Alexander L. Nereson Ann E. Gibbs Li H. Erikson 20260313 raster digital data data release DOI: 10.5066/P13BXTXV Pacific Coastal and Marine Science Center, Santa Cruz, California U.S. Geological Survey https://doi.org/10.5066/P13BXTXV Alexander L. Nereson Ann E. Gibbs Li H. Erikson 2025 raster digital data Pacific Coastal and Marine Science Center, Santa Cruz, California U.S. Geological Survey Suggestion citation: Nereson, A.L., Gibbs, A.E., and Erikson, L.H., 2025, Topobathymetric digital elevation models – coastal Alaska: U.S. Geological Survey data release, https://doi.org/10.5066/P13BXTXV. https://doi.org/10.5066/P13BXTXV This dataset contains a 1-meter resolution, seamless topobathymetric digital elevation model (TBDEM) and associated spatial metadata for Shaktoolik, Alaska. The TBDEM contains best available multi-source topographic and bathymetric elevation data collected between the years 1900 and 2021. Processing was done by the U.S. Geological Survey (USGS), Pacific Coastal and Marine Science Center (PCMSC) and results are provided as a Cloud Optimized GeoTIFF (COG). This product was created to help advance coastal storm response and recovery in Alaskan coastal communities in the wake of the September 2022 extratropical Typhoon Merbok disaster. It is being used by the USGS to support the development of dynamic flood models for more than 20 communities along the northwest coasts of Alaska. This product is intended for reuse by scientists, managers, and the general public. These data can be opened with most geographic information systems (GIS) software for data visualization and analysis purposes. Work was funded by Title VII of Division N in the Consolidated Appropriations Act, 2023 (Public Law 117–328) to support direct recovery and rebuilding decisions in the wake of declared disasters related to hurricanes and typhoons in 2022. For more information on these efforts, see https://www.usgs.gov/supplemental-appropriations-for-disaster-recovery-activities/typhoon-merbok-coastal-community. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the dataset in nonproprietary form, this metadata file may include some vendor-specific terminology. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the dataset in nonproprietary form, as well as in Esri format, this metadata file may include some Esri-specific terminology. 1900 2021 ground condition at the time source data were collected Complete None planned -161.4148 -161.0711 64.4049 64.2571 USGS Metadata Identifier USGS:9a2bd6f1-5ef0-483c-8b30-6441ea19dbda ISO 19115 Topic Category elevation Data Categories for Marine Planning Bathymetry and Elevation USGS Thesaurus topography bathymetry digital elevation models geospatial datasets Marine Realms Information Bank (MRIB) coast None U.S. Geological Survey USGS Coastal and Marine Hazards and Resources Program CMHRP Pacific Coastal and Marine Science Center PCMSC Geographic Names Information System (GNIS) State of Alaska Nome Census Area City of Shaktoolik Norton Sound Shaktoolik Bay No access constraints USGS-authored or produced data and information are in the public domain from the U.S. Government and are freely redistributable with proper metadata and source attribution. Please recognize and acknowledge the U.S. Geological Survey as the originator(s) of the dataset and in products derived from these data. This information is not intended for navigation purposes. PCMSC Science Data Coordinator U.S. Geological Survey, Pacific Coastal and Marine Science Center mailing and physical

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Santa Cruz CA 95060 831-427-4747 pcmsc_data@usgs.gov shaktoolik_browse.png Quick view image of seamless topobathymetric digital elevation model for Shaktoolik, Alaska PNG Global Mapper v25.0 and ArcGIS Pro 3.4 No formal attribute accuracy tests were conducted. Quality checks were performed on the elevation raster and spatial metadata files, including review of minimum/maximum elevation values, shoreline positions, gridding artifacts, and descriptive attributes. Data values fall within expected ranges. Dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details. The horizontal accuracy of the final seamless TBDEM was not assessed quantitatively. Please refer directly to the elevation data sources for measures of accuracy and uncertainty, when available. The authors calculated the mean bias error (MBE), and root mean square error (RMSE) of the final, seamless TBDEM relative to the check point subsets for Shaktoolik, Alaska. The MBE (TBDEM minus all check points) is -0.003 m and the RMSE is 0.047 m. For other measures of vertical accuracy, please refer directly to the metadata for each input data source cited below. U.S. Army Corps of Engineers (USACE) Joint Airborne Lidar Bathymetry Technical Center of eXpertise (JALBTCX) 2024 raster digital data online NOAA Office for Coastal Management https://www.fisheries.noaa.gov/inport/item/73829/ Digital and/or Hardcopy 2021 ground condition at time data were collected 2021 USACE NCMP tblidar Elevations in this data source were used with the other source data to interpolate a seamless topobathymetric digital elevation model. Alaska Department of Natural Resources, Division of Geological & Geophysical Surveys 2016 raster digital data online Alaska Department of Natural Resources, Division of Geological & Geophysical Surveys https://dggs.alaska.gov/pubs/id/29548 Digital and/or Hardcopy 2015 ground condition at time data were collected 2015 DGGS sfm Elevations in this data source were used with the other source data to interpolate a seamless topobathymetric digital elevation model. U.S. Geological Survey 2015 raster digital data online U.S. Geological Survey https://www.sciencebase.gov/catalog/item/611359bcd34ed11898f71339 Digital and/or Hardcopy 2012 ground condition at time data were collected 2012 USGS ifsar Elevations in this data source were used with the other source data to interpolate a seamless topobathymetric digital elevation model. Karin Ohman 2012 tabular digital data online University of California, Santa Cruz https://escholarship.org/uc/item/1xd4884z Digital and/or Hardcopy 2011 ground condition at time data were collected 2011 UCSC sonar Elevations in this data source were used with the other source data to interpolate a seamless topobathymetric digital elevation model. Office of Coast Survey, National Ocean Service, NOAA, U.S. Department of Commerce 2004 tabular digital data online NOAA National Centers for Environmental Information https://www.ngdc.noaa.gov/nos/H02001-H04000/H02479.html Digital and/or Hardcopy 1900 ground condition at time data were collected 1900 NOS lead line Elevations in this data source were used with the other source data to interpolate a seamless topobathymetric digital elevation model. National Oceanic and Atmospheric Administration (NOAA) 2024 online National Oceanic and Atmospheric Administration (NOAA) https://tidesandcurrents.noaa.gov/ online database 2024 date data were accessed conversion constant Local conversion constants Alaska Department of Natural Resources 2024 online Alaska Department of Natural Resources https://dggs.alaska.gov/hazards/coastal/ak-tidal-datum-portal.html online database 2024 date data were accessed conversion constant Local conversion constants Define an area of interest (AOI) and gather published topographic and bathymetric elevation datasets with coverage in the AOI. 20240404 View and prioritize source elevation datasets based on date of acquisition, spatial distribution, accuracy, and point density. In general, more recent dates of acquisition, wider spatial distribution, higher accuracy, and higher point density result in a higher priority level. Source elevation datasets are listed in their order of priority in the Lineage section of this metadata file and in the associated spatial metadata, where the first source dataset is of the highest priority. 2021 USACE NCMP tblidar 2015 DGGS sfm 2012 USGS ifsar 2011 UCSC sonar 1900 NOS lead line 20240404 Prepare each source elevation dataset, as applicable. In Global Mapper software: A) transform the source dataset from its native horizontal and vertical spatial reference systems to the appropriate NAD83 (2011) Universal Transverse Mercator (UTM) zone projection and to NAVD88 GEOID12B, respectively. Convert source elevations to NAVD88 by adding a local conversion constant to the native tidal/ellipsoidal heights of the source dataset. Conversion constants used for this work come from NOAA Tides and Currents (https://tidesandcurrents.noaa.gov/) or the Alaska Tidal Datum Portal (https://dggs.alaska.gov/hazards/coastal/ak-tidal-datum-portal.html) for the most recent available tidal epoch for the tide station nearest to the AOI. The local constants used for this project are listed in the last process step of this metadata file, along