DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

noaa / NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

National Environmental Satellite,

Data, and Information Service

NOAA Technical Memorandum NESDIS NGDC-14

DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON:

PROCEDURES, DATA SOURCES AND ANALYSIS 

L.A.Taylor

B.W. Eakins

K.S. Carignan

R.R. Warnken

T. Sazonova

D.C. Schoolcraft

National Geophysical Data Center

Marine Geology and Geophysics Division

Boulder, Colorado

January 2008


DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

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-14

DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON:

PROCEDURES, DATA SOURCES AND ANALYSIS

Lisa A. Taylor1

Barry W. Eakins2

Kelly S. Carignan2

Robin R. Warnken1

Tatiana Sazonova2

David C. Schoolcraft1

1

NOAA, 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 LA PUSH, WASHINGTON

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..........................................................................................................12

3.1.4 Topography–Bathymetry.....................................................................................16

3.2 Establishing Common Datums .................................................................................................18

3.2.1 Vertical datum transformations ...........................................................................18

3.2.2 Horizontal datum transformations.......................................................................18

3.3 Digital Elevation Model Development .....................................................................................19

3.3.1 Verifying consistency between datasets..............................................................19

3.3.2 Smoothing of bathymetric data ...........................................................................19

3.3.3 Gridding the data with MB-System.....................................................................20

3.4 Quality Assessment of the DEM...............................................................................................21

3.4.1 Horizontal accuracy.............................................................................................21

3.4.2 Vertical accuracy .................................................................................................21

3.4.3 Slope maps and 3-D perspectives........................................................................22

3.4.4	 Comparison with source data files.......................................................................23

3.4.5 Comparison with NGS geodetic monuments......................................................24

4. Summary and Conclusions...............................................................................................................25

5. Acknowledgments............................................................................................................................25

6. References........................................................................................................................................25

7. Data Processing Software ................................................................................................................25

List of Figures

Figure 1. Shaded-relief image of the La Push, Washington DEM .............................................................1

Figure 2. Northern region of the Olympic Coast National Marine Sanctuary ...........................................2

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

Figure 4. Digital coastline datasets available in the La Push region..........................................................5

Figure 5. Aerial photo of La Push at Quillayute River entrance................................................................6

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

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

Figure 8. Digital USACE hydrographic survey coverage in the La Push region.....................................10

Figure 9. Spatial coverage of NOS shallow-water multibeam sonar survey H11083..............................11

Figure 10. Source and coverage of topographic datasets used to compile the La Push DEM...................12

Figure 11. Spatial coverage of CSC topographic LiDAR datasets used to compile the La Push 

DEM ..................................................................................................................................13

Figure 12. Aerial photo of breakwater at Neah Bay...................................................................................15

Figure 13. Spatial coverage of JALBTCX topographic–bathymetric LiDAR dataset used to 

compile the La Push DEM.................................................................................................17

Figure 14.	 Tidal flats at Cape Alava ...........................................................................................................19

Figure 15. Histogram of the differences between NOS hydrographic survey H09413 and the 

 1 arc-second pre-surfaced bathymetric grid ......................................................................20

Figure 16. Slope map of the La Push DEM ...............................................................................................22

Figure 17. Perspective view from the southwest of the La Push DEM......................................................23

Figure 18. Histogram of the differences between one PSLC survey and the La Push DEM.....................23

Figure 19. Histogram of the differences between NGS geodetic monument elevations and the La Push 

DEM ..................................................................................................................................24

Figure 20. Location of NGS geodetic monuments and the NOAA La Push tide station ...........................24
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Taylor et al.,2008

List of Tables

Table 1.	 PMEL specifications for the La Push, Washington DEM...........................................................3

Table 2. Shoreline datasets available in the La Push, Washington region................................................5

Table 3. Bathymetric datasets used in compiling the La Push DEM........................................................7

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

Table 5. Topographic datasets used in compiling the La Push DEM .....................................................12

Table 6. Topographic–bathymetric dataset used in compiling the La Push DEM..................................16

Table 7. Relationship between Mean High Water and other vertical datums in the La Push 

region .................................................................................................................................18

Table 8. Data hierarchy used to assign gridding weight in MB-System.................................................20


DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

Digital Elevation Model of La Push, Washington:

Procedures, Data Sources and Analysis

1. Introduction

In July 2007, the National Geophysical Data Center (NGDC), an office of the National Oceanic and Atmospheric

Administration (NOAA), developed a topographic–bathymetric digital elevation model (DEM) of La Push, Washington 

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

pmel.noaa.gov/). The 1/3 arc-second 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 La Push DEM. 

