RADAR SYSTEM:

World Radar is an acronym for Radio Detection and Ranging. Radar was developed to detect the presence of objects and their range using radio waves. Radars are active sensors. Detecting and ranging of an object by this system involves transmitting short bursts or pulses of microwave energy in the direction of interest and recording the strength and origin of echoes or reflections received from objects with in the system's field of view.

Radars are of various types, the simplest one being the DOPPLER RADAR that uses Dopplereffect frequence shifts in the transmitted and returned signals to determine the velocity of the object. Hand held radars used by thr traffic police to monitor speed of vehicles are of this type. Another common form of radar is PLAN POSITION INDICATOR (PPI) radar. These systems have a circular display screen on which a radial sweep indicates the position of radar echoes. Such systems are common in weather forecast, air traffic control and navigational applications. Among the airborne radars, the SIDE LOOKING RADAR (SLR) or SIDE LOOKING AIRBORNE RADAR (SLAR) are important. They find application in aviation. It has an all weather operating capability and is an active day and night operating system.

The most commonly used radar for space remote sensing is the SYNTHETIC APERTURE RADAR (SAR), a system employing a short physical antenna capable of synthesizing the effect of a very long antenna. the SAR system was employed for space based remote sensing aboard the Seasat program. SEASAT was planned as a system of ocean monitoring satellites.

The Seasat has been one of the most well known programs aiming at the study of oceans. The Seasat programmed was based on RADAR REMOTE SENSING. The space borne radars uses synthetic aperture radars and such radars are denoted by the term SAR, a side looking radar system operated from space. Seasat was the first of a proposed series of satellites oriented towards oceanographic research and it was launched in June 1978 into an 800 km near polar orbit.

The major space borne radar systems that have been employed in remote sensing include the Almaz-1 of Soviet Union, ERS-1 of European Space Agency, JERS-1 of Japan and Radiosat of Canada.

LIDAR:

Another active remote sensing system, a LIDAR (light detection and imaging) uses pluses of laser light, rather than microwave energy used by radar, to illuminate terrain. The lidar systems can be operated in either a profiling or a scanning mode. Measurement of laser induced fluorescence properties of earth surface also makes use of lidar technology.

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