Create A Topographic Survey With A Dual-Frequency GPS and Total Survey Station

Introduction
The ultimate goal of the first topographic activity was to conduct a topographic survey with a dual-frequency GPS and a Total Survey Station. We were to learn how to set up and connect the equipment, and be able to troubleshoot issues as they arose. After collecting data we were compare the two survey methods, analyze the advantages and disadvantages of each, and be able to apply each to appropriate projects.

Study Area
The study area for this activity was the UWEC campus mall between the Davies Center and Schofield Hall (Figure 1.) The area can be found behind 105 Garfield Avenue, Eau Claire, WI 54702.

Figure 1. Google Earth image of the UWEC campus mall.

This location was chosen because it was a large enough area (1 hectare) for our survey criteria and had adequate microtopography change with which to create a significant survey. It's recent construction in 2013 meant that it may not yet have been adequately surveyed using this equipment for this exercise. The wide open space allowed us to obtain 100 topographic points without the need to create break lines which would complicate the project beyond the scope of this exercise.

Methods For Dual-Frequency GPS
This exercise and the following topographic exercise seemed to be a hard lesson in "buttonology," or the maddeningly specific series of actions one must take in order to work with the equipment. In class Prof. Hupy treated us to a demonstration for the Topcon Tesla.(Figure 2.) The Tesla connects to a Topcon Hiper which is the dual-frequency GPS which gives survey grade accuracy.(Figure 3.) The Hiper attaches to the top of a standard height tripod. The height is standard so the GPS can account for the distance to the ground. We also employed the use of a portable wifi hotspot called Mifi. (Figure 4.) This ensured that our connection would remain steady and stable. This also meant we could collect data in more remote locations without wifi. If we had used the campus-wide wifi, the signal would be unstable and could drop which would severely impact the data. It was important that we didn't "wander off" with the portable wifi after connection lest we lose our signal and corrupt our data.

Figure 2. Topcon Tesla similar to the one used in the exercise.

Figure 3. Hiper Dual Frequency GPS mounted on a tripod of known height.

Figure 4. Mifi portable hotspot.

 We then had a lecture outside where each of us set up our project, specified collection criteria, and practiced connecting and disconnecting the device safely. We were warned that an incorrect disconnect could cause a whole host of issues so we were very conscious of our disconnection method.

My partner Grant and myself were to collect 100 data points. We opened up the job that we had created in the class demonstration and set the Tesla to take 15 points at each spot. The Tesla would then average the locations of those points to select the final data point. This is to account for any minor movement or error that can occur with any handheld device. We chose 15 because we felt it was accurate enough for the purposes of this exercise, but time efficient enough to enable us to collect 100 final data points within an hour.

In order to obtain a point, we moved the tripod over a desired spot and used the attached bubble level and adjustable legs to obtain as precise of a level as we could. We followed a back and forth meandering pattern in order to achieve a microtopographically diverse dataset.

After we completed our survey, we exported the data from the Tesla in the lab. After opening our project file we exported the data as a text file using Exchange. (Figure 5.) We had to "clean up" the data by removing extraneous text from the top line in order to make it more useable and clear when importing it into ArcMap. (Figure 6.)

Figure 5. Grant exporting the data into a .txt file.

Figure 6. "Cleaned up" text file.

In ArcMap, we chose 'Add XY data'  and selected our X field to specify for the Easting, the Y field to specify for the Northing, and the Z field to specify for our height. (Figure 7.) Because of licensing issues we were in Demo mode and could therefore only collect 25 points at a time so we had to repeat these steps three more times to get all 100 of our points into ArcMap (Figure 8.)

Figure 7. Add XY Data window. Here we specified the X,Y,and Z fields to the Easting, Northing, and Height fields.
 

Figure 8. Map of data from the Dual-Frequency GPS survey. Because the data had to be broken into four different files, I wasn't able to create an elevation map for this section.

Methods For Total Survey Station
A similar technique was used for the Total Survey Station survey, however some more equipment was used. This included a Topcon Total Survey Station (Figure 9.), the associated tripod, and a survey prism.(Figure 10.)

Figure 9. Total Station similar to the one used in the exercise.

Figure 10. Prism similar to the one used in the exercise.

In the class demonstration we learned how to properly level the total station through increasingly precise adjustments. The data collection demonstration proved to be an issue even for Prof. Hupy as buttononlogy claimed even a seasoned expert. (Figure 11.)

Figure 11. Prof. Hupy expressing visible anguish as he experiences 'buttonology issues.'

In our own survey Nik, Scott and I got our station leveled fairly quickly and needed to employ the help of Prof. Hupy to get us started.(Figure 12.) The next step was to establish backsight points. These points were taken by Scott with the Hiper using the same technique as the Dual-Frequency GPS survey. (Figure 13.) As we learned in the distance azimuth survey exercise, once an accurate location of a point is known, we can then use them to orient another survey method, in this case our total station.

