noaa / NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

National Environmental Satellite,

Data, and Information Service

NOAA Technical Memorandum NESDIS NGDC-63

DIGITAL ELEVATION MODEL OF PORT ALEXANDER, ALASKA:

PROCEDURES, DATA SOURCES AND ANALYSIS 

M.R. Love

B.W. Eakins

L.A. Taylor 

K.S. Carignan

D.Z. Friday 

P.R. Grothe 

National Geophysical Data Center

Marine Geology and Geophysics Division

Boulder, Colorado

August 2012

UNITED STATES

DEPARTMENT OF COMMERCE

Rebecca Blank

Acting 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-63

DIGITAL ELEVATION MODEL OF PORT ALEXANDER, ALASKA:

PROCEDURES, DATA SOURCES AND ANALYSIS 

Matthew R. Love 1

Barry W. Eakins1

Lisa A. Taylor 2

Kelly S. Carignan1

Dorothy Z. Friday 1

Pamela R. Grothe1 

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

2

NOAA, National Geophysical Data Center, Boulder, Colorado 

National Geophysical Data Center

Marine Geology and Geophysics Division 

Boulder, Colorado

August 2012
Love et al., 2011

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/coastal/

Also available from the National Technical Information Service (NTIS)

(http://www.ntis.gov)
Digital Elevation Model of Port Alexander, 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 7

3.1.3 Topography 12

3.2 Establishing Common Datums 14

3.2.1 Vertical datum transformations 14

3.2.2 Horizontal datum transformations 16

3.3 Digital Elevation Model Development 17

3.3.1 Verifying consistency between datasets 17

3.3.2 Smoothing of bathymetric data 17

3.3.3 Building the DEMs using MB-System 19

3.4 Quality Assessment of the DEMs 20

3.4.1 Horizontal accuracy 20

3.4.2 Vertical accuracy 20

3.4.3 Slope map and 3-D perspectives 20

3.4.4 DEM comparison with source data files 22

4..Summary and Conclusions 24

5..Acknowledgments 24

6..References 25

7..Data Processing Software 31

Appendix A. NOS Hydro Data Tables 32

Appendix B. ENC Data Tables 33

Appendix C. Vertical Datums in Southeast Alaska 34

List of Figures

Figure 1. Shaded-relief image of the Port Alexander 1/3 arc-second DEM. 1

Figure 2. Photograph of Port Alexander. 2

Figure 3. Overview of the Port Alexander, Alaska region. 3

Figure 4. Earthquakes in Alaska. 3

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

Figure 6. Spatial coverage of the bathymetric datasets used in compiling the Port Alexander DEM 7

Figure 7. Digital NOS hydrographic survey coverage in the Port Alexander region. 8

Figure 8. Spatial coverage of digital NOS hydrographic surveys in BAG format in the Port Alexander, 

Alaska region. 9

Figure 9. NGDC Multibeam survey coverage in the Port Alexander region. 10

Figure 10. Spatial coverage of ENC soundings in the Port Alexander, Alaska region. 11

Figure 11. Source and coverage of topographic datasets used in compiling the Port Alexander DEM. 12

Figure 12. The MLLW to MSL regional offset grid used to convert between vertical datums 15

Figure 13. The MSL to MHHW offset grid used to convert between vertical datums 15

Figure 14. Histogram of the differences between NOS hydrographic surveys and the 1 arc-second

pre-.surfaced bathymetric grid. 18

Figure 15. Histogram of the differences between NGDC multibeam swath sonar surveys and the

1 arc-second pre-surfaced bathymetric grid. 18

Figure 16. Slope map of the 1/3 arc-second Port Alexander DEM. 20

Figure 17. Perspective view from the southwest of the Port Alexander DEM 21

Figure 18. Data contribution plot of the Port Alexander DEM. 21

Figure 19. Histogram of the differences between the SRTM 1 arc-second topographic DEM data

points and the Port Alexander DEM. 22
Love et al., 2011

iv

Figure 20. Histogram of the differences between the ASTER 1 arc-second DEM data points and

the Port Alexander DEM. 22

Figure 21. Histogram of the differences between the NGDC multibeam swath sonar surveys and

the Port Alexander DEM. 23

Figure 22. Histogram of the differences between the NOS Hydro data points and the Port

Alexander DEM. 23

List of Tables

Table 1. Specifications for the Port Alexander DEM. 4

Table 2. Shoreline datasets used in developing the Port Alexander DEMs. 6

Table 3. Bathymetric datasets used in compiling the Port Alexander DEMs. 7

Table 4. Topographic datasets used in compiling the Port Alexander DEMs. 12

Table 5. Data hierarchy used to assign gridding weight in MB-System 19
Digital Elevation Model of Port Alexander Alaska:

Procedures, Data Sources and Analysis

1. Introduction

In April of 2011 the National Geophysical Data Center (NGDC), an office of the National Oceanic and Atmospheric Administration (NOAA), developed a bathymetric–topographic digital elevation model (DEM) centered on

Port Alexander, Alaska (Fig. 1) for the Pacific Marine Environmental Labratory (PMEL) NOAA Center for Tsunami

Research (http://nctr.pmel.noaa.gov/). The 1/3 arc-second DEM1was generated from diverse digital datasets in the

region (grid sources shown in Fig. 5) and was designed to represent modern morphology. This report provides a summary of the data sources and methodology used to develop the Port Alexander DEM.

1. The Port Alexander 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 Port Alexander, AK (56°14′24′′N

134°39′26′′W ) 1/3 arc-second of latitude is equivalent to 10.30982775 meters; 1/3 arc-second of longitude equals 5.74125383 meters.

Figure 1. Shaded-relief image of the Port Alexander 1/3 arc-second DEM. 
Love et al., 2011

2

2. Study Area

Port Alexander is a city at the southeastern corner of Baranof Island in Petersburg Census Area, Alaska, in the

panhandle of southeast Alaska. The 1/3 arc-second DEM of the region encompasses the region around Port Alexander

(Fig. 3). 

Southeast Alaska is a historically active earthquake region, which makes the area highly vulnerable to tsunamis (Fig. 4). Earthquakes are of concern in Port Alexander and the surrounding region because of the region’s proximity to large fault systems, as well as the likelihood of landslides, avalanches and tsunamis resulting from a significant

earthquake. Although most of Alaska’s earthquakes occur in the south-central and southwest regions, southeastern

Alaska experiences earthquakes from the Queen Charlotte-Fairweather fault, which runs from northwest to southeast

in close proximity to the Port Alexander region. The Fairweather fault system has caused several recent moderate to

large earthquakes: a magnitude 8.1 earthquake in 1949, a magnitude 7.9 event in 1958 that triggered the giant landslide-generated wave, a magnitude 7.6 quake in 1972, and a magnitude 6.8 event in 2004. Because of the steep slopes

around Port Alexander, landslide-induced tsunamis are also possible if an earthquake triggers a large landslide into the

channel (http://www.juneau.org/emergency/Earthquakes.php).

Figure 2. Photograph of Port Alexander. Source: http://icons-ecast.wunderground.com/data/wximagenew/f/FishermensInn/1.jpg
Digital Elevation Model of Port Alexander, Alaska

3

Figure 3. Overview of the Port Alexander, Alaska region.

Figure 4.

KOBUK FAULT

1964

KALTAG FAULT

DENALI

CASTLE MTN.

FAULT

TINTINA

FAULT

KIGLUAIKBENDELEBEN

FAULTS

JUNEAU

ANCHORAGE

1965

1986

1957 1957

1946

1938

1964

1979

1972

1949

1948

2.0 in./yr

2.0 in./yr

2.2 in./yr

2.5 in./yr

2.7 in./yr

2.9 in./yr

3.0 in./yr

CANADA

ALASKA

M E G A T H R U S T

P A C I F I C P L A T E

FAULT

QUEEN CHARLOTTE

FAULT

Magnitude 8.1

8/22/1949

Magnitude 8.0

9/10/1899 Magnitude 9.2

3/27/64

Magnitude 8.3

11/10/1938

Magnitude 8.0

5/7/1986

Magnitude 8.6

3/9/57

Magnitude 8.7

2/4/65

FAIRBANKS

The Queen Charlotte–

Fairweather fault presents

the greatest earthquake 

hazard to residents of 

southeast Alaska.

