Digital Elevation Model of Taholah, Washington:

Procedures, Data Sources and Analysis

Prepared for the Pacific Marine Environmental Laboratory (PMEL) NOAA Center for Tsunami 

Research by the NOAA National Geophysical Data Center (NGDC)

July 24, 2009

Medley, P.R., Taylor, L.A., B.W. Eakins, K.S. Carignan, R.R. Warnken, and E.D. Lim

NOAA, National Geophysical Data Center, Boulder, Colorado

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/
Digital Elevation Model of Taholah, Washington

i

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 ............................................................................................................8

3.1.3 Topography..........................................................................................................13

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

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

3.2.2 Horizontal datum transformations.......................................................................16

3.3 Digital Elevation Model Development .....................................................................................17

3.3.1 Verifying consistency between datasets..............................................................17

3.3.2 Smoothing of bathymetric data ...........................................................................17

3.3.3 Gridding the data with MB-System.....................................................................18

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........................................................................20

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

3.4.5 Comparison with NGS geodetic monuments......................................................22

4. Summary and Conclusions...............................................................................................................23

5. Acknowledgments............................................................................................................................23

6. References........................................................................................................................................23

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

List of Figures

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

Figure 2. Aerial photographs of the Washington coast ..............................................................................2

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

Figure 4. Digital coastline datasets used in developing a combined coastline of the Taholah, 

Washington region ...............................................................................................................5

Figure 5. Comparison between the La Push DEM coastline and the Taholah DEM 

‘combined coastline’............................................................................................................6

Figure 6. The 2002 CSC ALACE LiDAR data overlying a Google Earth satellite image of the 

Quinault River .....................................................................................................................7

Figure 7. Spatial coverage of bathymetric datasets used in compiling the Taholah DEM.........................8

Figure 8. Digital NOS hydrographic survey coverage in the Taholah region..........................................10

Figure 9. Spatial coverage of multibeam swath sonar surveys from the NGDC multibeam 

 bathymetry database..........................................................................................................11

Figure 10. Errors along the edge of a multibeam swath sonar survey .......................................................11

Figure 11. Color image of USGS multibeam swath sonar survey mb99 ...................................................12

Figure 12. Spatial coverage of topographic datasets used in building the Taholah DEM..........................13

Figure 13. Color image of a preliminary Taholah DEM and the surrounding coastline 

 before processing the LiDAR to bareearth ........................................................................15

Figure 14. Color image of the transition from the LiDAR to the NED data in the Taholah DEM ............15

Figure 15. Histogram of the differences between NOS hydrographic survey H08416 and 

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

Figure 16. Slope map of the Taholah DEM................................................................................................20

Figure 17. Perspective view from the southwest of the Taholah DEM......................................................21

Figure 18. Histogram of the differences between a section of the CSC ALACE LiDAR survey 

and the Taholah DEM........................................................................................................21
Medley et. al, 2009

ii

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

Taholah DEM..................................................................................................................................................22

Figure 20. Location of NGS geodetic monuments used to assess the Taholah DEM................................22

List of Tables

Table 1. PMEL specifications for the Taholah, Washington DEM...........................................................3

Table 2. Shoreline datasets used in developing the Taholah DEM...........................................................5

Table 3. Electronic Navigation Charts available in the Taholah, Washington region...............................6

Table 4. Bathymetric datasets used in compiling the Taholah DEM........................................................8

Table 5. Digital NOS hydrographic surveys used in compiling the Taholah DEM..................................9

Table 6. Multibeam swath sonar surveys used in compiling the Taholah DEM.....................................10

Table 7. Topographic datasets used in compiling the Taholah DEM......................................................13

Table 8. Data hierarchy used to assign gridding weight in MB-System.................................................18
Digital Elevation Model of Taholah, Washington:

Procedures, Data Sources and Analysis

1. Introduction

The National Geophysical Data Center (NGDC), an office of the National Oceanic and Atmospheric Administration 

(NOAA), has developed an integrated bathymetric–topographic digital elevation model (DEM) of Taholah, Washington, 

(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) 

developed by PMEL for the NOAA Tsunami Warning Centers. This report provides a summary of the data sources and 

methodology used in developing the Taholah DEM.

Figure 1. Shaded-relief image of the Taholah, Washington DEM. Contour interval is 200 meters for bathymetry and 100 meters for topography.

