An Introduction to Remote Sensing

Remote Sensing, like the name implies, means observing and gathering information of an object from afar. In this sense we humans perform remote sensing all the time with our eyes and ears, where eyes and ears are our remote sensing equipment. However when moving away from the basics and expanding the scope of observation, many factors become involved and remote sensing becomes a broad and detailed area of study. Incorporating all these ideas, a general definition for remote sensing can be given as,

"The art and science of obtaining information about an object without being in direct contact with the object"

Remote sensing is extensively used in observing the earth and the environment for various purposes. The most common application of remote sensing is done in mine development, disaster mitigation and large scale environmental studies. Depending on the application, the sensors and the type of radiation used, the method of recording and processing and the analysis of the data will differ.

The major components in remote sensing are,
- an energy source for illumination :- usually the sun or an artificial source of radiation.
- medium of travel for energy :- the atmosphere.
- sensor :- orbits in a satellite eg. Landsat, Quickbird
- receiver on earth :- gathers the data transmitted from the satellite.
- equipment for interpretation and analysis of data :- remote sensing software.

All remote sensing systems have four types of resolution. They are,
- Spatial resolution :- refers to the pixel resolution of the image produced.
- Spectral resolution :- refers to the range of EM radiation that can be detected. A broader range increases the scope of analysis.
- Temporal resolution :- refers to the orbital period of the satellite carrying the sensor. Faster the period, higher the resolution.
- Radiometric resolution :- refers to the differences of the intensity of radiation that can be distinguished by the sensor. Given as a bit range. A higher bit range can distinguish smaller variations.

Once all the above details are decided according to the application, remote sensing is performed. Then a "reflectance pattern" is produced from the gathered data. By comparing these patterns with the spectral signatures of known objects, the type and extent of the sensed objects on the earth can be inferred. In addition to various applications on earth, remote sensing is also used in other planets to gather data about surface conditions etc without landing on the planet.

Remote sensing in Mars. image form wikipedia