This grid represents processed dual-head Reson T20-P multibeam echosounder (MBES) bathymetry data gridded at 2-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 this processing, small areas of vessel motion and refraction artifacts remain in the data, particularly in deeper areas of the Colorado River. The small slot canyons terminating in the Colorado River presented several challenges to acoustic survey methods. The deep, sinuous canyons such as Rainbow Bridge, Navajo, and Wetherill Canyons are characterized by steep walls with overhangs, above-and below-the lake surface. The overhangs above the surface interfered with the GPS signal at times, requiring detailed editing of the navigation within these areas. The canyon wall overhangs beneath the lake surface produced multipathing of the acoustic signal that required significant editing to minimize the multipath artifact. Small "no data" gaps exist throughout the dataset. These are the result of editing the artifacts and, in some areas, eliminating low quality soundings. In addition, gaps exist in shallow areas where underwater obstructions created hazards for the safe navigation of the survey vessel. Despite editing of the attitude data, vertical offsets between adjacent lines still exist due to equipment malfunctions at the end of the survey in Wahweap and Warm Springs Bays.
Data were not collected on October 23, 2017 while the base of operations was moved from Bullfrog, UT in the northeast to Page, AZ in the southwest. Data were not collected between Nov 10 and 14 because of a cable failure of the Applanix navigation and attitude system. Operations resumed (and were completed) November 15, 2017 after installation of the new cable.
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 midships 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 accuracy of the raw data based on system specifications may be approximately 1 percent of water depth (ranging from 0.5 to 1.5 meters based on the water depth range of less than 5 meters to approximately 150 meters within the survey area). 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 fluctuations in lake levels during the survey. Fifty-six sound speed profiles acquired with an AML Minos X SVPT sound velocity profiler were used during processing to minimize acoustic refraction artifacts in the bathymetry data. Changes in vessel draft due to water and fuel usage were not considered.
Additionally, uncertainty associated with the vertical transformation of the bathymetric grid from WGS 84 (ITRF 2000) to the North American Vertical Datum of 1988 (NAVD 88) using VDatum transformation tool (NOAA) is approximately 7.6 cm as calculated by the VDatum tool (v. 3.8).
Originator: U.S. Geological Survey
Publication_Date: Unpublished Material
Title: raw MBES data in s7k format
Geospatial_Data_Presentation_Form: digital data
Source_Citation_Abbreviation: RAW RESON T20-P MULTIBEAM ECHOSOUNDER FILES
Source_Currentness_Reference: ground condition
Multibeam echosounder (MBES) bathymetry and backscatter data were collected using dual-head Reson 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 Stephens 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 fore and aft and mounted atop the MBES pole approximately midships on the starboard side of vessel, 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 deployed using an electric downrigger mounted on the port quarter was used to collect water column sound speed profiles 1 to 3 times each survey day (See shapefile 2017-049-FA_SVPdata.shp available from the larger work citation). The Reson SeaBat User Interface (version 188.8.131.52) 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 200 meters or typically 3 to 6 times the water depth. Data were monitored and recorded using the Reson SeaBat User Interface (UI) (version 184.108.40.206) and Hypack/Hysweep (version 2017, 220.127.116.11). The SeaBat User Interface logged the navigation, attitude, bathymetry, time-series backscatter, and water column data to s7k format files for each sonar. The line files were created by the Reson UI using the following naming convention: YYYYMMDD_HHMMSS_M/S. The line files were appended with an "M" and "S" suffix to denote the port (or primary) "M" and "S" starboard (or secondary) sonar heads
PROCESSING STEP 1: CARIS HIPS DATA PROCESSING.
Multibeam bathymetry processing within CARIS HIPS (version 10.2) during the survey consisted of the following flow:
1) Vessel configuration files were created in CARIS for the port ("M"=main, or primary) and starboard ("S"=secondary) sonars (RVStephens_DualT20P_M.hvf, and RVStephens_DualT20P_S.hvf) which includes, linear and angular installation offsets for each T20-P unit as well as vendor specified uncertainty values for each of the survey sensors.
2) A CARIS HIPS project (version 10.2) was created with projection information set to Universal Transverse Mercator (UTM) Zone 12N, WGS 84. Separate HIPS projects were created for the Port (M), and Starboard (S) line files using the two vessel configuration files in #1 above.
3) Each Reson s7k file (M and S) were imported to the new CARIS projects (M and S respectively) 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 survey 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) 2-m resolution Swath Angle Weighted (SWATH) surfaces were created to incorporate all the files (M and S) as they were processed, and the SWATH 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, which were 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 SWATH surfaces were recomputed to reflect the changes. Processing during the survey was primarily focused on QA/QC during acquisition. Editing processes did require trial and error, and were at times iterative. The contact person for this and all subsequent processing steps below is Brian Andrews.
Contact_Organization: U.S. Geological Survey
Contact_Person: Brian Andrews
Address_Type: mailing and physical address
Contact_Voice_Telephone: 508-548-8700 x2348
Address: 384 Woods Hole Rd.
City: Woods Hole
PROCESSING STEP 2: APPLY POST PROCESSED SBET FILES AND EDIT SOUNDINGS.
Post-survey 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) Navigation source was set to Applanix SBET, 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 (vertically 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 survey 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) 2-m resolution SWATH surfaces using both the M and S files were created using the Swath Angle method and a maximum footprint of 9.
7) Additional editing was conducted using the swath and subset editors to minimize inconsistencies and artifacts, and the SWATH surface was recomputed to reflect the changes. Finally, small "no data" holidays were filled using the "Fill Raster Holiday" tool and a 5x5 cell filter using data from a minimum of 5 neighboring cells.
PROCESSSING STEP 3: EXPORT AND TRANSFORM TO NAVD 88.
The CARIS HIPS SWATH surfaces were exported as 2-m per pixel ASCII files referenced to UTM Zone 12N, WGS 84 and WGS 84 ellipsoidal heights, but the desired vertical datum of the final composite bathymetric surface was the North American Vertical Datum of 1988 (NAVD 88). The National Oceanic and Atmospheric Administration's Vertical Datum Transformation tool (VDatum v. 3.8) was used to achieve that goal. The process required transformation of the horizontal and vertical reference frames from UTM Zone 12, WGS 84 and WGS 84 ellipsoidal heights to UTM Zone 12, North American Datum of 1983 (NAD 83) and NAVD 88 orthometric heights (all in meters) using the GEIOD12B geoid model. The resulting ASCII rasters were merged together into one 32-bit floating point GeoTIFF (2017-049-FA_T20PBathymetry_2m.tif.) using the "Mosaic to New Raster" tool within ArcMap (v. 10.3.1).
Added keywords section with USGS persistent identifier as theme keyword.
Contact_Organization: U.S. Geological Survey
Contact_Position: Marine Geologist
Contact_Person: VeeAnn A. Cross
Address_Type: Mailing and Physical
Contact_Voice_Telephone: 508-548-8700 x2251
Address: 384 Woods Hole Road
City: Woods Hole