| The deliverables provided
by Sewall will form a basis for our planning, engineering,
and environmental support for future projects to increase
the safety and reliability of our electric tranmission
corridors in the Greater Rhode Island area. |
David J. Aho,
PLS, LLS, Land Survey Coordinator--New England
Land Surveying Department, National Grid |
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Digital Aerial Acquisition and Mapping of
Electric Transmission Line
National Grid
In fall 2009, National Grid commissioned Sewall to fly and
map a portion of its electric transmission line corridor in
Rhode Island and Massachusetts. The firm, an international
investor-owned gas and electric utility that delivers electricity
to 3.3 million customers in Massachusetts, New Hampshire,
New York, and Rhode Island, needed to acquire new photography
for 1"=40' scale planimetric and 2-foot topographic mapping,
plus 0.25-foot pixel resolution orthophotography, of the 30-mile
corridor from Jepson Substation to Brayton Point. The deliverables--aerial
imagery of the entire route and mapping and orthos for five
out of six substations along the route--were key to National
Grid's planning and engineering of future electric transmission
projects in the region.
Sewall, a prequalified vendor with National Grid for aerial
photography and ground surveys, was the consultant of choice
based on previous successful projects with National Grid and
our ability to deliver a broad range of services to National
Grid's service territory.
At project launch, Sewall captured digital imagery of the
entire project area at 7.5 centimeter GSD resolution, using
our recently purchased DiMAC WiDE large format digital aerial
camera. Sewall also established control to support the 1"=40'
mapping and, as requested, developed the mapping and orthophotography
for the corridor and for the Brayton Point, Somerset, Bell
Rock, Dexter Street, and Jepson substations.
Use of the Sewall's large format digital camera produced
several benefits. First, the digital camera acquired brilliant,
crisp imagery with excellent detail in the shadows as well
as bright areas. Second, the clarity of the imagery was especially
beneficial during the compilation of planimetric features,
specifically of transmission line wires and catenaries. Third,
without the film processing or scanning requirements of an
analog solution, delivery of the project as a whole was expedited.
National Grid is now using the deliverables to assess, maintain,
and increase the safety and reliability of the electric transmission
corridor in the project area.
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