Mapping in the Arctic Circle
Nunavut is a remote area rich in precious gems and minerals, such as gold, silver, zinc, uranium and diamonds. Producing actionable geospatial information is useful for identifying and developing commercial opportunities throughout the area. Atlantic’s mapping project involved airborne surveying for a corridor 85 kilometers long by 1,500 meters wide, plus an additional area 25 kilometers long by 1,500 meters wide. The mapping deliverables included a classified, calibrated LiDAR point cloud in LAS format, 0.5-meter contours, hydro-conditioned DEMs, LiDAR intensity orthophotos and 20 centimeter RGB orthophotos.
Atlantic’s two-man crew flew this mission in a Piper Navajo Chieftain 310-A, equipped with a Leica ALS70-HP LiDAR sensor and a Leica RCD105 RGB medium-format camera system. The Navajo offered an advantageous combination of range, ample size and low-cost operation that suited the unique conditions. The crew was based in Cambridge Bay, Nunavut, more than 200 nautical miles from the project site. Due to weather delays combined with routine aircraft and sensor maintenance, the pilot and sensor operator lived north of the Arctic Circle for slightly more than a month.
Operating in an extremely remote location requires unique planning and the ability to function independently. There is a small human population, little infrastructure and few spare resources on which to rely. These conditions resulted in additional subtasks for both data acquisition and data production that are not typically associated with most large-scale mapping efforts. To ensure project success, all of the necessary supplies had to be identified ahead of time and pre-shipped, such as fuel, food supplies for the crew and regular aircraft maintenance items such as oil filters, oil and sparkplugs. Adequate fuel was a major concern. Preordering the fuel required complex calculations, taking into account distance, weather conditions and the potential loss of fuel volume en route. The fuel was delivered in 55-liter barrels via barges to Cambridge Bay, Nunavut. Cambridge Bay offered the closest lodging and fuel option for the crew, so they flew the 200-plus nautical miles to the project site at least twice and sometimes four times per day when conducting missions.
“The location in northern Canada created a large number of logistical challenges Atlantic had to overcome,” said Brian Mayfield, Atlantic President and COO. “Dealing with the frigid, shifting temperatures, even in an Arctic summer, and the lack of local resources required extensive planning and sometimes creativity on our part.”
Another difficulty was encountered when setting up adequate GPS base stations within an acceptable distance of the project site to achieve the required surveying data accuracies. Normally to achieve the proper accuracies, Atlantic would have established multiple base stations to ensure the aircraft is never more than a 20-30 kilometer baseline distance from the GPS receiver. But the remote location of this project site eliminated Atlantic’s ability to use this approach within a reasonable budget for the client.
As an alternative to multiple base stations, precise point positioning can be utilized to create a virtual base station for aerial photography and higher altitude remote sensing projects, although Atlantic’s research found few examples of PPP technology being applied for high accuracy LiDAR projects. Prior to accepting this project, Atlantic conducted numerous experiments by flying at the project mission altitude and processing the data using both techniques to determine if PPP could eliminate the need for multiple physical base stations.
Atlantic’s tests concluded that they would be able to utilize the PPP solution for establishing a virtual base station by doing the following:
• Placing a physical base station at the operational airport.
• Maintaining continuous observation times of at least 4.5 hours on the airplane GPS units.
• Flying a line over the GPS base station at the remote airport at the beginning and end of each mission.
Using this methodology, Atlantic was able to achieve a final vertical accuracy for the LiDAR data of 14.8 centimeters RMSEz, which exceeded the clients requirements of 18.5 centimeters RMSEz.
By incorporating a customized solution into the work flow for integrated PPP, Atlantic was able to achieve the desired accuracy results without establishing GPS base stations within or near the project site. This creative solution saved Atlantic and its client tens of thousands of dollars and many weeks on the overall schedule.
“The successful application of using PPP for a remote-area LiDAR project has given Atlantic the confidence to accept other challenging collection assignments,” said Steve Denney, Atlantic CEO. “Alaska, the Yukon Territories and British Columbia have similar terrain and working conditions. Based on our experience in Nunavut, we feel comfortable competing in those markets in the future.”