1. Characteristics of Unmanned Aircraft Systems Used in Agriculture.

According to the current classification and the Air Code of the Russian Federation, the following definitions apply to civil aviation in general and the agricultural sector in particular [1]:

- Unmanned Aerial Vehicle (UAV) – An aircraft controlled and monitored remotely by a pilot located outside the aircraft (external pilot).
- Unmanned Aircraft System (UAS) – As defined in Article 32, Paragraph 6 of the Air Code of the Russian Federation, a UAS consists of one or more UAVs, flight control and monitoring equipment (external pilot station and control line), as well as takeoff and landing systems. In accordance with Russia’s Strategy for the Development of Unmanned Aviation (up to 2030 and beyond to 2035, approved by Government Order No. 1630-r, June 21, 2023) [2], a UAS may also include additional equipment necessary for its intended use, which cannot be operated independently of the UAS.

The communication channel between the UAV and the remote pilot station includes data transmission equipment for flight control and monitoring and may also provide radio communication. UAVs can be controlled manually from the ground or operate autonomously based on a pre-programmed flight trajectory [3].

Drones (UAVs) offer a cost-effective alternative to small aircraft and ground equipment for agricultural tasks, as well as satellites and ground patrols for monitoring and surveillance. UAVs are more affordable to acquire and maintain than manned aircraft and can perform certain tasks faster than satellites, providing real-time georeferenced data, which is especially valuable for precision agriculture.

Based on their technical characteristics, UAVs can be classified into four main types:
1. Multirotor UAVs
2. Fixed-wing UAVs
3. Helicopter UAVs
4. Hybrid UAVs

1. Multirotor UAVs (Multicopters)

Multirotor UAVs, the most widely used category, feature multiple rotors—typically three or more. The most common configurations include:
• Quadcopters (four rotors)
• Hexacopters (six rotors)
• Octocopters (eight rotors)

By adjusting the thrust of each rotor, these UAVs can hover, maneuver in all directions, and rotate around their axis.

Advantages:
• Vertical takeoff and landing (VTOL) capability
• High maneuverability
• Ability to hover over specific locations
• Relatively low cost and ease of operation

Disadvantages:
• Higher energy consumption compared to fixed-wing UAVs
• Limited flight endurance, typically ranging from 20 to 30 minutes when carrying a payload
2. Fixed-Wing UAVs

Fixed-wing UAVs resemble traditional airplanes, utilizing aerodynamic lift generated by their wings rather than relying solely on thrust for flight. While they lack the ability to hover, they offer significantly longer endurance, with some models capable of exceeding 16 hours of continuous flight when equipped with internal combustion engines.

Advantages:
• Extended flight range and endurance
• Greater fuel efficiency compared to multirotor UAVs
• Ideal for large-scale aerial surveys, mapping, and environmental monitoring

Disadvantages:
• Requires a runway, catapult, or net system for takeoff and landing
• Cannot maintain a fixed position over a target

Given their endurance and efficiency, fixed-wing UAVs are widely utilized for applications such as precision agriculture, soil health assessment, and large-area crop monitoring.

3. Helicopter UAVs

Helicopter UAVs feature a single main rotor and a tail rotor, allowing for stable flight and hover capabilities similar to multirotors. In theory, they offer greater energy efficiency than multicopters, as they utilize a larger rotor disc area to generate lift. However, their operational reliability requires complex control mechanisms, making their production and maintenance costs significantly higher.

Advantages:
• Higher energy efficiency than multirotors under optimal conditions
• Capable of carrying larger payloads compared to multirotor drones of similar size

Disadvantages:
• More complex and expensive to manufacture
• Higher maintenance and operational costs
• Requires specialized training for pilots

As a result of these factors, small unmanned helicopters are rarely used in agricultural applications, with multirotor UAVs being the more practical alternative.

4. Hybrid UAVs

Hybrid UAVs integrate features of both fixed-wing and multirotor designs, offering VTOL capability alongside extended flight endurance. However, their dual propulsion systems add weight and complexity, making them less efficient than standard fixed-wing UAVs.

Advantages:
• Vertical takeoff and landing like multirotors
• Greater range and endurance than multirotor drones

Disadvantages:
• Lower flight efficiency compared to fixed-wing UAVs
• Increased structural complexity and weight due to multiple propulsion systems

Despite these trade-offs, hybrid UAVs present a viable solution for applications requiring both endurance and precise positioning.

UAV Classification by Weight

According to GOST R 59517-2021, UAVs are categorized by Maximum Takeoff Weight (MTOW) into:
1. 0.25 kg to 30 kg
2. Above 30 kg

The Russian Air Code further divides UAVs into:
• Below 0.15 kg
• 0.15 kg to 30 kg
• Above 30 kg

Other countries employ different classification standards.

India’s UAV classification:
• Nano: Below 0.25 kg
• Micro: 0.25–2 kg
• Small: 2–25 kg
• Medium: 25–150 kg
• Large: Above 150 kg

Additionally, India distinguishes between:
1. Remotely Piloted UAVs
2. Model UAVs (for educational and hobbyist purposes)
3. Autonomous UAVs

China’s UAV classification:
• Below 0.25 kg (limited to 50m altitude, 40 km/h speed)
• 4–7 kg MTOW (max speed 100 km/h)
• Up to 25 kg MTOW
• Up to 150 kg MTOW
• Above 150 kg MTOW

Both China and India have introduced regulatory exemptions for agricultural drones weighing up to 150 kg, recognizing their distinct operational requirements.

UAV Power Sources

UAVs can be powered by:
• Internal combustion engines (ICE)
• Hybrid (ICE + electric) systems
• Fully electric propulsion
• Fuel cells (hydrogen, methane, etc.)

