noaa / NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

National Environmental Satellite,

Data, and Information Service

NOAA Technical Memorandum NESDIS NGDC-31

DIGITAL ELEVATION MODEL OF ADAK, ALASKA:

PROCEDURES, DATA SOURCES AND ANALYSIS 

K.S. Carignan

L.A. Taylor

B.W. Eakins

R.R. Warnken

P.R. Medley

E. Lim

National Geophysical Data Center

Marine Geology and Geophysics Division

Boulder, Colorado

April 2009

UNITED STATES

DEPARTMENT OF COMMERCE

Gary Locke

Secretary

NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

Dr. Jane Lubchenco

Under Secretary for Oceans

and Atmosphere/Administrator

National Environmental Satellite,

Data, and Information Service

Mary E. Kicza

Assistant Administrator

NOAA Technical Memorandum NESDIS NGDC-31

DIGITAL ELEVATION MODEL OF ADAK, ALASKA:

PROCEDURES, DATA SOURCES AND ANALYSIS 

Kelly S. Carignan1 

Lisa A. Taylor2

Barry W. Eakins1

Robin R. Warnken2

Elliot Lim1

Pamela R. Medley1

1Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder

2NOAA, National Geophysical Data Center, Boulder, Colorado

National Geophysical Data Center

Marine Geology and Geophysics Division 

Boulder, Colorado

April 2009
Carignan et al., 2009

ii

NOTICE

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

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

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

or	advertising	purposes	is	not	authorized.	

Corresponding project contact:

Lisa A. Taylor

NOAA National Geophysical Data Center

Marine Geology and Geophysics Division

325 Broadway, E/GC 3

Boulder, Colorado 80305

Phone: 303-497-6767

Fax: 303-497-6513

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

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

Also available from the National Technical Information Service (NTIS)

(http://www.ntis.gov)
Digital Elevation Model of Adak, Alaska

iii

Contents

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

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

3.	 Methodology ......................................................................................................................................4

3.1	 Data Sources and Processing ......................................................................................................5

3.1.1	 Shoreline................................................................................................................6

3.1.2	 Bathymetry ............................................................................................................8

3.1.3	 Topography..........................................................................................................17

3.2	 Establishing Common Datums .................................................................................................21

3.2.1	 Vertical datum transformations ...........................................................................21

3.2.2	 Horizontal datum transformations.......................................................................21

3.3	 Digital Elevation Model Development .....................................................................................22

3.3.1	 Verifying consistency between datasets..............................................................22

3.3.2	 Smoothing of bathymetric data ...........................................................................22

3.3.3	 Gridding the data with MB-System......................................................................23

3.4	 Quality Assessment of the DEM...............................................................................................23

3.4.1	 Horizontal accuracy.............................................................................................23

3.4.2	 Vertical accuracy .................................................................................................23

3.4.3	 Slope maps and 3-D perspectives........................................................................24

3.4.4	 Comparison with source data files.......................................................................25

3.4.5	 Comparison with National Geodetic Survey geodetic monuments.....................26

3.4.6	 Comparison with topographic and bathymetric contours....................................27

4.	 Summary and Conclusions...............................................................................................................28

5.	 Acknowledgments............................................................................................................................28

6.	 References........................................................................................................................................28

7.	 Data Processing Software ................................................................................................................29

List of Figures

Figure 1. 	 Shaded-relief image of the Adak DEM.......................................................................................1

Figure 2.	 Google Earth image of Alaska’s Aleutian Island Chain and the

location of the Adak DEM...................................................................................................2

Figure 3.	 Names and locations of islands within the Adak DEM boundary ..............................................2

Figure 4.	 View of Adak from Bering Hill ..................................................................................................3

Figure 5.	 Source and coverage of datasets used in compiling the Adak DEM ..........................................5

Figure 6.	 Digital coastline datasets used in developing a combined coastline

for the Adak region ..............................................................................................................6

Figure 7.	 Spatial coverage of the bathymetric datasets used in compiling the Adak DEM.......................9

Figure 8.	 Digital NOS hydrographic survey coverage in the Adak region ..............................................12

Figure 9.	 Smooth sheet image of NOS hydrographic survey H06896 with

combined coastline ............................................................................................................12

Figure 10.	 Spatial coverage of the SIO multibeam survey used in compiling the Adak DEM..................13

Figure 11.	 Spatial coverage of NGDC multibeam data available for use in the Adak DEM area .............14

Figure 12.	 Spatial coverage of ENC sounding data used in compiling the Adak DEM ............................15

Figure 13.	 Spatial coverage of ETOPO1 extracted points used in compiling the Adak DEM...................16

Figure 14.	 Spatial coverage of the topographic datasets used in compiling the Adak DEM.....................17

Figure 15.	 Spatial coverage of the SRTM 1 arc-second DEM...................................................................18

Figure 16.	 Location of extracted land elevations in the DEM region ........................................................19

Figure 17.	 Location of areas where NGDC digitized land elevations in the DEM region ........................20

