noaa / NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

National Environmental Satellite,

Data, and Information Service

NOAA Technical Memorandum NESDIS NGDC-16

DIGITAL ELEVATION MODEL OF GARIBALDI, OREGON:

PROCEDURES, DATA SOURCES AND ANALYSIS 

K.S. Carignan

L.A. Taylor

B.W. Eakins

R.R. Warnken

T. Sazonova 

D.C. Schoolcraft

National Geophysical Data Center

Marine Geology and Geophysics Division

Boulder, Colorado

March 2009

UNITED STATES

DEPARTMENT OF COMMERCE

Gary Locke

Secretary

NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

Dr. Jane Lubchenco

Under Secretary for Oceans

and Atmosphere/Administrator

National Environmental Satellite,

Data, and Information Service

Mary E. Kicza

Assistant Administrator

NOAA Technical Memorandum NESDIS NGDC-16

DIGITAL ELEVATION MODEL OF GARIBALDI, OREGON:

PROCEDURES, DATA SOURCES AND ANALYSIS

Kelly S. Carignan1

Lisa A. Taylor2

Barry W. Eakins1

Robin R. Warnken2

Tatiana Sazonova1

David C. Schoolcraft2

1

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

2

NOAA, National Geophysical Data Center, Boulder, Colorado

National Geophysical Data Center

Marine Geology and Geophysics Division 

Boulder, Colorado

March 2009
Carignan et al., 2009

ii

NOTICE

Mention of a commercial company or product does not constitute an endorsement by the 

NOAA National Environmental Satellite, Data, and Information Service. Use of information 

from this publication concerning proprietary products or the test of such products for publicity

or advertising purposes is not authorized. 

Corresponding project contact:

Lisa A. Taylor

NOAA, National Geophysical Data Center

Marine Geology and Geophysics Division

325 Broadway, E/GC 3

Boulder, Colorado 80305

Phone: 303-497-6767

Fax: 303-497-6513

E-mail: Lisa.A.Taylor@noaa.gov

http://www.ngdc.noaa.gov/mgg/inundation/tsunami/inundation.html

Also available from the National Technical Information Service (NTIS)

(http://www.ntis.gov)
Digital Elevation Model of Garibaldi, Oregon

iii

Contents

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

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

3. Methodology ......................................................................................................................................3

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

3.1.1 Shoreline................................................................................................................5

3.1.2 Bathymetry ............................................................................................................7

3.1.3 Topography..........................................................................................................11

3.2 Establishing Common Datums .................................................................................................15

3.2.1 Vertical datum transformations ...........................................................................15

3.2.2 Horizontal datum transformations.......................................................................15

3.3 Digital Elevation Model Development .....................................................................................16

3.3.1 Verifying consistency between datasets..............................................................16

3.3.2 Smoothing of bathymetric data ...........................................................................16

3.3.3 Gridding the data with MB-System.....................................................................17

3.4 Quality Assessment of the DEM...............................................................................................18

3.4.1 Horizontal accuracy.............................................................................................18

3.4.2 Vertical accuracy .................................................................................................18

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

3.4.4	 Comparison with source data files.......................................................................20

3.4.5 Comparison with NGS geodetic monuments......................................................21

4. Summary and Conclusions...............................................................................................................22

5. Acknowledgments............................................................................................................................22

6. References........................................................................................................................................22

7. Data Processing Software ................................................................................................................22

List of Figures

Figure 1. Shaded relief image of the Garibaldi, Oregon DEM ..................................................................1

Figure 2. Tectonic features along the Oregon-Washington coast...............................................................2

Figure 3. Source and coverage of datasets used to compile the Garibaldi DEM.......................................4

Figure 4. Coastlines at entrance to Tillamook Bay ....................................................................................5

Figure 5. Wells Cove at Cape Lookout ......................................................................................................6

Figure 6. Spatial coverage of bathymetric datasets used to compile the Garibaldi DEM..........................7

Figure 7. Digital NOS hydrographic survey coverage in the Garibaldi region..........................................9

Figure 8. Digital USACE hydrographic survey coverage in the Garibaldi DEM....................................10

Figure 9. Source and coverage of topographic datasets used to compile the Garibaldi DEM.................11

Figure 10. CSC topographic dataset used to compile the Garibaldi DEM.................................................12

Figure 11. A preliminary 1 arc-second grid surface of the Garibaldi region .............................................13

Figure 12. The Tillamook Rock Lighthouse ..............................................................................................14

Figure 13. Detail image of the bathy ‘pre-surface’ in the southwest corner of the DEM boundary ..........16

