Lab 2: Distance Azimuth Survey

Introduction
GPS technology has enhanced the way one can plot data, being very precise with the assistance of survey stations.  Despite their accuracy, they cannot always be relied on.  Alternative methods ought to be available if this technology cannot cooperate in certain situations. This activity required students to conduct a survey by using a distance and azimuth technique.  This involved selecting two different sites along the trail of Putnam Park to gather data for tree species.  A variety of tools were used to record the distance, azimuth, and circumference of a tree.  Students were to make an educated guess on the species of tree.  After recording the data, it was imported into ArcMap in order to map out tree diameters.


Study Area
There were two points measured along the path of Putnam trail, which were both southwest of Phillips Hall at the University of Wisconsin - Eau Claire.  These points were at the edge of a gravel walking trail, both chosen because they were seen as ideal plots for measuring tree sites spanning 360 degrees to measure distance, azimuth and circumference of each tree.  Tree populations were dense in these two areas and were well in range of measurement.  The plot coordinates for both of these areas were 44.79646 ºN, 91.501848 ºW for site 1, and 44.79539 ºN, 91.500038 ºW for site 2.  Figure 1 below shows the survey areas for both points.

Figure 1: These two points display where azimuth and distance were recorded

Methods 

Students headed over to Putnam Trail in assigned pairs to begin the survey process.  Each group was given four measuring tools.  The objectives were to record the latitude and longitude of each base point, the distance from the base point to each tree, the azimuth from the base point to the tree, and the circumference of each selected tree.  The first measuring tool (displayed in figure 2 below) was a GPS unit which measured the exact coordinates of each point we conducted with the distance-azimuth survey.

Figure 2 - GPS used to record coordinates

The second tool used to gather data for this survey was a hand-held laser pointer, which was utilized to measure distance from the base point to a selected object.  In this case, students measured distance from 10 different trees spanning 360 degrees from the stationary point where they stood.  Figure 3 below displays the device.  

Figure 3 - Bosch professional laser measure used to record distance from tree

The third tool utilized was the azimuth compass.  This recorded the degree angle from where a student stood at the base point to the selected tree.  The dial recordings were written down in students' field notebook for data processing.  Figure 4 below displays the field compass. 

Figure 4- Compass which recorded azimuth

The last tool utilized was a tape measure in order to record the circumference of a selected tree.  As one student stood at the base point, recording the GPS coordinates, distance, and azimuth, the other walked through the brush to record the tree measurement by wrapping the measuring tape around the base of the tree and reading off the measurements to his/her partner so they could record it in the field notebook.  Figure 5 below shows the measuring device.

Figure 5 - Field measuring tape

Once both sites were measured and recorded for all 4 elements, students transferred this data to an Excel file.  Students had to manipulate the data a little bit in order to make it compatible for the next step in ArcMap. The compass broke measurements down into 90 degree quadrants (NE, NW, SW, SE), so this had to be accounted for when punched into Excel so that it would be in 360 degree intervals.  For example, if a measurement read 20 degrees SW, it would have to be converted to 200 degrees.  Circumference was also converted to diameter, so simply divided by pi.  The x and y in figure 6 below represent longitude and latitude, and distance being from the base point to the selected tree

Figure 6 - Recorded data processed from the two base points

Once the data was produced in Excel, students were to import the recordings into ArcMap.  This was done by selecting "Add Data" within the software, and it was imported into the geodatabase.  ArcToolbox was then opened, and the "Bearing Distance to Line" tool was used to display the survey area points to the distance to each tree.  Figure 7 shows the input table for this tool.

Figure 7 - Bearing Distance to Line Tool

Proceeding that, "Feature Vertices to Point" tool was used to display the diameters of each tree legibly, selecting "Diameter" as the selected variable to be visualized by navigating to Properties--Symbology.  The proportional display points of each tree could be customized to the students liking, in this case, trees were the symbols.  A map was then produced, adding a north arrow, scale bar, name and legend to represent tree diameter.


Results
After everything was processed on ArcMap, the resulting map was produced in figure 8 below, showing the (general) location of the two given sites, as well as the proportional size of tree diameters, the azimuthal angle, and distance from the trees to the recording points. 

Figure 8 - Final map produced displaying Tree diameter and approximate locations points

Conclusion
When other technology fails, the Distance-Azimuth survey method proves to be a reliable alternative field survey technique.  It might not necessarily be the most precise method of recording, as in this particular survey, the coordinates of the plot points seemed to not quite match up with the exact vicinity the initial recordings that were made, but it still gets the job done in that it gives clear representation of distance and azimuth readings from a given location. 


Sources


Hupy, Joseph. (2017). Field Activity #4: Conducting a Distance Azimuth Survey. [PDF Document]. Retreived from : UWEC D2L, Geography 336.001 Lab Contents.

Teh, Steve. Biology 3A: Ecology: Point-Quarter Sampling. Report no. 3A. Biologiical Services Department, Saddleback University.