Marine Resources
Mapping
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Mapping
Marine Res
For thousands of years people have noticed that sounds
Fig.2 Seismic image of seabed layers
Fig.1 Virtual 3-D image of Ireland and continental shelf
produced at a distance take time to travel. Thunder is usually
heard several seconds after the lightning flash that caused it.
For every kilometre it has to travel, sound is delayed by three
seconds. But what exactly is sound? Is it a thing or substance?
For actually
thousands
of years
people
noticed
What
travels from
the source
to thehave
hearer?
Does it that sounds
Fig.1 Virtual 3-D image of Ireland and continental shelf
travel
at a fixedat
speed?
Can sound
water?
Can
produced
a distance
taketravel
timethrough
to travel.
Thunder
is usually
sound be reflected? This lesson will answer some of these
heard several seconds after the lightning flash that caused it.
questions and may help you to re-examine your concept
every
kilometre
it hashow
to travel,
sound
is delayed
by three
ofFor
sound.
It will
also illustrate
sound can
be used
to
seconds.
But what
exactly
is sound?
Is itdetermine
a thing or substance?
construct
detailed
images
of the seabed
and help
itsWhat
composition.
actually travels from the source to the hearer? Does it
travel at a fixed speed? Can sound travel through water? Can
What exactly is sound?
sound be reflected? This lesson will answer some of these
Waves on water have the following properties: they can travel, they
questions
andone
may
youandtotheyre-examine
can
carry energy from
placehelp
to another
generally have ayour concept
than low-pitched sounds, and are used to produce higher resolution
regular repeating pattern of oscillation and a wavelength. Some other
images. The
of
sound.
It
will
also
illustrate
how
sound can be used
to human ear can detect sounds in the frequency range from
properties are less obvious; waves can add together, they can cancel
16 Hz to about 16 kHz. Sound whose frequency is above about 20 kHz is
construct
images
the seabed
andcan
help determine
out
one another,detailed
they can bend
around of
corners
and their speed
not audible (to people) and is called ultra-sound.
change, depending on the medium.
its composition.
More than 2000 years ago some Greek philosophers speculated that
INFOMAR/INSS – Mapping the Irish Seabed
Multibeam sonar
Fig.3 Airbourne laser
bathymetry
the propagation of sound was similar to the propagation of waves on
water. In the 1600s Mersenne was to first to measure the frequency of
a note and correctly interpreted how notes whose frequencies were in
Waves
onproduced
water harmony.
have the following properties: they can
simple
ratios
What exactly is sound?
This aco
detailed b
knowledge
its overlyin
Up to o
transducer
along the
precise p
are proce
informatio
Different fr
resolution
conditions
The Geological Survey of Ireland is currently carrying out a survey of the
seabed around the coast of Ireland, particularly of the continental shelf
on thethey
West Coast and all major bays and harbours – covering an area
travel,
of 525,000 sq. km. Several ships are engaged in the survey and many
can carry
energythat
from
one
place
another
they generally
have a
than
low-pitched
sounds,
and are
used
Robert
Boyle showed
sound
could
not to
travel
throughand
a vacuum;
it
different techniques are
used
to collect information
on water
depth,
the to produce higher
regular
repeating
pattern
of oscillation
andwas
a wavelength.
Some
other
needed
a medium.
In 1686
Newton proposed
that sound
a pressure
nature
of the seabed and
the structure
of the underlying
images.
The human
ear can rock.
detect sounds in the frequency range
disturbance
thatare
wasless
propagated
through
the air
or another
medium. they can cancel
properties
obvious;
waves
can
add together,
out one
another,
can
around
and
Because
sound
exhibits they
many of
the bend
properties
that arecorners
associated
withtheir
water
waves,depending
over the last 300
sound has been described in terms
change,
onyears
the medium.
of waves.
speed
can
Methods
from
This type o
16 Hz to about 16 kHz. Sound whose frequency is above about 20 kHz10
is km/h; t
not audible (to people) and is called ultra-sound.
about twic
The following techniques are used to collect data;
Sidescan
sonar
More than 2000 years ago some Greek philosophers speculated
that sonar, which
• multibeam
is the principal method used–inMapping
the survey
INFOMAR/INSS
the
Irish Seabed
Sound waves are not material things; they do not have an independent
the propagation
of sound
was similar
to the
of waves
In this tec
• singleon
beam echo sounder
existence.
They are merely
disturbances
of a medium
(air,propagation
water etc.).
