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A. Rango, A.E. Walker and B.E. Goodison
seasonal variability in microwave emission from the snowpack is to compile a time
series of satellite data spanning the entire season which can then be related to changes
in the pack over the season (Walker et a!., 1995).
SAR data has a major disadvantage of not being able to detect the dry snowpack.
Additionally, the SAR data is difficult to process with backscattering from rough
surfaces beneath the snow causing interpretation problems. The optimum bands
around 1 cm wavelength are not represented in any existing or planned SAR instrument.
Data AvaiJability and Platforms Used. Passive microwave data for hydrological and
climatological studies are available from sensors operated onboard NASA's Nimbus
7 (SMMR) and the US Defense Meteorological Satellites (DMSP). Massom (1991)
provides comprehensive details of the individual satellites. Data are archived and
available in a variety of formats at NSIDC; the EASE-Grid brightness temperature
product (Armstrong and Brodzik, 1995), a gridded 25km resolution global data set
(12.5 km at 85.5GHz) is particularly suited to historical hydrological analyses where
the user may wish to run different regional snow cover algorithms or integrate other
geophysical information. SSM/I data are available in near real-time for operational
hydrological applications from the NOAA National Environmental Satellite Data and
Information Services (NESDIS).
11.2.5 Related Applications
Hand-Drawn Snow Maps. It is possible to use a base map, such as a snow-free
Landsat image, and map the location of the snowline in a basin during an aircraft
overflight. This approach is even possible from the ground in a very small basin (say
less than several km 2 in area) by climbing to the highest point and visually transferring the area covered by snow to a base map. These techniques are most useful where
access to the basin or aircraft flights are easily arranged.
Photo interpretation. Where labor is inexpensive in certain developing countries, it
is still possible to take the photos from satellite overpasses and manually map the area
covered by snow and save a considerable amount of money. Computer systems have
become so reasonable in price, however, that the photo interpretive approach is no
longer used very much.
Frequency Modulated-Continuous Wave (FM-CW) Radar. In recent years FMCW radars of various types have found applications in snow and ice. Sturm et a!.
(1996) used an X-band FM-CW radar mounted on a towed sled to make dry snow
depth measurements in Alaska. Much care has to be taken in the data collection with
coincident field verification of the snow depths. With frequent field calibration, the
radar determined snow depths were accurate to about 2 cm. AKa-band FM-CW radar
was mounted on a helicopter to continuously measure the thickness profile of freshwater ice (Yankielun, 1992). The ice thickness resolution of this system is about 3 Cill.
There appear to be significant safety and trafficability applications for ponds, lakes,
and rivers using FM-CW radars.
A. Rango, A.E. Walker and B.E. Goodison
seasonal variability in microwave emission from the snowpack is to compile a time
series of satellite data spanning the entire season which can then be related to changes
in the pack over the season (Walker et a!., 1995).
SAR data has a major disadvantage of not being able to detect the dry snowpack.
Additionally, the SAR data is difficult to process with backscattering from rough
surfaces beneath the snow causing interpretation problems. The optimum bands
around 1 cm wavelength are not represented in any existing or planned SAR instrument.
Data AvaiJability and Platforms Used. Passive microwave data for hydrological and
climatological studies are available from sensors operated onboard NASA's Nimbus
7 (SMMR) and the US Defense Meteorological Satellites (DMSP). Massom (1991)
provides comprehensive details of the individual satellites. Data are archived and
available in a variety of formats at NSIDC; the EASE-Grid brightness temperature
product (Armstrong and Brodzik, 1995), a gridded 25km resolution global data set
(12.5 km at 85.5GHz) is particularly suited to historical hydrological analyses where
the user may wish to run different regional snow cover algorithms or integrate other
geophysical information. SSM/I data are available in near real-time for operational
hydrological applications from the NOAA National Environmental Satellite Data and
Information Services (NESDIS).
11.2.5 Related Applications
Hand-Drawn Snow Maps. It is possible to use a base map, such as a snow-free
Landsat image, and map the location of the snowline in a basin during an aircraft
overflight. This approach is even possible from the ground in a very small basin (say
less than several km 2 in area) by climbing to the highest point and visually transferring the area covered by snow to a base map. These techniques are most useful where
access to the basin or aircraft flights are easily arranged.
Photo interpretation. Where labor is inexpensive in certain developing countries, it
is still possible to take the photos from satellite overpasses and manually map the area
covered by snow and save a considerable amount of money. Computer systems have
become so reasonable in price, however, that the photo interpretive approach is no
longer used very much.
Frequency Modulated-Continuous Wave (FM-CW) Radar. In recent years FMCW radars of various types have found applications in snow and ice. Sturm et a!.
(1996) used an X-band FM-CW radar mounted on a towed sled to make dry snow
depth measurements in Alaska. Much care has to be taken in the data collection with
coincident field verification of the snow depths. With frequent field calibration, the
radar determined snow depths were accurate to about 2 cm. AKa-band FM-CW radar
was mounted on a helicopter to continuously measure the thickness profile of freshwater ice (Yankielun, 1992). The ice thickness resolution of this system is about 3 Cill.
There appear to be significant safety and trafficability applications for ponds, lakes,
and rivers using FM-CW radars.