Browsing by Author "Geldenhuys, Christiaan"

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    Kleinvoet: a spatially-distributed temporally-synchronised infrasonic recorder
    (Stellenbosch : Stellenbosch University, 2023-12) Geldenhuys, Christiaan; Niesler, Thomas; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: We present the hardware design of a temporally synchronised high-fidelity low-cost infrasonic-capable (6Hz) passive acoustic monitoring (PAM) device. This research instrument allows recordings made by independent spatially distributed nodes to be synchronised in time for the purpose of acoustic monitoring and localisation of the African elephant, using for example time difference of arrival (TDoA). Each recorder is capable of sampling with a 24-bit resolution at a sampling frequency that is adjustable between 8 kHz and 192 kHz. Audio samples are stored locally on a microSD card, along with global navigation satellite system (GNSS) derived timestamp metadata that is shown to be accurate to within 500 ns (6σ). Four prototype recorders were built and evaluated. Estimates of the acoustic frequency response were obtained using Welch spectral averaging and confirmed that the recorders have a flat (±3 dB) pass-band over the frequency range 30Hz to 450 Hz. An analysis of the sampling clock confirmed an oscillator bias within specification (±2.5 ppm) and an oscillator stability, estimated using Allan variance, that was substantially improved using a simple regular resynchronisation method based on the GNSS timestamp metadata. Finally, without additional post-processing, the temporal alignment error is to within half a sampling period. However, if additional signal processing techniques are used, this alignment error can be reduced to approach the GNSS timestamp accuracy of 500 ns, which is well below half the highest sample frequency. We conclude that the recorders are well suited for sparsely distributed PAM experimental data collection, especially over the frequency range of African elephant vocalisations, for which it is intended.