Fig.4 A towfi
Geological Survey of Ireland is currently carrying
out sh
a survey of the
called a to
water. aIn
thewave
1600s
Mersenne
was
todoes
firstnot
to– measure
of profilerThe
Although
water
can travel,
the water
itself
it just movesthe frequency
• sub-bottom
(shallow seismic) which enables layers of subsea
seabed
around(Fig.
the 2)coast of Ireland, particularly of the continental shelf
the water
upaand
down;
travels isinterpreted
the disturbance.
geological
to be detected
note
andwhat
correctly
how notes whose frequencies were
in structures
of about
on the conductivity,
West Coasttemperature
and all major
bays of
and harbours – covering an area
• measurement of salinity,
and speed
simple ratios produced harmony.
ultrasonic
of 525,000 sq. km. Several ships are engaged in the survey and many
sound
How is sound used for scanning and
microphon
Robert
Boyle
showed
that
sound
could
not
travel
through
a
vacuum;
it
different
techniques
are
used
to
collect
information
on
water
depth,
the
•
seabed
ground-truthing
(direct
measurement
to
verify
other
data)
frequency
measuring?
needed a medium. In 1686 Newton proposed that sound was a •pressure
nature of the seabed and the structure of the underlying rock.
kHz to 500
sidescan sonar
The speed of sound depends on the medium; in air at sea-level it is
echoes are
disturbance that was propagated through the air or another medium.
• gravity and magnetics
about 330 m/s, in seawater it is about 1500 m/s, increasing with depth
The resulti
and temperature. Sound emitted by a source, such as a loudspeaker,
• airborne
images of
Because sound exhibits many of the properties that are associated
with laser bathymetry for use in clear shallow water (Fig. 3)
bounces off surfaces; the reflected sounds or echoes can be detected
a few cent
information is used to provide coordinate data.
over the last
been describedGPS
in terms
bywater
one orwaves,
more microphones.
The 300
time years
it takessound
to travelhas
is proportional
The following techniques are used to collect data;
toof
thewaves.
distance travelled. Over small distances the time is quite small
Ground-truthing
Single-beam •echo
sounders
– less than 1 ms (millisecond) to travel a total distance of one metre
multibeam
sonar, which is the principal method
used in the survey
waves
are not
material things;
doare
notdetected
have an independent
in Sound
water. Using
an array
of microphones
severalthey
echoes
This involves the direct verification of the
In this process a short burst of sound (a ‘ping’) is emitted by a transducer
•
single
beam
echo
sounder
forexistence.
each soundThey
pulse are
emitted.
Calculations
based on
position of(air, water
merely
disturbances
ofthe
a medium
etc.).
indirectly obtained data. The following a
attached
to the underside of a ship. The sound is reflected from the
the sound source, the location of the microphones and the times of
seabed
and, using the
taken for profi
the refl
soundseismic)
(echo) to which enables layers of subsea
Although a water wave can travel, the water itself does not – it just
moves
• time
sub-bottom
lerected
(shallow
•
direct measurement of water d
the echoes can be used to compute the distance to various surfaces.
return, the distance can be
calculated.structures
If the delay to
is, be
saydetected
8 seconds (Fig. 2)
up and
down; what
travels
is the
geological
Using
sophisticated
computer
software
thisdisturbance.
process can be automated
•
direct sampling of the seab
then the distance the sound travelled is 8 x 1500 m = 12,000 m. The
and the resulting data can be used to construct virtual 3-D images of
geological
and chemical
measurement
temperature
and speed
of anal
depth is therefore half•of this
distance since of
the salinity,
sound hadconductivity,
to travel out
surfaces (Fig. 1). The sharpness or resolution of the images depends on
and back again.
•
deployment of video cameras
sound
the density of the measurements and on the wavelength of the sound.
that are indicated by indirect s
High-pitched sounds have higher frequencies and shorter wavelengths
• seabed ground-truthing (direct measurement to verify other data)
Methods
How is sound used for scanning and
measuring?
The speed of sound depends on the medium; in air at sea-level it is
about 330 m/s, in seawater it is about 1500 m/s, increasing with depth
and temperature. Sound emitted by a source, such as a loudspeaker,
bounces off surfaces; the reflected sounds or echoes can be detected
by one or more microphones. The time it takes to travel is proportional
to the distance travelled. Over small distances the time is quite small
– less than 1 ms (millisecond) to travel a total distance of one metre
in water. Using an array of microphones several echoes are detected
for each sound pulse emitted. Calculations based on the position of
the sound source, the location of the microphones and the times of
the echoes can be used to compute the distance to various surfaces.
Using sophisticated computer software this process can be automated
and the resulting data can be used to construct virtual 3-D images of
surfaces (Fig. 1). The sharpness or resolution of the images depends on
the density of the measurements and on the wavelength of the sound.