1. The Taholah 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 Taholah, Washington, (47°20.44′ N, 124°17.15′

W) 1/3 arc-second of latitude is equivalent to 11.12 meters; 1/3 arc-second of longitude equals 7.56 meters.
Medley et. al, 2009

2

2. Study Area

The Taholah DEM covers the southern to central coastline of Washington from Grays Harbor to Kalaloch (Fig. 1). 

It overlaps the southern region of NGDC’s La Push DEM (http://www.ngdc.noaa.gov/dem/showdem.jsp?dem=La%20

Push&state=WA&cell=1/3%20arc-second) and the northern region of NGDC’s Astoria DEM (http://www.ngdc.

noaa.gov/dem/showdem.jsp?dem=Astoria&state=OR&cell=1/3%20arc-second) by approximately 11 km, providing 

complete coverage of the Pacific coastline of Washington. Taholah, population of approximately 900, is located at the 

mouth of the Quinault River (Fig. 1).

The Washington coastline is unstable and continually eroding from wave action because of exposed softer 

sedimentary rocks. There are three main rock formations in the Taholah region: the Hoh rock assemblage of more 

resistant sandstone and conglomerate, the Quinault Formation of softer sandstones rich in marine fossils and sedimentary 

structures, and the Late Cenozoic deposits of semi-consolidated silt, sand, and gravel. The soft rocks are easily eroded, 

creating landslide hazards. Evidence of this can be seen south of Taholah where extensive slumped cliffs exist (Fig 

2A). North of Taholah, erosion-resistant rocks can be seen in the rocky headlands (Fig 2B). A unique feature in the 

Taholah region is a large gas mound, called the Garfield Gas Mound, found approximately a quarter mile inland from 

the mouth of the Quinault River. Natural gas seeps out of a mud-filled vent from the mound that is several hundred 

feet in diameter and about 50 feet above the surrounding terrain. The gas is derived from the Hoh rock formation, 

and has been tested for petroleum though none was found (http://www.nps.gov/history/history/online_books/geology/

publications/state/wa/1980-72/preface.htm).

Figure 2. Aerial photographs of the Washington coast; A) slump due to erosion just south of Taholah; B) rocky headland of erosion-resistant rock 

just north of Taholah. (http://apps.ecy.wa.gov/shorephotos/index.html)

A

B
Digital Elevation Model of Taholah, Washington

3

3. Methodology

The Taholah, Washington 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 19832 (NAD 83) and Mean High Water (MHW), respectively, 

for modeling of maximum flooding. Data processing and evaluation, and DEM assembly and assessment are described 

in the following subsections.

Table 1: PMEL specifications for the Taholah, Washington DEM.

Grid Area Taholah, Washington

Coverage Area 123.70o to 125.30o W; 46.99o to 47.65o N

Coordinate System Geographic decimal degrees

Horizontal Datum World Geodetic System 1984 (WGS 84)

Vertical Datum Mean High Water (MHW)

Vertical Units Meters

Cell Size 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 and 

state 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 Washington State Department of Transportation 

(WASDOT). Safe Software’s (http://www.safe.com/) FME3 data translation tool package was used to shift datasets to 

NAD 83 horizontal datum and to convert them into ESRI (http://www.esri.com/) ArcGIS shapefiles. The shapefiles 

were then displayed with ArcGIS to assess data quality and manually edit datasets. Vertical datum transformations 

to MHW were accomplished using FME and ArcGIS, based upon data from NOAA tide stations (see Section 3.2.1). 

Applied Imagery’s Quick Terrain Modeler software (http://www.appliedimagery.com/) was used for evaluating some 

datasets before the final gridding process.

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.
Medley et. al, 2009

4

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

5

3.1.1 Shoreline

Coastline datasets of the Taholah region were obtained from NOAA’s Office of Coast Survey as Electronic 

Navigational Charts (ENCs), and NGDC’s La Push, Washington (Taylor et al., 2008) and Astoria, Oregon (Carignan 

et al., 2009) DEMs (Table 2; Fig. 4). NGDC evaluated but did not use the Washington Department of Transportation 

(WASDOT; http://www.wsdot.wa.gov/) coastline, as the NGDC and ENC coastlines matched the bathymetric datasets 

more closely. 

Table 2: Shoreline datasets used in developing the Taholah DEM. 

