We had our share of snow this winter, but in New England it was an extremely snowy winter. So snowy, in fact, that flooding from snow melt will be a concern there this spring. Of course, to assess the flooding risk, you have to know how much water is locked up in the snowpack. These days, much of that information is measured from the air. Here's how it works.

Soil contains tiny amounts of rare elements such as uranium. These elements give off small amounts of a certain type of radiation - gamma radiation - and this can be measured from the air. But when snow is on the ground, the snow blocks some of this radiation from getting out. By comparing the measurements of gamma radiation made from bare ground with those from snow-covered ground, the amount of water in the snowpack can be estimated. This data is then fed to computer models that produce flood potential maps and forecasts.

Recent measurements show that in some places, there's nearly 10 inches of water locked up in the snowpack, and that has river forecasters in New England keeping a close watch on the weather.