Earthquakes

in Alaska

Earthquakes

in Alaska

6.0 - 6.9

7.0 - 7.9

8.0 - 8.4

8.5 - 8.9

9.0 or larger

Pre-1964 Earthquakes

Post-1964 Earthquakes

Earthquake Magnitude

Earthquake rupture zone

and date of most recent

rupture 

Active and potentially

active faults

KILOMETERS

0 MILES

0 500

300

Earthquake risk is high in much of the southern half of 

Alaska, but it is not the same everywhere. This map 

shows the overall geologic setting in Alaska that 

produces earthquakes. The Pacific plate (darker blue) 

is sliding northwestward past southeastern Alaska and 

then dives beneath the North American plate (light blue, 

green, and brown) in southern Alaska, the Alaska 

Peninsula, and the Aleutian Islands. Most earthquakes 

are produced where these two plates come into contact 

and slide past each other. Major earthquakes also occur 

throughout much of interior Alaska as a result of 

collision of a piece of crust with the southern margin. 

FAIRWEATHER

TRANSITION FAULT

N O R T H A M E R I C A N

P L A T E

BY PETER J. HAEUSSLER AND GEORGE PLAFKER

2003

OPEN FILE REPORT

95-624

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

SOURCES OF INFORMATION

Additional data and references to earthquake, faulting, and seismicity in Alaska can 

be found in Plafker and others (1994), Page and others (1991), and Taber and others 

(1991). The material on this map was modified chiefly from Plafker and others (1994), 

and earthquake epicenters were from the Alaska Earthquake Information Center, and 

cover the interval from 1899-2003. The location of earthquake epicenters and faults is 

approximate. 

Plafker, G., Gilpin, L.M., and Lahr, J.C., 1994, Neotectonic map of Alaska: in Plafker, G., and 

Berg, H.C., eds., The Geology of Alaska: Boulder, Colorado, Geological Society of 

America, Decade of North American Geology Volume G-1, 1 sheet, scale: 1:2,500,000.

Page, R.A., Biswas, N.N., Lahr, J.C., and Pulpan, H., 1991, Seismicity of continental Alaska: 

in Slemmons, D.B., Engdahl, E.R., Zoback, M.D., and Blackwell, D.D., eds., Neotectonics 

of North America: Boulder, Colorado, Geological Society of America, Decade Map 

Volume 1.

Taber J.J., Billington, S., and Engdahl, E.R., 1991, Seismicity of the Aleutian arc: in Slemmons, D.B., Engdahl, E.R., Zoback, M.D., and Blackwell, D.D., eds., Neotectonics of North 

America: Boulder, Colorado, Geological Society of America, Decade Map Volume 1. 

This map is preliminary and has not been reviewed 

for conformity with U.S. Geological Survey editorial standards or the North American Stratigraphic 

Code. Any use of trade, product, or firm names is 

for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

1987

1988

A L E U T I A N

N O R T H A M E R I C A N

P L A T E

The Denali fault generated a 

magnitude 7.9 earthquake in 

2002. This part of the fault 

ruptured, with horizontal 

offset of up to 29 feet.

A fault beneath a fold in 

Cook Inlet resulted in a 

magnitude 7 earthquake 

in 1933 that strongly 

shook Anchorage.

These arrows show the

speed and direction at

which the Pacific plate

moves by and underneath Alaska.

Magnitude 7.9

11/3/2002

The 1964 earthquake 

was the second largest 

ever recorded in the 

world. The area within 

this pink patch slipped 

seaward up to 66 feet. 

1958

FAULT

VERSION 1.1

This piece of crust is being 

pushed into and beneath the 

southern Alaska margin. As a 

result it causes large 

earthquakes here and 

throughout interior Alaska.

Three magnitude 7 

earthquakes occurred within 

50 miles of Fairbanks in the 

last 90 years.

Earthquakes in Alaska. Sources: http://www.aeic.alaska.edu/html_docs/pdf_files/earthquakes_in_Alaska.pg.pdf; http://geopubs.

wr.usgs.gov/open-file/of95-624/.
Love et al., 2011

4

3. Methodology

The Port Alexander DEM was developed in the World Geodetic System 1984 (WGS 84) geographic horizontal datum and Mean High Water (MHW) vertical datum in vertical units of meters. The final grid format for the DEM

is ESRI Arc Ascii Grid. The Port Alexander DEM was also developed to meet PMEL specifications listed in Table 1,

based on input requirements for the development of Reference Innundation Models (RIMs) and Standby Inundation

Models (SIMs) in support of NOAA’s Tsunami Warning Centers use of SIFT to provide real-time tunami forecasts in

an operational environment. The best available bathymetric and topographic digital data were obtained by NGDC and

shifted to common horizontal and vertical datums: North American Datum of 19832 (NAD 83) and MHW, for modeling of maximum flooding, respectively.

Table 1. Specifications for the Port Alexander DEM. 

Grid Area Port Alexander, AK

Coverage Area -135.5, -134. 55.53, 56.71

Grid Spacing 1/3 arc-second

Coordinate System Geographic decimal degrees

Horizontal Datum World Geodetic System 1984 (WGS 84)

Vertical Datum Mean High Water (MHW)

Vertical Units Meters

Grid Format ESRI Arc ASCII

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 DEM so that they can model

the wave’s passage across ocean basins. These DEM are 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 Port Alexander, Alaska

5

3.1 Data Sources and Processing

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

local agencies, including: NGDC; NOAA’s National Ocean Service (NOS), Office of Coast Survey (OCS); the U.S.

Fish and Wildlife Service (USFWS); the U.S. Forestry Service (USFS); the U.S. Army Corps of Engineers (USACE);

the U.S. Geological Survey (USGS); the National Aeronautics and Space Administration (NASA). Proj43 was used to

shift datasets to NAD 83 geographic horizontal datum. The Geographic Dataset Abstraction Layer (GDAL)4 was used

to convert the datasets into ESRI ArcGIS shapefiles and xyz format. The shapefiles and xyz files were then displayed

with ArcGIS and Applied Imagery’s Quick Terrain Modeler (QT Modeler) to assess data quality and manually edit

datasets. The methodology used for vertical datum transformations is described in Section 3.2.1.

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

3. Proj4 is a cartographic projections library, originally written by Gerald Evenden, then of the USGS. The software is released under an MIT style

Open Source license. Proj4 was used to horizontally transform datasets that originated in State Plane datums before vertical transformations were

performed .

4. GDAL is a translator library for raster geospatial data formats that is released under an X/MIT style Open Source license by the Open Source

Geospatial Foundation. As a library, it presents a single abstract data model to the calling application for all supported formats. It also comes with

a variety of useful commandline utilities for data translation and processing.
Love et al., 2011

6

3.1.1 Shoreline

Two coastline datasets of the Port Alexander, Alaska region were analyzed for inclusion in the Port Alexander

DEM: NOAA Electronic Navigational Charts (ENCs)5 and the USFWS statewide Alaska digital coastline (Table 2).

The USFWS coastline best fit the topographic and bathymetric data overall and was merged with higher resolution

(e.g., at least 1:80,000 scale) ENC coastlines only within the immediate vicinity of Port Alexander. These datasets

were used to develop a “final coastline” of the Port Alexander, Alaska region.

The final coastline was subsequently modified to include large offshore rocks and small islets shown on the

larger-scale NOAA raster nautical charts (RNCs) and clipped to an area 0.05 degrees larger than the DEM boundary.

Piers and docks were deleted from the coastline. The coastline was further modified based on ESRI World 2D imagery

to reflect the most current coastal morphology.

Table 2. Shoreline datasets used in developing the Port Alexander DEM.

