Electromagnetic Spectrum

ELECTROMAGNETIC SPECTRUM

The first requirement for remote sensing is to have an energy source to illuminate the target (unless thesensed energy is being emitted by the target). This energy is in the form of electromagnetic radiation. All electromagnetic radiation has fundamental properties and behaves in predictable ways according to the basicsof wave theory.

Electromagnetic radiation consists of an electrical field (E) which varies inmagnitude in a direction perpendicular to the direction in which the radiation is traveling, and a magnetic field (M) oriented at right angles to the electrical field. Both these fields travel at the speed of light (c). Two characteristics of electromagnetic radiation are particularly important to understand remote sensing. These are the wavelength and frequency.

Electromagnetic radiation (EMR) as an electromagnetic wave that travels through space at the speed of light C which is 3x10⁸ meters per second.

Theoretical model of random media including the anisotropic effects, random distribution discrete scatters, rough surface effects, have been studied for remote sensing with electromagnetic waves.

Light can be thought ofasawave in the 'electro magnetic field'of the univer Awave can be characterized by its wavelength or its frequency  

The wavelength is the length of one wave cycle, which can be measured as the

distance between successive wave crests. Wavelength is usually represented by the Greek letter lambda (?). Wavelength is measured in metres (m) or some factor of metres such as nanometres (nm, 10-9 metres), micrometres (?m, 10-6 metres) (?m, 10-6 metres) or

centimetres (cm, 10-2 metres). Frequency refers to the number of cycles of a wave passing a fixed point per unit of time. Frequency is normally measured in hertz (Hz), equivalent to one cycle per second, and various multiples of hertz.

Wavelength and frequency are related by the following formula:

Therefore, the two are inversely related to each other. The shorter the wavelength, the higher the frequency. The longer the wavelength, the lower the frequency. Understanding the characteristics of electromagnetic radiation in terms of their wavelength and frequency iscrucial to understanding the information to be extracted from remote sensing data.

The electromagnetic spectrum ranges from the shorter wavelengths (including gamma and x-rays) to the longer wavelengths (including microwaves and broadcast radio waves). There are several regions of the electromagnetic spectrum which are useful for remote sensing.