Swath bathymetry collected by the U.S. Geological Survey in Woods Hole, MA and St. Petersburg, FL offshore of the Gulf Islands, MS, 2010 (ESRI binary grid, tmunro_50m)

SwathPlus Software (version: 3.7.0) was used to acquire the raw swath data (*.sxr) and output a processed soundings file (*.sxp). Several bathy filters were applied to the processed file within SwathPlus to remove erroneous soundings and reduce the density of the data. Corrections were also applied for speed of sound changes (using sound velocity profiles), ship motion, GPS antennae offsets, and transducer depth and angle below the surface. Bathy filters included a low amplitude (100), range (1-m below the surface), box (2-m to avoid nadir), alongtrack 1 (depth difference of 10-m, window size 10-m, and learn rate of 0.6), alongtrack 2 (depth difference of 1-m, window size 1-m, and learn rate of 0.9), and a mean filter (0.1-m).

CARIS (version: HIPS and SIPS 6.1; service pack 2) was used to import the processed bathy files (*.sxp) from SwathPlus format to CARIS HDCS data format using the conversion utility. The data were corrected for errors in soundings due to additional sound refraction not accounted for by sound velocity profiles using the CARIS refraction editor. These artifacts can be recognized in a cross-swath profile of a relatively flat patch of sea floor. When viewing the swath data across a profile, the sea floor will appear to have a "frown" or "smile" when in fact the data should be flat across the profile. Insufficient and/or erroneous sound velocity information, which is usually due to too widely spaced or non-existent velocity profiles within an area, results in an under or over-estimate of water depth which increases with distance from the center of the swath. The bathymetric data were also corrected to mean lower low water (MLLW) using a discrete tidal-zoning model (DTZ) developed by NOAA/NOS's Hydrographic Planning Team (Huang, personal communication, 2010) (<http://www.tidesandcurrents.noaa.gov/hydro.html>). The DTZ model corrects differences in tidal phase and amplitude between the survey area and observations made at NOS tide gauges at Gulfport Harbor (8745557) and Pascagoula NOAA Lab (8741533). The tidal zone models were imported into CARIS (version: HIPS and SIPS 6.1) as text files and used to correct tidal observations for each survey. Once the tidal zone model was imported into CARIS using the tide editor, the tidal range and phase offsets were applied and remerged in CARIS(version: HIPS and SIPS 6.1), making all the soundings relative to MLLW. A 5-meter base surface of tide corrected bathymetric soundings was created in CARIS, then exported as ASCII x,y,z data.

The 5-m ASCII x,y,z file (for each cruise; St. Pete and WHCMSC) was gridded in GMT (version: 4.2.1; Wessel and Smith, 1998) using 'blockmedian' with a cell size of 50 meters. This routine was conducted to minimize edge effects in the 'surface' gridding routine because these data were collected at approximately 40-50% seafloor coverage. Next a tension spline routine (at 0.1) in GMT was used ('surface') to create a netCDF grid.

The GMT grid (*.grd) was then converted to an ESRI Binary Grid via Mirone (version 1.5.0; Luis, 2007) and MATLAB R2007b (version 7.5.0.342) - save grid as - ArcGIS binary grid. The projection was defined in ArcMap (version: 9.3) using Data Management Tools - Projections and Transformations - Define Projection: UTM, zone 16N, WGS84 Datum.

Edits to the metadata were made to fix any errors that MP v 2.9.36 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.). Attempted to modify http to https where appropriate. Added a landing page link as the first link in the identification section. Updated the link to the field activity. The source information was incomplete and had to be modified to meet the standard. The distribution format name 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.