GIS & Remote Sensing

This article is prepared to understand the role of reflectance and spectral signature in a satellite image. How the reflectance vary with change in EMR and characteristics of earth surface feature.
It is very important to understand that how the reflection which is received by sensor, converts into an image. It is explained in earlier article that how the reflectance taking place and its behavior of incident energy after interaction with surface. The reflectance completely depends on incident energy and characteristics of material/earth’s surface feature. So reflectance which is created during this process is called SIGNATURE.
Every object on the earth surface reflects and emits incident radiation is defined as signature of that object. It can be also called re-radiation from earth surface feature. These signatures are recorded by sensor boarded on satellites. As it is understood that basically only three natural land covers, it includes vegetation, soil and water. So behavior of these…

In this article discuss the interaction of Electro-Magnetic Radiation (EMR) with earth surface features. After passing through atmosphere, the EMR reached to earth and as already discussed EMR which have lest or almost no interaction with atmosphere is used in remotesensing process. This part of spectrum is called atmospheric windows. When EMR reached and interact with earth’s feature, three things take place with incident energy. ReflectionAbsorptionTransmission
When EMR is incident on any earth feature then part of it, as shown in figure
ReflectedAbsorbedTransmitted Figure showing Interaction of sun energy (EMR) with Earth Surface Features
Estimated radiation states that sum of these energies (reflected, absorbed and transmitted) is equal to incidental energy on earth’s feature How much amount will be reflected or absorbed or transmitted depends upon material to material as well as many other conditions. These quantities are sometimes expressed in non-dimensional way asTransmittance –This i…

ElectroMagnetic Radiation (EMR) propagates through the Earth’s atmosphere, however atmosphere may influence

   Speed of radiation   Wavelength   Intensity   Spectral Distribution   Change in Direction due to refraction So EMR may refracted, scattered and absorbed by atmosphere before reaching to ground/Earth's surface Refraction-Refraction may take place, when EMR come across substances of different density, like air and water. Refraction is bending of light when it passes through one medium to another medium. Refraction is taking place due to change in speed to EMR in media of different density. Major errors can occur in location due to refraction as images formed from energy detected at high altitudes or at acute angles. Scattering- Scattering is different from refraction as the direction of scattering is unpredictable. Scattering is unpredictable diffusion of EMR by particles present in the atmosphere.Scattering depends upon wavelength of EMR and diameter of particles. There are di…

Remote Sensing

Introduction The term "remote sensing," first used in the United States in the 1950s by Ms. Evelyn Pruitt of the U.S. Office of Naval Research.‘Remote’ means far away and ‘sensing’ means observing or acquiring some information. Therefore, remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object.
In our everyday living, one employ remote sensing to view different objects. Our eyes can be considered as sensors that respond to the light reflected from various objects. The data acquired by our eyes are the impulses corresponding to the amount of light reflected from light and dark areas of the object.This data is analyzed and interpreted by our brain which works like computer, to enable us to recognize the object.
Remote sensing is a tool/technique that use sensors to measure the amount of electromagnetic energy emitting an object or geographic area from a distance and then extracting the informatio…