Survey of a Terrain Surface

Field Activity #1: The "Sandbox" Test

By: Joseph Mandelko

 

Introduction

• Define what sampling means, with a strong focus/emphasis on what it means to sample in a spatial perspective.
• List out the various sampling techniques
• What is the objective(s) of the lab

Sampling refers to the action of collecting data for the use of analysis on that data. When sampling with a spatial perspective it is key to focus on not just the data itself but the implications of that data and how it could relate to, affect and be affected by, other variables near it. After all, the goal of sampling is to create a representation of a larger whole. Spatial sampling will also always be able to be tied back to some sort of space that can be shown visibly on a map to represent the space the data is found in. Sampling methods for spatial data are random, a difficult method to ensure, systematic, and stratified. The objective for the Field Activity #1 is to construct an elevation surface of terrain on a small scale and analyze it as would be done in the field on the surface of the earth.

 

Methods

• What is the sampling technique you chose to use? Why? What other methods is this similar to and why did you not use them?
• List out the location of your sample plot. Be as specific as possible going from general to specific.
• What are the materials you are using?
• How did you set up your sampling scheme? Spacing?
• How did you address your zero elevation (sea level)?
• How was the data entered/recorded? Why did you choose this data entry method?

The sampling method used was a systemic area sample method. This means that the data was collected from the grid pattern of squares with equal area so the larger area could be measured one space at a time. This method is similar to stratified sampling in that an area was measured for the sample yet stratified uses the data in the area as a percentage of the whole area and that would not work when applying it to terrain. The plot where the terrain was created and measured was in the Phillips Science Hall courtyard on the University of Wisconsin Eau Claire campus in Eau Claire Wisconsin. The box was the farthest West in a row of three on the south side of the courtyard.

            To take the sample we employed the use of a long roll of twine, sever dozen thumbtacks, a scrap wooden one by three board, a shovel, a meter stick, and a ruler. In order to keep the grid square the area of stud was limited to one meter by one meter on the north side of the selected box. In a systematic sampling method it is important to make the size of the grid spaces equal and so, every 5 centimeters around the 1x1 meter a thumbtack was placed so the string could be wrapped around the tacks and strung across the terrain (figure 2). The result was an even grid of 5cm by 5cm squares within the area of study (figure 3-4). The grid was strung over a terrain made out of snow with the sea level resting at the top of the box so it could be ensured that sea level was universal across the terrain (figure 1). From the sea level base a hill was added on top and a valley and depression was dug out to create negative space.

            The data was entered when two members of the group measured the length from the string to sea level with a ruler on the northwest edge of the grid space. The two members working together would then call back the resulting number including a positive or negative identifier if it was above or below sea level. The third member then recorded the number on a grid in a notebook with numbers 1-20 on the east side and letters A-T on the north side so a space, for example, “A5”, could be found easily.

Figure 1

Figure 2Figure 3

Figure 4

Results and Discussion

• What was the resulting number of sample points you recorded?
• Discuss the sample values? What was the minimum value, the maximum, the mean, standard deviation, etc.
• Did the sampling relate to the method you chose, or could have another method met your objective better.
• Did your sampling technique change over the survey, or did your group stick to the original plan. How does this relate to your resulting data set?
• What problems were encountered during the sampling, and how were those problems overcome.

In the end of the sample gathering there were a total of 400 data points collected. The sample values were measured above or below sea level in centimeters. There were several sea level measurements and those were recorded as 0 cm above sea level. The maximum value recorded was 26 cm above sea level on top of the hill, the minimum value was 13 cm below sea level at the trench on the south side of the terrain. The sampling method was thorough and could be used again though I believe the spaces could be made larger and still have quality data the method that the group employed served the purpose of several data points for later display accuracy. Luckily we did not need to change our collection method so we had no issues with recording the data in different spaces or having gaps in numbers. One of the largest issues that was encountered was the recording of positive values. Measuring down from sea level was easy enough but at times the rises were difficult so we had to come up with a method to use another ruler to measure the height of the rise across to a stable sea level measure point this is best described by figure 5.

Figure 5

 

Conclusion

            The method of sampling that was used was similar to how any recording method would measure a terrain area, by recoding what lies in a certain grid and piecing those accurate measurements to create a whole. This method is very similar to how an artist would paint a mural, by focusing on creating several spaces out of the intended drawing and recreating them larger space by space. The artist would never attempt to paint the entire wall at once. This sample is the same, a large area is taken and scaled down grid by grid. This method is needed because often time areas are needed to be evaluated for crop cover, terrain type, foliage density, land cover, and slope, as well as several others. In order to understand the area of interest and understanding needs to be had of the pieces that make up that whole. The resulting sample data was accurate as could be had on an area of terrain collected in a box and made out of snow. There would likely be devices that would be able to accurately measure every rise and fall in the area but with the tools, budget, and time an accurate test was done.