Lecture 4: Depth Determination

Medium or body of water

Refers to the type of water body being measured, which can influence depth measurement techniques and accuracy.

Underwater acoustics

The study of sound in the underwater environment, particularly how sound waves propagate through water.

Lead line/sounding weight

A traditional method of measuring water depth using a heavy weight attached to a line lowered into the water.

Fathom

A unit of length used in nautical contexts, equal to 6 feet.

Echosounding

A depth measurement technique that uses sound waves to determine the distance to the seafloor.

Light Detection and Ranging (LiDAR)

A remote sensing technology that uses laser pulses to measure distances to the seafloor.

Acoustic pulse

A sound wave sent from a transducer that travels through water and reflects off the seafloor to determine depth.

Decibels (dB)

A logarithmic scale used to measure sound intensity.

Source Level Sound

The amount of energy transmitted into the water, measured in decibels relative to a reference intensity.

Sound Propagation

The behavior of sound as it interacts with water boundaries and its components.

Single-beam echosounder (SBES)

An echosounder that emits a single vertical sound pulse to provide depth information at one point.

Multi-beam echosounder (MBES)

An echosounder that emits multiple sound beams across a wide swath for comprehensive depth measurements.

Sweep System

A technique within multi-beam echosounding that uses multiple single-beam transducers on a boom to widen coverage.

Swath System

A true multi-beam system that provides continuous swath of depth measurements using a single transducer array.

Narrow beam

A focused echosounder beam that provides high-resolution depth readings and is ideal for detailed surveys.

Wide beam

An echosounder beam that covers a larger area with less detail, useful for general depth measurements.

Transmitter

The echosounder component that generates sound pulses at a certain frequency.

T/R Switch

A component of echosounders that controls the flow of electrical energy between the transmitter and transducer.

Transducer

The device that converts electrical power into acoustic power and receives echo signals.

Receiver

Amplifies the weak return signals (echoes) for signal processing.

Recorder

Creates a visual or digital output from the amplified signals.

Acoustic Parameters

Characteristics that influence sound behavior in the water, including frequency, bandwidth, and pulse length.

Frequency

The rate at which sound waves oscillate, influencing the attenuation of the signal in water.

Bandwidth

The range of frequencies used in a sound pulse, affecting resolution and target separation.

Pulse Length or Width

The duration of a sound pulse transmitted, which impacts the energy delivered to the water.

Sources of Errors

Factors such as mounting angle and tidal variations that can affect depth accuracy.

Corrections

Adjustments made to observed depths to account for errors and obtain chartered depths.

Corrected depth

The depth obtained after applying various corrections to the observed depth.

Observed depth

The initial depth measurement before any corrections are applied.

Dynamic draft correction

Adjustment related to the vessel's movement affecting the transducer's depth measurement.

Static draft

The depth of the transducer when the vessel is at rest.

Squat

Change in a vessel's trim due to movement through water.

Water level

Tidal corrections applied to ensure depth measurements are accurate to a reference datum.

Intensity

The power of an acoustic pulse, which can be affected by spreading and attenuation losses.

Spreading Loss

Loss of intensity as sound spreads out from the source in all directions.

Attenuation Loss

Loss of sound intensity due to scattering or absorption by water or the seafloor.

Hydrophone

A device used for receiving and converting sound into electrical signals in underwater acoustics.

Wave travel time

The time it takes for sound waves to travel to the seafloor and back, used in depth calculation.

Charted depths

Depth measurements that have been corrected and referenced to a standard datum.

International Hydrographic Organization

An organization that establishes standards for hydrographic surveying and nautical charting.

Depth measurement procedures

Steps and protocols followed to ensure accurate hydrographic measurements.

Acoustic signal attenuation

The reduction in sound signal strength as it moves through water, influenced by various factors.

Instrument Offset

The displacement of measurement instruments from the true depth point, affecting accuracy.

Sound Velocity Profile

The variation of sound speed with depth in water, crucial for accurate depth calculations.

Tidal variations

Changes in water level due to tides that can impact depth measurements.

Echosounder accuracy

The degree to which an echosounder's measurements reflect actual seafloor depths.