5/2/2017
Surveying Point Features with Dual Frequency GPS
Introduction:
This weeks project is part of a two week project that involved surveying point features with a survey grade dual frequency GPS. The second portion of the project will also involve a drone flight over the survey area. Therefore, the purpose of collecting GPS points will be to use them as ground control points for the aerial photographs that will be taken with the drone. Aside from collecting survey points other attributes were taken at the GPS point locations. These included soil attributes such as pH, soil temperature, and volumetric water content.
The location the survey is taking place includes the community garden to the south of South Middle School in Eau Claire, Wisconsin (Figure 1) (Figure 2). The garden (outlined in red) is bordered to the north by a row of pine trees and a football field. To the south the garden is bordered by a road and a marsh area.
Since this aerial photo is dated, a more recent photo of the community garden is also provided to gain a better understanding of the study area (Figure 3).
Figure 1. Locator map for the survey location.
Figure 2. The topographical survey location south of South Middle School.
Figure 3. Google Earth image of the community garden that was also the location of the topographical survey.
Methods:
First, the class was divided into groups to perform the different tasks. However, everyone got a chance to use the GPS unit.
To begin the survey the dual frequency GPS unit was deployed to collect ground control points and soil attributes (Figure 4). The survey unit possessed two components which included a top receiver and a TESLA unit (Figure 5). The TESLA unit is essential a mobile field collecting device (tablet). After both of the components were turned on the accuracy of height and vertical distance of unit were set. This would insure the points that were collected were accurate.
Once the survey platform was leveled at each of the desired GCP locations the GPS captured 30 points. The points each varied in height and vertical distance, and the points were then averaged by the GPS unit to provide an accurate reading. After the GCP was taken an orange flag was placed at the location of the GCP for soil attributes to be collected. These soil attributes were then entered into the GPS unit tablet.
At each of the orange flags (GCP locations) soil attribute data were collected. As stated before the attributes that were collected included pH, soil temperature, and volumetric water content. PH was collected by using a high accuracy pH meter. Soil temperature was sampled using a soil temperature thermometer, while volumetric water content was taken with the use of a TDR Probe.
Figure 4. Dr. Hupy demonstrating how to deploy the GPS unit.
Figure 5. GPS unit deployed at one of the GCP locations. Orange marking flag is also visible.
UAS Flight
Unmanned aerial systems are becoming ever more present, useful, and can perform a vast array of tasks. After, GPS and soil data were gathered an unmanned aerial flight demonstration took place with a Phantom 3 Drone (Figure 6). A key aspect of unmanned aerial flights is the initial planning portion of the flight. This is done in detail to insure that the drone flies on the correct path and collects quality data. During the initial pre-flight planning specific altitudes and sensors are selected depending on the data that are to be collected. In our case the flight over the Eau Claire community gardens took around 10 minutes and many aerial images were taken. It is important that many overlapping images are taken to insure data quality. Once the flight had taken place a quick post flight procedure followed. The conditions of the environment were taken by the drone incase another flight over the area was to take place (Figure 7). After the images are taken the data can be processed in Pix4D (see previous lab Pix4D Lab). In our case Dr. Hupy processed the flight data in Pix4D to save time.
Unmanned aerial systems are becoming ever more present, useful, and can perform a vast array of tasks. After, GPS and soil data were gathered an unmanned aerial flight demonstration took place with a Phantom 3 Drone (Figure 6). A key aspect of unmanned aerial flights is the initial planning portion of the flight. This is done in detail to insure that the drone flies on the correct path and collects quality data. During the initial pre-flight planning specific altitudes and sensors are selected depending on the data that are to be collected. In our case the flight over the Eau Claire community gardens took around 10 minutes and many aerial images were taken. It is important that many overlapping images are taken to insure data quality. Once the flight had taken place a quick post flight procedure followed. The conditions of the environment were taken by the drone incase another flight over the area was to take place (Figure 7). After the images are taken the data can be processed in Pix4D (see previous lab Pix4D Lab). In our case Dr. Hupy processed the flight data in Pix4D to save time.
Figure 6. Phantom 3 Drone
Figure 7. Post flight
Results and Discussion:
The first result includes a comparison between elevation and moisture (Figure 8). Soil samples indicated that the soil with the lowest moisture could be found in the eastern section of the garden. However, there were other dry section in the northern part of the garden as well. The elevation was also the highest in the eastern portion of the garden where the soil was the most dry. But upon looking at other portions of the garden this pattern was not consistent. Many other factors could account for soil moisture other than elevation. Soil cover could be a great example of another factor that can influence soil moisture.
Figure 8. Soil elevation and moisture. Dry and high areas are shown in darker colors.
Soil moisture was also compared with pH (Figure 9). Upon first glance there appears to be a correlation between soil pH and moisture. However, there are several discrepancies that would indicate the relationship is small at best. There are dry areas that have both higher and lower pH levels. For example the north section of the garden is dry with low pH and the east section of the garden is dry with high pH.
Figure 9. Soil moisture and pH. Darker colors indicate dry areas and high pH.
When looking at the relationship between soil moisture and temperature it can be seen that there may be a relationship (Figure 10). The most dry area in the east section of the garden was also the warmest area. Other dry areas around the garden correspond to other areas of warm temp. This can been displayed in the north section of the garden. The relationship between moisture and temperature is present but not extremely strong.
Figure 10. Soil moisture and temperature. Warm and dry areas are displayed in darker colors.
A digital surface map was also created by using the data from the aerial flight (Figure 11). Surfaces with high elevations are displayed in darker colors such as red. The areas that are the most red include the tops of trees while the lowest area included the marsh. The marsh can be located in the southern portion of the map.
Figure 11. Displayed above is the DSM of the community garden area. Tree tops are represented by dark red.
Conclusion:
Overall the lab proved to be very practical and applicable. Whether a power line company needs to survey power lines with an unmanned system to save money or an agricultural company needs to collect crop data, unmanned systems are certainly going to become common place in the future. Developing familiarity with unmanned systems during this lab will prove valuable in future geospatial projects. Using the GPS total station was another key component to the lab. This piece of equipment demonstrated how survey grade GPS coordinates can be efficiently gathered with the use of a portable system. Finally, the biggest learning curve of the lab was becoming familiar with the Phantom 3 Drone. Although the drone is not overly complex to operate, there are logistical matters that take time to become familiar with.
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