Seismic-Reflection Profiles in SEG-Y Format from Eastern Rhode Island Sound Collected in 1975

Original seismic records of cruise ASTR-75-JUN were obtained using a towed EG&G Uniboom system with a half-second fire rate. The signal was amplified and filtered to a 200- to 4000-Hz bandpass. The seismic data have 1- to 2-m resolution. Seismic data were printed on EPC recorders at a quarter-second sweep rate. The hydrophone array and catamaran float with mounted transducer were towed about 15 meters astern of the survey vessel. This configuration, coupled with ship speed, resulted in a sound source/receiver separation of approximately 10 meters.

Original seismic records were scanned at 300 dpi, 8-bit grayscale on an Ideal Contex Crystal TX 40 scanner using Ideal ScanOS version 2.5.4 software and saved as TIFFs, after being roughly rotated and cropped. Some seismic lines were too long to scan at once and were cut into sections, other lines were collected in sections. These sections are noted in the file names with lower-case letters after the line number. For instance, a75_625Ab_1.tif signifies the cruise as R/V Asterias in 1975 (ASTR75-June), line 25A, section b, SEG-Y segment _1, and TIFF format. Capitalized letters are part of the original line number, as recorded on the seismic line.

TIFFs were then opened in Adobe Photoshop CS2 and saved as 200 dpi grayscale TIFFs.

Grayscale TIFFs were further processed in Adobe Photoshop CS2 in order to aid in creating the SEG-Y files. These TIFF images were rotated so they were nearly perfectly horizontal, cropped to start and end shots with known positions, and resampled using bicubic filtering, such that each horizontal pixel of the image corresponds to a trace and each vertical pixel corresponds to a time sample, based on a 0.5 second fire rate and 0.25 sec sweep rate (250 ms) and an assumed 0.08 sample rate. For instance, a 30-minute image is 3600 shots/pixels wide (30*60/0.5) and 3125 pixels high (250 ms/0.08 ms). Seismic-reflection profiles that had noted changes in ship speed or places where recording stopped for belt changes were split into segments, so each file was obtained at roughly the same speed. These segments are labeled with _1 or _2 after the section, thus the file names differ slightly from the line names as used in the logbook. Since TIFF images were clipped in the process of making SEG-Y files, users are encouraged to view the TIFF images available in this report (shttp://pubs.usgs.gov/of/2009/1003/html/eris_prof.html) in order to see field notes related to data acquisition and weather conditions, which were written directly on the paper records.

Rotated, cropped, and resampled grayscale TIFFs were run through tif2segy, a Unix shell script written by Andrew MacRae (Saint Mary's University, Nova Scotia) and used to convert TIFFs to SEG-Y format. Tif2segy requires two other programs to run successfully: Seismic Unix (http://www.cwp.mines.edu/cwpcodes) and Netpbm tools (http://netpbm.sourceforge.net). The default sample interval within the Tif2segy script was edited and set to 80 microseconds using the Unix text editor, vi. The ASCII header was also edited to reflect the current processor and processing date. Quality control was performed by viewing the SEG-Y files using SeisVU SEG-Y File Viewer (1.0.0.1).

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. An online link was added to a cross-reference. Fixed an online link to a cross-reference. 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.

Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog.

Additional information regarding file availability through GeoMapApp was added to the metadata. This included an additional distribution link pointing to CMGDS.

Added keywords section with USGS persistent identifier as theme keyword.