Figure 14. Histogram of the difference between NOS hydrographic survey H04746 and the 

1 arc-second pre-surfaced bathymetric grid ......................................................................17

Figure 15. Slope map of the Garibaldi DEM .............................................................................................19

Figure 16. Perspective view from southeast as modeled in the Garibaldi DEM........................................20

Figure 17. Histogram of the difference between one CSC LiDAR survey and the Garibaldi DEM. ........20

Figure 18. Histogram of the differences between NGS geodetic monument elevations and the 

Garibaldi DEM ..................................................................................................................21

Figure 19. Location of NGS monuments and NOAA tide station in the Garibaldi region ........................21
Carignan et al., 2009

iv

List of Tables

Table 1.	 PMEL specifications for the Garibaldi, Oregon DEM................................................................3

Table 2. Shoreline datasets used in compiling the Garibaldi DEM..........................................................5

Table 3. Bathymetric datasets used in compiling the Garibaldi DEM......................................................7

Table 4. Digital NOS hydrographic surveys used in compiling the Garibaldi DEM ...............................8

Table 5. Topographic datasets used in compiling the Garibaldi DEM ...................................................11

Table 6. Relationship between Mean High Water and other vertical datums in the Garibaldi region....15

Table 7. Data hierarchy used to assign gridding weight in MB-System.................................................17
Digital Elevation Model of Garibaldi, Oregon:

Procedures, Data Sources and Analysis

1. Introduction

InAugust 2007, the National Geophysical DataCenter(NGDC), an office ofthe National Oceanic andAtmospheric

Administration (NOAA), developed a bathymetric–topographic digital elevation model (DEM) of Garibaldi, Oregon 

(Fig. 1) for the Pacific Marine Environmental Laboratory (PMEL) NOAA Center for Tsunami Research (http://nctr.

pmel.noaa.gov/). The 1/3 arc-second1 coastal DEM will be used as input for the Method of Splitting Tsunami (MOST) 

model developed by PMEL to simulate tsunami generation, propagation and inundation. The DEM was generated 

from diverse digital datasets in the region (grid boundary and sources shown in Fig. 3) and will be used for tsunami 

inundation modeling, as part of the tsunami forecast system SIFT (Short-term Inundation Forecasting for Tsunamis) 

currently being developed by PMEL for the NOAA Tsunami Warning Centers. This report provides a summary of the 

data sources and methodology used in developing the Garibaldi DEM. 

Figure 1. Shaded relief image of the Garibaldi, Oregon DEM. Contour interval is 100 meters.

1. The Garibaldi DEM is built upon a grid of cells that are square in geographic coordinates (latitude and longitude), however, the cells are not 

square when converted to projected coordinate systems, such as UTM zones (in meters). At the latitude of Garibaldi, Oregon (45°33.6167′ N, 

123°54.6833′ W) 1/3 arc-second of latitude is equivalent to 10.291 meters; 1/3 arc-second of longitude equals 7.229 meters.
Carignan et al., 2009

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2. Study Area

The Garibaldi DEM covers the coastal region surrounding the town of Garibaldi, Oregon, located on the northern 

edge of Tillamook Bay. Included within the DEM boundary are the neighboring communities of Cannon Beach, 

Manzanita, and Rockaway Beach to the north and Oceanside, Netarts, and Pacific City to the south (Fig. 1). Garibaldi

has a small population of approximately 1000 people, working primarily in the agricultural, fisheries, lumber, and

recreation industries. The U.S. Coast Guard maintains a station in town.

Garibaldi lies near an active convergent tectonic zone (Fig. 2) making it especially vulnerable to seismically 

generated tsunamis. The Oregon Department of Geology and Mineral Industries (DOGAMI) has prepared a community 

tsunami plan in order to increase public awareness and safety of the threat of tsunamis.

“Tsunamis rank as one of the most dangerous natural disasters that could affect the Oregon coast. 

Although not frequent in occurrence, the damage caused by these catastrophic events is immediate 

and life threatening. The most destructive type of tsunami would be generated locally by a Cascadia 

subduction zone earthquake of magnitude of 8.0 to 9.0, or greater. Devastating tsunami waves 

would be expected to arrive along the Pacific Northwest coast including Oregon within 5 to 30 

minutes after such an event, providing very little evacuation time” (http://www.coastalatlas.net/

learn/topics/hazards/tsunami/index.asp).

 Figure 2. Tectonic features along the Oregon-Washington coast. The leading edge of the Cascadia subduction zone is shown as dark blue triangles. 

