DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

noaa / NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

National Environmental Satellite,

Data, and Information Service

NOAA Technical Memorandum NESDIS NGDC-4

DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA:

PROCEDURES, DATA SOURCES AND ANALYSIS 

L.A.Taylor

B.W. Eakins

K.S. Carignan

R.R. Warnken

D.C. Schoolcraft

T. Sazonova 

G.F. Sharman

National Geophysical Data Center

Marine Geology and Geophysics Division

Boulder, Colorado

January 2008


DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

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-4

DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA:

PROCEDURES, DATA SOURCES AND ANALYSIS 

Lisa .A. Taylor1

Barry .W. Eakins2

Kelly .S. Carignan2

Robin .R. Warnken1

David C. Schoolcraft1

Tatiana Sazonova2

George F. Sharman1

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 DUTCH HARBOR, ALASKA

Contents

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

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

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

3.1 Data Sources and Processing ......................................................................................................4

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

3.1.2 Bathymetry ............................................................................................................9

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

3.2 Establishing Common Datums .................................................................................................17

3.2.1 Vertical datum transformations ...........................................................................17

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

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

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

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

3.3.3 Pre-gridding of multibeam swath sonar data.......................................................19

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

3.4 Quality Assessment of the DEM...............................................................................................20

3.4.1 Horizontal accuracy.............................................................................................20

3.4.2 Vertical accuracy .................................................................................................20

3.4.3 Slope maps and 3-D perspectives........................................................................21

3.4.4	 Comparison with source data files.......................................................................22

3.4.5 Comparison with NOAA tidal stations................................................................22

3.4.6 Comparison with USGS topographic elevations.................................................23

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

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

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

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

Appendix A. Computation of Unalaska to NAD83 horizontal datum shift ...................................................25

List of Figures

Figure 1. Shaded-relief image, derived from the DEM, of the Dutch Harbor, Alaska area.......................1

Figure 2. Photographs of the Scotch Cap Lighthouse, 40 feet above sea level, before and after the 

April Fool’s Day earthquake and tsunami of 1946..............................................................2

Figure 3. Aleutian Islands Habitat Conservation Area southwest of Dutch Harbor ..................................3

Figure 4. Coverage of data sources used to compile the Dutch Harbor, Alaska DEM ..............................4

Figure 5. Spatial coverage of digital ENCs in the Dutch Harbor region....................................................6

Figure 6. Offset between small-scale and large-scale ENCs along part of Unalga Island’s coast.............6

Figure 7. Manmade features present in coastline datasets .........................................................................7

Figure 8. Digital coastline segments combined for use in the Dutch Harbor DEM...................................8

Figure 9. Digital NOS hydrographic survey coverage in the Dutch Harbor region.................................10

Figure 10. Spatial coverage of multibeam swath sonar surveys into and out from Dutch Harbor that 

were utilized in DEM development...................................................................................12

Figure 11. Color image of the NED DEM extracted from the USGS web site..........................................13

Figure 12. Example of gaps in SRTM data coverage.................................................................................14

Figure 13. Land elevation points extracted from ENCs and digitized from NOAA nautical charts..........15

Figure 14. Histogram of the difference between NOS soundings for survey H06234 and the NOS 

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

Figure 15.	 Failure of sparse NOS hydrographic soundings to capture rugged seafloor relief ...................19

Figure 16. Slope map of the 1 arc-second Dutch Harbor DEM.................................................................21

Figure 17. Perspective view from the northeast of the Dutch Harbor DEM..............................................21

Figure 18. Histogram of the difference between the multibeam swath bathymetry data and the 

Dutch Harbor DEM ...........................................................................................................22
iv

Taylor et al., 2008

Figure 19. Histogram of the difference between the USGS topo elevations and the Dutch 

 Harbor DEM.......................................................................................................................23

List of Tables

Table 1.	 PMEL specifications for the Dutch Harbor, Alaska DEM..........................................................3

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

Table 3. Electronic navigational charts in the Dutch Harbor, Alaska region............................................5

Table 4. Non-digitized NOAA nautical charts in the Dutch Harbor, Alaska region.................................6

Table 5. Bathymetric data sources used in gridding .................................................................................9

Table 6. Digital NOS hydrographic surveys used to build the Dutch Harbor, Alaska DEM..................11

Table 7. Cruises with multibeam swath sonar data that were utilized in the Dutch Harbor DEM.........12

Table 8. Topographic data sources used in gridding...............................................................................13

Table 9. Topographic features digitized from published NOAA nautical charts in the Dutch Harbor, 

 Alaska region.....................................................................................................................16

Table 10. Relationship between Mean High Water and other vertical datums in the Dutch 

 Harbor region.....................................................................................................................17

Table 11. Data hierarchy used to assign gridding weight in MB-System.................................................20

Table 12. Comparison of NOAA tidal benchmark elevation with the Dutch Harbor DEM.....................22

Table A-1. Computation of Unalaska to NAD83 horizontal datum shift ...................................................25


DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

Digital Elevation Model of Dutch Harbor, Alaska:

Procedures, Data Sources and Analysis

1. Introduction

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

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

Harbor,Alaska (Fig. 1) for the Pacific Marine Environmental Laboratory (PMEL), NOAACenter for Tsunami Research

(http://nctr.pmel.noaa.gov/). The 1 arc-second (~30 meter) elevation grid was generated from several, diverse digital 

datasets in the region (grid boundary and sources shown in Fig. 4). The DEM will be used as input for the Method of 

Splitting Tsunami (MOST) model (http://www.pmel.noaa.gov/pubs/PDF/tito1927/tito1927.pdf) developed by PMEL 

to simulate tsunami generation, propagation and inundation. This report provides a summary of the data sources and 

methodology used in developing the Dutch Harbor DEM. 

Figure 1. Shaded-relief image, derived from the DEM, of the Dutch Harbor, Alaska area. Red 

triangle locates tidal station listed in Table 12; green stars locate USGS bench marks listed in Table 

13. Contour interval (referenced to MHW): 100 meters, bold every 500 meters.


Taylor et al., 2008

2. Study Area

Dutch Harbor is the official name of the port of the city of Unalaska, the 11th largest settlement in Alaska. The 

city and harbor are located on Unalaska Island, one of the largest islands in the Aleutian chain, which forms a rugged, 

volcanic island arc curving from the tip of the Alaska Peninsula and approaching Russia. The Aleutians lie along the 

edge of the North American plate, where the Pacific plate is subducting underneath it. The great majority of the islands

bear evident marks of volcanic origin, and there are numerous volcanic cones on the north side of the chain, some of 

them active. Many of the islands, however, are not wholly volcanic, but contain crystalline or sedimentary rocks, as 

well as amber and beds of lignite. The coasts are rocky and surf-worn, and the approaches are exceedingly dangerous, 

the land rising immediately from the coasts to steep, bold mountains.

