Surveying on the Fast Track
At roughly 3,000 square miles in total and rising to its highest height at 12,799 ft above sea level, the Beartooth Mountains in Montana are among the largest landmasses in North America. The Beartooth Plateau is located on the Montana/Wyoming state line near the northwest corner of Wyoming, just east of the renowned Yellowstone National Park. In August 1882, Lt. General Phillip H. Sheridan and 120 men guided by an old hunter simply known as "Geer" pioneered the first organized and recorded trip across the Beartooth Plateau. While the trek was admirable and provided a usable trail, travelers were not satisfied with the steep and difficult path. In the early 1920s, the Forest Service and Bureau of Public Roads (known today as the Federal Highway Administration) performed reconnaissance surveys to determine the feasibility of constructing a new trail across the plateau. Subsequently, President Herbert Hoover signed a bill in 1931 authorizing funding to build one of Montana's most impressive structures: the Beartooth Highway.
Beartooth Highway is essentially untouted in comparison to Montana's Yellowstone and Glacier National Parks, and the Going-to-the-Sun Road, which receive much of the tourist attention. But Beartooth Highway is another of the state's wonders. The road opened on June 14, 1936 at a cost of $2.5 million and serves as a main entrance to the east side of Yellowstone National Park. Beartooth Highway reaches its highest point at 10,974 ft and is home to wildlife such as grizzly bears, elk, bison, mountain goats and mule deer. Travelers on Beartooth Highway traverse across alpine tundra for views of the Absaroka and Beartooth Mountain Range, year-round snowbanks and pristine lakes. Unfortunately, the picture perfect roadway was later decimated and surveying expertise would be necessary for its rebuild.
Mudslides Destroy HighwayDuring May 2005, the area surrounding the Beartooth Mountains received record amounts of rain. Combined with the spring runoff, the rain created massive mudslides along a section of the highway that ascends more than 2,400 ft in just 10 miles through four major switchbacks that reach the Beartooth Plateau. Due to the steep terrain and switchbacks, the mudslides destroyed the highway in 13 locations, and removed the ground below the highway. The devastation caused Beartooth Highway to be closed for the summer of 2005, negatively impacting the economies of the communities of Red Lodge and Cooke City.
Since tourism is one of the top industries in Montana, and the lifeblood of Red Lodge and Cooke City, Jim Lynch, director of the Montana Department of Transportation (MDT), immediately committed all available resources to the reconstruction and reopening of the highway.
Surveyors Called for ControlMDT hired contractors for the highway repair, but retained survey control duties in-house. On Thursday, June 2, the MDT Survey Department in Helena where I work as a project surveyor was notified that we were to perform a GPS control project along seven miles of highway ascending more than 2,230 ft through four switchbacks. And we had only 131â2 days to complete the project.
Overcoming Mountainous ObstaclesWe had to move quickly to formulate a plan of action. We had several obstacles to overcome, including the greatest obstacle: getting to the top of the mountain. The highway was closed from the Wyoming side across the approximately 50 miles of highway on top of the 9,000 to 11,000 ft Beartooth Plateau. Due to the large amount of snow still on the plateau in June and the typical high winds, we knew we couldn't plow it open-drifting snow would easily reclose the road within hours. We settled on a helicopter for mobilization. By Friday afternoon our department had secured a Department of Natural Resources and Conservation (DNRC) helicopter to transport our crews and equipment.
Coordinating personnel, equipment and safety were our next major concerns. Pooling the resources of MDT's districts, we were able to round up a 20-person team consisting of six PLSs, three LSITs and 11 helpers.
Obtaining ControlMDT wanted this project on NAD83 state plane coordinates and NAVD88 elevation; however, we lacked horizontal and vertical control. In Montana we usually use a HARN (High Accuracy Reference Network) station to control our projects because Montana is severely lacking in any published densification of the HARN. The three closest HARN stations ranged from 30 to 74 km away from the project area; using them would have taken an entire day even if everything went perfectly. Therefore, we decided to set up three base stations strategically around the project area on each of the four days of fieldwork and to utilize the NGS Online Positioning User Service (OPUS) to obtain NAD83 state plane coordinates.
