This lab explored surveying points and finding attribute data for each point. The data measured included location, pH, temperature, and volumetric water content. A variety of tools was necessary to measure this information. This lab ties into the subsequent lab, involving UAS, to combine aerial imagery with ground data.
METHODS
Ground Data
The survey was taken at a community garden in Eau Claire, pictured below in figure 1. To determine locations of data points that would be measure, flag were inserted into the ground every ~3 meters across a section of the garden. First, measurements of the point were taken. This data was then entered into the GPS unit, which would store the data with the coordinate.
Figure 1: Garden that was surveyed |
The pH, temperature, and water content were measured with handheld tools. The pH measurement was performed by scooping a small amount of soil near the flag into a plastic cap, where water was added to create a slurry. Then, the instrument was inserted into the cap, as shown below in figure 2, and the pH readout was shown on the LED screen. Note that the instrument had to be calibrated using samples of known pH before use. The temperature was recorded by inserting an electronic thermometer a few centimeters into the soil next to the marker flag. The volumetric water content was measured using a TDR probe. This probe used time delays in electrical signals to measure the percent water per volume in the soil. Similar to the thermometer, this was inserted into the soil and a measurement was recorded.
Figure 2: Measuring the soil pH |
To measure the location, a TopCon Dual Frequency Survey Grade GPS with sub-centimeter accuracy was used. This was placed over the flag, as shown below in figure 3. After the GPS was centered, the previously recorded measurements for the point were entered into the GPS unit using the touch-screen on the device. After the data was entered, the GPS took 30 readings of the coordinates for the point and averaged them to find the location within centimeters. The attribute data was stored with each point of the device.
Figure 3: Using the GPS for a data point |
UAV Data
The next step was taking aerial imagery through the use of a UAS, or unmanned aerial system. The UAS used, pictured below in figure 4, was a DJI Phantom. The Phantom was fitted with 6 propellers and a bottom-mounted camera. It could be flown manually or follow a flight plan.
Figure 4: DJI Phantom UAS before flight |
These GCPs were placed across the study area to provide data necessary to properly align the aerial imagery. The plates were left on the ground for the flight, as their purpose is to be seen in the aerial imagery to assign coordinates to.
Figure 5: GCP preparation |
Figure 6: Landing the Phantom UAS |
RESULTS
Shown below in figure 7 is the orthomosaic map created with Pix4D. An orthomosaic is a number of smaller tiles mosaicked together. Notice there are no seems within the image.
Figure 7: Orthomosaic map |
Figure 8: DSM of study area |
Figure 9: Oblique views of study area |
Figure 10: pH values of garden |
Figure 11: Temperature data |
Figure 12: Water content data |
DISCUSSION
This lab explored several methods of field data acquisition. Ground data was used in conjunction with aerial imagery. These methods are commonly used in agricultural studies, among other things.
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