Figure 1. Shaded-relief image of the La Push, Washington DEM. Contour interval is 100 meters.

. The La Push 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 La Push, Washington (47°54.48′ N, 124°38.1′

W) 1/3 arc-second of latitude is equivalent to 10.295 meters; 1/3 arc-second of longitude equals 6.922 meters.


Taylor et al.,2008

2. Study Area

The La Push DEM covers the coastal region surrounding the town of La Push, Washington. Included within the 

DEM boundary are the Native American communities of the Makah, Quileute, and Ho tribes and the coastal town of 

Neah Bay to the north (Fig. 2). Nearly all the area covered by the DEM lies within the Olympic Coast National Marine 

Sanctuary boundary. The name La Push is derived from the Chinook translation of the French ‘la bouche’ meaning 

‘the mouth’, as the town is located at the mouth of the Quillayute River.

The near shore region is subject to sediment deposition and transport, making the sea floor relatively shallow for

upwards of 40 miles offshore. Farther from the coast, the shelf is cut by many submarine canyons that carry sediments 

to the deep ocean floor. Tectonic activity, such as earthquakes and volcanism, are relatively common in the region as

the Juan de Fuca oceanic plate subducts underneath the continental North American plate (http://olympiccoast.noaa.

gov/living/physical_environment/geo/welcome.html).

Figure 2. Northern region of the Olympic Coast National Marine Sanctuary (http://olympiccoast.

noaa.gov/visitor/vismap/welcome.html).
DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

3. Methodology

The La Push,Washington DEM was developed to meet PMELspecifications(Table 1), based on inputrequirements

for the MOST inundation model. The best available digital data were obtained by NGDC and shifted to common 

horizontal and vertical datums: World Geodetic System 1984 (WGS84) and Mean High Water (MHW), for modeling 

of “worst-case scenario” flooding, respectively. Data processing and evaluation, and DEM assembly and assessment

are described in the following subsections.

Table 1: PMEL specifications for the La Push, Washington DEM.

Grid Area La Push, Washington

Coverage Area 124.35o to 125.05o W; 47.55o to 48.45o N

Coordinate System Geographic decimal degrees

Horizontal Datum World Geodetic System 1984 (WGS84)

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, topographic, and topographic–bathymetric digital datasets (Fig. 3) were obtained from 

several U.S.federal,state and local agenciesincluding: NOAA’s National Ocean Service (NOS), Office ofCoast Survey

(OCS) and Coastal Services Center (CSC); the Joint Airborne LiDAR Bathymetry Technical Center of Expertise 

(JALBTCX); the U.S. Geological Survey (USGS); the Puget Sound LiDAR Consortium (PSLC); the U.S. Army 

Corps of Engineers (USACE); and the Washington State Department of Transportation (WSDOT). Safe Software’s 

(http://www.safe.com/) FME data translation tool package was used to shift datasets to WGS84 horizontal datum 

and to convert them into ESRI (http://www.esri.com/) ArcGIS shape files. 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 NOAA La Push, Quillayute River tide station. 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.
Taylor et al.,2008

Figure 3. Source and coverage of datasets used to compile the La Push DEM.
DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

3.1.1 Shoreline

Coastline datasets of the La Push region were obtained from the Washington State Department of Transportation 

(WSDOT) and NOAA’s Office of Coast Survey electronic navigational charts (ENCs; Table 2; Fig. 4).

Table 2: Shoreline datasets available in the La Push, Washington region.

