Gary Final Project Ppt 1

7/30/2019 Gary Final Project Ppt 1

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Development of Robust Signal Processing

Techniques for Detection of UnderwaterImpact and Burst Noise

A. R. Mohanty (PI)

C. S. Kumar (Co-PI)

Department of Mechanical Engineering

Indian Institute of Technology, Kharagpur

22nd November, 2011

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Department of Mechanical Engineering, IIT Kharagpur

Underwater Noise

Outline of presentation

Objectives of the project

Introduction

Experimental setups usedResults

Future scope of work

References

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Underwater Noise

Aim

To find the characteristics of individual drops and artificially generated

bubbles. The research work focuses on time and frequency domain analysis of

impact of falling drops and underwater bubbles bursting to enhance the

understanding of characteristics of rainfall measurements on water bodies.

[Source: Acoustics and Condition Monitoring Lab Mech. Dept, IIT Kharagpur]

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Objectives

Passive underwater noise measurements

Development of artificial rain gauge

(1) Experimental generation and analysis of rain drop impact.

(2) Experimental generation and analysis of underwaterbubble noise.

(3) Comparative analysis of natural and artificial rain

measurements.

(4) Calculation of Total Rainfall Rate (TRR).

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Underwater Noise

Objectives (contd.)

Active underwater noise measurements

(1) Generation of Square pings and study effects of

reflections from tank bottom and side walls.

(2) Applicability of Maximum Length Sequence signals(MLS) for underwater acoustics.

(3) Comparison of various Time Delay Estimation (TDE)

methods using MLS signals .

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Underwater Noise

PASSIVE UNDERWATER

MEASUREMENTS

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Introduction

Underwater rain noise consists of two components viz., noise

due to impact and entrained bubble oscillation noise.

Generation of underwater bubbles

- Natural (Natural rain, Benthic zone, breaking of waves)

- Artificial (Cavitation, artificial rain generation, air hose

underwater)

Mechanism of bubble formation and underwater noise

- Impact of rain drop on water surface- Collapses creating noise (splat)

- Subsequent formation of a bubble underwater

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Underwater Noise

Underwater Noise from a single drop

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(a) Rain signal (b) Impact noise (c) Bubble generated noise



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Introduction (contd.)

When a bubble is created, the pressure is not in equilibrium with its

surroundings.

Water pushes against the bubble thereby compressing it.

As the bubble shrinks, the air inside expands rapidly altering the equilibrium

again.

The bubble thus oscillates between high and low pressure at high frequency

creating a distinctive sound.

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Underwater Noise

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Underwater bubble entrainment is a random process.

Rain drops can be classified as small (0.8-1.2 mm), medium (1.2-2.0 mm) and

large (>2 mm) drops.

Rain drops larger than 6 mm rarely exist in nature.

Small raindrops are remarkably loud because they generate bubbles with

every splash. Medium raindrops do not generate bubbles and are therefore

surprisingly quiet. Large raindrops trap larger bubbles, which produce sound

frequencies as low as 1 kHz.

Introduction (contd.)


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1. Experimental setup and procedurefor measuring drop impact


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Underwater Noise

Set up for drop generation

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Drop size measurement


2mm drop 4mm drop 6mm drop

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Measurement Setup of Underwater noise



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Experimental Procedure

A total of nine experiments (three for each drop size) were

conducted with 2mm, 4mm and 6mm drops.

For each experiment, time history signal data was recordedfor 0.250 sec.

The data was then analyzed in both time domain as well as

in the frequency domain.

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Underwater Noise

Time domain analysis of water drops

Drop size vs

RMS

Drop size vs

KurtosisDrop size vs RMS*

Kurtosis

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Frequency analysis of water drops

0 2000 4000 6000 8000 10000 12000 14000 16000 180000

500

1000

1500

2000

2500

3000

3500

Frequency of 6 mm drop (Hz)

Pressure

(pa)

5898

Hz

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Spectrograms of water drops

6mm drop

Time s

Frequency(H

z)

0 0.05 0.1 0.15 0.20

2000

4000

6000

8000

10000

12000

14000

16000

18000

-60

-40

-20

0

20

40

60

80

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Results (Experiment 1)

Generation of drop of 2 mm, 4 mm and 6 mm sizes isconsistent and having very good repeatability with thepresent experimental setup.

The pressure variation range has been observed highestin a drop impact if the bubbles formation takes place.

As the drop size increases, the range of pressurevariation, kurtosis and RMS, RMS*Kurtosis valueswere found to increase linearly.

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Underwater Noise

Results (contd.)

The frequency of drop impact decreases as the drop sizeincreases.

The frequencies of bubble bursting are observed fromspectrum and spectrogram analysis to vary from 4000Hz to 14000 Hz.