Source Year Data Type Spatial 

Resolution

Original Horizontal Datum/

Coordinate System

Original Vertical 

Datum URL

OCS 2009 ENC 1:20,000 to

1:80,000 WGS 84 geographic MHW http://w1.nauticalcharts.noaa.

gov/staff/chartspubs.html

USFWS 2006 Compiled

coastline 1:63,360 WGS 84 geographic Undefined ftp://ftp.dnr.state.ak.us/asgdc/

adnr/alaska_63360.zip

1) Office of Coast Survey extracted Electronic Navigational Chart coastlines

Seven ENCs were available in the Port Alexander, Alaska region (Appendix B) and were downloaded

from NOAA’s Office of Coast Survey web site. The ENCs were in S-57 format and included coastline data

referenced to MHW. The coastline shapefiles were extracted from the ENCs using ArcCatalog and compared

to large-scale RNCs and ESRI’s World 2D imagery. Only the ENCs with 1:80,000-scale or higher that were

within the 8/15 arc-second DEM boundary were used.

2) U.S. Fish and Wildlife Service vector coastline

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

of Alaska from a variety of sources, including: the National Hydrography Dataset, NOAA nautical charts,

USFWS, National Geographic Topo Software, USACE, and Alaska Department of Natural Resources. This

dataset was provided by Bret Christensen, USFWS. Though efforts were made to obtain the highest resolution coastlines available, vertical datums were not determined or controlled in the compilation of the USFWS

coastline; the horizontal datum is WGS 84 geographic. The USFWS coastline provides complete coverage

of the Southeast Alaska region.

5. 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://www.

nauticalcharts.noaa.gov/mcd/enc/index.htm]
Digital Elevation Model of Port Alexander, Alaska

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3.1.2 Bathymetry

Bathymetric datasets available for use in the compilation of the Port Alexander DEM include 33 NOS hydrographic surveys; 9 multibeam surveys downloaded from the NGDC multibeam database; and soundings extracted

from 7 ENCs. (Table 3; Fig. 6).

Table 3. Bathymetric datasets used in compiling the Port Alexander DEM.

Source Year Data Type Spatial Resolution

Downloaded 

Horizontal Datum/

Coordinate System

Original 

Vertical 

Datum

URL

NGDC

1883

to

2009

NOS

hydrographic

surveys

Ranges from less than 10 m

to 600 m (varies with scale

of survey, depth, traffic, and

probability of obstructions)

NAD 83 geographic

NAD 27 geographic

NAD 83 UTM Zone 8

NAD 83 UTM Zone 9

Early Alaska

Undetermined

MLW and

MLLW

http://www.ngdc.noaa.

gov/mgg/bathymetry/

hydro.html

NGDC

1994

to

2009

Multibeam

swath sonar Gridded to 3 arc-seconds WGS 84 geographic

Assumed

Mean

Sea Level

(MSL)

http://www.ngdc.noaa.

gov/mgg/bathymetry/

multibeam.html

OCS

1977

to

2009

ENC extracted

soundings

Ranges from several meters

to several kilometers (varies

with scale of survey, depth,

traffic, and probability of

obstructions)

WGS 84 geographic MLLW

http://w1.nauticalcharts.

noaa.gov/staff/chartspubs.html

Figure 6. Spatial coverage of the bathymetric datasets used in compiling the Port Alexander DEM. Land areas shown in tan. Regions of no data 

shown in white.
Love et al., 2011

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1) National Ocean Service hydrographic survey data

A total of 33 NOS hydrographic surveys conducted between 1883 and 2009 were available for use in developing the Port Alexander DEM (Appendix A; Figs. 7 and 8). Surveys were extracted from NGDC’s online

NOS hydrographic database using GEODAS6

. The surveys were downloaded in xyz format. The downloaded

hydrographic survey data were vertically referenced to mean lower low water (MLLW) or mean low water

(MLW) and horizontally referenced to NAD 27 or NAD 83 geographic, NAD 83 UTM Zone 8, NAD 83

UTM Zone 9, Early Alaska, or “undetermined” datums. NOS surveys in Early Alaska or “undetermined”

datums were manually shifted in ArcGIS to fit the final coastline.

Data point spacing for the NOS surveys varied by scale. In general, small scale surveys had greater point

spacing than large scale surveys. The data were converted to shapefiles using Python and GDAL. The surveys

were subsequently clipped to a polygon 0.05 degree (~5%) larger than the Port Alexander DEM area to support data interpolation along grid edges.

After transforming all NOS survey data to MHW (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 other bathymetric datasets, the final coastline, and NOS RNCs (see

Appendix A). Older surveys were clipped to remove soundings that have been superseded by more recent

NOS surveys or multibeam data.

Figure 7. Digital NOS hydrographic survey coverage in the Port Alexander region. Several older surveys were not used as they have been 

superseded by more recent surveys. Land areas shown in tan. Regions where NOS data were not available are shown in white. 

6. GEODAS uses the North American Datum Conversion Utility (NADCON; http://www.ngs.noaa.gov/TOOLS/Nadcon/Nadcon.shtml) developed

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

Standard for NAD 27 to NAD 83 datum transformations.
Digital Elevation Model of Port Alexander, Alaska

9

Figure 8. Spatial coverage of digital NOS hydrographic surveys in BAG format in the Port Alexander, Alaska region. Land areas shown in tan. 

2) NGDC multibeam swath sonar surveys

Nine multibeam swath sonar surveys were available from the NGDC multibeam bathymetry database for

use in building the Port Alexander DEM (Fig. 9). The data were referenced to WGS 84 geographic horizontal

datum and were assumed to be referenced to MSL vertical datum. The data were gridded at 3 arc-seconds at

extents approximately 5 percent (~0.10 degree) larger than the 8 arc-second DEM extents using MB-System7

(http://www.ldeo.columbia.edu/res/pi/MB-System/). The grids were converted to xyz format and viewed in

QT Modeler for quality analysis. Editing was done using QT Modeler and ArcMap to eliminate errors where

survey data overlapped. The elevations were then transformed from MSL to MHW (see Sec. 3.2.1) for use

in the final gridding process.

7. MB-System is an open source software package for the processing and display of bathymetry and backscatter imagery data derived from

multibeam, interferometry, and sidescan sonars. The source code for MB-System is freely available (for free) by anonymous ftp (including “point

and click” access through these web pages). A complete description is provided in web pages accessed through the web site. MB-System was

originally developed at the Lamont-Doherty Earth Observatory of Columbia University (L-DEO) and is now a collaborative effort between

the Monterey Bay Aquarium Research Institute (MBARI) and L-DEO. The National Science Foundation has provided the primary support for

MB-System development since 1993. The Packard Foundation has provided significant support through MBARI since 1998. Additional support

has derived from SeaBeam Instruments (1994-1997), NOAA (2002-2004), and others. URL: http://www.ldeo.columbia.edu/res/pi/MB-System/

[Extracted from MB-System web site.]
Love et al., 2011

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Figure 9. NGDC Multibeam survey coverage in the Port Alexander region.

3) Electronic navigation chart soundings

Soundings from seven ENCs were used to supplement other bathymetric data, particularly in the deep

water (Fig. 10; Appendix B). The ENCs were downloaded from NOAA’s Office of Coast Survey website and

were horizontally referenced to WGS 84 geographic. ENC soundings were included in the gridding process

only in regions where higher resolution and/or newer datasets were unavailable. The extracted soundings

were transformed from a vertical datum of MLLW to MHW (see Section 3.2.1).
Digital Elevation Model of Port Alexander, Alaska

11

Figure 10. Spatial coverage of ENC soundings in the Port Alexander, Alaska region. Land areas shown in tan.
Love et al., 2011

12

3.1.3 Topography

Topographic datasets of the Port Alexander, Alaska region were obtained from the USGS and the NASA Jet

Propulsion Laboratory (Table 4; Fig. 11). In addition, NGDC digitized elevation points to better represent several

breakwaters, jetties, and bridge pilings along Gastineau Channel in the vicinity of Juneau as they were not resolved

completely in the other topographic datasets.

NGDC reviewed the USGS National Elevation Dataset (http://ned.usgs.gov/) 2 arc-second gridded topography. The dataset was derived from USGS quadrangle maps and aerial photographs based on topographic surveys

conducted in the 1970s and 1980s. The NED data were not used in the development of the Port Alexander DEM due

to the following: morphological changes in regions of rapid deglaciation across Alaska; lateral shifts in the NED discovered during prior DEM development in Alaska (see Caldwell et al., 2009 for further details); and lower resolution

than other available topographic datasets.

