Alabama: shorelines (1849-2022) used to calculate shoreline change rates

The horizontal accuracy of the shoreline data varies with respect to the data source from which the shorelines were digitized, the lidar data from which the shorelines were extracted, the time period, and the method used to extract the shoreline data. T-sheet Shoreline Positional Uncertainty: Shorelines prior to 1960 (T-sheets) have an estimated positional uncertainty of plus or minus 10.8 meters (m). Shorelines from the 1960s-1980s (T-sheets) have an estimated positional uncertainty of plus or minus 5.1 m.
Contour Shoreline Positional Uncertainty: Four sources of uncertainty were accounted for regarding shorelines extracted using the contour method (described in Farris and others, 2018): 1) The vertical uncertainty of the lidar data (0.15 - 0.29 m) as found in the original lidar source metadata; 2) the horizontal uncertainty of the lidar data (0.12 - 1.0 m) as found in the original lidar source metadata; 3) a mean high water (MHW) vertical uncertainty of 0.15 m (Weber and others, 2005); and 4) a horizontal uncertainty due to the creation of a Digital Elevation Model (DEM) from lidar point cloud data (0.5 m).
The vertical uncertainty values (1 and 3 above) were converted to a horizontal uncertainty using the beach slope in order to calculate uncertainty by summation in quadrature of horizontal components. The beach slope was found by averaging slope values calculated from the lidar profile shorelines (see process steps for a description). Vertical uncertainty (VU) terms were divided by the average beach slope (expressed as rise/run) in order to get the horizontal component of the two vertical uncertainty terms: VU/TAN(slope*(3.14159/180)). In order to estimate the total horizontal uncertainty, the four horizontal components of uncertainty were added in quadrature (square root of the sum of the squares). These values are stored in the attribute table as Uncy. The average uncertainty, in meters, for the contour shorelines are as follows: AL 1998 = 3.01 m AL 2005 = 3.49 m AL 2007 = 3.07 m AL 2010 = 3.27 m AL 2015 = 1.86 m AL 2016 = 2.08 m AL 2018 (USACE) = 1.98 m AL 2018 (USGS) = 1.72 m AL 2020 = 2.42 m AL 2022 = 1.98 m
Profile shoreline extraction was completed for three lidar datasets (AL 2010, AL 2016 and AL 2022).
Profile Shoreline Positional Uncertainty: Four sources of uncertainty were accounted for regarding shorelines extracted using the profile method (method described in Farris and others, 2018): 1) the 95% confidence interval on the linear regression estimate of the shoreline position; 2) the uncertainty associated with the elevation of the raw lidar data; 3) a 15 cm vertical error in our chosen value of MHW; and 4) the uncertainty due to extrapolation (if the shoreline was determined using extrapolation). These components of uncertainty were added in quadrature to yield a total error for each shoreline point. These errors were averaged for each profile shoreline segment (up to 2 kilometers). The range of uncertainty the profile shorelines used is 0.99 to 5.25 m, with an average of 2.83 m (AL 2010), 2.05 m (AL 2016), and 1.87 m (AL 2022). See the Uncy field in the shorelines attribute table for the individual uncertainty values of profile shoreline segments.