Field Activity #3: Evaluation of UAS Platforms and GPS Units for Ground Control

Introduction:

On September 30th, 2017, the Geo-spatial Field Methods class went to the Litchfield Mine to record  ground control points using high and low quality GPS, and to gather aerial imagery using different types of UAS platforms. The end goal is to compare the gathered data in order to find out which of the equipment is the most accurate. The types of equipment used at the mine to collect the ground control points were: a Bad Elf GPS, a Mobile Device GPS, a Topcon HiPer HR, Topcon HiPer SR, Arrrow GPS Markers, and Ground Control Point markers. The UAS equipment used to gather aerial imagery included: the DJI Phantom 3 Pro , Sensefly Ebee, M600 Pro w/Zenmuse X5, M600 Pro with GeoSnap PPK, and a C-Astral Bramor w/ Sony a6000. On top of that the class also got to see two types of Toposurvey equipment which were the Topcon Total Station and the Topcon Robotic Station

The whole class started out the day walking around the study area and placing different control points. The two class sections were split up into three different groups. Each group was given a Bad Elf GPS and a Topcon Survey GPS unit. Each group then collected the latitude and longitude coordinates using the two GPS units as well as a mobile device GPS. Once all the GCPs were collected the class moved to an open area to which the UAS drones were deployed.

Study Area

The Litchfield Mine was southwest of Phillips hall, and roughly ten minutes away. This mine is an aggregate mine right along the west side of the Chippewa River, and is hundreds of feet deep of fluvial deposition river rock from the meandering river. The elevation was relatively the same throughout the study area, but there was many piles of the river rock spread out. The Mine was surrounded by Forests to the South and to the West.

Figure 1: Map of Study Area

Methods:

High quality Ground Control Points are needed in order for High quality UAS surveys. Professor Hupy instructed the students to lay down sixteen separate Ground Control Points spaced out equally throughout the Litchfield mine, making sure none of them were close enough to be overlap another. Once the GCPs were laid out, we gathered the coordinates using three different GPS units. The UAS equipment's will then use the GCPs to gather centimeter accurate aerial imagery. The following content will give an in-depth analysis of the different GPS, Toposurvey, and UAS equipment that was used during the field outing.

Topcon HiPer

When recording data with this survey GPS, you must wait until the control panel says fixed. If it is at 0% and yellow, stop it and start over. Once it completes collecting thirty coordinates, hit store than save. This will help give you real time accuracy of just two centimeters. However it is capable of achieving sub-centimeter accuracy.

Arrow GPS Markers

The GPS markers were explained by PJ Kirkpatrick, who flies drones for a company called Terra Viglis. These instruments are a 2 by 2 foam solar GCP. They communicate with satellites, and the propeller gets the accuracy around 2-6 centimeters. They are 500 dollars per unit. The limitations are that once you press the button to collect the point, it collects until it is done not allowing any real time access. The advantages to this GPS are that it is water proof, very accurate, durable, and light. On top of that the points talk to each other which helps get even more accurate points. This instrument is also good for topography, 3D-models, and measuring amounts of dirt.

DJI Phantom 3 Pro

The first drone the class got to see was a rotary-wing drone called the DJI Phantom 3 Pro, flown by PJ Kirkpatrick. It costs roughly 30,000 dollars. This drone includes a MOCO feature which is short for Minimal Obstacle Collision Avoidance, allowing for the safest flight path. It is a manual drone that records data from an average of 250 feet. PJ used an app called drone deploy to control the Phantom. The phantom has roughly 30 minutes of battery life, and can fly continuously. By the end of the flight path, it had taken 222 photos of the study area.

Figure 2 displays the DJI Phantom 3 Pro

Video 1 shows the Phantom take off

Sensefly Ebee

The first of the two fixed-wing drones was called the Sensefly Ebee flown by Josh Nave. This drone can cover a lot more ground on one battery and fly for 59 minutes, but due to military law, it can not be in the sky for more than an hour. It also has a autonomous flight plan, a multi spectral and thermal camera, and the prop is designed to breakaway. Josh holds the drone in the air, until it is ready for take off. It then marks the launch point as the home point, and will return home if the wind speed gets too high or the GPS signal is bad. The disadvantages are that it needs a run way when its about to land, and it is not the best for recording data of small spaces. Josh has an insurance package called Always-on which is a two-year, two-replacements within 48 hours of the crash.

Figure 3 displays Josh Nave prepping the Sensefly Ebee

M600 Pro w/ GeoSnap Pro

The second multi-rotar drone was the M600 Pro. This is a reliable drone that is separate from the platform. It has a built in GPS, and if you take the sim card out you can see the overlay quality right after. It also has built in RTK (Real Time Kinematic) which communicates with the GPS on the ground to fly withing centimeter accuracy.

C-Astrol Bramor w/ Sony a600

The second fixed-wing drone was brought by Peter Menet who owns a company called Menet Aero. This drone goes for 70,000 dollars on the market. It has a long time flight time, which can exceed the legal 59 minutes of flight time. It also has a parachute that is deployed when it is ready to land.

Video 2 shows the C-Astrol Bramor takeoff in Slow Motion

Topcon Robotic Total Station

This Toposurvey instrument gathers information by shooting lasers that reflect to create 3-D models. It is great at reading angular distance and can measure specific dimensions. It scans point about once every couple seconds, and costs 22,000 dollars.



Results/Discussion:

The Geospatial Field Methods class used various GPS units and UAS equipment to gather Ground Control Points and aerial imagery. For the GPSs, we know that the mobile device will be the most inaccurate, the Bad Elf's were the second most accurate, and the Topcons were definitely the most accurate. However, we still need to map the collected to coordinates out to get the physical proof. Each group entered their coordinates from the Bad Elf and Mobile Device into a Microsoft Excel Spreadsheets as seen in Figure 4 and 5. The class is still waiting for the centimeter accurate Topcons GPS results.

Figure 4 displays the coordinates recorded by the Bad Elf GPS

Figure 5 displays the coordinates recorded by the mobile device GPS

As far as the drones go, the fixed-wings a much higher crashing rate than the rotary wings. However, the fixed-wings tended to have a longer battery life for more flight time, and collected photos at a much more effective rate.