Evaluation of New Sensors for Emergency Management
3
Unfortunately, the time window for utilizing unique information extracted
from imagery in the management of the response is narrow. For disasters in the
continental United States, it is often a few hours to a few days.
Extent of damage
An additional significant issue relating to the use of commercial satellite
sensors is the problem of acquiring imagery with adequate spatial resolution.
Analysis of the imagery must lead to a reliable estimate of the extent and severity
of the damage. On one hand, satellite systems have to be tasked to acquire an
image and are only in position at cyclical intervals of several days. In the case of
systems operating in the visible and near-infrared portions of the electromagnetic
spectrum, cloudless weather conditions are required. Even then, most satellite
imagery is of low resolution. Questions related to damage to infrastructure, criti-
cal facilities, roofs, and rafters cannot be answered even with the 1-m pixel size
of the IKONOS satellite sensor. On the other hand, airborne film imagery, which
can provide the detailed information (sub-meter pixel size) necessary for some
USACE missions, is subject to delays due to the time required for scanning, digi-
tizing, and geolocation processing.
Geospatial database
In seeking alternative image acquisition and processing techniques that
would reduce the time from image acquisition to the delivery of a product that
can be directly accessed by GIS software, the research team evaluated a digital
imaging airborne system called EMERGE. This digital system provided the
opportunity to obtain high spatial resolution imagery and eliminates both the time
needed for photo processing and the scanning needed to create a digital file from
film for entry into a geospatial database. Since the digital imagery was to become
part of this mapped database, it had to be orthorectified. The vendor accom-
plished this in post-processing of the data by using ground control points (GCPs)
and digital elevation models (DEMs) together with data about the sensor's
attitude and position that was acquired concurrently with the imagery.
Limited time value
There is an exceptionally limited time interval during which imagery pro-
vides added value because once ground observations are reliably available, the
imagery only provides duplicate information. A test was developed to evaluate
how quickly imagery could be acquired with an airborne sensor and could be
orthorectified into digital products that could be posted on an FTP site for the
RSGISC. Emerge Company of Andover, Massachusetts, was tasked to acquire
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