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Equipamentos Electrónicos
Marítimos I
Sonda Gráfica e SONAR
Princípios Gerais de Funcionamento
e Circuitos característicos
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Preia‐mar
Baixa‐mar
Nível do mar (actual)
Zero Hidrográfico
Fundo
Sonda actual
(Sonda à hora)Sonda verdadeira(Sonda reduzida)
Altura da
Maré
Sonda negativa
Medidas para a sonda e zero hidrográfico
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Posidonius
• conducted the first bathymetric studies
• 85 B.C.
http://www‐groups.mcs.st‐and.ac.uk/history/BigPictures/Posidonius.jpeg
2 km
Bathymetry = study of ocean floor contours
The early, simplest methods involved
lowering a weight on a line.
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http://www.nefsc.noaa.gov/history/ships/albatross1/sigsbee‐sounding.jpg
Sigbee sounding machine
• developed around 1880
Tanner sounding machine
• developed around 1880
http://woodshole.er.usgs.gov/operations/sfmapping/images/theb0914_small.jpg
Sometimes the weight was tipped with wax to
retrieve a sample of bottom sediment.
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V = speed of sound in
water
(about 1.5 km/sec)
T = time
Echo sounders sense the
contour of the
seafloor by
beaming sound
waves to the
bottom and
measuring the
time required for
the sound waves
to bounce back
to the ship.
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Echo Sounding
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Base de tempo Oscilador e Gerador de
impulsos
Transdutor
UNIDADE
INDICADORA
Amplificador de
recepção
Amplificador de
transmissão
Transdutor
Largura do
impulso
Largura do
feixe
ECOS
IMPULSO
Distância ao alvo = (te + tr)*c/2
te ‐ tempo de ida do impulso
tr ‐ tempo de retorno do impulso
c ‐ velocidade de propagação
Diagrama funcional da sonda acústica
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SOund NAvigationand Ranging• Developed for tracking submarines during World
War II
• Improvements were
made when first‐generation echo sounding
could not penetrate into
deep canyons where enemy submarines were
hiding.
SONAR
Sverdrup, Duxbury, & Duxbury, An Introduction to the World’s Oceans, 8th ed., McGraw Hill, Fig. x
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Sonar ‐ Sound Navigation And Ranging
• Paul Langevin (físico Francês – 1917)‐
localizarsubmarinos alemães
• Não foi usado antes do final da primeira guerra
mundial (1914–1918)
Esquema simplificado do sonar – O aparelho emite ultra‐sons (em vermelho) que atingem o objeto (em azul), sendo refletidas sobre a forma de eco (em
verde) e voltando ao aparelho receptor. Com base no tempo entre a emissão
e a recepção, é calculada a distância (r)
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The Ocean Floor
Hand soundings:20/hour in 33’
1/ 4 hours at 13,000’
Echo sounding
(original):36,000/hr in 33’680/hr in 13,000’
Echo sounding(modern systems):
293,000/hr in 33’
20,000/hr in 13,000’
Braça : Antiga medida de comprimento. usada no comprimento das amarras
e das linhas de prumo. A que hoje ainda se usa tem cerca de 1,83 m .
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• Sound waves are compressional
waves, longitudinal wave• Atoms in rock move
back and forth, parallel to the direction in which
the wave is traveling
• Less attenuation in water than EM
waves
Sonar; Sound Waves
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• A transducer generates a pulse of sound
• The sound wave hits an object
and bounces back• Transducer: converts electrical
energy to mechanical
vibrations
Elements of SONAR
From www.ndt‐ed.org/education
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Basic Sonar Systems
• Active – Echo Ranging Systems• Passive
– Listening Systems• Communications
– Underwater telephone
• Range of Penetration into the Medium.
• Ability to differentiate between
objects in the Medium.
• Speed of Propagation.
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Concepts of Sound
• Three (3) elements required for this to
work
– Source – Medium – Detector (Receiver)
• The source VIBRATES causing a series of compressions and rarefactions in the
medium
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Transmission Losses
Two main types:
• Spreading – Spherical (omni‐directional point source)
– Cylindrical (horizontal radiation only, or thermal layer, or large ranges compared to depth)
• Attenuation – Absorption
– Scattering and Reverberation
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Transmission Losses (cont.)
• Attenuation
– Absorption
• Process of converting acoustic energy into heat.• Increases with higher frequency
– Scattering and Reverberation
• Volume: Marine life, bubbles, etc.
• Surface: Ocean surface, wind speed
• Bottom: – Not a problem in deep water.
– Significant problem in shallow water; combined
with refraction and absorption into bottom.
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Speed of Sound in Seawater
V is dependent on:
• water
temperature
• salinity
• water pressure
Average speed of sound in seawater: 1500 m/s
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Self Noise
• Machinery Noise – Pumps, reduction gears, power plant, etc.
