Concepts Explained
You don't need an acoustics degree to use MuirWave — but understanding these five ideas makes every readout obvious. Read it once and the numbers stop being mysterious. No maths required; the app does that.
The one idea underneath everything
All of underwater acoustics is really a single question: a sound starts out at some loudness, weakens as it travels, and competes with background noise — can it still be heard? That balance is the sonar equation, and every panel in MuirWave is one term of it.
MuirWave computes each term from the real ocean at your pin. The rest of this page explains the two that do the heavy lifting: transmission loss (how the sea bends and weakens sound) and the sound-speed profile (why it bends the way it does).
The sound-speed profile — why sound bends
Sound doesn't travel in straight lines underwater. Its speed changes with depth — warmer, shallower water carries sound faster; cold deep water slower; then pressure speeds it up again very deep. Sound rays always bend towards slower water, so this profile shapes where sound goes.
MuirWave builds this profile at your pin from ocean climatology (or live data, with MuirWave Live). It's the single most important input — change the profile and the whole prediction changes. The Water Column panel shows it for any spot.
Where the profile comes from — and what Live changes
Drop a pin anywhere in the ocean and MuirWave always has a profile — it ships with global climatology built in, so it works offline, worldwide, with no subscription. MuirWave Live layers real-time ocean data and high-resolution operating areas on top. The app uses the best source available and tells you which one on the SSP chip at the top of the Acoustics screen.
Measured beats modelled
Models are the best guess available before you sail. Once you're on station with a bathythermograph or a live noise display, you have something better — and MuirWave treats it that way.
Enter a measured layer depth or measured noise points and they outrank every model tier — live feed included — for as long as you keep them switched on. The model keeps running underneath (live data keeps fetching, the comparison curves stay on the plots), so reverting never lands you on stale data, and the gap between model and measurement stays visible: that disagreement is field intelligence, not an error to hide.
Transmission loss, rays & convergence zones
Transmission loss (TL) is simply how much a sound has weakened by the time it reaches a given point — bigger TL means quieter. Because rays bend (§02), sound doesn't fade smoothly: it focuses in some places and thins out in others.
Detection & the sound field
Put the loudness, the loss and the noise together and you get how detectable a source is at each point. MuirWave can paint this across the map as a field — a bird's-eye view of where a source would and wouldn't be heard.
On the Ray Path plot you can switch what's drawn: RAYS shows the ray paths, FIELD shows the continuous detection/loss field, and BOTH overlays them. The structure of the field comes from transmission loss; its overall level comes from the source and receiver you set.
Impact thresholds
For assessment work, the question flips: instead of "can I hear it?", it's "how far out could this sound affect an animal?" Regulators define thresholds — sound levels above which injury or a behavioural response is expected — that differ by species hearing group and by whether the sound is impulsive or continuous.
Where do the thresholds come from?
MuirWave uses the recognised criteria: NMFS 2024 or Southall et al. 2019 (selectable) for marine mammals (grouped by hearing sensitivity) and Popper et al. 2014 for fish and sea turtles. The exact values used appear in your export.
What's an "impact range", then?
The distance from your source at which the received level drops below a given threshold. Inside that range the threshold is exceeded; outside it isn't. MuirWave computes one per threshold and hearing group — see the how-to.
Why does source type matter so much?
MuirWave distinguishes impulsive (pile driving, airguns), non-impulsive (vibratory piling, drilling) and continuous (turbines, shipping) sources — each is judged against a different threshold family, and accumulation over time is handled differently. Setting this correctly is essential for a defensible number.
Why does a fish or sea-turtle row sometimes show a rating instead of a range?
Popper 2014 doesn't publish a numeric threshold for every combination of hearing group, severity and source type. Where it publishes a quantitative dB value, MuirWave computes a real isopleth — a ring on the map, a range in the table. Where it publishes only a qualitative relative-risk rating — near-field / intermediate / far-field, each rated Low / Moderate / High — MuirWave reports that rating instead of inventing a number the standard doesn't provide. Sea-turtle recoverable injury and TTS are the clearest case: Popper rates both qualitatively, so that's what MuirWave shows, never a number borrowed from a fish row.
What about continuous noise — turbines, shipping?
For most fish groups Popper's continuous-noise criteria are qualitative too. One group is the exception: fish whose hearing involves the swim bladder have two published numeric criteria for continuous exposure — 170 dB re 1 µPa (rms) for 48 hours (recoverable injury) and 158 dB rms for 12 hours (TTS) — and MuirWave computes both as real isopleths. The duration is Popper's own exposure assumption, carried through to your export as a label, not something MuirWave models: the range marks where the received level falls to that rms threshold, not a dose accumulated over an animal genuinely staying there 48 or 12 hours. No other fish group, and no source type besides continuous, carries these two numbers.