Sub-bottom Profiler ORE Model 1036

8/16/2019 Sub-bottom Profiler ORE Model 1036

1/65

OPERATING ND

MAINTENANCE MANUAL

FOR THE

O.R.E.MODEL 1036

HIGH

POWER

MULTI-FREQUENCY

S U ~ O T T O M PROFILING SYSTEM


2/65

OPERATING AND MAINTENANCE MANUAL

FOR THE

O.R.E. MODEL 1036

HIGH POWER MULTI FREQUENCY

SUB-BOTTOM

PROFILING

SYSTEM


3/65

CONTENTS

Page

l INTRODUCTION

1-1

2. GENER L

DESCRIPTION

2-1

2.1 Major

Sub-Systems

2-1

2 2

Transceiver

2-1

2 2 1 Receiver

2-1

2. 3 Prec i s ion

Recorder

2-2

2 4

Towed Transducer Vehicle

Sub-System

2-4

2 4 1

General

2-4

2 4 2

Fish

2-4

2 4 3

Towing Pos i t ion

2-4


4/65

4.

3.3

Tow

Cable-Model

143A

3.4 Winch

3.5 In te rconnec t ing Cable

(Winch

to

Transce iver

INST LL TION ND OPER TION

4.1 Operat ing

Notes

4 .1 .1 Towing

4 .1 .2

Transmit ter

Power

4 .1 .3 Transmit ter

Frequency

4 .1 .4 Pulse Dura t ion

4 .1 .5 Receiver Bandwidth

4 .1 .6 Adjustment

fo r

Optimum Resul ts

3-5

3-5

3-5

4-1

4-1

4-1

4-2

4-2

4-2

4-3

4-3


5/65

Page

5 2

Propagat ion

Loss

5 2

5 2 1

Spreading

Loss

5 2

5 2 2 Absorpt ion

5 2

5 3

Ref lec t ion

and

Refrac t ion

5 3

5 3 1 Ref rac t ion

5 3

5 3 2

Ref lec t ion

5 3

5 4

Sca t te r ing

and

Reverbera t ion

5 4

5 4 1 Volume

Reverbera t ion

5 4

5 4 2 Surface

Reverbera t ion

5 4

5 5

Noise

5 5

5 5 1 Background

Noise

5 5

5 5 2

Reverbera t ion Noise

5 7


6/65

LIST

OF FIGUR S ND

DR WINGS

Figure 2 1

Figure

2 2

Figure

4 1

Figure

4 2

Figure

4 3

Figure

4 4

Figure

4 5

Figure

4 6

Figure

4 7

Figure

5 1

O.R.E. Model 1036 Sub Bottom Pr o f i l i ng

System

O.R.E. Sub Bottom Prof i l ing System

O.R.E. Model

T610

Junc t ion

Box

North Sea

Fine

Sand

Bottom

North Sea Sand Bottom

Decca N V Survey

Decca Survey

Decca Survey

Pipe l ine

Locat ion

A1200 0001

Miss i s s ipp i River Gulf Out le t Channel


7/65

1.

INTRODU TION

The

O.R.E.

Model 1036 Sub-Bottom Prof i l i ng System i s

designed to obta in accura te ,

continuous

acous t ic pro f i l e s of

l aye r s

beneath

the sur face of the sea bottom as wel l as pre -

c i s i on bathymetr ic

data .

Records

are obta ined by t ransmi t t ing high-power pulses

of

acous t ic

energy from a

t ransducer

array towed in a fa i red

vehic le , or

f i sh ,

by the survey

vesse l .

Because of

the c lean

hydrodynamic

c h a ra c t e r i s t i c s

of

the f i sh ,

opera t ion of

the

system

can

be

mainta ined

a t normal

c ru i s i ng

speeds and

rough

sea condi t ions

without de l e t e r i ous e f fec t s on the acous t ic

t ransmiss ion

path .

a


8/65

opera t ing

frequency

pulse

width

power

and

r ece i ve r

charac-

t e r i s t i c s over

wide

range.

Spec ia l ly designed t ransducers

and rece ive r c i r c u i t r y fu r t he r

enhance

the ab i l i t y to reso lve

echoes from sub-bot tom l ayers


9/65

2. GENER L DESCRIPTION

2.1

Major Sub-Systems

The Model 1036 Sub-Bottom P ro f i l e r System cons i s t s of th ree

major sub-systems, connected

as

shown

in

Figures

2.1

and

2.2.

