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FIG 5a FIG 5beven years — afterward. “The ability todigitally catalog data as a permanent recordwill no doubt lead to more accuratedamage assessments for many types ofdisasters, and will help speed the processof categorizing damage data for analysisand reporting purposes.” See Figures 2-3.Figure 4 Pre- and post-Hurricane Katrina Landsat-5 TM imagery was used to detect storm surge damagein Mississippi (Landsat imagery from USGS and NASA).Figure 5 NASA’s Landsat-7 30-meter imagery reveals flooding extent in New Orleans on August 30,2005. (NASA imagery from Jesse Allen with data provided by USGS EROS Data Center and Landsat ProjectScience Office at Goddard Space Flight Center).Data Variet y is FundamentalThe complementary characteristics of thedifferent remote sensing platforms, which includedoptical, radar and LiDAR, afforded usthe ability to view the damage from multiplevantage points: optical imagery allowed usto view the landscape as it naturally appearsto the human eye, radar gave us the magicalability to “see” through clouds and darkness,and LiDAR helped us visualize the varyingheights of terrain and water. Suddenly, ourpicture was complete and led to the rapid,thorough, and consistent assessment of thesituation.Our team used post-Hurricane Katrinaremote sensing images that span awide variety of spatial resolutions. Thespatial resolution of an image determinesthe ability to view individual features suchas buildings and bridges. It also affectsthe ability to monitor and assess damageconditions, and depends on the nature ofthe hazard itself — for example, flooding,wind pressure, and storm surge.w w w . i m a g i n g n o t e s . c o mPixel sizes of approximately 10 metersor smaller are necessary to discern thepresence and location of individual buildings,while much smaller pixels, on theorder of one meter or less, can distinguishdamage conditions of individual buildings,such as damage to roofs caused bywind pressure. Widespread flooding canbe detected and monitored using less-detailedmoderate-resolution imagery.In addition to spatial factors, spectralresolution influences the use and usefulnessof the data. Physical materials have differentreflectance values in different portionsof the electromagnetic spectrum, and sofeatures of interest, such as constructionmaterials, water, and vegetation, can beidentified by unique and distinguishingcharacteristics. The use of multispectralremote sensing systems is therefore criticalfor the separation of constituent materialswithin an image, and for the interpretationof images for damage assessment.While post-disaster remote sensing imagesaccurately capture damage caused by adisaster, pre-disaster coverage is extremelyuseful for establishing the “normal” situation.Pre-storm images provide a benchmark“no-damage” baseline for changedetectionoperations, comparing pre- andpost-storm images on a regional and/orper-building basis, which creates importantvalidation of damage-assessment results,particularly for moderate damage levels.For the investigation of Hurricane Katrinadamage, pre-storm satellite imageryfrom Landsat-5 and QuickBird providedthis important comparative baseline. RecentLandsat-5 imagery for the New Orleans areaand Mississippi Coast was accessed throughthe United States Geological Survey (USGS)disaster Web site, and an older scene collectedin 2000 was obtained from the StennisSpace Center Web site. DigitalGlobe’sQuickBird imagery, which had been collectedover the area in March 2004, created criticalcapabilities for comparing the landscapeand infrastructure of the Gulf Coast regionbefore and after the disaster occurred.LiDAR airborne imagery was availables u m m e r 2 0 0 629