Rapid Debris Estimation after Hurricane Damage in Urban Areas Using High Resolution Aerial Imagery

Recent hurricanes have severely impacted communities in the southeast Gulf and Atlantic coasts. As part of each state’s response to natural disasters that affect urban areas, there is a need to support local governments with timely information on the extent and location of damage. Identifying post-hurricane downed trees by remote sensing is difficult in forests because they can be hidden by standing tree canopies. Urban trees are usually open-grown and adjacent to buildings, infrastructure and other vegetation, thus making it easier to distinguish them post-hurricane. We developed an assessment tool to estimate downed tree debris in hurricane affected urban areas based on Leica Airborne Digital Sensor (ADS40) very high resolution digital images. A Sobel edge detection algorithm was combined with spectral information based on color filtering with 15 different statistical combinations of RGB bands to detect downed trees. The Sobel method identifies downed tree edges based on contrasts between downed tree stems and grass or asphalt. Color filtering was then used to establish a threshold value where every color above or below a certain value was replaced and excluded from the identification processes. The results of the methods were overlaid and where lines (edges) from longer consecutive segments and color values within the threshold were met; an “edge line” was placed. Where two lines were paired within a very short distance in the scene a polygon was drawn automatically and, in doing so, downed tree stems were detected. The developed algorithm successfully detected downed trees and determined their diameter. Diameter data was then used to estimate volumes of posthurricane downed tree debris.