(http://www.washington.edu/burkemuseum/geo_history_wa/Cascade%20Episode.htm).
Digital Elevation Model of Garibaldi, Oregon

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3. Methodology

The Garibaldi, Oregon DEM was constructed to meet PMEL specifications (Table 1), based on input requirements

for the development of Reference Inundation Models (RIMs) and Standby Inundation Models (SIMs) (V. Titov, pers. 

comm.) in support of NOAA’s Tsunami Warning Centers use of SIFT to provide real-time tsunami forecasts in an 

operational environment. The best available digital data were obtained by NGDC and shifted to common horizontal 

and vertical datums: North America Datum 1983 (NAD 83) and Mean High Water (MHW), for modeling of maximum 

flooding, respectively2. Data processing and evaluation, and DEM assembly and assessment are described in the 

following subsections.

Table 1: PMEL specifications for the Garibaldi, Oregon DEM.

Grid Area Garibaldi, Oregon

Coverage Area 123.7o to 124.5o W; 45.1o to 45.95o N

Coordinate System Geographic decimal degrees

Horizontal Datum World Geodetic System 1984 (WGS 84)

Vertical Datum Mean High Water (MHW)

Vertical Units Meters

Grid Spacing 1/3 arc-second

Grid Format ESRI Arc ASCII grid

3.1 Data Sources and Processing

Shoreline, bathymetric, and topographic digital datasets (Fig. 3) were obtained from several U.S. federal agencies 

including: NOAA’s National Ocean Service (NOS), Office of Coast Survey (OCS) and Coastal Services Center (CSC);

the U.S. Geological Survey (USGS); and the U.S. Army Corps of Engineers (USACE). Safe Software’s (http://www.

safe.com/) FME data translation tool package was used to shift datasets to NAD 83 horizontal datum and to convert 

into ESRI (http://www.esri.com/) ArcGIS shape files3. The shape files were then displayed with ArcGIS to assess data

quality and manually edit datasets. Vertical datum transformations to MHW were accomplished using FME, based 

upon data from the local NOAA tide stations. VDatum model software (http://nauticalcharts.noaa.gov/csdl/vdatum.

htm) was not available for this area. Applied Imagery’s Quick Terrain Modeler software (http://www.appliedimagery.

com/) was used to edit and assess the quality of the LiDAR data.

2. The horizontal difference between the North American Datum of 1983 (NAD 83) and World Geodetic System of 1984 (WGS 84) geographic 

horizontal datums is approximately one meter across the contiguous U.S., which is significantly less than the cell size of the DEM. Most GIS applications treat the two datums as identical, so do not actually transform data between them, and the error introduced by not converting between 

the datums is insignificant for our purposes. NAD 83 is restricted to North America, while WGS 84 is a global datum. As tsunamis may originate

most anywhere around the world, tsunami modelers require a global datum, such as WGS 84 geographic, for their DEMs so that they can model the 

wave’s passage across ocean basins. This DEM is identified as having a WGS 84 geographic horizontal datum even though the underlying elevation

data were typically transformed to NAD 83 geographic. At the scale of the DEM, WGS 84 and NAD 83 geographic are identical and may be used 

interchangeably.

3. FME uses the North American Datum Conversion Utility (NADCON; http://www.ngs.noaa.gov/TOOLS/Nadcon/Nadcon.html) developed by 

NOAA’s National Geodetic Survey (NGS) to convert data from NAD 27 to NAD 83. NADCON is the U.S. Federal Standard for NAD 27 to NAD 

83 datum transformations.
Carignan et al., 2009

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Figure 3. Source and coverage of datasets used to compile the Garibaldi DEM.
Digital Elevation Model of Garibaldi, Oregon

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3.1.1 Shoreline

Coastline datasets of the Garibaldi region were obtained from NOAA’s Coastal Services Center (CSC) and Office

of Coast Survey Electronic Navigational Chart (ENC) #18520 (Table 2, Fig. 4). The ENC was not used in compiling 

a combined coastline for the Garibaldi DEM as it did not provide enough detail of coastal features, at a 1:185,238 

scale, for developing a coastline for a one-third arc-second DEM. NGDC created a partial shoreline from CSC coastal 

LiDAR data.

Table 2: Shoreline datasets used in compiling the Garibaldi DEM.