This resolved our horizontal control, but vertical control presented an even bigger problem. Only five NGVD29 bench marks set by USGS in 1947 were uncovered in the project area, and the only NAVD 88 bench mark was about 12 miles north of the project in Red Lodge. My prior GPS experience in the Red Lodge area revealed another problem: the geoid models could not be trusted. Gravity measurements are typically taken in accessible valley areas, and the geoid is then tweaked to NAVD88 bench marks. The fact that the closest NAVD88 bench mark was 12 miles away-and in some of the most rugged and inaccessible country in Montana-made for a very untrustworthy geoid model. We decided we needed to run levels to help verify our elevation. The levels would only be run one way due to time constraints and compared to the GPS elevations in order to catch any major errors.
Facing the ElementsOur last problem was the elements, and all of the employees involved in the project needed to deal with this individually-bringing enough clothing, food, lip balm, etc. to protect themselves. Even though it was June, the highest point of the project area was around 9,800 ft above sea level and temperatures would never rise much-if at all-above freezing. The winds could be counted on to blow at least 15 mph and at much higher speeds when storm fronts passed through.
Base Station 1 was placed at the bottom of the mountain and was easy to drive to. Base Stations 2 and 3 were located at the tops of two mountains with no shelter, so tents were pitched at both of these stations. Base Station 2 was run by Carole Sandin, PLS, and was placed where the highway reached the top of the mountain. We used the helicopter to place a Bombardier (Valcourt, Quebec, Canada) all-terrain vehicle (ATV) near Base Station 2 so she would have a way out in the case of a snowstorm. The ATV would get Sandin to the first major slide area, and from there she could walk to safety. (Thankfully, this option never had to be used, as the skies always seemed to clear for us in the morning and evening.)
Marty Tomlin, LSIT, ran Base Station 3, which was placed on top of a mountain to the west of the project. Tomlin was able to drive an ATV a good way up the mountain until the snowdrifts stopped him. He then had a 600-ft vertical hike to make through 4 ft of snow carrying a GPS pack and his base station. After the first day, Tomlin (who rarely complains) made it very clear that he needed the helicopter to drop him off at his base station. Due to the altitude, our helicopter pilot could not carry a large load to the top of the mountains, thus it cost us time each day to fly the base stations individually to the top.
Putting the Plan in ActionOn June 7 at 7:00 a.m., we started to put our plan into action. First we received safety training from the DNRC helicopter pilot. He instructed us on how to approach the helicopter, protect our ears and communicate with him once onboard.
For our three base stations, we used Trimble (Sunnyvale, Calif.) 4700s with Compact L1/L2 antennas; we also used six Trimble 5700s with Zephyr geodetic antennas for rovers. The plan was to work downhill, and to set the control as we went.
On Tuesday, the first day on the mountain, after positioning our base personnel and equipment, we flew all six GPS roving crews and both level crews to the top of the highway. We began at the top and worked downhill to create a continuous GPS measurement from station to station. Each station also had one measurement to at least one base station. Thus, each station had a GPS measurement from the station behind it and to the station ahead of it, plus a tie to a base station.
The GPS roving crews spread out so that they were intervisible to the crew ahead of them and the crew behind. They then set intervisible control points using radios to do three 20-minute-long simultaneous sessions. After the three sessions, all the crews moved down the road maintaining their order until the rover in the rear arrived at the point that the lead rover had set.
The process worked well and was repeated until the end of the project. It prevented us from needing to walk uphill in weather that changed by the hour.
I was on the rear GPS crew and used my Garmin Legend handheld GPS unit to note the mile marker to the nearest tenth of a mile for each control point so that we could add this information to the descriptions at a later time. After going downhill along five miles of curves, I was only four-tenths of a mile off when I finally found another mile marker to check into, noting it in the descriptions.
I processed all the GPS data each night from my hotel room to ensure the data collected was good. I submitted all four Trimble GPS .dat files for each base station to OPUS and received amazing results. When I compared the four different results/coordinates for each base station from OPUS, the coordinates matched within 1 cm horizontally and within 2 cm vertically.
