Field Activity #4: Creation of a Digital Elevation Surface using critical thinking skills and improvised survey techniques

Introduction

Sampling is a technique used to investigate a population by gathering data from a small portion of the entirety. Sampling is used to save both time and money and is used for many studies. Sampling provides an overall look at the spatial variations of a phenomena within a study site. There are three sampling methods; 1) random ,2) systematic, 3) stratified. The objective of the lab was to create a landscape containing a wide range of elevation and collect and record the elevation through systematic point sampling. This means that samples were collected evenly throughout the study area. In our case, the samples were in form of centimeters and represent elevation.

Methods 

               Figure 1: The landscape was created
with all of the parameters needed. 

The elevation of the landscape was collected by taking measurements through a systematic point sampling technique. In order to accurately portray the topography of the landscape measurements had to be taken fairly often at a regular interval. The landscape was created in a 45 by 45 in  (114 by 114 cm) sandbox located east of Philips Hill. Designing the landscape involved several parameters. It was required for the landscape to have a hill, ridge, valley, depression, and a plain. Creation of the landscape was done by hand (Figure 1). Materials given to us was string, wall tacs, tape, measuring tape, and a meter stick. Using the wall tacs and meter stick, every 5 cm was marked on all 4 sides of the sandbox. After placement of the tacs, the string was used to create a grid over the top of the landscape (Figure 2). Our sea level or zero elevation was the actual ground. This was chosen to ensure that negative values would not be measured.

         Figure 2: The string was wrapped around the
 tacs to create a grid over the landscape

To collect the elevation points a metal hanger was straightened and stuck into the ground within one of the grid squares (Figure 3). Once ground was met, the hanger was taken out and placed against a meter stick to read the measurement in centimeters (Figure 4).

Figure 3: The grid helped keep the measurements
 organized and at set increments of 5 cm

Figure 4: Elevation collection

The elevation points were placed in an excel file with 3 columns (Figure 5). The grid had a column for X, Y, and Z so that each point could be plotted on a grid with the elevation. This will help in later visualization of the landscape within ArcMap.

Figure 5: Excel table showing set
 up of elevation measurements 

Results

The overall table consisted of over 400 sample points taken of the to show the elevation change (relief) of the landscape we created. The excel table is the most important result of the project. Using the correct formatting that can be read in ArcMap, the goal for future work is to input the table to create a topography model of the landscape through various processing procedures.

After running statistical measurements of the Z column (which holds the elevation in cm) various statistics were found...
- Maximum elevation = 23.3 cm above sea level
- Minimum elevation = 6.6 cm above sea level
- Mode= 14 cm above sea level

These statistics show the wide range of elevation. the areas that were taken for the plain resulted in less sample values because of the extremely low elevation change. The mode shows that many of the areas was relatively high above sea level which could indicate thick lithosphere in the real world.

Conclusion

Gaining an understanding in sampling (in particular the systematic point sample method) both time and money can be saved. this was witnessed first hand during the collection of the data which lasted 4 hours.  To show even more detail, which might be needed, in areas of great elevation change the data points for that area can increase. The more data the more likely it will be accurately portrayed.