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Echosounders Types Monier
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Echosounders Types
Before we Illustrate any data or classifications about
Echosounders we have to know what is Echo sounders do?
Its making or help to draw Seabed Map or mapping of seabed
How it works?
An echo-sounder sends an acoustic pulse directly downwards to the seabed and
records the returned echo. The sound pulse is generated by a transducer that emits an
acoustic pulse and then listens for the return signal. The time for the signal to return is recorded and converted to a depth measurement by calculating the speed of sound
in water. As the speed of sound in water is around 1,500 metres per second, the time
interval, measured in milliseconds, between the pulse being transmitted and the echo
being received, allows bottom depth and targets to be measured.
The value of underwater acoustics to the fishing industry has led to the development
of other acoustic instruments that operate in a similar fashion to echo-sounders but,
because their function is slightly different from the initial model of the echo-sounder,
have been given different terms.
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The methods to obtain the seabed:
Multibeam Echosounder
Multibeam echosounder systems (MBES) first appeared in the 1970s
and primarily consisted in an extension of a singlebeam
echosounder. Echosounders are capable to transmit a pulse of
controlled length, repetition rate and frequency to an underwater acoustic transducer
and to accurately time the returning echoes (propagation velocity of sound waves in
water: ~1,500 m/s). Instead of transmitting and receiving a single
vertical beam, the MBES transmits several tens of beams (typically
100 to 200) with small individual widths (1 to 3) in the form of a
fan perpendicular to the navigation line. This configuration provides
depth informations out to several hundred meters each side of the
vessel which allows to survey large areas of the seabed with a higher
density and a better accuracy than singlebeam echosounders.
During recent years MBES have greatly evolved and nowadays they are a broadly
accepted tool for seabed mapping. Acoustic transducers were developed with
frequencies ranging between a few hertz and several megahertz depending on the
region and the water depth surveyed. A low frequency of 12 kHz is used for deep sea
research, whereas recently developed MBES with high frequencies between 200 and
300 kHz are applied for the investigation of shallow-water areas.
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Seabed Classification System
Conventional methods to classify the seabed are in situ sampling of
bottom sediments or optical methods like analyzing of photos and
videos. However, remote acoustic classification techniques are
becoming of increasing importance because they are less expensive
and time-consuming and provide a higher spatial resolution in
determining the seabed characteristics. Especially, echosounder-based
techniques, first developed for fishery purposes , are a useful tool to
classify a big area of the seabed in a relative short time period with a
high spatial resolution. In general, echosounders are used for bathymetric surveys.
However, acoustic signals reflected by the seabed contain more information than just
the water depth. The intensity and shape of a returning acoustic signal is affected by a
number of factors, primarily sediment grain size and sorting, seabed roughness,
bedforms, and presence, concentration and type of benthic fauna and flora. For
instance, the harder or rougher the seabed, the more energy is scattered back to the
transducer and vice versa. Therefore, echosounder-based classification systems are
utilized to reveal geological structures of the seabed composed of various types of
sediments and rocks.
QTC VIEW
The QTC VIEW system uses the first returning echo from the seabed
only and analyzes the shape of each echo with a series of five
algorithms. These algorithms characterize the waveform by using energy
and spectral components, yielding 166 descriptors of each echo.
Principal-Component-Analysis (PCA) reduces the large quantity of
information to three most useful descriptors (Q1, Q2, Q3), which prove
enough to recognize the different types of seabed. When plotting the points defined by
Q1, Q2, and Q3 on a three-axis plot, echoes of similar character form clusters that
stand for distinct acoustic classes. To correlate each acoustic class with seabed
characteristics groundtruthing by sampling bottom sediments has to be carried out.
The result is a georeferenced trackplot classified by sediment types.
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Sidescan Sonar
A basic Sidescan Sonar System consists of a topside processing unit,
a cable for electronic transmission and towing, and a subsurface unit
(a towfish) that transmits and receives acoustic energy for imaging.
Sidescan Sonar is a method of underwater imaging using narrow
beams of acoustic energy (sound) transmitted out to the side of the
towfish and across the bottom. Sound is reflected back from the
bottom and from objects to the towfish. Certain frequencies work
better than others, high frequencies (>500 kHz ) give excellent
resolutions but the acoustic energy only travels a short distance.
Lower frequencies (50-100 kHz ) give lower resolution but the
distance that the energy travels is greatly improved.
The towfish generates one pulse of energy at a time and waits for the sound to be
reflected back. The imaging range is determined by how long the towfish waits before
transmitting the next pulse of acoustic energy. The image is thus built up one line of
data at a time. Hard objects reflect more energy causing a lighter signal on the image,
soft objects that do not reflect energy as well show up as darker signals. The absence
of sound such as shadows behind objects show up as very dark areas on a sonar
image.
