Three-Dimensional Localization of Bats: Visual and Acoustical

Abstract

We introduce a multi-sensor array consisting of multiple microphones and a stereo-vision system that enables to track three-dimensional (3D) flight paths of bats. Field applicability is a major design factor which led to a portable battery powered system. Eight microphones form the acoustic array that allows the detection and localization of ultrasonic echolocation calls. Two near infrared sensitive cameras provide a visual identification of the three dimensional flight path. We minimized costs of this multi-sensor arrays by developing the system from ground up, including a novel acoustic signal recording and processing hardware. Our acoustic data acquisition system is the first to sample eight microphones simultaneously at 1MS/s/CH with 16 Bit resolution without the necessity of computers or laptops. All channels are processed in real time in the frequency and time domain to evaluate the occurrence of echolocation calls. Hereby, long term deployments of the system are achieved since only relevant signals are recorded. Parallel to the acoustic acquisition, the system records images of two near-infrared (IR) sensitive cameras at 12Hz frame rate each. Combined with IR illumination 3D flight paths can be extracted in post-processing. In addition, the system is able to log several environmental parameters, such as temperature and humidity. Recorded datasets can be associated with a global position and time-stamp through a GPS module and transformed to GPS coordinates with a three-axis accelerometer to determine the angle. The overall system (microphones, cameras, and sensors) was designed to be affordable, user-friendly, battery powered and without the necessity of an additional laptop.