As we know, snow is one of the forms of precipitation; however, hydrologist treats it differently

due to the temporal difference between the time of its fall and the time of its runoff, groundwater

recharge, and the fact that it is a part of various hydrological processes. The hydrological point

of view in relation with the snow is mostly considered in middle to high latitudes and mountainous

regions, where often melt period sometimes lasts for months following seasonal accumulation of

snowpack. During this accumulation period, there is a very small amount or no snow

melt. Precipitation (sometimes rain) falls and is temporarily retained as snowpack until the melt

season starts. It is mandatory for the hydrology to record how much amount of water is collected in

a basin in the form of snow. For a better knowledge of the hydrology of mountainous

terrain, detailed assessment of the areal distribution of snow, its quality, and the presence of

liquid water in it is also necessary. All of these snow indications are difficult to quantify and

measure, and they will most certainly differ from one location to the next.

Remote sensing (RS) provides a new tool for obtaining snow data for predicting snow and glacier

melt runoff. Researchers have manually collected snow data manually through snow- related

courses, which are labor-intensive, expensive, and potentially dangerous. Even when

accessible, snow course data represents simply a location in the region and can only be used as an

index of the available snow water content. Despite the fact that measurements are

considered automated, the difficulty of a single point measurement or observation of snow being

typical of a broader area or basin persists. It is one of the most easily identifiable forms of water resources

utilising aerial photography or satellite imaging in the case of remotely sensed snow data.

Satellite systems can currently only determine the area covered by snow, the depth of the snow, and

the snow water equivalent; physical snow parameters cannot be monitored directly by these satellite

systems.

The considerable amount of freshwater has been present in the nature in snow and glacier form in

the River basins which are, in most of the cases, located in high mountainous areas. Many other

water resources like lakes, Rivers, streams etc. are fed by the outflow of water from these

glaciers. The estimated glacier area in the world has about 14.9 x 10⁶ km², which is approximately

10% of the overall land area present on the earth (Singh and Singh, 2001). Although just 3% of this

snow is scattered over mountainous regions on many continents and even beyond the polar regions, it

serves a critical role in delivering water to the majority of the world's population. It has been

observed that the Himalayan mountains have a big contribution in freshwater supply

globally. Major Rivers present in south Asia certainly originate from the Himalayan mountain

systems. Among them, the Ganga, Indus, and Brahmaputra are said to be the lifeline of the Indian

sub-continent. Snow and glacier melt runoff also contribute to the Himalayan Rivers flow.