In Spain, a water company used drone imagery and a geographic information system (GIS) to calculate dam volume with much greater precision and five to 10 times less expensively than other surveying methods. Now that the Federal Aviation Administration (FAA) has loosened commercial drone regulations, U.S. water utilities are exploring how drones can help them do the same.
In late 2016, the South Florida Water Management District (SFWMD) and Florida Atlantic University in Boca Raton performed two proof-of-concept missions: one to see if volumetric calculations can be made on a reservoir and one to evaluate how a proposed reservoir would affect bat habitat. Their results support Spain's finding that drones and GIS are a less expensive and faster way to collect and analyze high-resolution imagery.
A memo of understanding gives the district free access to the Geoscience Department’s Trimble UX5, a 5.5-pound drone with 24-megapixel camera. Unlike a quadcopter that hovers up and down and is thus better for inspecting vertical assets like water towers, the UX5 is a fixed-wing model that looks like an airplane. It must be catapulted into flight but captures extremely high-resolution images at 50 miles an hour, perfect for quickly surveying large expanses. The university collects images the district uses to produce extremely detailed, highly accurate surface models, point clouds, mosaic images, and other two- and three-dimension visuals.
The first mission concerned the district’s L-8 reservoir, a 950-acre former rock mine that stores excess water from a nearby basin so homes and businesses won’t be flooded. Managers must know volume level so they can manage discharge limits, which affect water quality.
To begin, the team members set control points on the levees around the reservoir by using T-shaped markers for ground points for aligning images during image processing. Next, they programmed the drone’s flight path to ensure even coverage and its 24-megapixel camera with red, green, and blue (RGB) colors to capture one photo per second.
The weather was clear and not too windy when the pilot launched the drone from its catapult. Although the UX5 has the battery life to fly 50 minutes, the team limited flights to 40 minutes to 42 minutes at a lower speed. They kept the drone in sight so it wouldn't get away from them. Automatically following the preprogrammed flight path, the drone flew back and forth in a lawnmower pattern over the reservoir. It overlapped its pattern by 80% while the camera snapped photos continuously. Four flights captured 5,200 images.
Using Drone2Map’s “rapid” mode on sample data, the team verified the coverage and imagery quality while they were in the field, where they could spot problems and make corrections on-site. Esri’s Drone2Map for ArcGIS is a desktop application that turns raw, still imagery into orthorectified mosaics, terrain models, point clouds, 3D meshes, and other products as quickly and cleanly as possible. It’s designed to be used by people who aren’t necessarily seasoned GIS professionals or have a background in remote sensing, so many workflows are imbedded in the application. The product’s not for flight planning or to control the drone, but to process the images into products that can be immediately used in ArcGIS.
A real-time viewer allowed them to track the drone's location and ensure it was hitting its marks. The pilot found a smooth surface to land the drone on its belly.
Upon returning to the office, the team switched the application to “standard” mode and used its full processing power to create high-resolution images. The software automatically overlapped the imagery, aligned the ground points, and stitched them into mosaics.
Next, GIS generated 2D and 3D mosaic imagery. The team used the orthomosaic images as basemaps for depicting detailed spatial features on the ground and visually examining the surface. GIS displayed 3D point clouds and created digital surface models that helped the analyst assess natural features, such as sediment, and built features.
The university team used the data to simulate changes in reservoir water levels and then estimated volume.
The SFWMD study team integrated Esri ArcGIS with Blue Marble Geographics' Global Mapper to simulate water level rise and fall in a 3D representation of the reservoir. This approach will help district managers instantly see and understand water flow and make decisions grounded in science.
The second mission was to determine how a proposed reservoir would affect bat habitat. Much of the 15,000-acre site is virtually impassable, with collapsed culverts, vehicle-sized voids, agricultural debris, and aggressive bees. Without a drone, biologists would have required several weeks to gather necessary information.
Next, the district will use drone data to measure submerged aquatic vegetation (SAV) and emergent aquatic vegetation (EAV) over a stormwater treatment area.
These are a few applications that help water utilities better understand their systems. Drone mapping technology offers other water-management applications such as detecting change over time, displaying line of sight, and depicting water flow obstructions.