1) O.R.E. Model 140, 10 kw Transceiver

2)

Prec is ion Recorder

3) O.R.E. Model

136 Towed Transducer Vehicle

and Cable

Assembly

2.2 Transceiver

The Model

140

Transceiver conta ins a t r ansmi t t e r whose

e l e c t r i c a l power

output

i s

cont inuous ly

var i ab l e from to

10


10/65

switch routes

these

s i gna l s t o the rece iver , which i s the

other major component

of

the t ransce iver .

The rece iver i s

a

tuned

ampl i f ie r

with var i ab l e

cente r

f requency, bandpass, and a

t ime

varying gain TVG)

cont ro l .

Front

panel

adjustments permit the center f requency of the

r ece ive r

to be adjus ted to

match

the t ransmit f requency.

The

width

of the

bandpass

f i l t e r can a lso be adjus ted to

accommo

da te the spectrum of the t ransmi t t ed pulse and echo).

The

TV

automat ica l ly

holds

the

gain of

the

r ece i ve r

to

a

low

va lue u n t i l

the

point in t ime

where

the bottom echo

i s

received.

Afte r t h i s in s tan t , the

gain inc reases l i n e a r ly with

t ime

to

compensate

for

the

a t t enua t ion of

sound

through the

sub-bot tom


11/65

t r i c a l

s igna ls from the rece iver , represent ing echoes cause

curren t to

pass from the s ty lus

through the

paper

to

kni fe

edge extending the width of the paper . The

paper

i s

darkened

a t t h i s poin t in

propor t ion to

the i n t ens i ty of the

s igna l .

Since the

s ty lus

t r ave l s across the paper a t con-

s t an t , accura te ly known ra te , the elapsed t ime

between outgoing

pulse

and echo a r r i v a l

m y now be determined.

Using an

assumed

speed

of sound in water of

4 800

fee t per

second the

recorde r

i s

ca l ib ra ted

in uni t s

of t ime

or dis tance ,

e i the r

fathoms

or

meters . Se lec tab le s ty lus sweep speeds represent ing f u l l

sca l e from 20 to 2 000

fathoms

are se l ec t ed by panel

con

t r o l .


12/65

2.4

Towed

Transducer Vehicle Sub-System

2.4 .1

General

This sUb-system cons i s t s of the towed t ransducer vehic le ,

o r

f i sh ,

which

houses

the

acous t ic

t ransducer

array,

f a i r ed tow cable , r e t en t i on

fo r

connect ing the cable to

the

f i sh , deck

mounted

winch

and an in te rconnec t ing cable to

t i e the

winch

end

of the

tow

cable

to

the

t r ansce i ve r .

2 .4 .2

Fish

The f i sh

cons i s t s

of hydrodynamical ly fa i red housing

to enc lose the t ransducer a r ray , means for mounting the array

in the

housing

and s t a b i l i z i n g

t a i l .

The

f a i r ed

housing

f loods wi th water

and

the bot tom ha l f i s acous t i ca l l y t r ans -


13/65

2 .4 .4

Transducers

The t ransducers accept power from the t r ansmi t te r over

the range 3.0 to 7.0 kHz. Sound i s

pro jec ted

downwards in

a roughly conical beam 55 degrees wide a t 3.5 kHz

40

degrees

a t 5 .0

kHz

and

30

degrees a t

7.0 kHz.

Maximum permiss ib le

power

i n to

the t ransducers

i s

10 kw a t

a 1

duty cycle .

2.5

Tow

Cable

The

tow

cable

combines

a

core

of

e l e c t r i c a l conductors

fo r

the t r ansducer connect ions wi th two l ayers of s t a i n l e s s

s t e e l oute r armor for t e n s i l e s t reng th . spec ia l re ten t ion

f i t t i n g

combining

a water t igh t e l e c t r i c a l connec t ion

and

a

mechanica l s t reng th connect ion

i s

used to connect the

cable


14/65

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15/65

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16/65

3. SPECIFICATIONS

The

fo l lowing a re genera l spec i f i ca t ions or opera t iona l

spec i f i c a t i on s

fo r

the components which make up

the

1036

System

3.1

Model

140

Transce iver

3 .1 .1 Transmi t t e r Sect ion

Power

ou tpu t

Output impedance

Frequency

Output

power adjus tment

10

kw RMS

dur ing key pu l se .

