With an airborne camera capable of making precise and detailed ecological observations, biologists at Applied Ecological Services (Brodhead, WI) are bringing satellite imagery closer to earth.
After years of using satellite imagery for larger landscape-scale applications, AES has acquired a new high-resolution multispectral camera for imaging and mapping ecological projects. Instead of using a high-flying fast plane with a large format camera, AES and its partner Ayres & Associates (Madison, WI) have opted for a plane that flies low and slow over the ground, even beneath cloud cover, to obtain ecologically relevant imagery.
For AES, the timing of imagery to capture data on dynamic ecological processes is important. So is the flexibility to capture imagery on an as-needed basis — for example, when deciduous trees have lost their leaves but invasive, exotic common buckthorn is still dark green. Flexibility is often difficult for other aerial photography vendors who are more accustomed to imaging for engineering or infrastructure purposes that are not as sensitive to timing issues.
The Leica RCD30 camera acquires imagery as resolved as 2-inch, on-ground pixel size because of its fast shutter and AES’ slow-flying plane (see Figure 1). The digital mapping camera offers four spectral bands (red, green, blue, and infrared) that are capable of achieving engineer- standard mapping accuracy specifications in association with both vertical and horizontal measures.
Using the Infrared Band
The infrared band enables specific applications associated with the study of vegetation, and it offers a unique look at the “greenness” or “productivity” of vegetation. The infrared band is receptive to capturing reflectance associated with the amount and type of chlorophyll A or B pigments present in the tissue or cells of plants. This sensitivity, associated with detecting chlorophyll in vegetation, gives scientists at AES a unique understanding of ecological interactions that might otherwise go undetected (see Figure 2).
Plant productivity is a measure of the condition, vigor, moisture, and health of a plant. Identifying where and how that productive plant tissue is distributed on the landscape can be used to measure ecosystem conditions, including crop productivity, biomass volumes, detection and measurement of pest or disease impacts, and the mapping of vegetation community types. In some cases, it is also used to identify and map specific plant species including various grasses, sedges, forbs, or trees, as well as different aquatic patterns associated with algae growth.
After aerial images are collected, they are typically brought into high-powered software programs designed to seamlessly “mosaick” multiple images into a single image or set of image tiles that cover the entire area of interest. During this process, imagery is ortho-rectified, which is a method that adjusts the imagery to account for the topographic relief of the landscape. In addition, imagery is color balanced and histograms are normalized, which is critical for spectral analysis and remote sensing applications.
Once the imagery has been processed, it becomes an ecological tool for a team of trained remote-sensing and ecological professionals. By combining the understanding of advanced mathematics, statistics, and computer science with ecological expertise and in-depth knowledge in vegetation seasonality, senesence, and phenology, AES discovers spatial patterns that become the blueprints to understanding landscape change. Features are mapped using variables such as texture, size, shape, and reflectance. Analysis of imaged features offers spatial solutions to complex ecological trends, and informs critical decisions associated with landscape restoration.
Mapping an Invasive Shrub
One recent AES project involved the mapping of a woody invasive shrub, bush honeysuckle, which has colonized large forested areas of southern Illinois. The mapping of this 100-square-mile area, which includes Shawnee National Forest, was initiated with the (strategically timed) aerial flight, followed by on-theground work by AES ecologists. Ecologists took measurements of plant conditions, and then used survey-quality GPS-location to find dozens of the individual honeysuckle shrubs.
The plants measured on the ground were used to create a statistical “spectral signature” to “train” the GIS software to recognize the plant on the imagery. Refinement and further calibration produced maps with very high reliability that precisely showed the distribution of honeysuckle plants, distinguished from other desirable shrubs found across the entire project area, which was more than a million acres. AES was able to give private landowners and public land management agency staff precise maps, and the coordinates of each of the tens of thousands of individual invasive plants, so they could go to each plant and remove it as a part of an eradication program.
The imaging produced by AES is not impaired by cloud cover and lower light conditions as with higher flying planes and satellites, whose operations are shut down as cloud cover develops. The technology also obtains very precise infrared and color bands that are all geo-referenced, supporting a new type of analysis not previously available to ecologists.
The Benefits of “Band-Splitting”
Most multiple-band cameras have a separate lens for each band, which does not support the creation of precise, registered, and easily normalized imagery. With the Leica RCD30, all bands are obtained through one lens and register on aligned photo-receptors. This band-splitting technology reduces the down-time and maintenance required to calibrate and match multiple lenses in alignment, and also allows for shooting under lower light conditions.
The AES/Ayres camera is mounted to the underside of a Cessna Turbo 206, a single-engine workhorse capable of flight speeds of 130 knots, and as slow as 50-60 knots. On a normal, sunny day, it can shoot several million acres. Data is stored on portable hard drives, which are removed from the plane upon landing and “over-nighted” or sent via file transfer protocol (FTP) sites to image processing offices.
The camera technology has many land-based applications. By mapping water quality impairments in lakes and rivers, it is possible to identify the need for sediment management such as dredging, at least in higher clarity waterways. Mapping nuisance algae and even invasive aquatic plants is easily accomplished. Mapping agricultural crop failures as well, such as those that occurred during the summer drought of 2012, has been effective. Also, the imagery is valuable for early detection of tree diseases, such as Emerald ash borer, which helps to determine the need for and cost of urban street tree management.
In addition to ecological projects, the firm has recently found a new use for the technology. This fall, AES flew over a small Midwestern airport to produce precise maps of the conditions of the surface of the runway pavements. By mapping the development of cracks in runways, AES can help airport facility managers prioritize their maintenance program to design safe runway surfaces. The company is also currently exploring similar applications for highway or bridge maintenance.
This article was written by Steven I. Apfelbaum, principal ecologist and founder of Applied Ecological Services. For more information, Click Here