Infrasoniese, GPS-gesinkroniseerde klankopnemers vir die opsporing van olifantdreungeluide

[摘要] ENGLISH ABSTRACT: The automatic localisation of wild elephants in their natural habitat, without interaction withthe animals themselves, has many applications in wildlife conservation and conservation ecology.Current solutions require the attachment of devices to individual animals. Elephant rumbles havestrong infrasonic components and elephant habitats offer ideal conditions for the propagation ofthese rumbles over long distances. An integrated hardware solution for the localisation of thesesounds is designed and tested. It consists of sound recorders which are relatively inexpensive,are sensitive to low frequencies, are battery-powered, have low intrinsic noise, can communicatewirelessly, and are synchronised with one another via GPS. A custom recorder is designed sinceno commercially available audio equipment meets these requirements.The recorder uses a 12 V sealed lead acid battery. Power supplies are designed to power therespective parts of the recorder. A circular array of 6 Invensense ICS-40300 MEMS microphonesare used with each recorder. An audio interface is designed, consisting of ADCs, preamps andanti-alias filters. Each audio interface has a high input impedance, a high-cutoff frequency ofabout 1 kHz, a bit depth of 24 bits per channel, a sample rate of 4800 Hz and 6 independent,synchronously sampled audio channels. A digital audio buffer collects samples from the ADCand sends it to a RPI over SPI, where is it stored on an SD card for later processing. In thefuture, processing may be done online on the RPI.GPS modules are used to accurately timestamp each sample so that the audio channelsfrom independent recorders may be used as a wide-spaced array of microphones without explicitinter-device communication.Various sound source localisation algorithms are simulated and tested. Multilateration withwide-spaced microphones is investigated, and the conclusion is that at least four wide-spacedsound recorders with a single microphone on each is needed to accurately locate sound sources.A novel direction of arrival estimation algorithm based on the pairwise time delay estimationsof all 15 microphone pairs in the 6-microphone array is developed, simulated and tested. Thisalgorithm performed better than multilateration when only two wide-spaced sound recorderswere used. In both cases, tests were performed with a loudspeaker playing elephant rumbles orwhite noise. The results are shown in Figures 10.22–10.27.Suggestions are made for future work towards an end product that can be operated by parkrangers and ecologists. The localisation of elephant rumbles with infrasonic sound recordersappears to be a viable solution to various wildlife conservation problems.

[发布机构] Stellenbosch University