In the 2000 census, there was a population of 8,162 on the islands, of whom 4,283 were living in the main 

settlement of Unalaska. According to the U.S. Census Bureau, the city has a total area of 549.9 km2 (212.3 mi

2

): 287.5 

km2 (111.0 mi2) of it is land and 262.4 km2 (101.3 mi2) of it (47.71%) is water. Its economy is based on commercial 

fishing and shipping/transportation.

The large April 1st (April Fool’s Day), 1946 earthquake just south of Unalaska Island provided the impetus

to establish the tsunami warning network in the Pacific. An earthquake-generated tsunami greater than 100 feet high

obliterated the nearby Scotch Cap lighthouse (Fig. 2), on Unimak Island, though Dutch Harbor was protected. The 

tsunami also traveled across the Pacific, drowning 159 people in Hilo, Hawaii.

Figure 2. Photographs of the Scotch Cap Lighthouse, 40 feet above sea level, before and after the April Fool’s Day 

earthquake and tsunami of 1946. [Taken from http://www.usalights.com/alaska/scotchcap.htm]
DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

Just recently, NOAA Fisheries Service formally established the Aleutian Islands Habitat Conservation Area 

in Alaska, creating 279,114 square nautical miles of protected habitat to the southwest of Dutch Harbor (Fig. 3). The 

Fisheries Service worked with partners to develop a plan to restrict fishing activities that can destroy sensitive habitats

on the ocean floor. Designating the area as a habitat conservation area makes the plan a reality. Resulting from a

February 2005 recommendation by the North Pacific Fishery Management Council, the Aleutian Islands Conservation

Area establishes a network of fishing closures in the Aleutian Islands and Gulf of Alaska. The area protects habitat for

deepwater corals and other sensitive features that are slow to recover once disturbed by fishing gear or other activities.

While certain sites that have been trawled repeatedly in the past will remain open, fragile coral gardens discovered by 

NOAA scientists in 2002 will now be protected. NOAA worked closely with environmental groups, the commercial 

fishing industry, the fishery management council, and other partners to develop unprecedented protections over this

huge area (http://www.fakr.noaa.gov/).

Figure 3. Aleutian Islands Habitat Conservation Area southwest of Dutch Harbor. 

3. Methodology

The Dutch Harbor DEM was developed to meet PMEL required specifications (Table 1), based on input

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

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

Table 1: PMEL specifications for the Dutch Harbor, Alaska DEM.

Grid Area Dutch Harbor, Alaska

Coverage Area 167.2 o to 165.9o W; 53.5o to 54.35o N

Coordinate System Geographic decimal degrees

Horizontal Datum World Geodetic System (WGS84)

Vertical Datum Mean High Water

Vertical Units Meters

Grid Spacing 1 arc-second

Grid Format ASCII raster grid
Taylor et al., 2008

3.1 Data Sources and Processing

Shoreline, bathymetric, and topographic data (Fig. 4) were obtained from several federal and state government 

agencies, including: NOAA’s National Ocean Service (NOS), Office of Coast Survey (OCS), and NGDC; the Alaska

Department of Natural Resources; the U.S. Fish and Wildlife Service; and the U.S. Geological Survey (USGS). 

Safe Software’s (http://www.safe.com/) FME data translation tool package was used to convert datasets into ESRI 

(http://www.esri.com/) ArcGIS shape files. The shape files were then displayed to assess data quality and manually

edit datasets. Vertical datum transformations to Mean High Water (MHW) were achieved using FME and data from 

the Dutch Harbor tide station, as no VDatum model software (http://nauticalcharts.noaa.gov/csdl/vdatum.htm) was 

available for this area. 

Figure 4. Coverage of data sources used to compile the Dutch Harbor, Alaska DEM.

3.1.1 Shoreline

Five digital coastline datasets of the Dutch Harbor region were available for analysis: NGA Global Shoreline, 

OSC electronic navigational charts and one chart with vector MHW shoreline, U.S. Fish and Wildlife Service statewide 

Alaska digital coastline, and Alaska Department of Natural Resources statewide digital coastline.

Table 2. Shoreline data sources used in gridding.

Source Year Data Type Spatial Resolution

Original Horizontal 

Datum/Coordinate 

System

Original 

Vertical 

Datum

URL

OCS Electronic 

Navigational 

Charts

1989 to 

1991

inferred 

MHW 

coastline

Digitized from 1:20,000 and 

1:80,000 scale charts WGS84 geographic InferredMHW

http://chartmaker.

ncd.noaa.gov/

OCS MHW 

vector shoreline

of Chart #16522

2003 MHW 

coastline

Digitized from 1:40,000 and 

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

U.S. FWS 2006 compiled 

coastline Various WGS84 geographic unknown http://chartmaker.ncd.noaa.gov/
DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

1) NGA global shoreline

The National Geospatial-Intelligence Agency (NGA; http://www.nga.mil/) has developed a ‘Prototype 

Global Shoreline Data’ digital shoreline. The NGA Global Shoreline Data is an unclassified vector dataset

generated by Earth Satellite Corporation (http://www.earthsat.com/) of Rockville, Maryland for NGA, under 

contract to Boeing in 2004. The shoreline is an approximation to the High Water Line and constructed from 

consistently orthorectified Landsat TM satellite imagery (GeoCover Ortho), acquired between 1998-2002 for

NASA under the Global Land Mapping Program (GLMP). NDVI and SWIR models were used to define the

landward extent of inundation (i.e., MHW). Independently verified positional accuracy for the source product

(GeoCover Ortho) is consistently better than 50 meter root mean square (RMS) error.

The NGA coastline matches the topographic data along island edges but without the detail of other 

coastline datasets, due principally to its lower resolution. This dataset was not used in the gridding process.

2) OCS electronic navigational charts

Eight electronic navigational charts (ENCs) are available for the Dutch Harbor region (Fig. 5; Table 3), 

which were downloaded from NOAA’s Office of Coast Survey (OSC) website (http://chartmaker.ncd.noaa.

gov/); the ENCs are digital versions of NOAA’s published nautical charts. The NOAA Coastal Services 

Center’s ‘Electronic Navigational Chart Data Handler for ArcView’ extension was used to import the data 

into ArcGIS (http://www.csc.noaa.gov/products/enc/). The chart data include coastline data files (inferred

MHW, though not clearly specified), which were compared with the other coastline datasets, topographic

data, and NOS hydrographic soundings. They also include soundings (extracted from NOS hydrographic 

surveys) and land elevations (see Section 3.1.3).

The ENC coastlines for the 6 charts at 1:40,000 to 1:80,000 (Table 3) generally correspond well with 

NOS soundings and topographic data: the exception being occasional piers, docks, bridges and even ships 

that were erroneously included and had to be deleted manually. The two ENCs at 1:300,000 scale, however, 

exhibit significant offset in their coastline data (up to 200 meters to the west-northwest) compared with the

topographic data, NOS soundings and the larger-scale ENCs, and are also of lower resolution (e.g., Fig. 6). 

