Can terrestrial-based transceivers (LocataLites) be a solution to open-cut mining applications?

Acceptable RTK GNSS performance is heavily dependent on a relativity unobstructed sky-view, where there are at least five satellites with good geometry available, and on the reliability of the wireless data link used for differential corrections.

Figure 1. DeBeers Venetia Mine from East rim.

Open-cut mining techniques have come to rely heavily on GNSS technology as a critical input into machine control systems. However, as open-cut mines get deeper the visibility to GNSS satellites is greatly reduced, and therefore reducing the effectiveness of GNSS positioning systems placed on mining equipment. Locata and Leica have been working together to develop a solution to this problem using Locata’s terrestrially-based positioning technology.

The Locata technology concept is to deploy a network of terrestrially-based transceivers (LocataLites) that transmit positioning signals to augment or replace GNSS entirely. Theses transceivers form a time-synchronous positioning network called a LocataNet, potentially allowing single point positioning (with no differential correction and data links) with cm-level accuracy.

In the current system design the LocataLites transmit their own proprietary signal structure in the 2.4GHz ISM band (license free). This ensures complete interoperability with GNSS and allows enormous flexibility due to complete control over both the signal transmitter and the receiver. Details of the current system design have been detailed in Barnes et al. 2005 & 2006, together with kinematic positioning results demonstrating RTK-level performance independent of GNSS.

Venetia Mine Trial

During late 2006 through to early 2007 the first integrated loosely coupled Leica and Locata equipment was installed and tested at De Beers “flagship” Venetia diamond mine in South Africa (as shown in Figure 1). The LocataNet was established around the rim of the pit (covering an area approximately 1.2 x 0.8 km and 0.25 km deep) as shown in Figure 2. A backpack, dozer and drill system were equipped with integrated Leica/Locata positioning technology as shown in Figure 3. The desired positioning accuracy requirements at the outset of the trial was for a Locata-only solution (after GNSS RTK initialisation) to provide at the 95% level 10 cm in the horizontal and 20 cm vertical. In all three systems the Leica GNSS RTK receiver was used to resolve the Locata receiver’s carrier ambiguities. Following initialization the Locata receiver delivered position solutions independent of GNSS.

Figure 2. Map showing LocataLite site locations and LocataLite site setup with mast and solar panel

Figure 3. Drill, Dozer and Backpack mining equipment installed with Leica/Locata positioning technology.

Performance Analysis

During the trial data was collected to assess the performance of the three Leica/Locata integrated mining systems installed on the Drill, Dozer and Backpack. In all performance analysis a Locata-only solution was compared to a GNSS RTK ‘truth’ solution. Therefore performance evaluation of Locata can only be conducted where there was sufficient GNSS coverage for an RTK solution. In certain areas of the pit at certain times of the day getting a ‘truth’ solution from GNSS RTK was difficult due to the lack of satellite availability

Extensive data analysis of data collected over two months shows that overall performance of a Locata-only solution is within the 10 centimeters horizontal and 20 centimeters vertical guidelines identified at the outset of the project, when there is sufficient LocataNet geometry to support a navigation solution. Detailed results and analysis are given in Barnes et al. 2007. Figure 4 (left) shows typical GNSS RTK and Locata results for one test site with the East, North and Height components time series for GPS (red) and Locata (black), with Figure 4 (right) ‘zoomed’ in at epochs 80 to 110. From the figures it is clear that the GNSS and Locata positioning time series compare to better than 5 cm in all three positioning components.

Figure 4. Typical results at one test site showing Locata-only and GPS East, North, Height positioning results. Figure on top ‘zoomed’ in at epochs 80 to 110.

Based on the success of the trial Leica and Locata are continuing to improve the proof-of-concept system with the goal to developing Locata enabled technology products for the open-cut mining market.

References

Barnes, J., Rizos, C., Kanli, M., Pahwa, A., Small, D., Voigt, G., Gambale, N., & Lamance, J., 2005. High accuracy positioning using Locata’s next generation technology. 18th Int. Tech. Meeting of the Satellite Division of the U.S. Institute of Navigation, Long Beach, California, 13-16 September, 2049-2056.

Barnes, J., Rizos, C., Kanli, M., & Pahwa, A., 2006. A positioning technology for classically difficult GNSS environments from Locata. IEEE/ION PLANS, San Diego, California, 25-27 April, 715-721.

Barnes, J., Lamance J., Lilly, B., Rogers, I., Nix, M., & Balls, A., 2007. An integrated Locata & Leica Geosystems positioning system for open-cut mining applications. 20th Int. Tech. Meeting of the Satellite Division of the U.S. Inst. of Navigation, Fort Worth, Texas, 26-29 September,

Dr. Joel Barnes, Director of Navigation R&D
Locata Corp. Pty Ltd,
Visiting Senior Research Fellow
School of Surveying &SIS
University of New South Wales
joel.barnes@locatacorp.com