Table 4. Topographic datasets used in compiling the Port Alexander DEM.

Source Year Data Type Spatial 

Resolution

Original 

Horizontal Datum

Original Vertical 

Datum URL

NASA

SRTM 2000 TopographicDEM 1 arc-second WGS 84geographic

WGS 84/ EGM 96

Geoid (meters) http://srtm.usgs.gov/

NASA

ASTER 2009 TopographicDEM 1 arc-second WGS 84geographic

WGS 84/ EGM 96

Geoid (meters)

http://asterweb.jpl.nasa.gov/

gdem.asp/

NGDC 2009 Digitized

elevation points ~ 10 meters WGS 84geographic MHW

Figure 11. Source and coverage of topographic datasets used in compiling the Port Alexander DEM. Areas of water indicated in white.
Digital Elevation Model of Port Alexander, Alaska

13

1) NASA space shuttle radar topography

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

(60° S to 60° N) to generate a complete high-resolution digital topographic database of Earth8

. The 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 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 the Port Alexander, Alaska region, the data have 1 arc-second spacing and are referenced to the WGS

84/EGM 96 Geoid. The SRTM provides nearly complete coverage of Prince William Sound but exhibits

numerous small areas with “no data” values necessitating the use of the ASTER data in these areas (see Fig.

11). The SRTM DEM also contains values over the open ocean, which were deleted by clipping the data to

the final coastline.

2) NASA ASTER topography

ASTER provides complete 1 arc-second topographic data coverage of Alaska9. Data are in WGS 84

geographic coordinates and vertically referenced to the WGS 84/EGM 96 Geoid. The dataset is available for

download as 1 degree x 1 degree raster files. The extracted non-bare-earth elevations have a vertical accuracy

of +/- 20 meters and horizontal accuracy of +/- 30 meters, both at the 95 percent confidence level.

The ASTER data contain values over the open ocean, which were deleted by clipping the data to the final

coastline. As discussed, the ASTER data was used to fill “no data” regions within the SRTM dataset (see Fig.

19). The ASTER data were not used as the primary topographic dataset due to the improper representation

of areas along the immediate coastline. NGDC considered the SRTM to be most representative of the current

coastal morphology, particularly in the immediate vicinity of Port Alexander.

3) NGDC digitized elevation points

Several jetties, breakwaters, and large bridge pilings were not resolved completely in the topographic

datasets. Using the nearby elevations from SRTM and ASTER, a point shapefile was created using elevations

of 1 or 1.5 meters at MHW to best represent these features in the final DEM.

8. 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]

9. ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) is an imaging instrument flying on Terra, a satellite launched in

December 1999 as part of NASA’s Earth Observing System (EOS). ASTER is a cooperative effort between NASA, Japan’s Ministry of Economy,

Trade and Industry (METI) and Japan’s Earth Remote Sensing Data Analysis Center (ERSDAC). ASTER is being used to obtain detailed maps of

land surface temperature, reflectance and elevation. The three EOS platforms are part of NASA’s Science Mission Directorate and the Earth-Sun

System, whose goal is to observe, understand, and model the Earth system to discover how it is changing, to better predict change, and to understand

the consequences for life on Earth. METI and NASA announced the release of the ASTER Global Digital Elevation Model (GDEM) on June 29,

2009. The GDEM was created by stereo-correlating the 1.3 million scene ASTER visible and near-infrared (VNIR) archive, covering the Earth’s

land surface between 83N and 83S latitudes. The GDEM is produced with 30 meter postings, and is formatted in 1 x 1 degree tiles as GeoTIFF

files. Each GDEM file is accompanied by a Quality Assessment file, either giving the number of ASTER scenes used to calculate a pixel’s value, or

indicating the source of external DEM data used to fill the ASTER voids [Extracted from NASA JPL ASTER website]
Love et al., 2011

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3.2 Establishing Common Datums

3.2.1 Vertical datum transformations

Datasets used in the compilation and evaluation of the Port Alexander DEM was originally referenced to

a number of vertical datums including MLLW (feet and meters), MLW, MSL, MHW, WGS 84/EGM 96 Geoid, and

undefined (assumed to be MSL). All datasets were transformed to MHW for modeling of maximum flooding. Vertical datum transformations to MHW were accomplished using Proj4 and GDAL, based upon data from tide stations, a

DART buoy, and dominant tidal components (Brown et al., 1989) in the region.

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

MSL for the Southeast Alaska region. The grids were built in ArcGIS using the ‘Kriging’ tool and the differences, in

meters, between the vertical datums as measured at 8 NOAA tide stations (http://tidesandcurrents.noaa.gov/), 10 tide

prediction sites (http://co-ops.nos.noaa.gov/tides05/tab2wc2b.html), one deep-ocean DART buoy (http://www.ndbc.

noaa.gov/dart.shtml), and 74 CHS tide stations (Appendix C; Figs. 12-14). In using the differences between the vertical datums, the final offsets grids contained negative values (Figs. 12-14).

1) Bathymetric data

The NOS hydrographic surveys, multibeam swath sonar surveys, ENC soundings, and USACE surveys

were transformed from either MSL to MHW or MLLW to MHW by adding the corresponding grid value

to the point elevation value using GDAL . For the two remaining MLW surveys, NGDC first converted the

surveys to MHW using the MLLW to MHW conversion grid and then adjusted the values by +0.41, the average difference between MLLW and MLW at the NOAA tide stations, tide prediction sites, and DART buoy.

2) Topographic data

The topographic datasets were originally referenced to WGS 84/EGM 96 Geoid. There are no survey

markers in Southeast Alaska that relate the geodetic datum to local tidal datums. Therefore, it was assumed

that the datum is essentially equivalent to MSL in this area. Conversion to MHW, using GDAL, was accomplished by adding the MSL to MHW offset grid. Values less than 1 meter following the conversion were set

equal to 1 meter, as both the SRTM and ASTER data are in integer format.
Digital Elevation Model of Port Alexander, Alaska

15

Figure 12. The MLLW to MSL regional offset grid used to convert between vertical datums. 

Tide stations, tide prediction sites, and DART buoy are shown in orange. Coastline is in blue.

Figure 13. The MSL to MHHW offset grid used to convert between vertical datums. Tide stations, tide prediction sites, and DART buoy are 

shown. Coastline is in black.
Love et al., 2011

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3.2.2 Horizontal datum transformations

Datasets used to compile the Port Alexander DEM were originally referenced to WGS 84 geographic, NAD

83 geographic, NAD 83 UTM Zone 8 North, NAD 83 UTM Zone 9 North, NAD 83 Alaska State Plane Zone I (feet

and meters). The relationships and transformational equations between the geographic horizontal datums are well

established. Transformations to NAD 83 geographic were accomplished using Proj4.
Digital Elevation Model of Port Alexander, Alaska

17

3.3 Digital Elevation Model Development

3.3.1 Verifying consistency between datasets

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

ArcMap and QTModeler for inter-dataset consistency. 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:

•	 Inconsistent, overlapping high-resolution bathymetric datasets. Older datasets were clipped to newer datasets

when possible. Datasets were weighted based on quality and year during the gridding process.

•	 Data values over the ocean in the SRTM and ASTER DEM datasets. These datasets required automated

clipping to the final coastline or were edited manually.

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

as the multibeam surveys, differed from older NOS data by as much as 70 meters vertically. The older NOS

survey data were removed where more recent bathymetric data exists.

•	 Lack of bathymetric data in the delta regions of the Mendenhall and Stikine Rivers. An upper limit was set

during the generation of the bathymetric surface to ensure depths near -0.50 meter in those regions.

3.3.2 Smoothing of bathymetric data

The older NOS hydrographic survey data and extracted ENC soundings are generally sparse at the resolution of the Port Alexander DEM in both deep water and in some areas close to shore. In order to reduce the effect of

artifacts in the form of lines or “pimples” in the DEM due to the low resolution datasets, and to provide effective interpolation into the coastal zone, ‘pre-surface’ bathymetric grids in MHW vertical datum were generated using GMT10.

