Source_Citation:
Citation_Information:
Originator: U.S. Geological Survey
Publication_Date: unpublished material
Title: SB-424 trackline data
Geospatial_Data_Presentation_Form: vector digital data
Type_of_Source_Media: disc
Source_Time_Period_of_Content:
Time_Period_Information:
Range_of_Dates/Times:
Beginning_Date: 20171012
Ending_Date: 20171017
Source_Currentness_Reference: ground condition
Source_Citation_Abbreviation: SEG-Y SB-424 data
Source_Contribution:
Chirp seismic data were collected using an EdgeTech 3100 portable sub-bottom profiling system and an SB-424 towfish (4-24 kHz), which was towed from a port side davit on the R/V Stephens with the transducer approximately 1 m below the water line, and 2.8 meters astern of the DGPS antenna mounted atop the port side of the cabin. Edgetech Discover Sub-Bottom (version 4.04) seismic acquisition software was used to control the 3100 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 250 milliseconds (ms) shot rate, a 10-ms pulse length, and a 4 to 20 kHz frequency sweep. Traces were recorded with a 23-microsecond sample interval over lengths of approximately 236 ms.
Process_Description:
PROCESS STEP 1:
SIOSEIS (version 2015.3.1), OpenCPS (version 3.3.0), and Seismic Unix (version 4.2) were used to process SEG-Y data, create navigation files, and plot images. The processing flow and scripts used to produce navigation files including trackline shapefiles are summarized below and in the following processing steps.
1) SIOSEIS was used to read the raw SEG-Y files, extract the envelope-detected trace, renumber shots starting from one, and write out new SEG-Y files.
2) OpenCPS was use to run the following flows:
A) read_segy.flow - SegyTapeRead read the traces. HeaderMath and UTMLatLong were used to convert the source lat/lon positions from seconds of arc to decimal degrees, project them to UTM Zone 12N WGS 84 meters, and write each to new header words (NRP_LAT, NRP_LON, NRP_X, and NRP_Y). DBWrite wrote the UTM positions for the first channel of each FFID to an internal OpenCPS database table. Finally, Output wrote the traces to a new file "*.sht-raw.seis" in the internal OpenCPS format.
B) layback_shift.flow - Input read the "*.sht-raw.seis" file and sorted the traces to FFID/CHANNEL. The custom Python module ShotlineLayback (developed by Nathan Miller of USGS-WHCMSC) was used to define the measured horizontal offset between the DGPS antenna and the SB-424 transducer (-2.8 m). The algorithm interpolated a sail line from the source shot positions (NRP_X and NRP_Y), then computed layback positions for the SB-424 shots by translating them back along the sail by the measured offset. ApplyStatic was used to shift the traces down by 1.35 ms to account for the approximate 1 m tow depth of the SB-424 (the sound speed of 1480 m/s, a typical value observed from SVP profiles during the survey, was used to convert the depth in meters to 1-way travel time in ms). Output wrote the shifted traces to a new SEG-Y files in which the trace header words SRC_X, SRC_Y represent the calculated layback coordinates, and REC_X, REC_Y maintain the original DGPS coordinates.
3) The SIOSEIS script Read424 was used to read layback and static corrected SEG-Y files, write a Seismic Unix file, and extract SEG-Y trace header information, including shot number, pre-layback and layback longitude and latitude, year, Julian day, and time of day (UTC). Header information from each SEG-Y file was saved to text files after an AWK (no version) filter was used to maintain the first and last shots, shots at multiples of 100, 500, and shots with unique navigation coordinates. Geographic coordinates (WGS 84) were converted to UTM zone 12 N coordinates (WGS 84) using Proj (version 4.6.0). End shots and shots at multiples of 100 may not have unique navigation coordinates. Separate text files containing the first and last shots and even 500 shot intervals were also saved. A 500 shot interval was chosen because it corresponds to the annotation interval provided along the top of the seismic-reflection profile images. Read424 called a Python script 424toSQL17049.py, written by Wayne Baldwin, which imported the CSV files to a Spatialite (version 4.3.0) enabled SQLite (version 3.21.0) database, creating two tables containing point geometries for the unique and 500 shot interval navigation. The script also created line geometries from the unique navigation (sorted by LineName and Shot) and wrote them to an additional database table. The tracklines are based on all the shot navigation.
These process steps and all subsequent process steps were conducted by the same person - Wayne Baldwin.
Process_Date: 201806
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: Wayne E. Baldwin
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
Contact_Voice_Telephone: (508) 548-8700 x2226
Contact_Facsimile_Telephone: (508) 457-2310
Contact_Electronic_Mail_Address: wbaldwin@usgs.gov
Process_Description:
PROCESS STEP 2:
The SB-424 trackline features were added (Add Data) into ArcMap (version 10.3.1) from the SQLite database, then exported (Right click on database feature class >Data> Export Data) to the new Esri polyline shapefile 2017-049-FA_Edgetech424_Tracklines.shp
Process_Date: 201806