Source Year Data Type Spatial 

Resolution

Original Horizontal 

Datum/Coordinate System

Original Vertical 

Datum URL

OCS ENC 2006-

2007 Coastline 1:40,000 to 1:176,253 WGS84 geographic Mean High Water http://nauticalcharts.noaa.gov/mcd/enc/index.htm

Washington 

State Dept. of 

Transportation

1995 Digitized 

hydrography 1:100,000 NAD83 geographic

http://www.wsdot.

wa.gov/mapsdata/

GeoDataCatalog/default.

htm#georef

Washington 

State Dept. of 

Transportation

1996 Digitized 

hydrography 1:24,000 NAD83 geographic

http://www.wsdot.

wa.gov/mapsdata/

GeoDataCatalog/default.

htm#georef

Figure 4. Digital coastline datasets available in the La Push region. DEM boundary shown in brown.
Taylor et al.,2008

1) OCS electronic navigational chart

Three electronic navigational charts (ENCs) were available for the La Push area (#18460, 18480, and 

18485) and were downloaded from NOAA’s Office of Coast Survey website (http://nauticalcharts.noaa.gov/

mcd/enc/index.htm). The ENCs are available in S-57 format and include coastline data files at Mean High

Water. ENCs #18460 and 18480 were at a scale significantly smaller than the 1:24,000 WSDOT dataset. ENC

#18485, at 1:40,000 scale, provided limited coverage in the Makah Bay region and did not reflect the NED

topographic dataset as accurately as the WSDOT 1:24,000 dataset. Other nautical charts were available as 

georeferenced raster nautical charts (RNCs; digital images of the charts) and were used to QC bathymetric 

and topographic datasets.

2) Washington State Department of Transportation 1:100,000

The Washington State Department of Transportation (http://www.wsdot.wa.gov/) has developed 

a hydrography dataset for entire state of Washington. The dataset is derived from 1:100,000 scale USGS 

topographic maps, though, while offering complete coverage of the DEM area, did not provide as much 

resolution as the 1:24,000 scale WSDOT coastline.

3) Washington State Department of Transportation 1:24,000

The Washington State Department of Transportation has also developed a more detailed hydrography 

dataset from 7.5 minute USGS topographic quads (1:24,000 scale). This dataset is divided by county and 

available from the WSDOT web site. Clallam and Jefferson County hydrography data, which fully cover the 

La Push region, were downloaded and edited in ArcMap to remove inland water bodies and rivers.

The WSDOT 1:24,000 scale coastlines of Jefferson and Clallam counties were merged to create a ‘combined 

coastline’ of the La Push area. River inlets were included in the ‘combined coastline’ where digital bathymetric 

data was present. Modifications to the coastline include adjustments to fit most recent topographic and topographic–

bathymetric data. In addition, the breakwater at Neah Bay and the jetties to the north and south of the Quillayute 

River entrance at La Push (Fig. 4) were added as they were not represented in the 1:24,000 WSDOT coastlines. All 

modifications were done using ArcMap editing tools.

Figure 5. Aerial photo of La Push at Quillayute River entrance 

(http://apps.ecy.wa.gov/shorephotos/index.html).
DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

3.1.2 Bathymetry

Bathymetric datasets used in the compilation of the La Push DEM include 26 NOS hydrographic surveys, two 

USACE surveys located at the La Push and Neah Bay harbors, and an NOS shallow-water multibeam sonar survey 

that covers Makah Bay (Table 3; Fig. 6).

Table 3: Bathymetric datasets used in compiling the La Push DEM.

Source Year Data Type Spatial Resolution

Original Horizontal 

Datum/Coordinate 

System

Original 

Vertical Datum URL

 NOS 

1891

to 

2001

Hydrographic 

survey 

soundings

Ranges from 10 m to 1

km (varies with scale 

of survey, depth, traffic,

and probability of 

obstructions)

NAD27 or NAD83 

geographic

Mean Low 

Water or Mean 

Lower Low 

Water

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

mgg/bathymetry/hydro.html

USACE 2006 Hydrographic 

survey profiles

Profiles 50 to 200

meters long, spaced 50 

meters apart, with point 

spacing < 1 meter 

NAD83 Washington 

State Plane North

Mean Lower 

Low Water

NOS 2003

Shallow water 

multibeam 

sonar

10 meters NAD83 geographic Mean Lower 

Low Water

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

mgg/bathymetry/hydro.html

Figure 6. Spatial coverage of bathymetric datasets used to compile the La Push DEM.
Taylor et al.,2008

