Bernd Kiefer and  Abraham Gebru Tesfay and  Dietrich Klakow,  Terrain Classification for Ground Robots Based on Acoustic Features.   journal   = {International Journal of Computer and Information Engineering}, [online]. World Academy of Science, Engineering and Technology.
    April 2017, vol. 126(6). 626 - 630
    [viewed 14 October 2019]. Available from: https://publications.waset.org/pdf/10007196.