DATE: November 2012
MEMORANDUM FOR: Nicole Metzger and Darryl Hathaway
BakerAECOM
FROM: Bill O’Reilly and Michele Okihiro
Scripps Institution of Oceanography
SUBJECT: SHELF Model Bathymetry Upgrade
---------------------------------------------------------------------------------------------------------------------
PURPOSE:
The purpose of this memorandum is to describe the integration of newly acquired bathymetric data into the Scripps SHELF model in southern California.
BACKGROUND
The bathymetric grids used in the original Monitoring and Prediction (MOP) and SHELF model
Version 1.0 (northern California) were created by Scripps personnel for experimental purposes prior to the California Coastal Analysis and Mapping Project (CCAMP) Ocean Protection
Council (OPC) project. Detailed information on the various sources of bathymetry used and the process by which these data were combined was not retained. The creation of new bathymetric
SHELF model grids using current, documented, publicly available data is described below.
Bathymetry from the California Seafloor Mapping Project (CSMP) was originally selected for the SHELF model upgrade. The CSMP data was anticipated to be a seamless compilation of near-shore multibeam with LIDAR surfzone bathymetry and topographic data. The CSMP data provided to Scripps by BakerAECOM however, proved to be inadequate for the project.
Limitations with the CSMP data available in early 2012, include insufficient documentation, inconsistent formats, and large spatial gaps in spatial coverage. In light of the shortcomings with the CSMP data, alternative bathymetric data were proposed by Scripps and accepted by the
BakerAECOM in April 2012.
DATA SOURCES
The data selected to upgrade the MOP/SHELF model bathymetric grids are from the National
Oceanic and Atmospheric Administration (NOAA) National Geophysical Data Center (NGDC).
These data are in the public domain and include detailed Federal Geographic Data Committee
(FGDC) compliant metadata detailing the sources and processes used to create them. Summaries of the data sets used for the upgrade are described below.
NGDC U.S. Coastal Relief Model
The NGDC U.S. Coastal Relief Model (CRM) summarized in Table 1, seamlessly integrates offshore bathymetry and topography and was the first comprehensive view of the coastal zone. Sources of the bathymetry data include NOS, USGS, Monterey Bay Aquarium
Research Institute, USACE, and various other academic institutions. CRM volume 6 covers southern California. The CRM grid cell size is 3 arc seconds (~90 meters). Metadata
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reports are included in Appendix A. The CRM spatial coverage in southern California is shown in Figure 1.
NOAA Tsunami Inundation Digital Elevation Models
The Tsunami Inundation Digital Elevation Model (TDEM) summarized in Table 2, were developed by the Pacific Marine Environmental Laboratory (PMEL) to support tsunami forecasting and modeling at the NOAA Center for Tsunami Research. Various sources of bathymetric, topographic, and shoreline data were used to create this coastal Digital
Elevation Model (DEM) including NGDC, the U.S. National Ocean Service (NOS), the U.S.
Geological Survey (USGS), the U.S. Army Corps of Engineers (USACE), the Federal
Emergency Management Agency (FEMA), and other federal, state, and local government agencies, academic institutions, and private companies. For most regions in California, the
TDEM compiled in 2010-2011, incorporates the newly acquired multi-beam bathymetry collected for the California Seafloor Mapping Project. Details on the steps involved in building DEMs using multiple datasets are described at: http://www.ngdc.noaa.gov/mgg/inundation/tsunami/general.html
The TDEM has a grid cell size of 1/3-arc seconds (~10 meters). Metadata reports are included in Appendix A. The spatial coverage of this data is shown in Figure 2.
NOAA Electronic Navigational Charts
The NOAA Electronic Navigational Charts (ENC) are a vector database of chart features encompassing the same areas covered by NOAA’s paper and raster charts. ENC sources include NOAA, USACE, and the U.S. Coast Guard. For this project ENC data were primarily used as a “ground truth” to evaluate the final grids obtained by merging the TDEM and CRM data. ENC point soundings in southern California are shown in Figure 3.
SOURCE DATA PROCESSING
The merging of multiple data sources to create a new SHELF model grid required a common geospatial framework consisting of a coordinate system, horizontal datum, and vertical datum.
Decimal degree latitude and longitude, referenced to the North American Datum of 1983
(NAD83) was chosen for the horizontal coordinates and meters, referenced to the mean lower low water (MLLW) vertical datum was selected for the vertical coordinates. Details on the preprocessing of the source data in preparation for merging are described below.
Horizontal Coordinate System and Datum
All data sources were downloaded in geodetic, latitude and longitude, coordinates. The
CRM and ENC are referenced to NAD83, the horizontal datum chosen for the upgraded merged dataset. The TDEM, referenced to the World Geodetic System of 1984 (WGS84), also required no horizontal transformation since WGS84 is navigationally equivalent to
NAD83 ( http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc95-19408.pdf
, Federal
Register Vol. 60, No. 157, Tuesday, August 15, 1995, Notices).
Vertical Datum
The CRM bathymetry and ENC are vertically referenced to MLLW, the selected common vertical datum. A vertical datum transformation was required to convert the TDEM from
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mean high water (MHW) to MLLW. Vertical datum conversion offsets were obtained from the NOAA tides and currents website ( http://www.tidesandcurrents.noaa.gov
). Details on the tide stations and offsets used for the conversions are given in Appendix B.
Mean sea level (MSL) was used as the vertical datum for the model hindcast production runs.
Grid Spacing
Previous model sensitivity work has shown that bathymetry resolved on spatial scales of
O(100m) on the inner shelf is required to resolve alongshore variations in nearshore wave conditions in California (O’Reilly, 1993). 3-arc seconds (~90 m) was selected for the upgraded SHELF model grid spacing to match the CRM native grids. The 1/3-arc second
(~10m) TDEM grids were decimated to 3-arc seconds.
DATA MERGING
The TDEM and CRM bathymetry were combined to create a SHELF model grid that spans the offshore region from 10m to 4500m depths. The TDEM was determined to be the best available bathymetry for southern California and was used as the basis for the grid upgrade. Gaps in the
TDEM spatial coverage were filled using CRM data. Figure 4 shows the spatial extent of each data source used and the overall coverage of the merged grids.
To evaluate the merged grid, data were parsed into 1-degree square areas and bathymetry contours in each square were visually compared to ENC contours. Discrepancies between the grids and ENC contours were identified and analyzed further. With the exception of the area south of the U.S. – Mexico, the merged grids were determined to be consistent with the ENC
(Figure XX).
The merged bathymetry south of the U.S. – Mexico border, overlain with the ENC contours is shown in Figure XX. Linear offsets (both horizontal and vertical) are evident…
The offsets in the merged data were smoothed by …
SHELF MODEL UPGRADED GRID
The final upgraded grid and bathymetry for southern California is shown in Figure XX.
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REFERENCES
DIGITAL ELEVATION MODELS OF CRESCENT CITY, CALIFORNIA:
PROCEDURES, DATA SOURCES AND ANALYSIS, August 2011, http://www.ngdc.noaa.gov/dem/squareCellGrid/getReport/693 (example
NOAA National Geophysical Data Center, U.S. Coastal Relief Model, April 9, 2012, http://www.ngdc.noaa.gov/mgg/coastal/crm.html
APPENDIX A – Metadata for Bathymetry
APPENDIX B – Vertical Datum Conversion Reports
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Table 1. NGDC U.S. Coastal Relief Model
Website http://www.ngdc.noaa.gov/mgg/coastal/crm.html
Metadata
&
Data
Download
Compiled
Date
Download
Date
Volume 6 (southern California)
NGDC Coastal DEM Metadata Record | ngdc.noaa.gov.pdf http://www.ngdc.noaa.gov/mgg/coastal/grddas06/grddas06.htm
2003
Data
Sources
April 9, 2012

