250
A. Rango, A.E. Walker and B.E. Goodison
product makes it useful on basins or sub-areas greater than 200 km 2 in area (Rango
et aI., 1985), and various users employ the data to assist in hydrological forecasting
using models. NOHRSC products are continually under development, and the latest
products and services can be accessed by visiting their World Wide Web homepage
at http://www.nohrsc.nws.gov.
In addition to producing operational snow cover extent data, NOHRSC also produces operational airborne gamma radiation snow water equivalent data. The difference between the NOHRSC airborne radiation measurements over bare ground and
snow covered ground is used to calculate a mean areal snow water equivalent value
with a root mean square error ofless than one cm (Carroll, 1995). Immediately after
each airborne snow survey, the snow water equivalent derived for each flight line are
used in a GIS to generate a contoured surface of snow water equivalent for the region
of the survey. After each survey, users of the data are able to operationally obtain by
electronic means a contour map of snow water equivalent in the region and the mean
areal snow water equivalent for each basin in the region.
11.3.2 Canadian Prairie Snow Water Equivalent Mapping
In Canada, a federal government program (Climate Research Branch, Atmospheric
Environment Service) has been ongoing since the early 1980's to develop, validate
and apply passive microwave satellite data to determine snow extent, snow water
equivalent and snowpack state (wet/dry) in Canadian regions for near real-time and
operational use in hydrological and climatological applications. Goodison and Walker
(1995) provide a summary of the program, its algorithm research and development,
and future thrusts. For the prairie region a snow water equivalent algorithm was
empirically derived using airborne microwave radiometer data (Goodison et aI.,
1986), and tested and validated using Nimbus-7 SMMR and DMSP SSM/I satellite
data (Goodison, 1989).
With the launch of the first SSMII on the DMSP F-8 satellite in 1987, came the
ability to access passive microwave data in near real-time and generate snow cover
products for users within several hours after data acquisition. Since 1989, the Climate
Research Branch prairie SWE algorithm has been applied to near-real time SSM/I
data to generate weekly maps depicting current SWE conditions for the provinces of
Alberta, Saskatchewan and Manitoba in western Canada. Thirkettle et aI. (1991)
describe the procedures for data acquisition, processing and mapping of the SWE
information. The prairie maps are disseminated by fax machine (see Fig. 1l.3) to
water resource agencies and meteorological offices throughout the prairie region
where they are used to monitor snow cover conditions, plan for field surveys, and
make forecasts regarding spring water supply conditions including potential flooding
or drought. In the winter and spring of 1994, the maps were particularly useful for
monitoring the high SWE conditions in southern Manitoba and North Dakota preceding the devastating Red River flood (Warkentin, 1997).
After 10 winter seasons in operation, the Canadian prairie SWE mapping program
has successfully demonstrated a useful application of SSMII derived snow cover
information for operational hydrological analyses. It is also a cooperative program in
A. Rango, A.E. Walker and B.E. Goodison
product makes it useful on basins or sub-areas greater than 200 km 2 in area (Rango
et aI., 1985), and various users employ the data to assist in hydrological forecasting
using models. NOHRSC products are continually under development, and the latest
products and services can be accessed by visiting their World Wide Web homepage
at http://www.nohrsc.nws.gov.
In addition to producing operational snow cover extent data, NOHRSC also produces operational airborne gamma radiation snow water equivalent data. The difference between the NOHRSC airborne radiation measurements over bare ground and
snow covered ground is used to calculate a mean areal snow water equivalent value
with a root mean square error ofless than one cm (Carroll, 1995). Immediately after
each airborne snow survey, the snow water equivalent derived for each flight line are
used in a GIS to generate a contoured surface of snow water equivalent for the region
of the survey. After each survey, users of the data are able to operationally obtain by
electronic means a contour map of snow water equivalent in the region and the mean
areal snow water equivalent for each basin in the region.
11.3.2 Canadian Prairie Snow Water Equivalent Mapping
In Canada, a federal government program (Climate Research Branch, Atmospheric
Environment Service) has been ongoing since the early 1980's to develop, validate
and apply passive microwave satellite data to determine snow extent, snow water
equivalent and snowpack state (wet/dry) in Canadian regions for near real-time and
operational use in hydrological and climatological applications. Goodison and Walker
(1995) provide a summary of the program, its algorithm research and development,
and future thrusts. For the prairie region a snow water equivalent algorithm was
empirically derived using airborne microwave radiometer data (Goodison et aI.,
1986), and tested and validated using Nimbus-7 SMMR and DMSP SSM/I satellite
data (Goodison, 1989).
With the launch of the first SSMII on the DMSP F-8 satellite in 1987, came the
ability to access passive microwave data in near real-time and generate snow cover
products for users within several hours after data acquisition. Since 1989, the Climate
Research Branch prairie SWE algorithm has been applied to near-real time SSM/I
data to generate weekly maps depicting current SWE conditions for the provinces of
Alberta, Saskatchewan and Manitoba in western Canada. Thirkettle et aI. (1991)
describe the procedures for data acquisition, processing and mapping of the SWE
information. The prairie maps are disseminated by fax machine (see Fig. 1l.3) to
water resource agencies and meteorological offices throughout the prairie region
where they are used to monitor snow cover conditions, plan for field surveys, and
make forecasts regarding spring water supply conditions including potential flooding
or drought. In the winter and spring of 1994, the maps were particularly useful for
monitoring the high SWE conditions in southern Manitoba and North Dakota preceding the devastating Red River flood (Warkentin, 1997).
After 10 winter seasons in operation, the Canadian prairie SWE mapping program
has successfully demonstrated a useful application of SSMII derived snow cover
information for operational hydrological analyses. It is also a cooperative program in