NASA satellite mission to map Earth's soil moisture (Forwarded)

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April 28, 2008

Mapping Earth's soil moisture

Entekhabi to lead science team for NASA satellite mission

By Denise Brehm, Civil and Environmental Engineering

Professor Dara Entekhabi will lead the science team designing a NASA
satellite mission to collect global soil moisture measurements and other
data seen as key to improving weather, flood and drought forecasts and
predictions of agricultural productivity and climate change.

At present, scientists have no network for gathering soil moisture data as
they do for rainfall, winds, humidity and temperature. Instead, that data is
gathered only at a few scattered points around the world. But NASA's Soil
Moisture Active-Passive mission (SMAP), scheduled to launch in December
2012, aims to change that.

"Soil moisture is the lynchpin of the water, energy and carbon cycles over
land. It is the variable that links these three cycles through its control
on evaporation and plant transpiration. Global monitoring of this variable
will allow a new perspective on how these three cycles work and vary
together in the Earth system," said Entekhabi, Bacardi and Stockholm Water
Foundations Professor.

"Additionally, because soil moisture is a state variable that controls both
water and energy fluxes at the land surface, we anticipate that assimilation
of the global observations will improve the skill in numerical weather
prediction, especially for events that are influenced by these fluxes at the
base of the atmosphere," added Entekhabi, who holds joint appointments in
MIT's Department of Civil and Environmental Engineering and the Department
of Earth, Atmospheric and Planetary Sciences and is also director of the
Parsons Laboratory for Environmental Science and Engineering.

The SMAP mission is based on an earlier satellite project led by Entekhabi
that had been selected by NASA from among 20 proposals and scheduled for a
2009 launch. However, the Hydrosphere State Mission (Hydros) was cancelled
abruptly in 2005 when funding for NASA's earth sciences missions was
diverted. But in July 2007, the National Research Council recommended that
NASA make the soil moisture measurement project a top priority and place it
on a fast track for launch. The Jet Propulsion Laboratory in Pasadena,
Calif., is the lead NASA center for the project.

SMAP's launch in 2012 is feasible in part because Entekhabi and other
scientists continued to develop the mission, even when NASA's support was
withdrawn in 2005.

The instruments that will be deployed in SMAP will gather both passive and
active low-frequency microwave measurements on a continuous basis,
essentially creating a map of global surface soil moisture. A 6-meter
deployable mesh antenna on a satellite will gather data across a swath of
1,000 kilometers, creating ribbons of measurements around the globe and
completing the cycle every few days.

In addition to measuring soil moisture, the satellite will detect if the
surface moisture is frozen. In forests, the freeze/thaw state determines the
length of the growing season and the balance between carbon assimilation
into biomass and the loss of carbon due to vegetation respiration. The
result of this balance can tell scientists if a forest is a net source or
net sink of carbon.

One mission obstacle that Entekhabi and team solved last year was
integrating the two types of measurements the satellite would gather:
passive measurements collected by radiometer, and active collected by radar.
The radiometer measurements provide highly accurate data at a coarse
resolution of 40 kilometers. The radar measurements provide much higher
resolution (3 kilometers), but with less sensitivity. The combination of the
two measurements through algorithms designed by the SMAP science team will
result in accurate mapping of global soil moisture at 10 kilometers.

RELATED LINK

* Soil Moisture Active-Passive (SMAP) mission
http://smap.jpl.nasa.gov/