U.S. National Ocean Service (NOS)

U.S. Army Corps of Engineers (USACE)

Monterey Bay Aquarium Research Institute
Vertical
Datum
Horizontal
Datum
Mean Lower Low Water (MLLW), bathymetry data only
North American Datum (NAD83)
Cell Size 3 arc second (~90 m)
Citation
NOAA National Geophysical Data Center, U.S. Coastal Relief Model, April
9, 2012, http://www.ngdc.noaa.gov/mgg/coastal/crm.html
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Table 2. NOAA Tsunami Digital Elevation Model
Website http://www.ngdc.noaa.gov/mgg/inundation/
Metadata
&
Data
Download
Port_San_Luis_1-3sec: Development Report Port_San_Luis_vers2.pdf
( http://www.ngdc.noaa.gov/dem/squareCellGrid/download/1841 )
Santa_Barbara_1-3sec: NOAA Technical Memorandum NESDIS NGDC-29
( http://www.ngdc.noaa.gov/dem/squareCellGrid/download/603 )
Santa_Monica_1-3sec: NOAA Technical Memorandum NESDIS NGDC-46
( http://www.ngdc.noaa.gov/dem/squareCellGrid/download/663 )
San_Diego_1-3sec: Development Report San_Diego_California.pdf
( http://www.ngdc.noaa.gov/dem/squareCellGrid/download/3543 )
San_Diego_1-3sec_2005: Devolpment Report NOT AVAILABLE
( http://www.ngdc.noaa.gov/dem/squareCellGrid/download/549 )
Compiled
Date
2005-2012
Download
Date
April 9, 2012
Data
Sources

National Geophysical Data Center (NGDC)

U.S. National Ocean Service (NOS)

U.S. Geological Survey (USGS)

U.S. Army Corps of Engineers (USACE)

Federal Emergency Management Agency (FEMA)

Other federal, state and local government agencies

Academic institutions

Private companies
Vertical
Datum
Mean High Water (MHW)
Horizontal
Datum
World Geodetic System of 1984 (WGS 84)
Cell Size 1/3 arc second (~10 m)
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Table 3. NOAA Electronic Navigational Charts (ENC)
Website http://www.nauticalcharts.noaa.gov/mcd/enc/index.htm
Metadata
&
Data
Download
Compiled
Date
1997-2008
Download
Date
Data
Sources
October 2012

National Oceanic and Atmospheric Administration (NOAA)

U.S. Army Corps of Engineers (USACE)

U.S. Coast Guard (USCG)
Vertical
Datum
MLLW
Horizontal
Datum
Citation
North American Datum (NAD83)
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Figure 1. NGDC U.S. Coastal Relief Model Spatial Coverage
Figure 2. NOAA Tsunami Inundation Digital Elevation Model Spatial Coverage
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Figure 3. Electronic Nautical Chart Point Soundings
Figure 4. Merged Data Coverage
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Figure 5. Linear and Horizontal Offsets in Merged Data Near U.S. – Mexico Border
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