Point Shapefile of the Interpreted Flooding Surface Isopach Based on Seismic-Reflection Profiles Collected in Apalachicola Bay in 2006 from U.S. Geological Survey Cruise 06001 (FLOODISO_GEOG.SHP, Geographic, WGS84)

Two different seismic systems acquired data in Apalachicola Bay in 2006. One system was the EdgeTech FSSB 424 (4-24kHz) aboard the R/V Rafael. These data were acquired as SEG-Y files using SBLogger. The second seismic system was also an EdgeTech FSSB 424 chirp system mounted on the USGS autonomous vehicle IRIS. These data were acquired with JSTAR in JSF format and converted to SEG-Y format using a C-program written by Tom O'Brien (USGS, Woods Hole). These SEG-Y files were then converted from IEEE format to IBM floating point using SIOSEIS, and the shots were renumbered starting at one. With initial preparation work on the seismic data complete, these data and navigation needed to be loaded into Landmark SeisWorks software for interpretation. In order to load the seismic data and navigation into Landmark SeisWorks software the navigation needed to be extracted from the header of the seismic data. An AWK script was used to extract the navigation from the seismic data headers and export in UTM, Zone 16 eastings and northings, rounded to the nearest meter.

Once the navigation is extracted from the seismic data, this navigation has to be loaded into the interpretation software - Landmark SeisWorks version R2003. The navigation is loaded using Data - Management - Seismic Data Manager. A new survey is created for each acquisition system (06001 for the Rafael data, asv06 for the IRIS data). Then, Data - Import - Seismic Data Loader and point to the navigation text file. When loading the navigation, use a decimation of 0, use first shot point if duplicates are found, and overwrite data in target project if necessary. A decimation of zero was used because the IRIS navigation had already been decimated to take every 5th record from the complete navigation extracted from the headers of the IRIS seismics. The Rafael data did not need decimation. The Rafael data had a 1/4 second fire rate while the IRIS data fired at approximately 15 shots per second. Once the navigation is loaded and verified, then the actual seismic data can be loaded. To do this, use PostStack Data Loader. There was a small issue in working with seismic data in SeisWorks where it's better to have all the seismic profiles at the same sample rate. It's a display issue in the interpretation phase where opening a profile in a window with a different sample rate than the previously loaded profile doesn't always refresh the window properly. The result is an incorrect interpretation - the interpreted line falls in the wrong spot vertically. The seismic data were resampled to the same sample rate to eliminate this problem. The Rafael acquired data at two different sample rates: 40 microseconds and 80 microseconds. The Rafael seismics were all resampled to 40 microseconds in the PostStack data loader. Additionally, the lines had an automatic 8-bit scaling applied to each profile when loaded. The IRIS seismic lines were acquired with two sample rates - 23 microseconds and 46 microseconds. All of the lines were resampled to a 40 microsecond sampling interval in PostStack data loader and had an automatic 8-bit scaling applied to each profile when loaded. With the seismic data now loaded, the project has to be modified so these changes are reflected in the surveys and the data can be interpreted.

The ravinement horizon was created in SeisWorks, and this surface was digitized from each seismic reflection profile where present. Initially the interpreted surface was referred to as a ravinement surface, so most of the processing steps will use that terminology instead of the more appropriate flooding surface. On seismic-reflection profiles this surface has a high-amplitude signature where it separates Pleistocene deposits from Holocene estuarine fill and has a moderate amplitude signature where it crosses the paleo-valleys and separates the underlying seismic unit characterized by parallel, continuous, closely-spaced reflectors with moderate acoustic amplitude from the overlying unit characterized by weak-amplitude reflectors.

Once the interpretation was complete, the ravinement horizon was subtracted from the sea floor horizon to create a ravinement isopach unit. This isopach unit was then exported as a text file with the following information in separate columns for each point: line name, easting, northing, and thickness of the unit in milliseconds (two-way travel time). This process step and all subsequent process steps were overseen by the same person - VeeAnn A. Cross.

A header line is added to the exported text file, and converted from a tab-delimited file to a comma-delimited file.

ArcMap 9.2 was used to load this text file as an event theme using Tools - Add XY data. The projection is defined on input as UTM, Zone 16, WGS84.

This event theme is converted to a shapefile by right mouse click - Data - Export Data and generating the output shapefile raviso.shp.

Any points falling outside Apalachicola Bay were deleted. The following attributes were added to the shapefile: filter_ms, and mtrs_1800. The Selection tool (select by location) was used to select any points falling within 75 meters of a man-made feature. Features were selected that intersected ApalachicolaBaseMap polygon shapefile with a buffer applied to the polygon of 75 meters. The ApalachicolaBaseMap polygon is available from USGS Open-File Report 2006-1381. With these records selected, a value of -9999 was assigned to the filter_ms attribute using field calculator. The selection was switched to the other records and the field calculator was used to copy the ms attribute values to the filter_ms attribute. Field calculator was used to populate the attribute mtrs_1800 by converting the isopach thickness in milliseconds to thickness in meters using 1800 meters per second where filter_ms does not equal -9999. In cases where filters_ms=-9999, mtrs_1800 is set to the value -9999 (a common NODATA value).

The original shapefile in UTM, Zone 16, WGS84 was projected to Geographic, WGS84 using ArcMap 9.2 - ArcToolbox - Data Management Tools - Projections and Transformations - Feature - Project. No datum transformation was necessary. The shapefile was renamed to the more appropriate floodiso_geog.shp.

Edits to the metadata were made to fix any errors that MP v 2.9.32 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 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.