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Merging the Data from datasets came together seamlessly and precisely to create a
digital terrain model (DTM) of the entire quarry site.
Two Remote Sensing Syblon used this data to create their best practices for the

Platforms to Help Build construction of the new coffer dam system. Having the data of
the underwater and surrounding terrain readily available, allowed
them to identify potential issues and develop solutions to employ
a Dam when actually assembling the new coffer dam system.

By: Jed Gibson, PLS, UAV Pilot

In the ever-evolving world
of construction, the need
for surveyors to stay ahead
of the technology curve is
critical. New techniques
for building, refurbishing,
and enhancing the safety
of America’s critical
infrastructure calls for the
use of new technologies.
On most projects, a single
form of measurement
technology is deployed, The data was collected on two different days using the same
but with new projects GPS base point and control to geo-reference both datasets to the
calling for more intricate same datum. After collection in the field, the data was processed,
tracking and modeling, a and a seamless point cloud extending from below the water
combination of methods of
collecting data becomes a must. When Syblon Reid Construction surface to the highest cliffside, was created. Using UAV LiDAR,
the uneven edges and sheer rock faces were easily collected,
needed to deploy a new type of coffer dam system for the where traditional photogrammetry would have been able to map
Fordyce Dam Seepage Mitigation Project in the rugged terrain what could only be seen from straight above. Additionally, the
of the Sierra Nevada mountains in California, they called R.E.Y. terrain was covered in medium to thick vegetation, making LiDAR
Engineers, Inc. (R.E.Y.) to meet the challenge. R.E.Y. is a leader in a sensible choice to identify the actual ground throughout these
the survey industry in developing and employing cutting edge areas. When compared with fixed wing LiDAR (manned flight),
technology. Having previously worked on complex projects with such a small area makes for a quicker deployment and higher
Syblon Reid, they knew they could rely on R.E.Y. to find the right fidelity datasets from the UAV which can fly lower and slower
solution for their unique problem. over the subject area. From these combined datasets a single

The task at hand was to
assist Syblon in identifying
a way to quickly assemble
a new coffer dam system.
Having little to no hands-on
experience with the new
system, they needed a way
to develop best practices
and techniques. This was
not something they wanted to take on as “on the job” learning.
They turned their attention to a quarry some 86 miles away from
the site. This would become their “practice pit.” They planned to
use the similar uneven and steep terrain to test and prove the
system before utilizing it on the actual jobsite. How could they
build an accurate model of not only the terrain below the water
surface, but up the steep hillsides and surrounding topography digital model could be created, and the part of the coffer dam
above the waterline? The solution that R.E.Y. employed was system needing modification could be identified in the office. A
multibeam SONAR and plan could then be created prior to deployment, thus saving time
Unmanned Aerial Vehicle and energy of the crews installing the new coffer dam system.
(UAV) LiDAR together. The Along with the point cloud created from both systems, the UAV
SONAR captured everything LiDAR system has a nadir mounted camera that simultaneously
below the water level, and captures still photography. These photos are then stitched
the UAV LiDAR gathered together and draped over the surface model to create a digital
all the data above. Both colorized orthophoto. The high-resolution photo can be used in

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The Nevada Traverse Vol.49, No.2, 2022 15