The National Operational Hydrologic Remote Sensing Center (NOHRSC) has developed,
and currently maintains, an operational Airborne Gamma Radiation Snow Survey Program
to make airborne Snow Water Equivalent (SWE) and soil moisture measurements.
Airborne SWE measurements are used by NWS Weather Forecast Offices (WFO) and
NWS River Forecast Centers (RFC) when issuing river and flood forecasts, water supply
forecasts, and spring flood outlooks. Each flight line is typically 16 km long and 300 m
wide, covering an area of approximately 5 sq. km. Consequently, each airborne snow water
equivalent measurement is a mean areal measure integrated over the 5 sq. km. area of the
flight line. More background on this program is provided on the NOHRSC web site at:
An airborne gamma snow water equivalent (SWE) data collection program was initiated in Alaska in August of 2002 with the collection of background gamma radiation data on 107 flight lines. Additional flight line background data were collected in summer of 2003 to complete the initial set of flight lines (see map below). Associated soil moisture data were collected and analyzed. To see a list of the Alaska flight lines, click here.
Detailed maps showing locations of flight lines are available for three locations:
Flight lines are flown in mid-April to evaluate the water equivalent of the
snowpack on the flight line. The pilots disseminate products each evening following the flight.
Standard dissemination of the data is via a SHEF encoded product that lists the
flight line number, date, percent of snow cover on the flight line, average SWE for the flight
line, and other supportive information that may include comments by the pilots about snow
or ice conditions in the vicinity of the flight line. A guide for interpreting the SHEF message
can be found at: http://www.nohrsc.nws.gov/html/opps/asw_key.htm.
The pilots also take digital photos
during the flights if conditions warrant. All the products on the NOHRSC web site on the
airborne snow survey page and clicking on Alaska Snow Survey in the table in the middle of the page: