Data Sources & Acknowledgements

TopoBathySim relies on a federation of open-access geospatial datasets. We gratefully acknowledge the following agencies and specific surveys used for development, validation, and simulation.

The datasets are listed below in inverse order of priority (from global context to high-resolution survey truth).

Global Coverage (Tier 4)

General Bathymetric Chart of the Oceans (GEBCO)

  • GEBCO_2025 Grid

    • Description: A continuous terrain model for ocean and land, providing global context at 15 arc-second intervals.

    • Citation: GEBCO Compilation Group (2025) GEBCO 2025 Grid (doi:10.5285/1c44ce9e-0a53-431f-9780-3843464522c5).

    • Access: GEBCO Grid Download

Continental / Land (Tier 3.5)

U.S. Geological Survey (USGS) - 3DEP

  • 3D Elevation Program (3DEP)

    • Description: The source for high-quality topographic data of the conterminous United States, Hawaii, and U.S. territories.

    • Citation: U.S. Geological Survey, 2017, 3D Elevation Program (3DEP): U.S. Geological Survey Fact Sheet 2017–3081.

    • Access: 3DEP Homepage

Regional Bathymetry (Tier 3)

NOAA NCEI - CUDEM

  • Continuously Updated Digital Elevation Model (CUDEM)

    • Description: Ninth Arc-Second Resolution Bathymetric-Topographic Tiles. Used as a critical gap-filler for coastal inundation zones.

    • Citation: Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado, Boulder. 2014. Continuously Updated Digital Elevation Model (CUDEM) - Ninth Arc-Second Resolution Bathymetric-Topographic Tiles. NOAA National Centers for Environmental Information.

    • Access: Dataset Homepage | Bulk Access

Regional High-Resolution (Tier 2)

NOAA Office of Coast Survey - BlueTopo™

  • BlueTopo™

    • Description: A compilation of the best available public bathymetric data of U.S. waters, merged into a simplified product.

    • Citation: NOAA Office of Coast Survey. BlueTopo™.

    • Access: BlueTopo Portal

Local High-Resolution Lidar (Tier 1)

NOAA National Geodetic Survey (NGS)

  • Topobathymetric Lidar

    • Description: High-resolution nearshore bathymetry captured via green-wavelength Lidar.

    • Citation: National Geodetic Survey, 2026: 2023 NOAA NGS Lidar DEM. NOAA National Centers for Environmental Information.

    • Example (Long Island Sound): Methodology Report (PDF)

    • Access: NOAA Digital Coast

    Coverage Maximization & Survey Selection Strategy

    To manage the hundreds of overlapping proprietary surveys available via NOAA’s Digital Coast, TopoBathySim employs a dynamic Spatial Index to select the optimal data source for any given area of interest.

    When a simulation region intersects multiple available surveys, the system prioritizes them using the following Fusion Hierarchy:

    1. Vertical Datum Quality: Surveys referenced to NAVD88 (Geoid18) are strictly preferred over legacy NAVD88 or Ellipsoidal references, ensuring consistent vertical integration with water levels.

    2. Recency: Among surveys with equal datum quality, the most recently completed survey (based on end_date) is selected.

    3. Spatial Overlap: The system identifies all surveys intersecting the requested bounding box. Currently, the single “best” survey is selected to provide a self-consistent foundation, rather than blending multiple surveys which may have slight vertical offsets or temporal discrepancies.

    Within a selected survey, individual data tiles are fused using a Mosaic operation, where valid data overwrites NoData/Void areas.

Survey “Truth” Data (Tier 0)

NOAA NCEI - Bathymetric Attributed Grid (BAG)

  • Bathymetric Attributed Grids (BAG)

    • Description: The definitive format for multi-beam sonar surveys. When found, these overwrite all other sources.

    • Citation: NOAA National Centers for Environmental Information. “Bathymetric Attributed Grid (BAG) File Format.”

    • Access: NCEI Bathymetry Data Viewer

    • Programmatic Access: NOAA GeoPlatform Hydrographic Surveys

Fusion Strategy: Redundancy & Spatial Overwrite

A frequent scenario in TopoBathySim is the overlap between BlueTopo (Tier 2, Regional) and NCEI BAG (Tier 0, High-Res Truth). BlueTopo is distributed as large geographic mosaic tiles (e.g., BH5245GP) which contain compiled data from dozens of underlying surveys. Many of the newer sub-surveys inside these mosaics are also natively available via the NCEI BAG provider at much higher resolutions (e.g., 50cm).

Because BlueTopo macro-tiles aggregate both sparse historic data (which has no BAG equivalent) and modern high-resolution arrays, TopoBathySim intentionally fetches both layers without attempting to pre-filter redundancies at the network level.

The engine gracefully resolves this redundancy automatically in memory:

  1. Base Canvas: The full BlueTopo mosaic (e.g., 4m resolution) is fetched and instantiated, establishing a continuous base elevation canvas that includes the older historical soundings.

  2. High-Res Overlay: The engine simultaneously fetches the hyper-resolution 50cm or 1m BAG geometries for the modern surveys inside the bounding box.

  3. Spatial Overwrite: Using the policy’s defined transition operators (such as metric_feather blending), the native BAG arrays seamlessly overwrite their exact spatial footprints directly on top of the BlueTopo canvas in VRAM.

This top-to-bottom geographic override guarantees that older, non-BAG surveys inside the BlueTopo macro-tile are preserved, while the modern active swaths are dynamically upgraded to their highest possible fidelity with zero visual seams, duplicated points, or wasted network requests.

NoData Sentinel Evidence Matrix

TopoBathySim treats NoData handling as a provider-specific ingest concern and a merge-boundary safety concern. The table below records currently implemented, evidence-backed handling:

Implementation Note:

Shared sanitization is centralized in topobathysim.providers.base.sanitize_elevation_nodata. This keeps provider behavior consistent while still allowing provider-specific sentinel overrides.