Astronomers use radio telescopes to study distant stars and galaxies.
They use a band of microwave frequencies reserved for scientists
studying the heavens and the earth.
By international treaty there are no transmissions allowed in this band, so I can't set up a television transmitter,
say, and operate here. It's dedicated, set aside,
for what we call "passive use," or in this case the microwave radiometer
listening to the natural signals from the Earth.
NASA is using this band to study the water content of soil for its
Earth-observing SMAP mission, which stands for "Soil Moisture Active Passive."
The "active passive" part really refers to the instrument,
so the active portion is a microwave radar,
and the passive portion is a microwave radiometer that we built here at Goddard Space Flight Center.
Every molecule naturally gives off or absrobs microwave energy
to maintain a balance with its surroundings. The amount given off
by the soil depend on its temperature and its water content. The molecules in the soil
with the water, they're bouncing around off of each other and emitting microwaves.
The dry soil lets out a lot of these microwaves and the wetter soil lets out
fewer of these microwaves. The challenge is that the neighboring bands
have radars and communications systems
and those transmissions can unintentionally leak into our spectrum.
So we had to develop dedicated technology for SMAP
to try to separate out the
natural signals from the earth and the human-made signals
that we don't want. The signals that we want
the SMAP radiometer to listen to, they vary slowly in time.
they are very broadband. And in fact what they are is,
it sounds like - if you were to hook up a radio receiver and listen to it
yourself, it would sound like noise, it would sound like static.
So we look for signals that don't look like static and that's what we want to throw away
and keep the static for ourselves.
So the team here at Goddard developed specialized hardare and software.
It separates out the signals that the radiometer receives in time and frequency
and for every spot on the ground,
looks for outliers and if it sees those, it just removes them from the measurement.
Throws away the bad, keeps the good, and produces the data
to give us good measurements of soil moisture here today
to allow us to improve weather forecasting, drought and flood predictions,
and forecast crop yields better.