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