For this reason they were deemed unreliable and were not used in the gridding process. The 6 larger-scale 

ENCs did not, however, provide complete coastline coverage for the Dutch Harbor region and were therefore 

combined with other datasets to build a ‘combined’ coastline (Fig. 8).

Several NOAA nautical charts do not exist in digital form (Table 4), but were nevertheless useful in 

evaluating the completeness of the coastline datasets. For example, several small islands (rocky knolls) are 

identified on Chart #16528 and on the small-scale ENC/Chart #16520. Such features from the small-scale

ENCs were included in the combined coastline.

 Table 3. Electronic navigational charts in the Dutch Harbor, Alaska region.

Nautical Chart # ENC ref.# Region Scale Pub. Date

16500 US3AK60M Unalaska I. to Amukta I. 1:300,000 8-1990

16514 US5AK65M Kuliliak Bay to Surveyor Bay 1:40,000 7-1990

16515 US5AK66M Chernofski Harbor to Skan Bay 1:40,000 7-1990

16517 US5AK68M Makushin Bay 1:40,000 12-1991

16518 US5AK69M Cape Kovrizhka to Cape Cheerful 1:40,000 9-1989

16520 US3AK61M Unimak and Akutan Pass 1:300,000 4-1989

16521 US5AK6AM Protection Bay to Eagle Bay 1:40,000 12-1990

16531 US4AL6FM Krenitzin I. 1:80,000 12-1990
Taylor et al., 2008

.

Figure 5. Spatial coverage of digital ENCs in the Dutch Harbor region. Small-scale charts are 

hachured, large-scale colored.

 Table 4. Non-digitized NOAA nautical charts in the Dutch Harbor, Alaska region.

Nautical Chart # Region Scale Pub. Date

16522 Beaver Inlet 1:40,000 05-1992

16528 Unalaska Bay & Akutan Pass 1:40,000 05-1992

16529 Dutch Harbor 1:10,000 08-1994

16530 Captains Bay 1:10,000 04-1996

Figure 6. Offset between small-scale, #16520, and large-scale, #16531, ENCs along part of Unalga 

Island’s coast. Note WNW offset (~200 meters) of the small-scale, #16520, ENC coastline. Color 

image derived from USGS 2 arc-second NED topography.
DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

3) OCS mean high water vector shoreline

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

charts (http://chartmaker.ncd.noaa.gov/): in the Dutch Harbor gridding region the data is from Nautical Chart 

#16522 (‘Unalaska Island—Beaver Inlet’, 1:40,000). Digital chart data are in NAD83 horizontal datum.

This shoreline dataset is consistent with the topographic data, NOS hydrographic soundings and the 

large-scale ENC coastlines, and was used in developing the combined coastline (Fig. 8), though it also 

contained manmade features (piers, ships, rivers, etc.) that had to be deleted before gridding (e.g., Fig. 7). 

Figure 7. Manmade features present in coastline datasets. Left panel shows original, unedited coastline extracted from OSC MHW 

vector shoreline (Chart #16522), and the edited version used in building the combined coastline. Google Earth satellite image in right 

panel permitted identification of piers, ships, docks, rivers, etc. that had to be deleted from the combined coastline.

4) U.S. Fish and Wildlife Service

The U.S. Fish and Wildlife Service (FWS) has compiled a seamless digital coastline of the State of Alaska 

from a variety of existing sources, including: the National Hydrography Dataset, NOAA nautical charts, U.S. 

Fish and Wildlife Service, National Geographic Topo Software, U.S. Army Corps of Engineers, and Alaska 

Department of Natural Resources. Though efforts were made to obtain the highest resolution coastlines 

available, their vertical datums were apparently not determined nor controlled in any way in compiling the 

FWS coastline; horizontal datum of the compiled FWS coastline is WGS84. This coastline is consistent with 

the topographic data and NOS hydrographic soundings, and the large-scale ENC coastlines and was used in 

developing the combined coastline (Fig. 8).

5) Alaska Department of Natural Resources

The Alaska Department of Natural Resources has also made a “first cut” at building a statewide digital

coastline for Alaska, nominally at 1:63,360 scale, though not in entirety (some areas at 1:250,000 scale). The 

primary dataset appears to be USGS topographic quadrangles. Horizontal datum is WGS84, vertical datum is 

undefined. The coastline exhibits good resolution, however, it is shifted roughly 150 meters to the northeast

relative to NOS soundings, topographic data, and the other, reliable coastline datasets. It was not used in the 

combined coastline.
Taylor et al., 2008

To obtain the best digital MHW coastline, NGDC combined the OSC large-scale ENC and MHW shorelines 

with the FWS coastline. Where overlap occurred, the FWS coastline was excised, as the OSC coastlines were 

determined to more reliably define the MHW line and were more consistent with the topographic data. This ‘combined

coastline’ (Fig. 8) was subsampled to 30-meter spacing and converted to point data for use in the gridding process. The 

combined coastline was also used as a coastal buffer for the NOS pre-surfacing algorithm (see Section 3.3.2) to ensure 

that interpolated bathymetric values reached “zero” at the coast.

Figure 8. Digital coastline segments combined for use in the Dutch Harbor DEM. Most segments 

are derived from digitized versions of large-scale NOAA nautical charts.
DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

3.1.2 Bathymetry

Bathymetric datasets used in the compilation of the Dutch Harbor DEM include 42 NOS hydrographic 

surveys, and multibeam swath sonar data archived at NGDC and the Marine Geoscience Data System.

Table 5. Bathymetric data sources used in gridding.

Source Year Data Type Spatial Resolution

Original 

Horizontal Datum/

Coordinate System

Original 

Vertical 

Datum

URL

NOS 1934 to 

1991

Hydrographic 

survey 

soundings

Ranges from 20 meters to 5 

kilometers (varies with scale 

of survey, depth, traffic and

probability of obstructions)

NAD27, NAD83, 

Unalaska

MLLW

(meters)

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

mgg/bathymetry/hydro.html

NGDC, 

MGDS

1988 to 

2004

Multibeam 

swath sonar

Ranges from 10 to 150 meters 

(varies with water depth)

WGS84 

geographic

MSL

(meters)

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

mgg/bathymetry/multibeam.

html; http://www.marine-geo.

org

1) NOS hydrographic survey data

A total of 42 NOS hydrographic surveys conducted between 1934 and 1991 were included in the Dutch 

Harbor DEM compilation (Fig. 9; Table 6); two very sparse surveys from 1910 and 1913 were excluded 

(H03194 and H03579). The survey data were originally vertically referenced to Mean Lower Low Water 

(MLLW) and horizontally referenced to either Unalaska, NAD27, or NAD83 datums. Many smooth sheets 

contain registration marks for both Unalaska and NAD27 datums (e.g., Fig. 15), which necessitated careful 

assessment to determine the datum to which each of these surveys were referenced to when digitized in the 

1990s. Dave Doyle, National Geodetic Survey, computed the shift necessary to convert from Unalaska to 

NAD83 (see Appendix A). 

