Distance Azimuth Survey

Introduction

          For the most part, the majority of surveying is done with the use of extremely accurate GPS technology coupled with survey stations. There may come a point in any geographers career where that technology may not be accessible or it could even fail completely. This lab focuses on building a skill set that can be used in many different settings and could be a real selling point to future employers. The purpose of this lab is to be able to create a survey using the distance and azimuth technique. This is a technique that is not very technical and it is only feasible on a reasonable scale and the accuracy will not be that of a GPS. Using low tech options assures that if ever faced with unfortunate circumstances, data will still be able to be collected. A distance azimuth survey is an implicit survey technique. Implicit survey data means that the data was collected relative to a know GPS coordinate. In contrast an explicit form of data collection means that there will be specific geographic locations.

          This lab took place in Putnam park, just to the south of the University of Wisconsin Eau Claire. The area where the lab was conducted was fairly heavily wooded, with exception of the jogging trail that runs through the park. A GPS unit was used to get three specific locations where a sample of ten trees was taken and the distance from the GPS point to the tree was recorded, along with the azimuth (degree) which gives the direction the tree is from the GPS point. Additionally the diameter of the trees was recorded. Each of the three survey locations were within 150 meters of each other, roughly 50 meters apart, though the distances were not measured. From there 10 trees were selected that had a clear line of sight from the reference point in which one group member stayed at all times until the survey was complete. The tools used for this lab include a GPS for reference point location, a notebook for data recording, a tape measure that calculates the diameter of the tree by taking a measurement around the tree at chest height and a compass for the azimuth. The tools used to record distance include laser distance finders and a more basic meter tape in an effort to get exposure to multiple data collection methods.

Methods

Figure 1

          The survey area was in Putnam park, south of UWEC roughly 150 meters away. This lab can not be completed without first understanding how each of the tools work, Professor Hupy offered assistance in explaining the uses of each of the devices. From there the first step in the lab is to use the GPS unit to get the coordinates of the reference point that was used, the reference point being where the group member will stand to get distance measurements along with where the tree is in association to the reference point using the azimuth tool. From here 10 trees were selected that offered a clear line of site to where the GPS coordinates were recorded. It is essential to note that the person who is on the GPS coordinate should not move at all because that will helps with data integrity. A table was made for each of the three locations, each table included latitude, longitude, distance, azimuth, and diameter. In the first station the distance and azimuth were both recorded using the TruPulse laser which is shown to the left by figure 1. This is done by simply pressing the black button on top of the handheld device, as noted before it is essential to make sure that the line of sight is clear or there could be interference with the laser. By using the arrows on the side of the laser the user can scroll through the setting to select distance and then degrees. Finally. the diameter of the trees should be collected at chest height. This was the least hands on of the three approaches. Figure 2 that is located to the bottom left shows the GPS unit which is pictured in the bottom of figure 2 and the tape measure used to measure the trees circumference is pictured in the top of figure 2.

Figure 2

          Area two was down Putnam trail to the east of the initial survey area roughly 50-75 yards. With the same steps as the first location the GPS was used to get a base point where one of the group members stood until the entire survey was complete. Again, ten trees were chosen at random and again the line of sight from reference point to trees must be clear. This time the azimuth was recorded using a tool that is called an azimuth compass. Next the distance from reference point to tree was measured using a meter tape. The azimuth compass is very easy to use, basically the same manner as the laser range finder, the point and shoot method. Again, the diameter of the trees was collected at chest height.

Figure 3

           Area three was roughly another 50-75 yards further east down the trail from the second survey area. The first step yet again is to get an accurate GPS location and to then have one group member stay in exactly that spot for the duration of the survey in area 3. Next, 10 trees should be selected for surveying. In this survey location the Sonin sound wave device was used to record the distance from the reference point to the trees. The device is used by the person on the reference point point at the another part of the device that another group member was holding up against the target trees. A sound wave is sent from one device and back to the other and a distance is registered. The diameter of the tree was then again recorded using the same method of hooking the tape around the tree at chest height, the method for getting the tree diameter is shown by figure 3 to the right. The azimuth was recorded using a good old fashioned compass, this is to show that many different methods can provide the same results. Figure 4 below shows the method that was used in the third survey area to record the distance. It is important to note that the tape measure was pulled tight before a measurement was taken, in order to ensure data integrity.

