The first field activity in this Geospatial Field Methods course was to create a landscape with various elevation features in a snow covered area. In the courtyard area of Phillips Hall on the UW-Eau Claire campus groups used planter boxes to create the elevation features. Along with these features it was necessary to create a coordinate system in order to later download the elevation data into ArcMap or ArcScene to produce a 3D interpretation of the study area and it's features. This exercise helped the groups to begin to develop many geospatial techniques and think critically about how to achieve the goal of the activity.
Methods
On a cold Wednesday afternoon on Jan. 28th, my group of 5 students met in the Phillips Hall courtyard to begin the activity. The first step was to create the various surface features in our assigned planter box which included: a ridge, hill, valley, plane and depression. Rather than constructing these features in the sand filled planter boxes, we utilized the overly abundant snow here in the northern part of Wisconsin to create them. This is just one example of how important it is to maintain flexibility when in the field.
The first step in adding the features was to smooth out the snow in the planter box to make the original surface level. Once the area was level we were able to begin creating the features themselves using our hands to sculpt the snow into a ridge, hill, valley, and carve out a depression. We decided to utilize the area which we had originally leveled off as the plane surface. After all the surface features were added we measured the planter box dimensions and began to figure out the intervals in which we should use to make our coordinate system.
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| (Fig. 1) After adding more snow to the top of the planter box we constructed the ridge, hill, valley, depression and plane features with our hands throughout the area of the planter box. |
Using a meter stick and push pins, we began to measure out 12 cm intervals along the edge of the planter box eventually creating 12 cm x 12 cm squares. We used twine to create the square pattern however we ran out of twine and were forced to be flexible yet again. Since we were only able to run the string along the length of the planter box we had none left to run it along the width to make a complete grid system. To make it work we decided to remove one of the strings that stretched lengthwise to make a single piece which we could move along the push pin markers to make a temporary line along the width. When it came time to being taking measurements of the 10 x 20 square grid system, we measured the z axis values as the depth from the base of the feature within the planter box to the twine. This value was then recorded along with the x and y coordinate of the box with the corresponding depth.
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| (Fig. 2) In order to create our coordinate system we needed to determine the size of the grid blocks we would be using to collect our elevation data points We did so by measuring the length and width of the entire planter box and decided to use a 12 cm x 12 cm grid system. |
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| (Fig. 3) We used push pins to mark every 12 cm along the length and width of the planter box so we could then use twine to run from each pin to the opposite pin creating our grid system. |
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| (Fig. 4) Since we ran out of twine we needed to be flexible so we decided to string a single piece of twine along the width of the planter box and move it to the next set of pins 12 cm down each time we took measurements. |
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| (Fig. 5) We took our elevation data samples in each grid measuring the distance from the base of the surface feature to the twine and recorded all of the measurements for later use. |
Discussion
Since there was very little direction given as to how to complete this activity we were able to use whatever method we felt would be most effective. This was a key part of this first lab activity, to make us begin to think critically about how to accomplish the given task. The fist thing that we needed to decide how to do was how to make the coordinate system, including the size, what materials we would need etc. With this we had to determine if we wanted the features to be built higher than the coordinate system which would make the process of taking measurements easier but make our final data less accurate or have all the features built below the coordinate system.
We first determined that we would not make our features taller than the coordinate system to improve our overall accuracy and make taking the measurements a bit easier. After all of our features were built in the snow, our twine and pins were used to construct our 12 cm x 12 cm resolution coordinate system. We thought that this would be best because we would then take a total of about 200 points of data which would make our overall data more accurate in the end. Since we did not build our features above he coordinate system taking measurements of the snow features was rather easy.
All of the elevation point data was taken in each of the 12 cm x 12 cm squares of the coordinate system which stretched across the entire planter box, or rather, our landscape. Collecting the elevation from each of these squares we found was not the most accurate way to determine overall elevation because of the drastic changes in the elevation from one square to an adjacent square.
Another major problem with the methodology we used was the possible inaccuracy of the elevation data due to the uneven surface that made up the top layer of soil in the planter box. Since the dirt in the box was completely frozen, we were not able to dig it up to level out the surface before building our features from snow above it. We tried to create the most level plane we could with the snow, attempting to compensate for these potential errors but there could be some inaccuracy in our data from this.
We also were limited with our supplies which was a challenge we had to work through. Since we did not have enough twine to construct our entire coordinate system throughout the length of the planter box we needed to problem solve and figure out another way. The way we decided to work with the limited supplies was to create a single piece of twine which we would move along the width of the box as we took our elevation points. This proved to be more time consuming but it was the best way we could work around the problem. We learned quickly how important it is to be flexible when conducting field work.
Conclusion
As a group we were forced to think critically and spatially in order to solve the problem we were assigned: to create our own elevation surface including a ridge, plane, valley, depression and hill feature and record the elevation data using a coordinate system of our own design. We were able to create a working coordinate system and collect around 200 elevation data points which we can use to produce a digital elevation surface in ArcMap. This first field experience was a good example of how necessary it is to be flexible in the field and how important it is to think critically.