Data point spacing for the surveys ranged from about 20 meters in shallow water to 5 kilometers in 

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

bathymetry/hydro.html) in their original datums (Table 6). The data were then converted to WGS84 using 

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

(http://www.safe.com). The surveys were subsequently clipped to a polygon 0.05 degrees (~5%) larger than 

the final gridding area to support data interpolation along grid edges.

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

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

current NED topographic data, the combined coastline, and Google Earth satellite imagery.
10

Taylor et al., 2008

Figure 9. Digital NOS hydrographic survey coverage in the Dutch Harbor 

region. Red line denotes DEM boundary; combined coastline in gray.
11

DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

Table 6. Digital NOS hydrographic surveys used to build the Dutch Harbor, Alaska DEM.

Survey ID Year Survey Scale Original Horizontal Datums Digitized 

Horizontal Datum

Original Vertical 

Datum

H05672 1934 20,000 Unalaska Unalaska MLLW

H05684 1934 5,000 smooth sheet is not available Unalaska MLLW

H05728 1934 40,000 Unalaska Unalaska MLLW

H05737 1934/35 20,000 Unalaska Unalaska MLLW

H05738 1934/35 20,000 Unalaska Unalaska MLLW

H05739 1934 80,000 Unalaska Unalaska MLLW

H05740 1934 160,000 Unalaska Unalaska MLLW

H05745 1934 20,000 Unalaska, NAD 1927 NAD 1927 MLLW

H05759 1934 80,000 Unalaska, NAD 1927 NAD 1927 MLLW

H05762 1934 20,000 Unalaska, NAD 1927 Unalaska MLLW

H05949 1935 20,000 Unalaska, NAD 1927 Unalaska MLLW

H05964 1935 20,000 Unalaska Unalaska MLLW

H05966 1935 20,000 Unalaska, NAD 1927 Unalaska MLLW

H05967 1935 160,000 Unalaska Unalaska MLLW

H05970 1935 20,000 Unalaska, NAD 1927 NAD 1927 MLLW

H05971 1935 40,000 Unalaska Unalaska MLLW

H05972 1935 80,000 Unalaska Unalaska MLLW

H05973 1935 40,000 Unalaska Unalaska MLLW

H05974 1935 20,000 Unalaska Unalaska MLLW

H05977 1935 20,000 Unalaska Unalaska MLLW

H05978 1935 20,000 Unalaska, NAD 1927 NAD 1927 MLLW

H05979 1935 20,000 Unalaska Unalaska MLLW

H05980 1935 5,000 Unalaska Unalaska MLLW

H05981 1935 5,000 Unalaska Unalaska MLLW

H06109 1935 10,000 Unalaska Unalaska MLLW

H06111 1935 20,000 Unalaska, NAD 1927 NAD 1927 MLLW

H06160 1936 80,000 Unalaska, NAD 1927 NAD 1927 MLLW

H06175 1936 20,000 Unalaska, NAD 1927 NAD 1927 MLLW

H06176 1936 40,000 Unalaska, NAD 1927 NAD 1927 MLLW

H06183 1936 10,000 Unalaska, NAD 1927 NAD 1927 MLLW

H06212 1937 20,000 Unalaska, NAD 1927 NAD 1927 MLLW

H06233 1937 40,000 Unalaska, NAD 1927 NAD 1927 MLLW

H06234 1937 20,000 Unalaska, NAD 1927 NAD 1927 MLLW

H06235 1937 20,000 Unalaska, NAD 1927 NAD 1927 MLLW

H06241 1937 10,000 Unalaska, NAD 1927 NAD 1927 MLLW

H06378 1938 20,000 Unalaska, NAD 1927 NAD 1927 MLLW

H06508 1939 10,000 Unalaska, NAD 1927 NAD 1927 MLLW

H06509 1939 20,000 Unalaska, NAD 1927 Unalaska MLLW

H06510 1939 20,000 Unalaska, NAD 1927 Unalaska MLLW

H06761 1941 2,000 Unalaska Unalaska MLLW

H10389 1991 5,000 NAD 1983, Polyconic projection NAD 1983 MLLW

H10391 1991 5,000 NAD 1983, Polyconic projection NAD 1983 MLLW
12

Taylor et al., 2008

2) Multibeam swath sonar data

The websites of NGDC (http://www.ngdc.noaa.gov/mgg/bathymetry/multibeam.html) and the Marine 

Geoscience Data System (MGDS; http://www.marine-geo.org) were queried for multibeam swath sonar 

bathymetric data in the vicinity of Dutch Harbor (Fig. 10). Non-proprietary data from 8 cruises were 

downloaded (Table 7) and utilized in the Dutch Harbor DEM. Cruise ‘FOCI93’ required manual editing to 

remove anomalous soundings along the northwest flank of Unalaska Island; cruise ‘RNDB06WT’ was not

included due to significant mismatch with other multibeam cruise data. All multibeam data were originally in

WGS84 geographic coordinates and inferred mean sea level (MSL) vertical datum.

Figure 10. Spatial coverage of multibeam swath sonar surveys into and out from Dutch Harbor that 

were utilized in DEM development.

Table 7. Cruises with multibeam swath sonar data that were utilized in the Dutch Harbor DEM.

Cruise Ship Year Sonar Source

EW0204 Ewing 2002 Simrad EM-120 MGDS

EW9408 Ewing 1994 Atlas Hydrosweep MGDS

EW9411 Ewing 1994 Atlas Hydrosweep MGDS

FOCI93 Surveyor 1993 SeaBeam “Classic” NGDC

FOCI95 Surveyor 1995 SeaBeam “Classic” NGDC

HLY-04-Ta Healy 2004 SeaBeam 2112 MGDS

NBP0304B Palmer 2003 Simrad EM120 MGDS

RNDB09WT Thomas Washington 1988 SeaBeam “Classic” NGDC
13

DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

3.1.3 Topography

Topographic data were obtained from several sources: USGS National Elevation Dataset (NED) 2 arc-second 

(~60 meter) gridded topographic DEMs; NASA shuttle radar topographic DEMs (1 arc-second), and NOAA OCS 

electronic navigational charts (Table 8).

Table 8. Topographic data sources used in gridding.

Source Year Data Type Spatial Resolution

Original Horizontal 

Datum/Coordinate 

System

Original Vertical 

Datum URL

USGS 

NED 2006 Topographic 

DEM 2 arc-second grid NAD27 geographic NGVD29(meters) http://ned.usgs.gov/

NASA

SRTM 2000 Topographic 

DEM 1 arc-second grid WGS84 geographic WGS84/EGM96 Geoid (meters) http://srtm.usgs.gov/

OCS ENCs

1989 to 

1991

Surveyed land 

elevations

Digitized from 1:20,000 

to 1:80,000 scale charts WGS84 geographic MHW(feet)

http://chartmaker.ncd.

noaa.gov/

1) USGS NED topography

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

2 arc-second coverage of Alaska. Data are in NAD27 Alaska geographic coordinates and NGVD29 vertical 

datum (meters). The extracted bare-earth elevations have a vertical accuracy of +/- 7 to 15 meters depending 

on source data resolution. See the USGS Seamless web site for specific source information (http://seamless.

usgs.gov/). The dataset was derived from USGS quad maps and aerial photos based on surveys conducted in 

the 1970s and 1980s.