A Port Alexander 1 arc-second, ‘pre-surface’ grid was compiled from NOS hydrographic point data, USACE

surveys, ENC soundings, and NGDC multibeam swath sonar bathymetry data by converting the files to xyz format.

These xyz files were combined into a single file, along with points extracted every 10 meters from the final coastline.

To provide a slightly negative buffer along the entire coastline, the extracted points were assigned values of -0.23

meter, the average difference between MHW and MHHW at the NOAA tide stations, to make sure that the offshore

elevations remained negative; this was necessary due to the sparseness of the bathymetric data near the coast. These

point data were then smoothed using the GMT tool ‘blockmedian’ onto a 1 arc-second grid. The GMT tool ‘surface’

was then applied to interpolate values for cells without data values. The GMT grid created by ‘surface’ was converted

into an ESRI Arc ASCII grid file using the MB-System tool ‘mbm_grd2arc’for viewing in ESRI ArcMap. GDAL software was used to clip the grid to the final coastline to eliminate data interpolation into land areas.

The ‘pre-surface’ grid was compared with the original soundings to ensure grid accuracy, and then exported

as an xyz file for use in the final gridding process (Table 9; Figs. 15 and 16). The statistical analyses of the differences

between the 1 arc-second bathymetric surface at Port Alexander with the NOS hydrographic surveys and NGDC

multibeam swath sonar surveys show that the majority of the surveys are in good agreement (Figs. 23 and 24) with

the bathymetric surface. The few exceptions where the differences reached up to 36.13 meters are attributed to rugged

bathymetry or overlapping datasets, where two or more closely positioned points were averaged to obtain the elevation

of one grid cell. Some inconsistencies were identified while merging the bathymetric datasets due to the range in ages

and resolutions of the surveys. In areas where more recent data were available, the older surveys were either edited or

not used. The gridded bathymetric surfaces were then converted to xyz files for use in building the final DEM.

10. GMT is an open source collection of ~60 tools for manipulating geographic and Cartesian data sets (including filtering, trend fitting, gridding,

projecting, etc.) and producing Encapsulated PostScript File (EPS) illustrations ranging from simple x-y plots via contour maps to artificially

illuminated surfaces and 3-D perspective views. GMT supports ~30 map projections and transformations and comes with support data such as

GSHHS coastlines, rivers, and political boundaries. GMT is developed and maintained by Paul Wessel and Walter H. F. Smith with help from a

global set of volunteers, and is supported by the National Science Foundation. It is released under the GNU General Public License. URL: http://

gmt.soest.hawaii.edu/ [Extracted from GMT web site.]
Love et al., 2011

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Figure 14. Histogram of the differences between NOS hydrographic surveys and the 1 arc-second pre-surfaced bathymetric grid. 

Figure 15. Histogram of the differences between NGDC multibeam swath sonar surveys and the 1 arc-second pre-surfaced bathymetric grid.
Digital Elevation Model of Port Alexander, Alaska

19

3.3.3 Building the DEM using MB-System

MB-System was used to create the Port Alexander DEM. 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 6. Greatest weight was given to the high resolution multibeam surveys, NOS BAG data, USACE hydrographic surveys, and the NGDC digitized features. Least

weight was given to the pre-surfaced bathymetric grid and ENC soundings.

Table 5. Data hierarchy used to assign gridding weight in MB-System

Dataset Relative Gridding Weight

NGDC multibeam 100

NGDC digitized features 100

NOS hydrographic surveys 10

ENC soundings 10

NASA SRTM 1

NASAASTER 1

Pre-surfaced bathymetric grid 1
Love et al., 2011

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3.4 Quality Assessment of the DEM

3.4.1 Horizontal accuracy

The horizontal accuracy of topographic and bathymetric features in the Port Alexander DEM is dependent

upon DEM cell size and source datasets. Topographic features have an estimated horizontal accuracy of 30 meters:

SRTM has a horizontal accuracy of ~20 meters and ASTER, approximately 30 meters. Bathymetric features are resolved only to within a few hundreds of meters in deep-water areas. Shallow, near-coastal regions, rivers, and harbor

surveys have an accuracy approaching that of sub-aerial topographic features. Positional accuracy is limited by the

sparseness of deep-water soundings 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 in the Port Alexander DEM is also dependent upon the source datasets

contributing to DEM cell values. Topographic data have an estimated vertical accuracy between 16 meters for the

SRTM DEM and 20 meters for the ASTER DEM. Bathymetric values have an estimated accuracy between 0.1 meters

and 5% of water depth. Those values were derived from the wide range of sounding measurements from the early

20th century to recent, GPS-navigated multibeam swath sonar survey. Gridding interpolation to determine bathymetric

values between sparse, poorly located NOS soundings degrades the vertical accuracy of elevations in deep water.

3.4.3 Slope map and 3-D perspectives

ESRI ArcCatalog was used to generate a slope grid from the 1/3 arc-second Port Alexander DEM to allow

for visual inspection and identification of artificial slopes along boundaries between datasets (Fig. 17). The DEM was

transformed to NAD 83 UTM Zone 8 North 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 QTModeler revealed suspect data points, which were corrected before recompiling the DEM. Figure

1 shows a color image of the 1/3 arc-second Port Alexander DEM in its final version. Figure 18 shows a perspective

rendering of the final 1/3 arc-second Port Alexander DEM. Figure 19 shows a data contribution plot of the Port Alexander DEM.

Figure 16. Slope map of the 1/3 arc-second Port Alexander DEM. Flat-lying slopes are shown in white; dark shading denotes steep slopes.
Digital Elevation Model of Port Alexander, Alaska

21

Figure 17. Perspective view from the southwest of the Port Alexander DEM. Vertical exaggeration–times 2.

Figure 18. Data contribution plot of the Port Alexander DEM. Black depicts DEM cells constrained by source data; white depicts cells with 

elevation values derived from interpolation. Due to the scale of the image, sparse soundings may not be visible in the graphic. Coastline is shown 

in blue.
Love et al., 2011

22

3.4.4 DEM comparison with source data files

To ensure grid accuracy, the Port Alexander DEM was compared to source data files. A histogram of the differences between the SRTM and ASTER topographic DEMs and the Port Alexander DEM are shown in Figures 20

and 21. Differences cluster around zero. The major differences in elevations in SRTM and ASTER data points with the

grid (> 10 meters) are located in regions of steep slopes and forests, primarily along the coast.

Comparisons of the USACE hydrographic survey data and the Port Alexander DEM are shown in Figure 22.

Largest differences occur where the USACE data overlap other higher resolution datasets, which may occur due to

changes in dredged depths or sediment deposition in channels.

Figure 19. Histogram of the differences between the SRTM 1 arc-second topographic DEM data points and the Port Alexander DEM.

Figure 20. Histogram of the differences between the ASTER 1 arc-second DEM data points and the Port Alexander DEM.
Digital Elevation Model of Port Alexander, Alaska

23

Figure 21. Histogram of the differences between the NGDC multibeam swath sonar surveys and the Port Alexander DEM.

Figure 22. Histogram of the differences between the NOS Hydro data points and the Port Alexander DEM.
Love et al., 2011

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4. Summary and Conclusions

An integrated bathymetric–topographic digital elevation model of Port Alexander, Alaska, with cell size of

1/3 arc-seconds, was developed for the Pacific Marine Environmental Labratory (PMEL) and the National Tsunami

Hazard Mitigation Program in support of the State of Alaska’s tsunami inundation modeling efforts led by the Geophysical Institute at the University of Alaska at Fairbanks. The best available digital data from U.S. federal, state, local, and academic agencies were obtained by NGDC, shifted to common horizontal and vertical datums, and evaluated

and edited before DEM generation. The data were quality checked, processed and gridded using ESRI ArcGIS, ESRI

ArcGIS World Imagery 2-D, GMT, MB-System, QT Modeler, GDAL, Proj4, and VDatum software.

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

•	 Conduct a high-resolution topographic lidar surveys near Port Alexander and Sitka.

