Originator: U.S. Geological Survey
Publication_Date: unpublished material
Title: AA-251 single channel seismmic trackline data
Geospatial_Data_Presentation_Form: vector digital data
Source_Citation_Abbreviation: SEG-Y AA-251 data
Source_Currentness_Reference: ground condition
Boomer seismic-reflection data were collected using an Applied Acoustics AA-251 Boomer as a seismic source and a Benthos Aq-4 single-channel streamer. The AA-251 boomer plate mounted in a catamaran was towed on the lake surface from the starboard quarter of the R/V Rafael about 8 meters aft of the DGPS antenna. The receiver, a Benthos AQ-4 single-channel hydrophone streamer, was towed from a port side davit on the R/V Rafael at approximately 2 m below the water line. The AA-251 Boomer was power with an Applied Acoutics D-700 power supply, which was set to a 100 joules at low power. The active hydrophone section was approximately 14 meters aft of the DGPS antenna that was about 8 meters aft of the DGPS antenna mounted atop the port side of the cabin. The analog output from the streamer was connected to a Geopulse receiver which was used to apply a 150 to 5000 Hz bandpass filter and set a linear gain to 16 db in shallow water and 21 db in deeper water. The analog signal was output to a NI DAQ analog to digital converter. The digital signal was input to the acquisition computer where Chesapeake Technology SonarWiz (version 7.00.0009) seismic acquisition software was used to digitally log trace data in the SEG-Y Rev. 1 format (IEEE floating point), and record DGPS navigation coordinates to the SEG-Y trace headers (in arc seconds of Latitude and Longitude, multiplied by a scalar of 360000). Data were acquired using a 500 milliseconds (ms) shot rate. Traces were recorded with a 100-microsecond sample interval over lengths of approximately 200 ms (2000 samples per trace).
PROCESS STEP 1:
SIOSEIS (version 2015.3.1), Seismic Unix (version 4.2), and Shearwater Reveal (version 2019) 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) The Seismic Unix script readboomer was used to read the SEG-Y files, write a Seismic Unix file, and extract SEG-Y trace header information, including shot number, longitude and latitude, year, Julian day, and time of day (UTC). Header information from each SEG-Y file was saved to text files containing shots with unique navigation coordinates. Geographic coordinates (WGS 84) were converted to UTM zone 16 N coordinates (WGS 84) using Proj (version 4.9.3). An Esri shapefile was generated from the ascii shot navigation file with ArcCatalog (version 10.3.1) using Create Feature Class from XY Table. When the shapefile was added to an ArcMap project, observation of shot point locations showed uneven spacing. Even when the boat speed was relatively constant, shot spacing ranged from less than one meter to as much as five meters. This was likely due to the high rate (10 Hz) that the GPS was providing navigation strings to SonarWiz. Shot spacing would be anomalously short (less than one meter) for several shots and then jump ahead several meters. This may have been caused by a buffering and recording issues in SonarWIZ. The unique shot point navigation shape file was edited in ArcMap by graphically deleting anomalous shot points with distances from the last shot location was less than one meter. The first and last shot point locations were retained. The edited shapefile was exported to a ascii CSV file using XTools Pro (version 12) Table Operations, Export Table to File. This file was reformated to a SIOSEIS navigation file using and AWK (version 20070501) script.
2) SIOSEIS was used to read the raw SEG-Y files, insert edited shot point navigation that was created in the previous step into the SEG-Y trace headers with the process Geom (type 6), and then write new SEG-Y files with the edited navigation in the trace headers.
3) Shearwater Reveal was used to read the SEG-Y files containing edited navigation that used SegyTapeRead to read the trace and header data. 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 Reveal database table. Finally, Output wrote the traces to a new file "*.sht-raw.seis" in the internal OpenCPS format.
4) Shearwater Reveal was used to read the sht-raw.seis files and apply a top mute above the lake floor, apply a bandpass filter from 200 Hz to 2000 Hz, and apply a de-spike to remove high amplitude noise spikes created by the T20P multibeam. The processed file was saved as new file, *.proc.seis in the internal OpenCPS format.
5) Shearwater Reveal was used to read the "*.proc.seis" file. A 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 boomer source (-8 m) and the horizontal offset from the DGPS antenna and the single-channel streamer (receiver). The algorithm interpolated a sail line from the source shot positions (NRP_X and NRP_Y), receiver positions (REC_X and REC_Y), and the midpoint locations (MPT_X and MPT_Y) locations between source and receiver locations. Then the computed layback positions for the midpoint locations were translated back along the sail line by the measured offset. 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 Seismic Unix script readboomer was used to read layback 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 (version 20070501) 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 16 N coordinates (WGS 84) using Proj (version 4.9.3). 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. A Python script BoomerinlbtoSQL2018043.py, written by Wayne Baldwin (USGS-WHCMSC), which imported the CSV files to a Spatialite (version 2.7) enabled SQLite (version 3) 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 - David Foster.
Contact_Organization: U.S. Geological Survey
Contact_Person: David S. Foster
Address_Type: mailing and physical address
Contact_Voice_Telephone: (508) 548-8700 x2271
Contact_Facsimile_Telephone: (508) 457-2310
Address: 384 Woods Hole Rd.
City: Woods Hole
PROCESS STEP 2:
The boomer trackline features intervals 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 2018-043-FA_Boomer_Tracklines.shp.