The NED data included “zero” values over the open ocean (see Fig. 11), which were removed from the

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

inspected and compared with NOAA nautical charts, the combined coastline, and Google Earth satellite 

imagery. These points were removed in ArcCatalog by clipping to the combined coastline.

Figure 11. Color image of the NED DEM extracted from the USGS web site. Note data values over 

the open ocean (light pink) that had to be excised prior to gridding.

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

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

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

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

horizontal datum is NAD83, except for AK, which is NAD27. The vertical datum is NAVD88, except for AK, which is 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]
14

Taylor et al., 2008

2) NASA space shuttle radar topography

The NASA Shuttle Radar Topography Mission (SRTM) obtained elevation data on a near-global scale 

to generate the most complete high-resolution digital topographic database of Earth. SRTM consisted of a 

specially modified radar system that flew onboard the Space Shuttle Endeavour during an 11-day mission in

February of 2000. Data from this mission have been processed into 1 degree × 1 degree tiles that have been 

edited to define the coastline, and are available from the USGS Seamless web site (http://seamless.usgs.gov/). 

The data have not been processed to bare earth, but meet the absolute horizontal and vertical accuracies of 

20 and 16 meters, respectively.

For U.S. regions, the data have a 1 arc-second spacing and are referenced to the WGS84/EGM96 Geoid. 

While providing mostly complete coverage of the Aleutian Islands in the vicinity of Dutch Harbor, there are 

numerous small areas with “no data” values (e.g., Fig. 12) that were filled with NED topographic data (see

Table 11). The SRTM DEMs also contain “zero” values over the open ocean, which had to be excised prior

to gridding.

Figure 12. Example of gaps in SRTM data coverage. Numerous gaps (white areas) exist over land areas in the SRTM 

DEMs, which also include “zero” values (blue) over water that had to be excised. Gaps were filled with data from the NED 

DEM. Combined coastline in red; NOS soundings (green dots) from survey H06510.

. The SRTM data sets result from a collaborative effort by the National Aeronautics and Space Administration (NASA) and the National Geospatial-Intelligence Agency (NGA – previously known as the National Imagery and Mapping Agency, or NIMA), as well as the participation of the 

German and Italian space agencies, to generate a near-global digital elevation model (DEM) of the Earth using radar interferometry. The SRTM 

instrument consisted of the Spaceborne Imaging Radar-C (SIR-C) hardware set modified with a Space Station-derived mast and additional antennae

to form an interferometer with a 60 meter long baseline. A description of the SRTM mission can be found in Farr and Kobrick (2000). Synthetic 

aperture radars are side-looking instruments and acquire data along continuous swaths. The SRTM swaths extended from about 30 degrees off-nadir 

to about 58 degrees off-nadir from an altitude of 233 km, and thus were about 225 km wide. During the data flight the instrument was operated at

all times the orbiter was over land and about 1000 individual swaths were acquired over the ten days of mapping operations. Length of the acquired 

swaths range from a few hundred to several thousand km. Each individual data acquisition is referred to as a “data take.” SRTM was the primary

(and pretty much only) payload on the STS-99 mission of the Space Shuttle Endeavour, which launched February 11, 2000 and flew for 11 days.

Following several hours for instrument deployment, activation and checkout, systematic interferometric data were collected for 222.4 consecutive 

hours. The instrument operated almost flawlessly and imaged 99.96% of the targeted landmass at least one time, 94.59% at least twice and about

50% at least three or more times. The goal was to image each terrain segment at least twice from different angles (on ascending, or north-going, 

and descending orbit passes) to fill in areas shadowed from the radar beam by terrain. This ‘targeted landmass’ consisted of all land between 56

degrees south and 60 degrees north latitude, which comprises almost exactly 80% of Earth’s total landmass. [Extracted from SRTM online documentation]
15

DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

3) OCS electronic navigational charts

Electronic navigational charts (ENCs; Table 3) were downloaded from NOAA’s Office of Coast Survey

(OSC) website (http://chartmaker.ncd.noaa.gov/). The chart data includes land elevations for local topographic 

highs (in MHW vertical datum, feet; Fig. 13), which were compared with the other topographic datasets and 

Google Earth satellite imagery. As these points represent surveyed values taken from USGS topographic 

quadrangles, they are considered to have greater accuracy than the NED and SRTM data (see Table 11). 

Numerous coastal rocks and small islands on the non-digital NOAA nautical charts (Table 4) that also have 

land elevations were digitized by NGDC for inclusion in the Dutch Harbor DEM (Table 9; Fig. 13).

Figure 13. Land elevation points extracted from ENCs and digitized from NOAA nautical charts. 

Points manually digitized by NGDC (yellow) are listed in Table 9.
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Taylor et al., 2008

Table 9. Topographic features digitized from published NOAA nautical charts in the Dutch Harbor, Alaska region.

Nautical Chart # Feature Longitude Latitude Elevation (m above MHW)

