Interaction Of Emr With The Earths Surface

Radiation from the sun, when incident upon the earth's surface, is either reflected by the surface, transmitted into the surface or absorbed and emitted by the surface (Fig. 3). The EMR, on interaction, experiences a number of changes in magnitude, direction, wavelength, polarization and phase. These changes are detected by the remote sensor and enable the interpreter to obtain useful information about the object of interest. The remotely sensed data contain both spatial information (size, shape and orientation) and spectral information (tone, colour and spectral signature).

ei (à) = Incident energy ei (à) = Incident energy

Figure 3: Interaction of Energy with the earth's surface. ( source: Liliesand & Kiefer, 1993)

ea(A) = Absorbed energy et(à) = Transmitted energy

Figure 3: Interaction of Energy with the earth's surface. ( source: Liliesand & Kiefer, 1993)

From the viewpoint of interaction mechanisms, with the object-visible and infrared wavelengths from 0.3 ^m to 16 ^m can be divided into three regions. The spectral band from 0.3 ^m to 3 ^m is known as the reflective region. In this band, the radiation sensed by the sensor is that due to the sun, reflected by the earth's surface. The band corresponding to the atmospheric window between 8 prn and 14 ^m is known as the thermal infrared band. The energy available in this band for remote sensing is due to thermal emission from the earth's surface. Both reflection and self-emission are important in the intermediate band from 3 ^m to 5.5 p,m.

In the microwave region of the spectrum, the sensor is radar, which is an active sensor, as it provides its own source of EMR. The EMR produced by the radar is transmitted to the earth's surface and the EMR reflected (back scattered) from the surface is recorded and analyzed. The microwave region can also be monitored with passive sensors, called microwave radiometers, which record the radiation emitted by the terrain in the microwave region.

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