Source Year Data Type Spatial Resolution

Original Horizontal 

Datum/Coordinate 

System

Original Vertical 

Coordinate System URL

OCS ENC 

extracted 

shoreline

2004 vector 1:180,789 WGS 84 geographic Mean High Water

http://www.

nauticalcharts.noaa.

gov/

NGDC Astoria 

DEM coastline 2008 vector WGS 84 geographic Mean High Water http://www.ngdc.noaa.

gov/dem/selectdem.jsp

NGDC La Push 

DEM coastline 2007 vector WGS 84 geographic Mean High Water http://www.ngdc.noaa.

gov/dem/selectdem.jsp

Figure 4. Digital coastline datasets used in developing a combined coastline of the Taholah, Washington region.
Medley et. al, 2009

6

1) OCS Electronic Navigational Chart Coastline

 Two electronic navigational charts (ENCs) were available for the Taholah area (Table 3) and downloaded 

from the NOAA’s Office of Coast Survey web site (http://chartmaker.ncd.noaa.gov/MCD/enc/index.htm). 

The coastline data were extracted from the ENC S-57 format to vector line shapefiles. The ENC coastline 

dataset from chart #18500 was used to create a ‘combined coastline’. Chart #18502 covers the southern 

region of the DEM and had been used in developing the Astoria DEM coastline.

Table 3: Electronic Navigation Charts available in the Taholah, Washington region.

Chart Title Edition Edition Date Format Scale

18500 Columbia River to Destruction Island 29 2004 ENC and RNC 1:180,789

18502 Greys Harbor - Westhaven Cove 86 2007 ENC and RNC 1:40,000

2) NGDC Astoria DEM coastline

The southern Taholah DEM boundary overlaps the Astoria DEM (http://www.ngdc.noaa.gov/dem/

selectdem.jsp) northern boundary by approximately 11 kilometers. The coastline used in developing the 

Astoria DEM (Carignan et al., 2009) was clipped to the Taholah DEM boundary and merged with the OCS 

chart coastline dataset using ArcCatalog tools.

3) NGDC La Push DEM coastline

The northern Taholah DEM boundary overlaps the La Push DEM (http://www.ngdc.noaa.gov/dem/

selectdem.jsp) southern boundary by approximately 11 kilometers. The coastline used in developing the La 

Push DEM (Taylor et al., 2008) was clipped to the Taholah DEM boundary and merged with the OCS chart 

coastline dataset using ArcCatalog tools. The coastline was edited to align with datasets transformed to a 

common vertical datum using an improved methodology (Fig.5; see Section 3.2.1).

Figure 5. Comparison between the La Push DEM coastline (red) and the Taholah DEM ‘combined coastline’ (black), aligned with the MHW 

2002 ALACE LiDAR data. NGDC used an improved vertical datum transformation method in developing the Taholah DEM, resulting in an 

approximate 50 m horizontal difference in the position of the La Push and Taholah coastlines. 
Digital Elevation Model of Taholah, Washington

7

The ‘combined coastline’ datasets were visually compared to Google Earth satellite imagery (http://earth.google.

com/userguide/v4/#imagery_dates), the Washington State Department of Ecology aerial photo collection (http://apps.

ecy.wa.gov/shorephotos/), and USGS topographic maps available on NASA World Wind (http://worldwind.arc.nasa.

gov/index.html) to ensure features such as jetties, levees, and rocks were present in the coastline and to accurately 

reflect morphologic changes along the coastline (Fig. 6). The ‘combined coastline’ was adjusted to match the 2002 

ALACE LiDAR data available from the Coastal Services Center (see Section 3.1.3). The ‘combined coastline’ was 

converted to xyz data with 10 m point spacing, using NGDC’s GEODAS software, for use in building a pre-surfaced 

bathymetric grid (see Sec. 3.3.2).

Figure 6. The 2002 CSC ALACE LiDAR data overlying a Google Earth satellite image of the Quinault River. The image was georeferenced and 

used in combination with recent aerial photographs to manually adjust the ‘combined coastline’ , shown in red.

0 315 630 1,260

Meters
Medley et. al, 2009

8

3.1.2 Bathymetry

Bathymetric datasets used in the compilation of the Taholah DEM include 25 NOS hydrographic surveys, five 

multibeam swath sonar surveys from NGDC and USGS, and extracted ENC sounding data (Table 4; Fig. 7). Two 

additional multibeam surveys provided to NGDC by the National Marine Sanctuary were evaluated but not used 

because of errors in the sound velocity measurements during collection of data, which created artificial “ridges” along 

the edges of each track.

