Multibeam backscatter data collected in the eastern Gulf of Alaska during USGS Field Activity 2016-625-FA using a Reson 7160 multibeam echosounder (10 meter resolution, 8-bit GeoTIFF, UTM 8 WGS 84, WGS 84 Ellipsoid)

STEP 1: DATA ACQUISITION multibeam bathymetry data were collected along the Queen Charlotte fault in southeast Alaska using a Reson SeaBat 7160 multibeam sonar operating at a frequency of 44 kHz that was mounted on wing-mount from the starboard side of the R/V Medeia owned and operated by the Alaska Department of Fish and Game. The sonar collected depth, backscatter (time series), and water column data along approximately 4178 kilometers of survey lines oriented parallel with the gradient of the continental shelf west of Chichagof and Baranof islands in southeast Alaska. Data were collected using the Reson 7k Control Center and HYPACK (v. 2016).
TerraSond LLC of Seattle Washington was responsible for leasing, mobilizing and operating all equipment related to the Reson 7160. Doug MacGillivray and David Maggio of TerraSond were in charge of all multibeam data acquisition. The contact person for this and all subsequent processing steps below is Brian D. Andrews.

STEP 2: IMPORT RAW BATHYMETRY FILES TO CARIS HIPS.
Multibeam bathymetry processing within CARIS HIPS (v. 9.1.1) during the survey consisted of the following flow:
1) Vessel configuration file was created in CARIS (RVMedeia.hvf) which includes, linear and angular installation offsets and vendor specified uncertainty values for each of the survey sensors.
2) A CARIS HIPS project (v. 9.1.1) was created with projection information set to Universal Transverse Mercator (UTM) Zone 8N, WGS 84.
3) Each survey line was recorded to both a Reson .s7k, and a Hypack (v. 2016) .HSX, .RAW, and .7k files. The Hypack .HSX files were 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 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) Total Propagated Uncertainty (TPU) was calculated for each line file using the manufacturer's offset values in the vessel configuration file.
9) A 10-m resolution depth surface was created using the Combined Uncertainty Bathymetric Estimator (CUBE) method for each of the six blocks. Surfaces were reviewed for inconsistencies and anomalies. 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 CUBE surfaces were recomputed to reflect the changes. Processing during the survey was primarily focused on QA/QC during acquisition. Editing processes required trial and error, and were at times iterative.

STEP 3: APPLY POST PROCESSED SBET FILES AND EDIT SOUNDINGS.
Vessel attitude data were processed using PosPac (v. 7.2) after the final ephemeris data were available 2 weeks after completion of the survey.
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 the post-processed 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 time method, delayed heave source, and use surface sound speed.
5) Data were remerged selecting the GPS tide and delayed heave sources.
6) New CUBE surfaces were created for each of the 6 survey blocks and interpolated to fill small "no data" gaps.

STEP 4: IMPORT RESON 7K AND HIPS PAIRS TO FMGT
Backscatter mosaic was created using QPS Fledermaus GeoCoder Toolbox-FMGT (v.7.7.3) processing software. Raw 7k files containing the time series values were paired with the HIPS line files containing the corrected depth data to create a 10-m resolution time-series backscatter mosaic that followed the steps below:
1) Create new FMGT project for each of the 6 general blocks of the survey area using the UTM 8N, WGS 84 coordinate system.
2) Set processing parameters for Reson Seabat 7160 Focused MBES.
3) Added source/paired files using the Reson 7k files for the backscatter and the "processed depth" files from the HIPS line file directory.
4) Created 10-m time series mosaics of each of the 6 general blocks covering the survey area. Once these were reviewed for quality a final 10-m mosaic of the entire survey area was created.
5) Exported the FMGT mosaic to 8-bit unsigned gray-scale GeoTIFF (2016-625-FA_Reson7160_Backscatter_10m.tiff).