The purpose of this field activity was to learn the concept of distance and azimuth by conducting a survey using related methods. Most surveys can be accurately handled through the most modern and advanced GPS technology. However, it is irresponsible to rely solely on technology. Situations can arise where the appropriate technology is unavailable or fails to work when it's needed. Therefore, it's important to know the basic concept of distance and azimuth - a technique that can be applied with basic instruments that have been used for surveying for decades. In addition, it can be utilized in numerous conditions and is even the basis of other sampling techniques, like the point-quarter method.
Methods
This field activity can be divided into two parts: "data collection" and "GIS processing."
The study area of the survey was Putnam Drive, located on the south side of the Davies Center parking lot on the UW - Eau Claire campus in Eau Claire, Wisconsin (Figure 1). Putnam Drive is a dirt/gravel road that runs through a narrowly forested area at the foot of a hill. The trees are mostly deciduous, rooted in a swamp-like ground.
Figure 1: A locator map of where the study was conducted in the state of Wisconsin.
There are certain instruments that made this activity possible. A GPS was used to note the coordinates that a student stood at. A compass was used to get the bearing (90 degrees per quadrant - NE, SE, SW, and NW) and azimuth (0-360 degrees). The laser distance finder measured the distance of a central point to a tree. The measuring tape was used to measure the tree's circumference. Of course, this information was recorded in a notebook immediately (Figure 2).
Figure 2: Tools and devices used in the field: GPS, compass, field notebooks, pencil, laser distance finder, and measuring tape
To begin the first part of the field activity, each student in a group of three took responsibility for a portion of the lab. One student remained in one place known as the central point and took measurements of the tree's distance from the central point and it's azimuth. It's crucial that the student maintains the central point for all measurements - designated by the GPS. A second student measures the circumference of each tree. A third student records all measurements, including the coordinate location of the central point.
The first step is to determine your location for the central point. Student 1 measures this using the GPS and will maintain this position for the duration of the survey. Student 3 records the coordinates.
Then, student 1 will use the laser distance finder to measure the distance from the central point to a randomly selected tree in meters (the term "randomly selected" does not denote the sampling definition so it is not truly random). Student 1 will also determine the azimuth of the tree's location using a compass (Figure 3). Remember, some compasses measure bearing and not azimuth. Student 3, in addition to recording all measurements, should compute the correct azimuth.
For example, you measure that a tree is 63 degrees SE. You would get its azimuth by subtracting 63 from 180 to get 117 degrees - the azimuth
Figure 3: Image of how a student uses the compass to read the compass bearing with the laser distance finder in hand to use in the same coordinate location.
Next, student 2 would measure the selected tree's circumference at chest height (Figure 4).
Figure 4: Image of how a student measures the circumference of a tree at chest height.
These steps are repeated for ten trees total at a given central point. The group conducted a second survey at another location on Putnam drive following the same method. Once completed, the group returned to the computer lab to transfer the data collected (Figure 5) into an Excel sheet for the second part of the activity.
Figure 5: Sample of the hardcopy notes and measurements recorded in the field.
Table 1: Excel sheet of the data collected. Note that the last 2 decimal places were not recorded in the first survey due to a lapse in judgement. All decimals should be used for better accuracy.
Once the data is in a saved Excel sheet, open ArcMap. From the ArcCatalog window, create a new folder for this survey and create a geodatabase within it. From this geodatebase, import the Excel sheet.
However, the data isn't useful yet. The Bearing Distance to Line command will import your Excel data into a feature class that can be displayed on ArcMap. This tool is in the toolbox, under Data Management and then Features. The data is now a feature class as lines. However, the ends of the lines should be points. Use the Feature Vertices to Points command, which also located in Data Management and Features, to create a point feature class from the vertices of the lines. There should now be two feature classes.
The resulting feature classes in this lab were displayed over a basemap to assess its accuracy. The attribute table of the point feature class the the original Excel sheet were joined in order to use attributes in the Excel sheet in the layer's symbology tab. This concluded field activity 2.
Results
3 maps were created with the given data. First, a general map was established to assess the accuracy (Figure 6). The points indicate the trees measured, and the lines indicate the distance from the central point. One thing that was noticed was how inaccurate the surveys' locations are. The first survey's inaccuracy can be attributed to the lack of decimal places in the x-y coordinates. However, this group was unable to determine why the second survey, for which the decimal mistake was rectified, is the most inaccurately placed survey. In fact, it is placed where the Davies Center is (built after the basemap image was taken). Figure 7 shows approximately where the surveys were actually taken.
Figure 6: Azimuth and distance lines from a central point to trees sampled.
Figure 7: Approximately the true location the the surveys.
The second map created was a unique values map of the different tree species (Figure 8). However, in this instance, this information means little as descriptive words were used instead of the actual species. Species names are need for an actual analysis of the data. Still, the methods for acquiring the data and displaying the data remains the same.
Figure 8: Unique values map showing the different tree "species."
The third map created was a graduated symbols map of the trees' circumferences (Figure 9).
Figure 9: A graduated symbols map of the circumferences of the sampled trees.
Conclusion
This field activity did have its hiccups, but they were easily fixed. Some mistakes were avoided by learning from past classes. The inaccuracy of the data coordinates in ArcMap is concerning. There are a number of explanations: inaccurate coordinates from the GPS, user error, or recording error. It'd be helpful to know which to avoid it in the future.
The distance-azimuth survey method has proved to be a key technique for data sampling. It's concepts are related to the point-quarter method, which samples plants (or anything that doesn't move) to determine its density in an area. That is where the species names would be important (Tah).
Even though advances in technology are more accurate and convenient, distance-azimuth method is still be a reliable back-up should the technology fail. It's also important to understand different sampling methods, even if they're s little outdated, to better understand the concepts of how the technology works now.
Sources
Tah, S. (n.d.).
Ecology: Point-Quarter Sampling. Retrieved September 25, 2017, from
Saddleback University:
http://www.saddleback.edu/faculty/steh/bio3afolder/Point-Quarter%20Lab.pdf
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