•	 Establish, via survey, relationships between tidal and geodetic datums in the Southeast Alaska region.

•	 Determine the relationship between Early Alaska and NAD 83/WGS 84 geographic horizontal datums.

5. Acknowledgments

The creation of the PortAlexander DEM wasfunded by the Pacific Marine Environmental Labratory (PMEL).

The authors thank Nazila Meratia and Vasily Titov (PMEL).
Digital Elevation Model of Port Alexander, Alaska

25

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Digital Elevation Model of Port Alexander, Alaska

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Love et al., 2011

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Nautical Chart #17372 (ENC and RNC), 11th Edition, 2003. Keku Strait-Monte Carlo Island to Entrance Island; The

Summit; Devils Elbow. Scale 1:20,000 with 1:10,000 inset. U.S. Department of Commerce, NOAA, National

Ocean Service, Coast Survey.

Nautical Chart #17375 (ENC and RNC), 22nd Edition, 2009. Wrangell Narrows; Petersburg Harbor. Scale 1:20,000

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

Nautical Chart #17376 (RNC), 8th Edition, 2008. Tebenkof Bay and Port Malmesbury. Scale 1:40,000. U.S.

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

Nautical Chart #17377 (RNC), 1st Edition, 1999. Le Conte Bay. Scale 1:25,000. U.S. Department of Commerce,

NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17378 (RNC), 14th Edition, 2004. Port Protection, Prince of Wales Island. Scale 1:20,000. U.S.

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

Nautical Chart #17379 (RNC), 1st Edition, 2002. Shakan Bay And Strait, Alaska. Scale 1:10,000. U.S. Department of

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17381 (RNC), 10th Edition, 2002. Red Bay, Prince of Wales Island. Scale 1:20,000. U.S. Department

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

Nautical Chart #17382 (ENC and RNC), 17th Edition, 2007. Zarembo Island and Approaches. Scale 1:80,000 with

1:40,000 and 1:20,000 insets. U.S. Department of Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17383 (RNC), 3rd Edition, 2005. Snow Passage, Alaska. Scale 1:30,000. U.S. Department of

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17384 (ENC and RNC), 9th Edition, 2008. Wrangell Harbor and approaches. Scale 1:20,000 with

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

Nautical Chart #17385 (ENC and RNC), 17th Edition, 2009. Ernest Sound-Eastern Passage and Zimovia Strait;

Zimovia Strait. Scale 1:80,000 with 1:20,000 inset. U.S. Department of Commerce, NOAA, National Ocean

Service, Coast Survey.

Nautical Chart #17386 (RNC), 4th Edition, 2006. Sumner Strait-Southern part. Scale 1:40,000. U.S. Department of

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17387 (RNC), 13th Edition, 2001. Shakan and Shipley Bays and Part of El Capitan Passage;

El Capitan Passage, Dry Pass to Shakan Strait. Scale 1:40,000 with 1:10,000 inset. U.S. Department of

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17400 (ENC and RNC), 17th Edition, 2007. Dixon Entrance to Chatham Strait. Scale 1:229,376. U.S.

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

Nautical Chart #17401 (RNC), 12th Edition, 2006. Lake Bay and approaches, Clarence Strait. Scale 1:10,000. U.S.

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

Nautical Chart #17402 (RNC), 11th Edition, 2005. Southern Entrances to Sumner Strait. Scale 1:40,000. U.S.

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

Nautical Chart #17403 (RNC), 14th Edition, 2006. Davidson Inlet and Sea Otter Sound; Edna Bay. Scale 1:40,000

with 1:10,000 inset. U.S. Department of Commerce, NOAA, National Ocean Service, Coast Survey.
Digital Elevation Model of Port Alexander, Alaska

29

Nautical Chart #17404 (ENC and RNC), 14th Edition, 2008. San Christoval Channel to Cape Lynch. Scale 1:40,000.

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

NauticalChart #17405 (ENCandRNC), 16th Edition, 2008. UlloaChannel to SanChristovalChannel; North Entrance,

Big Salt Lake; Shelter Cove, Craig. Scale 1:40,000 with 1:10,000 inset. U.S. Department of Commerce,

NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17406 (ENC and RNC), 7th Edition, 2004. Baker, Noyes, and Lulu Islands and adjacent waters. Scale

1:40,000. U.S. Department of Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17407 (RNC), 15th Edition, 2003. Northern part of Tlevak Strait and Uloa Channel. Scale 1:40,000.

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

Nautical Chart #17408 (RNC), 8th Edition, 2004. Central Dall Island and vicinity. Scale 1:40,000. U.S. Department

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

Nautical Chart #17409 (RNC), 10th Edition, 2002. Southern Dall Island and vicinity. Scale 1:40,000. U.S. Department

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

Nautical Chart #17420 (ENC and RNC), 28th Edition, 2007. Hecate Strait to Etolin Island, including Behm and

Portland Canals. Scale 1:229,376. U.S. Department of Commerce, NOAA, National Ocean Service, Coast

Survey.

Nautical Chart #17422 (RNC), 9th Edition, 2006. Behm Canal-western part; Yes Bay. Scale 1:79,334 with 1:40,000

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

Nautical Chart #17423 (RNC), 14th Edition, 2006. Harbor Charts-Clarence Strait and Behm Canal DeweyAnchorage,

Etolin Island; Ratz Harbor, Prince of Wales Island; Naha Bay, Revillagigedo Island; Tolstoi and Thorne

Bays, Prince of Wales lsland; Union Bay, Cleveland Peninsula. Scale 1:40,000, 1:20,000, and 1:10,000. U.S.

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

Nautical Chart #17424 (ENC and RNC), 9th Edition, 2009. Behm Canal-eastern part. Scale 1:80,000. U.S. Department

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

Nautical Chart #17425 (ENC and RNC), 6th Edition, 2002. Portland Canal-North of Hattie Island. Scale 1:80,000.

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

Nautical Chart #17426 (RNC), 15th Edition, 2006. Kasaan Bay, Clarence Strait; Hollis Anchorage, eastern part;

Lyman Anchorage. Scale 1:40,000 with 1:10,000 inset. U.S. Department of Commerce, NOAA, National

Ocean Service, Coast Survey.

Nautical Chart #17427 (RNC), 7th Edition, 1998. Portland Canal - Dixon Entrance to Hattie Island. Scale 1:80,000.

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

Nautical Chart #17428 (ENC and RNC), 10th Edition, 2007. Revillagigedo Channel, Nichols Passage, and Tongass

Narrows; Seal Cove; Ward Cove. Scale 1:40,000 with 1:10,000 inset. U.S. Department of Commerce, NOAA,

National Ocean Service, Coast Survey.

Nautical Chart #17430 (RNC), 11th Edition, 2005. Tongass Narrows. Scale 1:10,000. U.S. Department of Commerce,

NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17431 (RNC), 11th Edition, 2004. North End of Cordova Bay and Hetta Inlet. Scale 1:40,000. U.S.

Department of Commerce, NOAA, National Ocean Service, Coast Survey.
Love et al., 2011

30

Nautical Chart #17432 (RNC), 7th Edition, 2004. Clarence Strait and Moira Sound. Scale 1:40,000. U.S. Department

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

Nautical Chart #17433 (RNC), 11th Edition, 2004. Kendrick Bay to Shipwreck Point, Prince of Wales Island. Scale

1:40,000. U.S. Department of Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17434 (RNC), 13th Edition, 2005. Revillagigedo Channel; Ryus Bay; Foggy Bay. Scale 1:80,000

with 1:40,000 and 1:20,000 insets. U.S. Department of Commerce, NOAA, National Ocean Service, Coast

Survey.