Table 4: Bathymetric datasets used in compiling the Taholah DEM.

Source Year Data Type Spatial Resolution

Original 

Horizontal Datum/

Coordinate System

Original 

Vertical 

Datum

URL

NOS

1862 

to 

2005

Hydrographic 

survey 

soundings

Ranges from 10 m 

to 1.2 km (varies 

with scale of survey, 

depth, traffic, and 

probability of 

obstructions)

NAD 13, NAD 

27 or NAD 83 

geographic, or 

undetermined

MLLW

http://www.ngdc.noaa.

gov/mgg/bathymetry/

hydro.html

NGDC 

1993 

to 

1999

Multibeam 

swath sonar 

files

raw MB files gridded 

to 1 arc-second

WGS 84 

geographic

assumed 

MSL

http://www.ngdc.noaa.

gov/mgg/bathymetry/

multibeam.html

USGS 1999

Multibeam 

swath sonar 

files

~ 10 meters

NAD 83 State 

Plane Washington 

South (meters)

MLLW

http://walrus.wr.usgs.

gov/swces/data.

html#era4

OCS ENC 

#18502 2005

extracted 

soundings from 

ENC

1: 191,730 WGS 84 

geographic MLLW

http://www.

nauticalcharts.noaa.

gov/

Figure 7. Spatial coverage of bathymetric datasets used in compiling the Taholah DEM. The ‘combined coastline’ is in black, DEM boundary is 

in red, and neighboring DEM boundaries are dashed black.
Digital Elevation Model of Taholah, Washington

9

1) NOS hydrographic survey data

A total of 25 digital NOS hydrographic surveys conducted between 1862 and 2005 were available for 

use in developing the Taholah DEM. The hydrographic survey data were originally vertically referenced to 

Mean Lower Low Water (MLLW) and horizontally referenced to either NAD 1913, NAD 27, or NAD 83 

geographic datums, if the datum was known and recorded (Table 5; Fig. 8).

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) and were referenced to NAD 834. The 

surveys were subsequently clipped to a polygon 0.05 degrees (~5%) larger than the Taholah 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 other bathymetric datasets, the ‘combined coastline’, and NOS 

raster nautical charts (RNCs). The surveys were clipped to remove soundings that overlap the more recent 

multibeam surveys, and where soundings from older surveys have been superseded by more recent NOS 

surveys.

 Table 5: Digital NOS hydrographic surveys used in compiling the Taholah DEM.

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

Digital Records

H00809 1862 20,000 mean lower low water undetermined

H01589A 1883 20,000 mean lower low water undetermined

H04633A 1926 120,000 mean lower low water NAD 1913

H04633B 1926 120,000 mean lower low water NAD 27

H04710 1927 20,000 mean lower low water NAD 13

H04715 1927 20,000 mean lower low water NAD 13

H04716 1927 20,000 mean lower low water NAD 13

H04728 1927 40,000 mean lower low water NAD 13

H04729 1927 40,000 mean lower low water NAD 13

H04735 1927 80,000 mean lower low water NAD 27

H04775 1927 120,000 mean lower low water NAD 13

H05068 1930 40,000 mean lower low water NAD 27

H05107 1930 20,000 mean lower low water NAD 27

H05108 1930 20,000 mean lower low water NAD 27

H05110 1930 40,000 mean lower low water NAD 27

H05114 1930 120,000 mean lower low water NAD 27

H06647 1940 10,000 mean lower low water NAD 27

H06665 1941 10,000 mean lower low water NAD 27

H08250 1956 10,000 mean lower low water NAD 27

H08251 1956 10,000 mean lower low water NAD 27

H08252 1955 20,000 mean lower low water NAD 27

H08293 1956 10,000 mean lower low water NAD 27

H11282 2005 10,000 mean lower low water NAD 83

H11299 2005 10,000 mean lower low water NAD 83

H11300 2005 10,000 mean lower low water NAD 83

4. NGDC’s GEODAS 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.
Medley et. al, 2009

10

Figure 8. Digital NOS hydrographic survey coverage in the Taholah region. DEM boundary in red.