with any additional transformations that may have been used bring source datasets into NAVD88 GEOID12B. B) Save the transformed dataset as a LAZ point file. C) Clip LAZ point file to AOI polygon. D) Classify and remove non-ground points from structure-from-motion (SfM)-derived digital surface models (DSMs) using lidar auto-classification. E) Spatially thin LAZ file to one-meter resolution, using the minimum value method. F) Clip the LAZ file to all higher-priority datasets using a buffer of 2x the average point density/resolution of the source dataset being prepared. G) Split the LAZ file into two subsets, one containing 95 percent of the points (active points) and the other containing the remaining 5 percent, or every 20th point (check points). The active points are later gridded in the elevation model along with associated interpolation guides to derive the final topographic surface, while the check points are used to compute the interpolation accuracy of the derived surface. conversion constant 20240404 Create interpolation guides. Interpolation guides are author-defined 3D points, lines, or polygons used to help derive the final topographic surface. Interpolation guides are used to A) smooth or accentuate breaks in slope along shared boundaries of source datasets, B) prevent topographic creep/shoreline migration from onshore regions into offshore regions, C) fill data gaps in source datasets with plausible heights when local knowledge, qualitative field observations, remotely sensed optical imagery, or other information sources are available, or D) otherwise facilitate the seamless integration of all source datasets. Details of interpolation guides used to create the final elevation surface for this release are listed in the last process step of this metadata file. 20240404 Interpolate a one-meter resolution seamless elevation surface from input source data and interpolation guides using the Create Elevation Grid tool (triangulation method). 20240411 Export grid as a Cloud Optimized GeoTIFF (COG) using Global Mapper, clipping the grid bounds to the project AOI and snapping the output raster cells to the appropriate UTM zone projection, using a bilinear resampling method. 20240411 Quantify interpolation error in MATLAB by calculating the mean bias error (MBE) and root mean square error (RMSE) of the final, seamless TBDEM relative to the check point subsets. MBE and RMSE are reported in the Vertical Positional Accuracy section of this metadata file. 20240411 Create spatial metadata for each source dataset by converting LAZ points to simplified bounding polygons and save in an Esri file geodatabase feature class, along with descriptive attributes about the source dataset. Spatial metadata files are further described in the Entity and Attribute Overview section of this metadata file. 20240411 Perform quality checks on the output elevation raster and spatial metadata files, including review of minimum/maximum elevation values, shoreline positions, gridding artifacts, and descriptive attributes. 20240411 Metadata was modified to bring up to current USGS standards. The keyword for geospatial datasets was added. No data information was changed. 20260305 Manda Au U.S. Geological Survey Data Management Specialist Mailing

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Santa Cruz CA 95060 831-460-7575 mau@usgs.gov Special considerations: A) Vertical datum conversion constants: 0 m NAVD88 is -0.714 m above Mean Lower Low Water (at NOAA CO-OPS tide station: 9468691, Shaktoolik AK, via Alaska Tidal Datum Portal). B) Additional vertical transformations: i) 2011 UCSC sonar elevations were collected with respect to the water surface level at the time of collection. These values were converted to NAVD88 heights by calclating the average offset between spot elevations from each of the four 2011 UCSC profiles (a-d) and the 2021 USACE NCMP tblidar. The average difference for each profile was then used as a constant vertical offset and applied to each profile respectively. The values added to each profile are as follows: a=1.6 m, b=0.7 m, c=1.4 m, d=1.6 m. These offsets fall within the expected range of corrections required within the tidal range at Shaktoolik (via Alaska Tidal Datum Portal). C) Interpolation guides: Three types of interpolation guides were created by the authors to prevent topographic creep from onshore environments, fill data gaps, or reflect the