The frequencies of bubble bursting also depends onbubble size, turbulence of bubbles underwater and thedepth at which it is generated.

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2. Experimental setup and procedure

for measuring underwater bubble

oscillations


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Underwater Noise

Experimental setup for artificial generation

of bubbles


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Results (contd.)

The frequency of underwater bubble oscillation is givenby Minnaret [10]:

Where,

f is the resonance frequency of bubble

a is the drop size,

= 1.4 is the ratio of specific heat for airP is the atmospheric pressure

is the density of water

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P

af3

2

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Underwater Noise

Frequency analysis of bubble oscillations

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Bubble of sizes 0.5 to 2 mm Bubble of size 2 mm Bubble of size 3 mm

Bubble of size 4 mmBubble of size 6 mm

Bubble of size 5 mm



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Underwater Noise

Resonating Frequencies of

Underwater Bubbles

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Comparison between Theoretical and

Experimental Resonating Frequencies of Bubbles

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Underwater Noise

Spectrograms of underwater bubbles bursting

Time (s)

Frequency(H

z)

0 0.05 0.1 0.15 0.20

2000

4000

6000

8000

10000

12000

14000

16000

18000

-20

0

20

40

60

80

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Spectrum of underwater bubbles bursting

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Generation of underwater bubbles of various sizes is consistent andhaving very good repeatability with the present experimental setup.

Resonating frequencies of bubble analysis are similar to thetheoretically calculated results, with a slight deviation for smallerbubbles (< 2mm).

This deviation is due to the shorter life span and limitation ofmeasurement technique for bubbles less than 1mm in diameter.

Underwater Bubbles of 2mm size are mostly formed in all types ofrain.

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3. Experimental setup and procedure

for measuring natural and artificialRain Drop


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Underwater Noise

Experimental Setup for Natural and

Artificial Rain

Artificial Rain by hose ( 1- 5 mm)

Natural rain Artificial rain by shower head ( 1- 2 mm)

Artificial rain by tray of uniform drops

( approx. 5 mm)

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Time History Graph

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Spectra of Natural and Artificial Rains

0 1000 2000 3000 4000 5000120

140

160

180

200

220

240

260

280

300

Spectra of natural rain (Hz)

dB

/ref.1u

pa

0 1000 2000 3000 4000 5000120

140

160

180

200

220

240

260

280

Spectra of artificial rain by Hose(Hz)

dB/

ref.1u

pa

0 1000 2000 3000 4000 5000140

160

180

200

220

240

260

280

Spectra of artificial rain by tray of uniform drop(5 mm) (Hz)

dB/

ref.1u

pa

0 1000 2000 3000 4000 5000120

140

160

180

200

220

240

260

280

Spectra of artificial rain by Shower head (Hz)

dB/

ref.1u

pa

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Results of Time Domain Analysis of


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Natural and Artificial Rains

Rain types maximum minimum Range Mean RMS Variance Std Skew Kurtosis rk=rms*kurt

1. Natural rain 291.96 -290.64 582.6 0.03 180.07 32426.74 180.07 -0.002 1.36 244.78

2. Artificial rain by

hose361.08 458.13 819.21 -0.002 35.1 1232.04 35.1 0.07 3.53 124.23

3, Artificial rain byshower head

322.98 -317.21 640.19 -0.01 38.13 1454.26 38.13 0.02 4.08 155.88

4. Artificial Rain

drops ( 5 mm)

1608.68 -945.56 2554.25 -0.04 51.19 2620.19 51.19 0.58 16.86 863.03

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R lt f Ti D i A l i f


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Natural and Artificial Rains

Legend

NR- Natural Rain,

AR Hose- artificial Rain by hose (1-5 mm)

AR Sh- Artificial rain by Showerhead drop size (1-2 mm)

AR Ud5- Artificial Rain of uniform drops (5 mm )

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Underwater Noise


Large bubbles, above 10 mm in diameter, are not much useful

for underwater rain noise measurement as they have low

resonating frequencies (< 500Hz).

Underwater bubbles of 2mm diameter are mostly formed,

resulting in a corresponding 4 kHz peak in the spectra of all

types of rain.

During heavy rainfall, lower frequency peaks (less than 4

KHz) are always formed due to generation of large underwater

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During light rainfall, higher frequency peaks (up to 20 kHz)

are usually formed.

Strong signals of Frequencies 3500-4500 Hz can be observedin Natural and Artificial rains from FFT Spectra.

As the size of drop decreases, the frequencies of entrainment

increases; it can be seen in FFT spectrum and Spectrogram of

artificial rain by showerhead where drops size was 1-2 mm

diameter only.

