Seafloor Sensors

Equipment and technologies used to collect information about the seafloor.

Modeling the underwater surface and identifying objects or obstructions.

o Model the seafloor.
o Detect underwater obstructions and hazards to navigation.
o Ensure that a minimum navigational depth exists throughout an area.

A method using a horizontal bottom wire pulled between two ships or boats to detect underwater obstructions.

• Composition:
o Horizontal bottom wire of suitable length.
o Adjustable vertical supporting cables.
o Surface buoys with wooden floats.
o Weights or sinkers to keep cables vertical.

• Arrangement:
o Floats are attached to the wire at approximately 30-meter intervals.
o Supporting cables hold the wire at the desired depth.

• Mechanism:
o When the wire encounters an obstruction, it becomes taut and forms a V-shape.
o This indicates the presence of submerged rocks, wrecks, or other obstructions.
o The depth of the obstruction is determined by the depth of the wire.

Faster and less laborious than using lead lines and sounding poles.

A modification of the wire drag method.

o Vertical supporting cables have fixed lengths.
o Supporting cables are positioned farther apart.
o No intermediate floats are attached to the wire.

Faster to put into operation than wire drag.

Used where few obstructions are expected and water depth is greater than the required navigational depth.

A rigid bar suspended at a predetermined depth to detect underwater obstructions.

• Composition:
o Railroad rail, structural skeletal beam, or steel pipe.
o Two vertical supporting cables.

• Application:
o Determines minimum clear depths.
o Used in river channels and other constricted areas.
o Locates minor underwater obstructions.

Equipment used to detect objects on the seafloor.

Processes the collected data.

Apparatus towed behind the survey boat that sends transmission signals.

Connects the towfish to the vessel's system.

• Mechanism:
o The towfish transmits a signal.
o The returning echo is recorded to detect seafloor objects.

Can model only detected objects and features; cannot determine depth.

Sonar systems initially designed for navigation and obstacle/collision avoidance.

Mounted at the bow of the vessel.

Supplies power to the system.

Displays data in 3D.

offer bathymetric and seafloor classification capabilities.

• Applications:
o Primarily used for shallow-water navigation.
o Helps prevent oil spills, reef groundings, and whale strikes.

obtains seafloor information using sensors without direct physical contact.

Uses satellite optical sensors to obtain seafloor information by analyzing reflected sunlight.

• Mechanism:
o Measures reflectance intensity at different wavelengths.
o Detects spectral changes to obtain seafloor information, including depth.

Very useful for nearshore shallow waters.

• Limitations:
o Most electromagnetic radiation (EMR) cannot penetrate deeply into water.
o Cannot penetrate clouds.
o Ineffective under heavy cloud cover.

Requires ground truth data to verify the information obtained.

A remote sensing technique that uses longer electromagnetic wavelengths, from centimeters to meters.

• Mechanism:
o Transmits electromagnetic waves.
o Detects changes in wavelengths and collects echoes for processing.

Can penetrate through clouds.

Can capture seafloor information farther from the coast.

Produces images that give an unfamiliar view of the area.

A remote sensing technology that uses laser light instead of sound to determine bathymetry.

Uses two different colored lasers: green and red/infrared.

• Wavelength: 532 nm.
• Penetrates water up to approximately 70 meters.
• Reflects off the seafloor.
• Used to collect bathymetric data.

• Reflects off the water surface.
• Used to map adjacent shore topography.

Number of soundings collected per second.

Spacing or distribution of soundings over an area.

Width of the area covered by the sensor during a survey.

A measure of horizontal position accuracy

means there is a 95% probability that the true horizontal position lies within a circle of 5 m radius.

Bathymetric LiDAR Sounding Rate

Bathymetric LiDAR Soundings per Hour

Bathymetric LiDAR Area Coverage

Bathymetric LiDAR Sounding Density

Bathymetric LiDAR Other Density Capabilities

Bathymetric LiDAR Swath Width

Bathymetric LiDAR Flight Altitude

Bathymetric LiDAR Bathymetric Depth Range

Bathymetric LiDAR Maximum Topographic Height

Bathymetric LiDAR Depth Accuracy

Bathymetric LiDAR Position Accuracy