David S. Foster Wayne E. Baldwin John W. Pohlman Laura L. Lapham 20250428 1.0 SEG-Y, tabular, vector, and raster data release DOI:10.5066/P13DCCU3 Reston, VA U.S. Geological Survey, Coastal and Marine Hazards and Resources Program Suggested citation: Foster, D.S., Baldwin, W.E., Pohlman, J.W., and Lapham, L.L., 2025, Chirp seismic reflection and navigation data collected in Chesapeake Bay during USGS Field Activity 2022-020-FA: U.S. Geological Survey data release, https://doi.org/10.5066/P13DCCU3 . https://doi.org/10.5066/P13DCCU3 https://cmgds.marine.usgs.gov/data-releases/datarelease/10.5066-P13DCCU3/ In July 2022, the U.S. Geological Survey (USGS) and the University of Maryland’s Chesapeake Biological Laboratory conducted a study, USGS Field Activity Number (FAN) 2022-020-FA, in Chesapeake Bay to quantify greenhouse gas fluxes from the largest estuary in the United States. The team investigated the environmental factors that control the distribution and exchange of methane and carbon dioxide in the sediments, water column, and fluxes across the atmospheric boundary layer(sea-air interface) during the annual summer occurrence of widespread anoxia that threatens the health of the bay. As part of this study, chirp seismic-reflection profiles were collected along a series of transects to characterize the sediments, stratigraphy, and acoustic signatures of gas in the sediments. This dataset contains shotpoint and trackline navigation, profile images, and processed SEG-Y (Norris and Faichney, 2002) trace data for approximately 156.7 km of EdgeTech 3400 chirp seismic-reflection data collected by the USGS during USGS FAN 2022-020-FA in Chesapeake Bay. Images of each seismic profile were generated to provide portable and easily viewable alternatives to the SEG-Y versions of the data. Each profile image can be associated with its corresponding trackline navigation contained within the Esri polyline shapefile '2022-020-FA_ET3400_Tracklines.shp'. Shotpoint index and tick marks along the top of the Portable Network Graphics (PNG) images correlate to the positions of 500 shot intervals within the Esri point shapefile '2022-020-FA_ET3400_sht500.shp'. This information allows for spatial correlation of chirp seismic-reflection profiles images with other geophysical and sample data for investigating sea-floor morphology and stratigraphy in the area. Additional information on the field activity 2022-020-FA associated with this project are available at https://cmgds.marine.usgs.gov/fan_info.php?fan=2022-020-FA. 20220725 20220729 ground condition Complete None planned -76.483140 -75.920165 39.292964 37.201880 USGS Metadata Identifier USGS:48c998b2-be71-4304-8194-7692fc90fc90 ISO 19115 Topic Category location geoscientificInformation oceans None U.S. Geological Survey USGS Woods Hole Coastal and Marine Science Center WHCMSC Coastal and Marine Hazards and Resources Program CMHRP Department of the Interior DOI University of Maryland Center for Environmental Science UMCES field activity number 2022-020-FA R/V Rachel Carson shapefile trackline navigation seismic navigation seismic reflection seismic profile SEG-Y traces chirp EdgeTech 3400 Sub-bottom Profiling System image Portable Network Graphics PNG USGS Thesaurus seismic reflection methods sub-bottom profiling marine geophysics marine geology navigational data geospatial datasets image collections Common Geographic Areas United States North Atlantic Upper Chesapeake Bay Lower Chesapeake Bay Maryland Virginia None sea floor seafloor None 2022 None Public domain data from the U.S. Government are freely distributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the originator of the dataset. David S. Foster U.S. Geological Survey Geologist mailing and physical

384 Woods Hole Road

