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DEM and Uncertainty for the Bahamas

We provide an example of code to download and process depth and elevation data from the "gebco", "copernicus", and "mar_grav" data sources in Table 1, and then generate a DEM and accompanying interpolation uncertainty grid. First, we download all the data, and then process the data by masking out GEBCO data where TID is equal to 0 (Land) or 40 (Predicted based on satellite-derived gravity data - depth value is an interpolated value guided by satellite-derived gravity data). See the GEBCO Cookbook chapter on GEBCO TID generation for more information.

We then stack the raster data sources with higher weighted datasets masking out lower weighted datasets and apply spline interpolation to the bathymetry by limiting the interpolation to an upper limit value of zero and clipping the resulting grid to an automatically generated coastline from the Copernicus data.

Lastly, we combine this bathymetric surface with the other data sources that have a weighting above the min_weight specification (in this example, min_weight=.15), and apply spline interpolation with a weighted averages of these data sources to generate the final integrated bathymetric-topographic DEM.

To generate the configuration file that is then used to generate the 15 arc-second resolution DEM and the interpolation uncertainty grid, execute the following command:

waffles -R -79.5/-76.5/25/28 -E 15s -O gebcop -p -w -m -P epsg:4326 -M cudem:min_weight=.15:landmask=True:pre_count=1 gebco,-102:exclude_tid=0/40,.015 copernicus,-103,10 mar_grav,-106:bathy_only=True,.001 gmrt,-101:swath_only=True,1.5 --config

The contents of the generated config file configuration file (gebcop15_n28x00_w079x50_2023v1.json) are as follows:

{
    "mod": "cudem:min_weight=.15:landmask=True:pre_count=1",
    "mod_name": "cudem",
    "mod_args": {
        "min_weight": ".15",
        "landmask": true,
        "pre_count": "1"
    },
    "kwargs": {
        "verbose": true,
        "sample": "bilinear",
        "xsample": null,
        "ysample": null,
        "dst_srs": "epsg:4326",
        "srs_transform": false,
        "fltr": [],
        "name": "gebcop15_n28x00_w079x50_2023v1",
        "cache_dir": "/home/ncei/Projects/crm/software/.cudem_cache",
        "ndv": -9999,
        "xinc": 0.004166666666666667,
        "yinc": 0.004166666666666667,
        "want_weight": true,
        "want_mask": true,
        "data": [
            "gebco,-102:exclude_tid=0/40,.015,0",
            "copernicus,-103,10,0",
            "mar_grav,-106:bathy_only=True,.001,0",
            "gmrt,-101:swath_only=True,1.5,0"
        ],
        "src_region": [
            -79.5,
            -76.5,
            25.0,
            28.0
        ]
    }
}

To generate the DEM, execute the following command:

waffles -G gebcop15_n28x00_w079x50_2023v1.json

Output:

gebcop3_n28x00_w079x50_2023v1.json - json config file

gebcop3_n28x00_w079x50_2023v1_msk.tif - data mask

gebcop3_n28x00_w079x50_2023v1_stack.tif - stacks data 'stacked' output

gebcop3_n28x00_w079x50_2023v1_u.tif - uncertainty grid

gebcop3_n28x00_w079x50_2023v1.tif - final DEM

Figure 1. Final DEM generated from CUDEM code example.

Figure 2. Interpolation uncertainty grid generated from the best-fit interpolation uncertainty equation applied to the distance to the nearest measurement raster.