Sar

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