Figure 18.	 Aerial image of Adak from Google Earth.................................................................................20

Figure 19.	 Histogram of the differences between NOS hydrographic survey H08240 and

the 1 arc-second pre-surfaced bathymetric grid.................................................................22

Figure 20.	 Slope map of the Adak DEM....................................................................................................24

Figure 21.	 Perspective view from the northwest of the Adak DEM ..........................................................25
Carignan et al., 2009

iv

Figure 22.	 Histogram of the difference between the SRTM 1 arc-second topographic DEM

and the Adak DEM ............................................................................................................25

Figure 23.	 Location and PID for selected NGS datasheet points near the town of Adak ..........................26

Figure 24.	 Comparison of USGS topographic map to Adak DEM topographic contours ........................27

Figure 25.	 Comparison of NOAA ENC #16475 to Adak DEM bathymetric contours..............................27

List of Tables

Table 1.	 PMEL specifications for the Adak DEM ....................................................................................4

Table 2.	 Shoreline datasets used in the Adak DEM..................................................................................6

Table 3.	 ENCs available in the Adak region.............................................................................................7

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

Table 5.	 Digital NOS hydrographic surveys available within the Adak DEM boundary.......................10

Table 6.	 SIO multibeam sonar survey available in the Adak DEM region.............................................13

Table 7.	 NGDC multibeam sonar surveys available in the Adak DEM region ......................................14

Table 8.	 Topographic datasets used in compiling the Adak DEM..........................................................17

Table 9.	 Relationship between MHW and other vertical datums used in the Adak DEM......................21

Table 10.	 Data hierarchy used to assign gridding weight in MB-System..................................................23

Table 11.	 NGS datasheet NGVD29 heights compared to Adak DEM elevation......................................26
Digital Elevation Model of Adak, Alaska:

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 a bathymetric–topographic digital elevation model (DEM) of Adak (Fig.

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

noaa.gov/). The 1 arc-secondF

1

F 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. 5). It will be used for tsunami

forecasting as part of the tsunami forecast system Short-term Inundation Forecasting for Tsunamis (SIFT) currently

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

sources and methodology used in developing the Adak DEM.

Figure 1. Shaded-relief image of the Adak DEM. Contour interval is 100 meters.

1. The Adak 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 Adak, Alaska (51° 51′ 47.9′′ N, 176° 37′ 55.2′′

W) 1 arc-second of latitude is equivalent to 30.907 meters; 1 arc-second of longitude equals 19.137 meters.
Carignan et al., 2009

2

2. Study Area

Adak, Alaska is located in the Andreanof Islands on the Aleutian Islands Chain of Alaska (Fig. 2). The Adak

DEM encompasses the eastern half of Kanaga Island, Adak Island, Kagalaska Island, Little Tanaga Island, Umak

Island, Great Sitkin Island, and Igitkin Island (Fig. 3). Adak Island was formed from tectonic plate interaction and

resulting volcanic activity. The island consists of a thin sedimentary layer on top of volcanic rock. Tall coastal cliffs

and mountains dominate the landscape with the steep slopes continuing offshore into deep water canyons.

Figure 2. Google Earth image of Alaska’s Aleutian Island Chain and the location of the Adak DEM, as shown in the red box.

Figure 3. Names and locations of islands within the Adak DEM boundary.
Digital Elevation Model of Adak, Alaska

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The southernmost town in Alaska, Adak (Fig. 4) is located 350 miles west of Dutch Harbor, Alaska and has

a population of less than 400. Adak served as a military base from the onset of World War II until the late 1990s. The

current economy is based on the fishing and hunting industry and support for U.S. and foreign fishing fleets. A portion

of the island lies within the National Maritime National Wildlife Refuge, managed by U.S. Fish and Wildlife Service.

Copyright 1986 Kevin Butler

Figure 4. View of Adak from Bering Hill. Photo courtesy of Alaska Department of Commerce, Community, and Economic Development, Division 

of Community & Regional Affairs, Community Photo Library (http://www.commerce.state.ak.us/dca/photos/comm_list.cfm).
Carignan et al., 2009

4

3. Methodology

	 The Adak 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 of 1983 (NAD 83) and mean high water (MHW), for modeling of maximum flooding,

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

subsections.

Table 1: PMEL specifications for the Adak DEM.

Grid Area Adak, Alaska

Coverage Area 175.78o to 177.24o W; 51.25o to 52.16o N

Coordinate System Geographic decimal degrees

Horizontal Datum World Geodetic System of 1984 (WGS 84)

Vertical Datum MHW

Vertical Units Meters

Cell Size 1 arc-second

Grid Format ESRI Arc ASCII grid

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.
Digital Elevation Model of Adak, Alaska

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3.1 Data Sources and Processing

Shoreline, bathymetric, and topographic digital datasets (Fig. 5) were obtained from several U.S. federal

agencies and academic institutions including: NOAA Office of Coast Survey (OCS) and NGDC; the U.S. Fish and

Wildlife Service (USFWS); the U.S. Geological Survey (USGS); and the University of California, Scripps Institute

of Oceanography (SIO). Safe Software’s FME data translation tool package was used to shift datasets to NAD 83

horizontal datum and to convert them into ESRI ArcGIS shapefiles3. The shapefiles were then displayed with ArcGIS

to assess data quality and manually edit datasets. Vertical datum transformations to MHW were accomplished using

FME, based upon data from the NOAAAdak tide station (http://tidesandcurrents.noaa.gov/). Applied Imagery’s Quick 

Terrain Modeler software was used to evaluate processing and gridding techniques.

