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Questions and Answers
Why is maintaining a constant speed, direction, and depth critical for side-scan sonar?
Why is maintaining a constant speed, direction, and depth critical for side-scan sonar?
- To maximize the sonar's range and power consumption.
- To ensure clear images and avoid distorting the sonar image. (correct)
- To reduce the signal attenuation in the water.
- To ensure the transducer rotates consistently.
Which sonar type is designed to produce a cross-section image of a seabed or pipeline?
Which sonar type is designed to produce a cross-section image of a seabed or pipeline?
- Mechanical scanning (Navigational) sonar.
- Side-scan sonar.
- Profile scanning sonar (Profiler). (correct)
- Multi-beam fixed-head sonar.
What is the main advantage of using a multi-beam fixed-head sonar??
What is the main advantage of using a multi-beam fixed-head sonar??
- It provides real-time images in a forward-looking direction, ideal for navigation in poor visibility. (correct)
- It offers 360° coverage around the ROV.
- It can map a wide seabed area with a 3D image.
- It can be easily mounted on tow fish for deep sea searches.
In mechanical scanning sonar, what does the color intensity on the screen represent?
In mechanical scanning sonar, what does the color intensity on the screen represent?
How do spreading loss and attenuation affect the receiver in a mechanical scanning sonar system?
How do spreading loss and attenuation affect the receiver in a mechanical scanning sonar system?
What is the primary function of castor oil within the boot of a sonar head?
What is the primary function of castor oil within the boot of a sonar head?
Which of the following is most important to consider when using sonar on a ROV?
Which of the following is most important to consider when using sonar on a ROV?
How does increasing the rotational speed of a sonar head typically affect the image resolution?
How does increasing the rotational speed of a sonar head typically affect the image resolution?
Besides the Remote Access Terminal (RAT), where else can the main controls of a sonar system typically be accessed?
Besides the Remote Access Terminal (RAT), where else can the main controls of a sonar system typically be accessed?
What is a key consideration when selecting a longer range on a sonar system?
What is a key consideration when selecting a longer range on a sonar system?
What is the primary operational principle behind sonar systems?
What is the primary operational principle behind sonar systems?
What is the approximate speed of acoustic compression waves in sea water?
What is the approximate speed of acoustic compression waves in sea water?
What does the term 'Sonar' stand for?
What does the term 'Sonar' stand for?
What should an operator do to obtain accurate and clear sonar images using an ROV?
What should an operator do to obtain accurate and clear sonar images using an ROV?
What is a common application of Side-scan sonar?
What is a common application of Side-scan sonar?
Which factor most influences the intensity of the reflection displayed on a sonar screen?
Which factor most influences the intensity of the reflection displayed on a sonar screen?
Why might a large object at an oblique angle produce a weaker reflection on a sonar screen compared to a small object directly facing the sonar?
Why might a large object at an oblique angle produce a weaker reflection on a sonar screen compared to a small object directly facing the sonar?
Which sonar control, when reduced, is most likely to remove clutter from the sonar image?
Which sonar control, when reduced, is most likely to remove clutter from the sonar image?
What is a potential drawback of using a mechanical scanning sonar?
What is a potential drawback of using a mechanical scanning sonar?
What is indicated by the 12 o'clock position on a mechanical scanning sonar screen?
What is indicated by the 12 o'clock position on a mechanical scanning sonar screen?
What could be inferred if a sonar system displays the seabed while operating an ROV?
What could be inferred if a sonar system displays the seabed while operating an ROV?
In which scenario is a multi-beam fixed-head sonar most advantageous?
In which scenario is a multi-beam fixed-head sonar most advantageous?
Which sonar type relies on post-processing and image enhancement to produce detailed images?
Which sonar type relies on post-processing and image enhancement to produce detailed images?
Which principle is true regarding sonar image interpretation?
Which principle is true regarding sonar image interpretation?
What is the first side lobe sensitivity (% of Tx/Rx) of a mechanical scanning sonar system??
What is the first side lobe sensitivity (% of Tx/Rx) of a mechanical scanning sonar system??
Flashcards
What does SONAR stand for?
What does SONAR stand for?
Sound Navigation and Ranging.
How does SONAR work?
How does SONAR work?
Using acoustic signals, which travel ~1500m/sec in seawater, to detect objects by the time it takes for the echo to return.
Name the types of Sonar
Name the types of Sonar
Mechanical Scanning, Multi-beam Fixed-head, Profile Scanning, and Side-scan.
What is Mechanical Scanning Sonar?
What is Mechanical Scanning Sonar?
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What does the screen cursor represent in mechanical scanning sonar?
What does the screen cursor represent in mechanical scanning sonar?
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What is the role of the transducer in sonar?
What is the role of the transducer in sonar?
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What does the top of the screen represent?
