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SIDE-LOOKING AIRBORNE RADAR

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Contents• Introduction• Remote sensing• Types of remote sensing• Radars• Doppler radar• Side looking airborne radar• Ground resolution• Azimutal resolution• Synthetic aperture radar• Working of synthetic aperture radar• Applications• Conclusion

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Introduction• The airborne radar systems that form microwave

images of adjacent terrain in fine detail, regardless of weather or time of day or night, by looking to the side of an aircraft.

Fig.1 Airborne radar in sky

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Remote sensing• Remote sensing is a technology used for obtaining

information about a target through the analysis of data acquired from the target at a distance. It is composed of three parts,

• The targets• The data acquisition• The data analysis

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Types of Remote Sensing• Based on Source of energy1. Active sensors2. Passive sensors• Based on Range of Electromagnetic Spectrum1. Optical Remote Sensing2. Thermal Remote Sensing3. Microwave Remote Sensing

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Radars• Radar represents "radio detection and ranging".• A radar system transmits pulses in the direction of

interest and records the strength and origin of reflection received from objects

• Radar systems may or may not produce images

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Doppler radar

• Doppler radar is a specialized radar that uses the Doppler effect to produce velocity data about objects at a distance.

• It does this by bouncing a microwave signal off a desired target and analyzing how the object's motion has altered the frequency of the returned signal.

• This variation gives direct and highly accurate measurements of the radial component of a target's velocity relative to the radar.

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Side-looking airborne radar• The Side-Looking Airborne Radar (SLAR) is an image-

producing system.• SLAR is an active sensor.• Its name itself indicates radar beam is transmitted

from the side of the aircraft during data acquisition.

Fig.2 A Slar system transmiting radar beam

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SLAR system

Fig.3 A SLAR system components and organization

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Ground resolution• There is a spatial resolution which is determined by

the duration of a pulse and the depression angle.This resolution is called ground range resolution (rg).

• The ground resolution of slar system is determined by two independent sensing parameters: pulse length and antenna beam width

• We then can determine the distance or the 'slant range' between the antenna and the target

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whereSr: the slant range.c: the speed of light.t: time period for a returned transmitted pulse.

Fig.4 Sensing parameters

Cont.....

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Fig.5 The across track spatial resolution

Cont......

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Azimuth Resolution • The along track distinguishing ability of a SLAR system

is called azimuth resolution (ra).

where

• can be the actual physical length of an antenna or a synthetic one

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Synthetic aperture radar

• Synthetic aperture radar (SAR) an advance version of SLAR

• SAR is used to create images of objects, such as landscapes – these images can be either two or three dimensional representations of the object.

• SAR is typically mounted on a moving platform such as an aircraft or spacecraft

• The larger the aperture is, the higher the image resolution will be.

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• SAR records the frequency differences of backscattering signal at different aircraft position during the time period when the target is illuminated by the transmitted energy.

Fig.6 A SAR system continuously generating beam

Cont......

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Working of SAR

Fig.6 The synthesized expanding beamwidth

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• The SAR works similar of a phased array . • The SAR-processor stores all the radar returned signals,

as amplitudes and phases, for the time period T from position A to D.

• Now it is possible to reconstruct the signal which would have been obtained by an antenna of length v · T, where v is the platform speed.

• As the line of sight direction changes along the radar platform trajectory, a synthetic aperture is produced by signal processing that has the effect of lengthening the antenna.

• Making T large makes the „synthetic aperture” large and hence a higher resolution can be achieved

Cont......

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Applications• Synthetic aperture Radar produces images of

high-resolution at great distances, that appear to be taken from above

• Sensor Operators• Command, Control, Intelligence training• Research & Development

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Conclusion

• Side looking airborne radar systems that form microwave images of adjacent terrain in fine detail, regardless of weather or time of day or night, by looking to the side of an aircraft with good resolution.

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