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4. Calculation of Total Rainfall Rate

(TRR)


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Total Rainfall Rate (TRR)

TRR in mm/hr can be calculated by[2]

TRR= 6.10-4D D3VT(D)N(D)dDwhere

D is rain drop size (mm),

VT is terminal velocity (m/s),

N(D) is the rain drop size distribution

N(D) can be found by a Disdrometer or by acousticinversion methods.

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5. Conclusions


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Conclusions

Sources of underwater sound of rainfall are impact sound and

pulsations of entrained bubble.

Impact sound depends upon drop size, impact speed and drop

shape.

Small bubbles (0.8-1.2mm) produce sound both due to impact

and bubble oscillations in the range of 13-20 KHz.

Tiny bubbles (< 0.8mm) and medium bubbles (1.2-2mm)

produce relatively weak sound which is mainly due to impact.

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Conclusions (contd.)

Large bubbles (> 2mm) produce sound both due to impact and

bubble oscillations in the range of 1-30 KHz.

Maximum rain drop sizes found in atmosphere are till 5mm.

Rain drops of 2 mm size are commonly found in all types of

rainfall resulting in prominent peak at 14 KHz.

The frequency of drop impact decreases as the drop size

increases.

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Underwater Noise

Conclusions

Underwater bubbles of 2mm diameter are mostly formed, resulting

in a corresponding 4 kHz peak in the spectra of all types of rain.

Large bubbles, above 10 mm in diameter, are not much useful for

underwater rain noise measurement as they have low resonating

frequencies (< 500Hz).

As the size of drop decreases, the frequencies of entrainment

increases; it can be seen in FFT spectrum and Spectrogram of artificial

rain by showerhead where drops size was 1-2 mm diameter only.

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ACTIVE UNDERWATER

MEASUREMENTS

E i t l S t f U d t


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Experimental Setup for Underwater

Time Delay Estimation



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Experimental Procedure for Square Ping

Two square waves of 20 kHz and 100 kHz were generated for

conducting this experiment

20 kHz and 100 kHz square ping of 4ms with a spacing

.0000125 sec was generated

The generated signals were then passed through the

experimental set up.

The time histories of the input and output signals were then

recorded using data recorder


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Calculate the time taken for the input signal to reach the

receiver hydrophone.

S = C * (del t/2)Del t= 2S/C=0.44/1500= 0.29 ms

where

C= speed of sound in water

Mathematical calculation of time delay in

under water transmitting and receiving signal


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0 1 2 3 4 5

[s]

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8Cursor values

X: 4.994 s

Y: -13.157m

Signal2 (Real)

0 1 2 3 4 5

[s]

-24m-16m

-8m

0

8m

16m

24mCursor values

X: 4.983 s

Y: -1.033m

Signal1 (Real)

Time domain analysis of Square Ping


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Time domain analysis of Square Ping

0.24 0.244 0.248 0.252 0.256 0.26 0.264 0.268

[s]

-24m

-20m

-16m

-12m

-8m

-4m

0

4m

8m

12m

16m

20m

24m

Cursor values

X: 0 s

Y: -0.989m V

Signal 6 (Real)

0.24 0.244 0.248 0.252 0.256 0.26 0.264 0.268[s]

-0.4

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-50m

0

50m

0.10.15

0.2

0.25

0.3

0.35

0.4

0.45Cursor values

X: 0 sY: 36.342m V

Signal 7 (Real)


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Maximum length sequence (MLS) is a type of pseudorandom binary sequence.

MLS are bit sequences generated using maximal linear feedback shift registers

because they are periodic and reproduce every binary sequence that can be

reproduced by the shift registers.

For length-m registers MLS signal produce a sequence of length

(2m 1) registers.

MLS is also sometimes called a n-sequence or a m-sequence.

MLS signals MLS measurements have a very high Signal/Noise ratio. The

cross-correlation used to compute the impulse response reduces all background

noise (uncorrelated with MLS), so that measurements can be performed also in

noisy environments.

Maximum Length Sequence Signal


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MLS Signal Properties

0 0.5 1 1.5 2 2.5 3 3.5

x 104

0

0.5

1Original MLS signal(m=15)

0 0.5 1 1.5 2 2.5 3 3.5

x 104

-5

0

5MLS signal with random signal

0 1 2 3 4 5 6 7

x 104

-1

0

1

cross correlation


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Experimental Procedure for MLS Signal

The generation and recording of Maximum length sequence (MLS) signal

of same length at different sampling frequencies.

The generated signals were then passed through the experimental set up.

The time histories of the input and output signals were then recordedusing data recorder.

MLS signals of length 32767 (m=15) and sampling frequency of 44100 Hz

was used for the finding the time delay.


