NoiseTracker glossary

Acoustic Habitat: The sound environment that surrounds marine animals, characterized by typical noise levels and patterns.

Acoustic Range: The maximum distance over which marine animals can effectively communicate or detect sounds in their environment.

Ambient Noise: The background sound always present in the ocean, created by natural sources like waves, wind, and marine life, as well as distant human activities like ship traffic. Ambient noise forms the acoustic backdrop against which marine animals must communicate, navigate, and detect prey.

Amplitude (Loudness): The strength or intensity of a sound wave, which determines how loud or quiet the sound appears.

Animated Frequency Spectrum: A moving display that shows which frequencies are present at each moment in a sound recording, revealing how the sound’s pitch content changes over time.

Anthropogenic Noise: Underwater sounds created by human activities like ships, construction, or sonar.

Anthrophony: All sounds generated by human activities in the marine environment, from ship engines to underwater construction.

Attenuation: How sound weakens and fades as it travels through water, with higher frequencies typically losing energy faster than lower frequencies.

Auditory Masking: When a loud or overlapping sound makes it harder for an animal to detect or recognize another important sound, like a call from a calf, an echolocation click, or the sound of approaching prey. This happens because the interfering sound raises the level at which the quieter sound can be heard, or the “threshold” at which the second sound becomes noticeable,  a process known as masking. For marine mammals, this can interfere with their ability to communicate, find food, or detect danger. 

Background Noise: The combination of all sounds present in an environment except the specific sound being studied or listened for.

Biophony: Sounds created by living marine organisms, including whale songs, dolphin clicks, fish calls, and snapping shrimp pops.

Broadband Sounds: Sounds that contain energy across a wide range of frequencies simultaneously. Examples include whale songs or ship noise. Broadband noise can mask multiple types of marine mammal sounds because it overlaps with many frequency bands. 

Call: A specific vocalization made by marine animals for communication. Calls can serve many purposes, such as coordinating movement, signalling danger, maintaining contact between mother and calf, or attracting mates.  Different species have distinct call types that may vary by region or social group. 

Critical Bandwidth: The range of frequencies around a desired signal within which noise can effectively mask or interfere with that signal, determined by how the auditory system of each species processes sound.

Cycle: One complete pattern of a sound wave, from compression through expansion and back to the starting point.

Decibels: A unit for measuring sound intensity on a logarithmic scale, where small increases in dB represent large increases in actual sound energy.

Decidecade Band: A narrow frequency range used to analyze sounds in more detail than octave bands, allowing researchers to better identify and study specific marine animal calls and environmental sounds.

Doppler Effect: The change in frequency of a sound when either the source or listener is moving, causing pitch shifts in recordings of moving animals or vessels.

Echolocation: The natural sonar system used by dolphins, whales, and other marine animals to navigate and hunt by producing sounds and interpreting the echoes.

Equivalent Continuous Sound Level (Leq): The average sound level measured over a specific time period.

Frequency (Pitch): How many sound waves pass a point each second, measured in Hertz – determines whether a sound is high-pitched or low-pitched.

Frequency Spectrum Graphs: Charts showing the energy content of a sound at each frequency, revealing which pitches are strongest.

Fundamental Frequency: The lowest frequency component of a complex sound, which typically determines the perceived pitch of animal vocalizations.

Functional Hearing Range: The span of frequencies that a marine species can effectively hear and use for communication or navigation.

Geophony: Sounds produced by natural physical processes like waves, wind, rain, earthquakes, and ice movement – the ocean’s natural soundtrack.

Hydrophone: An underwater microphone designed to detect and record sounds in aquatic environments.

Impulse Noise: Brief, sudden bursts of very loud sound that occur quickly and then stop, like explosions, pile driving, or seismic airgun blasts – these can be particularly startling and potentially harmful to marine animals.

Intensity: The amount of sound energy flowing through a specific area, measured in decibels (dB).

Longitudinal Waves: Sound waves where water particles move back and forth in the same direction the sound is travelling.

Narrowband Sounds: Sounds concentrated within a small range of frequencies, like pure tones or specific animal calls with distinct pitches.

Noise: Any unwanted sound that interferes with hearing or detecting other sounds of interest.

Ocean Acoustics: The study of how sound behaves in marine environments, including how it travels, reflects, and affects marine life.

Ocean Soundscape: The complete acoustic environment of a marine area, including all the natural and human-made sounds present at different times and frequencies.

Octave Band Levels: The total sound energy measured within a specific octave frequency range, where the upper frequency is twice the lower. These bands provide a useful way to analyze noise in relation to how marine mammals process sound through their auditory filtering capabilities.

Octave Band Sound: Sound measured across a frequency range where the highest frequency is exactly double the lowest frequency, reflecting how the inner ear naturally organizes and processes different sound frequencies.

Octaves: A frequency range where the top frequency is twice the lowest frequency, corresponding to how marine mammal auditory systems decompose complex sounds into manageable frequency bands for processing.

One-third-Octave Bands: Frequency ranges that divide each octave into three smaller parts. These bands closely match the natural auditory filters of dolphin species and provide conservative estimates for noise impact assessments when a species’ exact hearing characteristics are unknown.

Passive Acoustic Monitoring: Using underwater microphones to record marine life sounds over extended periods to study animal behaviour and populations.

Period: The time it takes for one complete sound wave cycle to occur, measured in seconds.

Piezoelectric Transducer: The sensor inside a hydrophone that converts underwater sound pressure into electrical signals for recording.

Power Spectral Density (PSD): A detailed measure of how sound energy is distributed across different frequencies, typically used to analyze noise levels over time or compare different sound sources. PSD helps researchers evaluate which frequencies dominate and how energy is concentrated.

Pressure Wave: A disturbance that travels through water by compressing and expanding the medium, carrying sound energy from one place to another.

Propagation: How sound waves travel and spread through the underwater environment, affected by water temperature, depth, and seafloor conditions.

Rarefaction: The stretched-out part of a sound wave where water particles are temporarily spread apart.

Reflection: When sound waves bounce off surfaces like the seafloor, surface, or underwater objects, they create echoes that can interfere with or enhance the original sound.

Signal-to-Noise Ratio (SNR): A measure comparing the strength of a signal (like an animal call) to the background noise level, indicating how clearly the sound can be detected. A high signal-to-noise ratio means the call is easy to detect, while a low ratio means it may be masked or lost in the noise. 

Sound: Pressure waves that travel through water, air, or other materials – what we hear as noise, music, or animal calls.

Sound Exposure Levels (SELs): A measurement that considers both how loud a sound is and how long an animal is exposed to it.

Sound Intensity: The rate at which sound energy passes through a given area perpendicular to the sound’s direction.

Sound Pressure: The tiny changes in water pressure caused by sound waves – what hydrophones actually detect and measure.

Sound Pressure Levels (SPLs): A standardized way to measure and compare the loudness of different sounds.

Sound Speed Profile: A chart showing how fast sound travels at different depths in the ocean, influenced by temperature, salinity, and pressure changes.

Spectrograms: A visual chart showing how sound frequencies change over time, with colours indicating sound intensity, like a musical score made of colours instead of notes.

Transmission Loss: The reduction in sound intensity as it travels away from its source, affected by distance, water conditions, and obstacles. Transmission loss affects how far marine mammals can hear each other, and how far noise from human activities can spread. 

Waveforms: A graph showing sound as positive and negative pressure changes over time, displaying the actual shape and intensity of sound waves.

Wavelength: The distance between two identical points on a sound wave, which determines how the sound travels through water.