5, 10, 20, 30, 40, 45, 50, 55,

60, 75, and

100

ohms.

Cont inuously adjus tab le

1

12

kHz.

o ther

f requenc ies ava i l ab l e .

Cont inuously adjus tab le

from

kw


17/65

3 .1 .2

Receiver

Sec t ion

Input

impedance

Frequency

Bandpass f i l t e r

Output impedance

Maximum ou tpu t vol t age

Sen s i t i v i t y

10 K ohms

Adjus tab le 1-12 kHz. Other f r e

quencies ava i l ab l e .

Center f requency cont inuously

va r i ab le

1-12

kHz. Bandwidth

ad jus t ab le

from 0 .5 kHz

up

to

e s sen t i a l l y f l a t .

Less

t han

100

ohms.

4 V

P-P

minimum.

3 microvol t s R S input

( fo r

2

db s igna l - t o -no i se r a t i o ) produce

V

RMS

output .


18/65

3 .1 .4

Specia l Fea tures

(1) Transmit ter

and r ece iver f requencies independently ad ju s t

able .

(2) Receiver f requency i s matched to

t r an sm i t t e r

frequency by

depress ing

Receiver Test

switch and t un ing fo r maximum

i nd ica t ion on

VU

meter.

The Receiver Tes t

switch pro-

duces

a c a l i b r a t e d s igna l

a t

r ece ive r

input , thus ,

a l so

checking

rece iver

sens i t i v i t y

and

bandwidth.

(3) VU meter

i s

usefu l

by

i t s e l f

for

l i s t en ing

to

remote

sound sources ( i . e .

pingers ,

e t c . ) .

Transmit ter

can

then

be s e t to

rece ive

frequency by

procedure

s imi la r

to

(2)

above.


19/65

Chass is

Power

suppl ies

Size

Weight

3.2

Model 136A

Spec i f i ca t ions

3 .2 .1

Transducer

Array

Transducers

four )

Frequency

range

Bench/rack

chass i s

fu l ly enclosed

and fan cooled.

Regulated,

shor t - c i r cu i t proof

suppl ies used throughout.

17 inches

wide

by 17 inches deep

by

7

inches h igh - - s tandard rack

or bench

mounting.

50

pounds.

Model 137D

3 .0 -7 .0

kHz


20/65

Transducer vehic le

number

l e s s

t r ansducer s )

Upper she l l number

Lower she l l number

3.3

Tow Cable-Model 43A

Standard l eng th

Length of f a i r ed

s ec t i on

Diameter

Armor

Conductors

D135-3732

D135-3769

D135-3770

100

f ee t

30

f ee t

3/8 inch

Two

l aye r s

con t r ahe l i c a l l y wound

s t a i n l e s s s t e e l

4,

Number

19, s t randed copper , po ly -

propylene

i n su la t ed ;

7.7 ohm/1,000 f t .


21/65

4.

INST LL TION ND OPER TION

sepa ra te manual

for each

of

the

t h r e e

major

components

of the

system - -

Model 140 Transceiver

Pre c i s ion

Recorder

and Model 136

Towed Transducer Vehicle

System - - exp la ins

in

de t a i l

opera t ion

maintenance

deployment and i n s t a l l a t i o n .

The fo l lowing i s a

b r i e f

summary of system

opera t ion .

t i o n

4 .2

provides s t e p -by- s t e p opera t ing

procedures .

4 .1 Operat ing

Notes

4 .1 .1 Towing

Sec-

The

f i sh tows wel l a t

speeds in

excess o f 12 knots.

Enough

cab le should be pa id out

so

tha t the f i sh

swims

seve ra l f ee t

below the l eve l o f the

keel . s u f f i c i e n t

l eng th of

f a i r i ng


22/65

4 .1 .2 Transmi t ter

Power

In

most cases , maximum power 10 kw

wi l l

give bes t r esu l t s .

In very sha l low water a shor t

i n t e rva l

of r ing ing a f t e r

t e rminat ion of the t ransmi t pulse may

obscure the

bottom.

