Verification of historical smooth sheet bathymetry for the Gulf of Alaska – Integrated Ecosystem Research Program

Abstract We verified the accuracy of interpolated bathymetric surfaces created from historic (1924–2003) National Ocean Service smooth sheet bathymetric soundings and shorelines with single-beam echosounder measurements of seafloor depth obtained in the spring and summer of 2013. Independent comparisons were made at ten inshore locations in the central and eastern Gulf of Alaska as an effort to groundtruth the fish habitat layers provided for NPRB's (North Pacific Research Board) sponsored Gulf of Alaska – Integrated Ecosystem Research Program (GOA-IERP). Ordinary least squares linear regressions determined that the GOA-IERP soundings could successfully predict interpolated smooth sheet bathymetry (gridded or raster surface) at all sites (best R 2 = 1.0), although the oldest smooth sheets from 1924 (R 2 = ~ 0.90) and 1925 (R 2 = ~0.80) had the poorest fits. Standardized residuals were geographically clustered at all sites, with larger residuals often observed in areas of rapid depth transition, but ≥ 93% of residuals at all sites were within two standard deviations. Residual analysis indicates that the standardized residuals increase with depth, slope, distance to nearest smooth sheet sounding, and distance to nearest smooth sheet navigation station. This indicates that errors in navigation were greater farther offshore, interpolations were worse in areas of sparse soundings, and the consequences were more significant in steeper and deeper areas. Overall, we conclude that the smooth sheet bathymetry was successfully ground truthed and useful for fish habitat descriptions.