Figure 5. Source and coverage of datasets used in compiling the Adak DEM.

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

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

83 datum transformations.
Carignan et al., 2009

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3.1.1 Shoreline

Coastline datasets of the Adak region were obtained from OCS and USFWS (Table 2; Fig. 6). NOAA

Electronic Navigational Charts (ENCs)4 and the USFWS coastline were used to develop a “combined coastline” for

the Adak DEM.

Table 2: Shoreline datasets used in the Adak DEM.

Source Year Data Type Spatial 

Resolution

Original Horizontal 

Datum/Coordinate 

System

Original 

Vertical 

Datum

URL

NOAA

ENCs

1990 to

2000

Digital

nautical

charts

Various WGS 84 geographic MHW http://nauticalcharts.noaa.gov/mcd/enc/

USFWS 2006 Compiled

coastline Various WGS 84 geographic Unknown

Figure 6. Digital coastline datasets used in developing a “combined coastline” of the Adak region.

4. The Office of Coast Survey (OCS) produces NOAA Electronic Navigational Charts (NOAA ENC®) to support the marine transportation

infrastructure and coastal management. NOAA ENC®s are in the International Hydrographic Office (IHO) S-57 international exchange format,

comply with the IHO ENC Product Specification and are provided with incremental updates, which supply Notice to Mariners corrections and

other critical changes. NOAA ENC®s are available for free download on the OCS web site. [Extracted from NOAA OCS web site: http://nauticalcharts.noaa.gov/mcd/enc/]
Digital Elevation Model of Adak, Alaska

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1) NOAA Electronic Navigational Charts

Seven ENCs were available for theAdak area (Table 3) and downloaded from OCS (http://nauticalcharts.

noaa.gov/mcd/enc/). The ENCs are in S-57 format and include coastline data files referenced to MHW. The

extracted coastlines were merged using ArcGIS and used in the combined coastline for the Adak DEM.

Table 3: ENCs available in the Adak region.

Chart # Title Edition Year of Source data Issue Date Scale

16012 Aleutian Islands, Amukta Island to Attu Island 5 1991 2008 1,126,321

16467 Adak Island to Tanaga Island 2 1994 2005 1:100,000

16471 Atka Pass to Adak Strait 3 2000 2007 1:120,000

16474 Bay of Islands, Adak Island 2 1990 2007 1:12,000

16475 Kuluk Bay and Approaches, Little Tanaga and

Kagalaska Straits 3 1998 2008 1:50,000

16476 Adak Island Sweeper Cove Finger and Scabbard

Bays 3 1997 2008 1:10,000

16478 Tagalak Island to Great Sitkin Island 2 1991 2007 1:30,000

2) U.S. Fish and Wildlife Service coastline

USFWS 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, USFWS, National Geographic

Topo Software, U.S. Army Corps of Engineers, and Alaska Department of Natural Resources. This dataset

was graciously provided to NGDC by Bret Christensen, USFWS. Though efforts were made to obtain the

highest resolution coastlines available, vertical datums were apparently not determined nor controlled in any

way in compiling the USFWS coastline; horizontal datum of the compiled USFWS coastline is WGS 84.

The combined coastline was compared to the topographic datasets and modified to include large offshore

rocks and small islets shown on NOAA Raster Navigational Charts (RNCs). The jetty at Adak was also added to the

coastline. An xyz file of the combined coastline was generated using GEODAS for use in compiling the Adak DEM.
Carignan et al., 2009

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3.1.2 Bathymetry

Bathymetric datasets available for use in the compilation of the Adak DEM included 63 NOS hydrographic

surveys; two multibeam surveys downloaded from the NGDC Multibeam Bathymetry Database; one SIO multibeam

survey; soundings extracted from NOAA ENCs; and data points extracted from ETOPO1 (Table 4; Fig. 7). Datasets

were originally referenced to mean lower low water (MLLW) or mean sea level (MSL).

