Environmental Engineering Reference
In-Depth Information
Survey
instruments Description
Data collected
Notes
Meter stick Layout orthogonal grid and measure the water
depth at grid nodes with a meter stick
Depth, using ambient water surface as the
datum. Depth precision of 1 cm is typical
Horizontal positions obtained with 50 or 100 m
tapes and cross section stakes. Technique is
limited by ambient water depth, so
surveying at high water will capture more
data. If water is flowing, the water surface
(datum) will not be constant through space
Survey
level
Lay out orthogonal grid for measurement.
Horizontal telescope pointed at a calibrated
leveling rod. “Autolevels” are able to fine-
level themselves after initial coarse leveling
Elevation precision of 1 cm is typical
Horizontal positions obtained with 50 or 100 m
tapes and cross section stakes. Requires two
surveyors
Rotating
laser
level
Same as above, but rotating laser level emits a
horizontal plane of laser light that strikes a
receiver on a calibrated leveling rod
Same as above
Same as above. Can be operated by one person
Handheld
GPS
Wide range of models available. Trimble
Explorer is a common model
Coarse horizontal position and very poor
vertical positions. Post-processing typi-
cally achieves 2 m horizontal precision
Used for horizontal mapping. Should not be
used for vertical positions. Data are
georeferenced
Total
station
Spherical 3D points are obtained through laser-
based distance measurements and ultra-
precise horizontal and vertical angle
measurements. Laser is shot at a pole-
mounted prism
3D coordinates with 1 cm precision. With
experience and research-grade equip-
ment, sub-centimeter precision is
possible
Total stations can obtain a precise 3D fix in a
few seconds, so hundreds of positions can be
shot in a day
Survey
grade
GPS
3D points are obtained by a tripod-mounted
GPS antenna, with reference to satellites and
either a local base station or regional set of
base stations
3D position with precision limited by local
conditions. One centimeter precision
is possible under ideal conditions
Surveys are commonly achieved with a “rover”
antenna that corrects positional errors by
radio communication with a “base” antenna.
This provides “precise” positions. “Accu-
rate” georeferencing is achieved by
correcting the base station data using fixed
GPS stations in the region
Ground-
based
LiDAR
Tripod-mounted, vessel-mounted, or
vehicle-mounted LiDAR scanner
Millions of 3D points are collected in a
LiDAR scan. The precision is limited by
vegetation, water, and GPS positioning
Excellent for expansive wetlands, such as large
tidal marsh environments. Very complex
data collection and post-processing system.