Woods Hole Massachusetts 02543-1598 US 508-548-8700 x2271 508-457-2310 whsc_data_contact@usgs.gov https://cmgds.marine.usgs.gov/data-releases/media/2025/10.5066-P13DCCU3/505e1c0f0ef449e0905548be4c201bf8/2022-020-FA_ET3400_browse.jpg Thumbnail image showing the extent of chirp seismic-reflection profile tracklines and example profiles collected in Chesapeake Bay, Maryland and Virginia. JPEG The authors acknowledge Captain Michael Hulme and Chief Mate Rob Nilson of the R/V Rachel Carson; and our sea floor mapping group onshore support team during this survey (Jane Denny, Eric Moore, and Charles Worley). Helpful reviews were provided by Arnell Forde and Seth Ackerman. Norris, M.W. Faichney, A.K. 2002 Tulsa, OK Society of Exploration Geophysicists https://library.seg.org/pb-assets/technical-standards/seg_y_rev1-1686080991247.pdf Hagen, R.A. Vogt, P.R. 1999 Marine Geology Volume 158, Issues 1–4 Amsterdam, Netherlands ELSEVIER Marine Geology https://doi.org/10.1016/S0025-3227(98)00185-6 Chirp seismic-reflection data were collected from July 25 through 29, 2022. '2022-020-FA_ET3400_sht500.shp' contains the first, last, and 500-interval shotpoints for each seismic trackline, and '2022-020-FA_ET3400_shotnav.csv' contains all unique shot navigation. The attribute fields 'LineName' and 'ImageName' associated with polyline feature in '2022-020-FA_ET3400_Tracklines.shp' correspond to the SEG-Y data files in '2022-022-FA_ET3400_SegyData.zip' and the PNG profile images in '2022-020-FA_ET3400_Images.zip', respectively. Two versions of the SEG-Y files (envelope and real traces), and two types of PNG images, one without time-varying gain (TVG) and one with TVG, exist for each trackline feature. Processed seismic data were converted to PNG format for ease of seismic trace display and browsing. Quality control was conducted during creation of seismic traces and images . Sections of tracklines where navigation was recorded but no seismic data were logged are not included such as during testing, some turns, and very short files. The line numbers were based on predetermined Hypack line numbers. Lines 8 and 10 were skipped due to time and priority constraints. The EdgeTech 3400 subbottom profiler consists of a tow vehicle (fish) containing a dual source transducer array (2 to 16 kHz) and a polyvinylidenfluorid (PVDF)receiver array that was towed between 0.5 and 2 meters (m) below the sea surface from a cable on the starboard a-frame and winch of the R/V Rachel Carson. The tow fish pressure-depth was recorded in each SEG-Y trace header. The tow fish was towed 19 meters astern and 3 m starboard of the differential global positioning system (DGPS) antenna mounted on the starboard side of the bow. Navigation data for the EdgeTech 3400 were acquired from a Hemisphere DGPS receiver. Positioning data were recorded using Discover (version 41.0.1.116) acquisition software, which logged coordinates in arcseconds to individual trace headers in SEG-Y and EdgeTech JSF format except for lines 3b when the navigation feed to Discover failed for part of the line. For this file, the position and time were derived from the Hypack raw files and merged using Shearwater Reveal software (v. 2021) with seconds from midnight derived from the SEG-Y trace headers. DGPS horizontal positional accuracy is assumed to be within 5 m when considering the across track offset from the tow fish and the DGPS antenna. PROCESS STEP 1: A C program, jsf2segy, written by Thomas O'Brien (last updated by William Danforth, July 2022), read the raw EdgeTech JSF format files, extracted (-x argument) the real (full waveform) trace data from the analytic traces, and wrote out SEG-Y and CSV files. The CSV files contained ping (shot) number (acquired at a tae of 4 Hz), time, motion data (heave, pitch, and roll) from the motion sensor on the ET3400 tow fish, and tow fish depth below the sea surface from the pressure depth sensor located on the ET3400 tow fish. Heave was also stored in the JSF converted to SEG-Y's extended trace header (bytes 225-226) and tow fish depth in the source depth standard SEG-Y Source Depth trace header (bytes 49-52). This process step and all subsequent process steps were performed by David S. Foster. 202207 U.S. Geological Survey David S. Foster Geologist mailing and physical address

