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across the flight path by a scanning mirror (USACE, 2002). Transmitted light interacts with and
is changed by the target. Some of the light is reflected/scattered back to the instrument where it is
analyzed. Upon capture by a receiver unit reflectance from features are relayed to a
discriminator and a time interval meter (measures the time elapsed between transmittal and
received signal (USACE, 2002). Changes in properties of the light allow some property of the
target to be determined. The first returns show the highest feature (i.e. tree canopy) and the final
returns are from the ground surface. The time for light to travel out to the target and back is used
to determine the range to the target. LIDAR collects measures of elevation every few square
meters within a surveyed swath hundreds of meters wide (Sallenger et al., 2003). The system is
capable of collecting elevation data with a vertical accuracy of 15 cm and a horizontal accuracy
of 1/1000 th of the flight height (USACE, 2002). Raw LIDAR data is in the form of x,y,z
coordinates (ASCII file) for each object the laser hits, measures and records distance to (USACE,
2002). The raw data is combined with GPS positional data to georeference datasets (USACE,
2002). The data is then edited and processed to generate surface models, elevation models and
contours (USACE, 2002). With the data it is possible to create Digital Elevation Models (DEM)
with vertical accuracies of 0.15-1 m (Gibeaut et al., 2003).
In addition to using LIDAR data to study shoreline change, Synthetic Aperture Radar
(SAR) data can also be used. This was done to a limited extent for this project. SAR uses a
small antenna that transmits a broad radar beam. A digital system records the amplitude and
phase history of the returns from each target as the repeated radar beams pass across a target.
The digital record is computer processed to produce an image (Sabins, 1997).
Ground Penetrating Radar (GPR)
Ground penetrating radar (GPR), was developed in the 1970s to map near subsurface
geologic structures. GPR is a non-destructive geophysical method that provides a continuous
cross sectional profile or record of subsurface features without drilling, probing or digging. The
method is based on wave propagation and reflection of microwave range electromagnetic
radiation (Van Dam and Schlager, 2000). It uses short pulses of high frequency (microwave
range) electromagnetic energy (radar pulses) (Harari, 1996). These pulses are propagated into
the ground by a transmitting antenna that is placed on the ground surface (Harari, 1996). The
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