579
coral reefs and carbonate banks. Mangrove forests are usually characterized by uniform type of trees and shrubs and the species diversity decreases with increasing
latitudes.
19.4 Remote Sensing
Remote sensing is the science of acquiring information about objects from measurements made by scientific devices called “sensors” without there being any physical
contact between the target and the sensing device. Any force field i.e. gravity, magnetic or electromagnetic could be used for remote sensing measurements. However,
in the modern context, the term remote sensing refers to the identification of earth
features by detecting the characteristic electromagnetic radiation that is reflected or
emitted by the earth surface. The whole edifice of remote sensing is built on the
premise that all objects reflect/emit/scatter a portion of the electromagnetic energy
incident on it depending upon its physical characteristics. For example, a red rose
flower absorbs all the solar radiation falling on it except the red portion of the EM
radiation and thus it appears red in colour. Similarly, leaves of the plant appear
green to human eyes because it absorbs all the sun light falling on it except the light
in green wavelength. In addition, the objects on the earth emit radiation depending
on their temperature and other characteristics. If we study the reflectance/emittance
of any particular object as a function of wavelength, we get a typical reflectance/
emittance response pattern of the object as a function of wavelength, which is
unique for that object. This reflectance/emittance pattern is known as ‘spectral signature’ and is characteristic of the object (Joseph 2007). Thus, proper interpretation
of the spectral signature enables identification of the objects. This could be achieved
by aerial as well as space-based remote sensing for large area coverage.
The main thrust of modern satellite-based remote sensing, apart from providing
vantage point in space for viewing large areas on ground, has been to extend human
eye’s visibility range. This is done by converting interaction of non-visible part of
electromagnetic radiations like infrared, short wave Infra-red (SWIR), thermal
infrared, microwave etc. with matter into interpretable information. There are sensors which can detect the electromagnetic radiations in the above mentioned nonvisible portion of the electromagnetic spectrum. These sensors can be mounted on
the aerial or space based platforms for collecting the reflected or emitted solar radiations. Sensors for detecting electromagnetic radiations are of two types: (i) passive
sensors and (ii) active sensors. Passive sensors do not have their own source of
electromagnetic radiations for illuminating the target/objects, they measure the
radiations reflected/emitted by the object. Active sensors have their own source of
electromagnetic radiation for illuminating the target. RADARS and LIDARS are
examples of active sensors. By analysing the radiations measured by the sensors, it
is possible to detect, identify and classify various objects/phenomena.
Space borne remote sensing of the earth resources began with the successful
launch of the Earth Resources Technology satellites ERTS-1 (later renamed as
19 Mangrove Inventory, Monitoring, and Health Assessment
coral reefs and carbonate banks. Mangrove forests are usually characterized by uniform type of trees and shrubs and the species diversity decreases with increasing
latitudes.
19.4 Remote Sensing
Remote sensing is the science of acquiring information about objects from measurements made by scientific devices called “sensors” without there being any physical
contact between the target and the sensing device. Any force field i.e. gravity, magnetic or electromagnetic could be used for remote sensing measurements. However,
in the modern context, the term remote sensing refers to the identification of earth
features by detecting the characteristic electromagnetic radiation that is reflected or
emitted by the earth surface. The whole edifice of remote sensing is built on the
premise that all objects reflect/emit/scatter a portion of the electromagnetic energy
incident on it depending upon its physical characteristics. For example, a red rose
flower absorbs all the solar radiation falling on it except the red portion of the EM
radiation and thus it appears red in colour. Similarly, leaves of the plant appear
green to human eyes because it absorbs all the sun light falling on it except the light
in green wavelength. In addition, the objects on the earth emit radiation depending
on their temperature and other characteristics. If we study the reflectance/emittance
of any particular object as a function of wavelength, we get a typical reflectance/
emittance response pattern of the object as a function of wavelength, which is
unique for that object. This reflectance/emittance pattern is known as ‘spectral signature’ and is characteristic of the object (Joseph 2007). Thus, proper interpretation
of the spectral signature enables identification of the objects. This could be achieved
by aerial as well as space-based remote sensing for large area coverage.
The main thrust of modern satellite-based remote sensing, apart from providing
vantage point in space for viewing large areas on ground, has been to extend human
eye’s visibility range. This is done by converting interaction of non-visible part of
electromagnetic radiations like infrared, short wave Infra-red (SWIR), thermal
infrared, microwave etc. with matter into interpretable information. There are sensors which can detect the electromagnetic radiations in the above mentioned nonvisible portion of the electromagnetic spectrum. These sensors can be mounted on
the aerial or space based platforms for collecting the reflected or emitted solar radiations. Sensors for detecting electromagnetic radiations are of two types: (i) passive
sensors and (ii) active sensors. Passive sensors do not have their own source of
electromagnetic radiations for illuminating the target/objects, they measure the
radiations reflected/emitted by the object. Active sensors have their own source of
electromagnetic radiation for illuminating the target. RADARS and LIDARS are
examples of active sensors. By analysing the radiations measured by the sensors, it
is possible to detect, identify and classify various objects/phenomena.
Space borne remote sensing of the earth resources began with the successful
launch of the Earth Resources Technology satellites ERTS-1 (later renamed as
19 Mangrove Inventory, Monitoring, and Health Assessment