DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

noaa / NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

National Environmental Satellite,

Data, and Information Service

NOAA Technical Memorandum NESDIS NGDC-3

DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA:

PROCEDURES, DATA SOURCES AND ANALYSIS 

L.A.Taylor

B.W. Eakins

K.S. Carignan

R.R. Warnken

D.C. Schoolcraft

G.F. Sharman

National Geophysical Data Center

Marine Geology and Geophysics Division

Boulder, Colorado

January 2008


DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

UNITED STATES

DEPARTMENT OF COMMERCE

Carlos M. Gutierrez

Secretary

NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

VADM Conrad C. Lautenbacher, Jr.

Under Secretary for Oceans

and Atmosphere/Administrator

National Environmental Satellite,

Data, and Information Service

Mary E. Kicza

Assistant Administrator

NOAA Technical Memorandum NESDIS NGDC-3

DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA:

PROCEDURES, DATA SOURCES AND ANALYSIS 

Lisa A. Taylor1

Barry W. Eakins2

Kelly S. Carignan2

Robin R. Warnken1

David C. Schoolcraft1

George F. Sharman1

1NOAA, National Geophysical Data Center, Boulder, Colorado

2

Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder 

National Geophysical Data Center

Marine Geology and Geophysics Division 

Boulder, Colorado

January 2008
ii

Taylor et al., 2008

NOTICE

Menton of a commercal company or product does not consttute an endorsement by the 

NOAA Natonal Envronmental Satellte, Data, and Informaton Servce. Use of nformaton 

from ths publcaton concernng propretary products or the test of such products for publcty

or advertsng purposes s not authorzed. 

Corresponding author contact:

Lsa A. Taylor

NOAA, Natonal Geophyscal Data Center

Marne Geology and Geophyscs Dvson

35 Broadway, E/GC 3

Boulder, Colorado 80305

Phone: 303-497-6767

Fax: 303-497-653

E-mal: Lsa.A.Taylor@noaa.gov

http://www.ngdc.noaa.gov/mgg/nundaton/

Also avalable from the Natonal Techncal Informaton Servce (NTIS)

(http://www.nts.gov)
iii

DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

Contents

1. Introduction........................................................................................................................................1

2. Study Area..........................................................................................................................................2

3. Methodology ......................................................................................................................................2

3.1 Data Sources and Processing ......................................................................................................3

3.1.1 Shoreline................................................................................................................4

3.1.2 Bathymetry ............................................................................................................6

3.1.3 Topography..........................................................................................................10

3.2 Establishing Common Datums .................................................................................................16

3.2.1 Vertical datum transformations ...........................................................................16

3.2.2 Horizontal datum transformations.......................................................................17

3.3 Digital Elevation Model Development .....................................................................................18

3.3.1 Verifying consistency between datasets..............................................................18

3.3.2 Smoothing of sparse NOS data ...........................................................................18

3.3.3 Gridding the data with MB-System.....................................................................19

3.4 Quality Assessment of the DEM...............................................................................................19

3.4.1 Horizontal accuracy.............................................................................................19

3.4.2 Vertical accuracy .................................................................................................19

3.4.3 Slope maps and 3-D perspectives........................................................................19

3.4.4	 Comparison with source data files.......................................................................21

3.4.5 Comparison with NOAA tidal bench marks........................................................21

3.4.6 Comparison with USGS bench marks.................................................................21

4. Summary and Conclusions...............................................................................................................24

5. Acknowledgments............................................................................................................................24

6. References........................................................................................................................................24

7. Data Processing Software ................................................................................................................24

List of Figures

Figure 1. Shaded-relief image, derived from the DEM, of the Port San Luis, California area..................1

Figure 2. Coverage of data sources used to compile the Port San Luis, California DEM.........................3

Figure 3. Digital coastlines in the area of Port San Luis............................................................................5

Figure 4. Digital NOS hydrographic survey coverage in the Port San Luis region...................................7

Figure 5. Spatial coverage of USACE hydrographic surveys in Morro Bay .............................................9

Figure 6. Color image of Morro Bay derived from a USGS NED 1/3 arc-second DEM ........................11

Figure 7. Example of anomalous CSC beach LiDAR data values...........................................................12

Figure 8 Color-relief image of CSC IfSAR topographic DEM in Port San Luis region.........................13

Figure 9. Map view of BEG grid of Point San Luis LiDAR survey ........................................................14

Figure 10. Perspective view of BEG grid of the breakwater off of Point San Luis...................................15

Figure 11. VDatum coverage for coastal California ..................................................................................16

Figure 12. VDatum model software Java input window............................................................................16

Figure 13. Bathymetric area outside VDatum region.................................................................................17

Figure 14. Histogram of the difference between NOS soundings for survey H10532 and the NOS 

pre-surface grid..................................................................................................................18

Figure 15. Slope map of the 1/3 arc-second Port San Luis DEM ..............................................................20

Figure 16. Perspective view from the west of the Morro Bay region of the Port San Luis DEM .............20

Figure 17.	 Histogram of the difference between one CSC coastal LiDAR file and the Port San Luis

DEM. .................................................................................................................................21

List of Tables

Table 1.	 PMEL specifications for the Port San Luis, California DEM.....................................................2

Table 2. Shoreline data sources used in gridding......................................................................................4

Table 3. Bathymetric data sources used in gridding .................................................................................6

Table 4. Digital NOS hydrographic surveys included in compilation of the Port San Luis DEM...........8
iv

Taylor et al., 2008

Table 5. Topographic features digitized from NOS sounding sheets........................................................8

Table 6. Topographic data sources used in gridding...............................................................................10

Table 7. Relationship between MHW and other vertical datums in the Port San Luis region ...............17

Table 8. Data hierarchy used to assign gridding weight in MB-System.................................................19

Table 9. Comparison of NOAA tidal benchmark elevations with the Port San Luis DEM....................21

Table 10. Comparison of USGS topographic quadrangle benchmark elevations with the 

Port San Luis DEM............................................................................................................22


DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

Digital Elevation Model of Port San Luis, California:

Procedures, Data Sources and Analysis

1. Introduction

In July 2006, the National Geophysical Data Center (NGDC), an office of the National Oceanic and

Atmospheric Administration (NOAA), developed a bathymetric/topographic digital elevation model (DEM) of Port 

San Luis, California (Fig. 1) for the Pacific Marine Environmental Laboratory (PMEL), NOAA Center for Tsunami

Research (http://nctr.pmel.noaa.gov/). The 1/3 arc-second (~10 meter) elevation grid was generated from numerous, 

diverse digital datasets in the region (grid boundary and sources shown in Fig. 2). The DEM will be used as input 

for the Method of Splitting Tsunami (MOST) model (http://www.pmel.noaa.gov/pubs/PDF/tito1927/tito1927.pdf) 

developed by PMEL to simulate tsunami generation, propagation and inundation. This report provides a summary of 

the data sources and methodology used in developing the Port San Luis DEM. 

Figure 1. Shaded-relief image, derived from the DEM, of the Port San Luis, California area. Red triangle locates tidal 

bench mark listed in Table 9; green stars locate USGS bench marks listed in Table 10. Contour interval (referenced to 

MHW): 100 meters.


