Chapter 8

UAV Remote Sensing in Precision Agriculture

Components of UAVs

At the heart of every UAV lies a harmonious integration of several key components, each meticulously engineered to ensure optimal performance, reliability, and versatility. These components work together to enable flight, navigation, sensing, and communication.

Airframe

The main body of a UAV, also known as the airframe, is a crucial component. It serves as the supporting structure for all other components, including motors, propellers, flight controllers, and payloads. Depending on the UAV's intended use, the airframe can vary greatly in size and complexity. Designed with precision, it balances durability with lightness, enabling drones to withstand environmental challenges while maintaining maneuverability. Frames are typically made from lightweight materials such as carbon fiber or plastic to minimize weight while maintaining strength.

Power Source

UAVs are powered by various power sources, including batteries, fuel cells, and hybrid systems. Batteries, particularly lithium-ion (Li-Ion) and lithium-polymer (Li-Po), are common for smaller UAVs due to their high energy density and lightweight nature. Hybrid systems combine multiple energy sources like batteries, fuel cells, and solar cells to increase endurance and efficiency.

Batteries

Drones typically use high-rate lithium batteries, which are lightweight and have high energy density and high current resistance. The drone battery system provides the actual power needed by the engines to take off, and its performance will significantly affect the overall flight time, speed, and stability of the drone. Therefore, the demand for high-quality drone batteries is also growing.

UAV Flight Controller

One of the most important parts of a drone is the flight controller, which acts as the “brain” of the UAV. The flight controller is connected to a set of sensors. These sensors give the flight controller information about its height, orientation, and speed. Common sensors include an inertial measurement unit (IMU) for determining the angular speed and acceleration, a barometer for the height, and distance sensors for detecting obstacles. A flight controller controls the motion of the drone.

Core Functions of a Flight Controller

The flight controller performs several crucial functions:
Stabilization. Balances roll, pitch, and yaw using sensors (IMU, gyroscope, accelerometer)
Navigation. Uses GPS and magnetometer to determine position and heading.

Software

Flight controller software is the firmware and logic system that runs on a UAV’s flight controller hardware. It processes inputs from sensors (GPS, IMU, barometer), manages motor outputs, executes flight missions, and enables both manual and autonomous flight. It plays a crucial role in collecting and processing essential UAV data, which enhances the overall system’s effectiveness.

UAV Navigation and Positioning System

UAV navigation and positioning systems are critical components that allow a drone to accurately determine its location, orientation, and movement in 3D space. These systems enable autonomous flight, precision mapping, obstacle avoidance, and mission execution in agriculture, surveying, and other applications.

GNSS Receiver

The GNSS receiver is a core component of a UAV’s navigation and positioning system. It enables the drone to determine its precise geographic location (latitude, longitude, and altitude) using signals from satellite navigation constellations. GNSS provides global coverage and includes several satellite systems (GPS, GLONASS, Galileo, and BeiDou).

Ground Control Points

Ground control points (GCPs) are crucial elements in UAV remote sensing and are used to physically mark locations on the ground with precisely known geographic coordinates (latitude, longitude, elevation), obtained via GNSS/RTK surveying. Typically, UAV GCPs are rectangular panels with a 2 × 2 black-and-white checkerboard pattern, of which the center point serves as the reference. The points must be visible on aerial photographs or point clouds.

RTK/PPK Base Station

A base station serves as a high-precision positioning anchor, dramatically improving the geospatial accuracy of UAV data, reducing the need for GCPs, placed at a known, fixed location to provide high-precision corrections to the UAV’s GPS—either in real-time (RTK) or through post-processing (PPK).

UAV Ground Control Stations

The ground control station (GCS) is a central hub that collects flight-related data and facilitates communication with the UAV control system. Sensors, both ground-based and onboard, contribute to data collection. Some UAVs incorporate collision avoidance systems, utilizing sensors to detect obstacles and enhance operational safety. These integrated systems collectively contribute to the UAV’s ability to operate autonomously or under human supervision across a diverse array of applications, from PA to surveillance and beyond.

Core Functions of Ground Control Stations

Command and Control (C2): Enabling seamless communication between the operator and the UAV for reliable flight operations and payload management.
Mission Planning: Allowing operators to plan flight paths, set waypoints, and define autonomous behaviors.

UAV Communication Systems

The communication system of an UAV is fundamental to its functionality. It ensures that operators can reliably control the drone’s movements, adjust its altitude, and make real-time changes to its course. Beyond basic control, these systems also allow for transmitting critical data, such as GPS coordinates, telemetry, and video feeds, which are essential for effective operation and mission success. Drone communication systems are responsible for maintaining three primary functions:

UAV Protocols in Communication Systems

Communication protocols are the set of rules and standards that define how data is transmitted and received between devices. In drone systems, these protocols play a critical role in ensuring that information sent from the controller reaches the drone accurately and promptly. Different protocols are optimized for specific types of data, such as control commands, telemetry data, and video feeds, making them essential for reliable and efficient drone operation.

UAV Communication Links

UAV communication links are crucial for transmitting data and control messages between the UAV and the GCS. They facilitate tasks like control, video transmission, and telemetry. Common types include line-of-sight (LOS) and beyond line-of-sight (BLOS) links, as well as tactical data communication systems.

Real-Time Data Transmission Software

Real-time data transmission software in UAVs allows the live exchange of data between the UAV (airborne system) and the GCS (Table 8.3). This software is essential for monitoring flight status, receiving live sensor feeds (e.g., camera, multispectral, LiDAR), and making in-flight decisions or adjustments.

UAV Payload (Mission-Specific Sensors or Tools)

In agricultural UAVs, the payload refers to the tools and equipment a drone carries to perform tasks like crop monitoring, spraying, or seed distribution. These payloads can range from cameras and sensors for data collection to liquid tanks for pesticides and fertilizers. The specific payload and its capacity depend on the drone's type and the desired application. Unlike core flight components (e.g., motors, GPS), payloads are modular and tailored to agricultural, environmental, mapping, surveillance, delivery, or inspection missions.

UAV Sensors

UAVs, or drones, are revolutionizing precision agriculture by using advanced sensors to monitor crops, analyze soil conditions, and optimize farm management. Different types of UAV sensors provide unique insights into plant health, water stress, and field conditions. Unmanned aircraft equipped with sensors provide remote sensing imagery with ground resolutions ranging from approximately 1 centimeter to 20 meters and spectral ranges spanning from visible to thermal infrared spectroscopy (TIR).

UAV Spray Systems

UAV spray systems utilize several key components for effective application of liquid pesticides and fertilizers. These components include a tank for storing the spray solution, a pump to generate pressure, a system of nozzles to distribute the liquid, hoses and filters to transport and clean the solution, and control mechanisms for regulating pressure and flow.

UAV Failsafe and Safety Systems

UAV failsafe and safety systems are designed to prevent or mitigate damage and injury in the event of system failures or emergencies during flight. These systems utilize various techniques, including redundancy, automatic recovery mechanisms, and flight termination procedures, to ensure safe operation, particularly in situations where human intervention is not possible. Key features of UAV failsafe system include:

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