**Remote Sensing of Cryosphere**

Shrinidhi Ambinakudige and Kabindra Joshi *Mississippi State University USA* 

#### **1. Introduction**

368 Remote Sensing – Applications

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The cryosphere is the frozen water part of the Earth's system. The word is derived from the Greek "kryos," meaning cold. Snow and ice are the main ingredients of the cryosphere and may be found in many forms, including snow cover, sea ice, freshwater ice, permafrost, and continental ice masses such as glaciers and ice sheets. Snow is precipitation made up of ice particles formed mainly by sublimation (NSIDC, 2011). Ice is the key element in glaciers, ice sheets, ice shelves and frozen ground. Sea ice forms when the ocean water temperature falls below freezing. Permafrost occurs when the ground is frozen for a long period of time, at least two years below 00 C, and varies in thickness from several meters to thousands of meters (NSIDC, 2011). Glaciers are thick masses of ice on land that are caused by many seasons of snowfall. Glaciers move under their own weight, the external effect of gravity, and physical and chemical changes. The cryosphere lowers the earth's surface temperature by reflecting a large amount of sunlight, stores fresh water for millions of people, and provides habitat for many plants and animals.

Apart from the Arctic and Antarctic regions, the cryosphere is mainly a high altitude phenomenon. It is found on Mount Kilimanjaro in Africa, the Himalayan mountain range, high mountains of United States, and in Canada, Russia, Japan, and China. Researchers in the cryosphere are often hindered by the lack of accessibility due to the rugged terrain. In such cases, remote sensing technologies play an important role in cryosphere research. These techniques are imperative for researchers studying glacial retreat and mass balance change in relation to global climate change.

The cryosphere has a significant influence on global climate and human livelihoods. Change in spatial and temporal distribution of the cryosphere influences the water flow in the world's major rivers. Among the various parts of the cryosphere, glaciers play the most important role in climate change studies since glacier recessions are indicators of global climate change (Oerlemans et al., 1998; Wessels et al., 2002; Ambinakudige, 2010). Retreating glaciers can pose significant hazards to people (Kaab et al., 2002). Glacier retreat often lead to the formation of glacial lakes at high altitudes, the expansion of existing lakes, and the potential for glacial lake outburst floods (GLOFs) (Fujita et al., 2001; Bajracharya et al., 2007). A GLOF is the sudden discharge of a huge volume of water stored in a glacial lake due to huge ice falls, earthquakes, avalanches, rock fall or failure of a moraine dam (Grabs & Hanisch, 1993). There are more than 15,000 glaciers and 9,000 glacial lakes in the Himalayan mountain ranges of Bhutan, Nepal, Pakistan, China and India (Bajracharya et al., 2007). All

Remote Sensing of Cryosphere 371

Fig. 1. Astronaut photograph of Colonia Glacier, Chile. Photographer: International Space

characteristic assists in delineating glacier boundaries and classifying various cryospheric

In figure 2, the Landsat TM bands 1 to 6, acquired on 25 April 2010, are shown to compare spectral characteristics of glaciers. This figure presents the area around the Imja glacier in the Sagarmatha National Park in the Himalayas of Nepal. TM1 (0.45 – 0.52 µm) is useful to distinguish snow/ice in cast shadow, and also in mapping glacier lakes. Snow and firn areas get saturated in TM1. TM2 (0.52 – 0.60 µm) and TM3 (0.63 – 0.69 µm) have very similar spectral reflectance. TM2 is also useful in distinguishing snow and ice in cast shadow. TM3 is used in band ratio such as the normalized difference vegetation index (NDVI), which helps in classification of ice and snow in areas of dense vegetation. TM4 (0.76-0.90 µm) in the near infrared wavelength region has less reflectance from snow than TM2 and TM3. The clean ice region looks darker in near infrared band, indicating lower reflectance due to the presence of water at the surface (Hall et al., 1988). In TM5, the snow-covered area absorbs nearly all radiation and appears almost dark. This band is also useful in identifying clouds. The thermal band TM6 (2.08-2.35 µm) registers thermal emissions from the surface. Debris has a higher temperature and thus brighter pixels. Thick debris on ice can be easily

The high reflectance of the snow compared to the ice makes it easy to separate snow and ice. Snow and clouds are often difficult to distinguish when single imagery is used. Clouds and snow have similar reflectance at wavelengths below 1 µm in the near infrared region. The distinction between snow and ice is clearer near 1.55 and 1.75 µm. Therefore a ratio of two

distinguished as it will have a higher temperature (Pellika and Rees, 2010).

Station (2000).

surface types (Pellika and Rees, 2010).

these countries within the Himalayan region have at some time or another suffered a flood from a glacial lake outburst causing loss of property and lives, and these floods can be disastrous for the downstream riparian area (Richardson & Reynolds, 2000; Bajracharya et al., 2007). The significance of the glaciers as fresh water resources for millions of people is another reason to justify the continuous monitoring of these glaciers (Shiyin et al., 2003). Therefore, monitoring glaciers has significant importance both in understanding global climate change and in sustaining the livelihoods of the people downstream of the glaciers.

This chapter explores the use of remote sensing technologies in studies of the cryosphere and particularly in glaciers. First, we will discuss remote sensing sensors that are effective in monitoring glaciers. Then we will discuss the global effort to create glacier data, using remote sensing tools to delineate glacier areas, estimate volume and mass balance.
