This grid represents processed dual Reson T20P multibeam echosounder (MBES) bathymetry data gridded at 8-m resolution. Quality control and data processing were conducted to remove spurious points and reduce sound speed artifacts (refraction) using Computer Aided Resource Information System (Caris) Hydrographic Information Processing System (HIPS; versions 10.2 and 10.4). Despite processing, noticeable vessel motion and refraction artifacts remain in the data, particularly in the area surveyed adjacent to Southwest Pass (this data set). Several factors contributed to difficulty during acquisition and processing. As the initial deployment of the dual system configuration on a vessel of opportunity, considerable testing and troubleshooting was expected. Environmental conditions were also challenging over the five-day cruise, including several periods of inclement weather with high winds and waves and the Mississippi River in flood stage, a combination of factors that certainly contributed to the residual artifacts present in the data. While the navigation and attitude data in the backscatter and bathymetry data are identical, the extents of the processed bathymetry grid and backscatter mosaic differ slightly due to differences in processing of the HYPACK HSX bathymetry and SeaBat User Interface s7k backscatter data. Relatively poor MBES data quality at the Southwest Pass site necessitated rejection of larger numbers of soundings than other areas. As such, a larger grid cell size (8 m versus 2 m) was utilized to create a relatively continuous surface, and smooth some of the residual motion artifacts.
Most T20P MBES bathymetry data collected near Southwest Pass during the cruise were used to produce this grid. This includes the time periods: 04:09 (UTC) 5/22/2017 (JD142) - 09:03 5/23/2017 (JD143). The only omissions consisted of data collected during transits, dip lines (lines run generally perpendicular to the shoreline, occupied primarily for seismic-reflection acquisition), and some turns.
Horizontal_Positional_Accuracy:
Horizontal_Positional_Accuracy_Report:
Navigation data were acquired using the WGS 84 coordinate system with an Applanix POS MV Wavemaster (model 220, V5), which blends Global Navigation Satellite Systems (GNSS) with acceleration data from a Motion Reference Unit (MRU) and GPS azimuthal heading. The POS MV was configured with two AeroAntenna Technologies GPS antennas located at either end of a 2-m baseline, which was oriented fore and aft and mounted atop the MBES pole, approximately amidships on the starboard side of vessel. DGPS positions were obtained from the primary antenna located on the forward end of the baseline, and the positional offsets between the antenna and the navigational reference point (the POS MV IMU) were accounted for in the Applanix POSView (version 8.60) acquisition software. DGPS positions are horizontally accurate to 0.5 - 2 meters, but accuracy can increase to less than 10 cm after post-processing with Applanix POSPac (version 8.1).
Vertical_Positional_Accuracy:
Vertical_Positional_Accuracy_Report:
Vertical accuracy of the raw data based on system specifications may be approximately 1 percent of water depth (0.3 to 0.7 m within the area covered by this grid). The Applanix Wavemaster POS MV Attitude and Positioning system, used to correct for vessel roll, pitch, heave, and yaw, has a theoretical vertical accuracy of a few mm. Post-Processed Kinematic (PPK) GPS height corrections (from Applanix POSPac smoothed best estimate of trajectory (SBET) files) were used to reference soundings to the World Geodetic System 1984 (WGS 84) ellipsoid and remove water depth variations caused by tides. Sound speed profiles (more than 70) acquired with an ODIM MVP30 moving vessel profiler were used during post-processing to minimize acoustic refraction artifacts in the bathymetry data. Changes in ship draft due to water and fuel usage were not considered.
Source_Information:
Source_Citation:
Citation_Information:
Originator: U.S. Geological Survey
Publication_Date: Unpublished Material
Title: raw MBES data in HSX format
Geospatial_Data_Presentation_Form: digital data
Type_of_Source_Media: disc
Source_Time_Period_of_Content:
Time_Period_Information:
Range_of_Dates/Times:
Beginning_Date: 20170522
Ending_Date: 20170523
Source_Currentness_Reference: ground condition
Source_Citation_Abbreviation: Reson T20P multibeam echosounder raw bathymetry
Source_Contribution:
Multibeam echosounder bathymetry, backscatter, and water column data were collected using dual Reson T20P MBES. The pair of Mills Cross transmit and receive arrays were placed 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 Point Sur 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 3.04 m below the waterline when deployed. Vessel navigation and attitude data were acquired with 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 fore and aft and mounted atop the MBES pole approximately amidships on the starboard side of vessel, and the wet pod 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 ODIM MVP30 moving vessel profiler (MVP), mounted on the stern, was used to collect water column sound speed profiles at 1 to 5 hour intervals while underway (See shapefile 2017-003-FA_MVPdata.shp available from the larger work citation). The Reson SeaBat User Interface (version 5.0.0.6) was used to control the sonars, which were operated in intermediate mode at full power (220 db), with frequency modulated pulses between 200 to 300 kHz. The range of the 1024 across track beams formed by the sonars were adjusted manually depending on water depth, and resulted in combined swath widths of 60 to 500 meters or typically 3 to 6 times the water depth. Data were monitored and recorded using the Reson SeaBat User Interface (version 5.0.0.6) and HYPACK/HYSWEEP (version 2017, 17.1.3.0). The SeaBat User Interface logged the navigation, attitude, bathymetry, time-series backscatter, and water column data to s7k format files for each sonar. HYSWEEP logged the navigation, attitude, and bathymetry data for both sonars to a single HSX format file, the time series backscatter data for both sonars to a single 7k format file, and water column data to 7k format files for each sonar. HYPACK HSX data were used to produce the final processed bathymetry grids, and Reson SeaBat User Interface s7k data were used to produce the final processed backscatter mosaics.