384 Woods Hole Rd.

Woods Hole MA 02543-1598 (508) 548-8700 x2271 (508) 457-2310 dfoster@usgs.gov PROCESS STEP 2: (2.1) A Shearwater Reveal processing flow 0100_ImportSEGY read the SEG-Y files created with jsf2segy and mapped SEG-Y trace header values needed for processing: shot/ping number (FFID); tow fish depth (Source Depth in millimeters (mm)/1000); Navigation Reference Point (NRP) coordinates (both in Source and Receiver coordinates in arcseconds/1000); Date and time (Year, Julian Day, Hour, Minute, Second); and Heave (bytes 225-226 as 16-bit integer in mm). For lines 1 and 2, the Discover acquisition software was set to automatic file changes that resulted in multiple SEG-Y files for each line. These files were concatenated on input to create a Reveal SEIS proprietary file for each line. The trace length was reduced to 100 milliseconds (ms) from the original trace length of 200 ms after it was determined there were no reflections, other than multiples, observed greater than 100 ms within the profiles. The HeaderMath tool in the Reveal flow converted NRP geographic coordinates to decimal degrees, source depth (m) to two-way travel time (TWT) in ms, and heave from meters to TWT ms. Due to acquisition equipment issues, navigation was absent in the Line 3b SEG-Y trace headers, see the horizontal position accuracy report for more details. For this line, Hypack navigation was imported as a CSV file to create Reveal NRP geographic coordinate headers using the SEG-Y time of day trace headers, converted to seconds after midnight, and the Hypack data, also as seconds after midnight. The tool DBWrite wrote a CSV file with the fields NRP_LON, NRP_LAT, FFID, GPS_OFFSET (-19 m), YEAR, DAY, HOUR, MINUTE, SECOND that was used to calculate the layback navigation subsequently described in step 2.4. The tool CTAN converted the real traces to envelope (instantaneous amplitude) and these envelope traces were output to another SEIS format file to be used as input in step 2.2. Both files maintained the imported and calculated headers. (2.2) A Reveal processing flow, WBTpick, input the envelope trace data and applied static corrections from the Heave header and the tow fish depth (both TWT ms), after the tow fish depth values were smoothed with a 151-point boxcar filter. A custom Python tool (ObspyPicking) was used to automatically pick the peak amplitude within a user defined TWT window from the envelope trace data resulting in consistent picks of the sea floor, which contained some outlier picks, that were saved in a Reveal table file. These files were edited graphically in Reveal by overlaying the picked seafloor on the static-corrected, shifted envelope data and deleting outliers. The edited table was saved, so it could be used later to apply swell filtering (if necessary) and to apply a TVG function hung from the seafloor, rather than starting from TWT 0. (2.3) A Python script written by Wayne Baldwin was run in Jupyter Notebook to create SQLite tables containing the ET3400 navigation data. Using the Reveal CSV tables created in step 2.1 as input, the script: removed duplicate navigation coordinates caused by the 5 Hz DGPS rate and 4 Hz ping rate and interpolated unique coordinates for each trace, calculated layback (-19 m) tow fish positions relative to the NRP coordinates, and transformed the layback geographic coordinates to Universal Transverse Mercator (UTM) Zone 18 North (N) coordinates. Point navigation data were output to two SQLite tables, one containing point features for every trace, and the other containing point features for the first and last traces, and traces at even 500 shot intervals in between for all lines. The script also created tracklines (polyline vector dataset) from the final navigation