NASA has soil moisture covered

NASA plans to launch a satellite that will be able to accurately measure moisture content over most of the Earth’s surface.

Using data from NASA’s Aqua satellite — due to launch in December 2001 — scientists hope to be able to map the moisture content of soils over most of the Earth’s surface. This information will also improve forecasts of potential rainfall and other meteorological factors such as winds, temperature and humidity.

‘What this improved information on current soil moisture means for farmers is that we can improve long range weather forecasting and consequently improve forecasts of crop yields,’ said Bill Crosson, a scientist with the Universities Space Research Association (USRA) working through NASA’s Global Hydrology and Climate Centre (GHCC). ‘The key is a combined system through which we obtain global data on soil moisture and integrate it into weather prediction models.’

Farmers will be able to use the data and the potentially improved long-range weather forecasts to help plan growing seasons, schedule crop irrigation, prevent excessive fertiliser use, and predict plant strength and resistance.

‘When the soil is dry, there is less water for plant nutrition — but there is also less evaporation, and drier soil heats up faster,’ Crosson said. ‘There is a direct link between soil moisture and atmospheric humidity. Both humidity and rising heated air affect local and regional temperatures and winds.’

Until recently, environment and climate measurements were either on a small scale involving ground-based readings on fields less than one kilometre square — or they looked at huge areas of oceans and continents from space.

Now scientists will attempt to fill in the void for local areas and regional zones with more diverse and accurate remote sensing techniques, said Charles Laymon, another USRA scientist working on the project.

‘Any farmer can stick his finger in the soil to measure soil moisture, but there is no global context in that,’ Crosson noted. ‘He doesn’t know the large scale moisture patterns that influence the future weather for his fields. A wet patch in one corner of a field, or a dried-out hilltop, reveals little about the farm’s imminent crop productivity — especially if he’s farming thousands of acres.’

The instrument on Aqua that will sense soil moisture is called the Advanced Microwave Scanning Radiometer-EOS (AMSR-E, dubbed ‘amser’).

The Aqua satellite — the second in a series of satellites called NASA’s Earth Observing System (EOS) — will have an orbit that covers the globe every 16 days during a planned six-year mission life. AMSR-E’s moving ‘footprint’ will be about 25-by-25-kilometers.

The deployment of AMSR-E will, according to NASA, mark a bold step in applied soil moisture research.

Other past and present space-based instruments obtained some soil moisture data, but were not specifically designed for that purpose. Crosson and Laymon said that what was once a practice of ‘using the wrong tool for the right task’ is now being replaced with designed and targeted observations.

‘Putting microwave scanning radiometer technology to use in the Earth Observing System is an important step for soil hydrology,’ concluded Laymon. ‘Combining the diverse long-term daily observations of land, oceans and atmosphere by EOS will produce knowledge that ultimately improves everyone’s quality of life by improving the way we use natural resources. ‘

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