sar
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Presented by,B. Arthi
2012610031Anna University, Chennai
Synthetic Aperture RADAR (SAR)
Book : Introduction to RADAR Systems (2nd edition)Author : Merrill I. Skolnik
Page No : 517 - 523
Airborne or spaceborne sidelooking radar systemFlight path : To simulate extremely large antenna or apertureHigh - resolution remote sensing imagerySignal processing uses,
Magnitude Phase
After a number of cycles, The stored data is recombined High resolution image of the terrain is created
Introduction
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 speed
As LOS direction changes along radar platform trajectory, SA is produced by signal processing Effect of lengthening the antenna
Making T large makes the “synthetic aperture” largeHence, the higher resolution
How SAR works ?
An Example
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
Conventional antenna beam width,θB = kλ / D
SA antenna beam width,θS = kλ / 2Le
Problem : Limits on the maximum effective length, Le ≤ RθB
Unfocused SAR
Resolution of the SAR
Solution : Phase correction at each “element”
Δφ = 2πx2 / λR Focused SAR
Different correction for each range RCross - range resolution,
δcr = RθS = D / 2
Independent of Range Independent of frequency Depends on dimension, D
Resolution of the SAR
Prf must be high enough to avoid, Angle ambiguities Image - foldover
The resolution and the coverage can not be selected independently
Distance travelled by radar between pulse transmissions should be less than λ / 2
Constraint on resolution & swath
General form of radar eqn.,
SAR radar equation,
On further substitutions,
Radar Equation for SAR
SAR Processing Flow
Military reconnaissanceMeasurement of sea state & ocean wave conditionsGeological & mineral explorationsSurveillance & TargetingGround PenetrationMoving Target IndicationChange DetectionEnvironmental Monitoring
SAR Applications
SAR combines many viewing angles to, Effectively create a large aperture radar
Resolution improves with, BandwidthIntegration angle
Good focus requires precise motion measurementImage interpretation requires,
Training Practice
Summary
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