Bathymetric change of South San Francisco Bay, California: 1979 to 2020

Using ESRI’s Aggregate tool (Environmental Systems Research Institute, Inc., 2021), the 2010s DEM was converted to 50-m resolution.

1980s South Bay bathymetric DEM was constructed using steps from Foxgrover and others (2004)

The 1980s DEM was adjusted for changes in tidal epoch and grid bias by subtracting 1.8 cm for tidal change and subtracting 0.3 cm for bias adjustment. The resulting grid was snapped to the 2010s 50-m DEM.

The 1980s adjusted DEM was subtracted from the 50-m 2010s DEM to determine bathymetric changes in the intervening decades.

Edits were made to the GeoTIFF’s internal projection assignment and to the altitude datum listed in the metadata. Although the horizontal datum and projection information were correctly defined as NAD83(2011) / UTM Zone 10 within the metadata files, the Geographic Coordinate System (GCS) and associated DATUM definition description stored internally, within the GeoTIFF itself, was incorrect. The originally assigned GCS was corrected from GCS_GRS_1980 to NAD 1983 (2011) and the projected coordinate system (PCS) from GRS_1980_UTM_Zone_10N to NAD 1983 (2011) UTM Zone 10N. Please note that the coordinate values and position of the GeoTIFF pixels did not change, only the projection definition. Within the metadata, the Altitude Datum Name, previously listed as Mean Lower Low Water (MLLW), was corrected. Although the input bathymetric DEMs are both referenced to MLLW, the change grid represents relative change between the two time periods and is not directly referenced to MLLW. This clarification was also applied to the Entity Type and Attribute Definition fields. The last two sentences of the abstract were edited to clarify that the 1980s DEM was corrected for both grid interpolation bias and a tidal datum adjustment prior to calculating the change DEM. The metadata available from a harvester may supersede metadata bundled within a download file. Users are advised to compare the metadata date of this file to any similar file to ensure they are using the most recent version. (afoxgrover@usgs.gov)