05 1uap Slides

8/9/2019 05 1uap Slides

http://slidepdf.com/reader/full/05-1uap-slides 1/21

2/23/20062/23/2006 11

Estimating UnderwaterEstimating Underwater Acoustic Propagation Acoustic Propagation

Ethem Mutlu SEthem Mutlu Söözerzer

Research EngineerResearch EngineerMIT Sea Grant College ProgramMIT Sea Grant College Program

8/9/2019 05 1uap Slides


OutlineOutline

What is decibel?What is decibel? Transducers and hydrophonesTransducers and hydrophones

Underwater acoustic propagationUnderwater acoustic propagation Ray tracingRay tracing

Delay and signal strength calculationsDelay and signal strength calculations

Channel impulse responseChannel impulse response

Estimating the range of a sourceEstimating the range of a source

Estimating the direction of a sourceEstimating the direction of a source

2/23/20062/23/2006 22

8/9/2019 05 1uap Slides


DeciDeci--belbel (dB)(dB)

A decibel (dB) is a unit for measuring the A decibel (dB) is a unit for measuring therelative strength of a signal in logarithmic scalerelative strength of a signal in logarithmic scale

P(dBP(dB) = 10 log10(P/Pr)) = 10 log10(P/Pr)

= 20 log10(V/Vr)= 20 log10(V/Vr)

V(dB V(dB) = 10 log10(V/Vr)) = 10 log10(V/Vr)

= 10 (log10(V)= 10 (log10(V) – – log10(Vr))log10(Vr))

2/23/20062/23/2006 33

8/9/2019 05 1uap Slides


Transducer and HydrophoneTransducer and HydrophoneSpecificationsSpecifications

Open Circuit Receiving Response (OCRR)Open Circuit Receiving Response (OCRR) Transmitting Voltage Response (TVR)Transmitting Voltage Response (TVR)

Directionality PatternDirectionality Pattern PrePre-- Amplifier Amplifier

2/23/20062/23/2006 44

8/9/2019 05 1uap Slides


Transmitting Voltage ResponseTransmitting Voltage Response(TVR)(TVR)

output SIL generated per 1 Voutput SIL generated per 1 Vof input Voltage at 1m rangeof input Voltage at 1m range

as a function of frequencyas a function of frequency

dB redB re µµPaPa / V / V

V = 200 V @@ fcfc=22 kHz=22 kHz

SIL (µµPaPa) = V (V) x TVR (µµPaPa / V) / V)

SIL = 10 log10(V) + TVR(fc)

ITC 1001 Transducer VTR = 26 + 144 = 170 dB re µµPaPa

2/23/20062/23/2006 55

110

2 10

120

130

140

150

18

Frequency in kHz

d B r e µ P a / V @ 1 m

26 34

Transmitting Voltage Response

Figure by MIT OCW.

8/9/2019 05 1uap Slides


Open Circuit Receiving ResponseOpen Circuit Receiving Response(OCRR)(OCRR)

output voltage (V) generatedoutput voltage (V) generatedby the transducer perby the transducer per µµPaPa of of

sound pressure as a functionsound pressure as a function

of frequencyof frequency

dB re 1V /dB re 1V / µµPaPa

SIL = 190 dB re µµPaPa @@ fcfc=22 kHz=22 kHz

V = SIL (V/µµPaPa) x OCRR (µµPaPa))

VdB = SIL + OCRR(fc)

ITC 1001 Transducer OCRR = 190 + (-190) = 0 dB re 1V

VdB re 1V = 10 log10 ( V / 1 ) V = 10

( VdB / 10 )= 1 V

2/23/20062/23/2006 66

102

-220-210

-200

-190

-180

18 26 34

Frequency in kHz

d B

r e 1 V / µ P a

Open Circuit Receiving Response

Figure by MIT OCW.

8/9/2019 05 1uap Slides


Directionality PatternDirectionality Pattern

ITC 1001 spherical transducerITC 1001 spherical transducer

ITC 2010ITC 2010

toroidaltoroidal

transdtransd

ucerucer

Uniform resUniform respponse oonse ovver aller all More gain over the sidesMore gain over the sides

angles ( 0 to 2angles ( 0 to 2ππ) on both) on both (horizontal plane) than the(horizontal plane) than the

horizontal and vertical planehorizontal and vertical plane over the top and bottomover the top and bottom

(vertical plane)(vertical plane)

2/23/20062/23/2006 77

Directivity Pattern at 2.0 kHz

240

10dB/div

270

300

120

90

60

210 180 150

330 0 30

Directivity Pattern at 18.0 kHz

240

10dB/div

270

300

120

90

60

210 180 150

330 0 30

Figures by MIT OCW.

