Field Exercise 1 – Creation of a Digital Elevation Surface

INTRODUCTION

 

            The objectives for lab 1: Creation of a Digital Elevation Surface were threefold. First, a variety of landscape features including a ridge, hill, depression, valley, and plain had to be created inside of a 3.5x7.5 foot snow filled planter box; second, an improvised surveying method had to be created in order to accurately obtain x, y, and z data for the landscape features created in the box; and third, the x, y, and z data collected would be imputed into arcmap for the purpose of creating a digital elevation model (DEM). I should be noted that this third objective will be completed in lab 1 part 2, after revisiting the chosen survey method. The challenge with this lab came with having to improvise a surveying system using only rudimentary tools such as a yardstick, twine, and of course the snow in the planter box.

METHODS
 

Creating the Landscape

            As stated above, a miniature landscape was created inside of a wooden planter box for the purpose of surveying said landscape. Creating the different landscape features in the box didn’t take long because it required very simple scooping techniques. The depression, however, was created by chipping out the frozen dirt, below the snow, with a hammer! Below (figure 1) is a photo of the group creating the snowscape.  

Figure1: Creating the landscape features out of snow

Creating a Surveying Method

            Once the snow landscape was finished, creating an accurate surveying system was the next step. A simple 12x12 cm grid system seemed to be the best way to accurately measure each landscape’s x, y, and z coordinates. Any smaller and the data set would be bogged down with unwanted detail; any larger and the data set would not have enough information to detect subtle changes in the landscape. This 12x12 cm grid pattern was created by measuring off 12 cm intervals down all four sides of the box, and then tacking twine across the box at its corresponding tack mark. The top of the box was considered a z-value of zero, and the deeper the depression in the snow, the more negative the z-value became. In other words while x and y-values measure where a given point is on the grid, the z-values measure depth of any given data point. An example of how an x, y, and z-coordinate system works is pictured below (figure 2).

Figure 2: Y = vertical measure X = horizontal measure Z = depth measure

            Since the top of the planter box had a z measurement of zero, the highest elevation or z-value a given landscape feature could have would be zero. Because no landscape features protruded above the box it was possible to create the twine grid system without having to work around landscape features. Below (figure 3) is the finished product of the completed landscape and 12x12 cm twine grid system.    

Figure 3: The 12X12 cm twine grid system laid over the snow landscape

Data Recording

            Next came the actual recording of the x, y, and z values for each 12x12 cm grid square. Starting with the front left grid in the box, the x-value began at 1 and the y-value began at 1. Moving from left to right there were nine 12X12 cm grid squares and therefore a total of nine x-values. Moving up a row every nine measurement intervals resulted in 19 different y-values for a total of 171 12x12 cm grid squares with both x and y-values. Once the x and y-values had been collected, the z-values had to be measured. By simply placing a yardstick in the front left intersection of every 12x12 cm grid square an accurate and consistent z-value was able to be obtained for all 171 squares. Table 1 below shows the z-values for the entire grid system. Table 1 is also set up in x y coordinate form. For example, grid square 1, A has an x-value of 1, a y-value of 1, and a z-value of 9. Also pictured below (figure 4) is an example of how the yardstick was used to obtain z-values. Be assured that the process of collecting this data was as tedious as reading the explanation of how it was obtained.

Figure 4: Collecting the z-values with a yardstick

Table 1: x, y coordinate plane of the 171 12X12 cm grid squares with corresponding z-values

DISCUSSION
 

             Creating the snowscape, devising a survey method, and collecting the data went off without a hitch. The snowscape was nothing elaborate, making it easy to create. The survey method was uniform and standard, making it easy to collect and interpret the x, y, and z data. Collecting data was tedious and time consuming, but it accurately reflected the elevations of the landscape features created in the planter box.

CONCLUSION
 

          Being able to gather such accurate results to be used later in a digital representation of the snowscape, was a huge boon to the lab as a whole. 171 different x, y, and z data values will surely reflect the changes in elevation over the entire planter box, and give the viewer a detailed digital representation of the snowscape, which will be created in lab 1 part 2.