16521 unnamed -166.56 53.60 1.219200

16522 unnamed -166.45 53.63 4.572000

16522 unnamed -166.18 53.73 2.133600

16522 unnamed -166.17 53.74 13.71600

16522 unnamed -166.15 53.77 8.839200

16522 unnamed -166.12 53.77 1.828800

16522 Inner Signal -166.09 53.79 38.4

16522 Outer Signal -166.05 53.80 9.1

16522 Outer Signal -166.04 53.80 3

16522 unnamed -166.09 53.84 23.77440

16522 unnamed -166.05 53.86 47.853600

16522 unnamed -166.12 53.86 38.100000

16522 Round Island -166.39 53.77 41.452800

16522 unnamed -166.35 53.86 1.8288000

16528 unnamed -166.29 53.87 12.192000

16528 unnamed -166.22 53.90 15.849600

16528 unnamed -166.21 53.91 15.240000

16528 unnamed -166.21 53.92 25.908000

16528 unnamed -166.20 53.90 6.7056000

16528 unnamed -166.23 53.94 4.572000

16528 unnamed -166.15 53.95 3.962400

16528 unnamed -166.18 53.96 30.48000

16528 unnamed -166.19 53.96 1.219200

16528 unnamed -166.20 53.97 2.438400

16528 unnamed -166.20 53.98 7.924800

16528 unnamed -166.19 53.99 5.181600

16528 unnamed -166.17 53.99 5.486400

16528 unnamed -166.18 54.00 12.192000

16528 unnamed -166.18 54.00 32.308800

16528 unnamed -166.25 53.93 2.133600

16528 unnamed -166.25 53.94 0.609600

16528 unnamed -166.28 53.98 20.421600

16528 unnamed -166.31 53.97 31.089600

16528 unnamed -166.36 53.98 13.716000

16528 Priest Rock -166.38 54.01 62.179200

16528 Princess Head -166.41 53.98 65.227200

16528 Second Priest Rock -166.47 53.90 22.860000

16528 Needle Rock -166.53 53.92 20.421600

16528 unnamed -166.59 53.96 27.432000

16528 unnamed -166.62 54.00 6.096000

16528 unnamed -166.65 54.01 16.764000

16530 unnamed -166.60 53.83 6.096

16530 unnamed -166.60 53.83 7.62

16530 unnamed -166.61 53.84 35.3568

16530 unnamed -166.60 53.84 20.726400

16530 unnamed -166.60 53.84 19.202400
17

DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

3.2 Establishing Common Datums

3.2.1 Vertical datum transformations

Datasets used in the compilation and evaluation of the Dutch Harbor DEM were originally referenced to a 

number of vertical datums including: Mean Lower Low Water (MLLW), Mean Sea Level (MSL), WGS84/EGM96 

Geoid, and North American Vertical Datum of 1929 (NGVD29). All datasets were transformed to MHW to provide 

the worst case scenario for inundation modeling. 

1) Bathymetric data

The NOS survey data were transformed from MLLW to MHW (see Table 10) using FME. Multibeam 

data were inferred to be relative to MSL and were also transformed using FME (see Section 3.3.3).

2) Topographic data

The NED and SRTM DEMs were originally in NGVD29 and WGS84/EGM96 Geoid vertical datums, 

respectively. There are no survey markers anywhere in the vicinity of Dutch Harbor that relate these two 

geodetic datums to the local tidal datums. Thus, it was assumed out of necessity that both datums are essentially 

equivalent to MSL in this area (Table 10). Conversion to MHW, using FME software, was accomplished by 

adding a constant value of -0.376 meters. Land elevations taken from the ENCs and NOAA nautical charts 

were already referenced to MHW.

Table 10. Relationship between Mean High Water and other vertical datums in the Dutch Harbor region.*3

Vertical datum Difference to MHW

MTL -0.364

MSL -0.376

NGVD29+ -0.376

WGS84 Geoid+ -0.376

MLW -0.728

MLLW -1.011

* Datum relationships determined by tidal station at Dutch Harbor, Alaska.

+ Assumed to be equivalent to MSL.

3.2.2 Horizontal datum transformations

Datasets used to compile the Dutch Harbor DEM were originally referenced to Unalaska, NAD27, NAD83, 

and WGS84 horizontal datums. The relationships and transformational equations between these horizontal datums 

are well established, with the exception of the Unalaska datum. The transformation from the early Unalaska datum 

to NAD83 was computed by Dave Doyle, National Geodetic Survey (see Appendix A). All data were converted to a 

horizontal datum of WGS84 using FME software. 

3. The Dutch Harbor, Aleutian Islands region of Alaska has anomalous relative sea-level trends compared to most other geographic regions in the 

United States. This is due to a general uplift of the land in the area, which has been occurring at a rapid rate. Because of the magnitude of the sea 

level trends in these areas, NOAA has adopted a procedure for computing accepted tidal datums for the National Water Observation Network (NWLON) using the last several years of sea level data rather than the 19-year tidal epoch. The tide ranges are still based on the 1983–2001. National 

Tidal Datum Epoch (NTDE) and are applied to the five year (1997–2001) Mean Tide Level (MTL) to compute other tidal datums. The adoption

of this procedure was necessary to ensure that these tidal datums accurately represent the existing stand of sea level. [Extracted from NGS bench 

mark sheet #9462620]
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Taylor et al., 2008

3.3 Digital Elevation Model Development

3.3.1 Verifying consistency between datasets

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

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

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

gridding. Problems included:

•	 Data values over the open ocean in the NED and SRTM topographic DEMs. Each dataset required automated 

clipping of the erroneous values and visual inspection and comparison of remaining offshore values with the 

combined coastline, NOAA nautical charts and Google Earth satellite imagery to determine their reliability.

•	 Offsets between various incomplete coastline datasets. Data from multiple sources were required to build the 

most accurate coastline.

•	 Multiple near-shore rocks and islands did not exist in any dataset and had to be manually digitized for 

inclusion in the DEM.

3.3.2 Smoothing of sparse NOS data

The NOS hydrographic surveys are generally sparse at the resolution of the 1 arc-second (30 meter) grid: in 

deep water, the NOS survey data had point spacings up to 5 kilometers 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 3 arc-second-spacing (~90 meter) ‘pre-surface’ or grid was generated using GMT, an NSF-funded 

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

The NOS point data were first combined into a single file, along with points extracted every 90 meters from

the combined coastline—to provide a “zero” buffer along the entire coastline. These point data were then smoothed

using the GMT tool ‘blockmedian’ onto a 3 arc-second grid 0.05 degrees (~5%) larger than the Dutch Harbor grid 

region. The GMT tool ‘surface’ then applied a tight spline tension to interpolate cells without data values; ‘surface’ 

does not support a data hierarchy (see Section 3.3.4). The GMT grid created by ‘surface’ was converted into an Arc 

ASCII grid file using the MB-System tool ‘mbm_grd2arc’. Conversion of this Arc ASCII grid file into an Arc raster

permitted clipping of the grid by the combined-coastline polygon (to eliminate data interpolation into land areas). 

The resulting surface was compared with the original soundings to ensure grid accuracy (e.g., Fig. 14), converted to a 

shape file, and then exported as an xyz file for use in the final gridding process.

Figure 14. Histogram of the difference between NOS soundings for survey H06234 (relatively dense survey on northwest 

flank of Unalaska Island) and the NOS pre-surface grid. The greatest differences derive from the averaging of multiple, 

closely-spaced soundings in shallow areas with highly variable relief.
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DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

One interesting type of anomaly in the pre-surfaced NOS grid is isolated pits and peaks along the flanks

of the islands. The NOS grid is consistent with the original soundings taken from the NOS hydrographic surveys, 

however, the surveys simply do not have enough resolution to capture detailed submarine relief. The coastal zone of 

the Aleutian Chain is known to have rugged topography that is hazardous to navigation, and it is expected that such 

relief continues into the deeper water. Figure 15 illustrates how the sparseness of the NOS soundings fails to define

what is probably a submarine canyon on the northwest flank of Unalaska Island—as the movement of sediment at the

coast would rapidly fill any near-shore pits. It is doubtful that any computerized gridding algorithm could faithfully

represent linear features such as submarine canyons from sparse point data. Thus, the pre-surfaced NOS grid, and the 

resulting Dutch Harbor DEM contain assorted pits and peaks (1-dimensional features) that are more likely parts of 

poorly resolved two-dimensional features, but nevertheless are consistent with available bathymetric data. Higherresolution near-shore bathymetric surveys are necessary to accurately characterize these 2-D features and ensure their 

representation in future DEMs.

