Mean High Water Shorelines for the Outer Cape of Massachusetts from Nauset Inlet to Race Point (1998-2005)

The SWASH system platform was a six-wheeled amphibious Max IV all-terrain vehicle, approximately 2.4 meters long, with a plastic body, enclosed cabin, and cargo bed manufactured by Recreatives Industries, Inc. of Buffalo, NY. Mounted on a custom frame were four Global Positioning System (GPS) antennas constituting the Magellan/Ashtech ADU2 array for measuring pitch, roll, and compass orientation to an accuracy of about 0.4 degrees. One of the antennas also served as the antenna for an Ashtech Z-surveyor GPS receiver. The GPS receiver, in combination with 3 base stations that were installed approximately equidistant along the length of the study area, provided position to about 4 cm accuracy.
The SWASH system was used to collect data along 45 km of the Atlantic-exposed coast of Cape Cod, Massachusetts from Nauset Inlet in the south to Race Point spit in the north. This section of coastline is virtually unaffected by coastal development or other human activities. The beach was surveyed 111 times from April 1998 to May 2005 with a mostly bi-weekly sampling interval through February 2002. Several pre- and post-storm surveys were conducted as well.
For each of the field surveys that were conducted, the vehicle operator navigated a single, shore-parallel track on the seaward-sloping face of the foreshore (avoiding the berm crest), estimating the position of the mean high water (MHW) contour. Surveys were conducted at low tide to allow for maximum foreshore exposure. The position (x, y, z) and slope of the vehicle were measured at 0.5-second intervals as the vehicle traversed the beach.
This dataset was collected and processed over a span of 7 years (1998-2005). The process date represents the most recent date.

Following the field surveys, the data were processed to determine the cross-shore location of the MHW shoreline. The elevation of MHW for the study area (0.92 m above NAVD88) was determined by local tide measurements. The GPS processing software (PNAV 2507 (Ashtech)) produced the data in geographic coordinates, and Corpscon 4.7 (U.S. Army Corps of Engineers) was used to convert the geographic coordinates to UTM eastings and northings (zone 19N, WGS84). Elevations were converted from ellipsoidal heights to orthometric heights (NAVD88) using Geoid96 (and then Geoid99 when it became available in 1999).
A coast-following reference line was created by fitting an 8 degree polynomial to a single driven track. Perpendicular transects spaced 2 meters apart were defined along the length of the reference line. The raw GPS data were interpolated onto the transects using Matlab (ver7.1). To do this, the equation of the line defining each transect was calculated and the equation of the line between the data points on either side of each transect was found as well. These two equations were solved simultaneously and their intersection point was identified as the location of the vehicle at each transect. The measured beach elevation and slope were linearly interpolated to this point. Using simple geometry and assuming a uniform foreshore slope, shoreline position was then found along each transect by extrapolating from the vehicle location to the MHW contour.
Outliers were identified and removed and an uncertainty estimate was computed for each shoreline point. The largest source of shoreline positional error stems from our assumption that the beach slope remained constant between the measured point and the MHW contour (termed the "uniform slope assumption"). This error is a function of the deviation between the elevation of the driven vehicle track and the MHW elevation, the measured beach slope, and an estimated mean foreshore slope variability of 1.5 degrees that was measured during tests. For each point, the beach slope was varied by 1.5 degrees to compute the most seaward and landward possible shoreline positions due to foreshore slope variability. The vertical GPS positional error was converted into a horizontal error and was added in quadrature to the error from the uniform slope assumption. This total error was divided by two to calculate the plus or minus error for each shoreline point.
This dataset was collected and processed over a span of 7 years (1998-2005). The process date represents the most recent date.

Using MATLAB (R2019a), the shoreline point locations were converted back into a geographic coordinate system (degrees latitude and longitude), and the data for each survey were written out to both netCDF (Network Common Data Form, netCDF 4 Classic) files and ASCII csv (American Standard Code for Information Interchange, comma-separated values) files. Each netCDF and csv file includes the following information for every shoreline point: distance along the reference line (meters), latitude (degress), longitude (degrees), an estimate of the beach slope near MHW (degrees), and the plus or minus horizontal uncertainty of the shoreline position (meters).

Repaired some issues that the ScienceBase turn live process introduced - removed empty elements (geospatial presentation form), in the distribution section added the additional links, access instructions, and second distribution format that had been deleted. Other elements were also adjusted such as the series information in the identification citation.