High-pitched sounds have higher frequencies and shorter wavelengths
• sidescan sonar
• gravity and magnetics
• airborne laser bathymetry for use in clear shallow water (Fig. 3)
GPS information is used to provide coordinate data.
Single-beam echo sounders
In this process a short burst of sound (a ‘ping’) is emitted by a transducer
attached to the underside of a ship. The sound is reflected from the
seabed and, using the time taken for the reflected sound (echo) to
return, the distance can be calculated. If the delay is, say 8 seconds
then the distance the sound travelled is 8 x 1500 m = 12,000 m. The
depth is therefore half of this distance since the sound had to travel out
and back again.
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Mapping
Marine Resources
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Resources
For thousands of years people have noticed that sounds
produced at a distance take time to travel. Thunder is usually
heard several seconds after the lightning flash that caused it.
For every kilometre it has to travel, sound is delayed by three
seconds. But what exactly is sound? Is it a thing or substance?
What
the source
Fig.2 actually
Seismictravels
image from
of seabed
layersto the hearer? Does it
travel at a fixed speed? Can sound travel through water? Can
sound be reflected? This lesson will answer some of these
questions and may help you to re-examine your concept
of sound. It will also illustrate how sound can be used to
construct detailed images of the seabed and help determine
its composition.
What exactly is sound?
Waves on water have the following properties: they can travel, they
can carry energy from one place to another and they generally have a
regular repeating pattern of oscillation and a wavelength. Some other
properties are less obvious; waves can add together, they can cancel
out one another, they can bend around corners and their speed can
change, depending on the medium.
Fig.1 Virtual 3-D image of Ireland and continental shelf
Fig.2 Seismic image of seabed layers
Ireland’s seabed area is an important Multibeam
national resource.
sonar
INFOMAR/INSS, managed jointly by the Geological Survey of
than low-pitched sounds,
and are
usedand
to produce
higherInstitute
resolutionin co-operation
Fig.3 Airbourne
Ireland
(GSI)
the Marine
withlaser
other
images. The human ear can detect sounds in the frequency range from
bathymetry
strategic
partners,
is
a
fi
rst
attempt
to
truly
understand
this
16 Hz to about 16 kHz. Sound whose frequency is above about 20 kHz is
not audible (to people) resource.
and is called ultra-sound.
The survey area is approximately ten times the size of Ireland’s
land area and represents one of the largest seabed mapping
The Geological Survey of
Ireland is undertaken
currently carrying
out a surveyin
of the
projects
anywhere
the world. The information
seabed around the coast of Ireland, particularly of the continental shelf
Multibeam sonar
collected will inform decisions about the management and
on the West Coast and all major bays and harbours – covering an area
sustainable
development
of Ireland’s
marine resources.
of 525,000 sq. km. Several
ships are engaged
in the survey
and many
This acoustic technique is providing
Robert
Boyle showed
that sound could not travel through a vacuum; it
different techniques are used to collect information on water depth, the
Fig.3 Airbourne
laser
detailedthat
bathymetry
depth) data
needed a medium. In 1686 Newton proposed
sound was (water
a pressure
natureand
of the seabed and
the structure of the underlying rock.
Objectives
bathymetry
knowledge
ofanother
the nature
of the seabed and
disturbance that was propagated through
the air or
medium.
overlying
The main objectives of the survey are:
Methods
Because sound exhibits many of theits
properties
thatsediment.
are associated with
More than 2000 years ago some Greek philosophers speculated that
the propagation of sound was similar to the propagation of waves on
water. In the 1600s Mersenne was to first to measure the frequency of
a note and correctly interpreted how notes whose frequencies were in
simple ratios produced harmony.
INFOMAR/INSS – Mapping the Irish Seabed
water waves, over the last 300 years sound has been described in terms
Up to one hundred high
of waves.
The following techniques
to collect
data;
frequency
• areToused
provide
detailed
information about the seabed around
Sidescan sonar
transducers (‘speakers’) are arranged
• multibeam sonar, which isIreland
the principal method used in the survey
Sound waves are not material things; they do not have an independent
along the hull of the survey ship
in abeam echo sounder
• single
• To develop national marine expertise and
spread
this
existence. They are merely disturbances of a medium (air, water etc.).
