Every three years or so, a small plane flies over Louisville firing laser beams at the city.

This isn’t the premise of a new science-fiction novel or an alien attack blockbuster. It’s a high-tech way of mapping the city’s terrain and built environment, and it may provide the road map to beating one of the city’s most pressing environmental problems: the urban heat island.

Meet LiDAR, which stands for Light Detection and Ranging.

Every few years, the Louisville/Jefferson County Information Consortium (LOJIC) commissions a flight, and a plane flies at a low altitude over Jefferson, Bullitt and Oldham counties. There’s a very sophisticated sensor and low-powered laser pulse mounted under the plane, and during the flight, the apparatus fires low-powered laser pulses at the ground. The pulses bounce back, and the sensor stores the information.

“The best way I can describe it is, if you can imagine every meter on the ground, there is a very accurate point location with an associated elevation,” said LOJIC director Curt Bynum.

The result is a sea of dots, each containing information that tells analysts whether there’s a tree, water, bare earth or a building in that particular location. And through it, there’s the potential to create a very accurate 3-D map of the city which can show, among other things, the rooftops and parking lots that get the most sun throughout the day.

Courtesy LOJIC

Where’s The Sun?

Louisville already has accurate LiDAR data — LOJIC analysts will be getting the information from this spring’s flight soon — and thus far, it’s been used in various ways. It helps inform terrain maps, and helps agencies like MSD map floodplains.

But last year, at a conference, Bynum met a Canadian professor who was working on another use for LiDAR data: using these laser data points to determine the solar potential of rooftops around the city.

While a professor at Penn State, Kirby Calvert advised a PhD project that used LiDAR data to look at Philadelphia’s solar potential. Now, he’s a geography professor at the University of Guelph, in Ontario, Canada. And Calvert mentioned at this conference that he had some undergraduate students who were looking for a capstone project using real-world data.

“I said, you know, we have all this data,” Bynum said. “We’d love to give it to you and let your students explore it, play with it.”

So, that’s what happened. A team of Guelph students — Mia Kilborn, Marissa Skinner and Ennoyaq Sudlovenick — spent their spring semester analyzing LiDAR data from two areas of Louisville. One of the areas was several blocks of downtown, and the other was in far northeastern Jefferson County. The students used the data to determine the slopes of roofs in the study areas and which direction the roofs were oriented, and concluded 30 percent of the suburban roofs and 9.7 percent of the downtown roofs were good candidates for solar panels.

“Depending on how the tool is set up, you could select only those rooftops which were totally exposed to the sunlight from sunrise to sunset,” Calvert said. “Alternatively, you could ask the system to show only those rooftops which are facing west — exposed to sunlight later in the day.”

This level of data could have huge implications for Louisville’s efforts to increase solar energy. The Louisville Sustainability Council’s Solar Over Louisville project has a goal of installing an additional two megawatts of new solar capacity in the city by the end of this year. Coordinator Paul Brooks said a map like this could help his group make the case.

“We’re always trying to convince folks that solar is a good option for them, not only environmentally but economically as well,” he said. “To have that evidence, that says wow, your commercial building or even your home is ripe, gives you more assurance that you’re not only doing the right thing, but that your return is the best it can be. That would just be great and should help some folks who are thinking about it to go ahead and decide.”

Courtesy LOJIC

Other cities have harnessed the data into user-friendly portals. The site Mapdwell lets residents of several large cities search rooftops and see the solar potential — as well as how much it will cost to install and how long it will take to pay off a solar installation.

This has a few potential implications for a city like Louisville. Anyone who’s really interested in installing solar panels will likely call an engineer to try to determine the feasibility of the project. But for others who are on the fence, a simple online tool that estimates a roof’s solar potential may provide enough impetus to take the next step in installing a system.

The data could also help city planners trying to decide where photovoltaic panels would make the most sense. If — and this is a big if — the city ever decides to start subsidizing solar installations on homes or businesses, LiDAR data could help officials determine which buildings have the greatest solar potential. The buildings with the greatest potential will produce the most energy and would be the best use of public funds.

Beating The Heat

LiDAR data is already being used in other cities to estimate solar potential, but there’s another untapped use that may prove especially valuable for Louisville. The same information that proves valuable for solar siting could tell officials which buildings and parking lots in Louisville are absorbing the most heat.

“Any process, any decision that requires you to have a better understanding of urban morphology, urban terrain, would benefit from access to high-quality LiDAR data,” Calvert said.

Courtesy LOJIC

Last month, the city got a look at a long-awaited study of Louisville’s urban heat island. The heat island is the difference in temperatures between the city’s urban core and outlying rural areas. In the summer, the difference is an average of five degrees, due to factors like a shrinking urban tree canopy and an abundance of hot, black roofs and paved parking lots.

The report by Brian Stone of Georgia Tech lays out neighborhood-level solutions to help cool the city. It recommends planting 2,202 trees in Germantown, for example, and converting three dark roofs to green roofs.

But Stone didn’t use the LiDAR data in his report, and combining the information could help Louisville officials further hone the city’s approach to tackling the urban heat island.

Sure, why not, Calvert said.

“You could identify those hottest areas based on hours exposed to sunlight and then compare what things would look like if you developed a solar system versus a green roof,” he said. “Maybe that’s a decision you want to make. And the panels will actually strip some of that energy and cool the area down a little bit, because some of the energy is being absorbed by the photovoltaic panel and converted to electricity.”

Stone’s report set goals for Louisville’s neighborhoods to beat the urban heat, but the LiDAR data could take it a step further and show the city which specific roofs, streets and parking lots they should be pursuing.

And this targeted, data-driven decision-making is exactly what Louisville Mayor Greg Fischer has been advocating during his five years in office.

For more on Louisville’s urban heat island, tune in Monday at 1 p.m. for an hour-long news special on 89.3 WFPL News.