National Aeronautics and Space Administration

Wallops Flight Facility

Coastline Elevation

COASTLINE TOPOGRAPHIC MAPPING/SHORELINE ELEVATION CHANGE

The Airborne Topographic Mapper (ATM) group at Wallops Flight Facility participates in a robust program in collaboration with the U.S. Geological Survey (USGS) Center for Coastal Geology in St. Petersburg, FL, to maintain reasonably current digital shoreline surveys of much of the coast of the continental U.S. Airborne LIDAR mapping provides the U.S. with a cost-effective method for obtaining observations on the state of the beaches and coastal regions along the U.S. coasts. The airborne LIDAR mapping group at Wallops is the lead U.S. center for developing this technology and is active in such international programs as PARCA, which is developing a mass balance for the Greenland Ice sheet using the LIDAR topographic mapping technology developed in this group.

Present Activities:

Presently, the entire coast from Portland, ME to Corpus Christi, TX has been surveyed within the past 3 years except for the coastal Everglades and portions of the Mississippi Delta. Approximately one-half of the Pacific Coast has been surveyed. Most of these coastal areas have been surveyed two or more times. A summary of the East and Gulf Coast is shown in Figure 1.

Wallops Flight Facility (WFF) has been involved in the development of airborne laser altimetry since its very beginnings in the mid 1970’s. However, it was not until the availability of the DoD’s Global Positioning System (GPS) in the late 1980’s that airborne laser altimetry became practical for applications such as coastal surveying. The primary application of the ATM since the early 1990’s has been to monitor the mass balance of Arctic ice sheets and glaciers in response to regional climate changes in the Northern Hemisphere. The ATM Project has demonstrated the ability to collect 10 cm quality elevation measurements in the pursuit of this program.

The surveying of Assateague Island (near WFF) was initiated to provide a test site for validating ATM sensor performance over targets of high reflectivity similar to arctic ice sheets. During the initial spin-off application of the ATM for coastal mapping, NOAA’s Coastal Services Center (CSC) in Charleston, SC also partnered with USGS and NASA in its implementation. Although CSC made a programmatic decision at the end of 2001 to emphasize and develop other remote sensing applications for coastal managers, CSC still maintains LDART (Lidar Data Retrieval Tool), a web-based facility for the distribution of the coastal mapping data resulting from the ATM surveys.

In addition to NOAA, NASA, and USGS, a number of state and academic institutions are actively utilizing data acquired with the ATM in coastal regions. Of particular note has been the utilization of the coastal mapping data to determine effects of major coastal storms such as hurricanes and northeasters on the east coast and the winter storms strengthened by El Nino on the west coast. Current direct collaborators with the Wallops ATM group include: NOAA Coastal Services Center, National Park Service, Natural Resources Departments in NY, SC,OR,WA, Rutgers University, NASA KSC, USGS centers at Woods Hole, MA and Menlo Park, CA, University of Puerto Rico, California Dept. of Highways, and University of MD Eastern Shore. Indirectly, the data is being accessed on LDART by a considerable number of researchers from various domains as indicated in Table 1. (NOAA CSC does not require the user to enter their institutions because of concerns about violating Freedom of Information statutes.)

Figure 1. Summary of historical US East and Gulf coast mapping missions.

Figure 2 illustrates the elevations of the ‘first line of defense’ of the beach system, either the first dune ridge or, in the absence of a dune, the beach berm. (For areas where dunes are absent and there are seawalls, or other shore-parallel coastal defense structures, the top of the structure becomes the ‘first line of defense.’). The NASA ATM collected all of the elevation data used to derive the map. The map illustrates the relative vulnerability of the South Atlantic coast to change for a storm of the same wave runup elevation on the beach, hitting the coast at approximately mid-tide level. For example, darker red shades on the strip along the shoreline indicate low elevations and relatively high vulnerability to overwash and inundation. Lighter red shades indicate high, well-developed dunes and relatively low vulnerability to overtopping and to net coastal change.

Table 1. Total web requests for Coastal Topographic Data

Month Total Number of Requests
Sep-99 15
Oct-99 9
Nov-99 38
Dec-99 26
Jan-00 42
Feb-00 50
Mar-00 80
Apr-00 68
May-00 117
Jun-00 117
Jul-00 129
Aug-00 96
Sep-00 123
Oct-00 129
Nov-00 166
Dec-00 48
Jan-01 137
Feb-01 137
Mar-01 180
Apr-01 196
May-01 166
Jun-01 98
Jul-01 182
Aug-01 106
Sep-01 43
Oct-01 195
Nov-01 302
Dec-01 161
Jan-02 165
Feb-02 192
Mar-02 171
Apr-02 65
Domain Total Number of Requests
edu 157
state 46
gov 60
mil 25
com 199
other 82

 

Figure 2. The following map (figure 2) is provided by Dr. A. Sallenger at USGS.

Another example of ATM data applied to coastal change studies is displayed in Figure 3. Shown on the left-hand side is color-coded topography of the northern half of Assateague Island, Maryland, following two nor’easter storms in February, 1998. Extracted from before and after surveys of the site are cross-sections showing several regions of interest. The two center figures are before and after 3D renditions of a section of beach that was completely overwashed during the storms. A cross section profile from the before and after data are plotted in the upper figure, with location further delineated in the 3D, showing that almost 2 meters of beach was eroded. Two similar plots in the lower figures are extracted from the Maryland State Park section of the beach (left), and the National Seashore Park area (right). Both park areas had been enhanced with beach renourishment projects in recent years; however, the National Park also planted dune grass to stabilize the new sand. The plot shows that the grass protected dune remained intact, with only minor erosion of the fore-dune, whereas the bare dune in the State Park area was leveled.

Figure 3. Example of application of beach topographic mapping data set to study the impact of coastal storms on beaches.

Beach mapping efforts can also be useful for observing the beach recovery processes (Figure 4). The ATM mapped the same stretch of Assateague shown in Figure 3 several months later (980403). Plotted in blue is the shoreline response due to the storm, showing nearly 100 m of erosion at one specific location, but with a tremendous amount of spatial variability. Red indicates the natural recovery of the shoreline in 2 months. The pattern is a mirror image of the erosion—where the greatest erosion occurred, the greatest recovery followed. The time scales of this recovery and determining the amount of net loss are critical questions that can be answered with ATM data.

Figure 4. An illustration of the beach recovery process at Assateague Island. Figure courtesy of Dr. A. Sallenger.

Future Plans:

Future plans for use of the ATM for coastal applications are for a complete survey of the US West Coast from the Canadian border to the Mexican border, and to be on standby (when an aircraft is available) to conduct a post-hurricane survey in a region previously mapped. The funding for the West Coast survey is mostly USGS, with some other federal agency support. Hopefully the hurricane flight will be supported by a pending SENH proposal. The Cryospheric Sciences Program provides base support for the ATM Project.

Contributors:

Lead Investigator: Bill Krabill