UAV Flight

The available sensors can collect data that is informative for the plant breeder when they are attached to the UAV. The key to collecting a complete data set of all the plant breeder’s plots at a specific location is to plan and execute a good flight. The flight plan and organizing the flight operation in the field require attention to details.

After the UAV pilot arrives in the field, they will set up ground-control points (GCPs). This is shown in Figure 9 to the right. GCPs are points on the ground that have a set of known GPS coordinates. GCPs are essentially large targets for drones to use as geo-reference points. Having these allows the UAV to be accurate when mapping data locations. To set up GCPs, the researcher will evenly distribute 4-8 targets around the perimeter of the field and one in the center of the field. It is important that GCP targets are placed in an unobstructed location, easily visible by the drone. Using a GPS device, the researcher will store points for each GCP target. GCPs are not always permanent objects, so it is important to mark the location of the target so it can be placed in the same position every time a flight is conducted.

The next step is to prepare the drone for flight. This may look different depending on the type of drone being flown. Smaller, more commercially used drones typically require less setup and may already have sensors attached. Large drones often need some assembly. This may include unfolding/attaching propellors, attaching battery packs, inserting the data chip, and attaching the appropriate sensors. Initially some calibration steps may be necessary as well to ensure the sensor is working correctly and accurately. 

Figure 9. Two researchers storing the GPS coordinates of a GCP. The yellow pole is the GPS receiver that records the GPS coordinates for the GCP location. The black and white checkerboard on the ground is the plate that the UAV will then visually capture during flight that can be connected to the GPS data point for that target.

Captured by C. Mick, 2022.

Figure 10. Two examples of drones used in research today. The DJI Phantom 4 (right) is a small commercial drone and DJI Matrice 300 (left), which is a large commercial drone.

Captured by C. Mick, 2022.

Following the calibration is the actual flight and data collection. When the drone is flying, it is switched over from manual control to ‘autopilot’ following a predetermined path the pilot programs.

Creating a flight plan can be done prior to leaving for a field or after arrival. While different drones and software have their own nuances, the major steps to creating a flight plan are the same. The first step is to create a project. Wherever you are located at the time of creating the project is where the software is going to initially place your project.  If the flight plan is created away from the field that has the breeders’ plots, the project can be moved around to find the right location. Once you determine that, you can edit the boundaries for your project to ensure the flight captures your desired area.

After you have set your boundaries, you are going to change some advanced settings to fit your needs. Some notable settings include height, overlap, and gimbal angle. The height is important to your mission because it determines how high the drone will be flying over the crop. No matter how many times you fly the mission to collect data, the height will stay the same. Because of this, you want to make sure you choose a height that is taller than the crop will be later in the season. The height a drone flies determines the number of pictures a sensor is going to take and the resolution of the pictures. The lower the height, the more pictures and higher resolution. The higher the height, the less pictures and lower resolution (see fig. 11). Plant breeders in Nebraska work with maize, soybeans, and wheat. To make sure we get a quality image, it is common to fly around 25-30 meters. While this does increase image resolution, it also increases the time it will take a drone to complete a mission and subsequently the number of batteries needed to complete a mission.

There are two settings to adjust when changing the overlap on a mission. These are the forward and side overlap (Fig. 12). As you can imagine, this determines how much the images overlap, an important aspect when it comes to stitching the photos together during data analysis. The overlap allows the images to be merged more easily. While this is at the discretion of the pilot/researcher, it is common practice to set the overlap between 70%-80%. Gimbal angle is the angle at which the camera or sensor is turned. When conducting 2D flights over crops, it is important to set the gimbal angle at –90 so the sensor is looking straight down at the crops.

Figure 11. Comparison of coverage area between a UAV flown at a low altitude and high altitude. Drones flying at higher levels are able to capture greater ground area.

Created by C. Mick using Microsoft PowerPoint, 2022.

Figure 12. Overlap in images taken with an RGB sensor. Forward overlap (left) and side overlap (right) as it would look before (blue dashed lines and red dotted lines) and after data processing (brackets).

Created by C. Mick using Microsoft PowerPoint, 2022.

Other settings to choose are speed, shooting mode, photo ratio, and white balance. Each of the settings affects the quality of data you will collect so it is important to determine and set these appropriate to your project.

At this point, you should double check your flight plan and drone to ensure everything is up to par. If you have determined it is safe to fly, the mission is started at which point the drone is switched over from manual control to ‘autopilot’ following the predetermined path the pilot programmed prior to traveling to the field site.

During the flight, any data collected is saved on a data chip for easy extraction. Once the flight is complete, the drone returns to the landing pad, is packed up, and the data is stored to be processed back at the office. Following the infield flights, the data will be further processed back at the lab.

Attaching Sensors and Autopilot - video showing how to attach cameras to larger drones and what the tablet looks like while the drone is collecting data.

Drone Setup - video showing how to set up larger drone