TN-40 : Metamorphism and remote sensing physics of snow

Abstract

Snow and ice are significant elements of the world hydrological system, which occur subject to tremendous variation space.

After the snow is deposited the particle shapes are modified by a process known as metamorphism. Thus dendritic crystals decompose into fragments and the larger fragments grow at the expense of the smaller ones. This process continues until the fragments have been reduced to more or less rounded grains of ice or until a significant temperature gradient develops within the pack. Snowflakes undergo a rapid metamorphism that reduces their surface area and brings them to a more stable thermodynamic state.

Since vapour pressure is temperature dependent, temperature gradients produce associated vapour pressure gradients, which cause water vapour to diffuse from warmer to colder parts of the snowpack. Metamorphism can also result from compaction caused by the pressure of overlying layers of snow. This process is responsible for transforming snow into glacial ice whose crystals sometimes attain sizes of the order of 10 cm. (Langham, 1981).

In case of snow, crystal size, temperature, liquid water, density, thickness vary within a short distance to a great extent. So the field measurements about snow which are point data may be misleading. Besides, the snow bound areas are remote and hazardous to access. Remote sensing techniques offer an excellent synoptic view in various spectral channels of electromagnetic spectrum which serve as a spatial data base for snow related studies.

Spectral reflectivity of snow is dependent on snow parameters such as grain size, and shape, impurity content, near surface liquid water content, depth and surface roughness, as well as solar elevation. Freshly fallen snow has a very high reflectance in the visible wavelength, but decreases as it ages. Thermal-infrared portion of the electromagnetic spectrum enables to the observations in the night-time passes of the satellite.

Microwave measurements have the capability to penetrate the snow and respond to variations in sub-surface properties. It permits remote observations of snow under nearly all weather and lighting conditions.

The objective of the report is to apply remote sensing studies on the metamorphism of snow. The report highlights the various remote sensing techniques available for the study of snow parameters. The reflectance goes down as density increases, as snow undergoes metamorphism.