for each line. The polyline features were output to an SQLite table with fields containing shot numbers, dates, and times for the start and end of lines, and the length of each line in kilometers. Attribute fields for line name, Survey ID, Vehicle ID, and Device ID were added to records in each table. Tables were saved in the SQLite database for each Julian Day for unique shot fixes, 500 shot intervals, and the tracklines. (2.4) A Reveal processing flow, named Statics-Layback, input the real trace data SEIS files, truncated trace lengths from 0.2 to 0.1 seconds, merged layback navigation CSV files with seismic headers, and applied static corrections from the Heave header and the tow fish depth (both TWT ms) after the tow fish depth values were smoothed with a 151-point boxcar filter. Due to higher sea states (roll) on Julian Day 206 and early Julian Day 207, lines 1, 2 and 3a required additional static corrections to remove residual heave and tow fish depth variation. The seafloor pick table (from step 2.2) was used to insert the seafloor picks to a Reveal header. The module, HeaderFiltering, applied a 151-point boxcar filter to the picks and the HeaderMath tool subtracted the original picks from the smoothed picks. The difference was used to shift the trace data. The DBMerge tool was used to import the layback navigation coordinates to Reveal headers for all the data. After converting the real trace data to envelope traces with the tool CTAN, processed SEG-Y files (envelope and real) were exported with layback coordinates in the SEG-Y headers. These are the SEG-Y files provided in this data release. Separate envelope trace files were exported after applying TVG for plotting as described in Process Step 4. In the Reveal tool Output-SEG-Y Options a summary of processing and header information are described and added to the EBCDIC header of each SEG-Y file, like the example from Line1_206_env.sgy below. Example SEG-Y textural file header: SURVEY_ID: 2022-020-FA Chesapeake Bay; VESSEL: R/V Rachel Carson YEAR: 2023 NAME(GEOMETRY): Line1_206_env.sgy DESCRIPTION: Envelope chirp with static (heave and fish depth) correction SYSTEM: EdgeTech SB3400, two 2-16 kHz transducer array, PVDF receiver CHIRP PULSE: 3 kHz to 16 kHz, 20 ms pulse length SHOT INTERVAL: 0.25 seconds TRACE LENGTH: 0.1 seconds SAMPLE RATE: 0.02 ms PROCESSING: Convert EdgeTech JSF format to SEG-Y using jsf2segy C program Input SEG-Y, set trace length from 0.2 to 0.1 seconds, read source depth and heave from SEG-Y headers. Set FFID to start at 1 Apply static shift (heave and source depth), merge layback (-19 m) navigation Output IEEE 32-bit floating point SEG-Y Shotpoint (FFID) navigation are stored in seconds of arc WGS84 (scaled by -100) in source coordinates, longitude in bytes 73-76 and latitude in bytes 77-80 Coordinate scaler in bytes 71-72, divide by 360,000 for decimal degrees Source depth below the surface (fish depth) is in bytes 49-52 (scaled by -1000) Heave stored in bytes 225-226 (16-bit integer) in millimeters For additional information concerning these data, refer to the associated data release: https://doi.org/10.5066/P13DCCU3 End of SEG-Y textural file header. 202404 PROCESS STEP 3: The SQLite database created in Process Step 2.3 was opened with Global Mapper (version 25) and Julian Day tables for tracklines and 500 shot intervals were added to the map view. The trackline Julian Day tables were exported as a single polyline shapefile (2022-020-FA_ET3400_Tracklines.shp). The Julian Day 500 shot interval tables were exported to a single point shapefile (2022-020-FA_ET3400_sht500.shp). These are the shapefiles provided in this data release. 