MA Bias_Feature – Feature class containing Massachusetts proxy-datum bias information to be used in the Digital Shoreline Analysis System.

The profile method of shoreline extraction (Stockdon and others 2002), extracts an elevation based shoreline from point cloud lidar data using a Matlab-based approach (Matlab version 2015b). Using a coast-following reference line with 20 m spaced profiles, lidar data is analyzed within a two meter swath around each profile. This method is used to extract MHW shoreline, slope and uncertainty information. The slope data for each profile was saved. The slope at each profile was averaged over time using data from the years 2000, 2011, 2014 and 2018.
Ruggiero, P., and List, J.H., 2009, Improving accuracy and statistical reliability of shoreline position and change rate estimates: Journal of Coastal Research, v. 25, no. 5, p. 1069-1081. [Also available at https://www.jstor.org/stable/27752753]
Stockdon, H.F., Sallenger, A.H., List, J.H., and Holman, R.A., 2002, Estimation of shoreline position and change using airborne topographic lidar data:  Journal of Coastal Research, v.18, no. 3, p. 502-513. [Also available at https://www.jstor.org/stable/4299097]
2000 NASA/NOAA/USGS Summer ATM Lidar: East Coast (SC, NC) Point Cloud files with Orthometric Vertical Datum North American Vertical Datum of 1988 (NAVD88) using GEOID18, https://coast.noaa.gov/htdata/lidar1_z/geoid18/data/10/
2011 USGS Lidar: Northeast (NY to ME) Point Cloud files with Orthometric Vertical Datum North American Vertical Datum of 1988 (NAVD88) using GEOID18, https://chs.coast.noaa.gov/htdata/lidar2_z/geoid18/data/2524/
2013-2014 USGS Lidar: Post-Sandy (MA, NH, RI) Point Cloud files with Orthometric Vertical Datum North American Vertical Datum of 1988 (NAVD88) using GEOID18, https://chs.coast.noaa.gov/htdata/lidar1_z/geoid18/data/4914/
2018 USACE NCMP Topobathy Lidar: East Coast (CT, MA, ME, NC, NH, RI, SC) Point Cloud files with Orthometric Vertical Datum North American Vertical Datum of 1988 (NAVD88) using GEOID18, https://chs.coast.noaa.gov/htdata/lidar4_z/geoid18/data/8688/

There is a known horizontal offset between the datum-based lidar MHW shoreline and the proxy-based historical shorelines on open-ocean sandy beaches that nearly always acts in one direction (Ruggiero and List, 2009). This bias is called the proxy-datum bias (PDB). The PDB is primarily due to wave run-up and thus is affected by the slope of the foreshore and the movement of water (waves, tides) onto the foreshore, see equation for the PDB and the PDB uncertainty in Ruggiero and List, 2009. These equations require beach slope and wave data. Ideally data collected at the time the proxy-based shoreline was collected would be used, however, for our purposes the PDB is estimated by averaging all available slope data (from step 1) and averaging at least 10 years of historical wave data from a nearby buoy ( https://www.ndbc.noaa.gov/) and the U.S. Wave Information Study (WIS - https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=gov.noaa.ncdc:C00071) The PDB is stored to a point shapefile at the intersection of the each profile with the coast-following reference line.
National Data Buoy Center, National Oceanic and Atmospheric Administration (NOAA) Stennis Space Center, MS 39529 https://www.ndbc.noaa.gov/
U.S. Wave Information Study, DOC/NOAA/NESDIS/NCEI National Centers for Environmental Information, NESDIS, NOAA, U.S. Department of Commerce, https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=gov.noaa.ncdc:C00071
NOTE: Many of the sheltered areas within the Massachusetts study area do not have nearby buoy data and a proxy-datum bias value cannot be calculated in these areas. Therefore, when this new datum-based MHW shoreline is compared to historic proxy-based HWL shorelines in these sheltered areas, there may be some artificial landward offset of the historic data that has not been quantified and could potentially influence the rates. However, because the PDB is primarily an estimate of wave run-up, and since sheltered areas have lower run-up, smaller values for the PDB are expected in sheltered areas. In addition, the equation for the PDB uses a wave run-up equation that has only been verified on sandy coasts. For that reason we do not apply the PDB to rocky headlands. Preliminary analysis suggests that the PDB is small on rocky headlands, however more work needs to be done to determine the correct value for PDB on rocky headlands and other non-sandy beaches.

Bias points are extrapolated to a polyline feature, in this case acopy of the baseline file. The final bias feature file holds the bias, and the bias uncertainty. These components are used by DSAS v5.1 to apply the proxy-datum bias correction to shoreline change calculations.

The bias_feature was imported into a personal geodatabase in ArcCatalog v10.7.1 by right-clicking on the geodatabase > Import > Feature class (single). The feature class is used with the Digital Shoreline Analysis System (DSAS) v5.1 software to apply the proxy-datum bias to rate calculations.

The bias_feature shapefiles weas projected in Esri's ArcToolbox > Data Management Tools > Projections and Transformations > Project. Input projection - WGS_1984_UTM_Zone_19N; output projection - geographic coordinates (WGS84); transformation = none.