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 w

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 least or almost no interaction with atmosphere is used by  remote sensing  sensors.  This part of spectrum is called atmospheric windows, which have zero or no interaction with atmosphere.  When EMR reached and interact with earth’s feature, three things take place with incident energy. Reflection Absorption Transmission When EMR is incident on any earth feature then part of it, as shown in figure Reflected Absorbed Transmitted 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

Remote sensing process depends on source of energy, it can be natural in the form of sun to illuminate object. Sun light has to pass many obstacle before reaching and interaction with object . This obstacle can be atmosphere, which absorb or scatter sun light at different wavelengths.   The quality of satellite image may affected by these obstacles and quality for correct interpretation   and accurate classification , one need to  improve satellite images by enhancement process. Electro-Magnetic 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 throug

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, r emote 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