Remote sensing
What is remote sensing?
Remote sensing is the science of acquiring information about an object (for example, the surface of the Earth) without being in contact with it. This is achieved by detecting reflected or emitted energy, and then analysing the data to obtain the required information.
Examples of remote sensing
The techniques of remote sensing are used in many research areas. The instruments and methods, and often their environments, are highly varied. Cost is often a significant factor in choosing among the various options. Some examples are given below:
Land
Remote sensing techniques are used in Seismology. In this case the quantity we are interested in measuring is the motion of the tectonic plates. This information can be used to predict earthquakes, volcanic eruptions, tsunamis and other geophysical phenomena. The measuring instrument most commonly used in seismology is the seismometer. An example of the output from a seismometer (a seismograph) is shown in the figure below. You can see live output from a seismometer here.
A Kinemetrics seismograph, formerly used by the United States Department of the Interior. (link)
Sea
Sonar methods can be used for remote sensing in sea-based research areas. Examples of this include topographic mapping of ocean floors, and locating ships lost at sea.
Sonar has been used to look at ships lost at sea. Two merchant vessels, the Frank Palmer and the Louise Craig, collided in December of 1962 and both sank. Here is a Sonar image of the two resting side by side: (link)
Using sonar technology from onboard ships, scientists from British Antarctic Survey (BAS) and the German Alfred Wegener Institute (AWI) captured the most extensive, continuous set of images of the seafloor around the Amundsen Sea embayment ever taken. (link)
You can find out more about how sonar methods work here.
Air
Aircraft based platforms for remote sensing have been highly successful. Aircraft are used to collect detailed images, and facilitate the collection of data, over virtually any portion of the Earth's surface at any time. An example of this was the NASA/JPL detector called AIRSAR.
AIRSAR collected many valuable and beautiful images during its operation. The photograph below shows a map of the Upolu Island, Western Samoa.
Here, colour is used to illustrate the topography of the Upolu Island. The AIRSAR detector was used in a variety of different research areas. The photograph below shows the Altamaha Priver Delta, Georgia Sea Islands.
In this image the colours represent different types of vegetation. The image supports historical evidence of farming in the region several hundreds of years ago.
An excellent source of images taken using different types of remote sensing methods is NASA's Visible Earth website.
Space
Space-based remote sensing is conducted mainly from man-made satellites. These satellites include platforms for remote sensing, communication, and telemetry (location and navigation) purposes. Because of their orbits, satellites permit repetitive coverage of the Earth's surface on a continued basis. An example of satellite photography is shown in the figure below.
A true colour image of a \href{http://en.wikipedia.org/wiki/Phytoplankton}{phytoplankton} bloom off the south-west cost of Ireland; the phytoplankton blooms are visible as blue-green swirls.
Remote sensing probes have visited other planets in our solar system too. Examples include the Voyager mission, the Cassini mission, and the Mars Odyssey probe.
Using remote sensing to study climate change
It is known that the Earth's climate has varied over millions of years. Today the term `climate change' is associated with changes to the climate caused by human activity e.g. the production of carbon dioxide and methane which build up in the atmosphere and trap heat. Therefore it is important to monitor any changes and their impact. One such change is the retreat of glaciers. This is seen in the figure below.
The retreat of Pedersen Glacier, Alaska. Left: summer 1917. Right: summer 2005. 1917 photo captured by Louis H. Pedersen; 2005 photo taken by Bruce F. Molnia. Credit: The Glacier Photograph Collection, National Snow and Ice Data Center/World Data Center for Glaciology.
Using remote sensing methods we can detect changes on the Earth's surface and in its atmosphere. For example we can monitor the reduction in size of the polar ice caps (see figure below).
The Arctic ice cap reached its smallest extent ever in 2007 (above, top), about 50 percent of its size in the 1950s. The image beneath it shows the ice caps' average area in 1979-1981. (NASA images)
There are many sources available on the web about climate change. You can find out more here.
Polarimetry in remote sensing
We can use polarimetric methods to analyse sea ice. This is important method for studying changes in the amount and size of sea ice. The figure below shows polarimetric SAR (Synthetic Aperture Radar) data used to create multi-polarisation intensity images. The imaged areas are in the Labrador Sea off the coast of Newfoundland with ice and open water.
A false colour composite and single channel intensity images from SIR-C for an ice infested region of the Labrador Sea off the coast of newfoundland. (link)