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

Source Year Data Type Spatial Resolution

Original 

Horizontal Datum/

Coordinate System

Original 

Vertical 

Datum

URL

NGDC 1933 to

2005

NOS

hydrographic

survey

soundings

Ranges from 1 meter to

1 kilometer (varies with

scale of survey, depth,

traffic, and probability of

obstructions)

Early Alaska or

NAD 83 geographic MLLW http://www.ngdc.noaa.gov/mgg/bathymetry/hydro.html

SIO 2004 Multibeam

swath sonar WGS 84 geographic AssumedMSL

NGDC 1989 to

1998

Multibeam

swath sonar 5 meters WGS 84 geographic AssumedMSL

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

bathymetry/multibeam.html

NOAA

ENCs

1954 to

2000

Extracted

soundings

From several meters to

hundreds of meters WGS 84 geographic MLLW http://nauticalcharts.noaa.gov/mcd/enc/

NGDC

ETOPO1 2008 GlobalRelief Model 1 arc-minute WGS 84 geographic MSL http://www.ngdc.noaa.gov/mgg/bathymetry/relief.html
Digital Elevation Model of Adak, Alaska

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Figure 7. Spatial coverage of the bathymetric datasets used in compiling the Adak DEM.
Carignan et al., 2009

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1) National Ocean Service hydrographic survey data

A total of 63 NOS hydrographic surveys conducted between 1933 and 1988 were available for use in

developing the Adak DEM. The hydrographic surveys were originally vertically referenced to MLLW and

horizontally referenced to either NAD 83 or Early Alaskan Datum. Only 51 of the 63 surveys were used in

building the Adak DEM, as some older surveys have been superseded (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. Surveys were extracted from NGDC’s NOS Hydrographic

Survey Database (http://www.ngdc.noaa.gov/mgg/bathymetry/hydro.html) in NAD 83. The surveys were

subsequently clipped to a polygon 0.05 degree (~5%) larger than the Adak DEM area to support data

interpolation along grid edges.

After converting all NOS survey data to MHW using a constant value based on the NOAA tide station

(see Sec. 3.2.1), the data were displayed in ESRI ArcMap and reviewed for digitizing errors against scanned

original survey smooth sheets and edited as necessary. The surveys were also compared to the topographic

and bathymetric datasets, the combined coastline, and NOAA RNCs. The older surveys were clipped to

remove soundings that have been superseded by more recent NOS surveys and multibeam data.

Some older survey data were offset from the combined coastline by nearly 1 km. These surveys were

manually shifted in ArcGIS to align with the combined coastline. Figure 9 shows a scanned smooth sheet

image overlaid with the combined coastline for survey H06896.

Table 5: Digital NOS hydrographic surveys available within the Adak DEM boundary.

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

H06881* 1933 40,000 MLLW Early Alaska Datums

H06882* 1933 40,000 MLLW Early Alaska Datums

H06883* 1933 10,000 MLLW Early Alaska Datums

H06884* 1933 6,000 MLLW Early Alaska Datums

H06886* 1933 6,000 MLLW Early Alaska Datums

H06888 1933 10,000 MLLW Early Alaska Datums

H06889* 1933 15,000 MLLW Early Alaska Datums

H06890* 1933 15,000 MLLW Early Alaska Datums

H06891 1933 5,000 MLLW Early Alaska Datums

H06892* 1934 30,000 MLLW Early Alaska Datums

H06893 1934 15,000 MLLW Early Alaska Datums

H06894* 1934 15,000 MLLW Early Alaska Datums

H06895 1934 15,000 MLLW Early Alaska Datums

H06896* 1934 15,000 MLLW Early Alaska Datums

H06897 1934 30,000 MLLW Early Alaska Datums

H06898* 1934 60,000 MLLW Early Alaska Datums

H06899* 1934 60,000 MLLW Early Alaska Datums

H06920 1943 10,000 MLLW Early Alaska Datums

H06971 1943 4,800 MLLW Early Alaska Datums

H06778* 1943 120,000 MLLW Early Alaska Datums

H06921* 1943 2,400 MLLW Early Alaska Datums

H06913 1943 20,000 MLLW Early Alaska Datums

H06915 1943 5,000 MLLW Early Alaska Datums

H06916 1943 4,800 MLLW Early Alaska Datums

H06917 1943 10,000 MLLW Early Alaska Datums

H06918 1943 20,000 MLLW Early Alaska Datums

H06919* 1943 20,000 MLLW Early Alaska Datums

H06924 1943 5,000 MLLW Early Alaska Datums

H06910 1943/44 10,000 MLLW Early Alaska Datums

H07079 1944/55 10,000 MLLW Early Alaska Datums
Digital Elevation Model of Adak, Alaska

