New Remote Sensing-based Damage Scales Implemented For Katrina
Example of a WF-3 damage classification in New Orleans using the new wind and flood (WF) damage scale
In the aftermath of major disasters such as earthquakes, hurricanes and floods, urban damage assessment has traditionally been conducted through time-consuming in-field surveys. Recognizing the need for rapid post-disaster damage assessment across wide geographic areas, coupled with the problem of limited access to areas isolated by flood waters or blocked roads, MCEER Thrust Area 3 (Response and Recovery) researchers are developing a new generation of damage scales based on satellite and aerial images.
Hurricane Katrina saw the first operational implementation of a remote sensing-based wind damage scale for categorizing wind-pressure damage along the Mississippi coast and within New Orleans (see MCEER’s Hurricane Katrina Special Report on Remote Sensing).
The damage scale classifies a given building into one of four categories, ranging from destruction to no apparent damage. Each damage level is defined in terms of remote sensing characteristics observed from high-resolution optical imagery collected by satellites such as Quickbird or aerial systems operated by ImageCat or NOAA. These diagnostic descriptors relate to changes in roof characteristics and local patterns of debris. The categories are:
- RS-A (HAZUS level 0): None. No apparent damage.
- RS-B (HAZUS level 1): Minor damage. Shingles/tiles removed, leaving decking exposed.
- RS-C (HAZUS level 2/3) Major damage. Decking removed, leaving roof structure exposed.
- RS-D (HAZUS level 4): Destruction. Roof structure collapsed or removed. Walls may have collapsed.
To streamline the integration of remote sensing-based damage assessments into the existing workflows of emergency managers, Government agencies, and private industry, the damage scale is consistent with damage levels employed by FEMA’s HAZUS-Hurricane model. In this way, remote sensing can be used to provide a quick and independent validation of building damage and loss.
Integrating Flood & Wind Damage
Hurricane Katrina was a multi-hazard event, in which wind, flood and surge damage were juxtaposed within affected areas. While existing damage scales typically focus on a single type of hazard, Katrina presented MCEER researchers with a unique opportunity to study multi-hazard effects. In the case of New Orleans, after the initial (relatively minor) impact from wind pressures, communities suffered major losses due to flood inundation and high-velocity flows caused by levee breakage. In order to assess damage in these neighborhoods, a customized damage scale was developed combining both wind pressure and flood effects.
The new scale, combining HAZUS-based damage scales for wind and flood, was developed to more accurately detail the integrated damage to buildings. The composite damage states were developed on a loss-consistent basis, by categorizing the respective damage curves into representative groups corresponding with the same level of damage/loss. The categories are:
- WF-0 (No Damage or Very Minor Damage)
- WF-1 (Minor Damage)
- WF-2 (Moderate Damage)
- WF-3 (Severe Damage)
- WF-4 (Destruction)
Remote sensing technology has an import role to play in classifying both the flood and wind components of this integrated damage scale. While wind damage is identified according to the remote sensing-based wind damage scale described above, flood depths are estimated by fusing pre-event lidar terrain imagery with a flood boundary obtained from optical or radar imagery.
These new damage scales were developed through research collaborations between Beverley Adams and Shubharoop Ghosh at ImageCat, Inc., Arn Womble at the Wind Science and Engineering (WISE) research center at Texas Tech/ImageCat, Inc. and Carol Hill, Louisiana State University. Research activities were supported by funding from MCEER, the National Science Foundation (SGER grant number 0454564 and the IGERT program), the Natural Hazards Research and Applications Information Center quick response program and the National Institute of Standards and Technology/Texas Tech Windstorm Mitigation Initiative Program.
Submitted by Beverley Adams, ImageCat, Inc.