With the spectral signature for water as their focus, the research team compared satellite imagery before and after the dates of floods reported by the Reidsville community, and found that after reported flood events, the contribution of water to particular pixels increased considerably. “There are different spectral bands that you can get from the satellite data,” Tiwari explains, “like RGB––red, green, blue, which we can see––and NIR, near-infrared, which we cannot see.” Vegetation, urban development and water are characterized by distinct spectral signatures, and “you can have different spectral signatures in different proportions in a pixel.” So, the research team tested different methods that could reveal changes in the proportion of water before and after reported flood events, based on the kind and amount of light reflected or absorbed in individual pixels. “Shadows from clouds, trees and buildings can also look like water in satellite imagery,” adds Gaines, making flood delineation with visual imagery tricky. “Even three-meter resolution isn’t enough to capture flooding in someone’s yard.” student Varun Tiwari, also a member of Tulbure’s lab. “When you’re using satellite imagery to find flooding in the backyards and front yards of people’s homes, resolution is a problem,” explains Geospatial Analytics Ph.D. “As the team of remote sensing scientists for this project, our goal was to determine how we could best use satellite imagery to validate the lived experiences of rainy day flooding reported by the residents of Reidsville and Collins, Georgia.” Spotting a flood from space is not as straightforward as it may seem. candidate Mollie Gaines, one of Tulbure’s advisees. Jackie had already collected data on whose properties flooded and the days that there was rain,” explains Geospatial Analytics Ph.D. Over the past year, she worked with a research team led by faculty fellow Mirela Tulbure at NC State’s Center for Geospatial Analytics, to corroborate Reidsville residents’ observations using remote sensing. To secure the extra evidence she needed to prompt flood control action in her community, Jones turned to the American Geophysical Union’s Thriving Earth Exchange, which finds scientists to partner with community groups. Yet, when she brought her concerns to the local city council, her observations were dismissed. In Reidsville, Georgia, one of the nondisclosure states, homeowner Jackie Jones learned only after purchasing her house that heavy rainfall meant substantial and costly flooding––and not only of her property but many others’ nearby. To make matters worse, 21 states lack flood disclosure laws, which require home sellers to notify prospective buyers about past flood damage. Across the United States, flood risk is underestimated, and many people experience frequent flooding despite living outside of the 100-year floodplain designated by the Federal Emergency Management Agency.
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