Multichannel seismic-reflection profile data were collected continuously throughout the cruise except during a survey hiatus between 19:19 (UTC) 5/21/2017 (JD141) and 02:17 5/22/2017 (JD142), a period of inclement weather, rough sea state, and system malfunction between 10:45 5/23/17 (JD 143) and 00:20 5/24/17 (JD144), and within Louisiana state waters, where the cruise was not permitted to use the seismic sources. Sparker and boomer sources were used with the multichannel streamer during the cruise to test their relative effectiveness in the delta front setting, and some lines were reoccupied with each source to provide comparative results over common sections of sea floor. Substantial flux of freshwater from the Mississippi River caused rather low at several locations during the cruise, which reduced the effectiveness of the sparker source, which is predicated on operation in sea water conditions. During these periods, the boomer source was deployed instead. Line numbering begins at FA2017003_transit4 and ends at FA2017003_bonus3. This feature class contains common midpoint (CMP) locations for each trackline, at the start (1000 or 1600), end (x), and even 100-CMP intervals in between. The CSV file contains unique CMP navigation. No duplicates exist. The attribute field 'imagename' lists the PNG brute stack image that corresponds to each line (see MCS.zip folder accompanying 2017-003-FA_MCS_Images_meta.xml available from the larger work citation).
Sections of tracklines where navigation was recorded but no seismic data were logged are not included such as some turns and transits (e.g. FA2017003_sw13a, from which the CMPs prior to 1600 are not included because many of the raw traces contain no data). There are no lines FA2017003_transit1, FA2017003_transit2, FA2017003_transit3, or FA2017003_dw13. Troubleshooting of the seismic power source during line FA2017003_sw9 caused shots 3003 - 4343 to not be logged. As a result, there is a gap in the CMP navigation for FA2017003_sw9 (see 2017-003-FA_MCS_cmp-nav.csv), as well as a conspicuous artifact in the form of an abrupt vertical sea floor offset in the PNG brute stack image corresponding to those CMPs (contained in the MCS.zip folder accompanying 2017-003-FA_MCS_Images_meta.xml available from the larger work citation). Similarly, the power source was briefly suspended and restarted during line FA2017003_sw25 causing shots 1014 - 1146 to not be logged. While the resulting gap is evident in the CMP navigation, the effect is less conspicuous in the PNG brute stack image.
Originator: U.S. Geological Survey
Publication_Date: Unpublished Material
Title: MCS reflection point data
Geospatial_Data_Presentation_Form: digital data
Source_Citation_Abbreviation: raw MCS data
Source_Currentness_Reference: ground condition
Multichannel seismic-reflection data were shot using Applied Acoustics S-Boom or SIG mini sparker (ELC 1050 and 1200) sources powered by Applied Acoustics CSP-D (700 and 2400) power supplies. Both sparker and boomer sources were used to test their relative effectiveness in the delta front setting, and some lines were reoccupied with each source to provide comparative results over common sections of sea floor. Shots were recorded using a 150-m long 32-channel (50 m active section) solid-state Geometrics GeoEel streamer with 1.5625-m spaced groups connected to a Geometrics Streamer Power Supply Unit (SPSU). The seismic sources were towed from the center of the stern approximately 17 m (lines FA2017003_transit4 - FA2017003_sw8) and 22 m (lines FA2017003_sw9 - FA2017003_bonus3) aft and approximately 4 m starboard of the DGPS antenna, and the GeoEel streamer was towed approximately 3 m outboard of the port side of the vessel from a boom crane, with the center of the first and last active groups approximately 73 and 123 meters aft of the DGPS antenna, respectively. The S-Boom source was powered at 600 joules (200 J per plate) and deployed from the start of surveying up to 19:19 (UTC) 5/21/2017 (JD141), between 02:17 and 15:31 5/22/2017 (JD142), and between 20:06 5/22/2017 (JD142) and 10:08 5/23/2017 (JD143). SIG mini sparker sources were supplied between 200 and 500 joules and deployed between 15:31 and 20:04 5/22/2017 (JD142), and between 00:20 5/24/2017 (JD144) and 00:44 5/26/2017 (JD146). Geometrics CNT-1 seismic acquisition software (version 5.361) running on a Windows PC was used to control the multichannel system and digitally log traces in the Geometrics SEG-D format, and record GPS navigation coordinates to the SEG-D external headers. Data were acquired at shot rates of 0.5 and 1 s, record lengths between 400 and 800 milliseconds (ms), and a sample interval of 0.25 ms.
A SIOSEIS (version 2015.3.1) seismic processing software script (sio_segd2segy) was used to read Geometrics SEG-D formatted (SIOSEIS process SEGDDIN) traces and write them (SIOSEIS process DISKOX) to SEG-Y Rev. 1 format (IEEE floating point) for each line.
