CARACAL: a versatile passive acoustic monitoring tool for wildlife research and conservation

Acoustic localisation technology has been widely tested and applied for passive acoustic monitoring and ecological research, however, hardware costs of commercially available devices limit scalability. Furthermore, few studies have explored its use with low-density arrays. We present a low-cost, custom-designed hardware and software system termed ‘CARACAL’ that is able to extract and localise weak acoustic signals. The key to this is the use of four microphones on each logger, allowing for phase-based measurements and the ability to enhance signal-to-noise ratio through beamforming. As a proof of concept, we test the functionality of the CARACAL system by conducting a gunshot localisation experiment and demonstrate animal call detection and localisation from a lion predation event. Results show the system could locate gunshots with an average accuracy of 33.2 ± 15.3 m within an array of 7 stations 500 m apart. When applied to animal call positioning, we show long range (> 1 km) localisation of three different species’ calls, Cape buffalo, chacma baboon and spotted hyaena. With a cost of approximately £150 per unit, the CARACAL system provides a cost-effective solution for acoustic localisation over large areas. The system is open source and can be customised to suit a variety of wildlife research applications.

声学定位技术已在被动声学监测与生态学研究中得到广泛测试与应用，但市售设备的硬件成本限制了其规模化应用的潜力。此外，鲜有研究探讨其在低密度阵列中的应用场景。本文提出一款名为“CARACAL”的低成本定制化软硬件系统，可实现微弱声学信号的提取与定位。该系统的核心设计在于每个记录节点搭载四只麦克风，可实现基于相位的测量，并能通过波束成形技术提升信噪比。作为概念验证，我们通过开展枪声定位实验验证了CARACAL系统的功能，并展示了其对狮子捕食事件中动物叫声的检测与定位能力。实验结果表明，在间距500米的7个监测站点组成的阵列中，该系统对枪声的定位平均精度可达33.2±15.3米。将该系统应用于动物叫声定位时，我们成功实现了3个物种（非洲水牛、南非大狒狒与斑鬣狗）叫声的超1公里远程定位。单台设备成本仅约150英镑，CARACAL系统为大范围声学定位提供了高性价比的解决方案。该系统采用开源设计，可根据各类野生动物研究场景进行定制化调整。