Assignment 3: Litchfield Mine Survey

Introduction

The purpose of this lab was to survey the Litchfield mine site, a mine in the southwestern portion of Eau Claire, by using various unmanned aerial system (more commonly known as UAS) platforms and geographic coordinate collection systems. Using a multitude of devices that ranged from entry-level to survey-grade, the class was able to conceptualize the differences in quality and accuracy between them.

Figure 1: Location of Litchfield Mine Site.

Methods

Upon arriving at the site, the class broke into small groups and walked around the site to set ground control points. Ground control points, or "GCPs", are used in UAS surveying to give the resulting composite imagery a location when mapping. Since the site covers roughly 1,550 acres, it was important to get good coverage of the site with GCPs. Putting GCPs too close together can distort the processed imagery, so the class was sure to spread out their placement. GCPs can be made of many different materials, and for this lab the class used high density polyethylene squares, pictured in figure 2 below.

Figure 2: Collecting GCP coordinates with Topcon HiPer SR GPS.

Once the 16 GCPs were placed throughout the site, the small groups went to each of the GCPs and collected geographic coordinates using several different GPS recievers. These consisted of: Apple Maps for iPhone, Bad Elf GPS Unit, Topcon HiPer HR Survey GPS, and Topcon HiPer SR GPS. When processing the data in a later lab, the differences in accuracy will be assessed.

Figure 3: Field log of BadElf GPS and Apple Maps coordinates.

Figure 4: Hand-drawn field map of GCP locations.

Some field notes were taken to record a "mental map" of where the GCPs were placed and the coordinates of the BadElf GPS unit and Apple Maps (Figures 3 and 4).

After collecting the GCP coordinates, the UAS platforms were flown. The first of which was a DJI Phantom 3 Pro. This UAS is a four blade multi-rotor aircraft and is considered a low-level commercial drone due to its somewhat limited capabilities for mapping, payload, and battery life/flight time. Although this drone is not as powerful as some of the other drones used that day, its still equipped with pre-flight mapping capabilities, smart batteries/return-to-home features, and a 20 megapixel (MP) camera. This flight was a successful one, capturing over 200 images of the site in around 15 minutes.

Figure 5: DJI Phantom 3 Pro

The next UAS platform flown was the Sensefly eBee. This UAS is considered a mid-level commercial fixed wing drone, equipped with standard pre-flight mapping and return-to-home capabilities, real time kinematics, and a 20 MP camera. Since this UAS is a fixed wing, it needed more space to land than the multirotors used during this lab. One interesting feature of this drone is that the propeller stalls when taking a photo, which is supposed to increase the quality of the images taken with this platform. 

Figure 6: Sensefly eBee

Unfortunately, this drone malfunctioned and crashed after the remote pilot noticed the lack of stability during flight due to high winds, aborted the mission, and attempted to return the drone to its launch point. The drone was recovered in the Chippewa River due west of the site by using another UAS' perspective to locate it; the DJI Matrice 600 Pro.

The DJI Matrice 600 Pro was the third UAS platform flown. This mid-level commercial, six-blade multi rotor was equipped with standard pre-flight mapping and return-to-home features, real-time kinematics, and a 16 MP GeoSnap Pro camera from Field of View. This wide angle sensor is especially good for remote mapping applications. This flight was a successful one, taking around 10 minutes to fly the site; a shorter amount of time than the Phantom 3.

Figure 7: DJI Matrice 600 Pro (a.k.a. M600 Pro)

The final UAS platform flown was the C-Astral Bramor. This high-level fixed wing drone costs over $70,000 and was equipped with advanced pre-flight planning and return-to-home features, a 24 MP camera, and a parachute landing mechanism. This platform uses a tension-loaded catapult launch that flings the aircraft into the wind, lifting it before engaging the automatic propellers which then raise the drone to its predetermined mission altitude. The planned flight took around 30 minutes, however there was a malfunction with the parachute deploying during landing. The aircraft flew over its designated landing zone and flew straight into the forest on the east side of the site. The drone was recovered and is being replaced by C-Astral free of charge due to a programming error.

Figure 8: C-Astral Bramor

In addition to the UAS flights, a Topcon GT ground station was used to demonstrate how it could be used to calculate volumetric data by collecting survey points on a stockpile at the site. This total station is survey-grade, collecting measurements automatically with less than millimeter accuracy- the most accurate measurement device of the day.

Figure 9: Topcon GT total station.

Discussion

Using the different GPS methods for collecting GCP coordinates will hopefully put accuracy of each platform into perspective. With the way technology is progressing nowadays, it was no surprise that each platform was fairly simple to use- each having a minimalist visual interface with icons and buttons to collect coordinates with a simple tap of the screen. There were noticeable pros and cons to each platform, however. For the mounted GPS receivers, the coordinates are stored electronically, and can be uploaded directly to the computer for use, however, these systems are usually quite expensive and less mobile than the BadElf GPS unit or iPhone. In turn, the BadElf GPS and iPhone requires that the user manually log their usually less accurate coordinates, but are also cheaper, usually more accessible, and more mobile than their more sophisticated counterparts. Ultimately, which platform to use is subjective to the project and the resources available to the user.

Watching the various UAVs fly was certainly helpful in understanding the differences of the mapping frontier that is unmanned aerial systems. Though both multi-rotors were successful in their flights, the fixed wings weren't so lucky. Both the eBee, a $30k aircraft, and Bramor, a $70k aircraft, malfunctioned and crashed in the same lab- a rarity I'm sure. It was surprising to me, considering how much these things cost, one would think they would be more reliable. Although the failure of both fixed wings was probably an isolated incident, it just goes to show that the industry is delving into some unknown territory and are still working out some kinks. I must say, it was a huge disappointment to not see either fixed wing perform a proper landing, but that's the way it goes sometimes. On the other hand, both multi-rotors proved to be a more reliable and versatile platforms. Having never personally witnessed a multi-rotor malfunction or crash, they can land in smaller areas than fixed wings and seem to give the user more control over the aircraft. In theory, I do feel as though fixed wings could provide more accurate imagery and data than multi-rotors, but the models I've seen fly tend to require more set-up and have a greater risk of error with characteristics such as belly landings, requiring a large and level path for landing, and less pilot control.

The Topcon GT total station was interesting to learn about as well. When observing the tools used on a construction site, one can expect to see a ground surveyor more times than not. These devices are very impressive in terms of accuracy, and for certain sectors, this is of utmost importance. The platform requires more set-up and time than using a UAV, but again, which tools to use are subjective to the what is needed for the project and if less than millimeter accuracy is necessary, than it would be worth it to use this platform. 
  
Overall, I got a lot out of this lab. Having taken a UAS class last semester, I was familiar with what GCPs were, how GPS receivers were used, and the process of flying unmanned aerial vehicles. In addition to seeing the eBee and Bramor fly for the first time, I was able to expand on and dive deeper into my prior knowledge of UAS and witness how survey ground stations work/why they're still used instead of UAVs. I also witnessed my first UAV crashes as well, something very shocking to me.