Seismic Reflection, Geometrics multi-channel streamer common midpoint brute stack profile images, USGS field activity 2017-003-FA, Mississippi River Delta front offshore of southeastern Louisiana (PNG images)

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Frequently anticipated questions:


What does this data set describe?

Title:
Seismic Reflection, Geometrics multi-channel streamer common midpoint brute stack profile images, USGS field activity 2017-003-FA, Mississippi River Delta front offshore of southeastern Louisiana (PNG images)
Abstract:
High resolution bathymetric, sea-floor backscatter, and seismic-reflection data were collected offshore of southeastern Louisiana aboard the research vessel Point Sur on May 19-26, 2017, in an effort to characterize mudflow hazards on the Mississippi River Delta front. As the initial field program of a research cooperative between the U.S. Geological Survey, the Bureau of Ocean Energy Management, and other Federal and academic partners, the primary objective of this cruise was to assess the suitability of sea-floor mapping and shallow subsurface imaging tools in the challenging environmental conditions found across delta fronts (for example, variably distributed water column stratification and widespread biogenic gas in the shallow subsurface). Approximately 675 kilometers (km) of multibeam bathymetry and backscatter data, 420 km of towed chirp data, and 550 km of multichannel seismic data were collected. Varied mudflow (gully, lobe), prodelta morphologies, and structural features were imaged in selected survey areas from Pass a Loutre to Southwest Pass.
Supplemental_Information:
Additional information on the field activity is available from https://cmgds.marine.usgs.gov/fan_info.php?fan=2017-003-FA.
  1. How might this data set be cited?
    U.S. Geological Survey, 2018, Seismic Reflection, Geometrics multi-channel streamer common midpoint brute stack profile images, USGS field activity 2017-003-FA, Mississippi River Delta front offshore of southeastern Louisiana (PNG images): data release DOI:10.5066/F7X929K6, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, Massachusetts.

    Online Links:

    This is part of the following larger work.

    Baldwin, Wayne E., Ackerman, Seth D., Worley, Charles R., Danforth, William W., and Chaytor, Jason D., 2018, High-resolution geophysical data collected along the Mississippi River Delta front offshore of southeastern Louisiana, U.S. Geological Survey Field Activity 2017-003-FA: data release DOI:10.5066/F7X929K6, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Baldwin, W.E., Ackerman, S.D., Worley, C.R., Danforth, W.W., and Chaytor, J.D, 2018, High-resolution geophysical data collected along the Mississippi River Delta front offshore of southeastern Louisiana, U.S. Geological Survey Field Activity 2017-003-FA: U.S. Geological Survey data release, https://doi.org/10.5066/F7X929K6.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -89.552178
    East_Bounding_Coordinate: -88.881535
    North_Bounding_Coordinate: 29.161339
    South_Bounding_Coordinate: 28.781718
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/5a959709e4b06990606a7e07/?name=2017-003-FA_MCS_Images_browse.jpg (JPEG)
    Thumbnail image of multi-channel seismic-reflection common midpoint brute stack profile images from the Mississippi River Delta front offshore of southeastern Louisiana.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 21-May-2017
    Ending_Date: 26-May-2017
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: raster digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Raster data set. It contains the following raster data types:
      • Dimensions, type Pixel
    2. What coordinate system is used to represent geographic features?
  7. How does the data set describe geographic features?
    Entity_and_Attribute_Overview:
    The PNG seismic reflection images can be hyperlinked to their corresponding trackline or common midpoint locations in ArcGIS using the shapefiles '2017-003-FA_MCS_Tracklines.shp' or '2017-003-FA_MCS_100cmp.shp', respectively (available from the larger work citation). The images show two-way travel time (seconds) on the y-axis and distance along profile (with 100 CMP tic marks and 500 CMP labels) on the x-axis.
    Entity_and_Attribute_Detail_Citation: U.S. Geological Survey

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • U.S. Geological Survey
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    U.S. Geological Survey
    Attn: Wayne E. Baldwin
    Geologist
    384 Woods Hole Road
    Woods Hole, Massachusetts
    US

    508-548-8700 x2226 (voice)
    508-457-2310 (FAX)
    wbaldwin@usgs.gov

Why was the data set created?

These PNG images represent approximately 550 km of multi-channel streamer seismic-reflection data collected by the U.S. Geological Survey during cruise 2017-003-FA along the Mississippi River Delta front offshore of southeastern Louisiana. Images of each common midpoint brute stack seismic profile were generated in order to provide portable and easily viewable alternatives to the SEGY versions of the data. Each profile image can be hotlinked to its corresponding trackline navigation contained within the Esri polyline shapefile '2017-003-FA_MCS_Tracklines.shp'. Even 100 common midpoint index marks (with labels every 500 CMPs) along the top of the PNG images correlate to the positions of 100-CMP intervals within the Esri point shapefile '2017-003-FA_MCS_100cmp.shp'.

