By identifying how much moisture is retained in soils, hydrologists will be able to determine how much more water can be absorbed, and thus better estimate the potential for flooding or how much water sinks into the water table.

During July and August, the U.S. Southwestern monsoon season is characterized by a wind pattern shift that exerts a strong influence on precipitation and temperatures across the Western United States, Mexico and adjacent ocean areas. This change in winds over the region creates many rainy days and heavy rainfall, which are ideal conditions for studying soil moisture.

The study, called the Soil Moisture Experiment 2004, or SMEX04, will use ground teams, airplanes and NASA satellites and instruments to measure soil moisture in Tombstone, Ariz., and Sonora, Mexico, where water supplies are critical.

Researchers from NASA, USDA, NOAA, Sonora Research Institute and more than a dozen universities will be on the ground and in the air with advanced technology to get a better read on soil moisture.

SMEX scientists also want to know what atmospheric conditions create long-lasting rainfalls over a large area. By knowing which factors create large or small rainfall, hydrologists can provide better forecasts and know how much water will be available to people.

"The Western U.S. relies on water from the Southwestern monsoon system to fill its aquifers. Accurate measurements of soil moisture will assist in better water supply forecasts associated with the monsoon in the water-scarce western U.S," said Tom Jackson, USDA Agricultural Research Service hydrologist and lead for SMEX.

From space, NASA's Aqua, Terra and QuikScat satellites will provide various measurements. Aqua's Advanced Microwave Scanning Radiometer (AMSR-E) instrument will measure soil moisture; Terra's Moderate Resolution Spectroradiometer (MODIS) will provide vegetation status; and Terra's Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) will measure the surface temperature.

The SeaWinds instrument on the QuikScat satellite will observe the monsoon winds that bring in the moisture from the Pacific Ocean to the U.S. Southwest.

Closer to Earth, microwave radiometers on the Naval Research Laboratory P-3 aircraft and the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) on NASA's ER-2 high-altitude aircraft will fly over the areas to measure soil moisture.

AVIRIS will also help test new methods for remotely sensing water content in plants. Meanwhile, ground instruments will measure the temperature and percentage of moisture in soils from 2 to 40 inches deep. The satellite, airplane and ground data will be compared.

The SMEX04 mission adds to two prior SMEX experiments in 2002 and 2003, and is part of the larger North American Monsoon Experiment (NAME), led by NOAA, which is dedicated to understanding how the Southwestern U.S. monsoon season works.

Monsoons need to be accurately understood and predicted by weather and climate models, because their influence on seasonal weather, including floods and droughts, can significantly disrupt regional economies and populations.

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