Figure 12. Scott and Nik setting up the total station.

Figure 13. Scott obtaining the backsight points.

Data points were collected by aiming the laser within the Total Station at a reflector within the prism mounted at a known height of two meters. The angle of the reflection and height of both the prism and the total station can then be used to generate highly accurate data points that can be used in a microtopographic analysis.

After connecting all of our equipment we were ready to take the survey points. Blessed with a steady hand and generally poor eyesight, I elected to hold to prism at various locations and elevations within the study area while Nik and Scott took turns aiming the laser housed within the total station and collected the data points. (Figure 14.)We collected points at a variety of elevations along Little Niagara because that area offered the steepest elevation gradient within the campus mall area and was where Scott had initially taken his dual-frequency data. The demo mode only allowed us to collect 25 points and with a heavy and unrelenting downpour adding to the geospatial fun, we collectively decided that enough data had been collected to achieve the purpose of the exercise. Data extraction to XY data followed the same process as above and resulted in the following map.(Figure 15.)


 

Figure 14. Nik getting ready to collect the datapoints using the total station.

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Figure 15. Elevation map created from collected data.

Results/Discussion
Both of the survey methods produced highly accurate elevation data. Unfortunately due both to weather, time constraints, and equipment issues, I was not able to use both survey methods to survey the same area.

I found the dual-frequency GPS survey method quick and easy to setup. There was less equipment to worry about and this method could realistically be completed with only one person. The disadvantages of this method is that I questioned the accuracy because I don't believe that we were ensuring that each data point was perfectly level; especially when we started going a little faster in order to return the equipment at the required time. The tripod was a little cumbersome especially with a broken leg and needing to adjust the legs at every point became a bother. If you are by yourself and need to collect a limited number of points (0-500) I would recommend this survey method.

I found the total station setup complicated and confusing. At first I had a hard time understanding what the backsights were for but I eventually connected it to the distance azimuth survey concepts which made the concept more palatable. Leveling the total station was not as difficult as I had anticipated and once we got the total station working I found that data collection went especially quick, even more than the dual-frequency method. Although set up took longer and there was more equipment to account for, the accuracy for this method was better because it was not necessarily relying on human adjustment, and instead relied on the established parameters. A disadvantage of this method is that it can take a novice a long time to set up and it requires at least two people; one to hold the prism and the other to take the data measurement.

Generally, I found these survey methods initially complicated, but ultimately accurate. I am sure that an expert can produce great quantities of data at an incredibly fast pace but I am unfortunately not presently at that level. Perhaps with practice I can increase my setup efficiency. I am thankful that I could rely both on my group members, Martin, and Prof. Hupy when we got stuck.

Conclusion
This field exercise was a good introduction to the realm of 'real world survey methods.' Data setup is often overlooked in the bigger picture, but it is nonetheless vital to achieve proper accuracy. Knowing how to troubleshoot is also an ever improving skill that I personally am working on for all fieldwork. As always I am thankful that I can add this method to my field survey repertoire.

Sources
Google Earth, UWEC Campus
Hiper image from Bunce Industries LLC website
Mifi image from Softpedia SoftNews website
Topcon Tesla, Prism, and Total Station image from Topcon website

Priory Navigation With Map and Compass

Introduction
This week was a continuation of the concepts of last week's exercise; using alternative non-technological navigation methods. One can never know if or when technology will fail, so it is essential to have many navigation methods in your repertoire. In this exercise we used the maps that we created in the previous week to aid us in navigating to various points in The Priory wilderness area.

Another purpose of this activity was to evaluate the effectiveness of the maps that we created last week. It is difficult to discern the usefulness of a map until one is in the field because the usefulness of a map greatly depends on field conditions which may not be able to be predicted. During this activity we found what information was extraneous, essential, and missing.

Study Area
The exercise took place in the wooded area behind The Priory. The Priory is an extension of the UWEC campus located approximately 3 miles south of the main campus and consists of 112 acres of wood and shrub land with deep ravines running through some areas.(Figure 1.) The building is a multipurpose institution featuring dormitories, child care, and Children's Nature Center.(Figure 2.)

Figure 1. Aerial image of the Priory area. Image taken from Google Earth

Figure 2. The Priory. Photo obtained from Priory Facebook page.

Woodland features of the priory whose importance became apparent during the activity was the decidedly steep ravines that crossed our study area multiple times. Some of the ravines still contained flowing water and access to and from the bottom was particularly treacherous. Tree growth was mostly hardwoods and undergrowth consisted of a high density of the invasive Common Buckthorn Rhamnus cathartica and Prickly Ash shrubs Zanthoxylum americanum. As our course was by the highway and some remote residential parcels, we also discovered large amounts of felled barbed wire fencing that more than one caught our knees and pant legs.

The temperature during the activity was mild for a late October day and while overcast, stayed reasonably light until after 6:00pm when we caught ourselves still within the woods.