Source Year Data Type Spatial Resolution

Original Horizontal 

Datum/Coordinate 

System

Original 

Vertical 

Datum

URL

CSC historical 

shoreline

1922-

1974

digitized 

T-sheets 1:5,000 to 1:24,000 NAD 83 geographic Mean High Water

http://www.csc.noaa.

gov/shoreline/data.html

NGDC/CSC 

LiDAR derived 

shoreline

Contour WGS 84 geographic Mean High 

Water

Figure 4. Coastlines at entrance to Tillamook Bay. NGDC’s CSC LiDAR derived coastline shown in 

red and the CSC historical coastline in blue. RNC #18558 in background.
Carignan et al., 2009

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1) Coastal Services Center historical shoreline

The CSC historical shoreline was downloaded from the CSC website. It was used in the bays and inlets 

where topographic LiDAR was not present. The historical shoreline provided more detail in these areas 

than the ENC #18520 extracted coastline. Features such as pilings, docks, and piers were edited out of the 

coastline dataset using ArcMap and by referencing the more detailed small scale RNCs for Tillamook Bay 

and Nehalem River (charts #18558 and #18556).

2) NGDC/Coastal Services Center LiDAR derived contour shoreline

In order to accurately represent the coastal topographic data, NGDC processed the most recent high 

resolution topographic LiDAR dataset available from CSC to create a zero elevation coastline at Mean High 

Water vertical datum. The zero contour line incorporated major off-shore rock features and the jetties located 

at the entrance to Tillamook Bay.

The two coastline datasets were merged to create a ‘combined coastline’. River inlets were left in the combined 

coastline where digital bathymetric data were present. Modifications to the coastline included adjustments to fit the

most recent topographic data. At Wells Cove on Cape Lookout, the combined coastline was adjusted to fit the NED

topographic DEM (Fig. 5). Additionally the jetty at the entrance to Tillamook Bay was extended to match RNC 

#18558. All modifications were done using ArcMap editing tools.

Figure 5. Wells Cove at Cape Lookout. A) USGS topographic map of Cape Lookout showing Wells Cove. B) Red circle highlighting gap in CSC 

LiDAR, shown in purple, where ‘combined coastline’ was modified to fit NED DEM, shown as green/brown.
Digital Elevation Model of Garibaldi, Oregon

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3.1.2 Bathymetry

Bathymetric datasets used in the compilation of the Garibaldi DEM (Fig. 6) include 23 NOS hydrographic surveys 

and three USACE surveys located at the entrance to Tillamook Bay (Table 3).

Table 3: Bathymetric datasets used in compiling the Garibaldi DEM.

Source Year Data Type Spatial Resolution

Original 

Horizontal Datum/

Coordinate System

Original 

Vertical Datum URL

 NOS 

1926 

to 

1987

Hydrographic 

survey 

soundings

Ranges from 10 

m to 1 km (varies 

with scale of survey, 

depth, traffic, and

probability of 

obstructions)

NAD 13, NAD 

27, or NAD 83 

geographic

Mean Lower 

Low Water

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

bathymetry/hydro.html

USACE

2005 

to 

2006

Hydrographic 

survey

10 to 35 meters 

NAD 83 Oregon 

State Plane North 

(feet) 

Mean Lower 

Low Water

https://www.nwp.usace.army.mil/op/

nwh/xyzcoastal.asp

Figure 6. Spatial coverage of bathymetric datasets used to compile the Garibaldi DEM.
Carignan et al., 2009

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1) NOS hydrographic survey data

A total of 27 NOS hydrographic surveys conducted between 1877 and 1987 were available for inclusion 

in the Garibaldi DEM (Table 4; Fig. 7). Four of the NOS surveys located within the DEM boundary were not 

used due to inconsistencies with neighboring surveys and more recent overlapping data. The hydrographic 

survey data were originally vertically referenced to Mean Lower Low Water (MLLW) and horizontally 

referenced to NAD 13, NAD 27, or NAD 83 datums.

Data point spacing for the NOS surveys varied by collection date. In general, earlier surveys had greater 

point spacing than more recent surveys. All surveys were extracted from NGDC’s online NOS hydrographic 

database (http://www.ngdc.noaa.gov/mgg/bathymetry/hydro.html). The data were then converted to NAD 83 

geographic and MHW 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 degree (~5%) larger than the Garibaldi DEM 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 edited as 

necessary. The surveys were also compared to the other bathymetric and topographic datasets, the combined 

coastline, and NOS raster nautical charts (RNCs). The surveys were clipped to remove soundings that overlap 

the more recent USACE surveys at the entrance to Tillamook Bay, and where soundings from older surveys 

have been superseded by more recent NOS surveys.

Table 4: Digital NOS hydrographic surveys used in compiling the Garibaldi DEM.

