Field Exercise #1: Creation of a Digital Elevation Surface

Introduction:

The purpose of this lab was to create a digital elevation model (DEM) of a landscape created in a 4'x4' box. The three members of our group created the model using a coordinate system and available supplies.

A digital elevation model is a digital cartographic dataset that has x, y, and z coordinates (Gould, 2012). The x and y coordinates are used for reference on the terrain surface, and the z value is used for elevation of the surface. Elevation values are collected at regular intervals on the surface to create an accurate representation of the surface (Gould, 2012). Coordinate systems can be used to collect data at regular intervals. The USGS provides DEM's for many differernt regions in a database called 3DEP View, which can be accessed at this link: http://viewer.nationalmap.gov/basic/?basemap=b1&category=ned,nedsrc&title=3DEP%20View.

Digital elevation models are very useful because they can be used to understand how changes in the model could affect the environment. These models also provide many different angles of the landscape under investigation. The activity helped develop my critical thinking and geospatial skills by learning how to create a digital elevation surface from a coordinate system model and available materials.

Methods:

Data was taken in the field for this exercise. Field conditions the day the data was taken include:

• Time: 17:45-19:30
• Location: UWEC campus, under the walking bridge on the point bar of the Chippewa River 
• Coordinates: 44.800553 N, -91.500898 W
• Temperature: 82°F starting and 79°F ending
• Weather: 10-15 mph winds, partly cloudy
• Terrain condition: Mosly sand, but some small pebbles

Materials used: 

• 4'x4' wooden box
• 1 roll of string
• 30 pins
• 1 foldable measuring stick
• 1 meter stick
• 1 small bucket

A terrain was created with the following features: a ridge, hill, depression, valley, and plain. A Cartesian coordinate system with resolution of 5cm spacing was set up in the 4'x4' wooden box (Figure 1). The terrain was created by hand by using sand on the point bar and water from the nearby Chippewa River. A small bucket was used to carry water from the Chippewa River to the sand terrain. The water was used to cement the sand in place, which would make taking measurements much easier and preserve the terrain.

We decided to create a terrain all below the top of the box, and deem the top of the box sea level. Measurements were taken from the top of the box to the surface of the terrain. These measurements were subtracted from the height of the box, which would give us the elevation values of the terrain "below sea level".

Pins were inserted into the wood every 5 cm along the x and y axes of the box. String was wooven around the pins to create the x axis, and a foldable meter stick was used as the y axis. Elevation data, recorded as z values, were sampled with a measuring stick to the closest millimeter (Figure 2). Point were collected for each "column", and all coordinate data was collected for a column before moving onto the next column (Figure 3). Based on our resolution, we collected 552 elevation points.  Data was recorded in the field on a Microsoft Excel spreadsheet containing x, y, and z columns (Figure 4). Pictures were taken with a smart phone camera.

Figure 1: Setup of the terrain shows the coordinate system that we used. The terrain includes real-world landscape features including a ride, hill, depression, valley, and plain.  

Figure 2: The picture shows a close-up view of how we sampled elevation data for the terrain.

Figure 3: Team members collect elevation data along the x,y coordinate system. Our team collected 552 elevation points based on our 5cm-spaced coordinate system. 

Figure 4: X, Y, and Z values were input into an Excel spreadsheet, which will later be exported as a shapefile into ArcMap 10.3.1 to create a digital elevation model.

Discussion: 

This exercise was great for developing our critical thinking skills because we had to think about how we would survey the terrain accurately. Team work was very important for finding the answer in an efficient manner. After looking at past student blogs and brainstroming, we concluded that using a coordinate system would be the best way to collect elevation data for the terrain surface. This used spatial thinking to help understand the terrain.

The excerise posed more questions to critically think about. First, should we create a terrain that was all above or below the top of the box? We decided to create a terrain all below the top of the box, and deem the top of the box sea level. Measurements were taken from the top of the box to the surface of the terrain. These measurements were subtracted from the height of the box, which would give us the elevation values of the terrain "below sea level". Another question we considered was where would be the best location to do this exercise? We concluded that the sandy point bar on the Chippewa River under the UWEC footbridge would give us a moldable environment to shape to our liking. To continue, what resolution was appropriate to accurately capture the elevational changes of the terrain? After trying differnt spacings, we concluded that a 5cm resolution would capture most significant elevational changes. Furthermore, this resolution balanced between the time input into collecting data and the quality of the model produced.

There may have been some possible inaccuracies in the data collection method. The main innaccuracy would come from the fact that the sand would shift slightly sometimes when we placed the meter stick on the sand. This was because the sand was dry, and therefore easily moved by an object touching it. Our group did the best we could to take measurements without disturbing the surface.

A challenge our group will face in the future will be resampling our terrain for the next exercise. This is because the dry sand will probably move slightly from being exposed to the elements for a week. If we could do this exercise over,we would use a different material for terrain that would hold better during measurements and for resampling. A more resistant material could be clay.

Conclusion:

In this exercise, we used critical thinking and spatial skills to collect elevation data for a terrain using a coordinate system and available supplies.The elevation data was put into a spreadsheet that will be later converted to a shapefile to use for creating the digital elevation model in ArcGIS 10.3.1.

We learned it is important to be able to think on your feet and use the resources you have available to you. The exercise taught us that sometimes the best way to complete a task is to use old school methods and simple technology. Finally, team work is a great way to accomplish tasks in an efficient and effecive manner.

Works Cited:

Gould, M., "Digital Elevation Model (DEM)." USGS. n.p., 13 December 2012. Web. 20 September 2015. http://tahoe.usgs.gov/DEM.html