The Weed Manager’s Guide To Remote Detection
The Weed Manager’s Guide To Remote Detection
Unmanned Aerial Vehicle (UAVs) platforms come in a variety of types, shapes and sizes, with their design typically driven by application and endurance requirements.
Unmanned Aerial Vehicles (UAVs), also known as Remotely Piloted Aircraft Systems (RPAS) or Drones, have revolutionised various industries with their versatility. These small, remotely operated aircraft are equipped with advanced sensors and cameras, enabling them to gather valuable data in real-time. UAVs find applications in agriculture for crop monitoring, vegetation mapping in disaster management for rapid response, and in surveillance for enhanced security. The various categories of UAVs may be classified according to their design, degree of autonomy, size and weight, and power source (De Rango et al., 2019). UAVs can be classified into fixed-wing, rotary-wing, hybrids such as VTOL (Vertical Take-off and Landing) and helicopter platforms.
UAVs come in a variety of types, shapes and sizes, with their design typically driven by application and endurance requirements. For example, large landscape surveys require UAV's that have long flight times and, in most cases, fixed wing designs will be a more suitable designed platform for this purpose. Where smaller areas with variable terrain need to be covered, a multirotor may be more suitable.
Fixed-wing UAVs, mimicking the structure of traditional airplanes, boast impressive endurance and speed, making them optimal for covering vast areas efficiently. Their aerodynamic design allows for extended flight durations and high cruising speeds, making them suitable for applications such as large-scale surveying, agricultural monitoring, and surveillance over expansive territories. However, fixed wing UAV can only travel forward and needs open space for horizontal takeoff and landing (Olson & Anderson, 2021).
The electric-powered wing design is a favoured platform as it can cover between 180 to 300 acres in its average 60-minute flight time. Most of these will come with High-resolution cameras and a pseudo-NDVI (Normalised Difference Vegetation Index (NDVI)) measuring capability. They are fairly stable platforms, relatively stable in moderate winds and maintain good ground height difference for optimal resolution for the cameras. These come in various sizes and are able to carry different payloads from cameras to fertiliser to herbicides and pesticides or a mix of payloads depending on the design. This capability offers many advantages to mapping, monitoring, and vegetation management potentials.
Fig. 1. Fixed Wing/Aeroplane[2] UAV (Source: F.A.A. Picks Diverse Sites to Carry Out Drone Tests - The New York Times (nytimes.com), accessed 9th November 2023)
Rotary-wing UAVs, resembling helicopters, are prized for their exceptional maneuverability and ability to hover in place. This type of UAV usually has three to eight wings (García et al., 2020). The different types of rotary wings includes Quadcopter, Hexacopter, and Octocopter are available for different purposes (Olson & Anderson, 2021 ).
These platforms require minimal space requirements for take-off and landing and possess large payload variability and capacity (depending on model being used). This however is offset by the generally limited short flight time, averaging about 20-60 minutes, and an area of coverage between 12-40 hectares, depending on payload.
Multi-rotor platforms come in a number of designs ranging with 4-8 propellers being the most common. Each has their own advantages and limitations relative to flight time or motor failure redundancy. The multi-rotors’ ability to take off and hover directly at the site of interest, along with their high maneuverability, make them very useful in small survey applications.
Fig. 2. M600 Multirotor UAV. Image source: Dr Jane Kelly, CSU
VTOL UAVs offer a unique blend of capabilities by combining vertical takeoff and landing with the efficiency of fixed-wing flight. This design allows them to operate in confined spaces and quickly adapt to changing mission requirements. VTOL drones find applications in tasks such as urban surveillance, maritime operations, and military reconnaissance.
Hybrid VTOL UAVs combine the advantages of multirotor platforms with those of fixed wing to overcome the disadvantages of the other platform types (fixed wing and rotary wing) (Pircher et al., 2017) (Chandar, 2021) (Carlson, 2014). Thus, it is possible to combine the extended range and payload capacity of a fixed-wing UAVs with the automated and landing strip-independent VTOL capabilities of a multi-rotor UAV (Pircher et al., 2017).
Additionally, no runway is necessary to fly the UAV in the field (Pircher et al., 2017). Additionally, VTOL fixed-wing UAVs with sensors can give real-time, accurate three-dimensional comparative data, critical for effective infrastructure development. As a result, current research has concentrated on fixed-wing VTOL ideas that combine the advantages of fixed-wing and rotary-wing UAVs (Carlson, 2014), (Vuruskan et al., 2014), (Ozdemir et al., 2014), (Aktas et al., 2016).
Helicopters are to a lesser extent currently used for agricultural and environmental surveillance, typically because of their complexity and cost. Very few dedicated helicopter platforms have suitable reliable autopilot systems and those that do typically cost in the order of hundreds of thousands of dollars. However, many helicopter systems have great potential with the ability to land directly at the field site and hover extended periods of time.
With further autopilot development, helicopters may benefit agriculture and environmental monitoring in areas outside remote sensing. Many of the large helicopters are capable of carrying large payloads in the order of 20-40kg for extended periods of time. This may be useful in areas such as herbicide and pesticide delivery along with nutrient delivery. A good example of the high-end helicopter is the Yamaha R-Max which is capable of carrying 28 kg of payload and has both granular and liquid spraying capacities.
Fig. 3. Helicopter UAV used for weed spraying in QLD
(Source: Mini helicopters use precision attacks in war on weeds, accessed on 9th November, 2023)
A great comparison between multi rotor and fixed wing drones is provided on the GeoNadir website