South Middle School Ponds and Garden Field Day

Introduction

  This lab was first time the class got out to actually fly some UAS platforms. The Phantom 3 Advanced was flown to collect nadir image data and oblique image data. Then, the DJI Inspire 1 was flown for fun so everybody in the class could get a a chance to fly it a bit. This lab took place at the community garden by South Middle School in Eau Claire. This can be seen below in Figure 11.0 in the study area map. 

Fig 11.0: Study Area Map

  Figure 11.1 is a photo of what the community garden looked like. It mostly consisted of a flat dirt area. However, there were some miscellaneous items in the garden as well such as hay bales, bags of dirt, and tarps. There were no big obstacles because it was a garden, although a few plots were already planted in, so they had to be avoided. The weather conditions were not ideal as air temperatures were in the lower 50s and the wind was sustained from the NE around 10 mph.

Fig 11.1: Study Area Photo

  This lab also focused on learning how to use GCPs in the field by using survey grade GPS to collect the location of them.

Methods

Fig 11.2: Survey Grade GPS Unit

  First, the GCPs created in last week's lab had to be laid out throughout the garden. They were laid out in a snake like pattern around the garden in order of their numbers so that it would be easier to keep track of each GCP when using the survey grade GPS unit. The survey grade GPS unit can be seen on the right in figure 11.2. In the photo, professor Hupy is teaching a student how to set up the GPS so that it is able to collect  the X,Y, and Z coordinates of the GCPs. The coordinate system used was the UTM WGS 1984 Zone 15N.

  Once the survey grade GPS unit was set up, it was fairly easy to record the X,Y and Z coordinates of the GCPs. All one had to do was press the button on the GPS screen which had the little surveyor man on it and then wait for the GPS unit to say that it was ready to collect data for the next point.

  The survey grade GPS unit needed WiFi in order to collect the data. This WiFi was provided by using a portable MiFi unit which can be seen below in figure 11.3.

Fig 11.3: Portable MiFi

Fig 11.5: Level Used for Accuracy

  While collecting the data, there were a couple things one needed to pay attention to before taking the survey point. First, one needed to be sure that the survey grade GPS unit was perpendicular to the earths surface. This was done by using a type of level included with the survey grade GPS. This can be seen on the right in figure 11.4. The bubble needed to be fully inside the circle for the GPS to be upright. Second, the data collector needed to make sure that the survey grade GPS unit was placed directly above the middle of the GCP so that the reading would be accurate. This can be seen below in figure 11.6. The placement didn't need to be perfect, but needed be within an inch or so.

Fig 11.6: Placement of the Survey Grade GPS Unit

  This process of collecting data using the survey grade GPS unit was done unit all 9 of the locations of the GCPs had been recorded.

  Next, it was time to prepare the Phantom 3 Advanced ready for flight. This included making sure the portable MiFi was nearby, updating firmware for the controller, checking the batteries for both the controller and the Phantom 3 Advanced, and planning the mission. The mission planning essentials learned in the Mission Planning Essentials lab were implemented here. The mission was planed by using the Pix4D Capture app on an I-Pad on site. Figure 11.7 is a photo of the Phantom 3 Advanced and its controller with the I-Pad attached. It is a small multi rotor UAS platform which costs around $800 when new.

Fig 11.7: Phantom 3 Advanced and its controller

    Then, the Phantom 3 Advanced was ready for its nadir mission. Professor Hupy took off manually and then did some circles and rotations to make sure everything was in good working condition. Then he pressed the button on the I-Pad to start the mission. The mission area was fairly small and only covered the community garden. The overlap was set fairly high around 80%, and the altitude was set to 70 meters. When it completed the mission, the Phantom 3 Advanced landed itself in roughly the same area it took off.

  Another mission was set up to collect oblique images of the all the students cars which were parked on the street. This flight was performed at a 75 degree oblique angle, and the altitude was set to 70 meters. The Pix4D Capture app was used to plan the flight again. Then, this mission was executed.

  Next, the DJI Inspire 1 was put up in the air. No data was collected with this platform. Once Professor Hupy got up in the air, the controller was passed around from student to student so that everyone could get a chance to fly it a little bit. Some people did circles, others tried to do figure 8's, and some people just swayed the Inspire back and forth.

  

Results / Discussion

  The data collected from the Phantom 3 Advanced flights were not made available in time for the author to process the data. Fortunately, very similar data was collected the next day in the same location in the Field Methods lab using the same GCPs but with the M600 UAS platform. This flight took nadir imagery of the community garden and the surrounding ponds. The data from this flight was processed just as laid out in the Using GCPs to Process UAS Data In Pix4D lab. Then, two maps were created from the DSM and Orthomosaics The first map is shown below in figure 11.8 which displays the orthomosaic of the middle school garden area. 

Fig 11.8: Orthomosaic of the M600 Flight

  This is a very high resolution image. The different plots in the garden can be identified, the location of cars can be found, and the placement of people can even bee seen. There are three main areas in the map: the north, the south, and the east. The north area is where the garden is. The trees here have leaves on them, but the grass is mostly bare. In the south region, this is where the two ponds are located. The vegetation here is mostly brown short and tall grass. The east region is where the parking lot and baseball field is located. Here the grass is a little greener, and this is where most people park their cars.

  This next map shown below in figure 11.9 displays the DSM overlaid with the hillshade of the M600 flight. The DSM was set to have 40% transparency so the hillshade can be seen beneath it. The hillshade scale is a grayscale so its legend isn't displayed because its values would be worthless. The hillshade is used in this map to help visualize the elevation differences. 

Fig 11.9: DSM Overlaid With a Hillshade

  Looking at the north, south, and east regions in this map some trends can be found. For the most part, the south region has the lowest elevation. This makes sense as this is where the ponds are located. The north region has a higher elevation than the south region, but a lower elevation than the east region. The east region has the highest elevation of the three regions. These elevation trends make sense as they relate looking at the surroundings in the orthomosaic. The south region contains two water ponds. This makes sense as water is generally located at a lower elevation than its surroundings. The parking lot and the baseball field have the highest elevations probably so that water doesn't pool up in these area when it rains hard. 

  There are a couple of places in the map where the elevation values are not super accurate. This is because there were some trees which cause havoc when trying make the DSM look nice. The camera used on the M600 can only take the elevation of the surface, not the ground. Therefore, objects such as trees and buildings will cause there to be abrupt changes in the DSM values. The minimum value in the map is 264.2 meters which is located in one of the two ponds. The maximum value is 283.3 meters which is located on the tops of the trees either in the southwest corner of the map, or in the northern part. The average surface elevation is 273.8 meters which is displayed as the yellow color. This elevation covers most of the roadways and parking lot.

Conclusion

  In conclusion, the processes of using GCPs and collecting nadir and oblique image data was implemented. Survey grade GPS is a good tool to use to gather very accurate  X,Y and Z data down to the inch which makes it perfect for collecting the location of GCPs. Learning how to use survey grade GPS is important because there are many other application of it. These include construction, utilities, or property surveying. The only downfall of survey grade GPS is that its expense. The one used for this lab costed north of $12,000.

  The Phantom 3 Advanced was a perfect fit for the size of its flight. It was also good to get a little hands on experience using the DJI Inspire 1. The Inspire was up fairly high and was GPS assisted which made it very difficult to crash it. It was also important to learn how to use the Pix4D Capture app for planning the mission. This app is much faster than the C³P software and can be used right in the field.