Evaluating vibroacoustic sensor performance and vibration attenuation: implications for soil biodiversity sampling

Jonathan Timperley, Catherine Parr, Dickson Mure, Kisiidi Maiyani, Immaculée Namahirwe, Margaret Njuguna, Lucy Smyth, Matt Rogan, Jonathan Baillie, Jafford Rithaa, Louise Roberts

Earth’s biodiversity is undergoing substantial changes in response to anthropogenic stressors, creating a need for efficient methods of assessing biodiversity, particularly in soil ecosystems where sampling remains challenging. Soil vibroacoustics - the use of substrate-borne vibrations or sounds to quantify or detect below-ground biological activity – offers a potentially rapid and scalable approach to sampling soil fauna, but several methodological gaps remain. There is currently a lack of standardisation across studies. For example, few studies have compared sensor performance, evaluated sampling procedures, or quantified how soil conditions influence attenuation in field settings. We assessed the performance of three sensors in dry-season tropical soils: an Aquarian H1a hydrophone (‘Hydrophone’), a JrF C-Series Pro contact microphone (‘JrF’), and a JrF sensor attached to a metal waveguide (‘Waveguide’). To test attenuation, sensors were positioned at varying distances from a buried speaker that emitted impulse tones (short broadband signals). The Waveguide approach was not suitable for dry, compacted soil because insertion caused structural damage to the waveguide. Recorded amplitudes did not differ significantly between sensors, but the Hydrophone exhibited a significantly higher signal-to-noise ratio (how clearly signals can be detected above unwanted background noise), whereas the JrF recorded significantly higher maximum frequencies in sandy soil. These differences may influence the detection of low amplitude vibrations from soil faunal activity. Soil type, compaction, moisture, temperature, and tree cover had minimal effects on attenuation and frequency loss. Further methodological refinement across different soil systems and geographical regions is vital for progressing soil vibroacoustic research.