Taylor et al., 2008

2. Study Area

The study area covers the coastal region of Port San Luis, California, approximately equal distances to Los 

Angeles and San Francisco. Located in San Luis Obispo County with coastal communities of Avila Beach, Pismo 

Beach, and Morro Bay, the area has populations of 797, 8,551 and 10,350 respectively. Avila Beach’s population is 

recovering after oil spill and soil contamination problems that occurred in 1992. Pismo Beach is famous for having 

one of the longest and widest beaches in California, as well as its large clams. San Luis Obispo Creek empties into the 

bay just northeast of Avila Beach. The Morro Bay 76-square mile watershed is an important biological and economic 

resource. Two creeks, Los Osos and Chorro, drain the watershed into the bay.

In contrast to the sandy beaches, rocky headlands composed of igneous rocks--granites and basalts—resist 

wave erosion and provide locally endangered Peregrine falcons with nesting sites. The volcanic formations along the 

coast include Morro Rock in San Luis Obispo County and outcroppings of basaltic lava. Morro Rock, located at the 

entrance to Morro Bay, is one of a chain of nine extinct volcanic necks that stretch approximately 12 miles from Morro 

Bay to San Luis Obispo. The chain is actually known by two names: The Seven Sisters, or the Nine Morros/Sisters, 

depending on how many of the peaks are counted. It is theorized that the 22–28 million year old chain originally 

erupted along an old fault line, south of where they are now located with their remnants (the extinct necks) moving 

along the San Andreas fault to their present day locations. Morro Rock itself is the youngest of the chain (excluding 

Davidson Seamount, submerged 2.5 miles offshore of Morro Rock), is also the most eastern of the chain, located along 

the California coast. Morro Rock was mined on and off until 1963 and provided material for the breakwater of Morro 

Bay and Port San Luis Harbor. South of Morro Bay, pillow basalts can be seen in beach cliffs near the Port San Luis 

commercial fishing pier. Visit http://nagt.org/files/nagt/field/fieldtrips/undfieldtrip.pdf and http://ceres.ca.gov/ceres/

calweb/coastal/geography.html for more information.

3. Methodology

The Port San Luis DEM was developed to meet PMEL required specifications (Table 1), based on input

requirements for the MOST inundation model. The best available data were obtained by NGDC and used to produce 

the DEM. Data processing, grid assembly, and quality assessment are described in the following subsections.

Table 1: PMEL specifications for the Port San Luis, California DEM.

Grid Area Port San Luis, California

Coverage Area 120.45 o to 121.3o W; 34.6o to 35.7o N

Coordinate System Geographic decimal degrees

Horizontal Datum World Geodetic System (WGS84)

Vertical Datum Mean High Water

Vertical Units Meters

Grid Spacing 1/3 arc-seconds

Grid Format ASCII raster grid
DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

3.1 Data Sources and Processing

Shoreline, bathymetric, and topographic data (Fig. 2) were obtained from numerous federal and state 

government agencies, and universities, including: the NOAA National Ocean Service (NOS), Office of Coast Survey

(OCS), and Coastal Services Center (CSC); the U.S. Army Corps of Engineers (USACE); the U.S. Geological Survey 

(USGS); and the University of California, San Diego (UCSD). Safe Software’s (http://www.safe.com/) FME data 

translation tool package was used to convert datasets into ESRI (http://www.esri.com/) ArcGIS shape files. The shape

files were then displayed to assess data quality and manually edit datasets. Vertical datum transformations to Mean

High Water (MHW) were largely achieved using VDatum model software (http://chartmaker.ncd.noaa.gov/csdl/

vdatum.htm) developed jointly by OCS and NOAA’s National Geodetic Survey. 

Figure 2. Coverage of data sources used to compile the Port San Luis, California DEM.
Taylor et al., 2008

3.1.1 Shoreline

Coastline datasets of the Port San Luis region were obtained from NOAA’s Office of Coast

Survey (Table 2).

Table 2. Shoreline data sources used in gridding.

Source Year Data Type Spatial Resolution

Original Horizontal 

Datum/Coordinate 

System

Original 

Vertical 

Datum

URL

OCS Electronic 

Navigational 

Charts

2001 to 

2006 coastline Digitized from 1:216,116 scale chart WGS84 InferredMHW

http://chartmaker.

ncd.noaa.gov/

OCS MHW 

vector shoreline

of Estero and 

Morro Bays

2003 MHW 

coastline

Digitized from 1:40,000 and 

1:80,000 scale charts NAD83 MHW http://chartmaker.ncd.noaa.gov/

1) NGA global shoreline

The National Geospatial-Intelligence Agency’s (NGA; http://www.nga.mil/) ‘Prototype Global Shoreline 

Data’ digital shoreline was used for evaluating the topographic LiDAR data (see Section 3.1.3). The NGA 

Global Shoreline Data is an unclassified vector dataset generated by Earth Satellite Corporation (http://

www.earthsat.com/) of Rockville, Maryland for NGA, under contract to Boeing in 2004. The shoreline 

is an approximation to the High Water Line and constructed from consistently orthorectified Landsat TM

satellite imagery (GeoCover Ortho), acquired between 1998-2002 for NASA under the Global Land Mapping 

Program (GLMP). NDVI and SWIR models were used to define the landward extent of inundation (i.e.,

MHW). Independently verified positional accuracy for the source product (GeoCover Ortho) is consistently

better than 50 meter root mean square (RMS) error.

The NGA coastline does not match the topographic data along the open ocean–land boundary, due partly 

to its lower resolution, but topographic features also have a consistent southward shift of about 30 meters (see 

Fig. 3). The dataset also includes many false islands along the California coast, some of which are the ends 

of piers. This dataset was not used in the gridding process.

2) OCS electronic navigational chart

One electronic navigational chart (ENC), #18700 (Point Conception to Point Sur, scale 1:216,116), was 

available for the Port San Luis region (#), which was downloaded from NOAA’s Office of Coast Survey

(OSC) website (http://chartmaker.ncd.noaa.gov/). The chart data includes a coastline data file (inferred MHW,

though not clearly specified), which was compared with the other coastline datasets, coastal topographic

LiDAR data, and Google Earth satellite imagery.

The ENC coastline corresponds fairly well with the higher-resolution coastal topographic LiDAR data. 

However, the coastline dataset does not include some offshore islands and includes some other false ones (see 

Fig. 3), which necessitated some manual editing of the data. 

3) OCS mean high water vector shoreline

OCS has also developed a MHW vector shoreline for the U.S., which was digitized from NOS navigational 

charts (http://chartmaker.ncd.noaa.gov/): in the Port San Luis gridding region the data is from Nautical Charts 

#18700, #18703 (Estero Bay, 1:80,000) and #18703 inset (Morro Bay, 1:40,000). Digital chart data are in 

NAD83 horizontal datum.

This shoreline dataset is also consistent with the coastal topographic LiDAR data, and the ENC coastline, 

though the Estero Bay and Morro Bay coastlines have significantly higher detail. These two OCS MHW

coastlines were also used in the grid compilation, though each required editing to delete data along map edges 

and to remove piers (e.g, Fig. 3). 
DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

The ENC coastline and the OCS MHW coastlines of Estero Bay and Morro Bay were used in the gridding 

process. Each dataset was first subsampled to 10-meter spacing and converted to point data. Estero Bay coastline

data were then excised where they overlapped the higher-resolution Morro Bay coastline; ENC coastline data were 

also excised where they overlapped the higher-resolution Estero Bay and Morro Bay coastlines. The edited coastlines 

were also combined, and used as a coastal buffer (30-meter spacing) for the NOS pre-surfacing algorithm (see Section 

3.3.2) to ensure that interpolated bathymetric values reached “zero” at the coast.

