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

Introduction
The purpose of this lab was to gather ground control points (GCP) using various GPS and ground based topographic survey technology, as well as compare different Unmanned Aircraft Systems (UAS) platforms. All of the equipment was provided by Menet Aero, Topcon Solutions, and UWEC. Descriptions of all the equipment used is mentioned along with upsides and downsides to them. The area of study for this excursion was Litchfield Mine, Eau Claire, WI located at 44°46'23.3"N 91°34'19.5"W. The total area of the mine was roughly forty acres. This area is located in a non-glaciated region of WI also known as Driftless WI. Since this area was never touched by glaciers it contains many aggregate rocks/minerals that are used in construction work. This area needs to be annually surveyed to shows its value to investors. Figure 1. Shows a satellite image of the site.

Figure 1. Litchfield Mine, Eau Claire, WI

Sixteen location markers were numbered and distributed throughout the mine to gather the best depiction in the variation of landscape, shown in Figure 2. Since this lab only consisted of collecting data there is no results/discussion for this lab. All of the data that was collected on this excursion will be discussed in a different field activity.

Figure 2. Location Marker #1

Methods

Multiple methods were done for gathering GCP data. Whilst using all of this equipment, GCP were taken in the center of the location markers to provide the most accurate display of measurement from every method. The handheld GPS device Bad Elf (UWEC) was used, shown in Figure 3. And a mobile smart phone using GPS coordinates. Our class was split into several groups so that we could collect multiple data for the same GCP. The link provided has the data collected: https://universityofwieauclaire-my.sharepoint.com/personal/hupyjp_uwec_edu/_layouts/15/guestaccess.aspx?docid=05b8e941db4824c55b78cf12ded2020e6&authkey=AQOdSe_vxvFhoRasQp5_wTw

A Bad Elf GPS unit uses triangular distance from at least three satellites to gather its coordinates. While a mobile smart phone uses a base station on Earth rather than satellites in the atmosphere to gather points.

Figure 3. Bad Elf GPS unit and Mobile phone. (Lab 2 shows an up close of Bad Elf unit)

Arrow GPS (Menet Aero) markers were used to gather more detailed topography of the site shown in Figure 4. The Arrow GPS markers run on solar power and are waterproof. They are simply activated by pressing a button to gather a satellite connection. Since these location markers are products of a company based out of Australia the data gathered via satellite is sent to the company and then processed and sent back to client/user. The manufacture estimated accuracy of these markers are around 2cm, but the user estimated accuracy is more around 6cm. They are quite durable and easy to use with just laying down to gather GCP; however, a downside to this is not being able to check the data at the time it is taken.

 Figure 4. Arrow GPS Marker (yellow), Trimble R2 was gathering GC to see how accurate Arrow GPS Marker was.

Ground Based Topographic Surveying Technology

The Trimble R2 Fig. 5 (Menet Aero) - Gathers GCP much like a GPS but has higher accuracy and uses Terra Flex program which allows cloud download collaboration. Takes multiple GCP and averages them.

Downside: Signal can be blocked by overhead canopy i.e. roofs.

Figure 5. Trimble R2

Topcon HiPer Fig. 6 (UWEC) - GCP gathered for use by UAS platform in flight plans for routes. This Surveying technology uses Global Navigation Satellite System (GNSS). Acts in same way as Trimble R2 with taking GC. 

Figure 6. Topcon HiPer

Topcon Robotic Total Station Fig.7 (Topcon Solutions) - reflects modal by using 3-D imagery at a horizontal level. Much like a sonar that reflects back wavelengths to depict imagery. Alternative for using UAS equipment. Has 360 degree angle.

Downside of the product- electromagnetic waves can be interfered with other equipment i.e. automobiles. 

Figure 7. Topcon Robotic Total Station

UAS platforms

Four different UAS were flown. Two were fixed wings i.e. airplanes and the other two were rotary wings i.e. helicopters. All flight plans were created with the Topcon HiPer and then pre-loaded into UAS. The UAS were used to gather imagery data for the site. All UAS platforms come with pre-flight checklists to insure that they are set up properly.

DJI Phantom 3 Pro Fig. 8 (Rotary wings, Menet Aero)-used 16 megapixel camera lens with Pix 4D. Follows grid pattern whilst creating polygons around area with elevation taken into consideration; takes pictures simultaneously. Has one battery, better for commercial use. Used in GIS vertical construction or Building Information Modalling (BIM) for architectural purposes. Needs landing pad or can be grabbed out of air.  For a test run it was flown at an elevation of 250ft. to see if it would overpass the structures. It has a backup flight plan in case of losing GPS signal. Flight time: ~30min.

Figure 8. DJI Phantom 3 Pro

Sensefly Ebee Fig. 9 (Fixed wings, Topcon Solutions) - Uses Wiscor software. Autonomous, meaning it doesn't need to be manually flown. Has 20 megapixle camera that captures photos simultaneous with GCP gathering.Has RTK- Real Time Kinetics, provides precise geotagging of GCP by using a GNSS. Is hand launched by being shook 3x to initiate flight as well as to turn off.  Flight time: ~ 59 min. (has to be below 60min. to not be registered as military UAS).

Downside: Has poor GPS and transitions at turns.

CRASHED

Figure 9. Sensefly Ebee

M600 Pro with Zenmuse X5 Fig 10. (Rotary wings, Menet Aero) - External X5 camera, six battery packs. Geo snap field of view, meaning it's able to snap to pre-downloaded points. RTK, requires base station for this UAS. Has SD card with flight log on UAS. Flight time: ~ depends on number of batteries.

Figure 10. M600 Pro w/Zenmuse X5

C-Astral Bramor with Sony a6000 Fig. 11 (Fixed wings, Menet Aero) - Two battery packs, slingshot takeoff and parachute landing. Uses GNSS and RTK.  Flight time: ~ 3 hrs.

CRASHED

Figure 11. C-Astral Bramor w/Sony a6000

Conclusion

Overall, we hope to conclude which methods of GCP gathering is most accurate based on the outcome of data gathered at this site.

A commonality of downsides for all of the UAS platforms is the weather variability. Most of the UAS cannot withstand very strong winds or flying in the colder months. Also, birds are a large predatorily issue with attacking them. 

While flying the four UAS, two of them crashed; however, since they were creating GCP with imagery we were able to use there last coordinates to get a rough estimation of where they initially lost connection and could be. The sensefly ebee lost connection and landed in the Chippewa River shown in Figure 1. Another UAS was used to look for it along the banks. It ended up downstream with minimal damages, with just the camera getting wrecked. The other UAS that crashed was the C-Astral Bramor. In this case its parachute didn't deploy and ended up hitting a tree. Its right wing was stuck in a conifer tree about 18ft. tall. Figure 12. Shows the aftermath of the wreckage.

All UAS platforms come with insurance/warranty or some system failure back up.

Figure 12. C-Astral Bramor aftermath

References:

https://www.verticalaspect.com/drone-mapping-accuracy-part-ii-real-time-kinematics-rtk/

http://www.wiscor.com/

https://www.topconpositioning.com/gnss-and-network-solutions/integrated-gnss-receivers/hiper-hr

http://www.c-astral.com/en/products/bramor-ppx