NOS Survey ID Year of Survey Survey Scale Original Vertical Datum Original Horizontal Datum

H04612 1926 20,000 mean lower low water NAD 13

H04613 1926 20,000 mean lower low water NAD 13

H04614 1926 20,000 mean lower low water undetermined

H04635 1926 40,000 mean lower low water NAD 13

H04636 1926 80,000 mean lower low water NAD 13

H04637 1926 40,000 mean lower low water NAD 13

H04638 1926 80,000 mean lower low water NAD 27

H04745 1927 20,000 mean lower low water NAD 13

H04746 1927 20,000 mean lower low water NAD 13

H04747 1927 20,000 mean lower low water NAD 13

H04754 1927 80,000 mean lower low water NAD 27

H04755 1927 40,000 mean lower low water NAD 13

H04756 1927 40,000 mean lower low water NAD 13

H08346 1956 10,000 mean lower low water NAD 27

H08368 1957 5,000 mean lower low water NAD 27

H08369 1956/57 5,000 mean lower low water NAD 27

H08370 1957 10,000 mean lower low water NAD 27

H08371 1957 10,000 mean lower low water NAD 27

H08372 1957 10,000 mean lower low water NAD 27

B00019 1985 50,000 mean lower low water NAD 83

B00020 1985 50,000 mean lower low water NAD 83

B00115 1987 50,000 mean lower low water NAD 83

B00116 1987 50,000 mean lower low water NAD 83
Digital Elevation Model of Garibaldi, Oregon

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Figure 7. Digital NOS hydrographic survey coverage in the Garibaldi region. Some older surveys were not used as they 

have been entirely superseded by more recent surveys. DEM boundary in red.
Carignan et al., 2009

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2) U.S. Army Corps of Engineers hydrographic surveys

The USACE, Garibaldi District provided NGDC with three recent bathymetric surveys located at the 

entrance to Tillamook Bay (Fig. 8). The surveys were collected in 2005 and 2006, and are referenced to 

Mean Lower Low Water (MLLW) vertical datum. The files were converted to NAD 83 geographic and MHW

using FME. Point spacing averages 10 to 35 meters.

Figure 8. Digital USACE hydrographic survey coverage.
Digital Elevation Model of Garibaldi, Oregon

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3.1.3 Topography

Topographic datasets in the Garibaldi region were obtained from NOAA’s Coastal Services Center (CSC), Office

of Coast Survey (OCS), and the U.S. Geological Survey (USGS; Table 5; Fig. 9).

Table 5: Topographic datasets used in compiling the Garibaldi DEM.

Source Year Data Type Spatial 

Resolution

Original Horizontal 

Datum/Coordinate System

Original 

Vertical Datum URL

CSC 2002 Topographic 

coastal LiDAR ~6 meters NAD 83 geographic NAVD88 (meters)

http://maps.csc.noaa.

gov/TCM/

USGS 1999-

2000 NED DEM 1/3 arcsecond NAD 83 geographic NAVD88(meters) http://ned.usgs.gov/

OCS ENC 

#18520

1998 to 

2005

Extracted land 

elevation points WGS 84 geographic MHW

http://chartmaker.ncd.

noaa.gov/MCD/enc/

index.htm

Figure 9. Source and coverage of topographic datasets used to compile the Garibaldi DEM.
Carignan et al., 2009

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1) Coastal Services Center topographic LiDAR

NGDC downloaded the topographic LiDAR dataset from the CSC website in NAD 83 geographic 

horizontal datum and NAVD88 vertical datum for the entire Pacific coast near Garibaldi (Fig. 10). These data

have point spacing approximately 5 meters apart and extend 50 to 800 meters inland from the coastline. As 

these data were not processed to bare earth, the data were filtered using FME to remove points with elevations

less than 0 meters and greater than 50 meters. This process removed some water surface returns from offshore 

areas (Fig. 11) and inland high-elevation forested areas while retaining high-resolution coastal elevations. 

The combined coastline was also used to clip the remaining positive elevation values that lay over water.

Figure 10. CSC topographic dataset used to compile the Garibaldi DEM.
Digital Elevation Model of Garibaldi, Oregon

13

Figure 11. A preliminary 1 arc-second grid surface of the Garibaldi region. The false looping peninsula off the end of Cape Lookout generated by 

water surface returns in the unedited CSC LiDAR data, was filtered using FME.