8/9/2019 05 1uap Slides


2/23/20062/23/2006 88

PrePre-- Amplifier Amplifier

Amplifies the signals generated at the receiving element Amplifies the signals generated at the receiving element(hydrophone or transducer)(hydrophone or transducer)

Gain defined in dBGain defined in dB

mV

mV

amplifier

V

pre-amplifier

Vin = 1 mV, Gain = 20 dB Vout(dB) = Vin(dB) + Gain(dB)

Vin(dB) = 10 log10(Vin) = 10 log(10e-3) = -30 dB

Vout(dB) = -30 + 20 = 0 dB

Vout = 10(-10/10) = 0.1 Volt

8/9/2019 05 1uap Slides


Shallow Water PropagationShallow Water Propagation

Assumptions: Assumptions: CoConstant sound speed (c = 1500nstant sound speed (c = 1500 m/sm/s))

Surface and bottom are smoothSurface and bottom are smooth

r=100m

d=20m

h=80m

source destination

θ2 θ2

θ1 θ1

2/23/20062/23/2006 99

8/9/2019 05 1uap Slides


Length of propagation pathsLength of propagation pathsDirect path => d0 = 100mDirect path => d0 = 100m

Surface reflection => d1 = 2d/cos(Surface reflection => d1 = 2d/cos(θθ1) = 107.7 m1) = 107.7 mθθ1 = atan(r/2d)1 = atan(r/2d)

Bottom reflection => d2 = 2h/cos(q2) = 188.7 mBottom reflection => d2 = 2h/cos(q2) = 188.7 m

θθ2 = atan(r/2h)2 = atan(r/2h)

SBS reflection => d3 = 2(2d/cos(SBS reflection => d3 = 2(2d/cos(θθ3)+ h/cos(3)+ h/cos(θθ3)) = 260 m3)) = 260 m

BSB reflection => d4 = (2d/cos(BSB reflection => d4 = (2d/cos(θθ4)+ 2(h/cos(4)+ 2(h/cos(θθ4))) = 399.5 m4))) = 399.5 m

2/23/20062/23/2006 1010

r=100m

d=20m

h=80m

source destination

θ2 θ2

θ1 θ1

8/9/2019 05 1uap Slides


2/23/20062/23/2006 1111

Time of arrival to the receiverTime of arrival to the receiver

ττii == ddii /c /c ττ0 = 66.70 = 66.7 msecmsec

ττ1 = 71.81 = 71.8 msecmsec

ττ2 = 125.82 = 125.8 msecmsec

ττ3 = 173.33 = 173.3 msecmsec ττ4 = 266.34 = 266.3 msecmsec

8/9/2019 05 1uap Slides


Transmission lossTransmission loss fcfc=22kHz=22kHz

T = 15T = 15 ˚̊C (fmC (fm==100100 kcycleskcycles /sec, A=6e /sec, A=6e--4, B=2.4e4, B=2.4e--7)7)

a = (A fm f2)/(f2+fm2)+Bf2 dB/ma = (A fm f2)/(f2+fm2)+Bf2 dB/m Surface reflection loss (Surface reflection loss (RLsRLs) = 1 dB) = 1 dB

Bottom reflection loss (Bottom reflection loss (RLbRLb) = 3 dB) = 3 dB

TL = TLs + TLa + RLs + RLbTLi = 20log(di) + adi + RLs + RLb

TL0 = 40.3 dBTL1 = 42.0 dB

TL2 = 49.1 dBTL3 = 54.0 dBTL4 = 60.2 dB

2/23/20062/23/2006 1212

8/9/2019 05 1uap Slides


8/9/2019 05 1uap Slides


8/9/2019 05 1uap Slides


Received VoltageReceived Voltage

OCRR =OCRR = --162 dB re V /162 dB re V / µµPA PA

PrePre--amplifier gain, G = 40 dBamplifier gain, G = 40 dB

VdB VdB == SILriSILri --162 + 40162 + 40

V = 10(VdB/10) V = 10(VdB/10)

V0 = 5.9 V V0 = 5.9 V

V1 = 4.0 V V1 = 4.0 V

V2 = 0.8 V V2 = 0.8 V

V3 = 0.2 V V3 = 0.2 V

V4 = 0.1 V V4 = 0.1 V

2/23/20062/23/2006 1515

8/9/2019 05 1uap Slides


2/23/20062/23/2006 1616

Results for 1000mResults for 1000m

8/9/2019 05 1uap Slides


8/9/2019 05 1uap Slides


8/9/2019 05 1uap Slides


Estimating the RangeEstimating the Range

CorrelateCorrelate p(tp(t) with) with p(tp(t--ττpp--ττtt--ττpp)) Find the peak of the correlation,Find the peak of the correlation, λλ

λλ = 2= 2ττpp--ττtt

ττpp is the propagation delayis the propagation delay

Range is, d=cRange is, d=c ττpp = 1500= 1500 ττpp

2/23/20062/23/2006 1919

8/9/2019 05 1uap Slides


2/23/20062/23/2006 2020

Correlation ResultsCorrelation Results

100m, delay estimate is 66.7 msec 100m, delay estimate is 666.7 msec

8/9/2019 05 1uap Slides


Determining the Direction of theDetermining the Direction of theTargetTarget

θθ r 1-r 4

d

Quadrant 1

Quadrant 2Quadrant 3

Quadrant 4

Η1

Η2Η3

Η4

Four hydrophonesFour hydrophones Measure delay atMeasure delay at

each hydrophoneeach hydrophone

Compare delay pairsCompare delay pairs((ττ11,, ττ22), (), (ττ22,, ττ33),),

((ττ33,, ττ44), (), (ττ44,, ττ11) to find) to find

which quadrantwhich quadrant Estimate the angleEstimate the angle

θ = sign(r1-r4)acos( |r1-r4| / d)

2/23/20062/23/2006 2121

Documents

05 1uap Slides