Fig.4 to
A towfi
sh
precise
returning •echoes
Although a water wave can travel, the
water itselfpattern.
does not – itThe
just moves
sub-bottom profiler (shallow
seismic) across
which enables
layers of subsea
expertise
government
agencies, third level institutions
up and down; what travels is the disturbance.
geological structures to be detected (Fig. 2)
are processed to generate water depth
and a strengthened private sector
information (bathymetry) and contour
• maps.
measurement of salinity, conductivity, temperature and speed of
sound
How is sound used for
scanning
and are used for different
Different
frequencies
The survey area
• seabed ground-truthing (direct measurement to verify other data)
conditions.
measuring?
Ireland’s designated waters extend over 1000 km out into
• sidescan sonar
The speed of sound depends on the
medium;
air atcan
sea-level
it is
This
type ofinscan
be carried
out •at about
the Atlantic Ocean to depths of more than 4500 metres. For
gravity and magnetics
about 330 m/s, in seawater it is about 1500 m/s, increasing with depth
10a km/h;
of the scanned• area
is
surveying
it has
been
into three distinct areas
and temperature. Sound emitted by
source, the
suchwidth
as a loudspeaker,
airborne laser bathymetry
for usepurposes
in clear shallow
water
(Fig. divided
3)
the can
water
depth.
bounces off surfaces; the reflectedabout
soundstwice
or echoes
be detected
GPS information is usedortocontours:
provide coordinate data.
This aco
detailed b
knowledge
its overlyin
Up to o
transducer
along the
precise p
are proce
informatio
Different fr
conditions
This type o
10 km/h; t
about twic
In this tec
called a to
the water
of about
ultrasonic
microphon
frequency
kHz to 500
echoes are
The resulti
images of
a few cent
by one or more microphones. The time it takes to travel is proportional
• 0 – 50 m contour (Zone 1)
to the distance travelled. Over small distances the time is quite small
Ground-truthing
Single-beam echo
– less than 1 ms (millisecond) to travel a total distance of one metre
• 50sounders
– 200 m contour (Zone 2)
in water. Using an array of microphones several echoes are detected
This involves the direct verification of the
•
200
–
4500
m
contour
3)
In this process a short burst
of sound
(a ‘ping’)
is emitted (Zone
by a transducer
In this technique
a torpedo-shaped
device
for
eachAsound
pulse emitted. Calculations
based on the
position of
indirectly obtained data. The following a
attached to the underside of a ship. The sound is reflected from the
Fig.4
towfish
the sound source, the location of called
the microphones
and(Fig.
the times
a towfish
4) isoftowed seabed
through
and, using the time taken for the reflected sound (echo) to
The
survey
generates
a
vast
amount
of
data
• which
directrequires
measurement of water d
the echoes can be used to compute
distance
to various
surfaces.
thethewater
close
to the
seabed at a
speed
return,
the distance can be calculated. If the delay is, say 8 seconds
Using sophisticated computer software this process can be automated
storage,
verifi
cation
and
analysis
and
sophisticated
manipulation
•
direct sampling of the seab
then
the
distance
the
sound
travelled
is
8
x
1500
m
=
12,000
m.
The
of
about
2
km/h.
The
towfi
sh
contains
and the resulting data can be used to construct virtual 3-D images of
and chemical anal
tothis
convert
into the
easily
accessible
such as geological
3-D images.
depth is therefore half of
distanceit since
sound
had to travelformats
out
underwater
surfaces (Fig. 1). The sharpness or ultrasonic
resolution of thetransducers
images dependsand
on
and back again.
• available
deployment
ofavideo cameras
Detailed
maps
and
other
information
are
made
on
the density of the measurements and
on the wavelength
of the sound.
microphones
(hydrophones).
Very high
that are indicated by indirect s
commercial basis by INFOMAR.
High-pitched sounds have higher frequencies
shorter wavelengths
frequencyand
ultrasound
pulses (typically 100
Sidescan sonar
kHz to 500 kHz) are directed laterally and the
echoes are picked up by the hydrophones.
The resulting data is processed to produce
images of extraordinary resolution (down to
a few centimetres).
Ground-truthing
Scientists from many different disciplines are involved in the
Irish National Seabed Survey (INSS). While many of these work
onshore some spend time on the survey vessels involved in data
collection. There are many university projects arising from INSS
data covering topics as diverse as geohazards, telecommunication
cabling, carbonate mounds and ancient landscapes.
This involves the direct verification of the interpretation of sonar and other
indirectly obtained data. The following are some of the techniques used:
•
direct measurement of water depth
•
direct sampling of the seabed and subsequent biological,
geological and chemical analysis in onshore laboratories
•
deployment of video cameras to inspect objects and features
that are indicated by indirect scanning methods.
