Merged topography and bathymetry, western Prince William Sound

This work integrated multiple topographic and bathymetric data sources to generate a merged topobathymetric map of western Prince William Sound. We converted all data sources to NAD 83 UTM Zone 6 N and mean higher high water (MHHW) before compiling.
 
In Barry Arm, north of Port Wells, we used a digital terrain model (DTM) derived from subaerial light detection and ranging (lidar) data collected on June 26, 2020, (Daanen and others, 2021) and submarine multibeam sonar bathymetric data collected between August 12 and 23, 2020 (NOAA, 2020). In College Fiord, adjacent to Barry Arm to the east, we used multibeam sonar bathymetric data collected between March 25 and August 26, 2021 (NOAA, 2021). These data were combined at 5 m horizontal resolution.
 
For the subaerial portions of the computational domain outside of Barry Arm, we used a 5 m interferometric synthetic aperture radar (IFSAR)-derived DTM for Alaska (U.S. Geological Survey, 2018, accessed through Alaska Division of Geological and Geophysical Surveys, 2013). Below the MHHW waterline and outside of Barry Arm and College Fiord, we used one of two existing topobathymetric sources. In Passage Canal, we used an 8/15 arc-second dataset (~12 m grid cells) for Whittier and Passage Canal (NOAA, 2009b). Elsewhere, we used an 8/3 arc-second dataset (~59 m grid cells) for Prince William Sound (NOAA, 2009a). These two topobathymetric datasets were themselves derived from multiple data sources, including, but not limited to: National Ocean Service hydrographic surveys, National Elevation Dataset topography, and digital coastlines datasets. The source data for both topobathymetric datasets were sparse in both deep water and near shore (up to 1.5 km spacing between observations), which necessitated interpolating over those areas. This process, which is detailed by Caldwell and others (2011), gave substantial weight to the shoreline topography in the assignment of interpolated depths in the nearshore zone. Because our results use the more recent and higher resolution IFSAR-derived topography, which has a different shoreline, we re-interpolated a narrow band of nearshore grid cells using a similar methodology.
 
We defined the nearshore re-interpolation zone based on a constant horizontal distance from the edge of valid IFSAR observation. We used a distance of 83 m because it results in the re-interpolation of at least one but no more than two of the 8/3 arc-second topobathymetric grid cells. We first removed any grid cell of either the Prince William Sound topobathymetric dataset (NOAA, 2009a) or the Whittier and Passage Canal topobathymetric dataset (NOAA, 2009b) at its original resolution that overlapped the near-shore re-interpolation zone. After removing the grid cells in the nearshore re-interpolation zone from these two topobathymetric datasets, we bilinearly interpolated and resampled both datasets from their original resolution to match the 5 m resolution of the IFSAR DTM. We then merged the two topobathymetric datasets with the IFSAR DTM. This yielded a 5 m dataset with missing values only in the nearshore re-interpolation zone. We then added the higher resolution and more recent Barry Arm and College Fiord multibeam sonar bathymetric data, as well as the Barry Arm lidar topographic data, directly to the regional dataset in their original footprints. These data were collected closer to shore, well within the re-interpolation zone that we defined for the lower resolution topobathymetric data and had no previously interpolated zones, thus requiring no additional clipping. Accordingly, we allowed the gap between the edge of the multibeam bathymetric data footprints and the lidar- or IFSAR-defined shoreline to represent the interpolation zone for these data. Finally, we interpolated across all the missing nearshore values using bilinear interpolation, thereby generating a single, continuous 5 m topobathymetric raster.
 
References Cited
 
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