2) USGS NED topographic DEM

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

complete 1/3 arc-second coverage of the Garibaldi region4. Data are in NAD 83 geographic coordinates and 

NGVD88 vertical datum (meters), and are available for download as 2 raster DEMs. 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 quadrangle maps and aerial photographs based on topographic surveys; it has been revised using data 

collected in 1999 and 2000. The NED DEMs included “zero” elevation values over the open ocean, which 

were removed from the dataset by clipping to the combined coastline.

4. 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 Georgia. 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 NAD 83, except for AK, which is NAD 27. The vertical datum is NAVD88, except for AK, which is NGVD29. 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]
Carignan et al., 2009

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3) OCS Electronic navigational chart data

An extracted land elevation point file from ENC #18520 was used to provide elevation values for major

off shore rock formations. As no topographic representation of Tillamook Rock was available, NGDC also 

digitized points with an elevation of 30 meters to augment the single ENC land elevation point on the rock. 

Adding the points resulted in a feature that more closely resembles the actual rock formation (Fig. 12).

Figure 12. The Tillamook Rock Lighthouse. Courtesy of TC3 Jason Wesley (http://www.uscg.mil/D13/units/gruastoria/

photo_gallery.htm).

The surface resulting from merging the NED DEMs and the CSC LiDAR, included a slight “berm” where the 

two datasets met. This effect is most likely due to the LiDAR data not being processed to bare earth. The substantial 

vegetation coverage in the areas directly inland from the coast resulted in LiDAR returns of generally higher elevation 

values than the NED DEM. In order to reduce this effect, the CSC LiDAR was filtered in FME to remove elevations

greater than 50 meters.
Digital Elevation Model of Garibaldi, Oregon

15

3.2 Establishing Common Datums

3.2.1 Vertical datum transformations

Datasets used in the compilation and evaluation of the Garibaldi DEM were originally referenced to a number of 

vertical datums including Mean Lower Low Water (MLLW), and North American Vertical Datum of 1988 (NAVD88). 

All datasets were transformed to MHW to provide the maximum flooding for inundation modeling. Units were

converted from feet to meters as appropriate.

1) Bathymetric data

The NOS hydrographic surveys and the USACE surveys were transformed from MLLW to MHW, using 

FME software, by adding a constant derived from the Garibaldi tide station (Table 6).

2) Topographic data

The USGS NED 1/3 arc-second DEMs, and the CSC LiDAR data were originally referenced to NAVD88. 

Conversion to MHW, using FME software, was accomplished by adding a constant offset of -2.102 meters 

(Table 6) derived from averaging the values from the two closest tide stations to the Garibaldi tide station 

referencing NAVD88, Depoe Bay #9435827 and Astoria, Tongue Point #9439040.

Table 6. Relationship between Mean High Water and other vertical datums in the Garibaldi region.

Vertical datum Difference to MHW

NAVD88 -2.102 meters

MLW -1.859 meters

MLLW -2.263 meters

* Datum relationships determined by values from tide station #9437540 at Garibaldi.

3.2.2 Horizontal datum transformations

Datasets used to compile the Garibaldi DEM were originally referenced to NAD 83, NAD 83 Oregon State 

Plane North, NAD 83 geographic, NAD 27 geographic, or WGS 84 geographic horizontal datums. The relationships 

and transformational equations between these horizontal datums are well established. All data were converted to a 

horizontal datum of NAD 83 geographic using FME software.
Carignan et al., 2009

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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 consistency between datasets. Problems and errors were identified and resolved before proceeding with

subsequent gridding steps. The evaluated and edited ESRI shape files were then converted to xyz files in preparation

for gridding. Problems included:

•	 Presence of extensive small streams and inland water bodies in the CSC historical coastline dataset, which 

had to be removed. The dataset also had piers, docks , and pilings that were deleted.

•	 Inconsistencies between the NED and CSC datasets. The cause of these inconsistencies could be the result of 

LiDAR data not being processed to bare earth.

•	 Data values over the ocean and rivers in the NED and CSC LiDAR data. Each dataset required automated 

clipping to the combined coastline.

•	 Digital, measured bathymetric values from NOS surveys date back over 100 years. More recent data, such 

as USACE surveys differed from older NOS data by as much as 10 meters. The older NOS survey data were 

excised where more recent bathymetric data exist.

3.3.2 Smoothing of bathymetric data

The NOS hydrographic survey data are generally sparse at the resolution of the 1/3 arc-second Garibaldi DEM: 

in both deep water and in some areas close to shore, the NOS survey data have point spacing up to 1900 m apart (Fig. 

