University of Texas Institute fore Geophysics 20190501 Raster digital data Austin, TX University of Texas Institute for Geophysics The University of Texas Institute for Geophysics (UTIG) conducted a reconnaissance survey ("TrinSab") in April of 2021, aboard the R/V Tommy Munro, to explore the stratigraphy of the outer Trinity River Paleovalley and its confluence with the Sabine River Paleovalley, with the broad goals of investigating the setting for the potential for sand resources, and for understanding the history of sedimentary deposition in this coastal/estuarine/marine setting in response to sea level rise in the Holocene. Two different types of subbottom data were collected during the survey, using (1) an Edgetech 216 (2-16 kHz) chirp towfish, and (2) a Dura-Spark source and seismic streamer. Our original plan was to use a lower-frequency 512i towfish (0.5-12 kHz); however, it was heavily damaged and unuseable after an accident at the outset of the survey. This report serves as an archive of unprocessed and processed digital chirp data, navigation files, survey log, and formal FGDC metadata. The unprocessed, archived trace data files are stored in the Edgetech JSF file format, merged files in each line, as well as processed data are stored in standard Society of Exploration Geophysicists (SEG) SEG Y revision 0 format and may be downloaded and processed with commercial or public domain software. Additionally, navigation are written to ArcGIS polygon shapefiles as well as formatted ASCII files of two forms: (1) "nav.txt" files that include full ping details, and ".xy" files that just include longitude and latitude values. Study collaboration and funding were provided by the U.S. Department of the Interior, Bureau of Ocean Energy Management, New Orleans, LA under Agreement Number M16AC00020 To archive all digital chirp subbottom profile data and associated files collected for the TRiPP. The 2021 "TrinSab" cruise on the R/V Tommy Munro included simultaneous acquisition of chirp subbottom profiler and sparker/streamer seismic data. This is possible as the low frequency of the chirp data (either 0.7 kHz or 2 kHz) are higher than the dominant usable high frequency energy of the sparker data. Specifically, the Dura-Spark used for this cruise produced a source that spanned from 150 Hz -2 kHz however some energy above ~1.3 kHz is largely noise and the majority of the higher amplitude signal lies within the 160-640 Hz range. The only concern regarding these two instruments operating simultaneously would be the chirp recording some of the sparker source energy. However, we did not observe any significant “cross-talk” during acquisition. All Chirp systems use a signal of continuously varying frequency; the system used during this survey produces high-resolution, shallow-penetration (typically less than 50-ms) profile images of sub-seafloor stratigraphy. The towfish contains a transducer that transmits and receives acoustic energy and is typically towed 1 - 2 m below the sea surface. As transmitted acoustic energy intersects density boundaries, such as the seafloor or sub-surface sediment layers, some energy is reflected back toward the transducer, received, and recorded by a PC-based seismic acquisition system. This process is repeated at regular time intervals and returned energy is recorded for a specific duration. In this way, a two-dimensional (2-D) vertical image of the shallow geologic structure beneath the towfish is produced. The source utilized for the TrinSab survey consisted of an EdgeTech SB-216 towfish running DISCOVER v. 3.51 acquisition software and towed about 5 m behind the GPS antenna. The data were acquired using a frequency sweep that 2-10 kHz, a 0.092 ms sample interval, and approximately 135 ms record length. Based on survey speeds of ~4.5 knots and a shot interval of 0.2 s, the shot spacing was about 0.450 m. The binary portion of the unprocessed seismic data are stored in Edgetech’s JSF file format (.jsf file extension), which includes both the full-waveform match filter output, and the envelope conversion of that record. Our usual chirp processing steps are fully described in Saustrup and others (2018), and involve merging files for each line into a single file, removal of towfish heave artifacts, correcting for towfish depth, equalizing trace amplitudes, secondary deconvolution (to sharpen image) on full-waveform records, and applying a layback correction to the navigation. However, after switching from the 512i to 216 towfish, our choice of the 2-10 kHz pulse was accompanied by, unknown to us at the time, a doubling of the usual sample interval (from .046 to .092 ms). This resulted in an undersampling the full-waveform signal and rendered our processing steps on the