2015, NASA's Soil Moisture Mapping satellite (SMAP) will track water in the soil. Data gathered with help forecast weather, floods, drought, crop yield and landslides - all from outer space.

"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."We call it the spinning lasso." ..."that the mesh doesn't hang up on the supports and tear when it's deploying—all of that requires very careful engineering. We test, and we test, and we test some more. We have a very stable and robust system now."
Scheduled for launch on January 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.

SMAP : Mission Description
Objectives: SMAP will provide global measurements of soil moisture and its freeze/thaw state. These measurements will be used to enhance understanding of processes that link the water, energy and carbon cycles, and to extend the capabilities of weather and climate prediction models. SMAP data will also be used to quantify net carbon flux in boreal landscapes and to develop improved flood prediction and drought monitoring capabilities. >> science
Observatory: The SMAP observatory employs a dedicated spacecraft with an instrument suite that will be launched on an expendable launch vehicle into a 680-km near-polar, sun-synchronous orbit, with equator crossings at 6 am and 6 pm local time.
Instrument: The SMAP instrument includes a radiometer and a synthetic aperture radar operating at L-band (1.20-1.41 GHz). The instrument is designed to make coincident measurements of surface emission and backscatter, with the ability to sense the soil conditions through moderate vegetation cover. The instrument measurements will be analyzed to yield estimates of soil moisture and freeze/thaw state. The measurement swath width is 1000 km, providing global coverage within 3 days at the equator and 2 days at boreal latitudes (>45 degrees N). >> more

 SMAP : Instrument Specifications

Radar

• Frequency: 1.26 GHz
• Polarizations: VV, HH, HV (not fully polarimetric)
• Relative accuracy (3 km grid): 1 dB (HH and VV), 1.5 dB (HV)
• Data acquisition:
• High-resolution (SAR) data acquired over land
• Low-resolution data acquired globally

Radiometer

• Frequency: 1.41 GHz
• Polarizations: H, V, 3rd & 4th Stokes
• Relative accuracy (30 km grid): 1.3 K
• Data collection:
• High-rate (sub-band) data acquired over land
• Low-rate data acquired globally

Antenna

• Conically-scanning deployable mesh reflector shared by radar and radiometer
• Diameter: 6 meters
• Rotation rate: 14.6 RPM
• Beam efficiency: ~90%
• Spatial Resolution:
• Radiometer (IFOV): 39 km x 47 km
• SAR: 1-3 km (over outer 70% of swath)
• Swath width: 1000 km