Field Activity: Conducting a Distance Azimuth Survey

Introduction
GIS, GPS, and survey technology have progressed astoundingly far in recent years. With this technology, it is now very easy to conduct an accurate survey. However, technology is not infallible. The survey equipment may break, the GPS could be seized at the airport, or maybe the battery refuses to charge. As unlikely as it may be, statistically speaking, something will stop working eventually. To prepare for this eventuality, it is necessary have an effective backup plan. One such option, a low-tech survey technique known as azimuth surveying, was conducted for this lab. In azimuth surveying, a single GPS point is taken, known as an origin, and data points are collected around this origin. The locations of these additional data points are referenced with a corresponding distance from the origin and azimuth bearing measurement. By using one or several origin points in an azimuth survey, the exact GPS coordinates do not need to be collected.
Study Area
The study area, Putnam Park, sits between upper and lower portions of the University of Wisconsin, Eau Claire campus. To avoid redundancy, the imagery of the survey area is included within the results section of this post. It is well known for the large variety of trees within it, do to the varying elevation and soil moisture produced by the steep slope. To practice azimuth surveying, ten trees would be surveyed around each of three origin points using three separate techniques to measure distance and azimuth, for a total of thirty surveyed trees. These points would then be imported into ArcMap for analysis.
Methods
First, three origin points were taken within Putnam Park using a personal GPS Unit. From the GPS, their x,y coordinate were recorded as "91.50034,44.79544", "91.49913, 44.79547", and "91.5017, 44.79642". This, along with the distance to each tree from the origin, the azimuth bearing, and the circumference of each tree were recorded for each surveyed tree in a data table (Figure 1).

Figure 1: The electronic Excel file datatable of all thirty trees surveyed in Putnam Park. The recorded data includes the x and y GPS coordinates of the corresponding origin, the distance in meters each tree is from its corresponding origin, the azimuth bearing of each tree from its corresponding origin, and the circumference of each tree surveyed. A column for the corrected x GPS coordinates was included, as it had to become negative in value before it could be properly imported into ArcMap.

The circumference of the tree was used as a stand-in for the tree species, as the species of each tree would be difficult for non-biology students to determine at this time of year (March 2015).
From the first origin point, ten trees were surveyed by using the GPS, a compass, and two measuring tapes. This was by far the most low-tech survey method used during this field activity. By looking through the compass and aiming it at the surveyed tree, the azimuth bearing could be recorded from the compass (Figure 2).

Figure 2: A surveyor recording the azimuth bearing of a tree
from its corresponding origin point using a compass.

The distance from each tree to the origin was recorded by measuring the distance using the longer measuring tape. The second measuring tape was utilized to measure the circumference of each surveyed tree (Figure 3).

Figure 3: A surveyor recording the circumference of a tree
using a measuring tape.

This was done for ten trees circling the first chosen origin. This is the most low tech survey method that was used, the GPS being the only electronic device necessary. This makes it the cheapest method with the fewest electronic components that may fail. However, it is also the slowest survey method with the greatest possibility for error. As the measuring tape must be physically stretching out between the origin and the survey tree, measurement is often hindered by such things as branches, bushes, and downed trees.
The second survey method, for the second origin and its corresponding ten surveyed trees, was a little more advanced. The measuring tape used to record the distance between the survey trees and the origin was instead replaced with a two part electrical device. One component of the device is aimed from an individual standing on the origin at the other component (Figure 4).

Figure 4: A surveyor aiming the first component of the two-
part distance measuring device from the the origin to the
survey tree.

The other component is placed on the survey tree by a second individual (Figure 5).

Figure 5: A surveyor holding the second component of the
two part electronic distance measuring device. The device
is being held against the trunk of the survey tree and is ready
to receive a signal.

The first component sends a signal toward the second, which is received by the second and sent back to the first, along with data recording the distance between the two components. Measurements for the tree circumference and the azimuth bearing were recorded as they were for the first survey method. This way, there is no need for a physical measuring tape to be stretched between the origin and survey point. This allows for faster surveying, at the cost of needing a more expensive electronic device. However, this method still requires multiple individuals in order to measure the distance between the origin and the survey tree.
The final group of survey points around the final origin were surveyed using a special, one-piece laser device. By aiming it at the target survey tree, it sends a laser signal which bounces back and is received by the same device (Figure 6).

Figure 6: A surveyor utilizing the single piece laser to
measure both the distance from the origin to the survey tree
and the azimuth bearing.

Not only does this measure the distance between the origin and the survey tree while eliminating the need for more than one surveyor, it also records the azimuth bearing of the targeted survey tree. This is by far the fastest way to record data used in this field exercise. However, this device is tremendously expensive. Thus, few organizations will have access to such technology, and great care should be taken with bringing this technology into the field.
Once the trees had all been surveyed, the data was converted into an excel spreadsheet. An additional column was added for the x origin data, as it needed to be properly formatted as negative values before being brought into ArcMap. If it wasn't, the points would likely be displayed somewhere in Asia in ArcMap. Once this was complete, the data was imported into ArcMap as X,Y data. Then, the Data Management tool Bearing Distance to Line was utilized to convert the datatable into a geodetic line feature class. Once this was completed, the Data Management tool was utilized to convert the end vertices of the geodetic line feature (the trees) into a point shapefile. Utilizing a table join, all of the data from the original excel table was reconnected to the tree survey points. This allowed for the tree point shapefile to display the circumference of the surveyed trees. This was utilized to create a map.
Results

Figure 7: A map displaying the trunk circumference of the surveyed trees in relation to their respective origin points. The survey was completed utilizing a Distance Azimuth Survey and utilized three techniques with varying levels of technology to obtain measurements. The location of the survey is Putnam Park, located on the University of Wisconsin, Eau Claire campus, and was completed on March 15, 2017.

After analyzing the data, it can be inferred that trees of both great and small relative circumference exist in fairly close proximity to one another (Figure 7). The very largest trees (in terms of circumference) are located along the southern and eastern portions of Putnam Park, furthest away from campus. Inferences on the levels of accuracy and precision of this survey technique can also be made from this map. While the grouping of trees around each origin is fairly similar to what actually exists, meaning a high level of precision, the accuracy of the data leaves much to be desired. The survey points in the northwestern portion of the map are roughly twenty-five meters farther north than their actually positions. The central survey points and their corresponding origin, likewise, are ten meters too south of their actual position. Only the third group of survey points remain in an area close to (within two meters) of their actual position.
Conclusion
While azimuth surveying leads much to be desired in terms of accuracy, its preciseness still makes it a valuable technique to know for anyone dealing in field survey methods. Remote sensing and increasingly powerful, modern GPS systems, while having replaced Azimuth surveying, are liable to equipment failure. So when these systems fail and when accuracy is not always an issue, distance azimuth surveys will continue to exist as a backup plan. By combining it with point-quarter sampling and properly recording species, other valuable data can be gathered. this includes density measurements, frequency, determining species coverage of an area, and calculating the importance value of surveyed species. Azimuth surveying, while dated, will continue to exist.
Sources
Hupy, J. (2017). Field Activity #4: Conducting a Distance Azimuth Survey. Eau Claire, WI.

Teh, S. (2017). Biology 3A: Ecology: Point-Quarter Sampling. Saddleback University. Available online at http://www.saddleback.edu/faculty/steh/bio3afolder/PointQuarter%20Lab.pdf