202404 PROCESS STEP 4: The Seismic Unix Release 42 script Plotchirp created variable density postscript plots of the envelope traces and the envelope traces with TVG applied. The profiles show TWT (seconds) along the y-axis (left margin) and shots (labeled at 500 shot intervals) along the x-axis (top of profile). The postscript images created with Seismic Unix were converted to 150 dpi PNG images using ImageMagick (version 6.9.11-60). The plots are labeled with additional profile details along the bottom of the x-axis. These labels may be truncated for short lines. 202404 Vector String 17 0.0197558850 0.0250382929 Decimal seconds WGS 1984 WGS 84 6378137.0 298.257224 2022-020-FA_ET3400_Tracklines.shp EdgeTech 3400Trackline shapefile for survey 2022-020-FA (17 polyline features). U.S. Geological Survey FID Internal feature number. Esri Sequential unique whole numbers that are automatically generated. Shape Feature geometry. Esri Coordinates defining the features. LineName Name of the trackline along which seismic-reflection data were collected in the format: Line_JulianDay as follows L#_JD# (i.e.'Line1_JD206'). U.S. Geological Survey Character set ImageName PNG image name of the envelope trace seismic-reflection profile corresponding to the survey line. U.S. Geological Survey Character set FFID_init Shot number at the start of the survey line. U.S. Geological Survey 1 1 shot 1 FFID_end Shot number at the end of the survey line. U.S. Geological Survey 1427 31176 shot 1 UTCDT_init Julian day and Coordinated Universal Time (UTC) time at the start of the survey line in the format: YEAR:JD:HH:MM:SS; Julian day is the integer number (although recorded here in text string format) representing the interval of time in days since January 1 of the year of collection. U.S. Geological Survey Character set UTCDT_end Julian day and UTC time at the end of the survey line in the format: YEAR:JD:HH:MM:SS; Julian day is the integer number (although recorded here in text string format) representing the interval of time in days since January 1 of the year of collection. U.S. Geological Survey Character set SurveyID WHCMSC FAN identifier (e.g. "2022-020-FA" where 2022 is the survey year, 020 is survey number of that year, and FA is Field Activity). U.S. Geological Survey Character set VehicleID Survey vessel name. U.S. Geological Survey Character set DeviceID Sonar device used to collect seismic-reflection data. U.S. Geological Survey Character set Length_km Length of seismic-reflection data line in kilometers, UTM Zone 18N, World Geodetic System of 1984 (WGS 84) calculated in the SQLite database. U.S. Geological Survey 0.701 19.869 kilometers 0.000001 2022-020-FA_ET3400_sht500.shp EdgeTech 3400 500-interval shot point shapefile for survey 2022-020-FA (524 point features). U.S. Geological Survey FID Internal feature number. Esri Sequential unique whole numbers that are automatically generated. Shape Feature geometry. Esri Coordinates defining the features. East Layback easting coordinate in UTM Zone 18 N meters, WGS 84 U.S. Geological Survey 370802.63 418896.20 meters .01 North Layback northing coordinate in UTM Zone 18 N meters, WGS 84 U.S. Geological Survey 4117996.08 4349981.84 meters .01 Lon Layback longitude coordinate in decimal degrees, WGS 84 U.S. Geological Survey -76.483100 -75.920165 degrees 1E-06 Lat Layback latitude coordinate in decimal degrees, WGS 84 U.S. Geological Survey 37.20188 39.292964 degrees 1E-06 LineName Name of the trackline along which seismic-reflection data were collected in the format: Line_JulianDay as follows L#_JD# (i.e., 'Line1_JD206'). U.S. Geological Survey Character set ImageName PNG image name of seismic-reflection profile corresponding to survey line. U.S. Geological Survey Character set FFID Shot (FFID) number (values are first, last, and every 500th shot