Figure 3. Digital coastlines in the area of Point San Luis. Left panel compares the NGA (red), ENC (green) and OCS 

MHW coastlines (Estero Bay, dark blue) with coastal topographic LiDAR data. Right panel is Google Earth view of same 

area, which is consistent with the LiDAR data. The NGA coastline exhibits a distinct southward shift, while the ENC and 

OCS coastlines are more consistent with the LiDAR data; the higher-resolution OCS MHW coastline best conforms to the 

LiDAR topography. Some NGA offshore “islands” are actually structures on a pier; OCS “islands” in southeast corner 

of left panel do not exist. Whaler Island, on the breakwater in the southeast corner, is represented in the NGA coastline 

(though shifted southward), but not in the ENC dataset. Whaler Island and its breakwater are represented in the OCS 

MHW coastline, though the pier to the north is also, inappropriately, represented.
Taylor et al., 2008

3.1.2 Bathymetry

Bathymetric datasets used in the compilation of the Port San Luis DEM include 36 NOS hydrographic 

surveys, and multiple hydrographic surveys of Morro Bay conducted by USACE (Table 3).

Table 3. Bathymetric data sources used in gridding.

Source Year Data Type Spatial Resolution

Original Horizontal 

Datum/Coordinate 

System

Original 

Vertical 

Datum

URL

NOS 1933 to 

1994

Hydrographic 

survey 

soundings

Ranges from 10 meters to 1

kilometer (varies with scale 

of survey, depth, traffic and

probability of obstructions)

NAD27, NAD83 MLLW, 

MLW

http://www.ngdc.

noaa.gov/mgg/

bathymetry/hydro.

html

USACE, 

Los Angeles 

District

2001 to 

2006

Hydrographic 

surveys of 

Morro Bay

1 to 5 meters

NAD83 California 

State Plane, Zone V 

(meters)

MLLW

http://www.spl.usace.

army.mil/cms/index.

php

1) NOS hydrographic survey data

A total of 36 NOS hydrographic surveys conducted between 1933 and 1994 were included in the Port 

San Luis DEM compilation (Fig. 4). The survey data were originally vertically referenced to either Mean 

Lower Low Water (MLLW) or Mean Low Water (MLW), and horizontally referenced to either NAD27 or 

NAD83 (Table 4). Data point spacing for the surveys ranged from about 10 meters in shallow water to 1

kilometer in deep water. All surveys were extracted from NGDC’s online database (http://www.ngdc.noaa.

gov/mgg/bathymetry/hydro.html) in NAD83 and MLLW or MLW datums. The data were then converted to 

WGS84 using FME software, an integrated collection of spatial extract, transform, and load tools for data 

transformation (http://www.safe.com). The surveys were subsequently clipped to a polygon 0.05 degrees 

(~5%) larger than the final gridding area to support data interpolation along grid edges.

After converting all NOS survey data to MHW (see Section 3.2.1), the data were displayed in ESRI 

ArcMap and reviewed for digitizing errors against scanned original survey smooth sheets and compared to 

current NED topographic data, the combined OCS coastline, and Google Earth satellite imagery. Several 

NOS chart features—specifically, rocks protruding near to or above the sea surface—did not have digital

representation and were thus digitized by NGDC for inclusion in the Port San Luis DEM (see Table 5). For 

much of the Port San Luis region, the NOS survey data come within only about 500 meters of the coast, 

leaving an unsurveyed gap in this critical area.
DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

Figure 4. Digital NOS hydrographic survey coverage in the Port San Luis 

region. Red line denotes DEM boundary; OCS coastline in black.
Taylor et al., 2008

 Table 4. Digital NOS hydrographic surveys included in the Port San Luis, California DEM.

Survey ID Year Survey Scale Original Horizontal 

Datum

Original Vertical 

Datum

B00085 1986 50,000 NAD83 MLLW

B00117 1987 50,000 NAD83 MLLW

B00118 1987 50,000 NAD83 MLLW

B00157 1988 50,000 NAD83 MLLW

B00161 1988 50,000 NAD83 MLLW

B00162 1988 50,000 NAD83 MLLW

H05476 1933 10,000 NAD27 MLLW

H05508 1933 10,000 NAD27 MLLW

H05509 1934 10,000 NAD27 MLLW

H05566 1933 40,000 NAD27 MLLW

H05567 1934 40,000 NAD27 MLLW

H05611 1933 80,000 NAD27 MLLW

H05642 1934 10,000 NAD27 MLLW

H05671 1934 10,000 NAD27 MLLW

H05681 1934 10,000 NAD27 MLLW

H05682 1935 10,000 NAD27 MLLW

H05692 1935 10,000 NAD27 MLW

H05708 1935 10,000 NAD27 MLLW

H05741 1934 10,000 NAD27 MLLW

H05742 1934 10,000 NAD27 MLLW

H05743 1934 10,000 NAD27 MLLW

H05746 1934 40,000 NAD27 MLLW

H05747 1934 10,000 NAD27 MLLW

H05748 1934 40,000 NAD27 MLLW

H05749 1934 10,000 NAD27 MLLW

H05750 1934 10,000 NAD27 MLLW

H05751 1935 5,000 NAD27 MLLW

H05772 1934 10,000 NAD27 MLLW

H05774 1934 40,000 NAD27 MLLW

H05776 1934 120,000 NAD27 MLLW

H05777 1933 120,000 NAD27 MLLW

H05831 1934 10,000 NAD27 MLLW

H05832 1934 10,000 NAD27 MLLW

H09737 1978 5,000 NAD27 MLLW

H10531 1994 10,000 NAD83 MLLW

H10532 1994 10,000 NAD83 MLLW

 Table 5. Topographic features digitized from NOS sounding sheets.

Feature Name NOS Survey ID Longitude Latitude Elevation (m above MHW)

Von Helm Rock H05681 -121.112376 35.538589 -5.9939

Cambria Rock H05681 -121.1358 35.858064 3.04799

Pico Rock H05681 -121.137725 35.596774 3.65759

White Rock H05682 -121.088406 35.532919 6.09599

Avila Rock H05772 -120.724605 35.170122 2.13359

Bird Rock H05772 -120.684285 35.148444 2.13359

White Rock H05772 -120.709765 35.163297 4.87679

Lone Black Rock H05831 -120.771652 35.159767 0.60959

Pecho Rock H05831 -120.816773 35.17954 12.19199

Lion Rock H05832 -120.872554 35.217402 41.4

Whale Rock H05692 -120.89 35.43 4.87679
DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

2) USACE hydrographic data in Morro Bay

The U.S. Army Corps of Engineers (USACE) has conducted multiple high-resolution (~1 meter) 

hydrographic surveys of Morro Bay in connection with dredging of that bay (Fig. 5). These surveys, in 

the form of xyz data files, were provided to NGDC by Art Shak, USACE, and represent surveys conducted

between 2001 and 2006, before and after dredging operations. The survey data are in NAD83 California 

State Plane, Zone V (meters) and MLLW (meters). According to USACE tidal estimates within Morro 

Bay, the difference between MLLW and MHW is 5.4 ft (1.646 m). NGDC utilized the most recent USACE 

hydrographic surveys of the bay, and offshore disposal site, that provided the most extensive spatial coverage 

for use in the gridding process.

Figure 5. Spatial coverage of USACE hydrographic surveys in Morro Bay that were utilized in DEM 

development.
10

Taylor et al., 2008

3.1.3 Topography

Topographic data were obtained from several sources: USGS National Elevation Dataset (NED) 1/3 arcsecond (10 meter) gridded topography; NOAA Coastal Services Center (CSC) coastal LiDAR and IfSAR surveys; 

and ultra-high resolution (0.5 meter) Bureau of Economic Geology (BEG) LiDAR DEM of Point San Luis, San Luis 

Obispo Bay (Table 6).