This i s minimized by opera t ion

a t

5 kHz.

n

i n t e rna l swi tch

in the t ransce iver (descr ibed in the Transceiver

Manual) al lows

the choice of a

mode

of opera t ion whereby two of the t r ansduce rs

in the array are

used

exc lus ive ly for t r ansmi t t i ng and t he o the r

two

for

rece iv ing

only.

This

conf igura t ion

i s

use fu l

where

a wider

beam

width i s des i rab le , such as in pipe

f inding

app l i -

ca t ions .

Cavi ta t ion when the t ransducer

i s

l e s s than f i f t e en fee t

deep

may reduce power output somewhat;

however, t h i s does not


23/65

4 .1 .5 Receiver Bandwidth

Bandwidth should be as wide as poss ib le and st ll r esu l t

in an acceptable s igna l - to -no ise

r a t i o .

This

adjustment

w i l l

give maximum pulse r i s e t ime and reso lu t ion

for

a given pulse

durat ion.

4 .1 .6

Adjustment

for

Optimum Resul t s

As

noted in

the

preceding sec t ion t ransmi t frequency,

pulse

dura t ion

and rece iver bandwidth

are i n t e r r e l a t e d .

Optimum

adjustment

depends on the r e s u l t s des i r ed

and

the

geology of

the

area being surveyed. I t

i s bes t

determined by

experiment .

4 .1 .7 Time Varying Gain


24/65

4.1 .8 Recorder

Scale

For

a l l informat ion

concerning the

s e t -up

and use of the

recorder ,

r e f e r

to the

spec i f i c

Recorder Manual.

4.2

Opera t ing Procedures

4 .2 .1 Equipment Required

I t i s advisable

to

have the fo l lowing

t e s t

equipment

ava i l ab l e to ope ra t ing

personnel fo r

systems check-out

and

t roubleshoot ing:

a. Simpson 260 VOM or equivalent .

b. Osci l loscope minimum bandwidth 1 MHZ minimum

s ens i t i v i t y .05 vjd iv . dual t r a ce .

c. 100 ohm,

100

watt dummy load

for t r ansce ive r .


25/65

should wet t ransducer

faces

when

washing i s

complete.

DO

NOT GET

SILICONE OIL

OR GREASE

ON TRANS

DUCER FACES.

4 .2 .3

Operat ion

a. Visual ly

inspec t

recorder s ty lus pa r t s

for

any

poss ib le

shipping

damage.

b. Set recorder

con t ro l s

as sugges ted

in

t he recorder

manual.

c. I n s t a l l r o l l of

paper -

plug in recorder .

d. Turn

recorder

ON.

e. I f necessary , place

STOP/START

to

START

to

s t a r t


26/65

j . Set XMT FREQ

a t des i red

operat ing f requency, 3.5

or

5.0

kHz.

k. Set

RCVR

W cont ro l two

pos i t ions

from

CCW.

This

corresponds to a

W

of

approximately

2 kHz.

Inh ib i t

keying

from

the r ecorder .

1. Depress

RCVR TEST

but ton;

ad jus t

RCVR

FREQ

fo r

maxi-

mum ind ica t ion

on

meter .

Readjustment of RCVR gain

vern ie r

may be necessary to keep

reading

on

the

meter

sca le .

m. Restore edge

keying from the recorder .

n. Remove

t r ansce iver top

cover .

Check

to see

t ha t

LOAD

MATCH i s

in the cor rec t s e t t i ng and t ha t the toggle

switches are in

the

combined pos i t ion .


27/65

q. STOP

SHIP.

Deploy f i sh . Check towing

cha rac t e r i s

t i c s as sh ip comes

up

to speed.

NOTE

I t

i s advantageous to

disconnec t f i sh

cable connector a t winch

while

deploying

and

recover ing f i sh

to avoid undue

twis t ing

of cable .

Be

su re power

to

t r ansce i ve r

i s

of f

before d isconnect ing or reconnect ing

cable .

r . Turn

system back on.

Increase XMT kw to fu l l power

as before wai t 30

seconds

before

advancing

power) .


28/65

w. To

use

automatic TVG, se t -up as

in

S-T

above.

Then

depress TVG FINDER and se t bl ip a t approximate ly

one-hal f

the

depth,

but

be

sure

t i s occur r ing in a

white

non-noisy)

sec t ion

of the water column above

the

bottom.

