30-m Topography and bathymetry grid produced from swath interferometric, multibeam, and lidar datasets (navd_bath_30m Esri binary grid, UTM Zone 19N, WGS84)

Each source bathymetric or topographic data were imported into ArcGIS (v. 9.3.1) from their native format and converted to an Esri grid. The coarsest resolution of any input grid was 30-m, so that was the target resolution for the composite grid. For any source data that was higher than 30-m resolution, the grid was resampled to 30-m in ArcMap (version 9.3.1). Each individual dataset was also projected to UTM-zone 19 N (WGS-84 datum). The following sources were already WGS-84 UTM zone 19N Esri grids and required no transformation or format conversion before resampling: Barnhardt and others 2006; Ackerman and others, 2006; Barnhardt and others, 2009; Andrews and others, 2010; and Barndhardt and others, 2010. The Butman and others, 2007 grid was in NAD83 UTM zone 19N, so NAD_1983_To_WGS_1984_5 was used to transform the projection before resampling. Poppe and others, 2006 was an ASCII text grid (4-m), which was converted to an Esri grid using the ASCII to raster converter, and was transformed from NAD83 UTM zone 19N to WGS84 UTM Zone 19N using NAD_1983_To_WGS_1984_5. Both of the NOAA Hydrographic surveys (H11421 & F00508) were converted from .bag format to xyz text using the online conversion provided by the NOAA/NGDC website. The xyz files in NAD84 UTM Zone 19N were converted to Esri grids by first 'adding xy data' in ArcMap and then converting features to raster. The NAD_1983_To_WGS_1984_5 transformation was used to get the data into WGS84. The Lidar data were provided as GeoTiffs in GCS NAD83. The GeoTiffs were converted to Esri grids in ArcMap and were reprojected in ArcToolbox to UTM Zone 19N WGS84 using the NAD_1983_To_WGS_1984_5 transformation. Finally, the GOMMI (SAIC, UNH, and NOAA) survey was provided as a NAD83 GCS xyz file. The xyz file was converted to raster the same way that the NOAA hydro surveys were converted, and it was converted from GCS NAD83 using reproject in ArcToolBox and the NAD_1983_To_WGS_1984_5 transformation. Resampling for each source grid was done in ArcMap (version 9.3.1) using the 'Resample' tool. The output cell size for all the source grids was 30m and the Resampling technique was 'Bilinear'.

The Lidar data was the only dataset that was in NADVD88 vertical coordinate system. All the other bathymetric surveys were published in MLLW. After resampling and mosaicking (using the 'mosaic to new raster tool with 32_bit_signed pixels and the blend method) all grids except the Lidar, the composite bathymetric Esri grid was converted to a shapefile using 'raster to feature'. Xtools (version 7.1.0) was used to add and populate x and y fields and export the attribute table to a text file. VDatum (v2.3.3) was used to convert the bathymetric surveys (soundings) to NAVD88 using the "Maine, New Hampshire, Massachusetts - Gulf of Maine, Version 01 (1983-2001) regional transformation grid." A new vertically adjusted xyz file was then converted to an Esri grid in ArcMap (version 9.3.1) using 'add xy data' and 'convert feature to raster'.

After the lidar and composite bathymetry data were in Esri format, a common resolution (30m), and horizontal and vertical coordinate system (WGS84 UTM Zone 19 N and NAVD88), the ArcMap (v. 9.3.1) mosaic tool was used again to combine the data into one grid (with 32 bit signed pixel depth). 30-meters was chosen as the output resolution and the blend function was chosen for overlapping areas.

Edits to the metadata were made to fix any errors that MP v 2.9.30 flagged. This is necessary to enable the metadata to be successfully harvested for various data catalogs. In some cases, this meant adding text "Information unavailable" or "Information unavailable from original metadata" for those required fields that were left blank. Other minor edits were probably performed (title, publisher, publication place, etc.). The distribution format was modified in an attempt to be more consistent with other metadata files of the same data format. The metadata date (but not the metadata creator) was edited to reflect the date of these changes. The metadata available from a harvester may supersede metadata bundled within a download file. Compare the metadata dates to determine which metadata file is most recent.

Added keywords section with USGS persistent identifier as theme keyword.