As of early 2024, fossil fuels continue to offer higher energy density (Wh/kg) than current battery technology, making them preferable for long-endurance UAVs. However, the simplicity, reliability, and reduced noise levels of electric UAVs have made them the dominant choice in agricultural applications.

UAV Control Methods

UAVs are classified based on their level of autonomy:
1. Autonomous UAVs – Operate independently without real-time communication with an operator.
2. Semi-Autonomous UAVs – Follow pre-programmed routes with optional operator intervention.
3. Remotely Piloted UAVs – Fully controlled by an operator via real-time communication.

While manual operation was once the norm, modern regulations increasingly favor autonomous pre-programmed flights, with direct operator control becoming an exception rather than the standard practice.

Conclusion

Each UAV type possesses distinct advantages and limitations, making them suited for different agricultural applications. Multirotor drones excel in precision spraying and localized monitoring, fixed-wing UAVs are ideal for extensive surveys, and hybrid UAVs provide a balance of both capabilities. As advancements in automation and energy storage continue, the role of UAVs in modern agriculture will further expand.

In the context of this review, the term “agrodrone” refers to an unmanned aircraft system (UAS) designed for the direct execution of agricultural operations, including crop spraying, fertilization, seeding, and other technological processes in field farming, horticulture, and rice cultivation.

Key Weight Characteristics of Agrodrones

Agrodrones are characterized by two critical weight parameters:
1. Payload Weight – This refers to the maximum capacity of the onboard tank for pesticides, fertilizers, or seeds. It determines how much liquid or granular material the drone can carry per flight cycle.
2. Maximum Takeoff Weight (MTOW) – This is the total weight of the agrodrone, including its airframe, power source (battery or fuel system), and payload.

By subtracting the payload weight from the MTOW, the empty weight of the UAV can be determined mathematically.

Classification of Agrodrones by Payload Capacity

Agrodrones can be categorized based on their payload capacity, which also correlates with their handling requirements:

1. Small Agrodrones (Payload < 10 kg)
• Designed for small agricultural plots, berry plantations, vineyards, and personal farms.
• Serve as a replacement for manual sprayers, offering higher efficiency with minimal operator effort.
• Easily handled and transported by a single person.

2. Medium Agrodrones (Payload 10–50 kg)
• The most commonly used category, featuring 30–50 L (30–50 kg) tanks.
• Compete with modern ground-based sprayers in terms of productivity while being more cost-effective and easier to operate.
• Typically require two operators for handling, e.g., loading and unloading from a vehicle.
• Often designed with interchangeable payload systems, allowing them to perform multiple agricultural functions:
• Application of plant protection products
• Liquid and granular fertilizer dispersion
• Entomophage deployment (biological pest control)
• Aerial seeding
• Antiviral and antibacterial treatments

3. Heavy Agrodrones (Payload > 50 kg)
• Designed for large-scale farming operations, but their adoption remains limited due to operational complexities.
• Require specialized boom manipulators for handling, making them less practical for widespread use.
• Typically used by enthusiasts and specialized agricultural enterprises rather than general farmers.

Among these categories, medium-sized agrodrones (30–50 kg payload) have gained the most widespread adoption due to their optimal balance between efficiency, cost, and ease of use.

For additional specifications, refer to Table 1.1 and Figure 1.1.

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In addition to agrodrones, which are designed for direct agricultural operations, there is a distinct category of drones used for inspection and monitoring in agriculture. These surveillance and data-collection drones do not have a specialized agricultural design but instead share the same technical features as drones used for monitoring forests, highways, mining sites, power lines, and other outdoor environments where aerial imaging and data transmission are required.

Unlike agrodrones, which serve as an alternative to ground-based and manned agricultural equipment, surveillance drones primarily compete with satellite-based monitoring. However, satellite imagery has inherent limitations, including lower spatial resolution, limited revisit frequency, and dependence on weather conditions (e.g., cloud cover interference).

Types of Agricultural Monitoring Drones

Monitoring drones can be classified into two primary categories based on their data processing and transmission capabilities:

1. Real-Time Monitoring Drones (“Remote Eyes”)

• These drones stream live data to the user, allowing immediate decision-making based on direct visual observation.

• Typically used by agronomists and farm managers for on-the-spot assessments, such as detecting crop diseases, pest infestations, or irrigation issues.

• Their effectiveness is limited by the observer’s ability to interpret the footage in real time.

2. Data-Collection Drones for Post-Processing and Analytics

• These UAVs capture and store large volumes of data for later analysis using specialized software.

• Capable of surveying thousands of hectares in a single flight, collecting data in both the visible spectrum and multispectral imaging.

• Equipped with sensors for measuring humidity, surface reflectivity, radiation levels, and gas emissions, providing valuable insights into crop health and soil conditions.

• The major limitation of this category is the time delay between data collection and actionable insights, often taking several days to weeks due to the need for data transmission, processing, and analysis. This issue is particularly pronounced in regions with limited broadband mobile internet access.

The Future of Agricultural Monitoring Drones

As advancements in onboard computing power (e.g., Nvidia AI chips) and real-time data transmission technologies (e.g., Starlink) continue to evolve, the delay between data collection and actionable insights is expected to diminish significantly. With the integration of AI-driven anomaly detection, drones will soon be able to autonomously identify irregularities in crops and soil conditions “on the fly”, providing real-time recommendations to farmers. This will effectively eliminate the distinction between “remote eyes” and post-processed analytics, making precision agriculture more responsive and efficient.

For a detailed discussion of the types of insights derived from aerial surveys, including examples of detected anomalies, their impact, and processing times, refer to Sections 2.1.1 – 2.1.4 of this review.