Rota te TVG THRESH f u l l clockwise and gradua l ly

ro t a t e

counter -c lockwise

un t i l TVG ac t ion resumes.

Exper i -

ment

with the

s e t t i ng

of

the TVG THRESH con t ro l .

I f

t i s se t too

low

(coun te r -c lockwise ) ,

the

TVG c i r

cu i t i s not

ac t i va t ed and

sub-bot tom records a re not

enhanced. I f t i s se t too high (c lockwise) , the

TVG

wi l l

f i r e

too

soon

on noise) and wil l cause sa tu ra


29/65

[) CONNECTOR

/

RMK

5

MP FS

\ E.NVIROCON

I

,

____

I SMALL

PIN(TYP)

o LARGE PIN TYP)

--l -

T80

l

0+-

PORT

__ = :J

- t - ~ - + - - - + _ T

(ONN ORE MODEL

137 A

TRANSDUCERS


30/65

4.2 .4

Recommended Order of

Shutdown

Transceiver

1) Reduce XMIT, W to OFF.

2) Wait un t i l H.V. i nd i ca to r goes out .

3)

Turn POWER OFF.

Recorder

1)

Turn of f Scan

switch , i f

appl icable .

2) Turn

of f

Power switch .

3) Remove remainder of

paper from recorder .

Transducer Vehicle

1) Stop sh ip .

2) Recover vehic le .


31/65

shape

used for sub-bottom pro f i l ing to a more

forward

and

a f t e r

looking fan

shape

pa t t e rn

idea l

fo r

objec t

loca t ion .

4.3 .1 Fine

Adjustments

As

in

sub-bot tom

pro f i l i ng ac t ua l

adjus tments of

the

t r ansce ive r cont ro l s wi l l depend a grea t deal upon the spec i f i c

condi t ions experienced.

The most

c r i t i c a l

adjustment wi l l probably be the

t r ans

mi t t e r

f requencies . In genera l t r ansmi t f requencies employed

in p ipe l ine work are higher than those used

fo r

sub-bot tom pro

f i l i ng . I t i s advisable to s t a r t a t kHz and

work up.

Higher f requencies wi l l make smal l e r p ipes v i s ib l e and improve

r e so lu t ion . Higher f requenc ies however a lso decrease

penet ra -


32/65

NOR H

SEA

FALL 1976

FINE SAND BOTTOM

r

13 L_1

''3&

:

.1S

i e JL .

·

._.,

F REQ:5 KHZ SUB BOTTOM

36 INCH DIAMETER PIPE

AT BOTTOM OF TRENCH

.

\

... :; ~ - . : ~ ~

., I'

1.......,.

- - - '7

-

FREQ;

HZ SUB-BOTTOM


33/65

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34/65

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35/65

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37/65

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38/65

5. THEORY OF SOUN

Propagat ion of sound in

sea

water and the mate r i a l s beneath

the

sea

bed

i s governed

by complex se t of phenomena. For

comprehensive t rea tment

of

the theory

of underwater

sound

the reade r

i s

r e f e r r ed

to

the

extens ive

l i t e r a t u r e

on

the

sub-

j ec t .

The

purpose

of

t h i s

sec t ion

i s to presen t

to

the

user

unfami l i a r

with acous t ic

techniques br i e f qua l i t a t i ve summary

of the

fac to rs in f luenc ing

echo sounding and

the

de tec t ion of

sub-bot tom

s t r a t a .

5 .1 Speed of Sound

The speed of sound in l i qu id

or

so l id medium i s func

t i on

of

the proper t i es of the medium. In water the speed

i s


39/65

Likewise

the ac tua l depth of

sub-bot tom

l aye r s observed

with the

system whi le

of ten

expressed

in

fathoms or

fee t

as

i nd ica ted

on the

recorder sca le wi l l

in

genera l be deeper

than

ind ica ted .

The

depth

can

only be determined from sound

speed measurements made from an

ac tua l

core taken

a t the

s i t e .

5 .2

Propagat ion Loss

The

i n t ens i ty

of sound

in any

medium decreases

with

d i s -

t ance

from

the source . The

t o t a l

decrease a t

given dis tance

i s ca l l ed

the propagat ion loss . This

loss

i s

in

genera l

composed

of

two

e lements :

spreading

loss

and

absorp t ion .

