Archive of Chirp Subbottom Profile, Imagery, and Geospatial Data Collected in 2022 from Seven Mile Island, New Jersey

Location information associated with each seismic profile was determined by post-processed differential correction using a base/rover setup. Processing the full-carrier phase data allows precise positioning of the base and rover receivers. Differential processing improves the rover positions by assessing positional errors computed at the base receiver and applying those errors or differences to the rover receiver. Forward and backward time-series processing of the kinematic (rover) data provides an independent calculation of the baseline trajectory and rover position relative to the base station; the positional accuracy can be estimated by differencing the time series (position separation). The base station was established upon the National Geodetic Survey (NGS) benchmark Permanent Identifier (PID) JU0450 providing base coverage within 12 kilometers (km). It was equipped with a SP90M GNSS receiver and Trimble Zephyr 3 Base antenna. Both subbottom and single-beam bathymetry data were collected aboard a towed seismic sled (rover) outfitted with a SP90M GNSS receiver (positioning), an SBG Ellipse Series-A (motion sensor), and a Teledyne Odom Echotrach CV100 single-beam echosounder with a 4-degree transducer (water depth). Differential positioning was obtained by post-processing the rover data to the concurrent base station data using GrafNav (Novatel Waypoint GNSS processing software version 8.9). Manufacture stated kinematic post-processing accuracy for the SP90M GNSS receiver in the horizonal is 0.008 m + 0.500 part per million (ppm). To ensure consistent spacing between survey lines (for example, 5 m in the nearshore and 10 m for offshore lines), an additional SP90M GNSS receiver was established aboard the R/V Sallenger, where pre-determined trackline locations were imported into HYPACK 2021 navigation software and followed during seismic data collection. During acquisition, positions from the SP90M GNSS receiver located on the R/V Sallenger were recorded and written to seismic trace headers in arcseconds every 0.20 s and were subsequently converted to latitude and longitude coordinates (World Geodetic System of 1984, WGS84, realization G2139). The approximate 18-m offset between the chirp shot/sled position and ship's GNSS antenna reference point was not accounted for during acquisition. For additional positional accuracy and navigation details specific to the GNSS and bathymetry data, please refer to the metadata included in Lyons and others (2023).