13). In order to reduce the effect of artifacts in the form of lines of “pimples” in the DEM due to this low resolution 

data and to provide effective interpolation into the coastal zone, a 1 arc-second-spacing ‘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 hydrographic point data, in xyz format, were clipped to remove overlap with the topographic LiDAR 

data and USACE soundings then combined into a single xyz file, along with points extracted from the combined

coastline. Applying a -0.5 meter value to the coastline ensured that coastal bays and rivers would have negative 

elevation values in the final DEM.

Figure 13. Detail image of the bathy ‘pre-surface’ in the southwest corner of the DEM boundary. Ridges are present in the 

original data values in deep water NOS survey data, shown as closely spaced lines.
Digital Elevation Model of Garibaldi, Oregon

17

These point data were then median-averaged using the GMT tool ‘blockmedian’ to create a 1 arc-second grid 0.05 

degrees (~5%) larger than the Garibaldi DEM gridding region. The GMT tool ‘surface’ was applied to interpolate cells 

without data values. The GMT grid created by ‘surface’ was converted into an ESRI Arc ASCII grid file, and clipped

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

original soundings to ensure grid accuracy (e.g., Fig. 14), converted to a shape file, and then exported as an xyz file

for use in the final gridding process (see Table 7). Outliers occurred where soundings from older surveys were located

near offshore rock features digitally represented in more recent surveys. These older soundings were subsequently 

deleted.

Figure 14. Histogram of the difference between NOS hydrographic survey H04746 and the 1 arc-second pre-surfaced 

bathymetric grid.

3.3.3 Gridding the data with MB-System

MB-System (http://www.ldeo.columbia.edu/res/pi/MB-System/) was used to create the 1/3 arc-second Garibaldi 

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

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

tool ‘mbgrid’ applied a tight spline tension to the xyz data, and interpolated values for cells without data. The data 

hierarchy used in the ‘mbgrid’ gridding algorithm, as relative gridding weights, is listed in Table 7. Greatest weight 

was given to the CSC LiDAR, the ENC land elevations, and the NED topographic data. Least weight was given to 

the pre-surfaced 1 arc-second bathymetric grid. Gridding was performed in quarters with a single cell overlap. The 

resulting Arc ASCII grids were seamlessly merged in ArcCatalog to create the final 1/3 arc-second Garibaldi DEM.

Table 7. Data hierarchy used to assign gridding weight in MB-System.

Dataset Relative Gridding Weight

USACE bathymetry 100

CSC topographic LiDAR 1000

USGS NED topographic DEM 1000

NOS hydrographic surveys: bathymetric soundings 100

ENC land elevations 1000

Combined coastline 100

Pre-surfaced bathymetric grid 10
Carignan et al., 2009

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3.4 Quality Assessment of the DEM

3.4.1. Horizontal accuracy

The horizontal accuracy of topographic and bathymetric features in the Garibaldi DEM is dependent upon the 

datasets used to determine corresponding DEM cell values. Topographic features have an estimated accuracy of up 

to 10 meters: CSC LiDAR data have an accuracy of approximately 6 meters; NED topography is accurate to within 

about 10 meters. Bathymetric features are resolved only to within a few tens of meters in deep-water areas. Shallow, 

near-coastal regions, rivers, and harbor surveys have an accuracy approaching that of sub aerial topographic features. 

Positional accuracy is limited by: the sparseness of deep-water soundings; potentially large positional uncertainty 

of pre-satellite navigated (e.g., GPS) NOS hydrographic surveys; and by the morphologic change that occurs in this 

dynamic region.

3.4.2 Vertical accuracy

Vertical accuracy of elevation values for the Garibaldi DEM is also highly dependent upon the source datasets 

contributing to DEM cell values. Topographic areas have an estimated vertical accuracy between 0.1 to 0.3 meters 

for CSC LiDAR data and up to 7 meters for NED topography. Bathymetric areas have an estimated accuracy of 

between 0.1 meters and 5% of water depth. Those values were derived from the wide range of input data sounding 

measurements from the early 20th century to recent, GPS-navigated sonar surveys. Gridding interpolation to determine 

values between sparse, poorly-located NOS soundings degrades the vertical accuracy of elevations in deep water.
Digital Elevation Model of Garibaldi, Oregon

19

3.4.3 Slope maps and 3-D perspectives

ESRI ArcCatalog was used to generate a slope grid from the Garibaldi 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 

was accomplished using ESRI ArcScene. Analysis of preliminary grids revealed suspect data points, which were 

corrected before recompiling the DEM. Figure 16 shows a color image in perspective of the 1/3 arc-second Garibaldi 

DEM in its final version.

