-Define what sampling means, with a strong focus/emphasis on what it means to sample in a spatial perspective.
Sampling is the process of gathering data on a given area or subject. To sample in spatial terms means to be able to represent the data being sampled in a 1,2, or 3D space.
-List out the various sampling techniques
Random- Random samples are taken, creates a non bias sampling
Systematic-Samples are assigned to give a thorough outline of the area of study, bias sampling
Stratified-Samples are taken within sub-sets to accurately portray varying portions of the whole area of study, bias sampling
-What is the lab objective(s)
The objective of this lab is to create a elevation surface within a sandbox and create sample points based on elevation. The terrain had to include: ridge, hill, depression, valley, and a plain. (
shown in Figure 1)
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| Figure 1. shows our sandbox and our terrain |
-What is the sampling technique you chose to use? Why? What other methods is this similar to and why did you not use them?
We used systematic sampling. We found it to be the most straightforward and easiest method in measuring out samples. Stratified sampling is similar to this and would have probably saved sometime; However, systematic is more uniform and suggests a better array of measurements with having increments for sampling.
-List out the location of your sample plot. Be as specific as possible going from general to specific.
The location of the sandbox for this sample plotting was outside of Phillips about 68 meters to the east, across the road, in the grass parallel to Little Niagara. In decimal degrees the location is:
44°47'48.9"N 91°29'54.7"W
-What are the materials you are using?
Sandbox, string, thumb tacks, measuring tape, meter stick, field book and pen.
-How did you set up your sampling scheme? Spacing?
We measured out the length of the sandbox and found it to be 114x114 cm. We then decided to create 6 cm increments (shown in Figure 2) that gave us 19 boxes to gather samples from.
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| Figure 2. shows the increments used |
-How did you address your zero elevation (sea level)?
We chose to have zero elevation be the top of the sandbox because we wanted to create a replication of a continental shelf meaning most of our samplings would be undersea level.
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| Figure 3. shows the terrain of our sandbox with 6 cm increments around. |
We created an excel document and recorded our Z-depth measurements as is.We used our field books to record the sandbox increments.
Results/Discussion
-What was the resulting number of sample points you recorded?
361 sample points
-Discuss the sample values? What was the minimum value, the maximum, the mean, standard
deviation, etc.
minimum= -12
maximum= 7
mean= -5.5144
standard deviation= 4.174627
Yes, we couldn't have chosen random because we wanted samples in each square. We could have possibly used stratified but that wouldn't have given us a grid system and as accurate data representation.
-Did your sampling technique change over the survey, or did your group stick to the original plan. How does this relate to your resulting data set?
Our group stuck with the original sampling technique.
-What problems were encountered during the sampling, and how were those problems overcome.
When sampling we would sometimes lose our location. We then had to count back to what number we were on.
Conclusion
-How does your sampling relate to the definition of sampling and the sampling methods out there.
Most sampling is done randomly so it's not biased; However, since we wanted to show the elevation in specific areas we went with systematic to best represent our data.
-Why use sampling in spatial situation?
Sampling would allow for data to gathered in a unbiased matter.
-How does this activity relate to sampling spatial data over larger areas
Using the same sample techniques, with a grid system and increments, one could do this over a much larger areas with less sample points to create reliable data.
-Using the numbers you gathered, did your survey perform an adequate job of sampling the area you were tasked to sample? How might you refine your survey to accommodate the sampling density desired.
To refine our survey more sampling points would be needed in the denser areas such as the ridges and depressions, to show accurate landscape data. The same could be said with gather less sample points from areas with the same landscape like plains.
Sources used:
http://www.rgs.org/OurWork/Schools/Fieldwork+and+local+learning/Fieldwork+techniques/Sampling+techniques.htm
http://www.spatialanalysisonline.com/HTML/index.html?spatial_sampling2.htm
