Prasad

BY

M.PRASAD

11U71A0465

SYNTHETIC APERTURE RADAR

Airborne or spaceborne sidelooking radar systemFlight path : To simulate extremely large antenna or

apertureHigh - resolution remote sensing imagerySignal processing uses,

Magnitude

PhaseAfter a number of cycles,

The stored data is recombined

High resolution image of the terrain is created

Introduction

TRANSMITTER

RECEIVER

CIRCULATOR

RADAR PULSE

"TARGET"

• RADAR = Radio Detection And Ranging• Since radar pulses propagate at the speed of light, the difference to the “target” is proportional to the time it takes between the transmit event and reception of the radar echo

PRINCIPLES OF RADAR

SAR-processor stores all radar returned signals, for time period T

Signal is reconstructed from antenna of length,

v · T

Where, 

v is the platform speedAs LOS direction changes along radar platform trajectory,

SA is produced by signal processing

Effect of lengthening the antennaMaking T large makes the “synthetic aperture” largeHence, the higher resolution

HOW SAR WORKS ?

The requirements are,

Stable, full - coherent transmitter

An efficient & powerful SAR - processor

Exact knowledge of the flight path & the velocity of the platform

SAR REQUIREMENTS

Cross - range resolution,

δcr = RθB

Sequential generation of antenna apertureSidelooking radar (SLR)Element spacing,

de = vTp = v / fp

SAR Basics

Prf must be high enough to avoid,

Angle ambiguities

Image - foldoverThe resolution and the coverage can not be selected

independentlyDistance travelled by radar between pulse transmissions

should be less than λ / 2

Constraint on resolution & swath

SAR Processing Flow

EMERGING SAR TECNIQUESThe accuracy with which one can measure the surface tilt is

determined by the signal to noise ratioOnce the surface tilts (surface slopes) are known, the slopes are

integrated in the azimuth direction to find the topography as a series of azimuth profiles

Ground control points are needed to find the correct absolute height, and to tie different azimuth profiles together

While the accuracy of this technique is not as good as that of interferometry, crude digital elevation maps can be produced.

Military reconnaissanceMeasurement of sea state & ocean wave conditionsGeological & mineral explorationsSurveillance & TargetingGround PenetrationMoving Target IndicationChange DetectionEnvironmental Monitoring

SAR Applications

SAR technology is able to produce high resolution images that are not dependent on distance or conditions by using a single radar antenna that is attached to an aircraft so that the antenna is carried in a line that is roughly perpendicular to the direction of flight. 

Synthetic Aperture Radar (SAR) produces crisp images of terrain in real time using a small, lightweight radar that is able to be integrated onto a wide variety of manned and unmanned aircraft.

ADVANTAGES

Time - Radar can take up to 2 seconds to lock on !Radar has wide beam spread (50 ft diameter over !200 ft range)Large targets close to radar can saturate receiver !Hand-held modulation can falsify readings !More interference sources.  

DISADVANTAGES

With the development of modern integrated circuits technology, the technique for signal digitally generation are evolving rapidly to maturity. The digital radar transmitter can obtain much higher precision and stability than analog ones. Furthermore it can retain the extreme flexibility of digital techniques.

The advent of digital radar transmitters is an evolution of modern SAR transmitter technology. The merit and demerit for each of the digital generation technique has been discussed and each is capable, according to the application, of outperforming the other

CONCLUSION

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