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

H07084 1945 5,000 MLLW Early Alaska Datums

H07049 1945 160,000 MLLW Early Alaska Datums

H07078 1945/46 10,000 MLLW Early Alaska Datums

H07182 1946 20,000 MLLW Early Alaska Datums

H07183 1946 20,000 MLLW Early Alaska Datums

H07605 1946 30,000 MLLW Early Alaska Datums

H07825 1951 2,500 MLLW Early Alaska Datums

H08055 1953 20,000 MLLW Early Alaska Datums

H08056 1953 60,000 MLLW Early Alaska Datums

H08070 1953 10,000 MLLW Early Alaska Datums

H08057 1954 60,000 MLLW Early Alaska Datums

H08139 1954 40,000 MLLW Early Alaska Datums

H08140 1954 40,000 MLLW Early Alaska Datums

H08142 1954 20,000 MLLW Early Alaska Datums

H08143 1954 20,000 MLLW Early Alaska Datums

H08145 1954 20,000 MLLW Early Alaska Datums

H08146 1954 20,000 MLLW Early Alaska Datums

H08147 1954 10,000 MLLW Early Alaska Datums

H08144 1955 20,000 MLLW Early Alaska Datums

H08233 1955 40,000 MLLW Early Alaska Datums

H08234 1955 40,000 MLLW Early Alaska Datums

H08235 1955 40,000 MLLW Early Alaska Datums

H08236 1955 20,000 MLLW Early Alaska Datums

H08237 1955 20,000 MLLW Early Alaska Datums

H08238 1955 20,000 MLLW Early Alaska Datums

H08239 1955 20,000 MLLW Early Alaska Datums

H08240 1955 25,000 MLLW Early Alaska Datums

H08306 1956 20,000 MLLW Early Alaska Datums

H08307 1956 20,000 MLLW Early Alaska Datums

H08309 1956 60,000 MLLW Early Alaska Datums

H08071 1956 10,000 MLLW Early Alaska Datums

H08454 1958 480 MLLW Early Alaska Datums

H10282 1988 5,000 MLLW NAD 83

* superseded survey not used in building the Adak DEM
Carignan et al., 2009

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Figure 8. Digital NOS hydrographic survey coverage in the Adak region. Some older surveys were not used as they have been 

superseded by more recent surveys. DEM boundary in red.

Figure 9. Smooth sheet image of NOS hydrographic survey H06896 with the combined coastline shown in red. Differences between smooth sheet 

coastline in gray and combined coastline are up to one kilometer, marked by green arrows. This survey was not used in compiling the Adak DEM.
Digital Elevation Model of Adak, Alaska

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2) University of California, Scripps Institute of Oceanography multibeam swath sonar survey

A 2004 multibeam swath sonar survey was provided to NGDC by SIO (Table 6). The survey is located

in the southwest corner of the DEM boundary (Fig. 10). The data were gridded using MB-System into smaller

sections and converted to point shapefile format, then transformed from MSL to MHW. The shapefile was

displayed in ArcMap and edited removing spikes and anomalous values. The edited shapefile was converted

to an xyz file for use in the final gridding process.

Table 6: SIO multibeam sonar survey available in the Adak DEM region.

Survey ID Year Original Vertical Datum Institute Ship

KRUS03RR leg 2 2004 Assumed MSL SIO Roger Revelle

Figure 10. Spatial coverage of the SIO multibeam swath sonar survey used in compiling the Adak DEM.
Carignan et al., 2009

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3) NGDC multibeam swath sonar surveys

Two multibeam swath sonar surveys were downloaded from the NGDC Multibeam Bathymetry

Database (http://www.ngdc.noaa.gov/mgg/bathymetry/multibeam.html; Table 7). Both surveys are located

in approximately the same area in the northwest corner of the DEM boundary (Fig. 11). The survey data were

gridded using MB-System into smaller sections and converted to shapefile format, transformed from MSL to

MHW, and clipped to the more recent SIO survey leaving a small portion of the Thomas Washington survey

to be used in the final gridding process.

Table 7: NGDC multibeam sonar surveys available in the Adak DEM region.

Survey ID Year Original Vertical Datum Institute Ship

PPTU11WT 1986 Assumed MSL SIO Thomas Washington

FOCI93 1993 Assumed MSL NOAA Surveyor

Figure 11. Spatial coverage of NGDC multibeam bathymetric data available for use in the Adak DEM area.
Digital Elevation Model of Adak, Alaska

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4) NOAA Electronic Navigational Chart soundings

In areas with little or no NOS data coverage, bathymetric soundings were extracted from the

ENC datasets and converted to MHW using FME (Fig. 12). Soundings from ENC #16478 were used

around Greater Sitkin Island to replace NOS survey H06896 which was not completely digitized.

The ENC data were converted to shapefiles and displayed in ArcMap to compare to the RNCs and

multibeambathymetric data.Extracted pointsthat do notreflect actual depth values, e.g.,wrecks, were removed

from the dataset before clipping to the SIO multibeam swath sonar survey and the most recent NOS surveys.

Figure 12. Spatial coverage of ENC sounding data used in compiling the Adak DEM.
Carignan et al., 2009

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5) ETOPO1 Global Relief Model

A portion of the 1 arc-minute (~2 kilometer cell size) ETOPO1 Global Relief Model was extracted

using NGDC’s GEODAS grid translator “Design-a-Grid” tool (http://www.ngdc.noaa.gov/mgg/gdas/gd_

designagrid.html?dbase=grdet1). ETOPO1 is an integrated bathymetric–topographic grid, however only the

bathymetric values were used in creating a bathymetric surface. Figure 13 shows the bathymetric portion of

the ETOPO1 grid that was used in building the Adak DEM. FME was used to convert the grid to MHW and

transform it to a pointshapefile. It wasthen edited to retain pointsin areas without direct depth measurements.

