ISRO’s Oceansat2 shows how changes in climate over the past 4 months in the Indian sub-continent, records the changes in Albedos.
This document describes IROS’s Oceansat-2 Land surface Albedo Products version 1.0 derived from the data acquired by Ocean Color Monitor (OCM2) sensor. Ocean Colour Monitor (OCM) – OCM is an 8-band multi-spectral camera operating in the Visible – Near IR spectral range.
0.3-0.7 µm for visible light
- Introduction to Albedo
Albedo is a key parameter that is widely used in land- surface energy balance studies, mid- to long-term weather prediction and global climate change investigation.
As albedo quantifies the capacity of surface to reflect solar radiation it is one of the main driving factors of the energy balance and interaction between land surface and atmosphere.
Any albedo in visible light falls within a range of about 0.9 for fresh snow to about 0.04 for charcoal, one of the darkest substances. Deeply shadowed cavities can achieve an effective albedo approaching the zero of a black body. When seen from a distance, the ocean surface has a low albedo, as do most forests, whereas desert areas have some of the highest albedos among landforms. Most land areas are in an albedo range of 0.1 to 0.4. The average albedo of Earth is about 0.3. This is far higher than for the ocean primarily because of the contribution of clouds.
- Application of albedo data
The availability of global land surface characteristics and albedo data over a wide range of spectral bands and at high spatial resolution has dramatically improved with the launch of the NASA’S MODIS instrument. The Filled Land Surface Albedo Product and Spectral land surface albedo reflect the consequences of natural and human interactions, such as anthropogenic, meteorological, and phenological effects on local and global climatological trends. Consequently, these products are integral parts in a variety of research areas, such as general circulation models, energy balance studies, modeling of land use and land use change, as well as biophysical, oceanographic, and meteorological studies.
Percentage of diffusely reflected sunlight in relation to various surface conditions
- Application of Albedo data in understanding the thermodynamic conditions in polar regions
Processes that affect the growth and melt of sea ice are referred to as thermodynamics. In the simplest sense, when the temperature of the ocean reaches the freezing point for salt water (-1.8 degrees Celsius, 28.8 degrees Fahrenheit), ice begins to grow. When the temperature rises above the freezing point, ice begins to melt. The amount and rates of growth and melt depend on the way heat is exchanged within the sea ice, as well as between the top and bottom of the ice.
Snow cover is one factor that dramatically alters the actual sea ice thickness, as snow is an effective insulator, it slows the transfer of heat from the ocean, through the ice, and to the atmosphere.
Sea ice has a much higher albedo compared to other earth surfaces, such as the surrounding ocean. A typical ocean albedo is approximately 0.06, while bare sea ice varies from approximately 0.5 to 0.7. This means that the ocean reflects only 6 percent of the incoming solar radiation and absorbs the rest, while sea ice reflects 50 to 70 percent of the incoming energy. The sea ice absorbs less solar energy and keeps the surface cooler.
Snow has an even higher albedo than sea ice, and so thick sea ice covered with snow reflects as much as 90 percent of the incoming solar radiation. This serves to insulate the sea ice, maintaining cold temperatures and delaying ice melt in the summer. After the snow does begin to melt, and because shallow melt ponds have an albedo of approximately 0.2 to 0.4, the surface albedo drops to about 0.75. As melt ponds grow and deepen, the surface albedo can drop to 0.15. As a result, melt ponds are associated with higher energy absorption and a more rapid ice melt.
Icebergs and sea ice melt during the southern hemisphere summer.
Courtesy: Ted Scambos and Rob Bauer, NSIDC