City Trees is a premier publication focused on urban + community forestry. In each issue, you’ll learn how to best manage the trees in your community and more!
Issue link: https://read.dmtmag.com/i/765222
minimal cost to delay (or move up) a UAV mission as well. UAVs can fly closer to the ground than piloted aircraft, result- ing in better image resolution—a key benefit when accuracy is essential. Typical sensor imagery from a UAV flying at 100 meters (330 feet) above ground level (AGL) is from 3-5 centi- meters (1.5-3 inches) per pixel side at ground level (the "Ground Sample Distance" or GSD)—smaller than many deciduous tree leaves. A typical manned aircraft image taken from 450 meter (1500 feet) AGL typically has a GSD of about 6-20 centimeters (2.5–8 inches) per pixel 5 . High-quality satellite imagery typically has a GSD resolution of 30-50 centimeters (12-20 inches), considerably larger than a typical deciduous leaf. What Data Can Be Collected with a UAV? The miniaturization of everything is driving the decreasing size, weight, and cost of sensors, making sophisticated sensors increasingly available to more users as prices fall. The most common sensor types carried by UAVs are visual, thermal infra- red, multispectral, hyperspectral, and LiDAR. Visual sensors—including video—are by far the most common payload carried by UAVs. Most quality UAV models come equipped with high-definition visual sensors. The real estate, construction, film, and infrastructure inspection industries are the main users of UAV visual imagery. Urban foresters and arborists likely will use visual imagery for most operations. Current standard visual sensors capture high-definition 4K images at 16 MB per image, with video at 1080p and frame rates at 30-60 frames per second. Thermal infrared (IR) sensors carried on UAVs are most common- ly used for infrastructure inspection—tiny cracks in wind turbine blades and faulty cells in photovoltaic panels are easily seen in the infrared. The United States Golf Association has started Plants utilize more of certain wavelengths of light. Courtesy Dan Staley Why collect data in visual and non-visual EM spec- tra? Calculating the amount of leaf reflectance both in and outside the visual spectrum allows for analyses using a Vegetation Index (VI)—a mathematical analysis of EM spectral bands to highlight and visualize certain features of plants. For example, general health, photosynthetic activity, vigor, water stress, overall biomass, and leaf senescence can be determined using the proper VI. The most commonly used VI in agriculture and environmental management is the Normalized Difference Vegetation Index (NDVI). Plant spe- cies often can be determined by their reflectance in specific wavelengths if the image resolution is sufficient. 20 City Trees 10 10