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Experience
in the Field
Bridge
Inspection Survey
In April 2000, Parsons Transportation Group, Inc., of New
York contracted James W. Sewall Company to perform a dimensional
inspection survey of the Waldo-Hancock Bridge in Verona and
Prospect, Maine. The bridge, which spans the Penobscot River,
is currently undergoing major renovation. In an innovative
process, Sewall used a combination of digital close-range
photogrammetry and GPS ground control techniques to obtain
critical location and elevation information for select cables,
trusses, piers, towers, and cable bents. Sewall also determined
road centerline elevations at 50-foot intervals on the bridge.
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To perform the survey,
Sewall captured 400 digital images, utilizing two digital close-range
camera systems and a helicopter as the camera platform. The
imaging was completed in twelve flight passes over the course
of one day. To control the imagery, Sewall surveyed specific
points on the ground and on the bridge before and after the
flight. At company production facilities, Sewall processed the
imagery using close-range photogrammetry software to measure
specific point locations as required. Deliverables included
positional information in text, tabular, and image formats. |
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Compared to traditional surveying methods, this measurement
approach was efficient and fast, reducing the number of labor
hours required to collect data in the field. It also was safe.
Sewall surveyors were able to obtain precise measurements
without walking the suspension cables to the bridge towers.
Finally, the method was nonintrusive, creating minimal impact
on traffic flow.
Sewall's innovative use of close-range photogrammetry on this
project was nominated for a 2003 Construction Innovation Forum
(CIF) NOVA Award. For more information, please see the CIF
web site at www.cif.org
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