You can find out more about the work of the
Geological Survey of Ireland (GSI) at
www.gsiseabed.ie or at www.sta.ie
Marine Resources
Mapping
For thousands of years people have noticed that sounds
produced at a distance take time to travel. Thunder is usually
heard several seconds after the lightning flash that caused it.
For every kilometre it has to travel, sound is delayed by three
seconds. But what exactly is sound? Is it a thing or substance?
Syllabus
Reference
What
actually travels
from the source to the hearer? Does it
travel at a fixed speed? Can sound travel through water? Can
Leaving Certificate Physics
sound be reflected? This lesson will answer some of these
Properties of waves
questions and may help you to re-examine your concept
Wave
nature
of sound
of
sound.
It will
also illustrate how sound can be used to
construct
detailed
images
of the seabed and help determine
Junior Certificate
Science
its composition.
Marine Res
Fig.2 Seismic image of seabed layers
Fig.1 Virtual 3-D image of Ireland and continental shelf
Practical Activities
Investigative Activities
If you lightly rub the surface of a table with your finger you cause a local
disturbance of the wood that is propagates through the table. If you put
your ear to the table you will find that the lightest touch can still be heard.
Get someone else to lightly tap a long piece of wood or a wall the see
how far the disturbance can travel.
Section 3B5 – Sound
What exactly is sound?
Waves on water have the following properties: they can travel, they
can carry energy from one place to another and they generally have a
regular repeating pattern of oscillation and a wavelength. Some other
properties are less obvious; waves can add together, they can cancel
out
another, they can
bend
around the
corners
and theirshould
speed canbe
Onone
completing
this
lesson
student
change, depending on the medium.
our
our
Mapping
Put on a blindfold and get someone to lead you into
several rooms
of
Multibeam
sonar
different size. Try to determine the relative size of the rooms merely by
This aco
than low-pitched sounds,
and to
area used
to produce
higheras
resolution
Airbourne
listening
simple
sound such
a finger click.Fig.3
Record
your laser
results detailed b
images. The human ear can detect sounds in the frequency range from
bathymetry
and try to explain them.
knowledge
16 Hz to about 16 kHz. Sound whose frequency is above about 20 kHz is
Learning Objectives
able
not to:
audible (to people) and is called ultra-sound.
its overlyin
Can you devise a way to test whether sound travels faster through the
Up to o
ground (or through water) than through the air. Investigate the origin of thetransducer
• Appreciate that high-frequency sound can be used to measure
water
More than 2000 years ago some Greek philosophers speculated that
INFOMAR/INSS
– Mapping the Irish Seabed
phrase “ear to the ground”.
depth andoftosound
scanwas
the similar
seabed
along the
the propagation
to the propagation of waves on
water. In the 1600s Mersenne was to first to measure the frequency of
Explain
why high-frequency
(ultrasonic)
sonar has
better
a•note
and correctly
interpreted how notes
whose frequencies
were
in
simple
ratios
produced
harmony.
than
audible
sound
The Geological Survey of Ireland is currently carrying out a survey of the
precise p
are proce
informatio
Different fr
conditions
seabed around the coast of Ireland, particularly of the continental shelf
resolution
on the West Coast and all major bays and harbours – covering an area
of 525,000 sq. km. Several ships are engaged in the survey and many
Robert Boyle showed that sound could not travel through a vacuum; it
techniques are used to collect information on water depth, the
• Distinguish between the main sonar scanning methods used different
by
needed a medium. In 1686 Newton proposed that sound was a pressure
nature of the seabed and the structure of the underlying rock.
INFOMAR/INSS
disturbance
that was propagated through the air or another medium.
True or False
Methods
Because
soundwhat
exhibits
many ofby
theground-truthing
properties that are associated
• Explain
is meant
and why itwith
is necessary
Indicate whether the following are
water waves, over the last 300 years sound has been described in terms
The following techniques are used to collect data;
of
• waves.
Appreciate the magnitude of the task of surveying a very large area.
drawing a circle around T or F.
• multibeam sonar, which is the principal method used in the survey
Sound waves are not material things; they do not have an independent
• single beam echo(a)
sounder
The unit of frequency is the hertz (Hz).
existence. They are merely disturbances of a medium (air, water etc.).
Although a water wave can travel, the water itself does not – it just moves
up and down; what travels is the disturbance.
General Learning Points
How is sound used for scanning and
• Sound is not an entity in itself; it is a physical disturbance that
measuring?
• sub-bottom profiler (shallow seismic) which enables layers of subsea
(b) to
Ultrasound
sound
geological structures
be detectedis
(Fig.
2) whose frequency
This type o
10 km/h; t
about twic
true (T) or false (F) by
Sidescan sonar
Fig.4 A towfish
is less than 16 Hz.
