Chapter 8

UAV Remote Sensing in Precision Agriculture

UAV Mission Planning

UAV mission planning is the process of designing and managing the flight of an unmanned aerial vehicle (UAV) to achieve specific objectives. It involves determining acquisition parameters such as the trajectory, speed, attitude, overlap, sensor configuration, and waypoints of the UAV. Mission planning is important for ensuring the safety and productivity of UAV operations in fields such as remote sensing and photogrammetry. Typically, missions are created using software that contains all the necessary tools, including background imagery, that allows the operator to design a flight plan that will provide all the necessary instructions a UAS will need to cover the area. Most mission planning software platforms draw inputs from sources such as Google Earth and other powerful mapping sources (e.g., ArcGIS StreetMap, ArcGIS World Imagery, BingMap) to incorporate imagery, topographical data, and other landscape characteristics of an area of interest to give the mission planner bearing and orientation to the area of interest for which they will collect data.

UAV Image Acquisition Parameters

Agricultural UAVs are specifically designed for farming applications, presenting a significant stride in the field of remote sensing. Despite its promise, this technique poses challenges, necessitating a thorough investigation of parameters for optimal UAV performance. UAV image acquisition for remote sensing involves parameters grouped into four crucial categories: quality, flight, image, and efficiency. Quality parameters, already discussed, focus on attaining precision and detail in the acquired images, encompassing sensor attributes such as resolution, exposure time (shutter speed), acquisition rate, focal length, and camera angle.

Selection of Sensors and Lenses

The first stage of flight preparation involves selecting the appropriate sensor type (i.e., RGB, multispectral, hyperspectral, thermal) or sensor combination, as well as the UAV platform. This decision ultimately depends on the specific application and objectives. Image quality in UAVs is a result of the interplay between several factors, including the sensor's characteristics (size and resolution), the lens's properties (focal length and type), and the overall mechanical integrity of the camera system, including the lens cone.

Flight Speed

Flight speed is the velocity at which the UAV moves while acquiring images, and it is intricately connected to the shutter speed or exposure time during the operation. Flight speed is the velocity at which the UAV moves while acquiring images, and it is intricately connected to the shutter speed or exposure time during the operation. Shutter speed, a fundamental camera setting, dictates how long the camera’s shutter stays open during the image capture process.

Time of Day

Time of Day (TOD) refers to a designated time frame for conducting aerial imaging, considering factors such as lighting conditions, sun angle, and shadows that influence the quality of acquired images. While limited research focuses on TOD effects, commonly cited hours range from 9:00 a.m. to 2:00 p.m., 10:00 a.m. to 3:00 p.m., or 11:00 a.m. to 2:00 p.m., coinciding with optimal sunlight conditions.

Flight Altitude

Flight altitude, the vertical distance between the UAV and the ground, plays a pivotal role in UAV image acquisition, influencing spatial resolution, coverage, and image quality. For agricultural UAV drone flights, altitude recommendations vary depending on the application, but generally, 50 to 400 feet (15–120m) is a common range. For mapping field crops, 50 meters (165ft) is suggested, while for orchards, flying higher than 150 meters (500ft) is recommended, but always check local air regulations.

Terrain Following

The terrain-following option is an option in which the flight height is adjusted to the relief (DTM) of the area. This is in some apps, also referred to as above-ground level (AGL), as opposed to the standard flight height, which is the height relative to the take-off point. Terrain following ensures a consistent distance between the UAV and the ground surface, providing a uniform GSD, minimizing out-of-focus issues, and enhancing safety—especially in mountainous regions.

Image Overlap

After selecting the camera and determining the GSD, the next crucial parameter to establish is the overlap. Image overlap refers to how much consecutive aerial images share in common (i.e., overlapping ground area, Figure 8.8). It’s critical for mosaicking images into maps, 3D models, or orthomosaics using software like Pix4D, Agisoft Metashape, or DroneDeploy. Forward overlap is managed by adjusting image capture rates, while side overlap is linked to the drone’s flight path. High overlaps increase processing time due to redundancy, while increased overlap improves spatial and geometric accuracy. Images captured at the edges of the projected area can result in blurred images due to the effect of the UAV’s maneuvering and the low number of overlapping images.

Flight Direction

The flight direction of the standard parallel flight lines is typically set by the flight app to minimize the flight time. One key consideration is wind speed. In windy conditions, headwinds can reduce flight time. However, it is unclear whether flying with a constant sidewind (perpendicular to the wind) is more energy efficient than alternating between tail- and headwinds.

Viewing Angle

In UAV-based remote sensing—especially in agriculture and environmental monitoring—viewing angle plays a critical role in ensuring accurate, consistent, and high-quality image data. Proper planning of the viewing angle can minimize distortion, reduce anisotropic effects, and optimize image overlap for mapping and analysis.

Waypoints

Waypoints are one of the most common and powerful methods of UAV operation in precision agriculture. In UAV navigation, waypoints are predefined points along a flight path that the UAV uses to navigate autonomously; however, they can also support assisted manual flight by guiding the operator or acting as checkpoints.

Flight Planning Apps

Most flight mapping apps offer user-friendly and reliable functionality with a similar workflow across platforms. This has made mapping flights significantly more accessible and user-friendly, reaching a broader community. First, the user can draw the area of interest or the linear feature to be covered and specify the UAV and sensor.

Core Functions of UAV Flight Planning Apps

Mission Planning. Define flight area, altitude, pattern (grid, polygon, corridor), and overlaps for image capture.
Automated Flight Control. Executes predefined flight paths autonomously, reducing human error and ensuring consistency.
Camera Triggering and Sensor Control. Automates image capture intervals, multispectral or thermal sensor control, and exposure settings.

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