• Flow Noise – High speed causes more noise
– Hull fouling ‐ Animal life on hull (not smooth) – Want LAMINAR flow
• Cavitation
– Low pressure area – Bubbles collapse, VERY NOISY
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Screw Cavitation
Screw Speed, Pressure behind screw blades, Water Boils,Bubbles form, The subsequent collapsing of the bubbles cause
the noise.Going deep increases pressure so can go
faster without cavitating.
Water
Flow Water
Flow
Blade Tip
CavitationSheet Cavitation
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Ambient Noise
• Hydrodynamic – Caused by the movement of water.
– Includes tides, current, storms, wind, rain, etc.
• Seismic
– Movement of the earth (earthquakes)• Biological – Produced by marine life
• Ocean Traffic
– At long ranges only low frequencies are present.
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Dissolved Components in Seawater
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Composition of Seawater
Salinity
Salinity is
the
total
amount
of
solid
material
dissolved in water
Typically expressed as a %
Dissolved substances
in
seawater
are
small
numbers
and therefore expressed in parts per thousand Most of the salt in seawater is sodium chloride
(table salt)
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Composition of Seawater
Salinity
Processes affecting seawater salinity
Primarily due to changes in the water content of the solution
These include the addition of fresh water
due to precipitation, runoff, icebergs melting, and sea‐ice melting
The removal of fresh water by evaporation
and the formation of sea ice also affect salinity
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Mapping the Ocean Floor
Multibeam
sonar
Employs and array of sound sources and
listening devices
Obtains a profile
of
a narrow
strip
of
seafloor
Measuring the shape of the ocean surface
from space
Employs satellites equipped with radar altimeters
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Echo Sounder
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Multibeam systems combine many echo sounders.
• up to 121 beams
• signal sent every 10 secs <200 research vessels are
equipped with multibeamsystems
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Seabed contours can be mapped using satellites.
Satellites cannot
measure ocean
depths directly
• but, they can
measure sea surface
height
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Gravitational attraction “pulls” water
Over a 2000 m seamount, water rises about 2
m
Seafloor
Sea surface
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Ocean‐floor topography varies with location
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Launching,Towing, and
Recovery ofROVs andAUVs
Wind Speed/ Direction System
CTD
Depth Finding System
Doppler Speed Log
NAVSTAR GPS
I-MET Sensors
AcousticPosition
Acoustic DopplerCurrent Profiler
HydrographicEcho Sounder
Deep Water MultibeamEcho Sounder
Shallow WaterMultibeam EchoSounder
Picture courtesy of Lockheed Martin
AcousticPositioning
System
OCEAN Class Sonar Systems
• EM 122 1 x 2 DegMultibeam
• EM 710 0.5 x 1 Deg
Multibeam• EA-600 Single Beam
Echosounders- 12,30 120, KHz
• HiPAP 500 - Acoustic PositioningSystem
• SBP 120 6 x 6Subbottom Profiler
• ADCP – 38, 150,300 KHz
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Ultra‐Som e Intervalos Sonoros
20Hz 20000Hz
Infra-Sons Ultra-Sons Audição Humana
Elefantes(2 km)
Cão, morcegoE golfinho
• Som = Vibração da matéria;
• Transmissão:
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Propagação do Som
• Objeto vibra = O movimento
das partículas carrega e
transmite a vibração.
• Expansão ‐ compressão e
corresponde à pressão máxima da propagação
sonora
• Contração ‐ rarefação e corresponde à pressão
mínima da propagação
sonora.
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Esquema de Onda Sonora
Individualmenteas ondas sonorassão caracterizadas por:
• O comprimento de onda , é a menor distância que vai de uma
crista à outra ou de uma depressão à outra.• A amplitude é a distância que vai de uma crista ao eixo depropagação da onda. Pode ser também a distância do pontomáximo da depressão ao eixo de propagação.
• Período é o tempo gasto para que uma oscilação sejacompletada. No exemplo da figura 2, o período é de 1 segundo.
• A velocidade de propagação das ondas é constante para umdeterminado meio.
Esquema de Onda
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Freqüência de uma Onda
• A frequência = número de oscilações por segundo;• A unidade é chamada de hertz (Hz).• As ondas tem a mesma frequência da fonte emissora,
independente do meio em que se propaga;• Período (inverso da frequência);
Esquema de Onda
F=1/T
T=1/F
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What do we mean by ultrasound?
• Acoustic waves with frequencies above those which can be detected by the human ear. In
practice, 20 kHz < f < 200 MHz.
• An acoustic wave is a propagating disturbance in a medium, caused by local pressure changes at a transducer.
• The molecules of the medium oscillate about their resting (equilibrium) positions, giving rise to a longitudinal waves.