Figure 15. Failure of sparse NOS hydrographic soundings to capture rugged seafloor relief. Left panel shows pits (light blue, arrows) in the presurfaced NOS grid along what is likely a submarine canyon on the northwest flank of Unalaksa Island. Right panel is corresponding image taken 

from NOS smooth sheet for survey H06233. A hint of the canyon is identifiable in the corresponding soundings (arrows), and in the hand-drawn 

bathymetric contours, however, GMT is incapable of accurately representing this feature with the sparse NOS soundings available. Soundings in 

right panel are in fathoms referenced to MLLW. Note registration marks for both Unalaska (black lines) and NAD27 (red lines).

3.3.3 Pre-gridding of multibeam swath sonar data

The multibeam swath sonar data, inferred to be in MSL vertical datum, were pre-gridded using the MBSystem tool ‘mbgrid’. MB-System (http://www.ldeo.columbia.edu/res/pi/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. This pre-gridding was necessary to permit vertical datum shift to 

MHW, a function that is not supported in MB-System. Data were pre-gridded to 1 arc-second cell-size (~30 meters) 

then exported to ArcGIS using the MB-System tool ‘mbm_grd2arc’. The resulting Arc ASCII file was converted to an

Arc raster in ArcCatalog, then converted again to an ESRI shape file and shifted to MHW using FME. The resulting

point data were consistent with overlapping NOS hydrographic soundings, though providing significantly greater

seafloor resolution.
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Taylor et al., 2008

3.3.4 Gridding the data with MB-System

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

The MB-System tool ‘mbgrid’ was used to create the Dutch Harbor DEM—a modeled surface draping the point 

data—of weighted sounding and topographic point data, using a tight spline tension to interpolate cells without data 

values. The data hierarchy used in the ‘mbgrid’ gridding algorithm as relative gridding weights is listed in Table 11. 

Greatest weight was given to the surveyed land elevation points extracted from the ENCs and digitized by NGDC 

from NOAA nautical charts. Least weight was given to the pre-surfaced NOS grid.

Table 11. Data hierarchy used to assign gridding weight in MB-System.

Dataset Relative Gridding Weight

ENC land elevation points 100

NASA SRTM topographic DEM 10

USGS NED topographic DEM 1

Combined coastline 10

Multibeam swath sonar bathymetry grid 10

NOS hydrographic surveys: soundings 1

NOS hydrographic surveys: gridded 0.01

3.4 Quality Assessment of the DEM

3.4.1. Horizontal accuracy

The digital elevation model has an estimated horizontal accuracy of no better than 30 meters for topographic 

features. Bathymetric features are resolved only to within a few tens to a few hundred meters in deep-water areas; 

shallow, near-coastal regions have an accuracy approaching the subaerial topographic features. Bathymetric positional 

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

navigated (GPS) hydrographic surveys.

3.4.2 Vertical accuracy

The Dutch Harbor DEM has an estimated vertical accuracy of between 10 and 15 meters for topographic 

areas, and 0.3 meters to 5% of water depth for bathymetric areas, depending upon source dataset. Topographic values 

are derived from the USGS NED DEM, which have an estimated vertical accuracy between 7 and 15 meters, and the 

SRTM DEM, which have a vertical accuracy better than 16 meters but are typically about 10 meters. Bathymetric 

values are derived from a wide range of input data, consisting of single and multibeam sounding measurements from 

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

and 1% of the water depth in 100 m of water. Gridding interpolation to determine bathymetric values between sparse, 

poorly located NOS soundings degrades the vertical accuracy of elevations in deep water. 
21

DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

3.4.3 Slope maps and 3-D perspectives

ESRI ArcCatalog was used to generate a slope grid from the Dutch Harbor DEM to allow for visual inspection 

and identification of artificial slopes along boundaries between datasets (Fig. 16). The DEM was transformed to UTM

Zone 3 coordinates (horizontal units in meters) in ArcCatalog for derivation of the slope grid; equivalent horizontal 

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

(e.g., Fig. 17) was accomplished using ESRI ArcScene. Analysis of preliminary grids revealed suspect data points, 

which were corrected before regridding the data. Edge effects are visible along the margins of the multibeam swath 

sonar data, where they abut the sparse NOS hydrographic data: this is due to the pre-surfacing of each dataset, but is 

not a significant submarine DEM feature.

Figure 16. Slope map of the 1 arc-second Dutch Harbor DEM. Flat-lying slopes are 

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

Figure 17. Perspective view from the northeast of the Dutch Harbor DEM. Combined 

coastline in red; vertical exaggeration–times 5.
22

Taylor et al., 2008

3.4.4	 Comparison with source data files

To ensure grid accuracy, the Dutch Harbor DEM was compared to select source data files. Files were chosen

on the basis of their contribution to the grid-cell values in their coverage areas, i.e., had the greatest weight and did not 

overlap other data files with comparable weight. A histogram of the comparison of the multibeam swath bathymetry

data with the Dutch Harbor DEM is shown in Fig. 18. 

Figure 18. Histogram of the difference between the multibeam swath bathymetry data and the Dutch Harbor DEM.

3.4.5 Comparison with NOAA tidal stations

The National Geodetic Survey (NGS) data sheets for U.S. tidal stations (http://tidesandcurrents.noaa.gov/) 

document benchmark elevations, in meters above MHW, allowing for direct comparison with DEM values at those 

locations. There is only one tidal station lying within the Dutch Harbor study area, which was compared with the value 

taken at the same locale from the 1 arc-second (~30 meter) Dutch Harbor DEM (see Fig. 1 and Table 12 for station 

location). The station has multiple benchmark stampings, all of which have the same geographic position, recorded 

to within 6 arc-seconds (~180 meters). The description of the location of one of its benchmark stampings, however, 

places it along the fence on the northeast side of the Holy Ascension Russian Orthodox Church in Unalaska. That 

location (53°52′35′′ N, 166°32′14′′ W, taken from the USGS topographic quadrangle: http://www.topozone.com) has a 

DEM value of 1.484 meters, which compares favorably with the bench mark’s elevation of 2.333 meters (Table 12).

Table 12. Comparison of NOAA tidal benchmark elevation, in meters above MHW, with the Dutch Harbor DEM.

