Merged topography and bathymetry, Glacier Bay and Icy Strait, Alaska

This work integrated multiple topographic and bathymetric data sources to generate a merged topobathymetric map of Glacier Bay, Alaska (AK) and vicinity, including Icy Strait and parts of Lynn Canal. Earlier topobathymetric sources covering the Glacier Bay region were originally developed by the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information at three resolutions: 8/3 arc-second (NOAA, 2010b), 8/15 arc-second (NOAA, 2010a, 2012a, 2012b), and 1/3 arc-second (NOAA, 2011). Our goal was to produce an updated high-resolution (5-m) topobathymetric dataset for the area that integrates newer multibeam bathymetry and 0.5-, 1-, and 5-m resolution topography. Where newer data sources were not available, we supplemented our dataset with the earlier NOAA topobathymetric rasters.

The methodology we used was (1) horizontally and vertically adjust datasets to the same grid registration, (2) clip overlapping datasets to ensure a continuous topographic gradient or to remove previously interpolated data, (3) merge datasets based on date of acquisition and resolution, with priority going to newer higher resolution datasets, and finally (4) interpolate any missing data values remaining between the datasets. Details on specific steps are outlined in the following section.
Processing Details
We converted all data sources to North American Datum of 1983 Universal Transverse Mercator Zone 8N and Mean Lower Low Water (MLLW) before compiling. The conversion between vertical datums used constant values based on the nearest tidal gage station, Bartlett Cove, Glacier Bay, AK (NOAA, 2023). Each dataset was also bilinearly interpolated and resampled to the same grid registration.

We combined three preexisting datasets in the subaerial portions of the domain with the following preference: (1) 0.5- to 1-m lidar-derived digital terrain models (DTMs) (U.S. Geological Survey, 2019), (2) 5-m interferometric synthetic aperture radar (IFSAR)-derived DTMs (U.S. Geological Survey, 2022), and (3) the merged topobathymetric 8/3 arc-second dataset for the portion in the northwest corner of the domain not covered by the prior two datasets (NOAA, 2010b).

In the submarine portion of the domain, we combined fifteen bathymetric and five topobathymetric sources. Variable resolution multibeam sonar bathymetric attribute grid (BAG) data covered the majority of Glacier Bay and Muir Inlet, as well as smaller areas in the region (NOAA, 2004a, 2004b, 2009a, 2009b, 2009c, 2009d, 2009e, 2018, 2020, 2021a, 2021b, 2021c, 2021d, 2021e). A 5-m resolution multibeam sonar bathymetric dataset collected by the U.S. Geological Survey (Carlson and others, 2002; Wong and others, 2002) covered the majority of the southern part of Glacier Bay. Areas without multibeam bathymetry were covered by one of the five NOAA topobathymetric rasters with preference given to the 1/3 arc-second, followed by the 8/15 arc-second, and lastly the 8/3 arc-second datasets.

During the merging process, we omitted areas for two reasons: first, to ensure a continuous topographic gradient between datasets, and second, to improve accuracy where observations were previously interpolated. If there was overlap between multiple datasets, we clipped the older or lower resolution dataset by the footprint of the newer higher resolution dataset. In locations with prograding deltas observed by multiple multibeam surveys, we removed all observations between the shoreline (defined as zero elevation in the North American Vertical Datum of 1988) and the footprint of the most recent survey. The nearshore bathymetry in the topobathymetric datasets (NOAA, 2010a, 2010b, 2011, 2012a, 2012b) was previously interpolated (Caldwell and others, 2012). These 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 topobathymetric datasets were sparse in both deep water and near shores (see data source resolutions in Table 3 of Caldwell and others [2012]), which necessitated interpolating over those areas. This process gave substantial weight to the shoreline topography in the assignment of interpolated depths in the nearshore zone. Because our merged dataset incorporates more recent and higher resolution lidar-and IFSAR-derived topography (U.S. Geological Survey, 2021), which have different shorelines, we re-interpolated a narrow band of nearshore grid cells using a similar methodology. We defined the nearshore re-interpolation zone as 115 m from the edge of lidar or IFSAR data 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 (the coarsest resolution of the topobathymetric datasets). We removed any grid cells from the topobathymetric datasets within this nearshore re-interpolation zone and any cells that remained between the shoreline and the more recent multibeam BAG surveys. We did not remove the remaining topobathymetric cells between the shoreline and the USGS multibeam survey because this would lead to the removal of ~700 m of data in some areas.

Finally, all datasets were merged and bilinearly interpolated across all the missing values, thereby generating a single, continuous 5-m topobathymetric dataset. We provide a 5-m raster file indicating the data source for each grid cell. In this file, 1 corresponds to NOAA merged topobathymetry, 2 corresponds to USGS multibeam bathymetry, 3 corresponds to NOAA multibeam bathymetry, 4 corresponds to USGS IFSAR-derived DTMs, 5 corresponds to USGS lidar-derived DTMs, and 0 is where there is no data (to be interpolated). Further details about processing can be found in the processing_steps folder.

This data release includes: (1) a continuous 5-m topobathymetric raster of Glacier Bay, AK (glacier_bay_5m_mllw.tif), (2) a 5-m raster showing where valid data is located (data_coverage.tif)  (3) a spreadsheet of data source references (data_sources.csv), and (4) a zipped folder containing files and scripts used to process the data sources (processing_steps.zip).

Disclaimer: Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
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