Mapping the Mojave Desert with Drones

As part of our mission to test drone technology and provide mapping services to the ANR community, IGIS recently completed data collection for our largest drone mapping project to date - 3600 acres of the Mojave Desert.

The drone data will be used to create fine resolution vegetation and elevation maps, as part of a desert tortoise research project led by Dr. Brian Todd in the Dept. of Wildlife, Fish, and Conservation Biology at UC Davis. The study seeks to better understand how the threatened desert tortoise navigates in its landscape, which will help biologists and land managers responsible for protecting the desert tortoise make management decisions, such as where to place road fences that don't cut off important resources for this long-lived species. Researchers on this project track the tortoises with GPS and temperature sensors, which they will now be able to overlay on the highly detailed maps of the desert generated from the drone imagery.

How does the desert look to a tortoise?

A Large Study Area

The study area is approximately 3600 acres, which is extremely large for a drone. We mapped the area in two trips in 2016 and 2017, with significant improvements to our mapping methods in between.

In mid-2016, IGIS Academic Coordinator Sean Hogan mapped the first 1200 acres using a 3DR Solo drone flying a consumer grade GoPro camera. GoPro cameras work surprisingly well for making 3D topographic models, thanks to their high resolution, wide field of view, and rapid shutter rate. Hogan programmed the drone to fly a lawnmower pattern with a lot of overlap between images, so every point on the ground is captured in multiple images taken from different angles. The stitching software uses photogrammetric algorithms to recreate the surface geometry, producing a 3D model of the topography.

The Solo+GoPro combo worked well, but the flight time of the Solo, its mediocre GPS receiver, and the lack of an integrated GPS module in the GoPro were limiting factors that required more time for both flying and processing the data.

New Drone Platform for 2017

In May 2017, Hogan returned to the Mojave with IGIS Academic Coordinator Andy Lyons, as well as new equipment and almost a year's worth of additional flight experience. For this campaign we flew our new DJI Matrice 100; a larger drone that can carry two batteries for longer flight times. Hogan also modified the bottom of the Matrice, outfitting it with an additional camera mount, so we were able to fly with a high quality RGB camera as well as the Parrot Sequoia multispectral camera. The combination worked brilliantly, allowing us to capture both high quality RGB images for the 3D surface model, as well as multispectral images for vegetation analysis during each flight. After a day of working out kinks with the cameras and software, we were able to reliably fly eight 100-acre flights per day with minimal downtime between each consecutive mission. Flying at 400 feet, the resolution of the resulting maps will be about 2.25 inches for the RGB orthomosaic and digital elevation model (DEM), and about 4.5 inches for the multispectral products.

Lessons Learned

Some lessons learned for mapping large areas include:

• Mapping large areas with a quadcopter is viable with careful planning
• The Matrice 100 is large enough has enough power to fly 100 acre flights with two cameras on board with two batteries and calm winds
• Heat can dramatically reduce flight time because the air is thinner and equipment less efficient
• Checking your data in the field and having backup plans for weather and equipment glitches are essential
• Having two or more people on the flight crew helps tremendously
• Developing individual mission plans before going to the field reduces time between flights and hence illumination differences between adjacent areas
• The dessert tortoise is a charismatic creature with amazing adaptations, and a great curiosity about the research equipment we were setting up alongside the road: