Robust Acoustic Positioning for Safety Applications in Underground Mining

The surroundings of underground mining machines still constitute an unsafe area for miners due to bad visibility conditions. In this paper, we present a novel acoustic position estimation system for safety applications in such hazardous environments. Our system is based on a pulse compression technique and utilizes linear (LFM) and hyperbolic (HFM) frequency-modulated signals in the frequency range of 5-20 kHz. As the miners are moving, we incorporated a means of Doppler-shift compensation. This system not only provides the positions of moving targets but also their velocity and direction. In stationary measurements, we evaluated LFM signals at noisy conditions both in an indoor laboratory environment and in the vicinity of a mining machine. The movement of a miner has been emulated in dynamic laboratory measurements at constant speeds up to 1 m/s using both LFM and HFM signals. Our results show that the acoustic signal can be evaluated down to a low signal-to-noise ratio of -30 dB. The results of the dynamic measurements clearly demonstrate the insensitivity of the HFM signals to Doppler-shifts both with regard to the estimated position and estimated velocity.