Table 6. Topographic data sources used in gridding.

Source Year Data Type Spatial Resolution

Original Horizontal 

Datum/Coordinate 

System

Original 

Vertical 

Datum

URL

USGS 

NED 2006 Topographic DEM 1/3 arc-second grid NAD83 geographic NAVD88

(meters)

http://ned.usgs.

gov/

BEG 2004 Topographic 

LiDAR 0.5 meter grid NAD 83, UTM Zone 10, meters

NAVD88 

(meters)

NOAA 

CSC

2002 to 

2003

Topographic 

IfSAR 3 meter grid NAD 83, UTM Zone 11 , meters

NAVD88 

(meters)

http://www.csc.

noaa.gov/lidar

NOAA 

CSC 1998 Topographic 

LiDAR 10 meter grid NAD 83 geographic, meters

NAVD88 

(meters)

http://www.csc.

noaa.gov/lidar

1) USGS NED topography

The U.S. Geological Survey’s (USGS) National Elevation Dataset (NED; http://ned.usgs.gov/) provides 

complete 1 arc-second coverage of the continental U.S. (Fig. 6)1. 1/3 arc-second DEMs are available for 

much of California and were downloaded by NGDC for use in the Port San Luis DEM. Data are in NAD83 

geographic coordinates and NAVD88 vertical datum (meters). The extracted bare-earth elevations have a 

vertical accuracy of +/- 7 to 15 meters depending on source data resolution. See the USGS Seamless web site 

for specific source information (http://seamless.usgs.gov/). The dataset was derived from USGS quad maps 

and aerial photos based on surveys conducted in the 1970s and 1980s.

The NED data include “zero” values over the open ocean (Fig. 6), which had to be clipped from the 

dataset before gridding. Some anomalous values still remained over the open ocean, which were visually 

inspected and compared with NOAA nautical charts, the OCS coastline, and Google Earth satellite imagery. 

Some of these data points represented wharfs in San Luis Obispo Bay, which were deleted. Most of the data 

values less than 1.0 meters above NAVD88 (0.365 meters below MHW) that lie along the coastline were also 

inconsistent with other datasets and were deleted; the beach face for most of the coastline in the Port San 

Luis gridding region was also covered by higher-resolution topographic coastal LiDAR surveys performed 

by CSC (see below).

. The USGS National Elevation Dataset (NED) has been developed by merging the highest-resolution, best quality elevation data available across 

the United States into a seamless raster format. NED is the result of the maturation of the USGS effort to provide 1:24,000-scale Digital Elevation 

Model (DEM) data for the conterminous U.S. and 1:63,360-scale DEM data for Alaska. The dataset provides seamless coverage of the United 

States, HI, AK, and the island territories. NED has a consistent projection (Geographic), resolution (1 arc second), and elevation units (meters). The 

horizontal datum is NAD83, except for AK, which is NAD27. The vertical datum is NAVD88, except for AK, which is NAVD29. NED is a living 

dataset that is updated bimonthly to incorporate the “best available” DEM data. As more 1/3 arc second (10 m) data covers the U.S., then this will 

also be a seamless dataset. [Extracted from USGS NED website]
11

DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

Figure 6. Color image of Morro Bay derived from a USGS NED 1/3 arc-second DEM illustrating “zero” values (blue) 

over the open ocean and inland waterbodies that had to be deleted; OCS coastline in magenta.
12

Taylor et al., 2008

2) NOAA CSC topographic coastal LiDAR data

Laser beach mapping of parts of the U.S. West Coast were conducted by the NOAA Coastal Services 

Center (CSC), in partnership with the NASA Wallops Flight Facility, the U. S. Geological Survey (USGS) 

Center for Coastal and Regional Marine Geology, and the NOAA Aircraft Operations Center. Data were 

collected in 1998 with a LiDAR instrument that uses a pulsed laser ranging system mounted onboard an 

aircraft to measure ground elevation and coastal topography2. Coastal LiDAR data in the Port San Luis region 

were downloaded from the CSC website (http://www.csc.noaa.gov/lidar/) in NAD83 geographic coordinates 

(meters) and NAVD88 (meters). The LiDAR elevation points are horizontally accurate to +/- 0.8 meters at 

an aircraft altitude of 700 meters; raw elevation measurements are vertically accurate to within 15 cm. No 

processing was done by CSC to remove returns from water or vegetation. Thus data values offshore primarily 

represent wave features on the ocean surface, not true topography. 

Examination of the nearshore data by NGDC indicated that a cutoff of 0.75 meters above NAVD88 

datum (0.615 meters below MHW) would effectively eliminate most of the open-ocean surface returns 

while retaining much of the beach-face morphology. Visual inspection of each ESRI shape file after clipping

revealed many remaining offshore data points that were evaluated in conjunction with NOAA nautical charts 

and Google Earth satellite imagery. Many of these were sea-surface returns, which were clipped, while others 

were of exposed rocks and islands that were retained. Others were of wharfs along the San Luis Obislo Bay 

coastline, which were deleted. There were also several patches of anomalous returns, greater than 100 meters 

above MHW in some cases, that did not correspond to offshore topographic features (e.g., Fig. 7); their origin 

is unclear but may be the result of laser reflections from low-lying clouds during the LiDAR surveys. These

data points were also excised prior to gridding.

Figure 7. Example of anomalous CSC beach LiDAR data values. Left panel: red values (highs) on 

mesa to north range from 50 to 110 meters above MHW; offshore reds are in the 50 to 140 meter 

range; NGA coastline in red. Google Earth satellite image on right panel shows no land offshore.

. The laser emits laser beams at high frequency and is directed downward at the Earth’s surface through a port opening in the bottom of the 

aircraft’s fuselage. The laser system records the time difference between emission of the laser beam and the reception of the reflected laser signal

in the aircraft. The aircraft travels over the beach at approximately 60 meters per second while surveying from the low water line to the landward 

base of the sand dunes. This data set was collected with a LiDAR (Light Detection And Ranging) instrument designed and developed by the Observational Sciences Branch (OSB) of NASA at the Wallops Flight Facility in Virginia. The instrument, originally designed for mapping ice sheets 

in Greenland, is called the Airborne Topographic Mapper or ATM. The ATM II (the latest version), operates with a Spectra Physics laser transmitter, which provides a 7 nanoseconds long, 250 microjoules pulse at a frequency-doubled wavelength of 523 nanometers in the blue-green spectral 

region. The laser transmitter can function at pulse rates from 2 to 10 kHz. The laser system, with a separate cooling unit, weighs approximately 45 

kg and requires approximately 15 amperes of power at 115 volts. The transmitted laser pulse is reflected to the surface of the earth with the aid of a

small folding mirror mounted on the back of a secondary mirror of a rotating scan mirror assembly mounted directly in front of the telescope. The 

scan mirror, which is rotated at 20 Hz, is comprised of a section of round aluminum stock, machined to a specific off-nadir angle. A scan mirror

with the off-nadir angle of 15 degrees was utilized, producing an elliptical scan pattern with a swath width equal to 50 percent of the approximately 

700-meter aircraft altitude. The reflected laser pulse is transmitted to a photo-multiplier assembly that consists of a lens, a narrow bandpass filter,

and a single photomultiplier tube. [Extracted from metadata]
13

DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

3) NOAA CSC topographic IfSAR data

The NOAA Coastal Services Center (CSC) collaborated with the Southern California Water Research 

Project to conduct IfSAR (Interferometric Synthetic Aperture Radar) surveys in coastal areas of Southern 

California3. This project was designed to collect, process and disseminate topographic elevation data to 

provide coastal managers and partners with the decision support tools to more effectively manage and 

preserve America’s coastal zone. IfSAR data within the Port San Luis region were extracted from the CSC 

website (http://www.csc.noaa.gov/lidar/) as a 3-meter cell-size DEM, created in ESRI ArcGIS (Fig. 8). The 

grid was in NAD83, UTM zone 11 (meters) and NAVD88 (meters), and was resampled to a 10-meter cellsize grid for use in gridding. Data were complied to meet 4.3-meter horizontal accuracy at 95% confidence

level; data are vertically accurate to within 2.20 meters. An edge-effect along the north side of the CSC DEM 

necessitated deletion of 2 rows of data on that edge of the resampled 10-m DEM.

