Eric Sitorus and  Septian Prahastudhi and  Turgod Nainggolan and  Erwin Riyanto,  Delineating Concern Ground in Block Caving – Underground Mine Using Ground Penetrating Radar.   journal   = {International Journal of Geological and Environmental Engineering}, [online]. World Academy of Science, Engineering and Technology.
    April 2019, vol. 149(5). 332 - 335
    [viewed 20 November 2019]. Available from: https://publications.waset.org/pdf/10010342.