USGS OFR 2011-1127: Construction of a 3-Arcsecond Digital Elevation Model for the Gulf of Maine, U.S. Geological Survey/MA Coastal Zone Management Geologic Mapping Data

U.S.Geological Survey and Massachusetts Coastal Zone Management Geologic Mapping

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U.S. Geological Survey/MA Coastal Zone Management Geologic Mapping Data

Figure 12. Map showing the extent of the geologic mapping data for the Gulf of Maine from the Massachusetts Seafloor Mapping Cooperative by the U.S. Geological Survey and the Massachusetts Office of Coastal Zone Management.

In cooperation with the Massachusetts Office of Coastal Zone Management (CZM), NOAA, the University of New Brunswick, UNH, and the CHS, the U.S Geological Survey (USGS) is conducting geologic mapping of the seafloor offshore Massachusetts to characterize the surface and subsurface geologic framework. The long-term goal of this mapping effort is to produce high-resolution geologic maps and a Geographic Information System (GIS) that will serve the needs of research, management and the public. (U.S. Geological Survey 2011)

Nahant-Gloucester, Boston Harbor, Cape Ann-Salisbury, Duxbury-Hull, and Northern Cape Cod Bay were surveyed as part of the program (fig. 12).

Data Properties:

Vertical Datum: MLLW
Vertical Accuracy: 0.2 m
Coordinate System: UTM Zone 19
Horizontal Datum: WGS84
Horizontal Accuracy: ± 2 m
Resolution: 5 m (cabath5m, ccb_bath_5m, dh_bathy5m, se_5mbath), 30 m (bh_30mbath)
Period Covered by Data: 2001 (bh_30mbath), 2005 (cabath_5m), 2006 (ccb_bath_5m), 2007 (dh_bathy5m), 2008 (se_5mbath)
Format: ESRI Grid 32 Bit Floating Point
Date Data Downloaded: June 2011

The ESRI 32-bit floating point grid was converted to geographic coordinates (degrees) using the GDAL gdalwarp tool, with output saved in GMT .grd format. The GMT grid was then converted to ASCII XYZ format using the GMT grd2xyz tool.

The vertical datum was adjusted to NAVD88 using the method described in Common Processing Steps and Data.

The data had to be processed to a coarser resolution of 30 m due to the large size of the 5 m resolution files. GMT blockmedian command was used to decrease the resolution from 5 m to 30 m using a grid spacing of 30 m for the region of interest (71°30' to 63° W, 39°30' to 46° N). For more information on blockmedian, see Common Processing Steps and Data.