Figure 8. Color-relief image of the CSC IfSAR topographic DEM in Port San 

Luis region. OCS coastline in red.

. The ‘GeoSAR Mapping of Southern California’ project was flown using EarthData’s modified Gulfstream-II jet aircraft. The IfSAR data was

captured using a dual-frequency, dual-polarimetric, interferometric airborne radar mapping system (GeoSAR) that generates digital elevation models (DEMs) and orthorectified radar reflectance maps near the tops of trees as well as beneath foliage. Data was captured simultaneously in both

X-band (first surface, near the tops of trees) and P-band (beneath the foliage). X-band antenna are mounted under the wings close to the fuselage

and have a 160 MHz bandwidth at a center frequency of 9.7 GHz. P-band antennas are mounted on the wingtips and have a center frequency of 

350 MHz. Each X-band and P-band antenna provides two looks at each point on the ground for a total of four looks on each side. Flight lines are 

overlapped to provide coverage of the space directly beneath the aircraft. As a result, some points on the ground are covered eight times. Left-right 

look angles on each side of the aircraft combined with mosaicking process mitigates radar shadow and layover. X-band data has been processed for 

the entire project area and P-band has been processed for an area of approximately 300 square kilometers within the Phase I project area. Due to 

flight clearance requirements all data was normally collected between the hours of 10 PM and 7 AM. Ground control and GPS base station locations

were established to provide the necessary control to meet the accuracy requirements of the project. Radar reflective corner reflectors were deployed

across the project area to be used in the mosaicking stage to ensue that the data met the accuracy requirements. A total of fourteen reflectors were

deployed across the total project area with six reflectors deployed within the Phase I project area. A total of ten additional ground control points

were established using GPS for vertical and horizontal coordinate values. These points were used during the quality control process to evaluate the 

accuracy of the final mosaicked data. Ground control references UTM Zone 11, NAD83, GRS80. [Extracted from metadata]
14

Taylor et al., 2008

4) BEG topographic LiDAR of San Luis Obispo Bay breakwater

The Bureau of Economic Geology, University of Texas at Austin (BEG), in partnership with the United 

States Army Corps of Engineers, collected topographic LiDAR data4 in 2004 over a breakwater at the mouth 

of the San Luis Obispo Bay/Point San Luis (Figs. 9 and 10). BEG compared the LiDAR data to the 1998 

NOAA coastal LiDAR data set (see above) for evaluation and processing; the data were not processed to 

bare earth. A DEM of the BEG LiDAR data—0.5 meter cell-size, created in GMT (nearest neighbor)—was 

supplied to NGDC by Randy Bucciarelli, U.C., San Diego. This grid, in NAD83 UTM Zone 10 (meters) 

and NAVD88 (meters) was resampled to 10-meter cell-size by NGDC for use in gridding. Points less than 1

meter above NAVD88 (0.365 meters below MHW) were clipped from the grid so as to exclude sea-surface 

reflections.

Figure 9. Map view of BEG grid of Point San Luis LiDAR survey. [Image courtesy of Randy 

Bucciarelli, UCSD]

4. The data set was created by combining data collected using an Optech Inc. Airborne Laser Terrain Mapper (ALTM) 1225 in combination with 

geodetic quality Global Positioning System (GPS) airborne and ground-based receivers. The Bureau of Economic Geology, the University of Texas 

at Austin owns and operates an ALTM 1225 system (serial number 99d118). The system was installed in a twin engine Partenavia P-68 Observer 

(tail number N6602L) owned and operated by Aspen Helicopter, Inc. The lidar data set described by this document was collected on 4 April 2004 

(Julian Day 09504) between 2100 and 2143 UTC on 09504 (see Lineage, Source_Information, Source_Contribution for pass information). Conditions on 4 April were clear skies over breakwater, low clouds surrounding study area, and few wispy clouds overland adjacent to the breakwater. 

99d118 instrument settings for this flight were; laser pulse rate: 25 kHz, scanner rate: 26 Hz, scan angle: +/-15-20 deg, beam divergence: narrow,

altitude: 580-780m AGL, and ground speed: 95-111 kts. Two GPS base stations (both at the San Luis Obispo County-McChesney Field Airport, see 

Lineage, Source_Information, Source_Contribution for coordinates) were operating during the survey. The ALTM 1225 has the following specifications: operating altitude = 410-2,000 m AGL; laser pulse rate = 25 kHz; laser scan angle = variable from 0 to +/-20deg from nadir; scanning

frequency = variable, 28 Hz at the 20 deg scan angle; and beam divergence = 0.2 milliradian (half angle, 1/e). The ALTM 1225 does not digitize

and record the waveform of the laser reflection, but records the range and backscatter intensity of the first and last laser reflection using a constantfraction discriminator and two Timing Interval Meters (TIM). ALTM elevation points are computed using three sets of data: laser ranges and their 

associated scan angles, platform position and orientation information, and calibration data and mounting parameters (Wehr and Lohr, 1999). Global 

Positioning System (GPS) receivers in the aircraft and on the ground provide platform positioning. The GPS receivers record pseudo-range and 

phase information for post-processing. Platform orientation information comes from an Inertial Measurement Unit (IMU) containing three orthogonal accelerometers and gyroscopes. An aided-Inertial Navigation System (INS) solution for the aircraftâ€TMs attitude is estimated from the IMU

output and the GPS information. Wehr, A. and U. Lohr, 1999, Airborne laser scanning - an introduction and overview, ISPRS Journal of Photogrammetry and Remote Sensing, vol. 54, no.2-3, pp.68-82. [Extracted from metadata]
15

DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

Figure 10. Perspective view of BEG grid of the breakwater off of Point San Luis, with Whaler Island 

in foreground (inset is corresponding aerial photograph). [Image courtesy of Randy Bucciarelli, 

UCSD]
16

Taylor et al., 2008

3.2 Establishing Common Datums

3.2.1 Vertical datum transformations

Datasets used in the compilation of the Port San Luis DEM were originally referenced to a number of 

vertical datums including: Mean Low Water (MLW), Mean Lower Low Water (MLLW), and North American Vertical 

Datum of 1988 (NAVD88). All datasets were transformed to MHW to provide the worst case scenario for inundation 

modeling. 

1) Bathymetric data

Most of the NOS survey data were transformed to MHW using VDatum (http://nauticalcharts.noaa.

gov/csdl/vdatum.htm) model software developed jointly by NOAA’s Office of Coast Survey and National

Geodetic Survey. For the Port San Luis gridding area, the VDatum Transformation Tool consists of a Java 

based program applicable to the North/Central California region (Fig. 11). 

Figure 11. VDatum coverage for coastal California.