Leveling It OutWhile the six roving crews performed the GPS sessions, our two level crews simultaneously ran the levels. Using Trimble DiNi 21 and DiNi 22 digital levels, we pegged and checked levels and rods against each other. We searched for and ran through the USGS bench marks as the survey progressed down the mountain.
Each level crew ran through basically half of each GPS session. Level Crew 1 ran through the first half of GPS session one, and Level Crew 2 ran through the second half of GPS session one and the first half of GPS session two. Meanwhile, Level Crew 1 would leapfrog Level Crew 2 and start on the same point Level Crew 2 would eventually end on. This process was performed repeatedly to create one continuous level run down the mountain. We used the NGS Vertcon program to convert the USGS NGVD29 datum to NAVD88 datum.
The plan was executed flawlessly and no return visits to the project were necessary. After spending 11â2 days planning, we set, surveyed and wrote descriptions on 76 points in just 3 1â2 days in the field.
Adjusting the VerticalWith all the field surveying done on Friday, June 10, and all the field data processed, I was able to take the weekend off. When I got back to the office Monday, I finished up the project. After I received all of my OPUS solutions, I ran a minimally constrained adjustment by fixing just latitude and longitude of one of the base stations. I determined the network integrity was good and proceeded to fix all three of the base stations' latitudes and longitudes using the OPUS solutions. I now had a horizontally constrained network and everything looked good.
As expected, when I needed to constrain the vertical component in the adjustment, I was faced with the lack of an accurate geoid model in the area. With just one point fixed vertically in the GPS adjustment, we saw as much as 1 ft difference from the GPS elevation compared to the elevation from the levels. The biggest problem was that it was not consistent; the geoid seemed to almost make a wave.
Normally when we fix just one vertical point in an adjustment and the geoid model is poorly mapped in an area, we see the GPS elevation differ from the conventional elevation in a very systematic direction. This time the separation between the GPS and the conventional elevations was all over the place. I ran many iterations of vertical adjustments. Each time I plotted out a to-scale map of all the points and then I wrote all of the differences between the GPS and conventional elevations. After analyzing all of the vertical adjustments, we were able to safely say the elevations from our conventional level runs were good. We then fixed all the elevation from the level run we ran in the final fully constrained adjustment.
Fast Track to QualityIn all, we surveyed 337 nontrivial vectors and only had to disable nine. For the final touch we imported all the control points into Micro-Station (Bentley Systems Inc., Exton, Pa.) and used MrSID images (LizardTech, Seattle) to create a .jpeg file to visually depict all the control points. On June 15, we presented final reports and coordinates to one of MDT's subcontractors, HKM Engineering, a private consulting firm headquartered in Billings, Mont.
The completion of this project demonstrated how quickly MDT's survey districts of Helena and Billings and the Department of Natural Resources and Conservation could pull together as a team to produce a quality product-on a challenging site and in unprecedented time.
Beartooth Highway was repaired and reopened by Oct. 7, 2005. Despite cold weather, the communities of Red Lodge and Cooke City turned out in force for the official opening ceremony, complete with a community band. While both communities felt the effects of decreased visitation during the summer season, they were relieved and grateful that MDT and its contractors, HKM Engineering, JTL Group (Billings, Mont.) and Kiewit Western (Littleton, Colo.), worked tirelessly to repair the notable Beartooth Highway before the 2006 tourist season.
Fast Track TimelineJUNE 2
1:00 pm: Survey department assigned Beartooth Highway project.
2:00 pm: Helena Survey Dept. holds meeting; John Hoechst assigned as lead surveyor.
1:00 pm: Helicopter secured from DNRC.
2:00 pm: Plan finalized.
8:00 am: Helena Survey Dept. holds coordination meeting; packing and mobilization begin.
10:00 am: All necessary personnel secured.
5:00 pm: All personnel attend field meeting in Red Lodge, Mont., for training and instruction.
7:00 am: Personnel meet at Red Lodge Airport and receive helicopter safety training.
12:00 pm: All personnel are in position and survey begins.
12:00 pm: Field survey completed.
5:00 pm: Crew returns to Helena and unloads trucks
7:00 am: Adjustment of network begins.
2:00 pm: Adjustment and final reports completed.
4:00 pm: Final reports turned over to consultants.