Using Satellite Imagery to Guide Natural Disaster Recovery: A Multi-agency Effort to Map Tornado Damage After Chattanooga Tornadoes

On the night of Easter Sunday, April 12, 2020, multiple tornadoes swept through the Tennessee Valley, including parts of both Tennessee and Georgia, according to the National Weather Service. One caused significant destruction in southeast Hamilton County’s communities.

Through a community support partnership with the City of Chattanooga, Hamilton County, the University of Tennessee at Chattanooga’s IGTLab, and the Lyndhurst Foundation, Skytec created a mapping application and tornado impact index to guide agencies clearing roads, providing relief, and restoring power. Beneficiaries of these apps and data services included the City of Chattanooga and Hamilton County governments, local non-profit organizations, and Chattanooga’s Electric Power Board (EPB).

Moving Quickly to Address a Need

The tornado destruction was widespread — and locally in Chattanooga, where Skytec is based, East Ridge, East Brainerd, and Collegedale neighborhoods experienced mass devastation. Estimates reported by the Times Free Press indicate an EF3 tornado with estimated wind speed of up to 145mph traveled 14.5 miles from southeast Chattanooga to Ooltewah. According to Skytec data, more than 5,000 acres were impacted.

By utilizing its dynamic suite of data acquisition technology and through its partnership with the University of Tennessee at Chattanooga’s Interdisciplinary Geospatial Technology lab, (IGTLab), Skytec was poised to track the damaged areas and to measure the area in need of relief with precision and accuracy through its tornado impact index. EPB, the city’s power utility, faced a challenge to restore power to upwards of 60,000 customers. Faced with navigating downed trees and structural damage, EPB deployed 1,400 workers to repair power and internet services (according to the TFP), which required constructing hundreds of new utility poles and restringing 56 miles of new power lines.

Within days of the storm, the Skytec team moved quickly to build an application to provide crucial data to utilities like EPB, the City of Chattanooga’s Department of Transportation (CDOT), Hamilton County GIS, and the City of Chattanooga Public Works. The result was a tool that these agencies incorporated directly into their systems to make more informed decisions for preliminary cleanup and recovery work.

An Interdisciplinary, Public-Private Partnership

Skytec reached out to UTC’s IGTLab, who received funding from the Lyndhurst Foundation to acquire satellite imagery from Planet within a few days of the storm. Planet uses its more than 150 satellites to capture images of the entire planet at least daily.

“Using images sourced from Planet, we worked with the IGTlab to create an application, as well as an image service underneath the hood of the application, that our community partners could access through the app to connect to their systems,” says Andy Carroll, CTO of Skytec. “We used change detection, using images before and after the tornado, and created specialized indices based on light reflection patterns that show vegetation and canopy to define the tornado and the extent of the damage.”

The team calculated more than 5,000 acres were impacted by the storm. While many structures were affected, the tool was specifically calibrated to identify damaged trees and vegetation to best guide utilities and road crews through the decision-making process to most quickly clear debris and safely restore power to customers.

According to Matthew Snyder, Engineering Manager for the Chattanooga Department of Transportation (CDOT), the imagery helped inform asset management by providing a definitive impact area for evaluations to take place.

“First and foremost, after a disaster of this magnitude is Public Works’ cleanup of debris and evaluation for disaster declaration,” Snyder says. That clears the way for FEMA and state services to make initial assessments and estimates for relief eligibility. Snyder used the assessment to identify and map proposed FEMA-funded repairs for CDOT.

Ongoing Studies and Unexpected Outcomes

As part of the ongoing data acquisition process for the area of Chattanooga affected by the April 12 tornado, and because of the partnership with community supporters, Skytec will track the area’s recovery process through monthly satellite images, which will be updated in the application, for the next year. That data, housed at UTC’s IGTLab, can be used by involved partners to evaluate everything from built infrastructure to natural resource recovery.

“This was a first for us to use Planet data to make this type of tool,” Carroll says. “Tools like this were made possible through community support — which covered the Planet images — as well as UTC and the Skytec team, who provided our services and time in-kind.”

The project also resulted in uses the team didn’t anticipate. green|spaces, a Chattanooga nonprofit supporting sustainability efforts, and the City of Chattanooga Forestry and Water Quality departments were able to use the data to prioritize the most impacted areas for tree restoration. Together, the agencies are seeking state agriculture funding to replant in the affected areas with a particular focus around streams and riparian buffers, or stream buffers.

“The City of Chattanooga Water Quality and Forestry departments, in partnership with green|spaces Chattanooga, were able to utilize the data analysis provided by Skytec to analyze the most suitable property for applying for a Tennessee Department of Agriculture, Division of Forestry grant for urban tree planting,” says Ongeleigh Underwood, a grant writer who works with green|spaces. “The grant specifically encourages restoring riparian buffers, so the tornado impact index was used to compare city-owned land parcels in the tornado path for damage of tree canopy from NDVI [normalized difference vegetation index] analysis and proximity to streams within the South Chickamauga Creek watershed.”

While much of tornado impact assessment focuses on structures, Carroll says this tool analyzes data to potentially restore the forest and important ecological systems.

“This data provides us with detailed information on change of tree canopy and overall forest health,” Underwood says. “With initial estimates of more than 5,000 acres of damage, we will look and approach properties and businesses with the possibility of a community-based replanting effort as part of a larger program currently in development with nonprofit and public partners.”

Satellite Images: A Tool for the Future

The use of satellite images for tracking and recovery is particularly relevant as cities and related agencies face the long-term effects of climate change. The increasing global surface temperatures lead to the possibility of increased intensity of storms, like hurricanes and tornadoes, and droughts, according to the U.S. Geological Survey. These storms, like the Easter Sunday tornados, have the potential to cause additional damage in the future.

Just as Skytec’s community support efforts tracked the damage and recovery process from the April 2020 tornado, satellite imaging could be used as a baseline tool, almost like a diagnostic map, before storms or natural disasters occur.

“Scientists and meteorologists are predicting an active hurricane season this year as active as 2005, which brought us three hurricanes in the gulf,” Carroll says. “This technology didn’t exist then. These types of diagnostic reports can help teams on the ground be more effective and efficient in their recovery and cleanup efforts.”

Read more about Skytec’s Planet partnership, acquisition services, and success stories on our blog.