• c ≈ 1540 m/s ≡ 6.5 μs/cm in most body tissues• λ = c / f = 1.5 mm at 1 MHz.
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Speed of sound• The speed of sound is a constant in a given material (at a
given temperature), but varies in different materials:
• Material Velocity ( m/s)
Air 330Water 1497
• Água doce 1435• Metal 3000 ‐ 6000
No vácuo, onde não existe o indispensável meio
material que o transporte, o som não se propaga.
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Fenômenos Sonoros
Interface:
Transmitida;
Refletida;
Refratada...
Onda Sonora
•Comportamento do som;
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Reflexão
• Quando encontra um meio que não pode ser contornado aonda "bate e volta“;
• Mudança de direção de propagação da energia ;
• Retorno da energia incidente em direção à região de onde ela éoriunda;
• O ângulo de incidência tem valor igual ao valor do ângulo de
reflexão;
Diagrama simples ilustrando o fenômeno da reflexão.
Ângulo deIncidência
Ângulo deReflexão
Normal
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Reverberação
• Chama‐se reverberação o fato de tantas reflexõeschegarem ao ouvinte que ele não as pode distinguirumas das outras.
• É a chamada continuidade sonora e o que ocorre em
auditórios acusticamente mal planejados.
O som breve refletido chegaao ouvido antes que otímpano, já excitado pelo
som direto, tenha tempo dese recuperar da excitação(fase de persistênciaauditiva).
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Refracção• A mudança da direção das ondas, devido a entrada em outro
meio;
• alteração da direção do feixe transmitido em relação ao feixe
incidente;• passagem da onda por meios com diferentes índices de
refração;
• mudança no comprimento e velocidade, freqüênciapermanece a mesma;
Refração do ar para a água
- Falta de ângulo
impede a refração eleva à reflexão
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Difracção•A onda tem a capacidade de contornar obstáculos;
•A difração sonora é imensa por ter seu comprimento muito
grande ‐ enorme quando comparado com o comprimento deonda da luz
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Interferência
• Representa a superposição de duas ou maisondas num mesmo ponto;
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Interferência Construtiva
• caráter de reforço quando as fases combinam
(interferência construtiva).
Exemplo: Quando escutamos música em nosso lar, percebemos que certos locais no
recinto é melhor para se ouvir a música do que outros. Isto é porque nestes pontosas ondas que saem dos dois alto‐falantes sofrem interferência construtiva
Interferência construtiva
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Interferência Destrutiva
• Caráter de aniquilação, quando as fases nãosão as mesmas (interferência destrutiva)
Ex: Ao contrário, os locais onde o som está ruim de ouvir é causado pela interferência destrutiva das ondas.
Interferência destrutiva
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Impedância
Impedância acústica de alguns materiais
Material (106 Rayls)Ar 0,0004
Água 1,48
Todo meio material elástico oferece uma certa"resistência" à transmissão de ondas sonoras;
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Mapping the ocean floor
Bathymetry – measurement of ocean
depths and the charting of the shape or topography of the ocean floor
Echo sounder (also referred to as sonar)
• Invented in the 1920s
• Primary instrument for measuring depth
• Reflects sound from ocean floor
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Detected
school
School
NOT
detected
Use of the Sonar
U f th S
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Use of the Sonar
Positioning & Orientation Systems for
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50
Positioning & Orientation Systems for MultiBeam Hydrography
To generate the
digital map of
water depth…
… the sounder measures
the length of each
echo return path
The sounder must
be supplied with
the vessel position ...
...and the individual
beam pointing angles
i i i & O i i S
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Caris200551
Positioning & Orientation System
Components
PCSPOS
Computingsystem
IMU Inertial Measurement System
GPS Antennae
h d d ff h b d
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Echo Sounders Bounce Sound off the Seabed
M ltib S t C bi M
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Multibeam Systems Combine Many
Echo Sounders
Multibeam systems can provide more accurate measurements than echo
sounders do. Multibeam systems collect data from as many as 121 beams to
measure the contours of the ocean floor.
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Mapping the ocean floor
Multibeam sonar
• Employs and array of sound sources and
listening devices
• Obtains a profile of a narrow strip of seafloor
Measuring the shape of the ocean surface
from space
Multibeam sonar
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Multibeam sonar
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Careful converge to map the seafloor
Major topographic divisions of the
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Major topographic divisions of the North
Atlantic
Ocean
The Ocean Floor
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A. Single‐beamsonar
B. Multibeam sonar
Side Scan Sonar Fish
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The Ocean Floor
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Single‐beam echo sounder trace
The Ocean Floor
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Example of multibeam echo soundings
The Ocean Floor
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A PIC
sonar
(ultrasonic) range
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( ) gfinding project using
a seven segment
display and
a PIC
micro
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