full-waveform records inadequate. We were therefore forced to restrict our attention to the envelope chirp records, and to restrict our processing steps on the envelope records to: heave compensation, towfish depth offset, trace equalization, and layback correction. Processed envelope records are stored in SEG Y rev. 0 (Barry and others, 1975), IBM float format (.segy file extension), which is a standard digital format that can be read and manipulated by most seismic processing software packages. The SEG Y files may be downloaded and processed with commercial or public domain. Unprocessed envelope data are given the extension "_env.segy" Unprocessed full-waveform data are given the extension "_real.segy" Processed envelope data are given the extension "_envproc.segy" Navigation data are provided as a single polygon ArcGIS shapefile, and also as longitude/latitude in formatted ASCII for each line (.xy files). 20190501 Publication Date Complete None planned -94.60 -94.14 29.24 29.01 None Geology Coastal Information Marine Subbottom profile Seismic Reflection Chirp Edgetech SEG Y Sand Resource Trinity River Paleovalley Sabine River Paleovalley Heald Bank Geographic Names Information System (GNIS) Content United States of America TX Gulf of Mexico Galveston None. These data are held in the public domain. The University of Texas Institute for Geophysics (UTIG) requests to be acknowledged as originator of the data in future products or derivative research. None None None The validity or accuracy of marine subbottom profiles is highly qualitative and depends on equipment and operating condition variables. Visual inspection of the images rendered from the data did not show any major anomalies. This dataset is from three field activities with consistent instrument calibrations. These data are collected along tracklines (2-D) and are therefore inherently incomplete. Geologic details between lines must be inferred. As the subbottom data were acquired, the position of the vessel was continuously determined by a differential GPS system with antenna mounted at the stern of the ship, near the tow point. A layback correction for the ~5 m offset between towfish and antenna has been applied to the processed data as well as the ASCII navigation files. These data are not to be used for bathymetry. Two-way travel (TWT) times in the processed data have been corrected for assumed towfish depth and have been filtered to remove heave artifacts. University of Texas Institute for Geophysics 20190501 Raster digital data online 20170521 20180809 publication date University of Texas Institute for Geophysics Chirp subbottom data in raw (.jsf files) and processed (.sgy) form Chirp processing: The following processing description is excerpted from Saustrup and others (Saustrup, S., Goff, J.A., and Gulick, S.P.S. 2019. Recommended “Best Practices” for Chirp Acquisition and Processing. Austin, TX: US Department of the Interior, Bureau of Ocean Energy Management, OCS Report BOEM 2019-039, 15 p.; doi:10.31223/osf.io/7csjh). Processing is conducted using Paradigm Echos software. Because the 2-10 kHz chirp pulse we used was undersampled with respect to the full-waveform ("real") data, only processing steps pertaining to the envelope data were conducted. Edgetech chirp data are recorded as “.jsf”-formatted files, a native Edgetech format that includes 4 different data channels: “real,” “imaginary,” “envelope,” and “spectrum.” The two channels of interest to the following processing scheme are “real”, which are the full waveform record, and “envelope”, which are the envelope-processed data more commonly displayed. Following data archiving (primary recording to top-side main drive and backup to secondary external drive), and prior to processing, these records must be converted to SEGY format files, which can be done with a number of available utilities. If a single survey line consists of multiple individual files, we find it useful to first convert and then concatenate these records into a single SEGY file for processing. The Edgetech acquisition software also provides an option to record directly to SEGY format. However, this format only includes envelope records; full waveform is only retained in the .jsf files. As noted above, we highly recommend acquiring field data in .jsf or an analogous format, such as .keb files for Knudsen systems, that retains both data types. Our chirp processing scheme involves three primary data streams. The first of these streams includes the critical step of picking the seafloor (to within a fraction of a wavelength at ~5000 Hz, or about 0.1ms), which provides the basis for the other two data streams: real and envelope processing. Processing of real and envelope data in turn involves 3 steps: static corrections (heave compensation, towfish depth and tides), signal processing to improved image clarity, and layback correction for navigation. As noted above, only the envelope processing was conducted on these data. The key step to being able to remove heave artifacts from chirp data, as well as for some signal processing, is to generate a precise pick of the seafloor reflection. A fully-automated bottom picker is desirable for ease-of-use but, in our experience, can fail regularly in the presence of high noise, low seafloor signal, or amplitude variability. Our own bottom-picking algorithm involves an iterative process, beginning with a coarse pick using a simple threshold algorithm, and successively refining using both automated methods and, optionally, user interaction in more difficult cases. The details of this algorithm are complex and beyond the scope of this document. Once completed, the bottom pick enables the user’s ability to move individual records up or down (i.e., apply a “static”) in relation to the seafloor arrival. Heave filtering, described below, is one such application. It is also possible to flatten record to the seafloor, which is useful for quality control; i.e., enhance both the user’s ability to visually identify bad bottom picks and the algorithm’s ability to iteratively refine the picks. Flattening is also a prerequisite for some of the processing steps described below. The seafloor flattening step is reversed later in the processing stream to preserve true topographic features at the seafloor. The data are corrected for any recording delay (nonzero start recording time, also called deepwater delay) that may have been used in the field. This is often the case when operating in deep water; a delayed start of the recording time (a simple option in Edgetech systems, for example) can be used skip over large quantities of potentially useless water column returns and thereby keep record lengths and file sizes to manageable values. A time series for towfish depth is recorded in the field, and used to correct to a sea-surface datum. This depth can be estimated using a variety of methods, including cable length/angle, a pressure sensor mounted on or integrated into the towfish, or ascertained with a USBL system. For best results, this step should be performed before the seafloor picking. We use a simple time interpolation between observed or recorded points. The seafloor picks are smoothed using a user-defined (nominally 35-75 pings) low-pass filter that is large enough to average out heave artifacts. The difference between the filtered and unfiltered seafloor picks forms a static correction to correspondingly shift the traces up or down to compensate for heave. Care must be taken during this step, if possible, to not over-smooth the seafloor and remove true topography (although this is not always possible if seafloor features are of similar wavelength to heave artifacts). Heave correction values as calculated on the full waveform data are stored in a database and applied identically to both envelope and full waveform data. An important best practice for processed data is to incorporate values for final picked seafloor time, smoothed seafloor time, and seafloor static into the trace header. This enables heave compensation filtering to be “undone” so that other correction algorithms can be applied (e.g., fitting the picked seafloor to a known bathymetric surface). Processed envelope records are stored in SEG Y rev. 0, IBM float format (.sgy file extension), which is a standard digital format that can be read and manipulated by most seismic processing software packages. Navigation in Edgetech SEGY files is stored in two places. Header bytes 73-76 (lon) and 77-80 (lat) are the standard SEGY locations containing low-resolution navigation in integer arcseconds. Edgetech also stores a high-resolution (decimal degrees with a scaling factor of 600000) in trace header locations 81-84 (lon) and 85-88 (lat). These original navigation points are preserved. In addition, we place a high-resolution, filtered, layback-corrected navigation in trace header locations 181-184 (lon) and 185-188 (lat). Layback-corrected navigation are also exported to ascii-formated, comma-separated values (csv) files, where each line indicates line name, ping number, fish latitude, and fish longitude. 20220415 Point 0.000001 0.000001 Decimal Degrees WGS84 WGS_1984 6378137.000000 298.25722210100002 20220501 None University of Texas Institute for Geophysics John A. Goff mailing and physical

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Austin TX 78758 USA 512-471-0476 goff@ig.utexas.edu 9am-5pm http://www-udc.ig.utexas.edu FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998 local time