5 .2 .1 Spreading Loss


40/65

At

the

f requencies 3 .5-7 .0 kHz)

used with

the

Sub-Bottom

Prof i l e r ,

the absorpt ion

l o s s

in the

water

pa th i s smal l

and

in fac t

i s neg l ig ib le for the shal low

depths

where the equip

ment

i s normal ly

used.

5 .3 Ref lec t ion and Refract ion

The

laws

governing

r e f l e c t i on and r e f r ac t i on of sound in

l i qu i d and s o l i d media are

analogous

to

those

governing l i gh t .

The methods of opt ics ,

in par t i cu l a r , ray t rac ing , a re

exten

s ive ly

used in ana lys is .

5 .3 .1

Ref rac t ion

In echo sounding and sub-bot tom prof i l ing work, the angle


41/65

medium. r e f l e c t i ng sur face i s charac te r ized by

a

parameter

known as

the

r e f l e c t i on l o s s which i s

the

r a t i o

of

the in ten

s i t y of

the

r e f l ec ted wave to the i n t ens i ty of the

inc iden t

wave a t the sur face .

5.4

Sca t t e r ing and

Reverbera t ion

f rac t ion

of the

energy from

a sound

source

may

a lso

be

re tu rned by

the process

of sca t t e r ing .

Sca t t e r ing r e s u l t s

from

p a r t i c l e s

or

smal l - sca le inhomogenei t ies

in

the medium,

whose dimensions are

of the

order

of l e s s than a wavelength.

Sound impinging on these s c a t t e r e r s i s

r e - r ad i a t ed

in

a l l

di rec t ions . The

por t ion

of

energy r ad ia t ed

back

toward

the

t r ansmi t t e r i s ca l l ed

backsca t te r .


42/65

now smal ler

than

the

order

of

a wavelength and the sur face

cannot be

cons idered as

a r e f l ec to r .

The i n t ens i ty

of

a backsca t t e red re tu rn i s ,

in

genera l ,

dependent

on the

prope r t i e s of

the

sca t t e r e r and the

sound

f requency, as well as the range.

5.5 Noise

Noise i s

def ined as

any

unwanted s igna l which t ends to

obscure

the des i r ed

echoes

being

recorded.

Several

types

and sources of noise wil l

be

encountered

in

sub-bot tom pro-

f i l i n g ; most important are background and reverbera t ion noise .

5 .5 .1 Background

Noise (See

Figure

5-4 of the

sample

records)


43/65

the towing

sh ip , and

re su l t s from prope l l e r cav i t a t i on ,

machinery

noise

t ransmi t t ed

through the hul l , and f low noise .

Noise

or ig ina t ing

from othe r sh ips

may

a lso cont r ibute . Flow

and

cav i t a t ion

noise

tends to

be broad

band

with

general

inve rse

r e l a t ionsh ip

to

frequency.

Machinery noise wil l

tend

to

show

d i s t i nc t peaks

a t

f requencies harmonical ly r e l a t ed

to

the

speed

of ro ta t ion .

E l e c t r i c a l noise may

cont r ibu te to

the background, al though

t

should not

be

apparent

unless

the

equipment i s

improper ly

grounded.

Ign i t ion

noise

from

a

gasol ine

engine

or

60

z

hum

from the power l i n e can

be

encountered , and wil l usua l ly be

e l imina ted by

proper

grounding.


44/65

The s igna l - to -no ise

r a t i o i s opt imized

by

including

band

pass f i l t e r in

the rece iver . This f i l t e r

passes

only

the band

of

f requencies

inc luded in the

t ransmi t ted

pulse .

I t s cent

e r

f requency i s the same as the

c a r r i e r f requency, and i t s

band

width

should

be inver se ly

propor t iona l

to the dura t ion of the

pulse .

Thus,

the noise energy ou t s ide the band necessary to

accommodate the pulse i s excluded and the s igna l - t o -no i se r a t i o

improved.

