Day and Night Satellite Coverage Helps Better Track Flooding for Damage Assessment, Recovery Efforts

A pair of researchers from the Hebrew University of Jerusalem and the University of Queensland have authored a paper detailing how optical imaging and radar data from satellites can be used to peer through the clouds and provide more rapid information in the event of floods.

"Monitoring floods in towns and cities is challenging, with flood waters often rising and then receding in a few days," explains Noam Levin, a professor at the University of Queensland's School of Earth and Environmental Sciences, of the problem the paper attempts to solve. "While large satellites in the past provided images every 7-14 days, now groups of small satellites can collect several images a day over the same location. Radar imaging sensors can provide images at night or on days with thick cloud cover — a huge advantage in stormy conditions. They use a flash, like on a camera, and the light is sent at wavelengths between 1mm and 1.0m, which can pass through clouds and smoke."

To prove the concept, the researchers used a combination of optical satellite imagery of Brisbane's flooding in February this year taken during the day and night-time captures from radar-based satellites as well as optical satellites capable of capturing city lights — using PlanetScope, Capella-Space, and NASA VIIRS satellite data to broaden the coverage. "We could see which areas became dark as the flood waters encroached," Levin explains. "We matched this with data from river gauges operated by the Bureau of Meteorology, and with changes in electricity loads reported by Energex, the power supplier."

"Altogether we demonstrate that using a variety of optical and radar sensors, as well as nighttime and daytime sensors, enable us to overcome data gaps and better understand the impact of flood events," the researchers conclude. "We also emphasize the importance of high temporal revisit times (at least twice daily) to more accurately monitor flood events."

"In combination with existing flood monitoring and modelling technologies, satellites could change the way we monitor major flood events, understand how they occur, and direct emergency and other responses," adds Stuart Phinn, professor at the University of Queensland. "With faster update times – at least twice a day – and more accurate and timely data, agencies monitoring the floods can assess changes and alert people in at-risk areas. This technique can also be used post-disaster to assess the extent of damage, direct recovery efforts, and for the assessment of insurance claims."

The pair's work has been published under open-access terms in the journal Remote Sensing.