Animal Movement Modelling

dBSea offers two ways of assessing marine animal sound exposure: a built-in fleeing model, and an integration with the external 3MB (Marine Mammal Movement and Behaviour) animat model. Both are post-processing tools that work on a scenario which has already been solved, and both are opened from the Results page.

Overview

• Fleeing model - a screening calculation on the solved sound field. A receiver starts at a chosen position and swims straight outward at constant speed; dBSea accumulates the sound exposure level (SEL) along the path and reports the worst-case direction.
• 3MB integration - 3MB simulates animal movement using bathymetry exported from dBSea. dBSea then reads the 3MB run output and calculates each animat’s exposure from its own solved sound field.

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Fleeing Model

Open the fleeing model with the Fleeing model button on the Results page. The button is enabled once the scenario has been solved.

How It Works

1. The receiver starts at the Initial position: the position of a source (for a moving source, its first track point) or a custom x, y.
2. For each radial slice of the project (the same slice angles used for the solve, taken from the first source), the receiver moves straight outward at the Fleeing speed in fixed 10 s steps, until it reaches the Final distance or the coast.
3. At each step dBSea reads the broadband level from the solved receiver-area grid (maximum over depth, all sources combined, with the scenario’s species weighting applied) and energy-sums level × 10 s into a cumulative SEL.
4. The result depends on the mode:
   • Specify SEL threshold - for each direction dBSea finds the smallest starting range from which an animal fleeing outward accumulates no more than the Assessment threshold (dB SEL_cum) over the rest of its path. The reported result is the worst case (largest range) over all directions: “Threshold met: initial range … m at …°”.
   • Specify initial distance - the receiver starts at the Starting distance in every direction, and the highest cumulative SEL over all directions is reported.
   • Custom path - waypoints with a speed per segment; the SEL accumulated along the path is reported. This mode cannot be combined with a starting distance.

The accumulation always uses the internal sound pressure levels of the solved field, so the fleeing result does not depend on the level type or assessment period selected for display.

Where a soft start is defined, each step uses the source level in force at that moment of the ramp, so an animal’s early retreat is credited against the reduced levels it actually experienced.

Setup

Control	Default	Notes
Initial position	first source	Choose a source, or Custom and enter x (m) and y (m)
Final distance (m)	10 000	Maximum range of the outward path
Fleeing speed (m/s)	1.5
Specify SEL threshold → Assessment threshold (dB SELcum)	150	Threshold mode
Specify initial distance → Starting distance (m)	200	Initial-distance mode
Soft or slow start	off	Sequential steps of Step length (s) and Level reduction (dB), default 1800 s and 10 dB; add or remove steps with + and −
Custom path tab → Edit custom path	one point at the source	Table of x (m), y (m), Speed (m/s) waypoints

Click Calculate to run. The settings are stored with the scenario.

Output

• A result line in the dialog: the worst-case initial range and compass bearing in threshold mode, or the SEL in the other modes.
• A chart of cumulative SEL against time for the worst direction (threshold mode), or of level against time (other modes).
• Levels to clipboard copies the results as CSV: in threshold mode the exceeded range and angle followed by time, range and SEL_cum per step; in initial-distance mode the cumulative SEL and the angle at which it occurs; for a custom path the SEL_cum followed by time and level pairs.

The fleeing model does not draw anything on the map and does not define the exclusion zone shown in the graphics area; see Results → Exclusion Zones for that.

Because the receiver flees directly outward from the start of the exposure, the result represents an animal that responds immediately and takes the shortest route out of the sound field. Animals that respond later or move tangentially would accumulate more exposure.

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3MB Integration

3MB (Marine Mammal Movement and Behaviour, from BOEM) simulates the movement of individual animats. dBSea does not export its sound field to 3MB; the exchange works the other way round:

1. Configure and solve your acoustic model in dBSea. A valid project UTM zone is required.
2. On the Results page click Animats model to open the Animat exposure dialog, and click Export bathymetry in .bth format (3MB / ESME). The same export is available from the export menu.
3. In 3MB, import the bathymetry, set up your species and scenario, and run. 3MB writes a run file (.3mb).
4. Back in the Animat exposure dialog, tick SEL threshold (dB) and/or Max threshold (dB) and enter the thresholds, then click Read animat data and open the .3mb file.

For every animat position record in the run file (latitude, longitude, depth and time), dBSea looks up its own solved level at that position and depth, with the scenario’s species weighting applied, and accumulates the animat’s SEL and maximum level.

Output

The dialog reports the number of animats, the number of simulation steps and the simulated duration, the mean and standard deviation of SEL and of maximum level, and the number and percentage of animats above each threshold. Data to clipboard copies a per-animat table (Animat, SEL, Max). Animat tracks are not drawn on the map.

For configuring and running 3MB itself, refer to the 3MB documentation: https://oalib.hlsresearch.com/Sound%20and%20Marine%20Mammals/3MB%20HTML.htm

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Choosing a Model

Use Case	Recommended Model
Quick screening of a worst-case fleeing range	Fleeing model
Soft-start credit for a fleeing animal	Fleeing model
Exposure statistics for a population with realistic movement	3MB
Regulatory submissions requiring behavioural simulation	3MB

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Probe to Source Back-Calculation

The source back-calculation tool can be useful for animal exposure work. By placing a probe at a location of interest (e.g. a known animal position or regulatory boundary), you can compare measured or target received levels against the model’s predictions and adjust the source spectrum accordingly. It compares unweighted per-band levels, is intended for a single stationary source, and is not available for moving sources.