Remote Sensing is the science of aquiring, processing and interperting images that record the interaction between the electromagnetic energy and matter (Sabins, 1997). Remote sensing offers extensive applicaations in almost every area of science from monitoring forest fires to geologic mapping . Although many aspects of remote sensing are complex and difficult to understand the basic theory behind remote sensing is simple physics.
http://www.gi.alaska.edu/~prakash/teaching/undergraduate/material/lecture02_emspectrum.pdf
There are four major stages of remote sensing. The first stage is the source of energy, usually the sun, which sends energy to a target. The second stage is the interactions that the energy will go through as it passes through a vacuum and the earth’s atmosphere. There is then interactions that occurs with the body on earth’s surface. The energy again, goes through the atmosphere and finally the sensor is able to detect and record the electromagnetic energy.