Interest in Satellite Data on Snow Accumulation Grows

Over thelast three years the National Oceanic and Atmospheric Administration's (NOAA) National Operational HydrologicRemote 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 howmuch water will result from the inevitable melt-off.

But whilethe accuracy of the Chanhassen, Minn.-based center'spredictions has increased dramatically, those who use the data would love tosee the government build a dedicated snow-cover remote sensing satellite thatwould provide even better data.

"If that could come to pass, and wewere able to launch a satellite that could measure this data reliably, thatwould be a huge breakthrough that would dramatically improve the science ofhydrology worldwide," said Tom Carroll, the center's director.

The center's chief responsibility isto collect snow water equivalency data in the 31 states that are most affected by snow, Carroll said.

This data is important because itcan be used to predict when flooding will occur or whether there will be awater shortage, according to Carroll. In the western

UnitedStates, 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 theoutlook is going to be for a particular time period.

Recipientsof the center's data include the National Weather Service, which uses it forits river-flooding forecasts, and a variety of federal agencies, such as theArmy Corps of Engineers or the U.S. Geological Survey. Local municipalities andentities such as the New York City Department of Environmental Protection,businesses and private individuals, such as snowmobile users, also use thedata, Carroll said.

The centeramasses weather data from a variety of sources, including two terrestrial gammaradiation detection systems. These are mounted on aircraft operated by NOAAwhich take over 1,000 measurements each season, using the sensors to measurethe radiation emitted from the soil below. This can help determine how much snow isblocking the materials in soil which normally give off radiation.

Data fromsensors aboard NOAA's Geostationary Operational Environmental Satellites (GOES)and Polar Orbiting Environmental Satellites help measure how far snow cover hasextended, Carroll said.

The center also depends onground-based snow water equivalent measurements, which are collected byeverything from NOAA National Weather Service stations to volunteers. Thecenter develops "prediction models" and adjusts them based on the data itobserves to create a "best estimate" for how much snow water will accumulate ina particular area, Carroll said.

"Nobodyelse in the world does this," Carroll said.

The data amassed by the center isturned into many products, Carroll said. The center produces everything fromcharts to movie loops that can depict a series of dailysnapshots covering a particular region. Daily snow analyses with graphs andtexts are also produced. Those interested in the snow data can simply visit thecenter's Web site (http://www.nohrsc.nws.gov/)and obtain products for a specifiedgeographic region, Carroll said.

Thetechnology used by the center to get its data has evolved over the years,beginning exclusively with airborne data in the early 1980s, adding satellitedata in the late 1980s and gradually shifting to amore-encompassing prediction model incorporating all different types of data,which has been used for about three years, Carroll said.

"What we'vefound is with our enhanced best estimate, which uses the best snow informationpossible, we've managed to reduce the errors associated with spring snow-meltforecasts by as much as 80 percent over the past two years or so," Carrollsaid.

Meteorlogix,a Minneapolis-based company that provides weather forecasts to smallbusinesses, is among those who depend on the National Operational HydrologicRemote Sensing Center for data, according to Jim Block, its chiefmeteorologist.

"We use itto incorporate into the data sets we redistribute to our customers," Blocksaid. The company also incorporates data from the National Weather Service andother sources. Meteorlogix serves entities such as individuals withsnow-plowing businesses, commercial airlines and those in the agricultural andenergy communities.

Meteorlogixhas used the center's data for about two years now, Block said, after relyingexclusively on a variety of National Weather Service-affiliated sources beforethat.

"Over the last 10 years, the qualityof snow data from the National Weather Service's official sources was so poorit was almost useless," Block said. "There's no question that the accuracy andspatial coverage is far better than what we had before."

But Carrollwould like to see that accuracy improve even more.

"What we'relooking forward to is the potential of actually making snow water equivalent measurementswhich are accurate, reliable, near real time and high resolution from space,"Carroll said. "You can't even come close to doing that now."

Whileoptical satellite sensors can take images of snow cover, pictures taken bysatellites today cannot determine how much snow is in a particular area.

"You can't tell whether you'relooking at an inch or ten inches or 100 inches," Carroll said. "But you need toknow that if you're going to issue reliable spring forecasts.

That is whyCarroll is among the advocates for a dedicated mission to use a satellite tocollect the kind of images useful for snow data. Carroll has worked with NASA'sJet Propulsion Laboratory in Pasadena, Calif., on the concept for a Cold LandProcesses Pathfinder Mission, which would spend three years collecting snowwater equivalent and snow water wetness data at 100-meter and 5-kilometerresolution, though nothing has been proposed formally. Such a mission wouldlikely cost between $250 million and $300 million, and could either beundertaken by NASA or the European Space Agency, Carroll said.

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