Historical coastal bluff edge positions at Barter Island, Alaska for the years spanning 1950 to 2020

Bluff edge positions were delineated from a combination of historical maps, aerial photography, declassified satellite photography, and very-high resolution satellite imagery spanning a 70-year period between 1950 and 2020. Spatial resolution of the datasets ranged from 0.08 to 3.9 m. Images were georeferenced and rectified using map coordinates, ground survey points, and/or image-to-image correlation of photo-identifiable ground features. A total root-mean-square rectification error was determined for each dataset based on the residuals. Vectors were digitized in a GIS from all data sources using standard editing tools in ArcMap 10.7 using criteria described in Gibbs and Richmond (2015) and Gibbs and others (2019). A total horizontal position uncertainty of the feature was determined as the quadrature sum of all uncertainties, including the georeferencing, digitizing, and RMSE on image rectification. Long- and short-term bluff change rates were calculated every 10 meters alongshore using the Digital Shoreline Analysis System 5.0 (Himmelstoss and others, 2018). Linear regression and weighted linear regression methods were employed for long-term change rate calculations and an end-point rate method was employed for annual and semi-annual change rate calculations. Additional details on methodology and uncertainty estimates can be found in Gibbs and Richmond (2015) and Himmelstoss and others (2018).