2) Multibeam swath sonar files

Four multibeam swath sonar surveys were downloaded from the NGDC multibeam database (http://

www.ngdc.noaa.gov/mgg/bathymetry/multibeam.html; Table 6, Fig. 9). The NGDC multibeam database is 

comprised of the original swath sonar files collected mostly by the U.S. academic fleet. The downloaded 

data were gridded to 1/3 arc-second resolution using MB-System, an NSF-funded free software application 

specifically designed to manipulate submarine multibeam sonar data (http://www.ldeo.columbia.edu/res/pi/

MB-System/).

Most of the multibeam swath sonar surveys were transits rather than dedicated sea-floor surveys. All 

have a horizontal datum of WGS 84 geographic and undefined vertical datum, which was assumed to be 

mean sea level (MSL).

Table 6: Multibeam swath sonar surveys used in compiling the Taholah DEM.

Cruise ID Ship Year Original Vertical 

Datum

Original Horizontal 

Datum Institution

REM-01MV Melville 1993 assumed MSL WGS 84 geographic University of California, Scripps Institution of 

Oceanography (UC/SIO)

REM-02MV Melville 1993 assumed MSL WGS 84 geographic University of California, Scripps Institution of 

Oceanography (UC/SIO)

SO108 Sonne 1996 assumed MSL WGS 84 geographic University of Kiel, Germany, GEOMAR 

Forshungszentrum

AVON09MV Melville 1999 assumed MSL WGS 84 geographic University of California, Scripps Institution of 

Oceanography (UC/SIO)
Digital Elevation Model of Taholah, Washington

11

Figure 9. Spatial coverage of multibeam swath sonar surveys from the NGDC multibeam bathymetry database.

After assessing individual survey quality, the gridded data were transformed to MHW (see section 3.2.1)

and xyz format using FME, displayed in QT Modeler and edited using ArcMap and QT Modeler. Figure 10 

shows data errors along the edge of the swath in survey SO108 due to noise. These deep valleys along the 

edges were seen in all four surveys, mostly in the shallower water, and were manually deleted in ArcMap

before creating the gridded bathymetric surface (see Section 3.3.2).

Figure 10. Errors along the edge of a multibeam swath sonar survey. The anomalous valley and ridge were 

removed using ArcGIS. Color image created with QT Modeler. 
Medley et. al, 2009

12

3) USGS multibeam swath sonar survey

The USGS multibeam swath sonar survey mb99 covered the southeastern region of the DEM offshore 

of Grays Harbor and was downloaded from the USGS Southwest Washington Coastal Erosion Study website 

(http://walrus.wr.usgs.gov/swces/data.html#era4). The survey was converted to a shapefile using ArcCatalog; 

vertical and horizontal datums were transformed using FME. When displayed for analysis, the data revealed 

horizontal lines across the entire dataset and anomalous depths inconsistent with adjacent bathymetric data, 

and were removed using ArcMap editing tools and QT Modeler (Fig. 11).

Figure 11. Color image of USGS multibeam swath sonar survey mb99. White arrows point to errors in data, which were removed 

before use in developing the Taholah DEM. Image created with QT Modeler.
Digital Elevation Model of Taholah, Washington

13

3.1.3 Topography

Two topographic datasets were used to build the Taholah DEM (Table 7; Fig. 12). The USGS NED 1/3 arc-second 

DEM provided full coverage for the Taholah region and the 2002 CSC ALACE LiDAR dataset provided coverage 

along the entire Pacific coastline. NGDC evaluated but did not use the lower resolution Shuttle Radar Topography 

Mission (SRTM) Elevation 1 arc-second DEM available from USGS. NGDC also digitized some elevations to ensure 

that features were accurately represented in the Taholah DEM.

Table 7: Topographic datasets used in compiling the Taholah DEM.

Source Year Data Type Spatial

Resolution

Original Horizontal 

Datum/Coordinate 

System

Original 

Vertical 

Datum

URL

USGS 1999-

2000

NED 

DEM

1/3 arcsecond NAD 83 geographic NAVD88

(meters) http://ned.usgs.gov/

CSC 

ALACE 2002 LiDAR ~2 meters NAD 83 geographic NAVD88(meters) http://maps.csc.noaa.gov/TCM/

NGDC 2009 digitized 

points WGS 84 geographic MHW

Figure 12. Spatial coverage of topographic datasets used in building the Taholah DEM. The 1/3 arc-second NED DEM shown in green 

covers the entire Taholah DEM area. The 2002 ALACE LiDAR shown in pink covers the entire Pacific coastline.

