Positioning Performance in Deep Pit Mines using GNSS Augmented with Locata

摘要

Remote mining operations, such as the De Beers' Venetia mine in the northeast corner of South Africa, require a reliable high level of positioning precision (< 10 cm) in order to automate mining operations. In open-cut mines the availability of GNSS can become limited as the line-of-site becomes compromised by the mine walls. Additionally, unpredictable atmospheric phenomena such as ionospheric scintillation can prevent GNSS from effectively providing position information. Traditionally, automated mining operations have operated using only GNSS for positioning, but now ground-based transmitters are being used to augment GNSS performance by acting as an independent constellation of positioning units. The objective of this investigation was to simulate a mine shape and calculate the position error for points in the mine in order to compare the positioning performance both with and without the assistant of LocataLite ground-based radio beacons made by Locata Corporation. Analysis included varying the latitude of the mine, the depth of the mine, and supplementing the GNSS network of GPS, GLONASS, Galileo, and Beidou with LocataLite ground-based positioning units around the mine rim. A simplified mine was modeled with an ellipsoidal mine floor and 45 degree walls. The top of the mine was set to be 1.5 km by 1 km, similar in size to the Venetia mine. The simulation was created using the Constellation Toolbox for MATLAB by Constell, Inc., using a rectangular grid of equidistant points within the mine. By examining points outside of the mine, on the walls/haul roads, and on the mine floor, results show that position error increases with mine depth and varies with latitude. Portions of the mine often experience positioning errors > 10 cm which make areas of the mine incompatible with continuous autonomous mining operations. Additionally, scintillation clouds further exacerbating line-of-sight issues with GNSS by interfering with signals in certain regions of the sky. These scintillation clouds obscure significant portions of the sky impacting the high precision carrier phase measurements required for precise positioning. This research effort shows that adding a network of eight ground-based positioning beacons, such as those made by Locata, positioned at equidistant points around the upper mine rim significantly reduces the average and median positioning precision (both severity and duration) for all points within the mine. The average and median error can be further reduced with the addition of a ninth LocataLite beacon halfway up the haul road on the eastern side of the mine. The addition of the LocataNet system of beacons allows for precise and continuous mining operations at depths previously unavailable using solely GNSS.