Environmental Engineering Reference
In-Depth Information
Fig. 2.5 Three pages from the field topic showing clear notations for each shot taken during a
survey
unvegetated, then LiDAR might be appropriate. On the other hand, if there is a
dense of ground cover and the site is small, then an autolevel might suffice.
Although automated survey equipment may appear simple, we have found that
data processing can be time consuming, so there is a trade-off when the technology
exceeds the products needed from the project. The following survey techniques can
be implemented using a combination of tools and in conjunction with one another.
The goal of surveying is to collect horizontal coordinates (X, Y), and vertical
ordinates (Z). These three-dimensional survey positions may be arbitrarily located
in space (e.g., relative to a local benchmark, center of the wetland, or other feature),
or they can be georeferenced, which means each point can be positioned on the
globe relative to other features. If the data are georeferenced, the horizontal
coordinates are often latitude and longitude, or northing and easting in a projected
coordinate system. In the georeferenced data set, Z is elevation above sea level,
referenced to a standard vertical datum. In some software packages, Z is considered
“depth” below a datum such as sea level.
In all mapping projects, you must first establish a horizontal and vertical datum.
The datum serves as the reference point from which all measurements will be
referenced. Datums can be local (arbitrary) and based on points set in the field, such
as rebar stakes, or they can be referenced to published locations. For example, the
National Geodetic Service (NGS) has survey data available on the internet ( http://
www.ngs.noaa.gov/cgi-bin/datasheet.prl ) . The NGS data system provides a report
on each benchmark.
A field survey establishes horizontal and/or vertical locations in relation to a
starting point, which is called a benchmark. The selection of permanent horizontal
and vertical reference frames is not critical if the wetland is to be surveyed and
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