Terrasurv has been performing Terrestrial Laser Scanning (TLS) projects
since first acquiring a laser scanner in 2006. Current equipment includes a
Trimble TX8, capable of performing high density/high accuracy scanning and A
Trimble SX10 which is used when less point density is required. Processing of
the point cloud data is done using Trimble Realworks.
Typical transportation uses include bridge clearances, pavement slope analysis
for drainage, and topographic map preparation. Other uses include deformation
analysis and as-built documentation.
Terrasurv has been performing small scale hydrographic surveys since
2006 using single beam fathometers and small watercraft. Projects range from
small stilling basins using kayaks to lakes/ponds up to 100 or more acres using
motorized boats. In addition, a remote controlled
vessel is available for use in dangerous or contaminated locations
Structures constructed by man such as dams, building, bridges, etc are subject to loads which can deform the structure and
can lead to failure. A deformation survey is a survey to determine if a
structure or object is changing shape or moving. The three-dimensional
positions of specific points on an object are determined, a period of time is
allowed to pass, these positions are then re-measured and calculated, and a
comparison between the two sets of positions is made. Deformation surveys are
performed at periodic intervals to monitor the stability of structures and to
give early warning of any unexpected behavior. Terrasurv has performed more
than 350 deformation surveys on more than 40 locks and dams operated by the US
Army Corps of Engineers. These surveys are custom designed for each structure
to best monitor potential movements and take into account
the type of structure (concrete, earthfill) as well as the past history of
each. A typical monitoring project consists of a
site visit to determine existing conditions and to plan the network. Pre-Analysis of each structure is preformed
using the simulation function in least squares programs to design the most
economical network which meets project specifications. Typical design
accuracies are ±3 mm for concrete structures and ±1 cm for earthen dams. This
information is then used in the office to plan a scheme of observations that
will meet the required accuracy. Next, the field observations are performed.
This data is then processed and adjusted in the office to yield data that can
be used as a baseline for future observations or to compare against previous
surveys.
Another type of deformation survey is the monitoring of ground
subsidence above mining operations, such as salt and coal mines. These surveys
are done using a combination of precise leveling, high accuracy
traverse/triangulation, and GNSS Surveys.
A geodetic control survey consists of establishing the horizontal
and/or vertical positions of points for the control of a project site.
Terrasurv uses multi-constellation/multi-frequency GNSS receivers, high
accuracy total stations, and geodetic leveling equipment to establish control
networks. Terrasurv has calibrated invar leveling rods and has executed
multiple second order leveling networks, several of which were submitted to the
National Geodetic Survey for inclusion in the National Spatial Reference System
(NSRS). See the Bluebook Services below for more information. All total
stations used by Terrasurv are calibrated yearly on NGS Calibration Baselines
(CBL).
Least Squares Adjustments are a fundamental part of achieving the
highest possible accuracies when performing Geodetic Control Surveys and
Deformation Surveys. We have more than 35 years of experience in performing
least squares adjustments on surveys of all kinds, including historic tape
traverse data, triangulation networks, and data collected by others. Custom
programming facilitates the intake of data in any readable format. Software
used included Geolab and Starnet.
A bluebook survey is a GNSS or leveling survey performed to certain
specifications which is formatted and submitted to the National Geodetic Survey
(NGS) for inclusion in the National Spatial Reference System (NSRS). Terrasurv
has performed dozens of GNSS bluebook surveys ranging from a single station to
countywide networks of more than 400 stations, as well as providing processing
and adjustments for submittal of projects observed by other agencies and
companies. Leveling projects from a single reset station to a 130 mile second order level run and subsidence monitoring
projects have also been submitted.