Figure 15. Slope map of the Garibaldi DEM. Flat-lying slopes are white; dark shading denotes steep slopes; 

combined coastline in red.
Carignan et al., 2009

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Figure 16. Perspective view from the southwest of the one third arc-second Garibaldi 

DEM. Combined coastline in black; vertical exaggeration–times 3.

3.4.4	 Comparison with source data files

To ensure grid accuracy, the Garibaldi 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 significantly overlap other data files with comparable weight). A histogram of the difference between a CSC

topographic LiDAR survey file and the Garibaldi 1/3 arc-second DEM is shown in Figure 17. Differences cluster just

below zero, with elevations, in heavily forested areas and near offshore rocks, exceeding 8 meters from the DEM.

Figure 17. Histogram of the difference between CSC LiDAR survey 007_005 and the Garibaldi DEM.
Digital Elevation Model of Garibaldi, Oregon

21

3.4.5 Comparison with NGS geodetic monuments

The elevations of 408 NOAA NGS geodetic monuments were extracted from online shape files of monument

datasheets (http://www.ngs.noaa.gov/cgi-bin/datasheet.prl), which give monument positions in NAD 83 (sub-mm 

accuracy) and elevations in NAVD88 (in meters). Elevations were shifted to MHW vertical datum (see Table 6) for 

comparison with the Garibaldi DEM (see Fig. 19 for monument locations). Differences between the Garibaldi DEM 

and the NGS geodetic monument elevations range from -88 to 216 meters (Fig. 18). Large negative differences occur 

where the NGS monument position varied from matching elevation in NED DEMs, generally at monuments located 

on offshore rock features. The largest positive difference occurs at an older monument last recorded in 1933. Prior to 

1977, a view point was constructed on the site.

Figure 18. Histogram of the differences between NGS geodetic monument elevations and the Garibaldi DEM. 

Figure 19. Location of NGS monuments and the NOAA tide station in the Garibaldi region. 

NGS monument elevations were used to evaluate the DEM.
Carignan et al., 2009

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4. Summary and Conclusions

A bathymetric–topographic digital elevation model of the Garibaldi, Oregon region, with cell spacing of 1/3 arcsecond, was developed for the Pacific Marine Environmental Laboratory (PMEL) NOAACenter for Tsunami Research.

The best available digital data from U.S. federal, state and local agencies, and academic institutions were obtained 

by NGDC, shifted to common horizontal and vertical datums, and evaluated and edited before DEM generation. The 

data were quality checked, processed and gridded using ESRI ArcGIS, FME, GMT, MB-System and Quick Terrain 

Modeler software. 

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

•	 Conduct bathymetric–topographic LiDAR surveys of the coastline between Seaside and Pacific City,

Oregon.

•	 Conduct hydrographic surveys near shore areas.

•	 Conduct topographic LiDAR surveys of entire region.

•	 Process CSC LiDAR data to bare earth.

5. Acknowledgments

The creation of the Garibaldi DEM was funded by the NOAA Pacific Marine Environmental Laboratory. The

authors thank Chris Chamberlin and Vasily Titov (PMEL), and Sheri Schneider (USGS, Portland, OR).

6. References

Nautical Chart #18520, 8th Edition, 2007. Yaquina Head to Columbia River; Netarts Bay. Scale 1:185,238. U.S. 

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

Nautical Chart #18556, 25th Edition, 2004. Nehalem River. Scale 1:20,000. U.S. Department of Commerce, NOAA, 

National Ocean Service, Coast Survey.

Nautical Chart #18558, 38th Edition, 2006.Tillamook Bay. Scale 1:50,000. U.S. Department of Commerce, NOAA, 

National Ocean Service, Coast Survey.

7. Data Processing and Visualization Software

ArcGIS v. 9.2, developed and licensed by ESRI, Redlands, California, http://www.esri.com/

FME 2007 GB – Feature Manipulation Engine, developed and licensed by Safe Software, Vancouver, BC, Canada, 

http://www.safe.com/

GEODAS v. 5 – Geophysical Data System, shareware developed and maintained by Dan Metzger, NOAA National 

Geophysical Data Center, http://www.ngdc.noaa.gov/mgg/geodas/

GMT v. 4.1.4 – 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. 5.1.0, 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/

Quick Terrain Modeler v. 6.0.1, LiDAR processing software developed by John Hopkins University’s Applied Physics 

Laboratory (APL) and maintained and licensed by Applied Imagery, http://www.appliedimagery.com/

NASA WorldWind 1.4, developed at NASA Ames Research Center, http://worldwind.arc.nasa.gov/index.html.