What does the top of the screen represent?
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What are the main sonar controls?
What are the main sonar controls?
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What does the Gain control do?
What does the Gain control do?
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What does the Rotate/Scan control do?
What does the Rotate/Scan control do?
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How do you interpret sonar images?
How do you interpret sonar images?
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What is Multi-beam (Fixed Head) Sonar?
What is Multi-beam (Fixed Head) Sonar?
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What is Multibeam Sonar useful for?
What is Multibeam Sonar useful for?
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What is Profile Scanning Sonar?
What is Profile Scanning Sonar?
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Pencil beam of sound used for seabed cross-sections.
Pencil beam of sound used for seabed cross-sections.
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What is Side-scan Sonar?
What is Side-scan Sonar?
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How does Side Scan produce an image?
How does Side Scan produce an image?
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Study Notes
Sonar
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Stands for Sound Navigation And Ranging
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Utilizes acoustic signals for wave propagation in water
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Acoustic compression waves travel at around 1500m/sec in seawater
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Waves reflect off solid objects; the echo's return time determines distance
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Echo sounders, ROV altimeters, and tracking systems all operate on this principle
Learning Outcomes
- Understand acoustic sound wave principles in water
- Understand available sonar tool ranges
- Understand basic sonar tool controls
- Understand sonar tool limits and advantages
- Understand the use of different sonar tools for different purposes
Types of Sonar
- Mechanical Scanning (Navigational)
- Multi-beam Fixed-head
- Profile Scanning (Profiler)
- Side-scan
Mechanical Scanning (Navigational) Sonar
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Navigation sonar emits a fan-shaped sound beam (approx. 30° high, 1.7° wide)
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It waits for an echo from a selected maximum range before moving and transmitting again
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A screen cursor follows the sonar head; bright colors indicate strong echoes, and dark indicates no echo
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The 12 o'clock position on the screen shows the forward direction relative to the ROV
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One transducer acts as both a transmitter and a receiver
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This system has side lobes: the 1st side lobe has 1/5 sensitivity (1/25 as Tx/Rx)
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With fixed transmit power, the receiver's gain must vary with time to account for spreading loss and attenuation
Sonar Head Maintenance
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Minimal maintenance needed, washing in fresh water is sufficient
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Must align with the vehicle; the screen's top represents the head's front
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Avoid silicon grease on the rubber cover (boot) as it severely attenuates the acoustic signal
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The boot is filled with castor oil for protection, not sealing
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Damaged heads can still run without the boot in emergencies, but the transducer becomes vulnerable
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The head typically takes 24v from an ROV power supply; it communicates with the surface through a screened twisted pair or multiplexer
Main Sonar Controls Interface
- Operate main controls from the Remote Access Terminal (RAT)
- Alternatively controls can be accessed via pull-down menus with a mouse
- Transfer frequently used controls to the main screen from the control panel
Main Sonar Controls
- Range may be 200-300m, but a longer range slows the scan
- Speed refers to the number of pings per revolution; faster rotational speed reduces image resolution
- Gain is mostly set to "Auto," but reducing it can remove clutter
- Rotate/Scan sets whether the head rotates or scans through a preset arc
- The arc's angle and center point are adjustable
Other Sonar Features
- Zoom in on specific screen areas
- Take distance measurements from the ROV or between objects
- Change the way information is displayed
- Save images to disk
Interpreting Sonar Images
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A large object at an oblique angle can give a weaker reflection than a small, square object due to the strength of the reflection
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Intensity on screen shows echo strength, influenced by object angle
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Sonar may overlook objects if the seabed slopes away from the ROV
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Objects may only be visible by their shadow if the seabed slopes towards the ROV
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For accurate images, the ROV should be stationary, whether on the seabed or other objects
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Run the rotation at the slowest speed for highest resolution
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Mounting on top of the ROV gives 360° coverage
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Slower speeds may take up to 2 minutes to generate images but produce the highest quality data
Multi-beam (Fixed Head) Sonar
- Multi-element array provides real-time images in a forward-looking direction:
- Offers an angle of view between 45° and 135° horizontally
- Features a beam height of approximately 20°
- Serves as an ideal navigational tool in poor or zero visibility
- Has a range of up to 100m
Profile Scanning Sonar (Profiler)
- Produce a pencil-beam of sound
- Mounted with the scanning head in a vertical plane
- Used to produce a cross-section across an area of seabed or pipeline
- For pipeline surveys, two profilers are installed on booms on either side of the ROV
Side-scan Sonar
- Wide area searches and mapping seabed areas producing a type of 3D image
- Produces a fan-shaped sound beam, but the transducer remains fixed
- Mounted on a tow fish towed by a boat, AUV, or ROV
- The transducer must move at a consistent speed, direction, and depth
- Any variation can distort the image
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