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AIRCRAFT LASER BEACH MAPPING

Assateague Island Case Study

Assateague Island map image


Assateague Island

Assateague Island consists of 1800 acres of beach, dunes, forest, marsh, and bay in the states of Maryland and Virginia. Seven miles from the northern entrance to Assateague Island is the busy boardwalk resort of Ocean City, Maryland while at the southern entrance to Assateague Island is the quiet fishing village of Chincoteague, Virginia. Between these two drastically different communities lie 37 miles of undeveloped coastal shoreline surrounded by the Atlantic Ocean and Chincoteague Bay.

Assateague Island has three major public areas: 1) Assateague Island National Seashore, managed by the National Park Service; 2) Chincoteague National Wildlife Refuge, managed by the U.S. Fish and Wildlife Service; and 3) Assateague State Park, managed by Maryland's Department of Natural Resources. Together, these three agencies provide the public with educational and recreational activities to protect and preserve the seashore wildlife and wetlands for future generations.

The island features famous wild horses that roam throughout the park and share beach to bay habitats with a host of other mammals and birds. These wild horses are called "ponies" by local residents and have been made famous by an annual July round-up and swim across the saltwater channel from Assateague to Chincoteague. Once in Chincoteague, the horses are auctioned off to buyers from all around the U.S.

Assateague Island is home to a multitude of birds; nearly 300 species have been documented. From late fall through winter, thousands of snow geese and other waterfowl can be found on the island. During spring and late summer along the surf, sandpiper and other shorebirds search the wet sand for food. From spring through early fall, the shallow bays are home to herons, egrets, and other marsh species. In addition, ospreys, brown pelicans, and bald eagles have occasionally taken up residence on this national seashore.

A 1933 hurricane passing just south of Ocean City, Maryland unleashed its most powerful forces in the northeastern quadrant of its path, breaching an inlet known today as Ocean City Inlet and separating Assateague Spit from Fenwick Island. The Ocean City Inlet quickly became a popular navigation channel, and pressure to protect against the natural processes that might eventually close the inlet led to the implementation of hard stabilization measures in the form of rock jetties extending over 500 feet seaward on both the north and south sides of the inlet. Due to changes in the sediment transportation processes from the jetty construction, an almost immediate change in the accretion or erosion rates was evident on both sides of the inlet. The southern end of Fenwick Island began to accrete seaward while the northern end of Assateague Island began to erode at an increasing rate. Since completion of the 1935 stabilization, the southern end of Fenwick Island has extended approximately 180 meters seaward while the northern end of Assateague Island has exhibited average erosion rates of about 7 meters per year.

Realizing the dynamic nature of a coastal environment and the possible effects upon habitat, animals, and plants, several studies have been conducted in an attempt to define the historical changes brought about by human intervention in coastal processes. In addition, these studies attempted to predict the future evolution and impacts of coastal changes around Ocean City Inlet. The National Park Service now periodically conducts traditional beach surveys to assess changes in rates of accretion and erosion. The beach survey measurements provide valuable coastal elevation and profile information, but it is limited to only those surveyed beach areas.

In November 1995, a trial project with the National Aeronautics and Space Administration (NASA), in conjunction with the National Park Service, supplemented these traditional beach survey efforts by creating continuous digital elevation maps of the Assateague Island survey area using airborne laser beach mapping. NASA's first generation of the Airborne Topographic Mapper (ATM-1) was mounted on the NASA/Wallops P-3B aircraft to collect the digital elevation data. In October 1996, Assateague Island was resurveyed using the latest generation of the ATM (ATM-2) aboard a NOAA DeHavilland Twin Otter aircraft.

The continuous elevation maps produced from the airborne surveys provided more accurate estimates of beach elevation changes and total sediment volume than the individual shore normal survey profiles obtained by traditional ground survey methods.

Some preliminary sample data products from the Assateague Island ATM mapping case study include:

Preliminary raw data image of the Ocean City, Maryland inlet and Assateague Island.

Beach profile of Assateague Island; because of the continuous elevation dataset created perpendicular to the beach, it is possible to extract a cross-sectional profile at any point within the surveyed area as is demonstrated by this animation of beach cross sections (Note: 3 Mb).

Elevation contour map for ATM survey of Assateague Island.

A shaded perspective fly-through (Note: 3.6 Mb) animation traveling from south to north, generated from November 1995 survey data of North Assateague Island.

The following three images divide the Assateague Island into three sections, each indicating unique features apparent from the airborne surveys. At the top of each image is an airborne photographic survey for visual reference when observing the ATM survey results. ATM elevation surveys from November 1995 and October 1996 are presented and then compared in a difference image. The gray lines perpendicular to the beach indicate locations at which ground surveys where taken. (See the next section for results comparing these locations with the airborne surveys.)

    Southern Assateague Island (cultural features)

    Central Assateague Island (erosional features)

    Northern Assateague Island (accretional features)

Comparisons of ground surveys with November 1995, may 1996, and October 1996 ATM surveys. These graphics clearly show the high accuracy of the elevations obtained by beach laser mapping. The large differences apparent at the beach face only in several of the cross-sections from the October 1996 ATM surveys could be due to the two to four week separation between ground and airborne surveys in a beach section previously noted for its instability. For the 1997 overflights, NOAA will work closely with coastal managers in an effort to coordinate ground survey efforts with the scheduled airborne surveys.


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