most recently known ground conditions: i) inland river and tidal channel guides (author-defined 3D points) were created in Global Mapper in the northern portion of the AOI. ii) source data gaps over inland lakes and ponds were digitized into 3D polygons with constant elevation values. iii) The floodplain of the Tagoomenik River in the southern portion of the AOI is covered in tall >2m-high vegetation that obscured ground levels in the 2015 DGGS sfm. In this region, floodplain elevations were modeled with the assumption that channel levees were at a constant elevation of 3.4 m NAVD88 and that elevations decayed linearly away from levee crests over a distance of 75 meters. conversion constant 20240411 Raster Grid Cell 15914 16067 1 Universal Transverse Mercator 4 0.9996 -159.0 0.0 500000.0 0.0 row and column 1.0 1.0 meters NAD83_National_Spatial_Reference_System_2011 GRS 1980 6378137.0 298.257222101004 North American Vertical Datum of 1988 0.001 meters Explicit elevation coordinate included with horizontal coordinates shaktoolik_tbdem_1m_1900_2021.tif Raster geospatial data file. U.S. Geological Survey Elevation Orthometric height in meters NAVD88 (GEOID12B). Values of -9999 = no data. Producer Defined -9999 No Data Producer defined -12.241 9.465 meters 0.001 These metadata describe a Cloud Optimized GeoTIFF (COG) raster file whose floating point grid cell values represent orthometric heights (elevations) in meters NAVD88 GEOID12B. The file name for the elevation raster follows the format: “location_tbdem_1m_YYYY_to_YYYY.tif”, where “location” is the geographic name of the place depicted in the data, “tbdem” indicates “topobathymetric digital elevation model”, “1m” indicates 1-meter grid resolution, and “YYYY_to_YYYY” indicates the date range (in years) of all the source data. The source data are further described in a supplementary "spatial" metadata file that contains polygonal boundaries and descriptive attributes for each source. Polygons and attributes are saved as a feature class in an Esri file geodatabase with a file name that follows the naming convention described above, along with the following suffix: "_spatial_metadata.gdb". The file geodatabase has been compressed into a ZIP file of the same name. The following attribute fields are included in the polygon feature class: Name of dataset (Title), the organization major project or activity (Source_Project), source dataset organization (Source_Organization), date(s) acquired (Date_Acquired), publication date (Publication Date), source elevation type (Data_Type), source projection (Source_Projection), source horizontal resolution (Source_Horizontal_Resolution), source horizontal datum (Source_Horizontal_Datum), source vertical units (Source_Vertical_Units), source vertical datum (Source_Vertical_Datum), source geoid (Geoid), spatial extent of source (Coverage_Area), source URL (Source_Publication), perimeter of polygon feature in meters (Shape_Length), and area of polygon feature in square meters (Shape_Area). Descriptive attributes for interpolation guides are set to Null. See Process Steps above for more information on how and where guides were created. U.S. Geological Survey U.S. Geological Survey - CMGDS mailing and physical

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Santa Cruz CA 95060 831-427-4747 pcmsc_data@usgs.gov These data are available in Cloud Optimized GeoTIFF (COG) raster file format accompanied by a spatial metadata geodatabase file and CSDGM FGDC-compliant metadata. Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. GeoTIFF Global Mapper v25.0 and ArcGIS Pro 3.4 Cloud Optimized GeoTIFF (COG) raster file whose floating point grid cell values represent orthometric heights (elevations). No data value is -9999. No compression applied. 440.9 https://doi.org/10.5066/P13BXTXV Data and metadata can be downloaded using the Network_Resource_Name link and scrolling down to the Topobathymetric digital elevation model of Shaktoolik, Alaska, 1900 to 2021 section. None Most geospatial data software and their supporting operating systems (for example, QGIS, Global Mapper, Esri ArcGIS Pro, or similar). 20260313 U.S. Geological Survey, Pacific Coastal and Marine Science Center PCMSC Science Data Coordinator mailing and physical

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Santa Cruz CA 95060 831-427-4747 pcmsc_data@usgs.gov Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998