1) NOS hydrographic survey data

A total of 26 NOS hydrographic surveys conducted between 1893 and 2001 were utilized in developing 

the La Push DEM (Table 4; Fig. 7). The hydrographic survey data were originally vertically referenced to 

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

or NAD83 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 WGS84 

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 La Push 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 topographic, bathymetric, and topographic–bathymetric 

datasets, the combined coastline, and NOS raster nautical charts (RNCs). The surveys were clipped to remove 

soundings that overlap the more recent USACE survey at Neah Bay, and where soundings from older surveys 

have been superseded by more recent NOS surveys. Five additional NOS surveys were located within the 

DEM boundary but were not used due to inconsistencies with more recent, overlapping data.

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

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

H02170 1893 80,000 mean low water undetermined

H02869 1907 50,000 mean lower low water undetermined

H04735 1927 80,000 mean lower low water NAD27

H05068 1930 40,000 mean lower low water NAD27

H05069 1930 20,000 mean lower low water NAD27

H05070 1930 20,000 mean lower low water NAD27

H05107 1930 20,000 mean lower low water NAD27

H05108 1930 20,000 mean lower low water NAD27

H05109 1930 20,000 mean lower low water NAD27

H05110 1930 40,000 mean lower low water NAD27

H05111 1930/42 40,000/20,000 mean lower low water NAD27

H05114 1930 120,000 mean lower low water NAD27

H05146 1931 20,000 mean lower low water NAD27

H05148 1931 40,000 mean lower low water NAD27

H05155 1931 20,000 mean lower low water NAD27

H05156 1931 20,000 mean lower low water NAD27

H05157 1931 40,000 mean lower low water NAD27

H07036 1945 5,000 mean lower low water NAD27

H07037 1945 10,000 mean lower low water NAD27

H08241 1955 5,000 mean lower low water NAD27

H08242 1955 10,000 mean lower low water NAD27

H09413 1974 80,000 mean lower low water NAD27

H09415 1974 40,000 mean lower low water NAD27

H09416 1974 40,000 mean lower low water NAD27

H09418 1974 80,000 mean lower low water NAD27

H11086 2001 5,000 mean lower low water NAD83
DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

Figure 7. Digital NOS hydrographic survey coverage in the La Push region. Some older surveys were not utilized as they 

have been superseded by more recent surveys. DEM boundary in red.
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Taylor et al.,2008

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

The USACE, La Push District provided NGDC with two recent bathymetric surveys located in Neah 

Bay and in the Quillayute River entrance at the La Push harbor (Fig. 8). The surveys were collected in 2006, 

and referenced to NAD83 Washington State Plane North and Mean Lower Low Water (MLLW) datums. 

The files were converted to WGS84 and MHW using FME. Point spacing averages less than 1 meter along

profiles 50 to 200 meters long and averaging 50 meters apart.

Figure 8. Digital USACE hydrographic survey coverage in the La Push region. Surveys shown in red, with RNCs as 

background. (A). Quillayute River entrance survey. (B). Neah Bay survey.
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DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

3) NOS shallow water multibeam survey

NOAA’s NOS conducted a shallow water multibeam sonar survey in Makah Bay and to the north around 

Cape Flattery (Fig. 9). The survey was downloaded from the NGDC hydrographic survey website (http://

www.ngdc.noaa.gov/mgg/bathymetry/hydro.html) in ASCII xyz gridded format in NAD83 geographic at 

10-meter resolution and referenced to MLLW. This dataset provided dense bathymetric coverage in the area, 

particularly around the small islands and rocks off Cape Flattery.

Figure 9. Coverage of NOS shallow-water multibeam sonar survey H11083. The high resolution multibeam 

survey covers the near-shore region of Makah Bay and around Cape Flattery.
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Taylor et al.,2008

3.1.3 Topography

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

Puget Sound LiDAR Consortium (PSLC), and the U.S. Geological Survey (USGS; Table 5; Fig. 10). NGDC digitized 

the breakwater as Neah Bay as it was not represented in any dataset.

