Any spurious data points were removed during processing. For each seismic trackline there is one seismic-profile image that is hyperlinked by the field 'ImageName'. No duplicates exist. Results of the layback calculation are erratic along some tracklines where the survey speed was slower than normal or changed significantly, as well as instances of sudden and/or drastic heading changes, and especially when the heading was nearly due south and the back bearing (reciprocal of the heading crosses back and forth across the 0 and 360 degree boundary (e.g. line MV_tie2). For users who wish, pre-layback corrected shot navigation is provide in the “Old_East” and “Old_North” attributes of the 500 shot shapefile as well as the '2013-003-FA_512ishotunique.csv' file (included in the zip file with the 500-shots shapefile) for all the unique shotpoint locations and the original non-layback positions. The navigation for lines L1-L13, which had to be taken from HYPACK navigation files due to the catamaran GPS technical difficulties described below, contain several fewer navigation fixes than shots that were recorded in the Seismic SEG-Y (and PNG images) because recording of the HYPACK navigation was stopped prior to stopping the seismic acquisition system. For the rest of the survey, the last shot point is reported to be 1 shot more than the range of shots shown in the seismic PNG image. This is due to a known glitch in the SIOSEIS software process ‘swell’, which erroneously causes the last two shots of the output SEGY file to be numbered the same.
Sections of tracklines where navigation was recorded but no seismic data were logged are not included. There is no line L47f1 (acquisition system froze 2 minutes into this line, no good data were recorded), there is also no line L132 and L133. Time gaps occurred during this field activity where no surveying was done due to bad weather, rough seas and stops in port for crew changes. Planned surveying was paused and no main survey line data were collected during these times:
JD143 15:20 - JD146 20:06 (no data were collected on JD144 or JD145)
JD149 15:40 - JD151 18:59 (no data were collected on JD150)
JD153 00:01 - JD153 14:32
JD155 18:16 - JD156 02:06
JD158 06:12 - JD160 19:15 (no data were collected on JD159)
Horizontal_Positional_Accuracy:
Horizontal_Positional_Accuracy_Report:
Field activity 2013-003-FA: The SB-0512i was mounted on a catamaran sled and towed at the sea surface approximately 30 - 40 m astern of the M/V Scarlett Isabella. Position data were provided by a Global Positioning System (GPS) navigation receiver mounted on the catamaran, and data were transmitted to the acquisition computer on the vessel via a 2.4 GHz radio link. Technical difficulties during portions of 2013-003-FA caused the GPS system mounted on the catamaran to malfunction, so DGPS navigation was obtained from a receiver mounted on top of the acquisition van. Layback positions, which account for the linear distance between the shipboard DGPS receiver and the towed catamaran vehicle, were calculated trigonometrically during post-processing. Positional accuracy is assumed to be +/- 20 m; increased uncertainty arises because layback calculations do not account for fish motion behind the vessel, which is caused by sea state and vessel speed induced changes in the angle and scope of the tow cable.
Source_Information:
Source_Citation:
Citation_Information:
Originator: U.S. Geological Survey
Publication_Date: Unpublished Material
Title: raw seismic navigation
Type_of_Source_Media: disc
Source_Time_Period_of_Content:
Time_Period_Information:
Range_of_Dates/Times:
Beginning_Date: 20130522
Ending_Date: 20130611
Source_Currentness_Reference:
ground condition of survey dates: 20130522-20130611; see Completeness_Report for more information
Source_Citation_Abbreviation: raw data
Source_Contribution:
Seismic-reflection data acquisition 2013-003-FA: Chirp seismic data were collected using an EdgeTech Geo-Star FSSB sub-bottom profiling system and an SB-0512i towfish (0.5-12 kHz), which was mounted on a catamaran and towed astern of the M/V Scarlett Isabella of Cape May, NJ. Chesapeake Technologies' SonarWiz (v.5.03.0016) seismic acquisition software was used to control the Geo-Star topside unit, digitally log trace data in the SEG-Y Rev. 1 format (IEEE floating point), and record GPS navigation coordinates to the SEG-Y trace headers (in arc seconds of Latitude and Longitude, multiplied by a scalar of 100). Data were acquired using a 0.25-s shot rate, a 5-ms pulse length, and a 0.5 to 8 kHz frequency sweep. Recorded trace lengths were approximately 100 ms (2170 samples/trace and .000046-s sample interval).
Process_Step:
Process_Description:
SIOSEIS (version 2013.2) was used to read SEG-Y files, renumber shots starting from one, and write out new SEG-Y files. The original shot numbers, which were assigned by SonarWiz sequentially over the duration of an acquisition session despite SEG-Y file changes, are preserved in the raw SEG-Y data. In the same process, channel one (trace one, which is the envelope detected trace) within each shot was output. Channels two and three (raw data) were discarded. This process step and all subsequent process steps were performed by the same person - Wayne Baldwin.