• measurement of salinity, conductivity, temperature and speed of
(c) Sound can travel through interplanetary
sound
space.
• seabed ground-truthing
(direct can
measurement
other data)
(d) Sound
bouncetooffverify
objects.
propagates through a medium. It therefore cannot travel through
• sidescan sonar
The speed
of sound depends on the medium; in air at sea-level it is
(e) Sound reflects more strongly from hard surfaces
a vacuum.
• gravity and magnetics
about 330 m/s, in seawater it is about 1500 m/s, increasing with depth
than from soft ones.
and
temperature.
Sound
emitted
by
a
source,
such
as
a
loudspeaker,
•
airborne
laser
bathymetry
for use in clear shallow water (Fig. 3)
• Audible sounds are in the frequency range 16 Hz to about 16,000 Hz
bounces off surfaces; the reflected sounds or echoes can be detected
GPS information is used
to
provide
data.
(f)
Sonar
is coordinate
the use of
radio waves to detect objects.
(16
kHz).
by one or more microphones. The time it takes to travel is proportional
T In
F this tec
called a to
T the
F water
of about
T ultrasonic
F
microphon
T frequency
F
T
T
kHz to 500
echoes are
The
F resulti
images of
aFfew cent
to the distance travelled. Over small distances the time is quite small
The sounders
International Space Station used sonar to
map the oceans T F
• Ultrasound refers to sound whose frequency is higher than about
Ground-truthing
Single-beam(g)
echo
– less than 1 ms (millisecond) to travel a total distance of one metre
20 kHz.
in water.
Using an array of microphones several echoes are detected
2
This
In this process a short
burst
of
sound
(a
‘ping’)
is
emitted
by
a
transducer
T cation
F of the
(h) The INFOMAR/INSS survey area is 500,000 m . involves the direct verifi
for each sound pulse emitted. Calculations based on the position of
indirectly obtained data. The following a
attached to the underside of a ship. The sound is reflected from the
•
Sound
travels
about
330
m/s
in
air
–
about
a
million
times
more
the sound source, the location of the microphones and the times of
seabed and, using (i)
the time
for the refl
(echo) could
to
The taken
first person
to ected
show sound
that sound
not travel
through
a
•
direct measurement of water d
slowlycan
than
the echoes
be light.
used to compute the distance to various surfaces.
return, the distance can vacuum
be calculated.
IfAristotle.
the delay is, say 8 seconds
was
T F
Using sophisticated computer software this process can be automated
•
direct sampling of the seab
then the distance the sound travelled is 8 x 1500 m = 12,000 m. The
• the
Theresulting
time ofdata
travel
ected
sounds virtual
(echoes)
can beofused todepth is therefore half of this distance since the sound had to travel out
and
canofberefl
used
to construct
3-D images
geological and chemical anal
(j) Sound travels faster in water than in air.
T F
surfaces
(Fig. 1).distances.
The sharpness or resolution of the images depends on
measure
and back again.
•
deployment of video cameras
the density of the measurements and on the wavelength of the sound.
that are indicated
(k) Direct verification of sonar data is called ground-truthing.
T byFindirect s
High-pitched
frequencies identify
and shorter
• We cansounds
easilyhave
andhigher
unconsciously
thewavelengths
direction from which a
sound comes to us; the minute time difference between the arrival of
the sound in our left and right ears enable us to do this.
•
People who are blind, and sighted people who are blindfolded, can
learn to use echolocation to detect objects around them – walls,
doors, the size of rooms etc.
•
Bats use high-frequency sound to facilitate catching their prey. Using
echo location alone they can identify the position and speed of an
insect and distinguish between different kinds of insect.
•
Sonar involves the use of sound to measure distances to objects that
are under water.
•
Modern sonar systems in conjunction with computer hardware and
software can be used to map the seabed.
•
High-energy ‘sounds’ (seismic waves) are used to map geological
structures below the seabed.
Check your answers to these questions on www.sta.ie
Examination Questions
2006 Leaving Certificate Higher Level
Describe an experiment to demonstrate that sound is also a
wave motion.
Sound travels as longitudinal waves while light travels as transverse waves.
Explain the difference between longitudinal and transverse waves.
2004 Leaving Certificate Ordinary Level
Sound from a vibrating object can cause diffraction and interference.
our
Mapping
Marine Resources
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Resources
For thousands of years people have noticed that sounds
Fig.2 Seismic image of seabed layers
Fig.1 Virtual 3-D image of Ireland and continental shelf
produced at a distance take time to travel. Thunder is usually
heard several seconds after the lightning flash that caused it.