Figure 13. Spatial coverage of ETOPO1 extracted points used in compiling the Adak DEM.
Digital Elevation Model of Adak, Alaska

17

3.1.3 Topography

Two topographic datasets in the Adak region were obtained from USGS and OCS and used to build the Adak

DEM (Table 8; Fig. 14). NGDC evaluated but did not use the National Elevation Dataset (NED) 2 arc-second DEM

available from USGS. NGDC digitized additional elevation points to supplement the available datasets on Adak and

Umak Islands.

Table 8: Topographic datasets used in compiling the Adak DEM.

Source Year Data Type Spatial

Resolution

Original Horizontal 

Datum/Coordinate 

System

Original 

Vertical 

Datum

URL

NASA

SRTM 2000 Globaltopography 1 arc-second WGS 84 geographic AssumedMSL http://seamless.usgs.gov/

NOAA

ENCs

1990 to

2000

Extracted

elevation points Varies WGS 84 geographic MHW http://nauticalcharts.noaa.gov/mcd/enc/

NGDC Digitized

elevation points < 10 meters WGS 84 geographic

Figure 14. Spatial coverage of the topographic datasets used in compiling the Adak DEM.
Carignan et al., 2009

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1) NASA Shuttle Radar Topography Mission

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 Earth5. The SRTM consisted of

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

in February, 2000. Data from this mission have been processed into 1 degree × 1 degree tiles and edited

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

raster DEMs. 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 1 arc-second spacing and are referenced to the WGS 84/EGM96 Geoid.

While providing near complete coverage of the Aleutian Islands in the vicinity of Adak, there are numerous

small areas with “no data” values (Fig. 15). The SRTM DEM also contains values over the open ocean, which

were deleted by clipping to the final coastline.

Points extracted from the NED 2 arc-second DEM were tested to fill holes in the SRTM data. However,

analysis of the resulting gridded topography showed discrepancies in the data values creating uneven

transitions between datasets. Leaving the holes unfilled created a smoother surface.

5. 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]

Figure 15. Spatial coverage of the SRTM 1 arc-second DEM, shown in gray. No data areas are shown in purple. 

Open ocean values shown in light blue.
Digital Elevation Model of Adak, Alaska

19

2) NOAA Electronic Navigational Chart land elevation points

Many of the offshore rocks and islets were not fully resolved in the digital topographic elevation datasets.

To include these features in the Adak DEM, land elevation points were extracted from ENCs #16471, 16474,

16475, 16476, and 16478 (Fig. 16). ENC land elevation data are referenced to MHW and WGS 84.

Figure 16. Location of ENC extracted land elevations shown as green dots in the DEM region.
Carignan et al., 2009

20

3) NGDC digitized elevation points

NGDC added digitized elevation points to three areas where there are significant holes in the SRTM

data (Fig. 17). Points were digitized along contour lines from USGS topographic maps. In the town of Adak,

the airport runways were more accurately resolved using a constant elevation of 3 meters within the airstrip

boundary shown in Figure 18. Elevation points of 1 meter were added to the jetty at Sweeper Cove to ensure

positive values in the final grid, as SRTM topography did not fully resolve this feature.

Figure 17. Location of areas where NGDC digitized land elevations, shown as orange boxes, in the DEM region.

Figure 18. Aerial image of Adak from 

Google Earth. Elevation points were 

added to resolve the airstrip and the 

eastern jetty.
Digital Elevation Model of Adak, Alaska

21

3.2 Establishing Common Datums

3.2.1 Vertical datum transformations

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

of vertical datums including MLLW, MSL, and WGS 84/EGM96 Geoid. All datasets were transformed to MHW to

provide the “worst-case scenario” for inundation modeling.

1) Bathymetric data

The NOS hydrographic surveys, NGDC multibeam swath sonar surveys, and the SIO multibeam swath

sonar survey were transformed from MLLW and MSL to MHW, using a constant based on the tide station

on Adak Island.

2) Topographic data

The USGS SRTM 1 arc-second DEM was originally referenced to WGS 84/EGM96 Geoid vertical

datum. There are no survey markers in the vicinity of Adak that relate this geodetic datum to the local tidal

datums. Thus, it was assumed that this datum is essentially equivalent to MSL in this area. Conversion to

MHW, using ArcCatalog tools, was accomplished by adding a constant offset of -0.406 meters (Table 9), the

difference between MSL and MHW at the Adak Island tide station (#9461380).

Table 9. Relationship between MHW and other vertical datums used in the Adak DEM.

MSL to MHW -0.406 meters

MLLW to MHW -1.055 meters

3.2.2 Horizontal datum transformations

Datasets used in compiling the Adak DEM were originally referenced to NAD 83 geographic, and WGS 84

geographic horizontal datums. Some NOS surveys were manually shifted in ArcGIS to fit the combined coastline.
Carignan et al., 2009

22

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:

•	 Gaps in SRTM topographic DEM.