 Neighboring NGDC DEM boundaries are shown as dashed brown lines.
Medley et. al, 2009

14

1) USGS NED topographic 1/3 arc-second DEMs

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

complete 1/3 arc-second coverage of the Taholah region5. Data are in NAD 83 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’. 

2) CSC LiDAR ALACE topography

The 2002 NASA/USGS Airborne LiDAR Assessment of Coastal Erosion (ALACE) Project topographic 

LiDAR dataset was downloaded from the NOAA CSC website (http://maps.csc.noaa.gov/TCM/) and 

transformed to NAD 83 and MHW using FME. This dataset was not processed to bare earth and contained 

elevation values over open water as well as vegetation and buildings (Fig. 13). NGDC processed the data using 

ArcMap to simulate bare earth. Because the morphology of the coastline differs though out the DEM, NGDC 

processed the LiDAR data with varying techniques to bare earth in different regions along the coastline. 

For the region overlapping the Astoria DEM, the data were compared to the USGS NED topographic DEM 

and points were retained where the difference in elevation between the NED and the LiDAR data were less 

than 12 meters. Most tall buildings and vegetation were eliminated, while the high sand dunes and berms 

along the beaches remain. For the region overlapping the La Push DEM, the LiDAR data were 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. For the remainder of the 

coastline, depending on the elevation of the coastal bluffs and comparison with the NED data, LiDAR data 

were removed with elevations values greater than 20 to 40 meters, to retain coastal features but to remove 

forested regions. In low lying coastal towns, such as Taholah, LiDAR data were manually edited in ArcMap 

by NGDC to remove most buildings and trees. The data were then clipped to the ‘combined coastline’ and 

filtered to remove elevation points below zero.

3) NGDC digitized points

NGDC digitized elevation points in the Taholah, Washington DEM of rocks off the coast, based on RNC 

#18500, and of low lying streams where returns from treetops from the non-bare earth 2002 ALACE LiDAR 

were manually deleted.

5. 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]
Digital Elevation Model of Taholah, Washington

15

Figure 13. Color image of a preliminary Taholah DEM and the surrounding coastline before processing the LiDAR to bare earth. The trees 

and buildings were manually removed by NGDC. 

After processing, the topographic data were viewed in ArcMap to make sure that the transitions along dataset 

edges were smooth. In some areas, the transition between the NED data and the LiDAR data formed a step of up 

to 30 meters. A 50 meter data buffer was generated in the NED data to reduce the sharpness of the border between 

the two datasets. Figure 14 shows a buffered cross section of the interpolated area between the NED and LiDAR 

datasets. Data were then converted to xyz format using FME for the final gridding process.

Figure 14. Color image of the transition from the LiDAR to the NED data in the Taholah DEM. A 50 meter buffer was created between the 

LiDAR and the NED data to prevent a steep step from one data source to the other. With the buffer, a gentle slope can be seen between the LiDAR 

and the NED.
Medley et. al, 2009

16

3.2 Establishing Common Datums

3.2.1 Vertical datum transformations

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

of vertical datums including Mean Lower Low Water (MLLW), Mean Sea Level (MSL), and NAVD88. All datasets 

were transformed to MHW to provide maximum flooding for inundation modeling. Units were converted from feet to 

meters as appropriate.

1) Bathymetric data

NGDC created two offset grids approximating the relationship between MLLW and MHW, and MSL 

and MHW for the west coast of Oregon and Washington. The grids were built in ArcGIS using the Inverse 

Distance Weighting (IDW) tool and the differences between the vertical datums as measured at 25 NOAA 

tide stations in the area (http://tidesandcurrents.noaa.gov/). The grids spanned from 40.7167° to 48.4167° 

N, and 124.6867° to 122.8868° W with a grid cell size of 0.1 degrees. The NOS hydrographic surveys, and 

the USGS and NGDC multibeam surveys were transformed from MLLW and MSL to MHW, using FME

software, by adding the appropriate offset grid.

