Glossary

Active data

Data collected while the echosounder is emitting sonar pulses (”pings”) at regular intervals. This is the normal operating mode for data in this project.

Algorithm

A finite sequence of well-defined, unambiguous, computer-implementable operations.

Bad data regions

Regions of data which must be excluded from analysis in their entirety. Bad data regions identified by echofilter come in two forms: rectangular regions covering the full depth-extend of the echogram for a period of time, and polygonal or contour regions encompassing a localised area.

Bottom line

A line separating the seafloor from the water column.

Checkpoint

A checkpoint file defines the weights for a particular neural network model.

Conditional model

A model which outputs conditional probabilities. In the context of an echofilter model, the conditional probabilities are \(p(x|\text{upfacing})\) and \(p(x|\text{downfacing})\), where \(x\) is any of the model output types; conditional models are necessarily hybrid models.

CSV

A comma-separated values file. The Sv data can be exported into this format by Echoview.

Dataset

A collection of data samples. In this project, the datasets are Sv recordings from multiple surveys.

Downfacing

The orientation of an echosounder when it is located at the surface and records from the water column below it.

Echofilter

A software package for defining the placement of the boundary lines and regions required to post-process echosounder data. The topic of this usage guide.

echofilter.exe

The compiled echofilter program which can be run on a Windows machine.

Echogram

The two-dimensional representation of a temporal series of echosounder-collected data. Time is along the x-axis, and depth along the y-axis. A common way of plotting echosounder recordings.

Echosounder

An electronic system that includes a computer, transceiver, and transducer. The system emits sonar pings and records the intensity of the reflected echos at some fixed sampling rate.

Echoview

A Windows software application (Echoview Software Pty Ltd, Tasmania, Australia) for hydroacoustic data post-processing.

Entrained air

Bubbles of air which have been submerged into the ocean by waves or by the strong turbulence commonly found in tidal energy channels.

EV file

An Echoview file bundling Sv data together with associated lines and regions produced by processing.

EVL

The Echoview line file format.

EVR

The Echoview region file format.

Inference

The procedure of using a model to generate output predictions based on a particular input.

Hybrid model

A model which has been trained on both downfacing and upfacing data.

Machine learning (ML)

The process by which an algorithm builds a mathematical model based on sample data (”training data”), in order to make predictions or decisions without being explicitly programmed to do so. A subset of the field of Artificial Intelligence.

Mobile

A mobile echosounder is one which is moving (relative to the ocean floor) during its period of operation.

Model

A mathematical model of a particular type of data. In our context, the model understands an echogram-like input sample of Sv data (which is its input) and outputs a probability distribution for where it predicts the turbulence (entrained air) boundary, bottom boundary, and surface boundary to be located, and the probability of passive periods and bad data.

Nearfield

The region of space too close to the echosounder to collect viable data.

Nearfield distance

The maximum distance which is too close to the echosounder to be viable for data collection.

Nearfield line

A line placed at the nearfield distance.

Neural network

An artificial neural network contains layers of interconnected neurons with weights between them. The weights are learned through a machine learning process. After training, the network is a model mapping inputs to outputs.

Passive data

Data collected while the echosounder is silent. Since the sonar pulses are not being generated, only ambient sounds are collected. This package is designed for analysing active data, and hence passive data is marked for removal.

Ping

An echosounder sonar pulse event.

Sample (model input)

A single echogram-like matrix of Sv values.

Sample (ping)

A single datapoint recorded at a certain temporal latency in response to a particular ping.

Stationary

A stationary echosounder is at a fixed location (relative to the ocean floor) during its period of operation.

Surface line

Separates atmosphere and water at the ocean surface.

Sv

The volume backscattering strength.

Test set

Data which was used to evaluate the ability of the model to generalise to novel, unseen data.

Training

The process by which a model is iteratively improved.

Training data

Data which was used to train the model(s).

Training set

A subset (partition) of the dataset which was used to train the model.

Transducer

An underwater electronic device that converts electrical energy to sound pressure energy. The emitted sound pulse is called a “ping”. The device converts the returning sound pressure energy to electrical energy, which is then recorded.

Turbulence

In contrast to laminar flow, fluid motion in turbulent regions are characterized by chaotic fluctuations in flow speed and direction. Air is often entrained into the water column in regions of strong turbulence.

Turbulence line

A line demarcating the depth of the end-boundary of air entrained into the water column by turbulence at the sea surface.

Upfacing

The orientation of an echosounder when it is located at the seabed and records from the water column above it.

Validation set

Data which was used during the training process to evaluate the ability of the model to generalise to novel, unseen data.

Water column

The body of water between seafloor and ocean surface.