in between). U.S. Geological Survey 1 31176 shot 1 Date Calendar date for first, last, and every 500th shot point between and along the survey line in the format: MM/DD/YEAR. U.S. Geological Survey Character set UTC_DT Year, Julian day, and UTC time for first, last, and every 500th shot point of the survey line in the format: YEAR:JD:HH:MM:SS; Julian day is the integer number (although recorded here in text string format) representing the interval of time in days since January 1 of the year of collection. U.S. Geological Survey Character set SurveyID WHCMSC FAN identifier (e.g. "2022-020-FA" where 2022 is the survey year, 020 is survey number of that year, and FA is Field Activity). U.S. Geological Survey Character set VehicleID Survey vessel name. U.S. Geological Survey Character set DeviceID Sonar device used to collect seismic-reflection data. U.S. Geological Survey Character set NRP_Lon Navigational reference point longitude coordinate in decimal degrees, WGS 84. U.S. Geological Survey -76.483040 -75.920000 degrees 1E-06 NRP_Lat Navigational reference point latitude coordinate in decimal degrees, WGS 84. U.S. Geological Survey 37.201850 39.293037 degrees 1E-06 2022-020-FA_ET3400_shotnav.csv EdgeTech 3400 unique shot point navigation comma separated values file for survey 2022-020-FA (249,627 point features). U.S. Geological Survey 2022-020-FA_ET3400_Images.zip Portable network graphic EdgeTech 3400 profiles (envelope and envelope with TVG) for survey 2022-020-FA (34 PNG images) U.S. Geological Survey ` 2022-020-FA_ET3400_SegyData.zip SEG-Y format files of envelope and real (full waveform) traces of processed EdgeTech 3400 profiles for survey 2022-020-FA (34 SEG-Y files). U.S. Geological Survey The column headings and range domain values in '2022-020-FA_ET3400_shotnav.csv' match those in '2022-020-FA_ET3400_sht500.shp' except for Line4b_JD207 where East, Lon, and NRP_Lon Range Domain Minimums are 370798.72, -76.48314, and -76.48314, respectively for '2022-020-FA_ET3400_shotnav.csv'). This is because the apex of a turn in Line4b_JD207 is between two 500 shot intervals.The PNG seismic reflection images can be hyperlinked to their corresponding trackline or shotpoint locations in a GIS using the shapefiles '2022-020-FA_ET3400_Tracklines.shp' or '2022-020-FA_ET3400_sht500.shp', respectively. The fist, last, and multiple of 500 shot features in '2022-020-FA_ET3400_sht500.shp' correspond to the x-axis tick marks on the PNG images, which show two-way travel time (seconds) on the y-axis and distance along the profile (annotation at 500 shot intervals) on the x-axis. The names of SEG-Y files included in 2022-020-FA_ET3400_SegyData.zip have the string 'env' or 'real' inserted between the profile line name and the .sgy extension to indicate that the files contain either envelope or real (full waveform) versions of the traces. The binary SEG-Y version 1 files (Norris and Faichney, 2002) provided for each survey line consist of 1) a 3200-byte textural file header containing general information; 2) a 400-byte binary record with information such as sample rate and record length specific to the dataset; and 3) multiple records, one seismic reflection trace per record. Each trace record is preceded by a 240-byte "trace header" containing information such as trace number and acquisition day and time specific to each trace. The trace data are represented as a time series of unitless 32-bit IEEE floating point numbers proportional to the sound pressure level received at the hydrophone. The SEG-Y file is useful only if you have access to specialized software designed to process and display seismic reflection data. U.S. Geological Survey David S. Foster U.S. Geological Survey Geologist mailing and physical address

