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this barrier to future storms but the distribution of the inlet fill sequences aided in
the delineation of hazard zones (Fig. 1; FitzGerald et al., 2001). The migrational pat-
terns and infilling characateristics of the paleo-inlets as imaged in the GPR records
also helped to determine historical patterns of longshore sediment transport along
Duxbury Beach. At Wells Inlet on the southern Maine coast, GPR data corrobo-
rated paleo-inlet shoreline positions. Additionally, the fillets on both sides of jettied
entrance were shown to have formed from beach progradation due to the seques-
tration of sand from the littoral transport system (Montello, 1992). At another site
on the central Maine coast accretionary patterns observed in GPR profiles at the
mouth of Kennebec River document that the inlet had narrowed and deepened as
the channel cross section reached a state of dynamic equilibrium (Fig. 2; FitzGerald
et al., 2002). These examples illustrate that GPR is a valuable tool for deciphering
inlet shoreline histories. The portable nature and ability to collect data rapidly make
GPR an ideal instrument in the field investigation of tidal inlets. One drawback in
the use of GPR is that saltwater attenuates the EM signal and thus it cannot be
utilzed near saltmarsh environments or close to the ocean or bay shorelines.
2.2. Topographic lidar
LIDAR surveys offer an efficient way to collect data with centimeter accuracy over
large areas. Collected from an aircraft, laser pulses are transmitted and then the re-
turn signal is recorded. The time lapse between the transmitted and return signal is
used to calculate the distance from the plane to the ground. The elevation can then
be calculated because the plane's location is simultaneously recorded with a Kine-
matic differential Global Positioning System (GPS). From an altitude of 1,000 m,
data can be collected at 2,000 to greater than 200,000 points per second (Brock and
Sallenger, 2001). Typical accuracy is 1015 cm vertically and 1 m horizontally
(Brock and Sallenger, 2001). NASA's Airborne Topographic Mapper (ATM) collects
elevation points every few meters that are 14 cm (Sallenger et al., 1999).
LIDAR data is extremely helpful when working on regional scale projects, such
as barrier island and flood plane mapping, regional sediment management projects,
and storm assessment, because the data are collected much more quickly than
with conventional survey techniques (Brock and Sallenger, 2001). Assateague Island
(∼ 100 km) was mapped in approximately 3 hours (Krabill et al., 2000). Another
survey to assess storm damage after Hurricane Opal along the pan handle of Florida
was completed in just over 2 hours. A conventional survey of the same area had pre-
viously taken 6 months to complete (Bolivar et al., 1995). Vegetation structure can
also be described by analyzing multiple return signals (Blair et al., 1999). This ex-
ample illustrates how effectively LIDAR can be used to map large shoreline segments
and determine the impact of major storms.
LIDAR data collected from tidal flats in Humboldt Bay, Humboldt, CA were
added to the circulation model for the Bay. The Bay is 70% tidal flats that are
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