NOS surveys were grouped by reference to original vertical datum (see Table 2) and input to VDatum 

using the batch mode utility (Fig. 12). 

Figure 12. VDatum model software Java input window.
17

DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

NOS survey data outside the California VDatum region (Fig. 13) were converted from MLLW to MHW 

using a constant offset of -1.4462 meters – the average offset on the south edge of the VDatum region. 

USACE hydrographic survey data within Morro Bay were converted from MLLW to MHW using a constant 

of ‐1.646 meters, determined by USACE tidal measurements in the bay.

Figure 13. Bathymetric area outside VDatum region. NOS survey data within the blue-hachured 

region were converted from MLLW to MHW using a constant offset of -1.4462 meters; OCS coastline 

in black, grid boundary in red.

2) Topographic data

Topographic LiDAR and IfSAR data, and the NED DEMs were converted from NAVD88 to MHW 

using FME software by adding a constant value of -1.365 meters (see Table 7), determined at the Port San 

Luis tide station (http://tidesandcurrents.noaa.gov/).

Table 7. Relationship between Mean High Water and other vertical datums in the Port San Luis region.*

Vertical datum Difference to MHW

NGVD29 -0.472

MSL -0.573

MLW -1.109

NAVD88 -1.365

MLLW -1.426

* Datum relationships determined by tidal station at Port San Luis, California.

3.2.2 Horizontal datum transformations

Datasets used to compile the Port San Luis DEM were originally referenced to NAD83, WGS84, UTM 

Zone 10, UTM Zone 11, or California State Plane Zone V horizontal datums; the relationships and transformational 

equations between these horizontal datums are well established. All data were converted to a horizontal datum of 

WGS84 using FME software. 
18

Taylor et al., 2008

3.3 Digital Elevation Model Development

3.3.1 Verifying consistency between datasets

After horizontal and vertical transformations were applied, the resulting ESRI shape files were checked in

ESRI ArcMap for inter-dataset consistency. Problems and errors were identified and resolved before proceeding with

subsequent gridding steps; the quality-assessed ESRI shape files were then converted to xyz files in preparation for

gridding. Problems included:

•	 Data values over the open ocean in the NED DEMs and coastal topographic LiDAR surveys by CSC and 

BEG. Each dataset required automated clipping of the erroneous values and visual inspection and comparison 

of remaining offshore values with NOAA nautical charts and Google Earth satellite imagery to determine 

their reliability.

•	 Significant offshore high values (in the tens of meters, up to 140 meters) within the CSC coastal LiDAR data

were determined to be data artifacts (cloud returns?) and were excised.

•	 Numerous offshore rocks and shoals on NOS survey charts had to be digitized by NGDC for inclusion of 

those features in the Port San Luis DEM.

•	 Data gap of roughly 500 meters between NOS hydrographic soundings and the coast.

•	 Inconsistency between topographic values of the NED DEMs with the CSC LiDAR and IfSAR data. Because 

of this, then NED data were given lower preference in the gridding hierarchy (see Section 3.3.3).

3.3.2 Smoothing of sparse NOS data

The NOS hydrographic surveys are generally sparse at the resolution of the 1/3 arc-second (10 meter) grid: in 

deep water, the NOS survey data had point spacings up to 4 kilometers apart. There is also an approximately 500 meter 

gap between the shallowest NOS soundings and the coastline. In order to reduce the effect of artifacts in the form of 

lines of “pimples” in the grid due to this low resolution dataset, and to provide effective interpolation into the coastal 

zone, a 1 arc-second-spacing (30 meter) ‘pre-surface’ or grid was generated using GMT, an NSF-funded share-ware 

software application designed to manipulate data for mapping purposes (http://gmt.soest.hawaii.edu/). 

The NOS point data were first combined into a single file, along with points extracted every 30 meters from

the combined OCS coastline—to provide a “zero” buffer along the entire coastline—and points from the CSC coastal 

topographic LiDAR, which defines the near-shore beach-face morphology for much, though not all, of the Port San

Luis region (see Fig. 2). These point data were then smoothed using the GMT tool ‘blockmean’ onto a 1 arc-second grid 

0.05 degrees (~5%) larger than the Port San Luis gridding region. The GMT tool ‘surface’ then applied a tight spline 

tension to interpolate cells without data values; ‘surface’ does not support a data hierarchy (see Section 3.3.3). The 

GMT grid created by ‘surface’ was converted into an Arc ASCII grid file using the MB-System tool ‘mbm_grd2arc’.

Conversion of this Arc ASCII grid file into an Arc raster permitted clipping of the grid by the OCS coastline polygon

(to eliminate data interpolation into land areas). The resulting surface was compared with the original soundings to 

ensure grid accuracy, converted to a shape file, and then exported as an xyz file for use in the final gridding process

(e.g., Fig. 14). 

Figure 14. Histogram of the difference between NOS soundings for survey H10532 (relatively dense 

1994 multibeam sonar survey) and the NOS pre-surface grid. The greatest differences derive from 

the averaging of multiple, closely-spaced soundings in shallow areas with highly variable relief.
19

DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

3.3.3 Gridding the data with MB-System

All processed xyz files were gridded using MB-System (http://www.ldeo.columbia.edu/res/pi/MB-System/). 

MB-System is an NSF-funded share-ware software application specifically designed to manipulate submarine

multibeam sonar data, though it can utilize a wide variety of data types, including generic xyz data. The MB-System 

tool ‘mbgrid’ was used to create the Port San Luis DEM—a modeled surface draping the point data—of weighted 

sounding and topographic point data, using a tight spline tension to interpolate cells without data values. The data 

hierarchy used in the ‘mbgrid’ gridding algorithm as relative gridding weights is listed in Table 6. Greatest weight 

was given to the topographic LiDAR and IfSAR data, and high-resolution USACE hydrographic surveys of Morro 

Bay. Least weight was given to the pre-surfaced NOS grid. Gridding was performed in quadrants, each with a 5% data 

overlap buffer. Resulting Arc ASCII grids were seamlessly merged in ArcCatalog to create the final DEM.

Table 8. Data hierarchy used to assign gridding weight in MB-System.

Dataset Relative Gridding Weight

CSC topographic coastal LiDAR 100

CSC topographic IfSAR 100

BEG topographic LiDAR 100

USACE hydrographic surveys, Morro Bay 100

OCS coastlines 1

USGS NED topographic DEMs 1

NOS hydrographic surveys: soundings 1

NOS hydrographic surveys: gridded 0.01

3.4 Quality Assessment of the DEM

3.4.1. Horizontal accuracy

The digital elevation model has an estimated horizontal accuracy of no better than 10 meters for topographic 

features; the LiDAR data have an accuracy of 0.8 meters for individual postings, IfSAR data are horizontally accurate 

to within 4.3 meters. Bathymetric features are resolved only to within a few tens to a few hundred meters in deep 

water areas; shallow, near-coastal regions have an accuracy approaching the subaerial topographic features. Positional 

accuracy is limited by the sparseness of deep-water soundings, and potentially large positional accuracy of pre-satellite 

navigated (GPS) hydrographic surveys.