5 .5 .2 Reverbera t ion Noise

Reverbera t ion noise

unl ike

background

noise i s

co r r e l a t ed

with

t he t r ansmi t t ed

pul se

and sweep r a t e s ince it i s

the

r e s u l t of

backsca t t e red energy or ig ina t i ng a t the

acous t ic

pro


45/65

t h i s poin t ,

the

gain s t a r t s to increase

as

l i nea r

funct ion

of

t ime

fo r the

remainder of the

sweep. The th resho ld

value

of gain and

the

r a t e of

increase are

ad jus tab le .

The

break

poin t where the gain begins to increase m y

be

manually

ad

jus ted , or in the

automat ic

mode, w i l l t r a ck

the

bottom. The

TV

r a t e i s

i dea l l y

se t to

compensate

fo r

spread ing and

absorp-

t i on

l o s se s in the bottom.

With

the

foregoing

comments es t ab l i shed , t i s now

poss ib le to make some

spec i f i c

s ta tements

rega rd ing

the

ac tua l

sub-bot tom

pr o f i l i ng

process .

5 .6 Pene t r a t ion and

Depth Resolut ion

In many cases

the user of

sub-bot tom

pr o f i l i ng equipment


46/65

The

presen t

system i s spec i f i c a l l y

des igned for

high

r e so lu

t i on in

the upper one or

two hundred

f ee t

of

sub-bot tom. The

power l eve l i s

the maximum achievable a t moderate cos t

and

weight

with

e l ec t ro - acous t i c

t r ansducer s .

Deeper penet ra t ion

i s

only

accomplished

with

systems

using

lower

f requencies .

In

t h i s

case ,

r e so lu t ion i s sac r i f i c ed for

deeper

pene t r a t i on .

Adjustment

of frequency over the

range

3.5 to 7.0 kHz

and pul se width over wide range a l lows t he use r

to

se l ec t

t he

bes t

compromise between

reso lu t ion

and

pene t r a t i on

for t he

condi t ions wi th in the c a pa b i l i t i e s o f the equipment .

5 .6 .2 Pulse

Energy

Fur ther

a f f e c t i n g t he

r e so lu t ion and pene t r a t ion of

the


47/65

5 .6 .3

Pulse Dura t ion and Rise Time

co r re l a ry to the r e l a t ionsh ip

between

pulse

dura t ion

and f i l t e r bandwidth i s t ha t t he r i s e t ime of

the

f i l t e r e d

pul se

i s

i nve r s e ly propor t iona l

to

the

bandwidth of the f i l t e r .

Note

t ha t

the

r i s e

t ime

dete rmines

t he

r e so lu t ion

with

which

the

i n s t an t

of a r r i v a l

of the pulse may be determined

while

the

pul se dur a t i on

dete rmines how c lose an

i n t e rva l between

two

pu l se s

or echoes

may

be resolved. Thus as t he pu l se

energy i s increased provided t he r ece ive r bandwidth i s pro

pe r ly

ad jus ted the s igna l - to -no i se

r a t i o

w i l l increase and

more

pene t r a t ion

may

be expected.

5 .6 .4

Pene t r a t i on

Versus

Resolu t ion


48/65

By the same token t he un i t

i s

i n sens i t ive in

the

rece ive

mode

to background

no ise

from

d i rec t ions

widely

sepa ra t ed

from the

ve r t i c a l .

The

pa t t e rn of r ad ia t ion

from the

t r ansducer

ar ray

may

be

regarded

as a

cone

whose

t o t a l

angle

i s

inver se ly

propor -

t i o n a l

to frequency.

The angle

var ies

f rom 55 degrees

a t

3.5

kHz

to

30

degrees a t 7 0 kHz. The beam angle i s def ined ,

accord ing to s t anda rd prac t i ce , as

the

angle between the poin t s

a t

a

f ixed

dis tance

from

t he t ransduce r

where

t he

power i s

one

h a l f t he l eve l

measured

on the axi s . At wider

ang les , the

power

f a l l s of f sha rp ly , but some energy i s r ad ia t ed beyond

the

l i m i t s

of t he de f ined beamwidth.

The a rea of t he bottom

i l l umina ted by the beam i s ,


49/65


50/65

p l us the r e f l e c t i on

l o s s encountered

a t

sub-bot tom hor izons

o r i n t e r f a c e s w i l l a l so be f ac to r s determining

the

ul t imate

depth of pene t r a t i on . Sca t t e r i ng may

a l so

occur in s t r a t a

t ha t are not pe r f ec t l y homogeneous.