Process_Date: 2013
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Wayne Baldwin
Contact_Organization: U.S. Geological Survey
Contact_Position: Geologist
Contact_Address:
Address_Type: mailing and physical address
Address: 384 Woods Hole Rd
City: Woods Hole
State_or_Province: MA
Postal_Code: 02543-1598
Country: USA
Contact_Voice_Telephone: 508-548-8700 x2226
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: wbaldwin@usgs.gov
Process_Step:
Process_Description:
During the acquisition of lines 1 to 13, erroneous coordinates were intermittently recorded to the SEG-Y trace headers due to technical difficulties with the GPS system mounted on the catamaran vehicle. Scripts utilizing AWK (no version), Proj (version 4.6.0), and the Unix commands egrep, join, sort, and cat were used to replace coordinates in the text files created by the process described above with correct navigation from HYPACK raw files. The following steps were performed for each file: 1) navigation data were extracted from HYPACK raw files, creating a text file containing fields for Longitude, Latitude, and Julian day/UTC time (JD:HH:MM:SS); 2) records for the first and last shots, shots at multiples of 100, and the first record for each UTC second (files generally contain 4-5 shots per UTC second since the chirp shot rate is 4 Hz, while navigation update frequency is 1 Hz) were extracted from the original text files, and saved to new text files, only maintaining fields for LineName, ImageName, Shot, Year, and Julian day/UTC time (JD:HH:MM:SS); 3) files from the two previous steps were joined using the common field Julian day/UTC time (JD:HH:MM:SS); and 4) Geographic coordinates (WGS84) were converted to UTM zone 19 coordinates (WGS84) using Proj (version 4.6.0). The corrected navigation text files were substituted for the original data extracted from the SEG-Y trace headers.
Beginning with Line 14, DGPS navigation was obtained from a Hemisphere receiver mounted on top, port side, forward end of the acquisition van. These coordinates were recorded in the SEG-Y source and receiver trace headers. Seismic Unix (version 4.2) was used to read renumbered SEG-Y files, write a Seismic Unix file, and extract SEG-Y trace header information, including shot number, longitude, latitude, year, Julian day, and time of day (UTC). Header information from each SEG-Y file was saved to text files containing records for the first and last shots, and all shots in between with unique navigation coordinates. Geographic coordinates (WGS84) were converted to UTM zone 19 coordinates (WGS84) using Proj (version 4.6.0).
Process_Date: 2013
Process_Step:
Process_Description:
A Python script was used to apply layback to all corrected (lines 1 to 13) and original (beginning with line 14) seismic navigation.
Layback positions, which account for the linear distance of 48 meters between the shipboard DGPS receiver and the towed catamaran vehicle, were calculated trigonometrically during post-processing. A moving median filter was applied to azimuths used in the layback correction.
A Proj command was used to convert the layback-corrected positions back into Geographic coordinates and an AWK script was used to save all of the unique shot point navigation and shot point files containing the start and end shots and shots at an even 500 shot interval. A 500 shot interval was chosen because it corresponds to the annotation interval provided along the top of the seismic-reflection profile images. The unique and 500-shot files contain attributes for the corrected shot position in both UTM and Geographic coordinates, as well as the original uncorrected (pre-layback) positions in UTM, date, time and other survey information.
Process_Date: 2016
Process_Step:
Process_Description:
Text files containing the layback-adjusted unique shot point positions for each seismic line were concatenated into a comma-delimited text file '2013-003-FA_512i_shotunique.csv', which is provided in the zip-compressed package of the 500-shot shapefile '2013-003-FA_512i_shot500.zip'. A Python script was used to import the CSV file into the SpatialLite (version 4.2.0_1) enabled SQLite (version 2.6) database. The geographic locations for each shot point were used to create point feature geometries in the SQL database. The point geometries were then used to create polyline geometries for each seismic trackline. An Esri polyline shapefile for the seismic tracklines was exported directly from the SQLite database using the Geospatial Data Library (GDAL 2.0.1) ogr2ogr executable with the Spatialite option and an SQL query.
Process_Date: 2016
Process_Step:
Process_Description: USGS Thesaurus keywords added to the keyword section.
Process_Date: 20180720
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: VeeAnn A. Cross
Contact_Position: Marine Geologist
Contact_Address:
Address_Type: Mailing and Physical
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: MA
Postal_Code: 02543-1598
Contact_Voice_Telephone: 508-548-8700 x2251
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: vatnipp@usgs.gov
Process_Step:
Process_Description: Crossref DOI link was added as the first link in the metadata.
Process_Date: 20191118
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: VeeAnn A. Cross
Contact_Position: Marine Geologist
Contact_Address:
Address_Type: Mailing and Physical
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: MA
Postal_Code: 02543-1598
Contact_Voice_Telephone: 508-548-8700 x2251
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: vatnipp@usgs.gov
Process_Step:
Process_Description:
Added keywords section with USGS persistent identifier as theme keyword.
Process_Date: 20200908
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: VeeAnn A. Cross
Contact_Position: Marine Geologist
Contact_Address:
Address_Type: Mailing and Physical
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: MA
Postal_Code: 02543-1598
Contact_Voice_Telephone: 508-548-8700 x2251
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: vatnipp@usgs.gov