For every kilometre it has to travel, sound is delayed by three
seconds. But what exactly is sound? Is it a thing or substance?
What actually travels from the source to the hearer? Does it
travel atthe
a fixed
speed? Can
sound travel through water? Can
Explain
underlined
terms.
• The speed of sound is about 330 m/s in air, about 1500 m/s in water,
sound be reflected? This lesson will answer some of these
about 4000 m/s in rocks, 13,000 m/s in beryllium, and 3000 to
Describe an experiment to demonstrate the interference of sound.
questions and may help you to re-examine your concept
6000 m/s in most other metals.
The
diagram
shows
stationary
(standing
wave)toon a vibrating
of sound.
It will
also aillustrate
howwave
sound
can be used
stretched
• Small children can hear frequencies up to about 20 kHz – a few notes
construct string.
detailed images of the seabed and help determine
higher on the musical scale than the upper limit for adults.
its composition.
L
•
What exactly is sound?
Waves on water have
they can travel,
they
X the following properties:
X
X
can carry energy from one place to another and they generally have a
Y
Y
Y
Y
regular repeating pattern of oscillation and a wavelength. Some other
properties are less obvious; waves can add together, they can cancel
out one
theygiven
can bend
around
corners
and
their speed
can(i)
What
is another,
the name
to the
points
on the
string
marked
change, depending on the medium.
X,
Ultrasonics can be used to detect discontinuities in materials, such as
tiny cracks in metal structures that are inducedMultibeam
by repetitive stress.
sonar
• Ultrasonic
transducers
than low-pitched sounds,
and are used
to produce(high-frequency
higher resolution
images. The human earhousehold
can detect sounds
in the
frequency
range from
vermin
such
as mice.
16 Hz to about 16 kHz. Sound whose frequency is above about 20 kHz is
(ii)not
Y?audible (to people) and is called ultra-sound.
‘speakers’)
are used to deterThis aco
Fig.3 Airbourne laser
bathymetry
How many wavelengths are contained in the distance marked L?
More than 2000 years ago some Greek philosophers speculated that
INFOMAR/INSS – Mapping the Irish Seabed
the propagation
of sound
was similar
the propagation
of waves
State
two factors
on which
the tonatural
frequency
of a on
stretchedThe
string
Geological Survey of Ireland is currently carrying out a survey of the
water. In the 1600s Mersenne was to first to measure the frequency of
depends.
seabed around the coast of Ireland, particularly of the continental shelf
a note and correctly interpreted how notes whose frequencies were in
on the West Coast and all major bays and harbours – covering an area
simple ratios produced harmony.
A note of wavelength 1.4 m is produced from a stretched string.
the sq. km. Several ships are engaged in the survey and many
of If
525,000
1588on
- 1648
Robert Boyle
showed
thatissound
could
travel through
a vacuum; itof the note.
different techniquesMarin
are usedMersenne
to collect information
water depth, the
calculate
the frequency
speed
of sound
in air
340 m
s-1,not
needed a medium. In 1686 Newton proposed that sound was a pressure
nature of the seabed
the structure
of the natural
underlyingphilosopher
rock.
Inand
1636
the French
published
(c
= fλ)
disturbance that was propagated through the air or another medium.
Biographical Notes
detailed b
knowledge
its overlyin
Up to o
transducer
along the
precise p
are proce
informatio
Different fr
conditions
a book called Les
This type o
preludes de l’harmonie universelle in which he proposed a theory of music10 km/h; t
Methods
Because
sound
exhibits
many
of
the
properties
that
are
associated
with
and harmony. He made the first direct measurement of the frequency of aabout twic
2003 Leaving Certificate Ordinary Level
water waves, over the last 300 years sound has been described in terms
The following techniques
arehappened
used to collect
data;
note (it
to be
84 Hz). He is known as the father of acoustics (the
of
waves.
In an experiment to measure the speed of sound in air, a student found the
Sidescan
sonar
concluded
that
the frequency
of notes that
together
• multibeam sonar,science
which is of
thesound).
principal He
method
used in the
survey
frequency
wavelength
a sound
wave.
Sound wavesand
are the
not material
things;of
they
do not have
an independent
produced
In this tec
• single beam echo
sounder a harmonious sound were in a simple ratio (1:2, 2:3).
existence. They are merely disturbances of a medium (air, water etc.).