Table 5: Topographic datasets used in compiling the La Push DEM.

Source Year Data Type Spatial 

Resolution

Original Horizontal 

Datum/Coordinate System

Original 

Vertical Datum URL

CSC 2002 Coastal LiDAR ~6 meters NAD83 geographic NAVD88 

(meters)

http://maps.csc.noaa.

gov/TCM/

PSLC 2005 LiDAR ~2 meters

NAD83 Washington State 

Plane North (feet) NAVD88 (feet) http://pugetsoundlidar.ess.washington.edu/

PSLC 2001 Bare-earth 

DEMs ~2 meters

NAD83 Washington State 

Plane North (feet) NAVD88 (feet) http://pugetsoundlidar.

ess.washington.edu/

USGS 1999-

2000 NED DEM 1/3 arcsecond NAD83 geographic NAVD88(meters) http://ned.usgs.gov/

NGDC 2007 Digitized 

breakwater < 10 meters WGS84 geographic MHW 

Figure 10. Source and coverage of topographic datasets used to compile the La Push DEM.
13

DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

1) Coastal Services Center topographic LiDAR

NOAA’s Coastal Services Center provided NGDC with topographic LiDAR datasets in NAD83 

geographic horizontal datum and NAVD88 vertical datum for the coastal area south of La Push (Fig. 11). 

These data have point spacing approximately 6 meters apart and extend 50 to 525 meters inland from the 

coastline. These data were not processed to bare earth and at higher elevations were inconsistent with the 

NED bare-earth DEMs. The LiDAR data were therefore filtered using FME to remove points with elevations

greater than 10 meters. This process removed suspect returns from heavily forested near-shore areas while 

retaining high-resolution beach elevations.

Figure 11. Spatial coverage of CSC topographic LiDAR datasets used to compile the La Push DEM.
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Taylor et al.,2008

2) Puget Sound topographic LiDAR data

The Puget Sound LiDAR Consortium (PSLC) provided NGDC with a topographic LiDAR dataset for 

northern coastal Clallam County (Fig. 10). The LiDAR data had been processed to bare earth and supplied in 

tiles covering approximately 1 km2 each. Data were in NAD83 State Plane Washington North and NAVD88 

(feet).

The LiDAR data files contained position and elevation values for both land and water areas. FME was

used in initial processing to remove elevation values less than zero. The LiDAR files were then evaluated and

edited using QT Modeler to remove points remaining over water.

3) Puget Sound topographic LiDAR DEMs

PSLC also provided NGDC with bare-earth topographic LiDAR DEMs of southwestern Clallam County 

(Fig. 10). Each DEM covers 5 km2 with a grid cell spacing of ~2 meters. DEMs were in NAD83 State Plane 

Washington North and NAVD88 (feet). Elevations in open-water areas reflect gridding interpolation from

nearby shoreline values and were removed by clipping to the combined coastline.

4) USGS NED topographic DEM

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

complete 1/3 arc-second coverage of the La Push region

. Data are in NAD83 geographic coordinates and 

NAVD88 vertical datum (meters), and are available for download as raster DEMs. The 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 DEM included “zero” elevation values over the open ocean, which 

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

. 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 NAD83, except for AK, which is NAD27. 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]
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DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

5) NGDC Neah Bay breakwater

As no topographic representation of the breakwater at Neah Bay was available, NGDC digitized this 

feature as a line segment with an elevation of 1 meter (Fig. 12). The line segment was then converted to points 

at less than 10 meter intervals to ensure representation of the breakwater in the La Push DEM.

Figure 12. Aerial photo of breakwater at Neah Bay (http://apps.ecy.wa.gov/shorephotos/index.html).