•	 Data values over the ocean and rivers in the SRTM topographic dataset. The SRTM dataset required

automated clipping to the combined coastline.

•	 Digital, measured bathymetric values from NOS surveys date back over 70 years. More recent data, such

as the multibeam swath sonar surveys, differed from older NOS data by as much as 100 meters vertically.

The older NOS survey data were excised where more recent bathymetric data exists.

•	 Some digital NOS survey data did not align with the combined coastline and were manually shifted in

ArcGIS.

3.3.2 Smoothing of bathymetric data

The older NOS hydrographic survey data are generally sparse at the resolution of 1 arc-second in both deep

water and in some areas close to shore. In order to reduce the effect of artifacts in the form of lines of “pimples” in the

DEM due to this low resolution dataset, and to provide effective interpolation into the coastal zone, a 1 arc-secondspacing “pre-surface” bathymetric grid was generated using GMT, an NSF-funded shareware software application

designed to manipulate data for mapping purposes.

	 The NOS hydrographic point data, in xyz format, were clipped to remove overlap with the SIO and NGDC

multibeam data and then combined with points extracted from the combined coastline—to provide a buffer along the

entire coastline. The coastline elevation value was set to -1.0 meter to ensure a bathymetric surface below zero in areas

where bathymetric data are sparse or nonexistent.

	 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 Adak 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 and exported as an xyz file

for use in the final gridding process (Table 10). Figure 19 shows a histogram of NOS survey H08240 compared to the

1 arc-second pre-surfaced bathymetric grid. Differences cluster around zero with only 11 out of 7483 points varying

more than 5 meters from the DEM. These few points are located along the coastline and where this survey adjoins an

older survey.

	 Some inconsistencies were identified while merging the bathymetric datasets due to the range in ages and

resolutions of the NOS hydrographic surveys. In areas where more recent data were available, the older surveys were

either edited or removed.

Figure 19. Histogram of the differences between NOS hydrographic survey H08240 and the 1 arc-second pre-surfaced 

bathymetric grid.
Digital Elevation Model of Adak, Alaska

23

3.3.3 Gridding the data with MB-System

MB-System was used to create the 1 arc-secondAdak DEM. MB-System is an NSF-funded shareware 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 10. Greatest weight was given to the ENC land elevation data and NGDC

digitized features. Least weight was given to the ENC soundings, ETOPO1 points, and pre-surfaced 1 arc-second

bathymetric grid.

Table 10. Data hierarchy used to assign gridding weight in MB-System.

Dataset Relative Gridding Weight

Combined coastline 1

Pre-surfaced bathymetric grid 1

ETOPO1 extracted grid points 1

ENC soundings 1

USGS STRM topographic DEM 1

NOS hydrographic surveys 10

NGDC multibeam survey 10

SIO multibeam survey 10

NGDC digitized elevations 100

ENC land elevations 100

3.4 Quality Assessment of the DEM

3.4.1. Horizontal accuracy

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

cell size and the datasets used to determine corresponding DEM cell values. Topographic features have an estimated

horizontal accuracy of 50 to 75 meters, based on the documented accuracy of the SRTM DEM. Bathymetric features

are resolved only to within a few hundred meter 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; and potentially large positional uncertainty of pre-satellite navigated (e.g., GPS)

NOS hydrographic surveys.

3.4.2 Vertical accuracy

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

contributing to DEM cell values. Elevation values, derived from the SRTM topographic data, have vertical accuracies

of between 10 and 15 meters. Bathymetric values were derived from the wide range of sounding measurements from

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

between sparse, poorly located NOS soundings degrades the vertical accuracy of elevations in deep water to about 5%

of water depth.
Carignan et al., 2009

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3.4.3 Slope maps and 3-D perspectives

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

identification of artificial slopes along boundaries between datasets (Fig. 20). The DEM was transformed to UTM

zone 1 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 using Quick Terrain Modeler

revealed suspect data points, which were corrected before recompiling the DEM. Figure 1 shows a color image of the

1 arc-second Adak DEM in its final version. Figure 21 shows a perspective rendering of the final DEM.

Figure 20. Slope map of the Adak DEM. Flat-lying slopes are white; dark shading denotes steep 

slopes; combined coastline in red.
Digital Elevation Model of Adak, Alaska

25

Figure 21. Perspective view from the northwest of the Adak DEM. 

Vertical exaggeration–times 2.

3.4.4 Comparison with source data files

To ensure grid accuracy, the Adak 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 the SRTM 1

arc-second DEM and the completed Adak DEM is shown in Figure 22. Differences cluster around zero with elevation

points with large difference values along the coastline and where ENC elevation points varied significantly from the

SRTM elevation.

