How do we study the CRYOSPHERE?
All types of the cryosphere form under harsh environmental conditions, the most obvious being cold temperature. As a result, most of the cryosphere occurs in remote regions of the Earth, making regular observations difficult and often dangerous. Therefore, in addition to the relatively small number of observations we can make from coastlines and ships in the polar regions, we also study the cryosphere using measurements obtained from aircraft and satellites. These types of measurements cover a much larger region giving us a better picture of the cryosphere than measurements made at the surface.
Surface Measurements: Measurements are made of the cryosphere at the surface of the Earth in a number of ways. Field experiments are organized trips to a particular location, whether on sea ice, continental ice or glaciers, when scientists conduct coordinated experiments designed to examine everything occurring at that location. Sometimes these experiments are automated in that scientists and technicians set up the instruments which are then left to collect specific data without further intervention.
In one type of field experiment, scientists who want to understand sea ice would set up a station on the sea ice to measure the temperature of the air at various elevations, the winds, the sea water temperature at the surface and at depth, the thickness and temperature of the ice, the thickness and temperature of the snow on the ice, the ocean currents, the composition of the sea water and the ice, the rate at which the ice is forming, the structure of the ice, the movement of the ice, and the relative amounts of open water and ice. With this information, scientists can put together a picture of the state of the sea ice at that location, how it formed, the processes that are occurring that make it, and how it is affecting its environment.
Field experiments on the surface of continental ice and glaciers would include measurements of the movement of the ice and the accumulation (snowfall) and ablation (snow and ice melt) which would give a picture of how the ice is currently moving and how it has changed over time. During field experiments on continental ice and glaciers cores of ice are also extracted. This gives us a picture of how the glacier grew and changed over time, essentially a climate history. This ice also contains small samples of the air at the surface at the time it was formed, allowing us to measure how the composition of the atmosphere has changed.
There are other kinds of field experiments. These are similar in that they involve taking measurements directly at the location of the phenomena you want to measure, however, they are different in that they are not in one location. Ship-based observations of sea ice and the environment surrounding sea ice are made as the ship travels through the sea ice field and is usually entered into shipboard computers immediately. Buoys move with the sea ice field and measure the environment they are in (there are also buoys which are anchored in one location and measure ocean currents and fluxes of other quantities). Some of these buoys transmit the data they collect and others store the data for retrieval by ships.
Remote Sensing: The other methods of measuring the cryosphere involve the use of remote sensors located either on aircraft or satellites. These sensors measure radiation coming from a particular location on the Earth in a variety of wavelengths. Scientists must determine where that particular radiation came from. For example, did it come from near the surface of the Earth, from the top of a cloud, or from some other elevation? Also different features, such as ice, land, ocean, cloud, and rain, radiate to space at different frequencies or wavelengths. So the measurements that these remote sensors make must be checked against what is actually happening at the time. This is called ground truthing. Scientists use ground truthing to determine what set of measurements indicates particular types of ice or different surface temperature.
The advantage of remote sensors is that from high elevations, aircraft or space, it is possible to get a much broader view of the Earth than can be obtained at the surface. NASA's ICESat, launched in 2003, monitors ice sheets and sea ice thicknesses, and use those data to monitor climate change. For more information see http://icesat.gsfc.nasa.gov/.
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