Practicing Damage Assessment: Structural Damage Caused by Hurricane Sandy

Assessing damage in the aftermath of a natural disaster is a weighty task- often there is significant loss of life and property involved, but someone has to actually quantify exactly how much and of what is damaged or gone all together.  This is easily accomplished using aerial photos and GIS analysis.

Above is an aerial image of a block on the New Jersey shore, taken shortly after the late October 2012 storm event of Hurricane Sandy.  This image was used in conjunction with one of the same areal extent, but taken before the storm.  Comparison of the two images allows for a quick, but not overly accurate, inventory of the structures directly affected, and some of the damage on the ground.  The final qualification of said damage is more than likely completed with reference to actual field-derived ground information, but image analysis such as this provides a decent estimate to start off with.  When the two aerial images, pre- and post- storm, are compared a point layer with locations of structures can be created, with descriptions of the types of damage observed as a part of the feature attributes.  Upon completion, the layer can be symbolized according to observed damage, and presented in map-form with an image like the one here.  This type of analysis provides maps that can give a good general overview of damages resulting from storm events such as Hurricane Sandy, and can also be used to analyze and quantify the extent of the damage.  

 Creating a feature layer of the actual coastline and drawing a buffer around it allows for a count of buildings, and their associated damage levels, within a specified distance of the water's edge.  The results of this analysis, in the table above, indicate that the majority of the damage- about 60%- occurred in the area 100 to 200 meters from the water.  Quantitative results within a table like this also support the intuitive assumption that the level of damage is greatest nearest to the water's edge, and the magnitude of structural damage generally decreases with increased distance.  It is worth mentioning, though, that despite the quantitative nature of this summary, the data it is based off of is anything but.  Subjective interpretation by one person of the amount of damage by way of visual comparison of aerial images would hardly suffice as an accurate assessment in a real-life scenario.