Figure 22. Histogram of the differences between the SRTM 1 arc-second topographic DEM and the Adak DEM.
Carignan et al., 2009

26

3.4.5 Comparison with National Geodetic Survey geodetic monuments

NGS datasheets were downloaded in shapefile format from the NOAA NGS web site (http://www.ngs.noaa.

gov/) in shapefile format, attributes generally providing monument positions in NAD 83 (typically sub-mm accuracy)

and elevations in NAVD88 (in meters). Datasheets for the Adak DEM region did not include this elevation data,

however they did include superseded elevation information referenced to NGVD29 (Table 11). NGDC used 9 of the

271 datasheet points to qualitatively assess the DEM accuracy surrounding the town of Adak. Figure 23 shows the

location and permanent ID (PID) for the selected points.

Table 11. NGS datasheet NGVD29 heights (meters) compared to Adak DEM elevation.

PID NGVD29 Height DEM elevation Difference

TT4803 11.2 4.5 6.7

TT4804 58.9 57.6 1.3

TT4814 187.8 183.5 4.3

TT4819 34.2 25.6 8.6

TT4827 5.6 6.6 -1.0

TT4899 156.0 155.5 0.5

TT4912 120.8 117.6 3.2

UW7916 116.6 111.5 5.1

UW7919 5.1 4.5 0.6

Figure 23. Location and PID 

for selected NGS datasheet 

points near the town of Adak.
Digital Elevation Model of Adak, Alaska

27

3.4.6 Comparison with topographic and bathymetric contours

Contours generated from the Adak DEM were compared to topographic contours from the USGS 1:250,000

topographic map in several locations. Figure 24 shows the area of northern Adak Island and Mt. Moffett on the

topographic map displayed with the Adak DEM topographic contours overlaid. Land features on the map are well

represented in the contour data. This technique was also used to qualitatively assess the bathymetric values of the

DEM. Bathymetric contours were compared to contour lines on the NOAA nautical charts (e.g., Fig. 25).

Figure 24.

Comparison 

of USGS Adak 

topographic map 

to Adak DEM 

topographic 

contours.

Figure 25. Comparison 

of NOAA ENC #16475 

to Adak DEM bathymetric contours.
Carignan et al., 2009

28

4. Summary and Conclusions

	 A bathymetric–topographic DEM of the Adak, Alaska region, with cell size of 1 arc-second, was developed

for the PMEL NOAA Center for Tsunami Research. The best available digital data from U.S. federal agencies and

academic institutions were obtained by NGDC, shifted to common horizontal and vertical datums, and evaluated and

edited before DEM generation. The data were quality checked, processed and gridded using ArcGIS, FME, GMT, MBSystem and Quick Terrain Modeler software.

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

•	 Conduct hydrographic surveys in near-shore areas, especially in harbors.

•	 Conduct bathymetric–topographic lidar survey of Adak Island.

•	 Conduct deep water multibeam surveys for regions north and south of Andreanof Islands.

5. Acknowledgments

	 The creation of the Adak DEM was funded by NOAA PMEL. The authors thank Nazila Meratia and

Vasily Titov (PMEL), Patrick Barnard (USGS), Bret Christensen (USFWS), and Scott White and Gene Yogodzinski

(Department of Geological Studies, University of South Carolina).

6. References

Nautical Chart #16012 (ENC and RNC), 5th Edition, 2008. Aleutian Islands, Amukta Island to Attu Island. Scale 1: 		

1,126,321. U.S. Department of Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #16467 (ENC and RNC), 2nd Edition, 2005. Adak Island to Tanaga Island. Scale 1:100,000. U.S.

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

Nautical Chart #16471 (ENC and RNC), 3rd Edition, 2007.Atka PasstoAdak Strait. Scale 1:120,000. U.S. Department

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

Nautical Chart #16474 (ENC and RNC), 2nd Edition, 2007. Bay of Islands, Adak Island. Scale 1:12,000. U.S.

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

Nautical Chart #16475 (ENC and RNC), 3rd Edition, 2008. Kuluk Bay and Approaches, Little Tanaga and Kagalaska

Straits. Scale 1:50,000. U.S. Department of Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #16476 (ENC and RNC), 3rd Edition, 2008. Adak Island, Sweeper Cove, Finger and Scabbard Bays.

Scale 1:10,000. U.S. Department of Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #16477 (RNC), 7th Edition, 2008. Tagalak Island to Little Tanaga Island. Scale 1:30,000. U.S.

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

Nautical Chart #16478 (RNC and ENC), 2nd Edition, 2007. Tagalak Island to Great Sitkin Island. Scale 1:30,000. U.S.

Department of Commerce, NOAA, National Ocean Service, Coast Survey.
Digital Elevation Model of Adak, Alaska

29

7. Data Processing Software

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

FME 2009 GB – Feature Manipulation Engine, developed and licensed by Safe Software, Vancouver, BC, Canada,

http://www.safe.com/

GEODAS v. 5 – Geophysical Data System, freeware 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, freeware developed and maintained by Paul Wessel and Walter Smith, funded

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

MB-System v. 5.1.0 – shareware developed and maintained by David W. Caress and Dale N. Chayes, funded by the

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

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

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