Nautical Chart #17435 (RNC), 16th Edition, 1999. Harbors in Clarence Strait Port Chester, Annette Island; Tamgas

Harbor,Annette Island; Metlakatla Harbor. Scale 1:40,000 with 1:20,000 and 1:5,000 insets. U.S. Department

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

Nautical Chart #17436 (RNC), 9th Edition, 2006. Clarence Strait, Cholmondeley Sound and Skowl Arm. Scale

1:40,000. U.S. Department of Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17437 (RNC), 9th Edition, 2004. Portland Inlet to Nakat Bay. Scale 1:40,000. U.S. Department of

Commerce, NOAA, National Ocean Service, Coast Survey.
Digital Elevation Model of Port Alexander, Alaska

31

7. Data Processing Software

ArcGIS v. 9.3.1 – developed and licensed by ESRI, Redlands, California, HUhttp://www.esri.com/UH

ESRI World Imagery (ESRI_Imagery_World_2D) – ESRI ArcGIS Resource Centers http://resources.esri.com/

arcgisonlineservices/.

GDAL v. 1.7.1 – Geographic Data Abstraction Library is a translator library maintained by Frank Warmerdam, http://

gdal.org/.

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

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

GMT v. 4.3.4 – Generic Mapping Tools, freeware developed and maintained by Paul Wessel and Walter Smith, funded

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

Gnuplot v. 4.2, free software developed and maintained by Thomas Williams, Colin Kelley, Russell Lang, Dave Kotz,

John Campbell, Gershon Elber, Alexander Woo, http://www.gnuplot.info/.

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

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

Proj4 v. 4.7.0, free software developed by Gerald Evenden and maintained by Frank Warmerdam, http://trac.osgeo.

org/proj/.

Quick Terrain Modeler v. 7.0.0 – LiDAR processing software developed by John Hopkins University’sApplied Physics

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

VDatum Transformation Tool, developed and maintained by NOAA’s National Geodetic Survey (NGS), Office of

CoastSurvey (OCS), and Center for Operational Oceanographic Products and Services (CO-OPS), http://

vdatum.noaa.gov/.
Love et al., 2011

32

Appendix A. NOS Hydro Data Tables

Survey ID Year Scale/Vertical Accuracy Original Vertical Datum Provided Horizontal Datum

H02333 1897 1:80,000 Undetermined Undetermined

H04264 1922 1:20,000 Undetermined Undetermined

H04274 1922 1:50,000 Undetermined Undetermined

H04325 1923 1:20,000 Undetermined Undetermined

H04326 1923 1:20,000 Undetermined Undetermined

H04331 1923 1:30,000 Undetermined Undetermined

Undetermined Undetermined Undetermined Undetermined

H04431 1924 1:20,000 Undetermined Undetermined

H04432 1924 1:80,000 Undetermined Undetermined

Undetermined Undetermined Undetermined Undetermined

H04515 1925 1:20,000 Undetermined Undetermined

H04516 1925 1:40,000 Undetermined Undetermined

Undetermined Undetermined Undetermined Undetermined

H04530 1925 1:20,000 Undetermined Undetermined

Undetermined Undetermined Undetermined Undetermined

H04624 1926 1:20,000 Undetermined Undetermined

H04625 1926 1:20,000 Undetermined Undetermined

Undetermined Undetermined Undetermined Undetermined

Undetermined Undetermined Undetermined Undetermined

H06284 1937 20,000 Undetermined Undetermined

H06285 1937 20,000 Undetermined Undetermined

H06795 1942 1,000 Undetermined Undetermined

H08112 1960 1:20,000 Undetermined Undetermined

H08444 1958 1:40,000 Undetermined Undetermined

H08604 1960 20,000 Undetermined Undetermined

H09083 1969 10,000 MLLW North American Datum 1927

H09976 1981 10000 MLLW North American Datum 1927

H09977 1981 10000 MLLW North American Datum 1927

H10050 1982 10,000 MLLW North American Datum 1927

H10085 1983 10,000 MLLW North American Datum 1927
Digital Elevation Model of Port Alexander, Alaska

33

Appendix B. ENC Data Tables

Chart Title Edition Edition Date Format Scale

US1WC02M Gulf of Alaska Strait of Juan de Fuca to

Kodiak Island

20.1 10/8/2010 ENC 1:2100000

US2AK30M Dixon Entrance to Cape St. Elias 12 1/6/2011 ENC 1:969756

US3AK3CM Etolin Island to Midway Islands, including Sumner Strait;Holkham Bay;Big

Castle Island

2 7/30/2010 ENC 1:217828

US3AK40M Dixon Entrance to Chatham Strait 2 5/5/2010 ENC 1:229376

US3AK4PM Coronation Island to Lisianski Strait 9 3/21/2011 ENC 1:217828

US5AK3GM Crawfish Inlet to Sitka, Baranof

I.;Sawmill Cove

8.1 3/25/2009 ENC 1:40000

US5AK3SM Snipe Bay to Crawfish Inlet,Baranof l. 6 1/5/2009 ENC 1:40000
Love et al., 2011

34

Appendix C. Vertical Datums in Southeast Alaska

Name ID Type Source Longitude Latitude MLLW MLW MSL MHW MHHW

Baranof Warm Spring 9451625 TPS NOAA -134.825000 57.088333 1.501 1.971 3.713 5.428 5.701

Big Salt Lake 9450623 TPS NOAA -132.950000 55.600000 17.437 17.466 17.904 18.363 18.601

Craig 9450551 TPS NOAA -133.141667 55.488333 1.606 2.024 3.233 4.448 4.707

DART 46410 46410 DART NOAA -143.804000 57.634000 0.000 --- 1.554 --- 2.950

Port Alexander 9452634 TS NOAA -136.346667 58.193333 2.878 3.326 4.635 5.977 6.251

Entrance Island 9451438 TPS NOAA -133.786667 56.811667 -1.022 -0.552 1.301 3.155 3.416

False Bay Chatham St 9452328 TPS NOAA -134.935000 57.966667 0.189 0.678 2.614 4.503 4.786

Juneau 9452210 TS NOAA -134.411667 58.298333 1.102 1.590 3.712 5.778 6.073

Ketchikan 9450460 TS NOAA -131.625000 55.331667 1.887 2.366 4.345 6.320 6.595

Magnetic Point Union 9450753 TPS NOAA -132.190000 55.788333 -2.349 -1.873 0.190 2.268 2.539

Monte Carlo Island 9451247 TPS NOAA -133.766667 56.535000 1.268 1.718 3.281 4.874 5.129

Port Alexander 9451054 TS NOAA -134.646667 56.246667 1.111 1.555 2.865 4.191 4.454

Sitka 9451600 TS NOAA -135.341667 57.051667 1.379 1.824 2.989 4.170 4.407

Skagway 9452400 TS NOAA -135.326667 59.450000 0.811 1.304 3.494 5.606 5.911

Target Island Mitche 9451953 TPS NOAA -134.416667 57.533333 15.559 15.881 17.302 18.697 18.975

The Summit 9451349 TPS NOAA -133.736667 56.681667 -0.992 -0.500 1.457 3.373 3.639

Trocadero Bay 9450463 TS NOAA -132.936667 55.351667 0.186 0.599 1.798 3.011 3.259

Turn Point 9451434 TPS NOAA -132.980000 56.800000 -1.152 -0.694 1.389 3.479 3.746

