Remote Sensing

Geographers are keen in using fieldwork as part of their professional toolkits for understanding the world. Fieldwork can be quite laborious, costly, and—sometimes—dangerous. Since the middle of the 20th century when aerial photography became widely available, geographers have made frequent use of remote sensing. Remote sensing is a term that refers to a set of techniques by which the environment is studied. Electromagnetic radiation is sensed by devices as it is reflected, refracted, scattered, transmitted, and emitted by matter in the environment. Each feature of Earth and the atmosphere has a “spectral signature,” that is, the interaction of the various electromagnetic wavelengths with that feature. Thus, we are able to identify,measure, andmodel features that are not in physical contact with the features under study. 

There aremanymeasurement devices that are in direct contact with what they are measuring and so, by definition, are not remote sensing devices. A thermometer is not a remote sensing device for air temperature because its temperature readings are dependent on the collision of atmospheric molecules with the device. A thermal radiometer, however, can be mounted in a satellite and measure the temperature in the atmosphere it is not touching. Table 3 illustrates the types of remote sensing commonly used by geographers, primary wavelengths involved, and typical uses. The most well-known and commonly used form of remote sensing is photography. 

A camera contains film sensitive to light. The film is kept in the dark until the lens is opened to expose the film. The image is made permanent by developing it with chemicals. Aerial photography is of oblique and vertical types. Oblique photography is the perspective we see looking out of an aircraft window. Much more useful to the geographer is vertical photography in which the camera is pointed underneath the aircraft and features can be mapped and measured.