Station 

number Station name Year Longitude Latitude Bench mark DEM Difference

9462620 DUTCH HARBOR 1982 166°32′14′′ W 53°52′35′′ N 2.333 1.484 -0.849
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DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

3.4.6 Comparison with USGS topographic elevations

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

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

converted to meters and shifted to MHW vertical datum (see Table 10) for comparison with the Dutch Harbor DEM 

(see Fig. 1 for station locations). Positional accuracy is to within .0002 degrees (~22 meters). Significant differences

exist between the Dutch Harbor DEM and the USGS topo elevations: from -101 to 19 meters, with a negative value 

indicating that the DEM is less than the topo elevation (Fig. 19). Much of the difference results from horizontal 

offsets between the positional information taken from the online quadrangles, and the corresponding feature in the 

DEM. Such offsets range up to 75 meters, though not in any consistent direction. The values of the topo elevations 

and the corresponding DEM feature, typically local highs, are often within about 10 meters. These differences may be 

attributable to the fact that the SRTM and NED topographic data represent averages of land elevations over 30 × 30 

meter, and 60 × 60 meter square areas, respectively, while the topo elevations represent maximum heights.

Figure 19. Histogram of the difference between the USGS topo elevations and the Dutch Harbor DEM. The pronounced 

negative values (DEM less than topo elevations) results partly from horizontal offsets of features, typically local highs, but 

may also result from comparing average elevation over an area with a local maximum.

4. Summary and Conclusions

A topographic/bathymetric digital elevation model with cell spacing of 1 arc-second (~30 meters) of the 

Dutch Harbor, Alaska area was developed for the Pacific Marine Environmental Laboratory (PMEL), NOAA Center

for Tsunami Research. The best available data from U.S. federal and state agencies were obtained for grid compilation. 

The data were quality checked, processed and gridded using ESRI ArcGIS, FME, GMT, and MB-System software. 

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

•	 Conduct bathymetric LiDAR surveys of the near-shore areas within the Dutch Harbor region to accurately 

incorporate tsunami-influencing offshore rocks and shoals.

•	 Obtain digital versions of several NOAA nautical charts (#16522, 16528, 16529, 16530) that have not yet 

been digitized.

•	 Establishment, via survey, of the relationships between tidal and geodetic datums in the Dutch Harbor 

region.

5. Acknowledgments

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

thank Chris Chamberlin, Angie Venturato, and Hal Mofjeld (PMEL), Dave Doyle (National Geodetic Survey), Bret

Christensen (U.S. Fish and Wildlife Service), and David Scharff (NOS).
24

Taylor et al., 2008

6. References

Nautical Chart #16522, 5th Edition, 1992. Unalaska Island—Beaver Inlet. Scale 1:40,000. U.S. Department of 

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #16528, 15th Edition, 1992. Unalaska Bay and Akutan Pass. Scale 1:40,000. U.S. Department of 

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #16529, 14th Edition, 1994. Unalaska Island—Dutch Harbor. Scale 1:10,000. U.S. Department of 

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #16530, 6th Edition, 1996. Unalaska Island—Captains Bay. Scale 1:10,000. U.S. Department of 

Commerce, NOAA, National Ocean Service, Coast Survey.

S.M. Carbotte, R. Arko, D.N. Chayes, W. Haxby, K. Lehnert, S. O’Hara, W.B.F. Ryan, and R.A. Weissel, LamontDoherty Earth Observatory, Palisades,N.Y.; T. Shipley, L.Gahagan, and K. Johnson, University of Texas Institute 

for Geophysics,Austin; and T. Shank, Woods Hole Oceanographic Institution, Mass. New Integrated Data 

Management System for Ridge2000 and MARGINS Research, Eos, Vol. 85, No. 51, 21 December 2004, http://

www.marine-geo.org

U.S. Geological Survey, Alaska topographic quadrangles. Scale 1:63,360. TopoZone, http://www.topozone.com

7. Data Processing Software

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

Electronic Navigational Chart Data Handler for ArcView, developed by NOAA Coastal Services Center, http://www.

csc.noaa.gov/products/enc/

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

http://www.safe.com/

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

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

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

National Science Foundation, http://www.ldeo.columbia.edu/res/pi/MB-System/
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DIGITAL ELEVATION MODEL OF DUTCH HARBOR, ALASKA

Appendix A. Computation of Unalaska to NAD83 horizontal datum shift

Computation of the shift from Unalaska horizontal datum to the North American Datum of 1983 (NAD83) 

was performed by Dave Doyle, National Geodetic Survey (NGS). The National Geophysical Data Center (NGDC) 

supplied NGS with the Unalaska datum position of survey control points taken from multiple National Ocean Service 

(NOS) smooth sheets in the Dutch Harbor region. NGS confirmed the contemporary NAD 83 values for these points

by searching the data maintained in the National Spatial Reference System and extracting the NAD 83 position 

information for 10 of these control points. The average shift over the survey region was determined by subtracting 

the NAD 83 latitudes and longitudes from the Unalaska positions, which yielded a change of -2.191 arc-seconds of 

longitude, and -6.081 arc-seconds of latitude (Table A-1). This average shift was then applied to all NOS hydrographic 

surveys that had been digitized in the Unalaska datum.

Table A-1. Computation of Unalaska to NAD83 horizontal datum shift.

DUTCH HARBOR, AK

UNALASKA DATUM

TO

NORTH AMERICAN DATUM OF 1983 (1986)

Computation by: David Doyle, National Geodetic Survey (July, 2006)

Source Data: Unalaska Datum -- NGS Archive #370-96-0291, Box 6

Source Data: NAD 83 -- National Spatial Reference System

Latitude Shift, UNALASKA DATUM to NAD 83 (1986) (seconds) -6.081

Latitude Shift, UNALASKA DATUM to NAD 83 (1986) (meters) -188.05

Latitude Shift, Standard Deviation (seconds) 0.088

Latitude Shift, Standard Deviation (meters) 2.73

Longitude Shift, UNALASKA DATUM to NAD 83 (1986) (seconds) -2.191

Longitude Shift, UNALASKA DATUM to NAD 83 (1996) (meters) -38.75

Longitude Shift, Standard Deviation (seconds) 0.037

Longitude Shift, Standard Deviation (meters) 0.65

PID STATION NAD 83 D/M NAD 83 S UNAK S Diff S

UV9341 BOLD 1896 53 52 43.15389 49.164 -6.010

166 34 36.03659 38.235 -2.198

UV9132 BRIDGE 1901 53 59 33.31155 39.487 -6.175

166 02 52.61265 54.744 -2.131

UW0110 CEMENT 1901 54 07 18.45465 24.630 -6.175

166 07 2.74326 5.005 -2.262

UV9362 GRASS 1896 53 49 49.95154 55.942 -5.990

166 35 39.22776 41.436 -2.208

UW0117 KALEKLITA 1901 54 00 16.45973 22.540 -6.080

166 22 33.77588 35.954 -2.178

UV9343 OBER 1896 53 51 21.98633 27.987 -6.001

166 33 48.19981 50.393 -2.193

UW0115 TRIPLET 1901 54 02 25.44180 31.638 -6.196

166 03 1.96702 4.150 -2.183

UV9308 UNALASKA SOUTH 

BASE 53 53 51.53100 57.550 -6.019

166 30 53.30916 55.480 -2.171