This process step and all subsequent process steps were conducted by the same person - Wayne Baldwin.
Contact_Organization: U.S. Geological Survey
Contact_Person: Wayne E. Baldwin
Address_Type: mailing and physical
Contact_Voice_Telephone: (508) 548-8700 x2226
Contact_Facsimile_Telephone: (508) 457-2310
Address: 384 Woods Hole Rd.
City: Woods Hole
OpenCPS (version 3.3.0) seismic processing software was used to perform the following series of processing flows:
1. 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 16N 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.
2. geom.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 source shot and streamer geometry based on measured horizontal offsets from the DGPS antenna to the source (-17.35 or -22.35) and the centers of the first (1) and last (32) channel groups (-73.43/-112.8) of the active streamer section. The algorithm interpolated a sail line from the source shot positions (NRP_X and NRP_Y), then computed layback positions for the source shot and 32 channel groups for each FFID by translating them back along the sail line by their respective measured offsets. Midpoint positions along the sail line were also computed for each shot/receiver pair, allowing the traces to be binned by common midpoints (CMPs) spaced evenly (by 0.781 m) along the sail line. Output wrote the traces to a new file "*.sht-raw_geom.seis" in which the trace header words SRC_X, SRC_Y, REC_X, REC_Y, MPT_X, MPT_Y, BIN_X, BIN_Y, and OFFSET were populated to reflect the layback Source X and Y, layback Receiver X and Y, layback Source/Receiver Midpoint X and Y, and CMP BIN X and Y positions, as well as the offset value (computed by sqrt((REC_X - SRC_X) * (REC_X - SRC_X) + (REC_Y - SRC_Y) * (REC_Y - SRC_Y))) for each trace in the resulting CMPs. *A limitation of the ShotlineLayback module is the inability to layback source shot/receiver locations that would have occurred prior to the start of the interpolated sail line (i.e. it does not project the sail line backward). This results in erroneous computation of those shot/receiver locations and their respective midpoints, making them unable to be stacked by bin location in the subsequent step. Consequently, up to 40 dead traces exist at the start of each common midpoint stack profile.*
3. brute_stack.flow - Input read the "*.sht-raw_geom.seis" file and sorted the traces to CMP/OFFSET. The Python module Butterworth applied an Obspy version (modified from Scipy version 0.17.1) of a zero-phase, four corner Butterworth bandpass filter to the traces, between 450 and 1800 Hz for data shot with the S-Boom, or between 350 and 1400 Hz for those shot with the mini sparker. NormalMoveout applied a travel time correction to each trace based on offset and a constant velocity of 1530 m/s (water column sound speed), as well as a 60 percent stretch mute with a 30 ms taper. Stack summed the traces within each CMP, computed the average amplitude for each trace sample, and wrote the computed samples to a single CMP trace, as well as averaging the Midpoint positions of the input traces and updating the header words MPT_X and MPT_Y with the resulting averaged values. Output wrote the stacked traces to a new file "*.stk-brute.seis" in the internal OpenCPS format.
4. geom2geojson.flow - Input read the "*.stk-brute.seis" file and sorted the traces to CMP. The custom Python module Header2GeoJSON (developed by Nathan Miller of USGS-WHCMSC) exported the stacked trace navigation (using coordinates from the BIN_X and BIN_Y headers) as point features in the GeoJSON format. Attributes for CMP, BIN_X, BIN_Y, linename, surveyid, vehicleid, and deviceid were also included in the GeoJSON output.
A batch shell script, MCSGeojson2SQL, was executed on the output GeoJSON file from the previous step. First, ogr2ogr (version 2.1.1) was used to import the GeoJSON formatted CMP navigation point geometries into a Spatialite (version 4.3.0) enabled SQLite (version 3.21.0) database table, and in the process add fields for the coordinates converted from UTM Zone 16N WGS 84 meters to GCS WGS 84 decimal degrees. Second, GJpts2lines.py created two new database tables, one containing line geometries generated from the CMP point navigation (with sort order defined by the linename and CMP fields), and another containing CMP navigation filtered to maintain the first and last CMPs, and CMPs at multiples of 100.
The MCS first, last, and multiple of 100 CMP features were added (Add Data) into ArcGIS desktop (version 10.3.1) from the SQLite database, and then exported (Right click on database feature class > Data > Export Data) to the new Esri point shapefile 2017-003-FA_MCS_100cmp.
Added keywords section with USGS persistent identifier as theme keyword.
Contact_Organization: U.S. Geological Survey
Contact_Position: Marine Geologist
Contact_Person: VeeAnn A. Cross
Address_Type: Mailing and Physical
Contact_Voice_Telephone: 508-548-8700 x2251
Address: 384 Woods Hole Road
City: Woods Hole