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
Depiction of the "Red Edge" on the reflectance spectrum of a typical leaf. Courtesy Dan Staley using thermal IR sensors on UAVs to study turfgrass health. Several manufacturers offer after-market IR sensors, with current typical costs ranging from about US$2,500-10,000. Multispectral sensors collect light in both the visual and near-infrared (NIR) electromagnetic (EM) spectra. The agricul- ture industry is by far the main user of multispectral imagery. Most multispectral sensor models collect four or five discrete, narrow bands of light per pixel; these bands coincide with wavelengths important to assess plant condition (Figure page 20). Most models collect one band each of red, green, and blue, plus one band in the NIR. Some models collect an extra band on the "red edge" 6 (Figure above). In 2016, a typical new multispectral sensor costs between about US$3,500-7,000. Hyperspectral sensors collect all wavelengths in the EM spec- trum between certain set values determined by the manufac- turer. For example, one sensor model may collect wavelengths between 400-1,100 nanometers (nm), another between 400- 2,500 nm. Each pixel in an image contains all wavelengths of light between the two set values. As a result, large amounts of data are contained in just one image. The sheer amount of data allows for a much more detailed analysis to be performed. Due to their current cost, hyperspectral sensors are not yet wide- spread and are mainly used by the mining and environmental monitoring industries. Currently, a typical new hyperspectral sensor for a UAV payload starts at about US$45,000 and can cost much more depending on additional features. LiDAR is a remote sensing platform that uses pulses of laser light to precisely measure surfaces or objects. LiDAR can—depend- ing upon how many points per unit area are collected—measure objects with accuracy measured in millimeters. LiDAR is used by the surveying, construction, energy, and infrastructure indus- tries and is becoming relatively more common as prices fall. Typical LiDAR sensors are still heavy enough (many are over 5kg/11 lbs) that specialized UAVs must be used to fly LiDAR missions, although weight is dropping rapidly. In 2016, a new LiDAR sensor for a UAV payload can start at about US$85,000 and can cost much more depending on weight, measurement accuracy, and other such features. How Can UAVs be Used in Municipal Forestry & Arboriculture? UAVs can be effectively used for a number of municipal forestry and arboriculture tasks, and it is important to know what type of work you are going to do with UAVs before making a decision to purchase equipment or hire a pilot to fly missions. It is also important to determine how you can share your data across departments for cost-sharing opportunities, or how to leverage the large amount of data you will collect but may not need, such as road surface or street furniture data. Rotor-wing UAVs are best used for smaller-scale projects, in strong wind, for hovering and close inspection of trees, or to set www.urban-forestry.com 21