UAS Platforms and GPS Units for Ground Control

Introduction

Hands-on field work with various UAS craft and GPS devices for ground control points were conducted at the Litchfield Mine located in Eau Claire, WI (see Figure 1).
Figure 1: The Litchfield Mine located on the Southwest side of Eau Claire, WI

Methods

Survey Ground Control Points

Ground control points (GCPs) are used to geo-reference the data collected by UAS technology to improve accuracy and be represented on a GIS. They connect data collection to real-world coordinates. The method we used was to fully cover the area of interest with variability in elevation, avoiding clustering GCPs, and placing them in a triangular pattern to best record accuracy. We used  markers to demarcate our GCPs shown in Figure 2. 
Figure 2: an AeroPoint GPS marker used as the 6/16 GCPs taken
After all GCPs were placed, a variety of equipment was used to record the coordinates of these markers including the Trimble R2, Septentrio, Altus NR2, Topcon HiPer, Bad Elf GPS units, and our cellular devices as shown by Figure 3. 
Figure 3: Collecting coordinates from various GPS devices
The reason for collecting on multiple devices was to gain exposure to various technology and compare accuracy among these. After all, no matter how expensive the drone is, the data is only as good as its 3D accuracy and methods used collecting and recording data. 

UAS Survey

After collecting GCPs, four UAS were used to collect the survey of the area. The DFI Phantom 3 Pro, Sensefly Ebee, M600 Pro, and C-Astral Bramor were used to compare type, takeoff, landing procedures, and specs for the mission. 

DJI Phantom 3 Pro

Figure 4: Takeoff of the DJI Phantom

This platform is a small rotary wing UAS with 30 minutes of available flight time on an hour charge. The drone first elevates to 250 ft. to make sure there aren't obstacles in the pre-programmed flight path (Figure 1). The flight ran smooth but was pushed to its battery limits on the larger area. The recovery of the drone also went smooth with a hover option while the operator was able to grab it avoiding the gravel surface.














Sensefly Ebee

Figure 5: Takeoff of the Sensefly Ebee
This platform is a light-weight foam fixed-wing drone. It can travel for 59 minutes and handle 28 mph winds. It houses a camera and tracking device and will return home with poor GPS signal or poor connection to the controller. When photos are collected, the motor briefly turns off. The flight was programmed from a laptop in the field with pre-loaded imagery. Takeoff was from a standing position (see Figure 5) and landing requires significant room to accomodate the light-weight, low-angle dive it skids to on the ground. The operator had been flying this drone for 4 years with no problems. However, the GPS location was lost and before it could return home it took a dive bomb into the Chippewa River.

M600 Pro with GeoSnap Pro

Figure 6: Takeoff of the M600 Pro


This platform was a larger, 6-rotor drone that is capable for flights up to 40 minutes depending on the equipment carried. The camera used on this mission was a pre-programmed GeoSnap Pro. Takeoff and landing is a breeze with it's nearly two-foot legs (Figure 6).
















C-Astral Bramor with Sony a6000

This large fixed-wing platform resembles a small airplane--built solid with more than enough time to takeoff. Takeoff requires at least 20 knots of wind and is launched by a sling (Figure 7). The flight is fully automated and is very quiet in the sky. The flight itself was efficient for the large area. However, upon landing the parachute (although correctly packed) never deployed and continued flying into nearby trees. 
Figure 7: Takeoff of the C-Astral Bramor

Conclusions

UAS features have drawbacks and advantages depending on the mission at hand and the conditions in which they're launched. In our flights, the fixed wings seemed to be at a disadvantage because they were less reliable with 2/2 crashes on that given day. Obvious advantages for the fixed-wing UAS however, were that they were able to cover much larger ground faster--although the Bramor required more pre-launch preparation. The drawbacks other than speed for the rotor UAS is the battery life and the need to return home to change batteries mid-flight. It will be interesting to compare the results of the data collected by all drones because data is more important than the specs. 

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