Multiparameter Probe with inductive Current Meter
The Multiparameter Probe Series 2001compact consists of 1+4
sensors, e.g. an inductive current sensors, as well as of an internal
compass and memory, cable interface and internal batteries.
for more information contact
Dr.-Ing. Helmut Schlter VDI, HS Engineer
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Types of Echo sounders:
SideScan sonar
The Geological Lineaments are single or plural linear pattern that appear in satellite images. The Analysis of natural linear structures provides important information to us. Lineament is considered that they reflect geological structure such as faults or fracture zones as well as artificial structure such as railroads and power lines. To classification lineament according to artificiality requires geologists, well-trained specialists, to find such as hidden seismic faults in the urban area at this moment. OHTI has been developing a mapping system for lineament classification to propel satellite image analyses. Those are shown below.
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Single Beam Echosounder
A single beam echosounder or 'depth sounder' is a system capable of accurately
measuring the water depth below a vessel (Figure 1). This is achieved by measuring
the two-way travel time (e.g. from the ship to the seabed, and back again) of an
acoustic pulse (or a burst of sound) emitted by the sonar transducer. The acoustic
pulse typically ranges in frequency from 12 - 200 kHz, with lower frequencies
required in deeper water. The reliability of the depth calculation is dependant on
accurately knowing the sound velocity in sea water, which is usually around 1500 m/s
depending on water temperature, salinity, and other factors. Single beam
echosounders are routinely mounted on most sea-going vessels, and when attached to
a GPS and recording device, provide an inexpensive seabed mapping tool.
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Multibeam Sonars
OVERVIEW
A multibeam sonar operates much like a single-beam echo sounder, ensonifying the
bottom and detecting echo arrival times.
Unlike the single-beam sonar, which illuminates a single point beneath the sonar, the
multibeam sonar illuminates a narrow swath elongated across the bottom and
perpendicular to the path of the boat. This illuminated swath is then sampled with
multiple, discrete "receive beams" formed by the sonar at known angles. For each
beam, the sonar attempts to determine the "best" echo arrival time. With the known
beam angle, the determined "best" echo travel-time, and the water-column sound
velocity, the cross-track distance and depth can be determined.
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Sub-bottom profilers
A sub-bottom profiler is effectively an echosounder that transmits a relatively low-
frequency acoustic pulse that can penetrate the seabed. This signal is reflected off sub-
surface boundaries between sediment or rock layers that have different acoustic
impedance, which is related to density and sound speed within each layer (Figure 1).
The strength of the reflected signal depends on the degree of impedance contrast. The
returning sound waves are recorded by an array of hydrophones (towed behind the
vessel), or by a transducer/transceiver, depending on the type of system. The first
useful signal received represents the seabed-water interface, and shows the
morphology of the seabed in a manner similar to a single beam echosounder. The time
of arrival and intensity of subsequent impulses provides information about layers that
exist below the seabed.
Several physical parameters of the acoustic signal emitted, such as output power,
signal frequency, and pulse length affect the performance of the instrument and
influence its usefulness in various marine environments. Increased output power
allows greater penetration into the substrate. However, in the case of harder seabeds
(e.g. gravels or highly compacted sands) or very shallow water, higher power will
result in multiple reflections and more noise in the data. Higher frequency systems (up
to 20 kHz) produce high definition data of sediment layers immediately below the
seabed, and are able to discriminate between layers that are close together (e.g. 10's of
cms). Lower frequency systems give greater substrate penetration, but at a lower
vertical resolution. Longer pulse length transmissions (or 'pings') yield more energy
and result in greater penetration of substrate. However, they decrease the system
resolution. The depth of penetration also depends on the hardness of the upper layers
and is significantly limited by the presence of gas deposits.
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The commercial names There is avarios commercial names for thes products
according to its company
And the following types is acommercial names for one
company:
Atlas Fansweep
The FANSWEEP multibeam system is manufactured by Atlas Hydrographic, Sydney, Australia.
The ATLAS FANSWEEP has 100-200kHz
broadband coverage that includes Simultaneous
Multi Ping technology allowing the system to
transmit up to eight pings into the water column
at any one time. This enables the system to
operate in smaller vessels at higher speeds and in
higher sea states than conventional multibeam
systems. The FANSWEEP uses proprietary "
High Order Beamforming", a technique that
provides superior resolution across the entire
swath of 8x water depth. The FANSWEEP
transmits survey data including bathymetry,
automatic feature detection, bottom type
classification and in-water column analysis.
Atlas Hydrosweep
The name ATLAS HYDROSWEEP
comes from "HYDROgraphic Multi-
Beam SWEEPing Survey
Echosounder". The HYDROSWEEP
MD (Medium Depth) is a beam-forming
multi-beam system suitable for surveys
from 10m to 2,000m, 4,000m, 5000m or
6000m depending on the transducer and
frequency configuration. Operating at
30kHz or 50kHz the ATLAS
HYDROSWEEP MD is optimized for
surveys on the continental shelf and on
the continental slope. The
HYDROSWEEP has a bathymetric
swath width of up to 10 times water
depth, and a side scan imagery swath of
12 times water depth.
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Odom Echoscan
The Odom Echoscan is manufactured
by Odom Hydrographic Systems, Inc.,
of Baton Rouge, Louisiana.
The Echoscan has a 200 kHz operating
frequency, with 2.5cm resolution, high
survey speed capability (17 knots max),
sidescan and heave/pitch/roll sensors
co-located in the transducer, a built-in
single-beam transducer and independent
bottom-tracking channels.