4 - Central Institute of Brackishwater Aquaculture

National Workshop-cum-Training on Mdnfonnatio ~d Information Management In Aqu8culture
enough for high geometric resolution measurements. The output of a remote
sensing system is usually an image representing the scene being observed. A
further step of image analysis and interpretation is required in order to extract
useful information from the image. The human visual system is an example of a
remote sensing system in this general sense.
2.1.1 Principles
Remote sensing encompasses the set of sensors, platforms, and the data
processing techniques that are used to derive information about the physical,
chemical and biological properties of the earth surface features (land and ocean)
and atmosphere using sensor onboard (air craft or balloons) or space borne
(satellite, space shuttles) platforms (Figure 1). The oldest form of remote
sensing is aerial photography where the sensor system is the camera and film.
The field of remote sensing has grown to include electro-optical sensors in optical
or microwave regions of electromagnetic spectrum (Figure 2) bands which
acquire multispectral digital images that can be processed and analyzed by
computers. Many of these sensors are on satellites, which regularly orbit the
earth.
In optical Remote Sensing, optical sensors detect solar radiation in the visible
and near infrared wavelength regions (commonly abbreviated as VNIR) reflected
or scattered from the earth, forming images resembling photographs taken by a
camera high up in space. Some remote sensing satellites carry passive or active
microwave sensors. The active sensors emit pulses of microwave radiation to
illuminate the areas to be imaged. Images of the earth surface are formed by
measuring the microwave energy scattered by the ground or sea back to the
sensors. These satellites carry their own "flashlight" emitting microwaves to
illuminate their targets. The images can thus be acquired day and night.
Microwaves have an additional advantage as they can penetrate clouds. Images
can be acquired even when there are clouds covering the earth surface.
Figure 1. Principle of Remote Sensing