VO: What we think of snow depends a lot on where it falls.
If you live in the eastern U.S., maybe it's fun.
Or, maybe it's just a pain.
Kim: But if you live in parts of the world where they
depend on the water that's in the snow for a large
fraction of their total water that they use for drinking, agriculture,
for industry or for hydropower, the snow is
a very important natural resource. For example, in the western part of the United States,
80 to 90 percent of their renewable water comes from snow.
[music]
VO: Snow is one part of the cryosphere that many of us
have actually encountered before. But it also plays a critical role in
regulating the Earth's climate. Through decades of remote sensing,
NASA has kept a close eye on the ebb and flow of snow cover.
Hall: We now have a 52-year record of
snow cover in the Northern Hemisphere, and we can see
changes in the extent of snow cover over the
time period--particularly in the last few decades--where we can see that the snow
cover has been retreating. It's been melting a lot earlier in the springtime.
Osmanoglu: The extent is relatively easy to do and it has been done over the
years. What's tricky is though how thick is that snow. And
it's even trickier how much water is in that snow.
VO: That tricky part is known as the snow water equivalent, or how much water would actually
be in a layer of snow if it melted. NASA and its partners have taken
to the air to help solve this elusive mystery. First there's the
Airborne Snow Observatory, or ASO, a small
plane outfitted with a couple of instruments, one of which measures snow depth using
lidar. Lidar measures distance using light from lasers. Since
2014, ASO has flown over basins in California and
Colorado, taking before and after looks at snow depth.
Scientists subtract the snow-free summer data from the snow-on winter
data to get an idea of the snow depth. There's no single way to
measure all types of snow across the globe, and so NASA's other airborne
campaign, SnowEx, is testing different combinations of sensors.
This winter, SnowEx will test a new instrument, the Snow
Water Equivalent Synthetic Aperture Radar and Radiometer, or SWESARR.
Osmanoglu: SWESARR consists of two main components,
one of them being the radar and the second one being the radiometer.
Bonds: So with the radar providing the depth of the snow and the radiometer
providing the density of the snow, we can put those two things together and get the
snow water equivalent. Here in the chamber we're going to measure different radiation
patterns that are different frequencies and do some full system testing,
in this chamber. This chamber kind of enables us to isolate
various types of radiation and interference. In about a month,
we're going to take the instrument and mount it on a Twin Otter in the Grand Mesa in Colorado.
We're going to fly it over the Grand Mesa and take various different measurements.
This is what we call our engineering flight. VO: Making sure the sensors are calibrated
is key in order to face the challenges nature will throw at them.
Kim: Half of the area that gets covered by snow every winter contains trees
and forest. And the trees make it difficult for the sensors to
see the snow that's underneath the trees so it makes it difficult for us to measure
how much snow there is. After the snow has had a chance to sit on the
ground for a while, it gets denser and denser and denser over time and it changes.
Which is another reason why snow is very challenging to remotely sense,
it doesn't stay the same. It's constantly changing. [shovel digging]
Kim: One of the things that we often do in the field is go dig what we call
a snow pit. You literally dig a pit in the snow so we can see all the different
layers. The layering is very important. VO: All this digging is part of ground
truthing SnowEx, a way of matching up what the airborne instruments see and what
is actually sitting on the surface. The ultimate
goal of SnowEx is to figure out what the best combination of instruments
would be for a future satellite mission in order to get a global picture
of snow. Hall: We need to know how much snow is in a
snowpack. Because if we have too much snow and the snow melts
too fast, then you can get flooding. And if you don't
have enough snow or if the snow melts too early, that can lead
to a longer wildfire season, a more
intense drought, and we need to know these things for water resource
planning. [music]
Parkinson: After we
had a record that was about 15, 20 years long,
we started noticing that the extent of
the ice in the Arctic was getting smaller over time.
[music]
[silence]