3.4.2 Vertical accuracy

The DEM has an estimated vertical accuracy of between 0.1 and 15 meters for topographic areas, and 0.15 

meters to 5% of water depth for bathymetric areas, depending upon source dataset. Topographic values are derived 

from: USGS NED DEMs, which have an estimated vertical accuracy between 7 and 15 meters; CSC coastal LiDAR 

surveys, which have an estimated vertical accuracy of 0.15 to 0.20 meters; and CSC IfSAR data, which are accurate 

to 2.20 meters. Bathymetric values are derived from the wide range of input data single and multibeam sounding 

measurements from the early 20th centuries to recent: NOS standards are 0.3 m in 0–20 m of water, 1.0 m in 20–100 m 

of water, and 1% of the water depth in 100 m of water. Bathymetric values in the shallowest coastal areas, where CSC 

coastal LiDAR were collected, area accurate to 0.15 to 0.2 meters. Gridding interpolation to determine values between 

sparse, poorly located NOS soundings degrades the vertical accuracy of elevations in deep water. 

3.4.3 Slope maps and 3-D perspectives

ESRI ArcCatalog was used to generate a slope grid from the Port San Luis DEM to allow for visual inspection 

and identification of artificial slopes along boundaries between datasets (Fig. 15). The DEM was transformed to UTM

Zone 10 coordinates (horizontal units in meters) in ArcCatalog for derivation of the slope grid; equivalent horizontal 

and vertical units are required for effective slope analysis. Three-dimensional viewing of the UTM-transformed DEM 

(e.g., Fig. 16) was accomplished using ESRI ArcScene. Analysis of preliminary grids revealed suspect data points, 

which were corrected before regridding the data.
20

Taylor et al., 2008

Figure 15. Slope map of the 1/3 arc-second Port San Luis DEM. Flat-lying slopes are 

white; dark shading denotes steep slopes; OCS coastline in red.

Figure 16. Perspective view from the west of the Morro Bay region of the Port San Luis 

DEM. OCS coastline in black; vertical exaggeration–times 5.
21

DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

3.4.4	 Comparison with source data files

To ensure grid accuracy, the Port San Luis DEM was compared to select source data files. Files were chosen

on the basis of their contribution to the grid-cell values in their coverage areas, i.e., had the greatest weight and did 

not overlap over comparable-weight data files. A histogram of the comparison of one CSC coastal LiDAR file with

the DEM is shown in Fig. 17.

Figure 17. Histogram of the difference between one CSC coastal LiDAR file and the Port San Luis DEM.

3.4.5 Comparison with NOAA tidal bench marks

The National Geodetic Survey (NGS) data sheets for the tidal stations document benchmark elevation above 

MHW, in meters, allowing for direct comparison with DEM values at those locations. There is only one tidal bench 

mark lying within the Port San Luis study area, which was compared with the value taken at the same locale from 

the 1/3 arc-second (~10 meter) DEM (see Fig. 1 and Table 9 for station location). The bench mark has a geographic 

position recorded to within 1 arc-second, with an accuracy of +/-6 arc-seconds (http://tidesandcurrents.noaa.gov/). The 

bench mark is flush with the concrete walkway surrounding the Port San Luis Harbor building.

The origin of the large difference between the bench mark elevation and the DEM likely stems from the large 

uncertainty in the position of the bench mark (+/- 6 arc-seconds; ~180 m). The coastal topography drops steeply to the 

coastline in this area: the coastline is ~130 meters to the east; 130 meters to the west the elevation reaches 108 meters 

above MHW. The DEM properly reflects the closest CSC coastal LiDAR data value (18.2 m), just 3 meters from the

recorded position of the tidal bench mark.

Table 9. Comparison of NOAA tidal benchmark elevation, in meters above MHW, with the Port San Luis DEM.

Station 

number Station name Year Longitude Latitude Bench mark DEM Difference

9412110 PORT SAN LUIS 1992 120°45’25” W 35°10’20” N 3.425 18.064 14.639

3.4.6 Comparison with USGS bench marks

USGS benchmark elevations were extracted from online digital USGS topographic quadrangles (http://

www.topozone.com), which give benchmark position and elevation in WGS84 and NGVD29 vertical datum (in feet). 

Elevations were converted to meters and shifted to MHW vertical datum (see Table 7) for comparison with the Port 

San Luis DEM (see Fig. 1 and Table 10 for station location). The USGS bench mark with the largest difference (18.1

m: 60.6 - 42.5 m) is at -120.5685° W, 35.1338° N and listed as 141 ft (42.5 m), though it lies next to the 200 ft (61 m) 

contour. The other USGS bench marks with large differences exhibit similar disconnects between their elevation and 

location relative to contour lines. The reason for this is unknown.
22

Taylor et al., 2008

Table 10. Comparison of USGS topographic quadrangle benchmark elevations, in meters above MHW, with the Port San Luis DEM.