       

Figure 4

            After the field work for the distance azimuth survey was complete, the data was entered from the notebook in Microsoft Excel. It was essential to make sure that the data was normalized before adding the data into ArcMap. It is important to note that distance was in meters, azimuth is measured in degrees, not degrees minutes seconds, and the diameter of the trees was measured in centimeters.

       Once the data is normalized, it is ready to be brought into ArcMap. The data was brought into ArcMap using the 'Bearing Distance to Line' tool. Once the tool is open it asks for the lat and long, the distance, azimuth and diameter all collected during the survey. This tool does not create point, rather just the lines that represent the distance from the reference points to the trees. Next, using the 'Feature Vertices to Points' tool, points were created on the actual locations of the trees. Essentially this tool put points at the end of the lines that were just created using the previous tool. Once both these tools were ran, the result is lines and points that represent the distance and azimuth.


          It is important to note that even when working with less technology there can still be a number of issues that arise. When using both the Sonin and the TruPulse devices there needs to be a clear line of sight from the group member on the reference point to the tree being surveyed. This limited which trees could be selected and there is really no way around it without leaving the reference point which would skew the data. When using the TruPulse device if the user hit a twig that was closer than the tree, the distances could have been way off. Similarly it was important to make sure both members using the Sonin device held the devices at the same level, and that the person on the tree kept the device tight to the tree when readings were being taken. Additionally there was several mix ups with tools, people were not leaving there tools at the stations as they were instructed, but rather many carried them to the next survey area with them. This led to some confusion and some time lost, though it was not a major issue. Yet another issue was the lack of consistency when collected the diameter of the trees. Some group members are nearly a foot taller than other, so chest height for one group member is not chest height for another. This did not influence the data all that much, the reason the same person did not complete every tree was because they exercise was designed to get everyone involved in every aspect.

Results

          This lab was originally designed to have multiple maps because when they lab is conducted in the fall semester it is much easier to tell the tree type. For this lab in spring 2017 the tree type was not recorded. Truth be told there is not a ton of data to be displayed here so it will all be conveyed in one map. A table is included below as well to show how the data looked before being brought into ArcMap.

Figure 5

          Above in figure 5 is a map showing the sizes of the trees diameters. The point at which all of the point start is the reference point and the red lines are the lines that show the azimuth degree and also illustrate the distance from reference point to the trees surveyed. The largest tree in the survey was 148.20 centimeters, it was a very large tree that took two people to get around, this was done just to show some of the diversity in the tree sizes sampled. In contrast the smallest diameter tree was 6.80 cm, this was about the smallest tree that the tape would do, due to the way it has a few centimeters of blank tape. There is a fairly even distribution of the sizes of trees. Though it does seem that survey area 1 in the northwest corner has slightly smaller trees in diameter compared to the other two survey areas.

Figure 6

        Figure 6 is simply a map that shows the location of the trees without incorporating the diameters. Survey area 1 is in the Northwest corner of the map, survey area 3 is in the Southeast corner and survey area 2 is in the middle. Survey area 2 had a much smaller survey area, meaning the trees sampled were closer together, this was done because this was where the tape was used to measure distance. The other methods of finding distance were much easier, also keeping the tape measure trees close to the reference point ensure less bow in the tape and a more accurate distance reading.

         Figure 7 below is the table of the normalized data that was used to get the data displayed in ArcMap. The P_Number column shows which survey area was associated with which coordinates, this was done simply to help keep the data in the correct order and to make sure that there was no issues when bringing the data into ArcMap.

Figure 7

         One thing that hindered the map making process was the fact that survey are 1 which was to the far east of the map had an error when collected the GPS coordinates. When the data was brought into ArcMap the survey 1 area showed up half way up the hill, nearly 40 meters away from the actual on earth location. To remedy this issue the identify tool was used in ArcMap to find the coordinates of the actual location and then the excel sheet was fixed and the data was re brought into ArcMap. The reason for the poor GPS location initially is more likely than not from the large hill, there must not have been enough satellites connected to get an accurate location.

Conclusion

          In closing this lab has so many real world applications. An employer would be thrilled to know that if something happens to the technology, they still have someone in the field who can collect data. Distance azimuth surveying is actually very interesting and it really gives a sense of pride to the surveyor because it is not a machine doing all the work. This is a hands on approach that is relatively low cost, depending on the survey area size relatively low time and it is just all together a good skill to have.