Glossary · The terms, plainly
Glossary
Every term MuirWave uses, in plain language — the acoustics, the sonar equation, the environment, and the impact-assessment vocabulary. If a readout or a label ever isn't obvious, it's defined here. For the why behind the physics, see Concepts.
§01
Propagation & the sound field
| Term | Plain meaning |
|---|---|
| Transmission Loss (TL) | How much a sound has weakened by the time it reaches a given point, in dB. Bigger TL means quieter. |
| Sound-Speed Profile (SSP) · c(z) | The speed of sound versus depth at your pin — the single most important input. MuirWave builds it from ocean data and computes the sound speed on the device. |
| Sound-channel axis | The depth where sound travels slowest. Rays bend toward it, so it can trap sound and carry it a long way. |
| Ray path | The curved route a sound ray follows as it refracts through changing sound speed. |
| Convergence Zone (CZ) | A ring of range where refracted rays refocus and sound is unexpectedly loud again. MuirWave marks the first zone (CZ1) and its spacing. |
| Bottom bounce (BB) | Sound that reflects off the seabed to reach farther. Its strength depends on the sediment at your pin. |
| Shadow zone | A region where refraction thins the sound out, so little reaches it directly. |
| Depth Excess (DE) | Whether the water is deep enough below the sound channel for reliable convergence zones. Colour-banded in fathoms (≥300 green · 200–300 amber · 0–200 grey · below 0 blank). |
| Duct · mixed layer | A near-surface layer that can trap and carry sound along the surface. |
| Sound field | A map view of where a source would and wouldn't be heard, painted across the area (the RAYS / FIELD / BOTH plot). |
§02
The sonar equation & detection
| Term | Plain meaning |
|---|---|
| Sonar equation | The balance that decides detectability: how loud it starts, minus how much it weakens, minus the background noise. |
| Source Level (SL) | How loud the source is, referenced to 1 m from it (dB re 1 µPa @ 1 m). |
| Signal Excess (SE) | How detectable a signal is at a point — positive means detectable. The colour-banded headline readout. |
| Figure of Merit (FOM) | The largest transmission loss a signal can suffer and still be detected — a single-number reach. |
| Directivity Index (DI) | The gain a directional array gets by listening in a preferred direction rather than everywhere. |
| Detection Threshold (DT) | The signal excess needed before you call it a detection. |
| Bandwidth | The width of the frequency band the receiver integrates over — it sets how much noise competes with the signal. |
| Slant range | The straight-line distance from source to receiver, accounting for depth (not just the surface distance). |
§03
Environment & noise
| Term | Plain meaning |
|---|---|
| Ambient noise (NL) | The background sea noise a signal competes against, summed from all its sources. |
| Wenz curves | The classic model of ambient noise by frequency, combining turbulence, shipping, wind and thermal noise. |
| Absorption (α) | Sound energy lost to the seawater itself as it travels — grows with range and frequency (François-Garrison). |
| Mackenzie | The standard equation that turns temperature, salinity and depth into a sound speed. MuirWave runs it on the device. |
| Sea state · Beaufort | The wind/wave regime (SS0 calm → SS6 gale). Drives surface roughness and wind noise. |
| Set & drift | Ocean current in maritime terms: set = the direction it flows toward; drift = its speed. |
| Sediment class · grain size (Φ) | The seabed type and its average grain size on the phi scale — the single knob that drives bottom loss. |
| Bottom loss | How much sound each seabed bounce loses, in dB — softer/finer sediment absorbs more. |
§04
Impact assessment
| Term | Plain meaning |
|---|---|
| Impact range | The distance from a source at which a given threshold is reached — inside it the threshold is exceeded, outside it isn't. |
| Threshold (injury / behavioural) | A sound level above which an effect (injury, or a behavioural response) is expected for a species group. |
| Hearing group | Species grouped by hearing sensitivity, each with its own thresholds (NMFS 2024 / Southall 2019 for mammals). The codes: LF low-frequency cetaceans (baleen whales) · HF high-frequency cetaceans (most dolphins) · VHF very-high-frequency cetaceans (porpoises) · PW / PCW phocid seals in water · OW / OCW otariid seals & sea lions in water. |
| Impulsive / non-impulsive / continuous | Source categories judged against different threshold families — e.g. airguns & impact piling (impulsive), vibratory piling (non-impulsive), turbines & shipping (continuous). |
| SPL · Peak · SEL | Sound-pressure metrics: SPL (a level), Peak (the instantaneous maximum), and SEL (Sound Exposure Level — energy accumulated, e.g. over 24 h). |
| M-weighting | A frequency weighting applied per hearing group, so thresholds reflect what each species actually hears. |
| Mitigation | Measures that lower the effective source level — e.g. bubble curtains, hydro-sound dampers. |
| Soft-start / ramp-up | Gradually increasing a source's level at the start so nearby animals can move away first. |
| Compliance jurisdiction | The regulator framing you're assessing against (NMFS, BSH, JNCC, EPBC, or Southall) — set in Settings. |
§05
App & data terms
| Term | Plain meaning |
|---|---|
| Probe | The sampling cursor (MuirWave's default) — move it to read conditions anywhere. It doesn't run a prediction. |
| Source · Receiver | The acoustic source pin and the receiver pin — the prediction runs between them. |
| Climatology | The built-in long-term-average ocean data (WOA23) used offline or when live data isn't available. |
| Live data | Real-time sound-speed, wind and currents from live feeds — an MuirWave Live feature. |
| Operating area · data pack | A downloadable, higher-resolution regional dataset for an area you work. Climatology and bathymetry packs are free; Regional Forecast packs (live ocean-model data) need MuirWave Live. |
| Compact / High Quality | The two resolution tiers a data pack comes in — light versus fine. |
| Provenance | The record of exactly where each number came from (live, regional pack, or climatology) — so every result is traceable. |
| AIS | Automatic Identification System — live vessel positions (a beta feature; not in the App Store release). |
Missing a term? Email [email protected] and we'll add it.