2) Topographic data

NGDC created an offset grid approximating the relationship between NAVD88 and MHW along the 

Pacific Northwest coast. The grid was built in ArcGIS using the Inverse Distance Weighting (IDW) tool 

and the difference between the vertical datums as measured at 16 NOAA tide stations in the region (http://

tidesandcurrents.noaa.gov/). The grids spanned from 40.7167° to 48.4167° N and 124.6867° to 122.8868° 

W, with a grid cell size of 0.1 degree. The USGS NED 1/3 arc-second DEMs and the CSC topographic 

LiDAR surveys were originally referenced to NAVD88. Conversion to MHW, using FME software, was 

accomplished by adding the offset grid to the survey data.

The offset grids are an improved method for vertical datum transformation of bathymetric and topographic 

datasets. This method was also used in developing the Astoria Oregon DEM (Carignan et al., 2009), creating a seamless 

overlap between the two DEMs. For the La Push, Washington DEM (Taylor et al., 2008), NGDC used a constant 

offset derived from the La Push Pier tide station #9442396 to perform vertical datum transformations. Because of the 

different vertical transformation methods, there is not a seamless overlap between NGDC’s Taholah DEM and the 

neighboring La Push DEM.

3.2.2 Horizontal datum transformations

Datasets used to compile the Taholah DEM were originally referenced to WGS 84 geographic, NAD 83 geographic, 

NAD 27 geographic, NAD 1913, and NAD 83 State Plane Washington South. The relationships and transformational 

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

83/WGS 84 geographic using FME software or ArcGIS.
Digital Elevation Model of Taholah, Washington

17

3.3 Digital Elevation Model Development

3.3.1 Verifying consistency between datasets

After horizontal and vertical transformations were applied, the resulting ESRI shapefiles were checked in ArcMap

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

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

Problems included:

•	 Elevations located over the open-ocean in the NED and LiDAR datasets.

•	 Inconsistent elevation values between the NED and LiDAR topographic data along the coast. 

•	 Data errors in multibeam swath sonar surveys. Manual editing of the multibeam sonar data was necessary to 

remove these artifacts. 

•	 Topographic CSC LiDAR dataset not processed to bare earth. 

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

from older NOS data by as much as 10 meters nearshore and up to 75 meters in deeper water. 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 Taholah 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 DEM due to these low-resolution datasets, 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 point data were median-averaged using the GMT tool ‘blockmedian’ to create a 1 arc-second grid 0.05 degrees 

(~5%) larger than the Taholah 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) and 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 H08416 and the 1 arc-second pre-surfaced 

bathymetric grid.
Medley et. al, 2009

18

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 Taholah 

DEM. MB-System is an NSF-funded free 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 digitized features, such as the near shore rocks. Least weight was given to the coastline and the pre-surfaced 

1 arc-second bathymetric grid. Gridding was performed in quadrants, with the resulting Arc ASCII grids seamlessly 

merged in ArcCatalog to create the final 1/3 arc-second Taholah DEM.

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

Dataset Relative Gridding Weight

NGDC digitized features 1,000

CSC topographic LiDAR 100

USGS NED topographic LiDAR 100

NOS hydrographic surveys 100

USGS Multibeam survey 100

NGDC Multibeam surveys 100

Extracted ENC soundings 100

Combined coastline 1

Pre-surfaced bathymetric grid 1
Digital Elevation Model of Taholah, Washington

19

3.4 Quality Assessment of the DEM

3.4.1. Horizontal accuracy

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

datasets used to determine corresponding DEM cell values. Topographic features have an estimated accuracy of 10 

meters: CSC topographic LiDAR data have an accuracy between 1 and 3 meters; NED topography is accurate within 

10 meters. Bathymetric features are resolved only to within a few hundreds 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 man-made morphologic change (i.e., channel 

dredging and building of jetties).

3.4.2 Vertical accuracy

Vertical accuracy of elevation values for the Taholah 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 source data have an estimated accuracy between 

0.1 meters and 5% of water depth. Values were derived from a wide range of input sounding data 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.
Medley et. al, 2009

20

3.4.3 Slope maps and 3-D perspectives

ESRI ArcCatalog was used to generate a slope grid from the Taholah 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. Analysis of preliminary grids revealed suspect data points, 

which were corrected before recompiling the DEM. Three-dimensional viewing of the UTM-transformed DEM was 

accomplished using ESRI ArcScene. Figure 17 shows a perspective view from the southwest of the 1/3 arc-second 

Taholah DEM in its final version.