Longitude Latitude Bench mark DEM Difference

-120.56850 35.13380 42.5 60.6 18.1

-120.51400 34.87620 112.3 122.5 10.2

-120.60510 34.73230 48.0 57.9 9.9

-120.73660 35.33170 74.5 81.7 7.1

-120.77090 35.19300 233.6 240.0 6.3

-120.69840 35.19990 15.4 21.0 5.6

-120.67880 35.16040 29.4 34.7 5.3

-120.63500 35.35170 409.8 415.1 5.3

-121.02350 35.50890 52.9 57.7 4.9

-120.86950 35.22220 30.0 34.9 4.8

-120.81260 35.33060 3.8 8.2 4.4

-120.56670 34.97950 23.6 27.0 3.4

-120.58630 34.83790 69.3 72.6 3.3

-120.59470 34.68680 2.6 5.4 2.8

-120.63230 35.13830 6.8 9.6 2.8

-121.07250 35.55290 73.6 75.8 2.2

-120.54710 35.13920 60.8 62.9 2.1

-120.93340 35.44970 5.6 7.7 2.1

-120.63770 35.36070 383.6 385.6 2.0

-120.56510 34.83310 76.6 78.6 1.9

-120.60640 34.73470 48.9 50.7 1.8

-120.45130 34.84390 125.7 127.5 1.8

-120.51960 34.64520 18.1 19.9 1.8

-120.50200 35.00910 44.6 46.2 1.5

-120.97350 35.46790 19.3 20.8 1.5

-120.57600 34.83760 76.3 77.8 1.5

-120.54950 34.82770 76.6 78.0 1.3

-120.91480 35.44980 16.3 17.5 1.2

-121.15860 35.62730 8.7 9.8 1.1

-120.56260 34.92350 46.8 47.9 1.1

-120.59610 35.05360 27.9 28.9 1.1

-120.53680 34.89600 81.2 82.2 1.0

-120.59410 34.82470 55.6 56.6 1.0

-120.62400 35.40470 304.6 305.6 0.9

-120.63280 35.14270 7.2 8.1 0.9

-120.84560 35.51080 430.8 431.7 0.9

-120.80950 35.24170 216.9 217.6 0.8

-120.46650 34.87190 69.3 70.0 0.7

-120.62550 35.38380 318.0 318.7 0.7

-120.60350 34.68500 12.3 13.0 0.6

-120.52820 34.64890 13.9 14.4 0.6

-120.84580 35.20490 38.5 38.9 0.3

-121.04590 35.52790 37.6 38.0 0.3

-120.65470 35.33730 276.6 276.8 0.2

-120.62440 35.10170 2.3 2.5 0.2

-120.57290 35.14560 81.8 82.0 0.2

-120.58310 35.01620 15.4 15.5 0.1

-120.60570 35.41220 292.4 292.5 0.1

-120.51040 34.64320 19.3 19.4 0.1

-120.68980 35.23120 25.1 25.2 0.1

-120.49300 34.64010 22.4 22.4 0.0

-120.56730 34.99110 27.6 27.5 0.0

-120.61930 35.40650 295.5 295.4 0.0

-120.62500 35.10400 2.9 2.8 -0.1

-120.61420 34.74330 60.8 60.7 -0.1

-120.96840 35.46310 8.7 8.6 -0.1

-120.99670 35.48190 37.9 37.8 -0.1

-120.63050 35.12410 5.9 5.8 -0.1

-120.87270 35.41230 5.6 5.5 -0.1

-121.10140 35.56710 5.6 5.5 -0.1

-120.73660 35.17950 3.2 3.0 -0.2

-120.60950 34.75710 63.8 63.6 -0.2

-121.28520 35.67680 13.6 13.3 -0.3

-120.58990 35.02800 14.8 14.5 -0.3

-120.61270 34.77100 57.1 56.8 -0.3

-121.00390 35.49360 52.0 51.6 -0.3

-120.45780 34.64880 28.8 28.4 -0.4

-120.74610 35.18800 46.8 46.4 -0.4

-120.45010 34.90140 71.2 70.7 -0.5

-120.53780 34.83300 80.9 80.4 -0.5

-121.26400 35.66530 20.0 19.4 -0.6
23

DIGITAL ELEVATION MODEL OF PORT SAN LUIS, CALIFORNIA

-120.57340 34.96240 26.1 25.5 -0.6

-120.60460 34.68250 15.4 14.8 -0.6

-121.13730 35.60700 18.1 17.5 -0.7

-120.55340 34.90970 62.0 61.4 -0.7

-120.57730 35.15840 140.4 139.6 -0.7

-120.56810 34.93240 35.8 35.1 -0.7

-120.81590 35.19030 53.8 53.0 -0.8

-120.60130 34.71980 33.4 32.5 -0.8

-120.60610 34.79900 31.8 31.0 -0.8

-120.45780 34.66080 27.3 26.4 -0.8

-120.58120 35.10440 19.3 18.5 -0.9

-120.62990 35.38310 329.6 328.8 -0.9

-120.60070 35.08980 8.4 7.5 -0.9

-120.57490 35.00360 22.4 21.5 -0.9

-120.57360 34.94430 24.5 23.5 -1.0

-120.59710 34.70590 18.1 17.0 -1.1

-120.62140 35.17300 33.1 32.0 -1.1

-120.49740 34.88100 57.1 56.0 -1.1

-120.52270 34.86690 120.8 119.7 -1.1

-120.57300 34.97060 25.4 24.3 -1.1

-120.98170 35.47210 10.5 9.3 -1.2

-120.45410 34.88420 74.8 73.6 -1.2

-120.53060 35.50830 348.8 347.6 -1.2

-120.50880 34.95710 46.2 44.8 -1.4

-120.52290 34.83780 95.5 94.1 -1.4

-121.11830 35.58120 7.5 6.0 -1.4

-121.12590 35.59590 7.5 5.9 -1.6

-120.56170 34.91690 52.6 51.0 -1.6

-120.59750 34.81160 42.5 40.8 -1.7

-120.76530 35.25300 406.7 405.0 -1.7

-120.80530 35.36140 16.9 15.2 -1.7

-120.51890 34.84410 104.1 102.3 -1.8

-120.52000 34.85710 118.4 116.5 -1.9

-121.16400 35.63430 12.9 10.9 -2.1

-120.75440 35.33440 56.5 54.4 -2.1

-120.50770 34.87760 77.9 75.7 -2.1

-120.66120 35.50040 254.3 251.9 -2.4

-120.67760 35.33280 219.0 216.6 -2.4

-121.17070 35.63850 16.3 13.8 -2.5

-120.62470 35.40090 346.1 343.6 -2.5

-120.59780 35.06500 29.1 26.5 -2.6

-120.60030 34.69130 5.0 2.4 -2.6

-120.61090 34.78880 34.9 32.2 -2.7

-120.56900 35.12420 38.5 35.8 -2.8

-120.56900 35.12420 38.5 35.8 -2.8

-120.51800 35.07270 113.2 110.2 -3.0

-121.29060 35.69230 4.1 1.0 -3.1

-120.74460 35.17900 62.0 58.9 -3.1

-121.27510 35.66880 29.4 26.2 -3.2

-120.60840 35.09520 8.7 5.5 -3.2

-120.78580 35.42380 114.1 110.7 -3.4

-120.70170 35.18740 18.4 14.2 -4.2

-121.05670 35.53760 29.4 25.2 -4.2

-120.58730 34.68670 6.8 2.5 -4.3

-120.63270 35.16080 18.7 14.2 -4.5

-121.22900 35.65190 5.6 0.8 -4.8

-121.22630 35.65210 6.2 0.8 -5.4

-120.56070 35.12790 45.9 40.2 -5.6

-121.24740 35.65580 9.9 4.2 -5.7

-121.07460 35.56600 21.5 15.4 -6.0

-121.03380 35.51930 44.9 38.3 -6.6

-121.11210 35.57160 9.9 2.4 -7.5

-121.08150 35.55730 83.0 75.1 -8.0

-120.63590 34.60730 34.3 23.0 -11.3

Average: -0.3

Standard Deviation: 3.4
24

Taylor et al., 2008

4. Summary and Conclusions

A topographic/bathymetric digital elevation model with cell spacing of 1/3 arc-second (~10 meters) of the 

Port San Luis, California area was developed for the Pacific Marine Environmental Laboratory (PMEL), NOAA

Center for Tsunami Inundation Mapping Efforts (TIME). The best available data from U.S. federal and state agencies, 

and academic institutions were obtained for grid compilation. The data were quality checked, processed and gridded 

using ESRI ArcGIS, FME, VDatum, GMT, and MB-System software. 

Recommendations to improve the DEM based on NGDC’s research and analysis are listed below:

•	 Conduct bathymetric LiDAR surveys of the nearshore areas within the Port San Luis region to accurately 

incorporate tsunami-influencing offshore rocks and shoals.

5. Acknowledgments

The creation of these grids was funded by the NOAA, Pacific Marine Environmental Laboratory. The authors

thank Chris Chamberlin, Angie Venturato, and Hal Mofjeld (PMEL), Randy Bucciarelli (U.C., San Diego), Art Shak 

(USACE), and Maureen Kenny and Adeline Wong (NOAA Coast Survey Development Lab).

6. References

Nautical Chart #18700, 18th Edition, 1995. Point Conception to Point Sur. Scale 1:216,116. U.S. Department of 

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #18703, 22nd Edition, 1993. Estero Bay, and Morro Bay inset. Scale 1:40,000, and 1:10,000. U.S. 

Department of Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #18704, 12th Edition, 1990. San Luis Obispo Bay. Scale 1:20,000. U.S. Department of Commerce, 

NOAA, National Ocean Service, Coast Survey.

7. Data Processing Software

ArcGIS v. 9.1, developed and licensed by ESRI, Redlands, California, http://www.esri.com/

FME 2006 GB – Feature Manipulation Engine, developed and licensed by Safe Software, Vancouver, BC, Canada, 

http://www.safe.com/

GMT v. 4.1.1 – Generic Mapping Tools, shareware developed and maintained by Paul Wessel and Walter Smith, 

funded by the National Science Foundation, http://gmt.soest.hawaii.edu/

MB-System v. 5.0.9, shareware developed and maintained by David W. Caress and Dale N. Chayes, funded by the 

National Science Foundation, http://www.ldeo.columbia.edu/res/pi/MB-System/

VDatum Transformation Tool v. 1.0.6, developed jointly by NOAA’s Office of Coast Survey and National Geodetic

Survey, http://chartmaker.ncd.noaa.gov/csdl/vdatum.htm