The NED DEM and both PSLC LiDAR datasets, all processed to bare earth, did not match up in elevation. One 

possible cause is LiDAR returns from forest canopy not being fully eliminated in PSLC bare-earth processing. The 

effect is a ‘step’ of up to 30 meters in the terrain surface when gridded at 1 arc-second for quality control. As a result 

of the elevation discrepancy between datasets, only two of the fourteen PSLC DEMs were used in developing the La 

Push DEM: those closest to the town of La Push. NED data at La Push were not as consistent as the PSLC DEMs, 

which were closer to matching the USACE hydrographic survey data and contained more accurate elevation values 

along both the north and south jetties and the entrance to the La Push harbor. To reduce the differences in elevation 

between the NED and PSLC data, a 75-meter buffer or data gap was created in the NED DEM by outlining the PSLC 

data. Gridding interpolation across the gap, when building the final La Push DEM, produced a more gradual “slope”

rather than an artificial “step”.
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Taylor et al.,2008

3.1.4 Topography–Bathymetry

One topographic–bathymetric dataset was available from the Joint Airborne LiDAR Bathymetry Technical Center 

of Expertise (JALBTCX), covering the northern portion of the La Push DEM from Cape Alava to Neah Bay (Fig. 13, 

Table 6).

Table 6: Topographic–bathymetric dataset used in compiling the La Push DEM.

Source Year Data Type Spatial 

Resolution

Original Horizontal 

Datum/Coordinate System

Original 

Vertical Datum

JALBTCX 

LiDAR 2005 Coastal LiDAR < 5 meters WGS84 UTM Zone 10 MLLW (meters)

1) JALBTCX topographic–bathymetric LiDAR

The JALTBCX LiDAR dataset provided topographic–bathymetric coverage for the coastal and near 

shore regions north of La Push. These data were obtained in WGS84 UTM Zone 10 horizontal datum and 

MLLW. FME was used to re-project the xyz data to WGS84 geographic and to MHW. Point spacing varied 

from less than 5 meters with full coverage at the shoreline to more sparse farther from shore, where ‘clumps’ 

of data surrounded rocks and kelp.

As with the CSC topographic LiDAR datasets, a discontinuity between the NED DEM and the JALBTCX 

dataset created an artificial ‘berm’ along the coastline in preliminary grids. This effect is interpreted to have

resulted from the JALBTCX LiDAR data having not been processed to bare earth and higher elevations 

therefore reflect returns from tree tops rather than land surface. In order to minimize this effect, elevation

values greater than 10 meters were removed from the JALBTCX dataset using ArcMap. This elevation 

filtering was not done off shore so as to retain elevations located on rocks and islets not present in the NED

DEM.
17

DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

Figure 13. Spatial coverage of JALBTCX topographic–bathymetric LiDAR 

dataset used to compile the La Push DEM.
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Taylor et al.,2008

3.2 Establishing Common Datums

3.2.1 Vertical datum transformations

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

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

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

modeling. Units were converted from feet to meters as appropriate.

1) Bathymetric data

The NOS hydrographic surveys, the USACE surveys, and the NOS multibeam sonar survey were 

transformed from MLLW and MLW to MHW, using FME software, by adding a constant derived from La 

Push Pier tide station #9442396 (Table 7).

2) Topographic data

The USGS NED 1/3 arc-second DEM, the PSLC LiDAR datasets, and the CSC coastal LiDAR data 

were originally referenced to NAVD88. As the La Push Pier tide station did not reference vertical datum 

NAVD88, conversion to MHW, using FME software, was accomplished by adding a constant offset of -1.882

meters (Table 7). This constant was derived by calculating the difference between MHW and NAVD88 at 

both Neah Bay and Sekiu tide stations and averaging the values.

3) Topographic–Bathymetric data

The JALBTCX topographic–bathymetric LiDAR data were transformed from MLLW to MHW by 

adding a constant offset of -2.43 meters using FME.

Table 7. Relationship between Mean High Water and other vertical datums in the La Push region.

Vertical datum Difference to MHW

NAVD88* -1.882 meters

MLW -2.002 meters

MLLW -2.43 meters

* Datum relationship determined by values from tide station #9443090 Neah Bay and #9443361 Sekiu.

3.2.2 Horizontal datum transformations

Datasets used to compile the La Push DEM were originally referenced to WGS84 UTM Zone 10, NAD83 

Washington State Plane North, NAD83 geographic, or NAD27 geographic horizontal datums. The relationships 

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

horizontal datum of WGS84 geographic using FME software.
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DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

3.3 Digital Elevation Model Development

3.3.1 Verifying consistency between datasets

After horizontal and vertical transformations were applied, the resulting ESRIshape files were checked inArcMap

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 WSDOT 1:24,000 hydrography dataset, 

which had to be removed.

