Evaluation of New Sensors for Emergency Management
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REQUIREMENTS
Ground sampling distance
The first requirement was based on a FEMA regulation that temporary roof-
ing will not be installed unless more than 50% of the rafters are undamaged. So
we asked the question: At what GSD can we tell from digital imagery if the roof
rafters of a damaged building are substantially intact? The contractor was tasked
to determine the GSD necessary to detect roof damage reliably.
Impact area
The second requirement had to do with the contractor's capability to collect a
large volume of image data per day. Since the federal government does not
become involved under the Federal Response Plan until the capabilities of the
state and local governments have been overwhelmed for disaster assistance, areas
affected by federally declared disasters are typically fairly large. Based upon
damage swaths from previously declared hurricane disasters, somewhere between
30 and 150 square miles of area should be imaged. Based on tables of data
volume versus square miles of coverage at 1-ft GSD, somewhere between 4 and
8 gigabytes of data will cover between 50 and 100 square miles of area. The
contractor was tasked to collect 5 Gb of data.
Post processing
The third requirement was to test the contractor's ability to orthorectify up to
500 single frames of imagery in 12 hours or less, write them to CD-ROM, and
post them on an FTP site. This number was derived from a table showing the
maximum number of frames that could be collected in a day from a small
Cessna-class aircraft. As already noted, images rapidly lose their value if they
cannot be delivered in a mapped and analyzed format to the ultimate user in a
timely manner. Since the digital images must be orthorectified before they can be
combined with the other geospatial data, an essential component of a successful
approach to incorporating digital imagery into the information stream is rapid
processing of large volumes of data once the plane has landed.
Maps
A fourth requirement for this study was that a digital location map file be
made at all collected resolutions, giving the nadir point of each image frame in
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