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

slopes; Taholah coastline in red.
Digital Elevation Model of Taholah, Washington

21

Figure 17. Perspective view from the southwest of the Taholah DEM. 

2x vertical exaggeration.

3.4.4	 Comparison with source data files

To ensure grid accuracy, the Taholah 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 section of the 

non-bare earth CSC ALACE LiDAR survey file, located at the town of Taholah, and the Taholah DEM is shown in 

Figure 18. Differences range from 2.7 to -31 meters, where negative values indicate that elevations of the LiDAR data 

are higher than the DEM elevations. The area where the greatest difference occurred is in the low lying coastal streams 

where some LiDAR tree top elevations were supplanted by NGDC digitized points of ground surface elevations in the 

DEM (see Table 8).

Figure 18. Histogram of the differences between a section of the CSC ALACE LiDAR survey and the Taholah DEM.
Medley et. al, 2009

22

3.4.5 Comparison with NGS geodetic monuments

The elevations of 332 NOAA NGS geodetic monuments were extracted from online shapefiles of monument 

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

sub-mm accuracy) and elevations in NAVD88 (in meters). 

 Elevations were shifted to MHW vertical datum using FME for comparison with the Taholah DEM (see Fig. 20 

for monument locations). Differences between the Taholah DEM and the NGS geodetic monument elevations range 

from -51.78 to 24.08 meters, with the majority of them within ± 5 meters (Fig. 19). Negative values indicate that the 

DEM elevation is less than the monument elevation. The marker with a difference of -51.78 meters is located on the 

beach and NGS metadata states that it is not a suitable place for a permanent marker and have had to recover this lost 

marker several times. Monuments on unstable bluffs and rapidly changing shorelines, and lost monuments had the 

greatest negative and positive values. The horizontal accuracy of the monuments can be off as much as 50 meters due 

to lost monuments, and locations on bridges and unstable terrain, such as beaches and high bluffs.

. 

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

Figure 20. Location of the NGS monuments used to assess the Taholah DEM.
Digital Elevation Model of Taholah, Washington

23

4. Summary and Conclusions

An integrated bathymetric–topographic digital elevation model of the Taholah, Washington region, with cell 

size 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 and state 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 Taholah DEM, based on NGDC’s research and analysis, are listed below:

•	 Conduct hydrographic surveys for near-shore areas, especially in bays and river inlets.

•	 Complete bathymetric–topographic LiDAR surveying of entire region, especially within coastal zones.

•	 Process CSC topographic LiDAR data to bare earth.

•	 Re-survey older, low-resolution NOS hydrographic surveys in deeper water.

5. Acknowledgments

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

authors thank Chris Chamberlin and Vasily Titov (PMEL); Ann Gibbs (USGS Pacific Science Center); Brooke 

McMahon and Crescent Moegling (NOAA/NOS Pacific Hydro Office) for processing raw multibeam data; and Nancy 

Wright (National Marine Sanctuary) for sending multibeam data not available on the their website.

6. References

Carignan, K. S., Taylor, L. A., Eakins, B. W., and Warnken, R. R., 2009. Digital Elevation Models of Astoria, Oregon: 

Procedures, Data Sources and Analysis. NOAA Technical Memorandum NESDIS NGDC-22.

Nautical Chart #18500 (RNC and ENC), 29nd Edition, 2004. Columbia River to Destruction Island. Scale 1: 180,789. 

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

Nautical Chart #18502 (ENC and RNC), 86th Edition, 2007. Greys Harbor – Westhaven Cove. Scale 1:40,000. U.S. 

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

Taylor, L. A., Eakins, B. W., Carignan, K. S., Warnken, R. R., Sazonova, T., and Schoolcraft, D. C. 2009. Digital 

Elevation Models of La Push, Washington: Procedures, Data Sources and Analysis. NOAA Technical Memorandum 

NESDIS NGDC-14.
Medley et. al, 2009

24

7. Data Processing Software

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

FME 2008 GB – Feature Manipulation Engine, developed and licensed by Safe Software, Vancouver, BC, Canada, 

http://www.safe.com/

GEODAS v. 5 – Geophysical Data System, free software 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, free software 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, free software 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/

Persistance of Vision Pty. Ltd,. (2004), Persistence of VisionTM Raytracer. Persistance of Vision Pty., Williamstown, 

Victoria, Australia, http://www.povray.org.

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/