Process_Step:
Process_Description:
Shipboard multibeam bathymetry processing within Caris HIPS (version 10.2) consisted of the following flow:
1) A Caris HIPS project (version 10.2) was created with projection information set to Universal Transverse Mercator (UTM) Zone 16N, WGS 84.
2) A vessel configuration file was created in Caris for the R/V Point Sur, which included relevant linear and angular installation offsets for each T20P unit as well as vendor specified uncertainty values for each of the survey sensors.
3) Each HYPACK HSX file was imported to the new Caris project using the Import/Conversion Wizard.
4) Delayed heave data from raw POS MV files were used to update HIPS survey lines using the import auxiliary data function.
5) Navigation was reviewed and edited as needed using the Navigation Editor tool.
6) Sound velocity correction was applied using the Caris algorithm, a master SVP file containing all the sound velocity profiles collected during the cruise and specifying the nearest in distance method, delayed heave source, and use surface sound speed.
7) Data were merged selecting no tide and the delayed heave source.
8) 5-m resolution Bathymetry Associated with Statistical Error (BASE) surfaces were created to incorporate files for each Julian day as they were processed, and the BASE surfaces were reviewed for inconsistencies and anomalies.
9) The swath and subset editors were used to remove spurious points through manual editing and filter application, and the refraction editor was used to adjust sound speed values in areas where velocimeter data did not adequately correct depth profiles obviously influenced by local anomalies in speed of sound through the water column.
10) Survey lines adjusted for refraction anomalies were remerged, and the respective BASE surfaces were recomputed to reflect the changes. Shipboard processing was primarily focused on QA/QC during acquisition. Editing processes did require trial and error, and were at times iterative.
This process step and all subsequent process steps were conducted by the same person - Wayne Baldwin.
Process_Date: 201705
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: Wayne Baldwin
Contact_Position: Geologist
Contact_Address:
Address_Type: mailing and physical address
Address: 384 Woods Hole Rd.
City: Woods Hole
State_or_Province: MA
Postal_Code: 02543-1598
Contact_Voice_Telephone: 508-548-8700 x2226
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: wbaldwin@usgs.gov
Process_Step:
Process_Description:
Post-cruise processing within Caris HIPS (version 10.4) consisted of the following flow:
1) Post-processed navigation, vessel attitude, and GPS height data from POSPac SBET files, and post-processed rms attitude error data from POSPac smrmsg files were used to update HIPS survey lines using the import auxiliary data function.
2) All lines were updated with Applanix SBET set as the navigation source, and navigation was reviewed and edited as needed using the Navigation Editor tool.
3) GPS tide was computed using delayed heave data, the vessel water line, and a single datum value of 0 m (referencing the data to the WGS 84 ellipsoid).
4) Sound velocity correction was reapplied using the Caris algorithm, the master SVP file containing all the sound velocity profiles collected during the cruise and specifying the nearest in distance method, delayed heave source, and use surface sound speed.
5) Data were remerged selecting the GPS tide and delayed heave sources.
6) Total Propagated Uncertainty (TPU) was computed specifying POSPac smrmsg and delayed heave values.
7) An 8-m resolution Combined Uncertainty Bathymetry Estimator (CUBE) surface was created with all files incorporated in the Southwest Pass survey area, using IHO S-44 Order, Special Order specifications, with a Density and Locale Disambiguation method as a CUBE parameter.
8) Additional editing was conducted using the swath and subset editors to minimize inconsistencies and artifacts, and the CUBE surface was recomputed to reflect the changes.
Process_Date: 201711
Process_Step:
Process_Description:
Gridded surface export and datum transformation:
The Caris CUBE surface was exported from HIPS as an 8-m per pixel Esri ASCII raster (UTM Zone 16N, WGS 84), with pixel values (depths) ranging from -51.91 to -99.46 m. The National Oceanic and Atmospheric Administration's Vertical Datum Transformation tool (VDatum version 3.7) was used to transform the Esri ASCII raster WGS 84, UTM 16N, meters to the North American Datum of 1983 (NAD 83), UTM 16N, North American Vertical Datum of 1988 (NAVD 88), meters, using the GEIOD12B geoid model. The resulting Esri ASCII raster was imported into Global Mapper (version 17.1.0) and exported as the 32-bit floating point GeoTIFF '2017-003-FA_T20P_Bathy_swpasssite.tif', which has pixel values (depths) ranging from -27.32 to -74.92 m.
Process_Date: 201801
Process_Step:
Process_Description:
Added keywords section with USGS persistent identifier as theme keyword.
Process_Date: 20200807
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: VeeAnn A. Cross
Contact_Position: Marine Geologist
Contact_Address:
Address_Type: Mailing and Physical
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: MA
Postal_Code: 02543-1598
Contact_Voice_Telephone: 508-548-8700 x2251
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: vatnipp@usgs.gov
