Drones

1. Introduction

Unmanned Aerial Vehicles (UAVs) or Drones have seen unprecedented levels of growth in military and civilian application domains. When initially introduced during World War I, UAVs were criticized heavily as being unreliable and inaccurate, and only a handful of people recognized at that early stage their potential and (future) impact on changing the battlefield.

 2. What is an Unmanned Aerial Vehicle (Drone)?

The term unmanned aerial vehicle (also known as a drone) refers to a pilotless aircraft, a flying machine without an on-board human pilot. As such, ‘unmanned’ refers to total absence of a human who directs and actively pilots the aircraft. Control functions for unmanned aircraft may be either onboard or off-board (remote control).

 3. Fixed Wing vs Copter

A fixed-wing UAV  refers to an unmanned airplane that requires a runway to take-off and land, or catapult launching. A helicopter  refers to an aircraft that takes off and lands vertically; it is also known as a rotary aircraft with the ability to hover, to fly in very low altitudes, to rotate in the air and move backwards and sideways. It is capable of performing non-aggressive or aggressive flight 

4.Terms related to Drones

 4.1. Quadcopter 

A four bladed drone, the most common basic type, because that number of blades gives more stability .

4.2. Payload

Anything the UAV / drone carry other that required for its flight like a camera .

4.3. Attitude

This is the orientation of UAV, whether its tilting forward or flying upside down. Includes Pitch, roll and Yaw. 

4.4. Pitch

It represents the orientation of UAVs in association with Roll and Yaw.. Pitch says wheher the UAV is tilted up or down. 

4.5. Roll

It represents the orientation of UAVs in association with Pitch and Yaw. Roll is when you twist the drone as if you intend to twist it all the way around its control axis. 

4.6. Yaw 

It represents the orientation of UAVs in association with Pitch and Roll. Yaw is when the drone is turning slightly left or right. 

4.7. Gyroscope 

It detects the whether the flying is at level .

4.8. Gimbal 

The type of mount that lets a camera stay steady on a UAV while turning and when in high wind .

5. Advantages of Drones

• Images of any area can be obtained at any time / season / date. 

• By virtue of their small size and easy operation, drones are cheaper and more efficient than manned aircrafts             or   satellite imaging.  

• They provide cheaper imaging, greater precision and Drone cameras can take centimetre-level images.

• Earlier detection of problems is possible. 

6.What does Drones do? 

Drones in agriculture are simply a low-cost aerial camera platform, equipped with an autopilot using GPS and sensors for collecting relevant data, like a regular point-and-shoot camera for visible images. While a regular camera can provide some information about plant growth, coverage and other things, a multi-spectral sensor expands the utility of the technique and unleashes its full potential. It allows you to see things which you cannot see in the visible spectrum, such as moisture content in the soil, plant health, stress levels and fruits. 

The basic principle of NDVI relies on leaves reflecting a lot of light in the near-infrared, in stark contrast to most non-plant objects. Leaves are green in colour due to the presence of a pigment called chlorophyll, which strongly absorbs almost all non-green light from the visible spectrum of sunlight and reflects mostly green light back to our eyes. Live green plants absorb solar radiation in the photosynthetically active region (PAR) and leaf cells re-emit the solar radiation in the near-infrared spectral region. Thus, a healthy plant appears dark in PAR and bright in near infrared. 

On the other hand, in an unhealthy or stressed plant, the leaves reflect less nearinfrared light even if its emissions in the visible spectrum remain unchanged. Tucker found that combining these two signals can help differentiate plants from non-plants and a healthy plant from a sickly plant. This work gave rise to indices like the NDVI, which is now used to assess plant health. 

With the advancement of technology, it is now relatively inexpensive to modify a consumer camera to collect infrared bands and to fly it aboard a small drone. The ground resolution of UAV imagery is more than one thousand times higher as the reflected radiation does not have to travel through the entire atmosphere to be collected, and the incident light is dramatically more varied. 

Using near-infrared, you can identify stress in a plant, ten days before it becomes visible to the eye. When a plant goes into stress, it’s either due to a water or fertilizer shortage, or because it’s being attacked by a pest. Photosynthetic activity decreases and that affects the chlorophyll. That’s what the near-infrared sensor can detect, but our human eye can’t see it until it’s more advanced. 

7. How does Drones work? 

To survey crop fields with a drone, you start by planning the flight path of the drone that will best cover the plot. Many of the latest agricultural drones come with flight-planning software that let you outline a box around the field you want to survey on Google Maps. The flight plan is then automatically computed. The drone then flies over the field in a pattern while taking pictures with one or more cameras with special light sensors. These pictures are geo-tagged and overlap each other. 

After landing, special software is used to stitch together the geotagged photos into a large mosaic and processed to interpret the amount of light that is reflected in different wavelengths. Processing this data makes areas of poor growth or stressed plants easy to identify. Generating this data immediately and quickly opens to doors to better interventions and decision-making. The last step in this process is reviewing and taking remedial action. Prescriptive software packages also come up with comprehensive recommendations based on the field survey but these are not completely reliable yet. 

Processing images is the most challenging part of any drone-based agricultural operation. Here, downstream software packages use the high-resolution images and data from the different sensors on a drone to generate a meaningful and insightful image. Most agricultural drone operators use a tool like Pix4D or Correlator3D to turn these aerial images into useful data. Some others use proprietary software packages custom-built for their devices. The challenge however is that, being computation intensive, they rely on cloud services that are not always available in agricultural areas, especially in the context of emerging economies like India.

While some other general-purpose programs (like Pix4D) are available, they involve a steep learning curve. In developed economies of the west, companies also provide only a back-end processing service that will analyse the data once uploaded and generate reports for you. Other smaller start-ups have developed their own sensors, software packages and extensive back-end analytics support that can be used with any UAV. 

Some of this software is also built to avoid reliance on cloud-computing; all analytics can be performed on a local computer once downloaded and set up. Some companies, like Slantrange, have also developed core intellectual property enabling the identification of weeds from crop plants using multi-parametric image analysis. This further extends the capabilities of drone-based agriculture systems. 

8. Challenges of Drone usage  

• Outdoor use is highly weather dependent  

• Imaging can vary depending on sunlight and cloud cover although one can account for ambient lighting conditions

• Limited internet access and cellular infrastructure can make it harder to rely on cloud-based computing services

• Higher costs especially for small landholders in emerging economies  

• Limited flight times 

• Maintenance costs and resources

• The need for skilled operators  

• Uncertain government regulation that need to be overcome before this technology can be widely applied. 

9. Application of Drones in Agriculture 

 The following are some of the applications of Drones in agriculture and in its allied fields: 

1.  Water stress detection.  

2.  Estimation of nitrogen level. 

3.  Pathogen detection.  

4. Aerobiological sampling.

5.   Plant health monitoring. 

6.   Mapping invasive weeds. 

7.   Monitoring herbicide applications 

8.  Forest fire monitoring 

9.  Monitoring biodiversity in forests

10.   Assessing erosion in agricultural fields