Fig.4 A towfish
Draw
a labelled
diagram
of the
apparatus
used
Although
a water wave
can travel,
the water
itself does
not in
– itthe
just experiment.
moves
• sub-bottom profiIn
ler 1640
(shallow
which enables
layersofof sound
subsea in air by timing echoes overcalled a to
heseismic)
measured
the speed
the water
up and down; what travels is the disturbance.
geological structures to be detected (Fig. 2)
Describe how the student found the wavelength of the sound wave.
of about
known distances; his estimate was 316 m/s.
• measurement of salinity, conductivity, temperature and speed of
ultrasonic
How
studentused
find the
frequency
of theand
sound wave?
sound
Howdidisthe
sound
for
scanning
microphon
frequency
kHz to 500
• sidescan sonar
The speed
of sound depends
on student
the medium;
airget
at sea-level
it is result.
Give
one precaution
that the
tookinto
an accurate
Robert Boyle, the seventh son of the Earl of Cork, was born in Lismoreechoes are
• gravity and magnetics
about 330 m/s, in seawater it is about 1500 m/s, increasing with depth
Castle, County Waterford. From the age of eight he studied in EnglandThe resulti
and temperature. Sound emitted by a source, such as a loudspeaker,
for use in clear shallow water (Fig. 3)
For further examples of past paper questions • airborne laser bathymetry
and in continental Europe. In 1654 he settled in Oxford and with theimages of
bounces off surfaces; the reflected sounds or echoes can be detected
a few cent
GPS information is used to provide coordinate data.
help of Robert Hooke began to study the the relationship between the
check
by one or more microphones. The
time itwww.sta.ie
takes to travel is proportional
to the distance travelled. Over small distances the time is quite small
pressure and the volume of a gas. He discovered that sound could not
Ground-truthing
Single-beam echo sounders
– less than 1 ms (millisecond) to travel a total distance of one metre
travel through empty space; it needed a medium. He also showed that air
in water. Using an array of microphones several echoes are detected
This involves the direct verification of the
In this process a short
burst
of
sound
(a
‘ping’)
is
emitted
by
a
transducer
was necessary for combustion.
for each sound pulse emitted. Calculations based on the position of
indirectly obtained data. The following a
attached to the underside of a ship. The sound is reflected from the
the sound source, the location of the microphones and the times of
seabed and, usingHe
thewas
timethe
taken
for
the
refl
ected
sound
(echo) in
to the modern sense to describe
fi
rst
to
use
the
term
‘element’
•
direct measurement of water d
the echoes can be used to compute the distance to various surfaces.
return, the distance can be calculated. If the delay is, say 8 seconds
a substance that could not be broken down into simpler
substances
Using sophisticated computer software this process can be automated
•
direct
samplingbut
of the seab
then the distance the sound travelled is 8 x 1500 m = 12,000 m. The
and the resulting data can be used to construct virtual 3-D images of
which
could
combine
with
other
to form compounds.
geological and chemical anal
depth is therefore half
of this
distance
since the
sound
hadelements
to travel out
surfaces (Fig. 1). The sharpness or resolution of the images depends on
and back again.
•
deployment of video cameras
the density of the measurements and on the wavelength of the sound.
Boyle together with other scientists formed the Royal Society
in London
that are indicated by indirect s
High-pitched sounds have higher frequencies and shorter wavelengths
in 1660. It is an independent scientific academic society dedicated to
How
did the student calculate the speed of sound in air?
measuring?
• seabed ground-truthing
(direct
measurement
verify other data)
Robert
Boyle
1627 -to1691
Did You Know?
•
•
Speed of sound increases with depth and temperature; in the sea it
travels more quickly at the surface (due to higher temperature). The
speed falls with depth for the first 1000 m or so and thereafter increases
(due to increasing pressure and relatively constant temperature). In
the sea, sounds propagate horizontally for long distance at a depth
at which sound has its minimum speed – about 1000 m. Sounds that
‘stray’ upwards or downwards are refracted back to this layer.
Some animals (elephants, whales) communicate using subsonic
frequencies. Whales can hear one another over tens or even hundreds
of kilometres.
•
Bats use both audible sound and ultrasound (10 kHz to more than
100 kHz). Higher-frequencies sounds have shorter wavelengths and
provide more detailed ‘information’.
•
Ultrasound is used to monitor the development of unborn babies.
promoting excellence in science.
Read more about other famous scientists at www.sta.ie
Revise the Terms
Can you recall the meaning of these terms? Reviewing the
terminology is a powerful aid for recall and retention.
Wave; wavelength; frequency; reflection; refraction; interference;
medium; hertz; kilohertz; sonar; ultrasonic; seismic; ground-truthing;
acoustic; bathymetry; transducer; hydrophone; microphone.
Check the Glossary of Terms for this lesson at www.sta.ie