•	 Inconsistencies between the NED, CSC, PSLC and JALBTCX topographic data. These inconsistencies could 

result from forest canopy returns in the datasets. The La Push region, located on the Olympic Peninsula in 

Washington State, has large areas of dense forest canopy inland and stretching close to the shoreline. Coastal 

LiDAR data were clipped to remove higher elevations from suspected forest canopy.

•	 Data values over the ocean and rivers in the NED and PSLC LiDAR topographic 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 the USACE hydrographic surveys differed from older NOS data by as much as 10 meters. The older NOS 

survey data were excised where more recent bathymetric data exists.

3.3.2 Smoothing of bathymetric data

The NOS hydrographic surveys are generally sparse at the resolution of the 1/3 arc-second La Push DEM: in 

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

order to reduce the effect of artifacts in the form of lines of “pimples” in the DEM due to this low resolution dataset, 

and to provide effective interpolation into the coastal zone, a 1 arc-second-spacing ‘pre-surface’ bathymetric 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 JALBTCX topographic–

bathymetric LiDAR data, then combined with the USACE soundings and the NOS multibeam data into a single file,

along with points extracted from the combined coastline—to provide a buffer along the entire coastline. In the Cape 

Alava region, NOS survey H05146 soundings were not clipped to the topographic–bathymetric LiDAR data in order 

to more accurately reflect the depths on the tidal flats and in areas with heavy kelp (Fig. 14).

Figure 14. Tidal flats at Cape Alava. (A) Kelp and other features fouling the coastal zone as shown on nautical chart 

#18485. Pink shaded area represents JALBTCX topographic–bathymetric LiDAR data, with NOS survey H05146 

represented by blue dots. (B) Aerial photo of Cape Alava (http://apps.ecy.wa.gov/shorephotos/index.html).
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The point data were median-averaged using the GMT tool ‘blockmedian’ to create a 1 arc-second grid 0.05 

degrees (~5%) larger than the La Push DEM gridding region. The GMT tool ‘surface’ was then used to apply a tight 

spline tension to interpolate elevations for 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. 15), converted 

to a shape file, and then exported as an xyz file for use in the final gridding process (see Table 8).

Figure 15. Histogram of the differences between NOS hydrographic survey H09413 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 La Push 

DEM. 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 apply a tight spline tension to the xyz data, and interpolate values for cells without data. The 

data hierarchy used in the ‘mbgrid’ gridding algorithm, as relative gridding weights, is listed in Table 8. Greatest weight 

was given to the PSLC bare-earth LiDAR data. Least weight was given to the pre-surfaced 1 arc-second bathymetric 

grid. Gridding was performed in northern and southern halves. The resulting Arc ASCII grids were seamlessly merged 

in ArcCatalog to create the final 1/3 arc-second La Push DEM.

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

Dataset Relative Gridding Weight

JALBTCX topographic–bathymetric coastal LiDAR 100

NOS shallow-water multibeam sonar survey 100

USACE bathymetry 100

CSC topographic coastal LiDAR 100

PSLC topographic bare-earth LiDAR 1000

USGS NED topographic DEM 10

NOS hydrographic surveys: bathymetric soundings 10

NGDC breakwater 100

Combined coastline 10

Pre-surfaced bathymetric grid 1
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DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

3.4 Quality Assessment of the DEM

3.4.1. Horizontal accuracy

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

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

10 meters: PSLC, CSC and JALBTCX topographic 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 

subaerial 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 La Push 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 PSLC, JALBTCX and 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.
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3.4.3 Slope maps and 3-D perspectives

ESRI ArcCatalog was used to generate a slope grid from the La Push DEM to allow for visual inspection and 

identification of artificial slopes along boundaries between datasets (e.g., Fig. 16). 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 (e.g., Fig. 17). Analysis of preliminary grids revealed suspect data points, 

which were corrected before recompiling the DEM. Figure 1 shows a color image of the 1/3 arc-second La Push DEM 

in its final version.

