Chirp seismic reflection data from the Edgetech 512i collected in Little Egg Inlet and offshore the southern end of Long Beach Island, NJ, during USGS field activity 2018-001-FA (shotpoints point shapefile, survey trackline shapefile, PNG profile images, and SEG-Y trace data).

PROCESS STEP 1: SIOSEIS (version 2016.3.1) and python were used to process SEG-Y data and extract navigation data. The processing flows and scripts used are summarized below and in the following processing steps.
1) The SIOSEIS script sio_renum read the raw SEG-Y files, extracted the envelope-detected trace, renumbered shots starting from one, and wrote 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.
2) The SIOSEIS script sio_medianstk was used to minimize system cross talk by performing a two-trace median stack (trim 50 percent of the values furthest from the median amplitude) which improves water bottom picking.
3) The script read512i_s was used to read the swell filtered 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 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 18 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.
4) The SIOSEIS script siothresh_pltwbt (which runs the sio_threshwbt script) was used to predict water-bottom times from the envelope SEG-Y traces in each file and write the predicted two-way travel times for the seafloor to a '*.wbt.csv' file. This created new swell filtered SEG-Y files (which are included in the archive '2018-001-FA_SB512i_SegyData.zip'). Note: there is a known bug in the swell filtering algorithm that removes the last trace that was recorded in the median stack filtered SEG-Y and duplicates time and position of the third-to-last trace as the new last trace of the SEG-Y file. This affects less than a second of time at the end of each seismic profile but does not otherwise affect the rest of the sub-bottom data.
5) Seismic Unix (version 4.2) was used to read all the swell filtered SEG-Y files and plot the data as 8-bit gray-scale Postscript files using the Seismic Unix 'psimage' algorithm. The profiles contain 80 milliseconds of two-way travel time within a 14-inch vertical window, yielding approximately 5.7 milliseconds per inch. Postscript images were converted to PNG format using ImageMagick (version 6.9.9-40). The x-axis units of the images are shot number while the y-axis is two-way travel time in seconds (note: extremely short lines may not display a complete x-axis in these images).
6) The python script 512intoSQL18001_py2.py imports the navigation, shot, year, day, and UTC time data from CSV files into a SpatiaLite (version 4.3.0a) enabled SQLite (version 3.27.1) database, creating two tables containing point geometries. The first contained records for all of the input shots with unique navigation coordinates, and the second maintained records for the first and last shots, and shots at multiples of 500. End shots and shots at multiples of 500 may not have unique navigation coordinates. The resulting database columns for each table consist of East, North (UTM18N m), Lon, Lat (WGS84 dd), LineName, ImageName, Shot, Year, JD_UTC (DDD:HH:MM:SS), SurveyID, VehicleID, DeviceID. A third table was created to contain trackline geometries generated from the unique navigation point geometries for each line (sorted by LineName and Shot), and the line length in kilometers was calculated. The resulting database columns of the line geometry table consist of LineName, ImageName, Shot_init, Shot_end, Year, JDUTC_init, JDUTC_end, SurveyID, VehicleID, DeviceID, and Length_km.
This process step was conducted between June 2018 and February 2020. This step and all subsequent process steps were conducted by the same person - Seth Ackerman.

PROCESS STEP 2: The SB-512i 500 shot, trackline and unique shot features were exported from the SQLite database as Esri point shapefile, polyline shapefiles, and text CSV file respectively, using the following SpatiaLite and SQLite commands creating the files '2018-001-FA_SB512i_Shot500.shp', '2018-001-FA_SB512iTracklines.shp' and '2018-001-FA_SB512i_ShotUnique.csv'.

>> spatialite_tool -e -shp 2018-001-FA_SB512i_Tracklines -d ./2018-001-FA-SQLdb_NEW2.sqlite -t track_ln -g geom_t -c CP1252 -s 4326 --type LINESTRING
>> spatialite_tool -e -shp 2018-001-FA_SB512i_Shot500 -d ./2018-001-FA-SQLdb_NEW2.sqlite -t sht500_pt -g geom_500 -c CP1252 -s 4326 --type POINT
>>sqlite3 -header -csv ./2018-001-FA-SQLdb_NEW2.sqlite "select * from unique_pt;" > 2018-001-FA_SB512i_ShotUnique.csv