The Physics Behind Remote Sensing :: Physics

Remote Sensing is the science of acquiring, processing and interpreting images that record the interaction between the electromagnetic energy and matter (Sabins, 1997). Remote sensing offers extensive applications 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. 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. Electromagnetic Energy Electromagnetic energy is a dynamic form of energy that is caused by the acceleration or oscillation of a charged particle. All substances above absolute zero (0 Kelvin) emit a range of electromagnetic energy. The sun emits electromagnetic energy and practically all of the natural electromagnetic energy injected into the earth is produced by the sun (Prakush, 2002). Electromagnetic Radiation Electromagnetic Radiation is the streams of mass-less particles, traveling in a harmonic, sinusoidal fusion at the velocity of light each possessing a specific amount of energy. The distance from one peak to the next is the wavelength and the number of peaks passing through a fixed point per unit time is the wave frequency (Lillesand and Kiefer, 1994). Electromagnetic radiation is Electromagnetic energy in motion and can be described by the basic wave theory. Electromagnetic Spectrum Electromagnetic waves are characterized by their wavelength location within the electromagnetic spectrum which is most commonly measured in micrometers. Names are often assigned to regions of the electromagnetic spectrum, but there is no clear cut dividing lines from one region to the next (Lillesand and Kiefer, 1994). Stefan - Boltzmann Law How much energy any objects radiates is a function of its surface temperature. The Stefan - Boltzmann equations tells one that as a temperature of a body increase the total radiance of the body will also increase. (Sabins, 1997). Interactions The way electromagnetic radation interacts with matter can be detected with different sensors. How the radation interacts depends upon the properties of the medium, the wavelength of the incedent radation and the incident angle. There are four major types of interactions that occur: transmission, reflection, scattering and absorption (Lillesand and Kiefer, 1994).