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Atmospheric RADARSignal Processing

E X T E R N A L G U I D E :

DR. T.V.C. SA RMA,

( S C I E N T I S T / E N G I N E E R - S G )

NATIONAL ATMOSPHERICRESEARCH LABORATORY,

DEPARTMENT OF SPACE

INTERNAL GUIDE :

M R . R A L P H T H A N G A R A J ,

V E L L O R E I N S T I T U T E O FT E C H N O L O G Y,

S E N S E D E PA RT M E N T

( A S S O C I AT E P R O F E S S O R )

PRE

B. L

1 M

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Outline

IntroductionMST radar

Research proposal

Literature survey

ontinuous !ave radar and pulse radar Ran"e

Ran"e resolution#ulse co$pression % Types

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Introduction RADAR% Radio Detection and Ran"in"Radars "enerally operated at &re'uency a(out ))*M+, %-.G+,

/+0 1 -*M % -**M+,

U+0 1 -**M % -G+,

S+0 1 -G % -*G+, T!o types o& radar syste$s

23 ontinuous 4ave Radar

)3 #ulse radar

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MST Radar

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Research Proposal The aim is transmitted wave is back scattered by radio refractive

index irregularities due clear air turbulence(CAT) towards the radarand it is received by the same antenna in the case of Monostaticsystem by using duplexer

The received echo is processed through superhetrodyne receiverfollowed by quadrature detection with !"# The $n%phase and&uadrature phase outputs are digiti'ed and pass through matched

lter and it is coherently integrated over inter pulse period

The resultant is nally sub ected to spectral moment estimation*we obtain parameters such as power* +oppler shift and spectralwidth

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Speci cations of MSTRadar : NARL !adan"i

5peratin" 0re'uency 1 .-M+, 6/+07Trans$itted po!er 1)3.M!

#ulse !idth 1 2 to -) $icro sec

Duty cycle 1 )3.8

Avera"e po!er 1 9 2* ; 4$ )

#ulse repetition 0re'uency 1 ?a"i%Uda antennas arran"ed in -) X -) s'uare "rid o&

*39@ spacin"

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Literature sur#e$ At$ospheric Layers +o! echoes received &ro$ At$ospheric Layers

Radar ran"e e'uations &or hard tar"et and distri(uted tar"ets

Ionospheric e ploration

Ran"e resolution #ulse co$pression

Radar receiver processin"

Matched &ilter

#o!erB Doppler and spectral !idth

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%ontinuous &a#e Radar

C, -".scillator

O'T

Tx Antenna

+etector MixerAM!

$ndicator

IN

-x Antenna

(istatic: Rt

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E$ploys continual RADAR trans$ission

Separate trans$it and receive antennas

Relies on the CD5##LER S+I0T

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Pulse Radar "requen Transm

!ulse wid

+uty

Average pow

!ulse repeti

PRT

P&

+Listening,Time

PRT*-.PR/

%arrier /re01

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S$nchroni2er Transmitter

Po3erSuppl$

Indicator Recei#er

Duple4er ANT1

Antenna Control

: c h o

$ n

- " . u t

Monostatic : R *%TR5

6+river*M.+*.;C

T

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Range The distance o& the tar"et can (e calculated &ro$ the

R 1 ct ) $eters

To tar"et short ran"e has to trans$it pulses !ith short duratios$all listen period 6>.** pulses per sec 7

0or lon" distancesB pulses !ith lar"e duration !ith $ore list period 6 F** pulses per sec 7

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Ma4imum 'nam8iguousRange The range corresponds to two%way time delay isknown as maximum unambiguous range

T 1 T 2 T 3 Tx

pulse

Rx echopulse

R2 1 c t )

t

Una$(i"uous ran"e

t

R) 1 c 6T t7 )

Echo 1 Echo 2

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Range Resolution

c T/4

c T/2

c T

c T c T

3 c T/2

R1 R2

R1 R2

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Pulse %ompression To increase the avera"e trans$itted po!er lon" pulse is used

It leads to de"rade in ran"e resolution

To overco$e this pro(le$ pulse co$pression is used

#ulse co$pression is achieved (y $odulatin" the pulse

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Pulse compression

Frequency Phase or Biphase

linear BarkerNon linear Complimentaryor Golays co de

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Linear /M

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Non 9 Linear /M

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%omparison of Linear and Nonlinear /M

L0M has $ore side lo(es

NL0M has less side lo(es

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t/7#73T ( Two Targets)

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t/7#730T

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t/7#710T

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t/7#73T (;>- %40d=)

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Tx signal

Pulse

coding

(ar"er %oding

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Barkercoderesponse

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t/7#30t (Two Targets)

t/7#0t

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t/7#0t

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t/7#60t

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t/t

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t/4#30t

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t/4#0t

/4#60

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t/4#60t

t/3t

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t/3t

t/7#30t (;> %40d=)

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t/7#30t (;>- %40d=)

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%omplimentar$ %oding Two length unimodular sequences x(t) and y(t) are

?olay complementary if the sum of theirautocorrelation functions satis es

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t/4#0t (Two Targets)

/4#60

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t/4#60t

t/3t

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t/3t

t/3#30t

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t/3#30t

t/4#0t (;> %34d=)

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t/4#0t (;>- %34d=)

% i f ( " d

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%omparison of (ar"er andcomplimentar$ code

Har=er code havin" sy$$etrical side lo(es

o$pli$entary codes totally eli$inates the side lo(es

4ea=er tar"ets also resolved in co$pli$entary

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References:23 CMiddle at$osphere pro"ra$ B hand (oo= &or $ap edited (y S3 0u=ao

)3 CA short history o& radar leadin" to at$ospheric pro&ilin" B H3H3HalsleyB IRESB University o&

-3 CRadar o(servation o& !inds and tur(ulence in the StratosphereB Mesosphere B Ronald 03 !ood$an aAl(erto GuillenB2F9>

>3 CSpectral $o$ent esti$ation in MST radars B Ronald3 03 4ood$anB 2F;.

.3 C+istorical Aspects of Radar At$ospheric Dyna$ics B (y S. Kato

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Than" ou