Figure 16. Slope map of the La Push DEM. Flat-lying slopes are white; dark shading denotes steep 

slopes; combined coastline in red.
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DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

Figure 17. Perspective view from the southwest of the La Push DEM. Combined 

coastline in red; vertical exaggeration–times 5.

3.4.4	 Comparison with source data files

To ensure grid accuracy, the La Push 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 differences between a PSLC

topographic LiDAR survey file and the La Push DEM is shown in Figure 18. Differences cluster around zero, with

only a handful of soundings, in regions of steep topography, exceeding 1.5-meter discrepancy from the DEM.

Figure 18. Histogram of the differences between one PSLC LiDAR survey and the La Push DEM.
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Taylor et al.,2008

3.4.5 Comparison with NGS geodetic monuments

The elevations of 260 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 NAD83 (typically 

sub-mm accuracy) and elevations in NAVD88 (in meters). Elevations were shifted to MHW vertical datum (see Table 

7) for comparison with the La Push DEM (see Fig. 20 for monument locations). Differences between the La Push 

DEM and the NGS geodetic monument elevations range from -61 to 58 meters, with the majority of them being within 

+ 12 meters range. Negative values indicate that the monument elevation is less than the DEM (Fig. 19). Only 15 

monuments out of 260 total showed significant deviations from the DEM. Such discrepancies are caused by the rough

terrain in La Push area, where significant changes in local relief could happen on the scale of less then 10 meters.

Figure 19. Histogram of the differences between NGS geodetic monument elevations and the La Push DEM. 

Figure 20. Location of NGS geodetic monuments and the NOAA La Push tide station. 

NGS monument elevations were used to evaluate the DEM.
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DIGITAL ELEVATION MODEL OF LA PUSH, WASHINGTON

4. Summary and Conclusions

A topographic–bathymetric digital elevation model of the La Push, Washington region, with cell spacing of 1/3 

arc-second, was developed for the Pacific Marine Environmental Laboratory (PMEL) NOAA Center for Tsunami

Research. The best available digital data from U.S. federal, state and local agencies 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 La Push DEM, based on NGDC’s research and analysis, are listed below:

•	 Conduct topographic–bathymetric LiDAR surveys for coastline between La Push and Cape Alava.

•	 Conduct hydrographic surveys for near-shore areas.

•	 Complete topographic LiDAR surveying of entire region.

•	 Process CSC and JALBTCX coastal LiDAR data to bare earth.

5. Acknowledgments

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

authors thank Chris Chamberlin and Vasily Titov (PMEL), Lonnie Reid-Pell (USACE, Seattle District), and Diana 

Martinez (Puget Sound Regional Council).

6. References

Nautical Chart #18460, 13th Edition, 2006. Strait of Juan de Fuca Entrance. Scale 1:100,000. U.S. Department of 

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #18480, 31st Edition, 2006. Approaches to Strait of Juan de Fuca. Scale 1:176,253. U.S. Department 

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

Nautical Chart #18484, 12th Edition, 2006. Neah Bay. Scale 1:10,000. U.S. Department of Commerce, NOAA, 

National Ocean Service, Coast Survey.

Nautical Chart #18485, 16th Edition, 2007. Cape Flattery. Scale 1:40,000. U.S. Department of Commerce, NOAA, 

National Ocean Service, Coast Survey.

Haugerud, R.A., 1999, Digital elevation model (DEM) of Cascadia, latitude 39N-53N, longitude 116W-133W, U.S. 

Geological Survey Open-file Report 99-369, http://geopubs.wr.usgs.gov/open-file/of99-369/

Intelmann, Steven S., Jonathan Beaudoin and Guy R. Cochrane, 2006, Normalization and Characterization of 

Multibeam Backscatter: Koitlah Point to Point of the Arches, Olympic Coast National Marine Sanctuary - Survey 

HMPR-115-2004-03, (http://olympiccoast.noaa.gov/research/mapping/hmpr_115_2004_03/cruisereport_files/

hmpr-115-2004-03_report.pdf)

7. Data Processing Software

ArcGIS v. 9.2, 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/

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/
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Taylor et al.,2008

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/