Methods
After assembling at The Priory parking lot, Professor Hupy gave us a brief demonstration on how to use the compass with the map. By lining up the compass with two points on map and aligning the north arrow with the arrow on the map, you can see the bearing for the direction you will have to travel. We discussed the term "red in the shed" meaning that if you can place the magnetic arrow within the red arrow outline etched on the bottom of the compass, you can find what direction you need to go.(Figure 3.) The USGS website has a more detailed description on the steps to take when using a map and compass for navigation. Because metal and magnetic forces can disrupt the accuracy of the compass it was stressed that the compass should not be used on or around metal.


Figure 3. Compass used in the navigation activity.

Each group was handed a colored printout of the chosen map using the UTM coordinates, the chosen map using lat/long coordinates, a compass, and a sheet of paper with five geographic points that we were to find in the activity. (Figure 4.)

Figure 4. Maps given to us and the sheet with the navigation points.

We plotted these points on the map and found that we all plotted them slightly differently. This was a good thing because we were able to compare and take an average to where the point was likely to be found. I discovered that because there were very specific locations, using a ruler to hold my place made my point placement much more accurate. (Figure 5.)

Figure 5. Marking navigation points on the map using coordinates.

We then drew lines between the points and calculated the distance between them and the amount of paces each of us would have to take in order to reach the point. (Figure 6.)

Figure 6. Distance calculations.

Because each of us took a different amount of paces to reach the same distance, we each calculated the number or paces to all of the points using each of our pace rates. For example, for every 100 meters I walk 65 paces. The distance between one point was 280 meters which means that I would have to walk 185 paces to reach the point. (Figure 7.)

Figure 7. Map used for navigation activity. We calculated that Casey needed to walk 187 paces to reach the first point.

We also established roles which we often switched. One person would determine the bearing and direct the pacer to a particular landmark. The remaining group member would 'leapfrog' to the next landmark to ensure that the pacer was remaining on track and also served to 'stamp down' some of the brush that might impede the pacer. (Figure 8.)

Figure 8. As Casey paced, I went ahead to stamp down obstacles and ensure the direction landmark.

Results
As often happens in life, this activity did not go perfectly according to plan. The first obstacle was that even with a somewhat standard pace and good faith in out initial direction, it was very difficult to accommodate steep elevation gradients into our pace count. Subsequently, we fell very short of the first marker and in estimating where the first navigation point actually was, we mistook another course point as our first point.(Figure 9.)


Figure 9. The first incorrect point. Casey is using GPS to determine that our actual navigation point is quite a ways north.

 This affected our search for the next point as we were not correctly set up to find the navigation point from a false point. Unfortunately, after we determined our mistake, it occurred a second time. (Figure 10.)

Figure 10. Casey at the second misidentified point.

We resorted to using our GPS to find the first navigation point. After that, we were fairly successful in finding the navigation points, excepting when the flag was missing or fallen. For this, we had to use the GPS to reset our direction.

A major challenge of this activity was the terrain. Our area consisted of decidedly downwards ravines that we had to slide down, sometimes literally, and subsequently ascend. Thorns and barbed wire added to the fun. This was made especially difficult as we often had to 'search' for the point with the GPS which resulted in some backtracking up and down gullies.(Figure 11.)

Figure 11. Casey running down one of the more shallow gullies we had to cross.

 Light also became a factor towards the end of the activity. Late fall sunset was occurring as we found the first point and the group decided that didn't find navigating these woods in the dark particularly appealing. (Video Figure 12.)

Figure 12. Survival log.

Discussion
Although the execution on the concept was a little shaky due to multiple factors, the concept was very helpful during navigation. We found the maps useful although we all decided that it would have been beneficial to have the guidelines darker as they became hard to discern as light began fading. It also would have been beneficial to increase the resolution of the topographic lines and coordinate point grid lines. What appeared to be a relatively small area on the map turned out to be fairly large in the field. This is why it is important to test our maps in field conditions for applicability. This activity also solidified some of our necessary teamwork skills.(Figure 13.)

Figure 13. Scott cross-referencing map information with GPS.

 When things went wrong we had to rely on each other to come up with alternative navigation methods including distance azimuth and simply 'fanning out' to find a point. This also resulted in 'in-field group discussion' as we planned our next method and best courses of action. (Figure 14.)

Figure 14. Lively group discussion as we determined the less treacherous path.

The track log of the path we took can be found on Scott Nesbit's blog. The GPS we were given was accidentally turned off so we relied on his personal device.

Conclusion
This activity was a great hands on activity that taught us not only the concepts, but in-field applicability which I also find immensely more helpful in my understanding of the concepts. Although our group faced some more physical challenges and missed out on the 'debriefing period,' I'm still glad that I got to apply the concepts in a way that will be more likely used in my future career as a biologist. It also taught us a good lesson on what is, and what isn't necessary on a map. This will improve our cartography skills and prevent our maps from becoming too cluttered with extraneous information.