San Francisco Bay Interferometric Bathymetry: Area B

High resolution sonar data were collected over ultra-shallow areas of the San Francisco Bay estuary system. Bathymetric and acoustic backscatter data were collected simultaneously in 10 survey blocks. All of these blocks were surveyed with 100% cover of backscatter imagery. These data were collected as source material for planned benthic habitat mapping. An earlier project had been completed to map the very-shallow subtidal and intertidal areas using optical methods. Interferometric sidescan bathymetry data were acquired using a 468 kHz Bathyswath sonar system aboard the RV MacGinitie and RV Kelpfly. Both of these platforms were well suited to acquire data in the very shallow subtidal areas of the bay.

Original contact information:

Contact Name: Jen Eckerle

Contact Org: Ocean Protection Council (OPC)

Title: Deputy Director, Ocean Protection Council

Phone: 916-653-9416

Email: jen.eckerle@resources.ca.gov

The primary purpose of this San Francisco Bay habitat mapping acquisition is to provide the California Ocean Protection Council (OPC), as required for the California Seafloor Mapping Program (CSMP), high-resolution accurately positioned sonar imagery data of San Francisco Bay coastal and near shore waters to delineate marine habitat types. Survey data from a combination of multi-beam and interferometric sonars, including the imagery and the bathymetry, will support OPC's goals as well as assist with NOAA's mandate for port and harbor maintenance (dredging), coastal engineering (beach erosion and replenishment studies), and coastal zone management.

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Ten survey blocks in Area B were acquired with the Bathyswath sonar and the bathymetric products are organized by these blocks. The blocks represent the priority areas determined by the project partners and were arranged to avoid areas where data had already been collected. Prior to data collection, a series of planned survey lines were created using the survey navigation and planning software HYPACK (Hypack, Inc). An Applanix Position and Orientation System, Marine Vessel (POS MV 320 v4) system was used on the RV MacGinitie and a Wavemaster on the RV Kelpfly to provide position and attitude data during data collection and accounted for vessel motion such as heave, pitch, and roll (position accuracy 2m, pitch, roll and heading accuracy +/-0.02 degrees, heave accuracy +/-5% or 5cm). KGPS altitude data were used to account for tide cycle fluctuations and sound velocity profiles were collected with YSI Castaway CTDs. Data acquisition, post-processing, and final products derived from bathymetry data were handled by the Seafloor Mapping Lab at CSUMB and submitted to Fugro Pelagos for inclusion in the San Francisco Bay Habitat Mapping project. Delivered formats included CARIS base surface, BAG, ESRI Grid, and color relief Geotiffs, for each block.

Bathymetric surveys for Block NBB01 were conducted on 11/18-19, 22, 2015; Block NBB02 on 6/6, 11/13-17, 19, 22-23, 12/10, 2015; Block NBB03 on 11/23-14, 12/7-11, 2015; Block NBB04 on 12/7, 10, 2015; Block NBB05 on 6/4-5, 11/28-29, 12/8, 11, 2015; Block CBB01/Islais Creek Channel on 5/2/2015; Block CBB02/India Basin on 5/2/2015; Block CBB03/South Basin on 5/2/2015; Block SBB01 on 3/16-18, 4/16-18, 4/30-5/1, 7/9, 8/3-4, 8/31-9/2, 2015; Block SBB02 on 4/16, 7/6-11, 9/3-5, 12/12. KF-includes RV Kelpfly surveys.

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To be determined by the California Ocean Protection Council (OPC) and its contracting research partners. These data depict the existing condition of the seafloor at the time of survey and should be considered only accurate for that time. Acknowledgment of the California Ocean Protection Council (OPC) would be appreciated in any publications or derived products.

Microsoft Windows 7 Version 6.1 (Build 7601) Service Pack 1; Esri ArcGIS 10.1.1.3143

These data are not attributed.

Interferometric horizontal positioning met IHO Order 1A specifications, meaning the horizontal accuracy of the data had to be within 5 meters + 5% of depth. The actual horizontal accuracy of the bathymetry exceeded these requirements, as the navigation/position data for the vessel was post-processed using an Applanix SmartBase post-processed kinematic solution, resulting in vessel horizontal positioning RMS values under 5 centimeters. Likewise, the vessel equipment offsets were measured to an accuracy of approximately 1 centimeter (1 sigma level) using laser levels and meter tapes. Vessel roll and pitch were measured to an accuracy of approximately 0.02 degrees (1 sigma level) using an Applanix POS MV. These factors created highly accurate horizontal positioning of the data that exceeded IHO Order 1A standards. Features in overlapping lines in the bathymetry were examined to confirm accuracy standards were met.

The Bathyswath 468 kHz interferometric swath bathymetry were not expected to meet IHO Order 1a standards across the entire width of the survey swath. Despite this, crossline analysis in CARIS HIPS indicated that 99.9% of cleaned crossline soundings achieved IHO Order 1a accuracy specifications, while 98.7% exceeded Order 1a and achieved Special Order specification. During acquisition, the interferometric system was set to acquire data at up to 60 m range. The majority of cleaned (accepted) soundings were within 40-45 m of nadir, but some soundings were retained out to the full 60 m range. The proportion of soundings satisfying Special Order accuracy specifications decreased at ranges greater than 40 m from nadir, but the relative scarcity of these outer-swath soundings mitigated their impact on the overall assessment. This analysis agrees with a manual review of the swath in the CARIS HIPS Subset Editor window.

The data set was derived after manually rejecting erroneous soundings. The final bathymetric product was generated using a CUBE surface model of the cleaned bathymetry.

Overlapping data sets were analyzed for agreement. Crossline analysis was performed to ensure IHO Order 1a standards were met at the 95% confidence level. Total propagation of uncertainty values were calculated in CARIS HIPS software to ensure standards were met or exceeded