384 Woods Hole Rd.

Woods Hole MA 02543-1598 USA 508-548-8700 x2271 508-457-2310 dfoster@usgs.gov USGS data release of EdgeTech 3400 chirp seismic-reflection data collected in Chesapeake Bay during USGS FA 2022-020-FA: includes '2022-020-FA_ET3400_sht500.shp' containing the first, last and 500-interval shotpoint locations, '2022-020-FA_ET3400_shotnav.csv' containing unique shot point locations, '2022-020-FA_ET3400_Tracklines.shp' containing survey trackline features, '2022-020-FA_ET3400_Images.zip' containing 34 PNG images named according to line convention, '2022-020-FA_ET3400_SegyData.zip' containing 34 SEG-Y files of the processed envelope and real traces, the browse graphic 2022-020-FA_ET3400_Tracklines_browse.jpg, and Federal Geographic Data Committee (FGDC) Content Standard for Digital Geospatial Metadata (CSDGM) file '2022-020-FA_ET3400_meta.xml'. These datasets can be downloaded individually (see the Digital Transfer Option section). Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Shapefile Global Mapper 25.0 Shapefile ZIP compressed folder "2022-020-FA_ET3400_Shapefile.zip" containing shapefiles of ET3400 shotpoints and tracklines collected by the USGS WHCMSC in Chesapeake Bay, Maryland and Virginia during USGS FA 2022-020-FA and the associated metadata. To utilize these data, the user must have software capable of uncompressing the ZIP file and reading shapefile format, or GIS software. 1.79 https://cmgds.marine.usgs.gov/data-releases/datarelease/10.5066-P13DCCU3/ https://doi.org/10.5066/P13DCCU3 https://cmgds.marine.usgs.gov/data-releases/media/2025/10.5066-P13DCCU3/2fba42ef4c2d40c1b317efae09575630/2022-020-FA_ET3400_Shapefiles.zip Comma-delimted text none Comma-Separated Values (CSV) ZIP compressed folder, 2022-020-ET3400_shotnav, containing a CSV file of ET3400 unique shotpoints collected by the USGS WHCMSC in Chesapeake Bay, Maryland and Virginia during USGS FA 2022-020-FA and the associated metadata. To utilize these data, the user must have software capable of uncompressing the ZIP file. 3.84 https://cmgds.marine.usgs.gov/data-releases/datarelease/10.5066-P13DCCU3/ https://doi.org/10.5066/P13DCCU3 https://cmgds.marine.usgs.gov/data-releases/media/2025/10.5066-P13DCCU3/59b46bc8dc9b48a0b37e22366e24d5d1/2022-020-FA_ET3400_shotnav.zip PNG ImageMagick (version 6.9.11-60) Portable Network Graphic (PNG) ZIP compressed folder "2022-0020-FA_ET3400_Images.zip" containing ET3400 seismic reflection profile images collected by the USGS WHCMSC in Chesapeake Bay, Maryland and Virginia during USGS FA 2022-020-FA and the associated metadata. Image files with filenames 'Line_JulianDay_env_tvg.png' have a time-varying gain applied to the envelope traces. To utilize these data, the user must have software capable of uncompressing the ZIP file. 378 https://cmgds.marine.usgs.gov/data-releases/datarelease/10.5066-P13DCCU3/ https://doi.org/10.5066/P13DCCU3 https://cmgds.marine.usgs.gov/data-releases/media/2025/10.5066-P13DCCU3/bb20ecac77724fea88792303c43255ac/2022-020-FA_ET3400_Images.zip SEG-Y SEG-Y Rev. 1 SEG-Y Zip compressed folder "2022-020-FA_ET3400_SegyData.zip" containing processed ET3400 seismic reflection trace data collected by the USGS WHCMSC during USGS FA 2022-020-FA and the associated metadata. SEG-Y files with filenames 'Line_JulianDay_env.sgy' consist of the processed envelope traces. SEG-Y files with filenames 'Line_JulianDay_real.sgy' consist of the processed real (full waveform) traces. To utilize these data, the user must have software capable of uncompressing the ZIP file and reading seismic data. 9200 https://cmgds.marine.usgs.gov/data-releases/datarelease/10.5066-P13DCCU3/ https://doi.org/10.5066/P13DCCU3 https://cmgds.marine.usgs.gov/data-releases/media/2025/10.5066-P13DCCU3/83173ee616904e3cb6438c3890f38c62/2022-020-FA_ET3400_SegyData.zip none To utilize these data, the user must have software capable of reading or viewing shapefiles, CSV files, PNG images, and/or SEG-Y seismic trace files. 20250428 U.S. Geological Survey David S. Foster Geologist mailing and physical

384 Woods Hole Rd.

Woods Hole MA 02543-1598 (508) 548-8700 x2271 (508) 457-2310 whsc_data_contact@usgs.gov The metadata contact email address is a generic address in the event the person is no longer with USGS. Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998 local time