5 .6 .7

I l l u s t r a t i v e

Records

Figure 5 .1 i s

a

por t ion of

a

record showing t he e f f ec t

o f

a

bot tom

where t he r e f l e c t i v i t y i s

so

high t ha t no use fu l

energy

pene t r a t e s .

The r eco rd i s of

a

t r ave r se

of

a

dredged

channel . The undredged por t ion a t

the

edges of the f igure

show mul t ip l e

echoes

of the bottom

and

no

v i s i b l e

s t r u c t u r e

beneath . The mul t i p l e echoes

a re caused

by

second bot tom ;

t ha t

i s the echo

from

t he bottom

i s

r e f l e c t e d

from

the

water


51/65

'\

\

\

)

[

j

I

f

>

c

il':

Q

i-

'-".

t

r

fJ


52/65

t h in l aye r of decaying organic mat ter conta in ing gas

bubbles

which

formed

a

b a r r i e r to the sound. Recent dredging, shown

by the deep pa r t , removed t h i s

l ayer ,

a l lowing sound

to

pene

t r a t e .

The

depth

of

penet ra t ion

in coarse

or

hard-packed

sand

or

grave l wi l l

be

l e s s than

in

s o f t e r

mate r ia l s such

as

mud

or silt.

n

Figure 5.2

a t the l e f t -hand

edge of

the record ,

no sub-bot tom l ayers

are c lea r ly

v is ib le .

The

bot tom

a t

t ha t poin t i s sand

extending to

a depth beyond the

capab i l i t y

of pene t ra t i on .

The no i se - l ike

r e t u rn

extending below

the

bot tom

i s

probably due to

sca t t e r ing from gravel

o r rocks

mixed with the sand.

A

second

bottom r e t u rn

i s

v i s i b l e

in the

lower

l e f t corner .


53/65

CV )

I f

Q

H

; l

j

b

.r {

I i ;


54/65


55/65


56/65

in

shal low water .

Figure 5 .4 i s an example of extreme noise condi t ions .

Under such condi t ions t may appear as a system malfunct ion .

In t h i s record on the r i gh t s i de the

noise from the

sh ip

complete ly

obl i t e r a t e s the record

and no bottom re tu rn

can

be

seen. When the

ship

was

s topped,

the l e f t

s ide

of

the record ,

the noise l eve l decreased

enough

to

obtain sa t i s f ac to ry records .

By changing the pos i t ion

of

the towed

vehic le

the survey was

ab le

to

cont inue with

good r e s u l t s .

Using a hul l mounted ar ray

with

16

t ransducers

4

x 4) wi l l

a l so produce good records

through

the hul l of a sh ip

as can

be

seen from

Figure

5.5 .

The hu l l

should

be

hor i zon ta l and

f l a t


57/65

6. TROUBLESHOOTING

Fai lu res

which

occur

in

the

system are

f i r s t i s o l a t e d

to a par t i cu l a r

sub-system.

Then the t roubleshoot ing sec t ion

of the appropr ia te

sub-system

manual can be used to i s o l a t e

the

f a i l u r e

to

a

pa r t i c u l a r

component

or

subassembly.

6.1

Quick Subsystem Checks Versus

Symptom

a .

Recorder

w i l l

not scan.

Problem i s

in r ecorder

-

most l i ke ly paper

in te r lock

switch

or

bad

s ty lus .

b.

Recorder

wi l l not

wri te .

Depress mark

but ton - i f no mark

with LIMIT

a t mid-sca le ,

check for

paper

or s ty lu s problem or f a i l u r e in r ecorder


58/65

2)

Check t ransce iver with

ummy

load. See

Trans

ce ive r

Manual.

3) Check

f i sh for

shor t /open c i r cu i t See

Fish

Manual.

e

Audible

output

from

f i sh

but

no

rece ived

s i gna l s

on

recorde r

1)

Check f i sh

for

open c i r c u i t

See

Fish Manual.

2)

Trouble-shoot t r ansce ive r rece iver sec t ion

See

Transceiver Manual.

3)

Check recorder as in b, a lso

check i n t e r f ace

wri t ing

s igna l

to recorde r

from

t r ansce i ve r

a t

i n t e r f ace connector .


59/65

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Documents

Sub-bottom Profiler ORE Model 1036