12.6 Snow Survey

12.6 Snow Survey

As snow cover has a very high reflectance, the aerial distribution of snow can be identified very easily from satellite remote sensing data. Several models to estimate water resources in units of snow water equivalent have been proposed with use of the estimated snow cover area.

Figure 12.6.1 shows a conceptual diagram of the estimation of basin-wide snow water equivalent with the three parameters of elevation h, latitudinal distribution of snow water equivalent S(h) and hydrometric curve A(h).

Snow water equivalent Ss in a river basin can be computed as follows.

where hH : maximum elevation
hL: minimum elevation

If snow appears over the average elevation of snow line ho, hL should be replaced by ho.

From the above formula, the latitudinal distribution of snow water equivalent S(h) and the hydrometric curve A(h) should be determined in order to estimate the snow water equivalent.

It is known that the snow water equivalent increases linearly proportional to the elevation, which can ve obtained from the existing snow survey. On the other hand the catchment area can be expressed in lower order of polynomials as a function of elevation. Therefore the snow water equivalent can be estimated as a function of percentage of snow cover area in a river basin.

Figure 12.6.2 shows an estimated curve of snow water equivalent which was obtained from sample data in the three years of 1979, 1982 and 1983 in the Takaragawa River Basin, Japan. From the curve, the snow water equivalent can be estimated if the snow cover area is detected from remote sensing imagery (see a series of examples, Figure 12.6.3(a), (b) and (c)).

Recently microwave remote sensing has been applied to estimate snow volume. Passive microwave radiometers can provide snow surface temperature with respect to inductivity of the snow, which may provide snow information. Active microwave radar can provide reflectivity or scattering of snow with respect to snow density, snow temperature, snow temperature, size of snow particles etc. It is still difficult to estimate snow volume from microwave data but several research projects are currently being carried out on this topic.