This image represents processed dual Reson T20P multibeam echosounder (MBES) bathymetry data mosaicked 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 bathymetric surface, and smooth some of the residual motion artifacts. The final backscatter mosaic for the Southwest Pass site was computed using a 4-m pixel after, testing suggested satisfactory results relative higher and lower resolutions.
Most T20P MBES backscatter 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).
Source_Information:
Source_Citation:
Citation_Information:
Originator: U.S. Geological Survey
Publication_Date: Unpublished Material
Title: raw MBES data in s7k 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 and backscatter
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 data 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 SeaBat User Interface s7k 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) 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.
4) Data were remerged selecting no tide and the delayed heave source.
5) Total Propagated Uncertainty (TPU) was computed specifying POSPac smrmsg and delayed heave values.
6) A 4-m resolution Combined Uncertainty Bathymetry Estimator (CUBE) surface was created incorporating 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.
7) 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: 201712
Process_Step:
Process_Description:
Processing within QPS FlederMaus Geocoder Tool (FMGT, version 7.7.5) consisted of the following flow:
1) Create a project and set project coordinate system to UTM zone 16 N NAD 83, so that the emosaic product will match the coordinate system of the equivalent bathymetric grid (see 2017-003-FA_T20P_Bathy_swpasssite.tif available from the larger work citation).
2) Set all import parameters for the Reson T20P (Edit - Processing Parameters). Defaults were accepted except for: Adjust tab, uncalibrated backscatter range of 85 decibels (db) to 125 db and Head 1 bias of -4; Filter tab, apply flat angle varying gain with a window of 300; Sonar Defaults tab, custom override all checked, Reson SeaBat T20P Focused MBES sonar type, primary frequency 300 kHz, no head 1 db reference value, and apply edits.
3) Import raw data as "Source/Paired Files". The source pairs consist of the Reson SeaBat User Interface s7k files, which contain the raw datagrams (bathymetry, attitude, time-series backscatter, navigation) needed for backscatter processing, and Caris HIPS files, which contain processed bathymetric solutions that FMGT uses to correct for slope and depth. WGS 84 navigation in the s7k headers are transformed to NAD 83 during the import process.
4) Set mosaic size to 4-m per pixel and mosaic data, creating an output Fledermaus SD (scientific data) file.
5) Use backscatter adjust function to adjust bias of individual line files to improve tonal balance of overall mosaic, and manually adjust histogram to encompass the range 98 db to 112 db.
6) Export mosaic to an 8-bit greyscale GeoTIFF image (UTM Zone 16N, NAD 83).
Process_Date: 201801
Process_Step:
Process_Description:
Create final single band 8-bit greyscale GeoTIFF and define spatial reference information:
GeoTiffExamine (no version) was used to read the exported GeoTIFF file and write an external world file (tfw) containing georeferencing information extracted from the GeoTIFF header. Adobe Photoshop CS6 (version 13.0) was used to flatten the two band raster, and save a single band image with a white background (8-bit value 255). The flattened image was imported into Global Mapper (version 17.1) and exported as the GeoTIFF '2007-003-FA_T20P_Backscatter_swpasssite.tif' in order to repopulate the GeoTIFF header with the georeferencing information.
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
