Sandbox Survey
Understanding Grids and Coordinates
Introduction:
Our task was to create several geological terrain features to be surveyed using various spatial sampling techniques. But what does the term sampling mean? Sampling is essentially a simplified means to collect information (1). In our case, "sampling" would refer to an efficient, and organized way to collect spatial information. Three common methods of sampling spatial information would include random, systematic, and stratified techniques. Each of these techniques has their own advantages, however, we chose the systematic technique for its ability to be easily used with a grid.
Overall, our lab objectives were to first, set up a sandbox with certain terrain features. The terrain features to be included in our sandbox included a ridge, hill, depression, valley, and a plain. Second, we were to survey/sample the entire sandbox using a specific sampling method. In our case we chose the systematic method for reasons preciously stated. In the coming weeks a digital terrain model of our sandbox environment will be generated.
Methods:
Our study area included a sandbox located outside of Phillips Hall. Specifically, our study area was located east of Phillips Hall near Little Niagara Creek. The sandbox measured 114 by 114 cm, and was 15 cm deep. The terrain features as shown bellow included a ridge, hill, depression, valley, and a plain. These features were hard to create due to the freezing temperatures.
Figure 1. The picture above shows the terrain features
As previously mentioned we decided to use the systematic sampling technique to survey our sandbox. This meant that our survey points had to be equally distributed throughout the sandbox. To evenly distribute our survey points a grid was placed on top of the sandbox. The use of this technique insured that our study area was evenly surveyed. The grid that we used included 20 x and 20 y coordinates meaning that every 5.7 cm there was a node. To generate a z (elevation) coordinate the depth of the sandbox was measured (15 cm). The bottom of the sandbox was declared sea level (0 cm) to insure no negative values were recorded. The yarn making up the grid was located at a height of 15 cm from sea level so all elevation (z) values were recorded based off of their distance from the yarn (15 cm). For example, the top of the hill was measured 6 cm above the yarn meaning the height was 21 cm, and the values below the yarn were measure by subtracting from 15 cm. A total of 400 points were surveyed, one point for each node. The materials used to survey the sandbox included one meter stick, yarn for the grid, and one surveying flag (for marking the node which was to be sampled).
Figure 2. The image above shows our grid pinned to our study area (sandbox). The grid included 400 nodes (places of intersection) and possessed 20 x and 20 y coordinates.
Results:
A total of 400 values were recorded. The tallest point in our study area measured 21 cm high, while the lowest point measured 7 cm high. Therefore, the range was 14 cm which showed a fair change in elevation respectively. The most common elevation measurement (mode) was 12 cm which was also the height of our plain terrain feature. Furthermore, the average elevation measurement was 12.48 cm. This was very close to the most common elevation. It should also be reported that the standard deviation was 2.14.
Figure 3. The photo above shows the hill terrain feature in our study area. The hill measured 21 cm above sea level (the bottom of the sandbox).
Discussion/Conclusion:
Overall, the systematic surveying technique implemented did a good job of surveying the entire grid equally and effectively. However, some of the areas with greater elevation changes may have been under surveyed. This is where the stratified surveying method may have worked better. There was also some difficulty initially in determining how to resolve the sea level issue. Specifically, how would we make sure that we did not record any negative values, and where would our measurements be taken from. However, this issue was resolved and the sampling went smoothly. In the future the surveying should be conducted in warmer temperatures, for it was below 10 degrees F when this exercise took place. These cold temperatures decreased the accuracy of the measurements and decrease length of time we could stay outside.
References:
1. Royal Geographical Society. (n.d.). Sampling techniques. Retrieved from http://www.rgs.org/OurWork/Schools/Fieldwork+and+local+learning/Fieldwork+techniques/Sampling+techniques.htm
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