Climatology of snow cover and snow water equivalent

• Chapter II: Physical snow characteristics determined from space
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• Satellite instruments' sensitivity
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• Snow detection in the visible spectrum
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• Snow detection in the infrared spectrum
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• Snow detection in the microwave spectrum
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• Factors which may lead to misidentification of snow

Snow detection in the visible spectrum

The reflectance values of different surfaces can be plotted as functions of wavelength called "spectral response curves" or "spectral signatures" (Fig. 1). Differences among the spectral signatures of landscape features are used to classify remotely sensed regions, since the spectral signatures of similar features have similar shapes. Snow cover has a high surface reflectance in the visible part of the spectrum (VIS), and is represented as a white region in visible images. However, in the visible spectrum, it may be difficult to distinguish snow from other Earth features, such as clouds or bright sand. Snow retrieval from optical satellite measurements requires clear skies and sufficient daylight. This limits the applicability of satellite measurements for snow detection. In short-wave infrared (SWIR) snow has a low reflectance and this enables distinguishing between snow and other bright surfaces.

Figure 1: Reflectances of different surfaces. Credit: Andreas Kaab, University of Oslo.