Yakutat 9453220 TS NOAA -139.733333 59.548333 0.550 0.975 2.159 3.357 3.620

Alice Arm 9448 TS CHS -129.483333 55.466667 1.270 --- 3.954 --- 6.290

Armentieres Channel 9605 TS CHS -132.383333 53.100000 0.960 --- 2.526 --- 3.770

Atli Inlet 9765 TS CHS -131.576667 52.713333 1.010 --- 3.180 --- 5.040

Barnard Harbour 9115 TS CHS -129.116667 53.083333 0.810 --- 3.080 --- 5.040

Beauchemin Channel 9082 TS CHS -129.298667 52.781333 0.960 --- 3.050 --- 4.850

Block Islands 9165 TS CHS -129.733333 53.150000 0.860 --- 3.048 --- 4.960

Borrowman Bay 9080 TS CHS -129.266667 52.733333 0.650 --- 2.801 --- 4.620

Brundige Inlet 9333 TS CHS -130.851817 54.614383 1.150 --- 3.640 --- 5.750

Butedale 9053 TS CHS -128.683333 53.150000 0.900 --- 3.050 --- 4.960

Casey Cove 9350 TS CHS -130.366667 54.266667 1.160 --- 3.810 --- 6.130

Claxton 9260 TS CHS -130.083333 54.066667 1.210 --- 3.781 --- 6.120

Dadens 9960 TS CHS -132.983333 54.183333 1.010 --- 2.913 --- 4.510

Davis River 9470 TS CHS -130.166667 55.766667 -0.170 --- 2.621 --- 5.030

Dawson Harbour 9635 TS CHS -132.459000 53.163000 0.740 --- 2.370 --- 3.680

Gillen Harbour 9105 TS CHS -129.600000 52.966667 0.970 --- 3.103 --- 4.950

Granby Bay 9443 TS CHS -129.816667 55.400000 1.170 --- 3.834 --- 6.120

Griffin Pass 9020 TS CHS -128.333333 52.766667 0.870 --- 2.804 --- 4.440

Griffith Harbour 9230 TS CHS -130.533333 53.583333 1.030 --- 3.553 --- 5.790

Hartley Bay 9130 TS CHS -129.233333 53.416667 0.900 --- 3.170 --- 5.140

Haysport 9266 TS CHS -130.000000 54.166667 1.230 --- 3.840 --- 6.150

Henslung Cove 9958 TS CHS -133.004167 54.191667 0.940 --- 2.780 --- 4.330

Higgins Passage 9056 TS CHS -128.750000 52.483333 1.040 --- 2.930 --- 4.540

Hudson Bay Passage 9329 TS CHS -130.850000 54.450000 0.980 --- 3.460 --- 5.580

Humpback Bay 9309 TS CHS -130.383333 54.083333 1.220 --- 3.697 --- 5.770

Hunger Harbour 9570 TS CHS -132.033333 52.750000 0.730 --- 2.328 --- 3.650

Hunt Inlet 9310 TS CHS -130.433333 54.066667 1.120 --- 3.794 --- 6.040
Digital Elevation Model of Port Alexander, Alaska

35

Name ID Type Source Longitude Latitude MLLW MLW MSL MHW MHHW

Juskatla 9927 TS CHS -132.316667 53.616667 0.070 --- 0.610 --- 1.290

Kemano Bay 9150 TS CHS -128.116667 53.466667 1.050 --- 3.440 --- 5.560

Khyex Point 9275 TS CHS -129.800000 54.233333 0.150 --- 2.599 --- 4.970

Kincolith 9422 TS CHS -129.966667 54.983333 0.980 --- 3.691 --- 6.000

Kitimat 9140 TS CHS -128.716667 53.983333 0.980 --- 3.290 --- 5.310

Kitkatla Islands 9242 TS CHS -130.350000 53.800000 1.040 --- 3.660 --- 5.930

Klemtu 9035 TS CHS -128.516667 52.583333 0.990 --- 2.901 --- 4.560

Kumeon Bay 9414 TS CHS -130.233333 54.700000 1.000 --- 3.605 --- 5.860

Kwinitsa River 9285 TS CHS -129.583333 54.216667 0.100 --- 1.453 --- 3.000

Langara Point 9964 TS CHS -133.033333 54.250000 0.850 --- 2.770 --- 4.360

Larsen Island 9232 TS CHS -130.566667 53.616667 1.370 --- 3.780 --- 5.980

Lawyer Island 9312 TS CHS -130.333333 54.100000 1.270 --- 3.900 --- 6.170

Lowe Inlet 9195 TS CHS -129.566667 53.550000 1.080 --- 3.453 --- 5.520

Masset 9910 TS CHS -132.149317 54.009683 0.480 --- 2.040 --- 3.420

McCoy Cove 9790 TS CHS -131.650000 53.033333 1.020 --- 3.277 --- 5.180

McKenney Island 9077 TS CHS -129.483333 52.650000 0.860 --- 2.830 --- 4.530

McPherson Point 9963 TS CHS -132.966667 54.233333 0.610 --- 2.493 --- 4.010

Meyers Narrows 9060 TS CHS -128.616667 52.600000 0.740 --- 2.743 --- 4.490

Mill Bay 9425 TS CHS -129.883333 54.983333 0.800 --- 3.374 --- 5.640

Milne Island 9063 TS CHS -128.766667 52.600000 0.920 --- 2.910 --- 4.640

Moffat Islands 9325 TS CHS -130.716667 54.433333 1.080 --- 3.581 --- 5.710

Morse Basin 9344 TS CHS -130.233333 54.250000 0.120 --- 2.166 --- 4.300

Pacofi Bay 9775 TS CHS -131.866667 52.816667 1.310 --- 3.510 --- 5.400

Port Clements 9920 TS CHS -132.183333 53.683333 0.200 --- 1.311 --- 2.370

Port Edward 9342 TS CHS -130.283333 54.216667 1.100 --- 3.711 --- 5.950

Port Louis 9671 TS CHS -132.950000 53.683333 0.840 --- 2.530 --- 3.880

Port Simpson 9390 TS CHS -130.416667 54.550000 1.220 --- 3.851 --- 6.070

Prince Rupert 9354 TS CHS -130.316667 54.316667 1.150 --- 3.849 --- 6.160

Qlawdzeet Anchorage 9315 TS CHS -130.766667 54.200000 1.130 --- 3.690 --- 5.860

Queen Charlotte 9850 TS CHS -132.066667 53.250000 1.170 --- 3.992 --- 6.320

Ranger Islet 9418 TS CHS -130.166667 54.833333 1.140 --- 3.733 --- 5.950

Refuge Bay 9306 TS CHS -130.533333 54.050000 1.150 --- 3.753 --- 6.000

Salmon Cove 9435 TS CHS -129.833333 55.250000 1.040 --- 3.666 --- 5.970

Seabreeze Point 9250 TS CHS -130.166667 53.983333 1.220 --- 3.731 --- 6.020

Seal Cove 9360 TS CHS -130.266667 54.316667 1.140 --- 3.780 --- 6.090

Sedgwick Bay 9753 TS CHS -131.583333 52.633333 0.770 --- 2.798 --- 4.520

Shields Bay 9650 TS CHS -132.416667 53.300000 0.900 --- 2.560 --- 3.880

Shingle Bay 9808 TS CHS -131.816667 53.250000 1.190 --- 4.008 --- 6.390

Skidegate Channel East 9823 TS CHS -132.233333 53.150000 1.170 --- 3.942 --- 6.390

Skidegate Channel West 9830 TS CHS -132.266667 53.150000 0.370 --- 2.084 --- 3.650

Stewart 9475 TS CHS -130.000000 55.916667 1.170 --- 3.947 --- 6.420

Surf Inlet 9090 TS CHS -128.900000 53.016667 0.900 --- 2.944 --- 4.710

Trail Bay 9406 TS CHS -130.350000 54.583333 0.990 --- 3.636 --- 5.880

Trounce Inlet 9625 TS CHS -132.316667 53.133333 0.480 --- 2.017 --- 3.480

Wainright Basin 9343 TS CHS -130.250000 54.250000 0.230 --- 2.218 --- 4.380

Wiah Point 9940 TS CHS -132.300000 54.100000 0.960 --- 3.078 --- 4.880
Love et al., 2011

36

Chart Title Edition Edition Date Format Scale

US1WC02M Gulf of Alaska Strait of Juan de

Fuca to Kodiak Island

20.1 10/8/2010 ENC 1:2100000

US2AK30M Dixon Entrance to Cape St.

Elias

12 1/6/2011 ENC 1:969756

US3AK3CM Etolin Island to Midway Islands, including Sumner

Strait;Holkham Bay;Big Castle

Island

2 7/30/2010 ENC 1:217828

US3AK40M Dixon Entrance to Chatham

Strait

2 5/5/2010 ENC 1:229376

US3AK4PM Coronation Island to Lisianski

Strait

9 3/21/2011 ENC 1:217828

US5AK3GM Crawfish Inlet to Sitka, Baranof

I.;Sawmill Cove

8.1 3/25/2009 ENC 1:40000

US5AK3SM Snipe Bay to Crawfish

Inlet,Baranof l.

6 1/5/2009 ENC 1:40000

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