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In 1997 project scientists in cooperation with NOAA personnel collected detailed bathymetric and acoustic backscatter data in central San Francisco Bay using a commercial multi-beam mapping system. The data were collected under highly accurate controls; navigation accuracy is estimated at 1 meter, horizontal and vertical resolution of the bathymetric data are 4 m and 0.1 m, respectively. The data were processed by USGS personnel and used to generate various image products for analysis and interpretation of sediment patterns and other features on the Bay floor. The image maps and derivative products are used to examine the morphology and composition of the Bay floor, which contributes toward the understanding of patterns and processes of sediment transport in the Bay. Also, an important utilization of these highly accurate maps and images has been in providing detailed size, location and volume estimates of rock pinnacles in central Bay which are considered to be potential hazards to navigation for deep draft tankers. Ongoing studies to determine the possible reduction of the size of these features prompted recent legislation passed by Congress that will use these data in the engineering analysis.
Annually, millions of dollars are spent by Federal, State, and local governments, as well as other entities, to dredge navigable waterways, ports, and harbors that shoal due to sedimentation. Dredging alleviates the problem in the short term, however, dredging creates the problem of disposal. The large deposit of dredged materials that resides on the Bay floor adjacent to Alcatraz Island has created continuing discussion of its fate and erodibility. The images produced in this project clearly identify the deposit and allow for future measurements of its size and shape. By providing highly detailed maps and images of the distribution, sources, sinks, and transport pathways of sediment, we can help managers, decision-makers, and regulators be more efficient in managing human activities like dredge-material disposal, maintenance of navigation waterways and coastal development.
The image products shown in this web page cover the regions around West-Central Bay, including Alcatraz Island. The image strips were collected during January to February 1997 using a Simrad EM 1000 multibeam swath mapping system. This system uses 60 independent beams to collect a swath of bathymetry and backscatter values that are then gridded into a 4-meter resolution grid of bathymetry and a 2-meter resolution grid of backscatter. All bathymetry values are tide-corrected to mean low water using actual measured tide values. The data are collected at a frequency of 95 kHz and are geometrically corrected using differential GPS. The data were collected under contract by C and C Technologies, Inc. from Lafayette, Louisiana, and processed by the U.S. Geological Survey.
The multibeam image strips were processed into digital mosaics by the USGS utilizing a software package developed by the University of New Brunswick. The digital image mosaics were post-processed and enhanced using the USGSMIPS software package to generate the images shown in this web page. One procedure used to help visualize the data was to digitally merge the bathymetric shaded relief mosaic with a portion of a Landsat Thematic Mapper (TM) satellite image of the San Francisco Bay area collected on October 24, 1995, having 30 meter resolution. These data were then further enhanced by digitally merging a protion of an IRS-IC (Indian Remote Sensing Satellite IC) image having approximately 6 meter resolution. The digital merging of the data sets helps visually show the location of the backscatter and bathymetry mosaics relative to on-land geographic features. Once zoomed in the data are shown at their full resolutions.
The links below lead directly to pages for either the multibeam bathymetry mosaic of the West-Central Bay area, or the multibeam backscatter and bathymetry mosaics of the more local Alcatraz Island area. The pages contain information about the data and image processing, and thumbnail images that access full resolution images. These pages are the same pages accessed by zooming in on the above regional satellite overview mosaic. Therefore, clicking on either a link below or inside the satellite image shown above will access these data at full resolution. (Satellite link zooms in once on the regional view, and then goes to the multibeam data).
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West-Central Bay Area
| Alcatraz Island Area |
Project Team: |
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| Dave Rubin | San Francisco Bay Project Chief |
| Dave Cacchione | Ex-Project Chief (now retired) |
| Pat S. Chavez, Jr. | Remote Sensing Scientist, Image Processing and Analysis |
| John Chin | Geologist, Geological and Bathymetric Mapping Task Leader |
| James V. Gardner | Research Geologist, Multibeam Processing and Analysis |
| Herman Karl | Geologist |
| Stuart C. Sides | Computer Scientist |
| Deborah L. Soltesz | Web Page Design |
| Miguel G. Velasco | Image Processor |
 For more information about this project, contact:
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Pat S. Chavez, Jr.
Email: pchavez@usgs.gov
U.S. Geological Survey 2255 N. Gemini Dr. Flagstaff, AZ 86001 Tel: (520) 556-7221 FAX: (520) 556-7169 |
John L. Chin
Email: jchin@usgs.gov
U.S. Geological Survey 345 Middlefield Road MS 999 Menlo Park, CA 94025 Tel: (415) 329-5270 |
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