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Topographic Surveying
Topographic surveying is a simple method of obtaining data that describes the nature of
the local terrain. Leveling is the process used to determine the elevation or the difference in
elevation of points on the ground. All elevations are determined relative to a datum. During this
investigation all elevations were measured relative to NAVD 88 (North American Vertical
Datum). All leveling was done using a laser scanner and rod marked with encoding bar strips.
The ground elevation was found by reading the rod values through the telescope lens at different
points along the line. The rod was held on the points whose elevation was being measured. The
horizontal position of the rod was determined by GPS. These elevations were based on a single
frequency differential GPS survey using Magellan Mark I receivers. The base station was set at
FDEP monument B396, which was located at the intersection of Road 2 and Road B. The
accuracy of the measurements was +/- 10 cm (2 sigma) based on a two to three hour occupation
of each survey site. The measurements were checked by replicate occupation of one survey site
(located at the intersection of Road 3 and Road F) and laser leveling between two of the GPS
stations. The data obtained during the topographic survey is presented in chapter 4.
Airborne Remote Sensing
Many techniques can be applied to the study of shoreline change (topographic maps,
aerial photographs, ground based surveys, Light Detection and Ranging (LIDAR)). To
complement the geochronologic, sedimentologic analyses and topographic data collected in this
investigation, LIDAR was used to attempt to establish a correlation between sea-level history
and mean ridge set height.
Two main types of LIDAR are commonly used in coastal applications: 1) bathymetric
LIDAR, which penetrates water and provides measures of water depth; and 2) topographic
LIDAR, which measures subaerial topography (Sallenger et al., 2003).
The LIDAR method measures the distance between airborne sensors and points on the
ground surface. Figure 3.9 depicts the basis of LIDAR. With this technique, it is possible to
collect elevation data with a vertical accuracy of 15 cm (USACE, 2002). LIDAR
instrumentation transmits light from a focused infrared laser that is beamed toward the ground
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