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Astronomers use radio telescopes to study distant stars and galaxies.

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They use a band of microwave frequencies reserved for scientists

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studying the heavens and the earth.

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By international treaty there are no transmissions allowed in this band, so I can't set up a television transmitter,

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say, and operate here. It's dedicated, set aside,

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for what we call "passive use," or in this case the microwave radiometer

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listening to the natural signals from the Earth.

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NASA is using this band to study the water content of soil for its

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Earth-observing SMAP mission, which stands for "Soil Moisture Active Passive."

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The "active passive" part really refers to the instrument,

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so the active portion is a microwave radar, 

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and the passive portion is a microwave radiometer that we built here at Goddard Space Flight Center.

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Every molecule naturally gives off or absrobs microwave energy

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to maintain a balance with its surroundings. The amount given off

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by the soil depend on its temperature and its water content. The molecules in the soil

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with the water, they're bouncing around off of each other and emitting microwaves.

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The dry soil lets out a lot of these microwaves and the wetter soil lets out

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fewer of these microwaves. The challenge is that the neighboring bands

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have radars and communications systems

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and those transmissions can unintentionally leak into our spectrum.

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So we had to develop dedicated technology for SMAP

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to try to separate out the 

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natural signals from the earth and the human-made signals

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that we don't want. The signals that we want

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the SMAP radiometer to listen to, they vary slowly in time.

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they are very broadband. And in fact what they are is,

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it sounds like - if you were to hook up a radio receiver and listen to it

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yourself, it would sound like noise, it would sound like static.

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So we look for signals that don't look like static and that's what we want to throw away

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and keep the static for ourselves.

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So the team here at Goddard developed specialized hardare and software.

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It separates out the signals that the radiometer receives in time and frequency

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and for every spot on the ground,

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looks for outliers and if it sees those, it just removes them from the measurement.

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Throws away the bad, keeps the good, and produces the data

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to give us good measurements of soil moisture here today

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to allow us to improve weather forecasting, drought and flood predictions,

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and forecast crop yields better.

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