Over the
last three years the National Oceanic and Atmospheric Administration's (NOAA) National Operational Hydrologic
Remote Sensing Center has begun combining multiple sources of data --
particularly satellite data -- to determine the amount of snow that falls in the United States, and how
much water will result from the inevitable melt-off.
But while
the accuracy of the Chanhassen, Minn.-based center's
predictions has increased dramatically, those who use the data would love to
see the government build a dedicated snow-cover remote sensing satellite that
would provide even better data.
"If that could come to pass, and we
were able to launch a satellite that could measure this data reliably, that
would be a huge breakthrough that would dramatically improve the science of
hydrology worldwide," said Tom Carroll, the center's director.
The center's chief responsibility is
to collect snow water equivalency data in the 31 states that are most affected by snow, Carroll said.
This data is important because it
can be used to predict when flooding will occur or whether there will be a
water shortage, according to Carroll. In the western
United
States, approximately 80 percent of the water supply comes from melted snow,
Carroll said, so the agricultural communities and cities are equally interested in data that can help them know what the
outlook is going to be for a particular time period.
Recipients
of the center's data include the National Weather Service, which uses it for
its river-flooding forecasts, and a variety of federal agencies, such as the
Army Corps of Engineers or the U.S. Geological Survey. Local municipalities and
entities such as the New York City Department of Environmental Protection,
businesses and private individuals, such as snowmobile users, also use the
data, Carroll said.
The center
amasses weather data from a variety of sources, including two terrestrial gamma
radiation detection systems. These are mounted on aircraft operated by NOAA
which take over 1,000 measurements each season, using the sensors to measure
the radiation emitted from the soil below. This can help determine how much snow is
blocking the materials in soil which normally give off radiation.
Data from
sensors aboard NOAA's Geostationary Operational Environmental Satellites (GOES)
and Polar Orbiting Environmental Satellites help measure how far snow cover has
extended, Carroll said.
The center also depends on
ground-based snow water equivalent measurements, which are collected by
everything from NOAA National Weather Service stations to volunteers. The
center develops "prediction models" and adjusts them based on the data it
observes to create a "best estimate" for how much snow water will accumulate in
a particular area, Carroll said.
"Nobody
else in the world does this," Carroll said.
The data amassed by the center is
turned into many products, Carroll said. The center produces everything from
charts to movie loops that can depict a series of daily
snapshots covering a particular region. Daily snow analyses with graphs and
texts are also produced. Those interested in the snow data can simply visit the
center's Web site (http://www.nohrsc.nws.gov/)
and obtain products for a specified
geographic region, Carroll said.
The
technology used by the center to get its data has evolved over the years,
beginning exclusively with airborne data in the early 1980s, adding satellite
data in the late 1980s and gradually shifting to a
more-encompassing prediction model incorporating all different types of data,
which has been used for about three years, Carroll said.
"What we've
found is with our enhanced best estimate, which uses the best snow information
possible, we've managed to reduce the errors associated with spring snow-melt
forecasts by as much as 80 percent over the past two years or so," Carroll
said.
Meteorlogix,
a Minneapolis-based company that provides weather forecasts to small
businesses, is among those who depend on the National Operational Hydrologic
Remote Sensing Center for data, according to Jim Block, its chief
meteorologist.
"We use it
to incorporate into the data sets we redistribute to our customers," Block
said. The company also incorporates data from the National Weather Service and
other sources. Meteorlogix serves entities such as individuals with
snow-plowing businesses, commercial airlines and those in the agricultural and
energy communities.
Meteorlogix
has used the center's data for about two years now, Block said, after relying
exclusively on a variety of National Weather Service-affiliated sources before
that.
"Over the last 10 years, the quality
of snow data from the National Weather Service's official sources was so poor
it was almost useless," Block said. "There's no question that the accuracy and
spatial coverage is far better than what we had before."
But Carroll
would like to see that accuracy improve even more.
"What we're
looking forward to is the potential of actually making snow water equivalent measurements
which are accurate, reliable, near real time and high resolution from space,"
Carroll said. "You can't even come close to doing that now."
While
optical satellite sensors can take images of snow cover, pictures taken by
satellites today cannot determine how much snow is in a particular area.
"You can't tell whether you're
looking at an inch or ten inches or 100 inches," Carroll said. "But you need to
know that if you're going to issue reliable spring forecasts.
That is why
Carroll is among the advocates for a dedicated mission to use a satellite to
collect the kind of images useful for snow data. Carroll has worked with NASA's
Jet Propulsion Laboratory in Pasadena, Calif., on the concept for a Cold Land
Processes Pathfinder Mission, which would spend three years collecting snow
water equivalent and snow water wetness data at 100-meter and 5-kilometer
resolution, though nothing has been proposed formally. Such a mission would
likely cost between $250 million and $300 million, and could either be
undertaken by NASA or the European Space Agency, Carroll said.
