4 - Central Institute of Brackishwater Aquaculture

Sensor is a device that gathers energy (EMR or other), converts it into an
electronic slgnal and presents tt in a suitable form for obtaining Information
about the target undet Investigations. These may be active or passive depending
on the source of energy.
Sensors used for remote sensing can be broadly classified as those operating in
optical infrared (OIR) region and those operating in the microwave region. OIR
and mlcrowave sensors can further be subdlvided into passive and active.
Active sensors use their own source of energy. Earth surface is illuminated
through energy emitted by Its own source, a part of it reflected by the surface in
the direction of the sensors is received to gather the infonnation, and passive
sensors recelve solar Electro-magnetic energy reflected from the surface of
energy emitted by the surface itself. These sensors do not have their own source
of energy and can not be used at night time, except thermal sensors. Again
sensors (active or passive) could either be imaging, like camera, or sensor which
acquires images of the area and non imaging types like non scanning radiometer
or atmospheric sounders. There are various types of sensors, which used in
different satellites.
6. Need for GIS
Development of an information system should be based on various aspects which
are environmentally friendly, economically feasible and socially acceptable. For
planning accurate, reliable and timely information which supports rules for
management such as variety of maps, large amount of spatial data, selectively
extract Information relevant to a planning task is required. Th~s type of need can
be fulfilled by developing an information system based on geographical data.
Geographic: Data referenced by some coordinate system to locations on the
surface of the earth.
Information: Provides answers to queries about the geographic world.
Syrtem: This is the environment which allows data to be managed and
questions to be posed.
A GIs is basically a computerized information system like any other database,
but with an important difference that all information in this linked to a
geographic (spatial) reference (latitude/longltude or other spatial coordinate
system)
There are no clear-cut definitions for GIs, different people defined GI5 according
to capabllity and purposes for which It Is applied. Few of them are:
Clarke defined it as a computer system for the capture, storage, retrieval and
display of spatial data, within a partlcular organization.