Hydrographic Surveying and Seafloor Sensors

A horizontal bottom wire pulled between two boats to detect underwater obstructions.

The horizontal wire set at a desired depth during wire drag.

Cables that support the bottom wire at regular intervals.

Weights attached to the lower ends of cables to keep them vertical.

Indicates that the wire has encountered an underwater obstruction.

A modified wire drag method with fixed-length vertical cables, farther spacing, and no intermediate floats.

A railroad rail, structural beam, or steel pipe suspended at a predetermined depth to detect obstructions and determine minimum clear depth.

The minimum unobstructed water depth available for navigation.

Detects and images objects or features on the seafloor but cannot determine depth.

Processes the signals collected by side-scan sonar.

Apparatus towed behind a survey boat that transmits sonar signals.

Connects the towfish to the vessel's equipment.

Signal reflected from an object or the seafloor and recorded by the sonar system.

Sonar mounted toward the front of a vessel, initially designed for navigation and collision avoidance.

Device mounted at the bow in FLS that transmits and receives sonar signals.

Supplies power to the forward-looking sonar system.

Displays sonar information, potentially in 3D.

Uses sunlight reflectance at different wavelengths to estimate shallow-water depth and classify the seafloor.

Actual field observations used to verify remote-sensing results.

Uses longer-wavelength electromagnetic waves to obtain information about coastal and marine areas; can operate through clouds.

Energy transmitted through electromagnetic waves, including sunlight and radar signals.

Uses laser pulses instead of sound to obtain bathymetric and topographic information.

LiDAR that measures underwater depth and maps the seafloor.

Typically 532 nm; penetrates water and reflects off the seafloor to obtain bathymetric data.

Reflects from the water surface and maps adjacent shore topography.

Cloudiness of water caused by suspended particles, which can limit laser penetration.

A measure of horizontal positional accuracy; a 5 m means a 95% chance the true position lies within a circle of 5 m radius, according to the lesson.

Faster and less laborious than lead lines and sounding poles

Requires boats, a bottom wire, and supporting cables

Faster to deploy than wire drag

Best where few obstructions are expected

Determines minimum clear depth in restricted channels

Primarily suited to constricted areas and minor obstructions

Detects and images seafloor objects

Cannot determine depth

Helps avoid collisions and underwater hazards

Primarily used for navigation in shallow water

Useful for nearshore shallow waters

Limited water penetration; ineffective through heavy cloud cover

Can penetrate clouds and uses longer wavelengths

Produces images that may be unfamiliar or difficult to interpret

Rapidly collects bathymetric and coastal topographic data

Expensive and limited by moderate to high turbidity

Bathymetric LiDAR Sounding rate

Bathymetric LiDAR Soundings per hour

Bathymetric LiDAR Area coverage

Bathymetric LiDAR Typical sounding density

Bathymetric LiDAR Other density capabilities

Bathymetric LiDAR Swath width

Bathymetric LiDAR Flight altitude associated with stated swath

Bathymetric LiDAR Bathymetric depth range

Bathymetric LiDAR Maximum topographic height

Bathymetric LiDAR Position accuracy

Bathymetric LiDAR Depth accuracy standard stated in lesson