How was the data set created?

  1. From what previous works were the data drawn?
    MCS data (source 1 of 1)
    U.S. Geological Survey, Unpublished Material, Raw MCS data.

    Type_of_Source_Media: disc
    Source_Contribution:
    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.
  2. How were the data generated, processed, and modified?
    Date: May-2017 (process 1 of 3)
    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. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Wayne E. Baldwin
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700 x2226 (voice)
    (508) 457-2310 (FAX)
    wbaldwin@usgs.gov
    Date: Nov-2017 (process 2 of 3)
    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. stk2segy.flow - Input read the "*.stk-brute.seis" file and sorted the traces to CMP. UTMLatLong projected the CMP BIN_X and BIN_Y headers from UTM Zone 16N WGS84 meters to Geographic WGS84 decimal degree, latitude and longitude. HeaderMath converted the geographic coordinates from decimal degrees to seconds of arc multiplied by 100, and set the coordinate unit header to 2, both to meet the specification of the SEGY Rev. 1 format standard. Output wrote the cmp stacked traces to SEG-Y Rev. 1 format (IEEE floating point) specifying header mappings for Ensemble Number, Trace ID code), Number of Horizontally Summed Traces, Ensemble Y coordinate, Ensemble X coordinate, Coordinate scalar, and Coordinate Units.
    Date: Dec-2017 (process 3 of 3)
    A Seismic Unix (version 4.3) script (plot_geomet) was used to read the stacked SEG-Y files and plot the data as 8-bit greyscale Postscript files using the Seismic Unix 'psimage' algorithm. All images were created with a horizontal scale of approximately 400 traces per inch. Images were plotted within a constant 14-inch vertical window and two-way travel time durations between 200 and 800 ms. The Postscript images were then converted to PNG format using ImageMagick (version 6.9.5-4).
  3. What similar or related data should the user be aware of?

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
    Multichannel seismic-reflection data were navigated using a Wide Area Augmentation System (WAAS) enabled Hemisphere Differential GPS (DGPS) receiver, with an antenna mounted on an 01 deck port side rail 7.35 m from the stern of the R/V Point Sur. 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. The 150-m long GeoEel 32-channel (50 m active section) 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 m and 123 m aft of the DGPS antenna, respectively. The Geometrics CNT-1 seismic acquisition software (version 5.361) logged the shot navigation coordinates to the to the SEG-D external header. Layback distance between the GPS antenna and the acoustic source and receivers were calculated in post processing (described in the processing steps). Although horizontal accuracy of WAAS enabled DGPS is estimated to be within 2 m, the actual accuracy is assumed to be coarser due to the additional uncertainty added from calculation of source/receiver layback and common midpoint positions.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    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). Up to the first 40 traces of the stacked images may be blank due to a limitation in the OpenCPS ShotlineLayback processing module (described in the "geom.flow" processing step). 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, which accompanies 2017-003-FA_MCS_100cmp.shp, available from the larger work citation), 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.
  5. How consistent are the relationships among the observations, including topology?
    Processed seismic data were converted to PNG format for ease of seismic trace display. Quality control was conducted during processing. 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. Images containing data froom the two different sources may have a slightly different appearance.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: none
Use_Constraints:
Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the originator of the dataset.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - ScienceBase
    Federal Center
    Denver, CO

    1-888-275-8747 (voice)
  2. What's the catalog number I need to order this data set? USGS data release 2017-003-FA MCS common midpoint brute stack data PNG imagery from the Mississippi River Delta front area: includes the zip archive 2017-003-FA_MCS_Images.zip containing 70 PNG images named according to filename convention with ".stk-brute.png" appended to note common midpoint brute stack processing, the browse graphic 2017-003-FA_MCS_Images_browse.jpg, and the Federal Geographic Data Committee (FGDC) Content Standards for Digital Geospatial Metadata (CSDGM) metadata file 2017-003-FA_MCS_Images_meta.xml.
  3. What legal disclaimers am I supposed to read?
    Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  4. How can I download or order the data?
  5. What hardware or software do I need in order to use the data set?
    These data can be viewed with any PNG image viewing software. The zip files must be uncompressed in order to view the images.

Who wrote the metadata?

Dates:
Last modified: 28-Feb-2018
Metadata author:
U.S. Geological Survey
Attn: Wayne E. Baldwin
Geologist
384 Woods Hole Rd.
Woods Hole, MA

(508) 548-8700 x2226 (voice)
(508) 457-2310 (FAX)
wbaldwin@usgs.gov
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/data_release/DR_F7X929K6/2017-003-FA_MCS_Images_meta.faq.html>
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