UAS terminology
color-infrared [CIR] image — This is a false color photograph that shows the reflected electromagnetic waves (near infrared as red, green light as blue, and red light as green).
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Multispectral cameras separate and measure discrete wavelength of the electromagnetic spectrum. Multispectral cameras for UAS operations are either modified RGB cameras or multi-camera arrays. Aside from being able to measure wavelength beyond the visual spectrum, the value of multispectral images is in how the wavelength data is combined. True- color images can be reproduced using wavelengths corresponding to red, green and blue.
False color: Green is red
Another popular combination is false color, also called color infrared [CIR] images, created by combining near-infrared, red and green. Vegetation in CIR images appear red, due to vegetation’s high reflectance of near-infrared light. Canopy cover calculations using CIR images instead of RGB images have increased accuracy, due to the difficulty discerning shadowed leaves from shadows. Near-infrared and red wavelength data can be used to calculate the Normalized Difference Vegetation Index [NDVI]. NDVI is used as a visual representation of crop health and biomass. Multispectral information can be used to determine real-time crop coefficients for estimating water use.
Thermal cameras are used to measure canopy temperature, which is an indicator of crop water status. UAS-mounted thermal cameras can also be set up to return live-feed video, which can be helpful in locating irrigation leaks in buried drip lines.
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for the Water Management and Systems Research Unit at the U.S. Department of Agriculture, Agriculture Research Service, Center for
Agricultural Resources Research facility in Fort Collins, Colorado.
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With different combinations of spectral information from the visible, near-infrared and thermal bands of UAS imagery and ground meteorological data, spatially distributed evapotranspiration can be estimated by energy balance models.
In recent years, sensors or cameras for UAS platforms have not only become cheaper, lighter and more readily available, but camera packages combining multiple sensors (such as combined thermal and RGB cameras) have become available. Modular mounted sensors on some UAS platforms allow for quick payload changes allowing for the system to be customized to match the current needs as they arise.
With the low barriers for entry and highly customizable systems, we expect UAS- based remote sensing to become a simple and promising tool to acquire spatial information within fields and assist with decision-making.
electromagnetic energy — This is a form of energy that is reflected or emitted from objects in the form of electromagnetic waves that travel through a space. Electromagnetic waves are further characterized by either the frequency of oscillations or by wavelength. Infrared radiation and visible light are examples of subcategories of the electromagnetic spectrum.
infrared radiation — Electromagnetic waves categorized as infrared radiation have wavelengths that are longer than those in the visible spectrum and are invisible to the naked eye; however, they can be sensed as heat. Infrared radiation is the region of the electromagnetic spectrum that is characterized by wavelengths between 700 nanometers and 1 millimeter. Objects with temperatures above absolute zero emit infrared radiation.
multispectral camera — This is a device that forms images using both the visible light and infrared radiation. This type of remote sensing is valuable to a grower in that it can identify areas where water stress is suspected.
near-infrared electromagnetic region — This is a subcategory of the infrared radiation region of the electromagnetic spectrum found at the upper edge of the visible light spectrum and the lower end of the infrared radiation spectrum.
orthomosaic image — This is a series of individual aerial photos that are matched up to form a new composite image.
thermal camera — This is a device that forms an image using infrared radiation, as opposed to a common camera that forms an image using visible light. Images from a thermal camera can be calibrated such that each pixel in the image gives a temperature reading.
rectified images — These are images that are transformed to remove lens distortion and make the image appear as if it were taken directly above the subject. Rectified images look like the background of a plan view in an architectural or engineering drawing.
thermal infrared electromagnetic region — This is a subcategory of the infrared radiation region of the electromagnetic spectrum found at the upper-middle end of the infrared radiation spectrum. Objects at normal environmental temperatures will emit infrared radiation with wavelengths in this region.
Kevin Yemoto (pilot in command – PIC) and Joe Miller (pilot at controls – PAC) collect multispectral and thermal images over a sorghum field at the Limited Irrigation Research Farm.
Kevin Yemoto is an engineer technician and certified UAS pilot for the Water Management and Systems Research Unit at the U.S. Department of Agriculture, Agriculture Research Service, Center for Agricultural Resources Research facility in Fort Collins, Colorado.
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Photo credit: Huihui Zhang, PhD
Photo credit: Scott Reid
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