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MLS Measurement Flow chart

[Source: MLS Impulse Response Measurement for Underwater Bottom Profiling [18]]

Underwater Time Delay Estimation


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Underwater Time Delay Estimation

using MLS signals

30 cm

55 cm

95 cm

25 cm

Direct Measurement.

S = C * (del t);

Del t= S/C=0.30/1500= 0.2 ms

= 200 us

Bottom reflected Measurement.

S = C * (del t/2);

Del t= 2S/C=0.44/1500= 0.733 ms

= 734 us

Direct Measurement.

S = C * (Del t);

Del t= S/C=0.95/1500= 0.633 ms

=634 us

Bottom reflected Measurement.

S = C * (Del t/2);

Del t= 2S/C=0.44/1500= 0.333 ms=

334 us

Case 1 Case 2


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Case 1

Direct

measurement

at 200us

Bottom

Reflections

at 750us

Side wall

Reflections


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Case 2

Bottom

Reflections

at 350us

Direct

measurement

at 670us

Side wall

Reflections


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Cross Correlation -Matlab

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-400

-200

0

200

400

Time (s)

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Generalized Cross Correlation (GCC) -Matlab

Rr1r2() = p(f) Gr1r2(f) ej2ft df

where,

Gr1r2(f) is cross spectrum

p(f) is PhaseTransform(PHAT) weighting

function

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Various Weighting Functions

Roth auto correlation

SCOT filter

CPS-m

Where n= 0.5 to 0.75

))((*)(

1)(

fSjconjfSif

n fSjconjfSjfSiconjfSif

))((*)(*))((*)(

1)(

))((*)(*))((*)(

1)(

fSjconjfSjfSiconjfSif


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TDE with Weighting Functions -Matlab

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Future Scope of work

W Ah d


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Way Ahead

Passive underwater noise measurements

- Acoustic Inversion method for estimation of drop size

distribution.

Active Underwater noise measurements

- Underwater imaging of objects using MLS signals.

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References


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References

[1] D. K. Woolf, Bubbles, Academic press, Southampton Oceanography Center, UK Academic press2001.

[2] L. Bjerne,Underwater rain noise: sources, spectra and interpretations, Journal de Physique IVColloque C5, supplement au Journal de Physique III, vol. 4-mai 1994.

[3] J. A. Scrimger, D. J. Evens, G. A. Mcbean, D. M. Farmer, and B. R. Kerman, Numericalcalculations of underwater noise of rain, Journal of Acoustical society of America vol. 81, pp.79 -86-1987.

[4] H. Medwin, J. A. Nystuen, P.W Jacobu, D. E. Snyder, and L. H. Ostwald, The anatomy ofunderwater rain noise, Journal of Acoustical society of America 92, 13 - 23, 1992.[5] H. Medwin and L. Bjerne, Underwater sound produced by individual drop impacts and rainfall,Industrial Acoustics Laboratory, Technical University of Denmark, Building 425, DK-2800 Lyngby,

Denmark, Journal of Acoustical Society of America, vol. 85(4) pp.1518-1526-April 1989.

[6] C.W. Hirt, Bubble bursting at a water surface, Flow Science, Inc. FST-91TN26-1991.

[7] A. Prosperetti and H. N. Oguz, The impact of drops on liquid surfaces and the underwater noise ofrain, Annual Review Fluid Mechanics vol.25, pp. 577-602-1993.[8]. L. K.Lawrence ,R.F. Austin, A. B. Coppens, Fundamentals of Acoustics, fourth edition, JohnWiley.

[9]. Hugh C. Pumphrey and L.A. Crum, Journal of Acoustical Society of America, Vol.85,

No. 4, April 1989, PP. 1518-1526.

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References

[10]. M. Minnaert, philos. Mag., Vol. 16, 1933, PP. 235-248.[11].G.J.Franz, Journal of Acoustical Society of America, Vol. 85, PP. 1080-1096.

[12]. T.E. Heindsman, R.H. Smith, and A.D. Arneson, Journal of Acoustical Society of America, Vol.

27, 1955, PP. 378-379.

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Underwater Noise

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Best Research paper Award

Srinivas Garimella , M. L. Chandravanshi, and A. R. Mohanty,

Characteristics of Underwater Bubble Noise, Proceedings ofNational Symposium on Acoustics,2011, Jhansi, Nov 17 to 19, 2011.

Papers pending for Publication

(1) Srinivas Garimella , M. L. Chandravanshi, and A. R. Mohanty,

Underwater Noise Spectra of Rainfall-An Analysis .

(communicated to JASA)

(2) Srinivas Garimella , S. Fatima, and A. R. Mohanty,UnderwaterTime Delay Estimation Techniques with Maximum Length

Sequence Signals . (under preparation)

Conference Publication


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THANK YOU

Gary Final Project Ppt 1

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