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Using Drones in Agriculture

Drones are fast become a ubiquitous platform for a number of services. They can be used to carry small payloads between retailers and customers, used in fishing to drop bait, there is even an under water drone, however, the most popular use of a drones by far is as a platform that can carry a camera. Originally these cameras, usually a GoPro, were attached to some form of crude gimbal but the results were reasonably impressive. The very fact that you were able to take a camera airborne opened up a whole new level of freedom and perspectives in photography.
Satellites have been with us since 1957 and they became platforms that carried amongst other things cameras or sensors to assist in weather forecasting and for the first time giving scientists the ability to map the earth's vegetation through the use of a multispectral camera. You may have heard of Landsat and the images that it produced, however, as good as they were
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Landsat 1 Image

Landsat 8 NDVI Image

the images suffered from resolution issues with resolutions as high as 30m. This was okay for a macro view of the earth's vegetation but was not useful to pinpoint problem areas on individual farms.
Moving ahead some 50 years from Landsat 1 there have been advances in drone technology and reliability. In parallel to these advances multispectral cameras have become less expensive and smaller to such an extent that a drone can carry up to three cameras on an aircraft that weighs less than 2kg. We use these drones to conduct photogrammetry flights and collect data and in turn this data is processed (stitched) to produce a 2D orthomosaic map of the field.
How Do Multispectral Cameras Work
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Our eyes can see a very small band of visible light in the electromagnetic spectrum. Cameras, in general, also operate within this narrow band, However, there are specialised cameras that can see beyond visible light, infrared cameras are a common example of this. The reason we see grass and leaves as green is because this plant matter absorbs red and blue light. You may be familiar with the term RED GREEN BLUE or RGB and know that is, for example, the primary colours that make up the light transmitters in televisions. All colours that a television emits is a combination of RGB pixels on the screen.
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All leaves contain chlorophyll which allows plants to absorb energy from light through photosynthesis. There is a direct correlation between chlorophyl and plant health. When chlorophyll breaks down either naturally, as in Autumn, or through poor nutrients or lack of water the reflectance value of the leaf changes. These changes may not be visible to the human eye however, a multispectral camera fitted with a sensor and filters capturing different wavelengths of light as dictated by the filters can detect minute changes before any real visible signs of plant stress is evident. As the image below indicates chlorophyll (leaves) absorbs more blue and red light extracting energy through photosynthesis and reflects more green (visible) light and much more NIR (invisible) light.
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We can use our knowledge of the electromagnetic spectrum and the reflectance value of leaves plus advances of multispectrum cameras to map out a field and determine how healthy or stressed the field is. This is achieved by using a drone to produce high resolution images from different and specific wavelengths or bands of light. This is a tool that can save farmers money in fertiliser, herbicide, etc costs by targeting only those areas that require treatment therefore, having the potential to increase yields and in turn profits.
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