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HydroMoth as a tool for quantitative underwater SPL measurements in benthic ecological research
Til Böttner1, René Ortmann1, Farhan Pasolong2
1General Zoology and Neurobiology, Ruhr-University Bochum, Bochum, Germany.
Plos One
|June 24, 2026
Summary
HydroMoth recorders offer accurate sound pressure level (SPL) estimates for benthic monitoring. These low-cost devices provide reliable data for studying marine invertebrates and ship noise within a few decibels of reference systems.
Area of Science:
- Marine bioacoustics
- Acoustic monitoring technology
- Benthic ecology
Background:
- Quantitative passive acoustic monitoring in benthic environments necessitates converting recorded amplitudes to absolute sound pressure levels (SPL).
- Accurate SPL estimation is crucial for analyzing low-frequency soundscapes, including those produced by marine invertebrates and anthropogenic sources like ships.
Purpose of the Study:
- To evaluate the accuracy of HydroMoth (HM) recorders for estimating SPL in the low-frequency band (100-1000 Hz).
- To determine if HM recorders are suitable for quantitative passive acoustic monitoring in benthic settings.
Main Methods:
- Nine HydroMoth recorders were calibrated using a single-point offset with a 1000 Hz reference tone.
- Recorders were compared against a factory-calibrated SoundTrap ST600 in a controlled playback experiment (100-1000 Hz).
- Both pool and field datasets were analyzed, with device orientation fixed to simulate benthic deployment conditions.
Main Results:
- HydroMoth recorders demonstrated deviations comparable to commercial reference systems, with mean absolute errors typically within 1-3 dB in pool tests and 0.9-2.4 dB in field tests.
- Deviations across frequencies were consistent, with mean deviations ranging from -2.6 to +1.8 dB (pool) and -0.5 to +1.0 dB (field).
- Consistent device orientation minimized orientation-related sensitivity differences, acting as a constant factor.
Conclusions:
- HydroMoth recorders provide sufficiently accurate SPL estimates for quantitative passive acoustic monitoring in defined benthic conditions (100-1000 Hz).
- These low-cost recorders are viable for applications requiring absolute accuracy within a few decibels, enabling broader research into benthic soundscapes.
