Creation of a Digital Elevation Surface

Introduction:
Our first activity was created so we could demonstrate the necessary requirements to survey a landscape. What we are trying to create in this activity is a Digital Elevation Surface. We were tasked to do this with relatively no instruction at all. All we were given was a 4x4 box that our professor built for us, along with tape, string, tacks, and rulers. It was up to our own group how we wanted to go about creating this surface and where. Once the Digital Elevation Surface is created we can look at it through various programs and then run more analysis on our landscape.

Study Area:
We conducted our study on September 15th, 2015 from 5:45pm to 7:30pm. Our study area was a 4x4 area located on the point bar underneath the footbridge on our campus here at UW- Eau Claire. We determined this location to be suitable for this activity due to the sand being deposited by the meandering Chippewa River. The sand allowed us to manipulate it into our own rendition of the City of Eau Claire so that we could survey it for this activity and create the required landforms; a ridge, hill, depression, valley, and plain. Since we were trying to create our own rendition of Eau Claire, we thought it would be appropriate to include the following features found inside Eau Claire; the "Campus Hill", Chippewa River,  Half Moon Lake, Carson Park, and the Putnam Park/Third Ward area.

Figure 1: Aerial of Eau Claire showing the location of Campus.

Figure 2: Aerial of Campus showing the study area underneath the footbridge.

Methods:
To begin developing the terrain we channeled our former days as sand castle champions and began modeling Eau Claire within our 4x4 box. Using only our hands we formed all the required features and to our astonishment, the sand held together quite well with the aid of some water to make for more well compacted moist sand.


Figure 3: Our landscape with captions over the appropriate landforms.

Next we had to develop a plan for how to survey our model. We decided through discussion that 5cm spacing would allow us to have enough detail necessary to create the Digital Elevation Surface, but also allowing us to complete the data collection in a reasonable amount of time. To make this happen we inserted tacks into the boards on the West and East side of our model, spaced our 5cm apart. This allowed us to take 24 data points along our X axis. We then took string and weaved it in and our of all the tacks to give us a guide when it came time to measure. To give us our 5cm spacing along our Y axis, we used a meter stick that we measured every 5cm along the North and South edges of our model giving us 23 data points. Using the meter stick allowed us to save time by not inserting more tacks and string but rather just quickly moving the meter stick. This ended up being a very efficient system because when it came time for data collection we had one person record measurements in a MacBook pro, while the other two took turns measuring the depth to the nearest millimeter. We simply recorded the depth from the string straight down until the meter stick hit the sand and recorded that depth. The data collection itself took roughly an hour which was good timing because the impending rain was about to wash us out.

Figure 4: Our method for data collection using a meter stick and the recorder using a MacBook Pro.

Figure 5: The meter stick at the angle needed to record the depth of the feature to the nearest millimeter.

Results:
Using our plan for data collection, we were able to look at our model in Microsoft Excel and use an equation to show the actual height of our features. Even though we recorded depth in the field, knowing that height of our box allows us to manipulate the data so that it will eventually show the height of the features on our landscape. We will use that data more in the next activity so for now, all we have is the recorded measures taken from our meter stick. The table below represents what our Excel sheet ended up looking like. Using this data we create more maps in ArcMap and ArcScene to show our landscape using a Digital Elevation Surface.

Table 1: Our data in an Excel sheet.

Discussion:
Since this lab was created so that had to use problem solving skills and critical thinking skills to just collect data, the discussion is mainly based upon our data collection methods and the resulting table. The trouble with this lab is you have to find a happy medium between excellent detail in your model and a realistic amount of time that you want to spend collecting the data. For instance we took data points in our model along a 23x24 point axis which resulted in 552 data points. If we would have went for 1cm spacing instead of 5cm spacing that would have resulted in 12,544 data points and an estimated data collection time of 22 hours. You can see that one is completely unrealistic even though it would provide for the best detail. It will be interesting to see once we create the model in Arc if 5cm spacing was the correct choice.

Figure 6: The group discussion how to go about data collection.

Conclusion:
Next week we will take this data and use it in Arc to create multiple TIN, rasters, interpolation, and others models using the data from this activity. It is hopeful that once we create those models that someone could look at them at discern that the landscapes with the model depict the City of Eau Claire. They then could see how the model was created and realize that this was the result of no more than playing in the sand and accurate data collection taken from an experienced group of Geographers.