Type_of_Source_Media: disc
Source_Contribution:
Multibeam echosounder (MBES) bathymetry and backscatter data were collected using dual-head Teledyne SeaBat T20-P sonars. The pair of mills cross transmit and receive arrays were mounted side-by-side within a bracket that oriented them at opposing 30-degree angles (relative to horizontal). The bracket was pole-mounted on the starboard side of the R/V Rafael so that the sonar arrays were oriented athwart ships (primary and secondary arrays facing outward and down to port and starboard, respectively) and located approximately 1.235 m below the waterline when deployed. Vessel navigation and attitude data were acquired using an Applanix POS MV Wavemaster (model 220, V5) configured with two AeroAntenna Technologies GPS antennas located at either end of a 2-m baseline, which was oriented athwartship and mounted atop the aft end of cabin, and the wetpod MRU mounted atop the sonar bracket just aft of the pole. An AML Micro X SV mounted on the sonar bracket monitored sound speed near the sonars during acquisition, and an AML Minos X SVPT was used to collect water column sound speed profiles 1 to 3 times each survey day. The Teledyne SeaBat User Interface (version 5.0.0.18) was used to control the sonars, which were operated in intermediate mode at full power (220 dB), with frequency-modulated pulses centered at 400 kHz. The range of across track beams (2048 for JD 160, 1024 for the rest of the survey) formed by the sonars were adjusted manually depending on water depth, and resulted in combined swath widths of 50 to 250 meters or typically 3 to 6 times the water depth. Data were monitored and recorded using the Teledyne SeaBat User Interface (UI) (version 5.0.0.18) and Hypack Hysweep (version 2021, 21.1.3.0). The SeaBat User Interface logged the navigation, attitude, bathymetry, time-series backscatter, and water column data to s7k format files for each sonar. The s7k line files were created by the Teledyne SeaBat UI using the following naming convention: M/S_YYYYMMDD_HHMMSS. The line files were appended with an "M" and "S" prefix to denote the port (or main/primary) "M" and "S" starboard (or secondary) sonar heads, respectively. Hypack Hysweep 2021 also was used to log the navigation, attitude, and bathymetry data for both sonars to a single HSX format file. Hypack Hysweep filenames have the format 'LLL_HHMM', where LLL indicates the three digit planned line number and HHMM is the UTC time. The Hypack Hysweep HSX data were used to produce the final processed bathymetry grid and the trackline shapefile.
