noaa / NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

National Environmental Satellite,

Data, and Information Service

NOAA Technical Memorandum NESDIS NGDC-27

DIGITAL ELEVATION MODELS OF CRAIG, ALASKA:

PROCEDURES, DATA SOURCES AND ANALYSIS 

E. Lim

L.A. Taylor

B.W. Eakins

K.S. Carignan

R.R. Warnken

P.R. Medley

National Geophysical Data Center

Marine Geology and Geophysics Division

Boulder, Colorado

March 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-27

DIGITAL ELEVATION MODELS OF CRAIG, ALASKA:

PROCEDURES, DATA SOURCES AND ANALYSIS

Elliot Lim1

Lisa A. Taylor2

Barry W. Eakins1

Kelly S. Carignan1

Robin R. Warnken2

Pamela R. Medley1

1

Cooperative 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

March 2009
Lim 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 Models of Craig, Alaska

iii

Contents

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

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

3. Methodology ......................................................................................................................................2

3.1 Data Sources and Processing ......................................................................................................3

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

3.1.2 Bathymetry ............................................................................................................6

3.1.3 Topography..........................................................................................................15

3.2 Establishing Common Datums .................................................................................................19

3.2.1 Vertical datum transformations ...........................................................................19

3.2.2 Horizontal datum transformations.......................................................................19

3.3 Digital Elevation Model Development .....................................................................................20

3.3.1 Verifying consistency between datasets..............................................................20

3.3.2 Smoothing of bathymetric data ...........................................................................20

3.3.3 Building the 1 arc-second and 1/3 arc-second DEMs with MB-System..............21

3.4 Quality Assessment of the DEMs.............................................................................................21

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

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

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

3.4.4	 Comparison with source data files.......................................................................24

3.4.5 Comparison with USGS topographic elevations.................................................24

4. Summary and Conclusions...............................................................................................................26

5. Acknowledgments............................................................................................................................26

6. References........................................................................................................................................26

7. Data Processing Software ................................................................................................................27

List of Figures

Figure 1. Shaded-relief image of the Craig 1 arc-second DEM.................................................................1

Figure 2. Source and coverage of datasets used in compiling the Craig DEMs ........................................3

Figure 3. Digital coastline datasets surrounding Craig Harbor..................................................................4

Figure 4. Coastline in Craig Harbor shown with USACE hydrographic data and USACE project 

overview map.......................................................................................................................5

Figure 5. Digital NOS hydrographic survey coverage in the Craig region..............................................10

Figure 6. USACE project layout image for Craig Harbor........................................................................11

Figure 7. An oblique photo of Craig Harbor............................................................................................12

Figure 8. NOS hydrographic lidar surveys in the Craig region................................................................13

Figure 9. Source and coverage of topographic datasets used in compiling the Craig DEMs..................15

Figure 10. Coverage of NED 2 arc-second topographic data in the Craig DEMs.....................................16

Figure 11. Example of gap in the SRTM data coverage ............................................................................17

Figure 12. Detail of Craig Harbor with USACE project overview georeferenced image 

underlying SRTM topographic data...................................................................................18

Figure 13. Histogram of the difference between NOS hydrographic survey H03547 and 

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

Figure 14. Slope map of the 1 arc-second Craig DEM in the vicinity of Craig, Alaska............................22

Figure 15. Perspective view from the southeast of the 1 arc-second Craig DEM. ....................................23

Figure 16. Perspective view from the southeast of the 1/3 arc-second Craig DEM ..................................23

Figure 17. Histogram of the difference between SRTM topographic dataset and the 

1/3 arc-second Craig DEM................................................................................................24

Figure 18 Comparison between USGS topography contours and the 1/3 arc-second Craig DEM 

topographic contours .........................................................................................................25
Lim et al., 2009

iv

List of Tables

Table 1a.	 PMEL specifications for the 1 arc-second Craig DEM...............................................................2

Table 1b.	 PMEL specifications for the 1/3 arc-second Craig DEM ...........................................................2

Table 2. Shoreline dataset used in compiling the Craig DEMs................................................................4

Table 3. Bathymetric datasets used in compiling the Craig DEMs..........................................................6

Table 4. Digital NOS hydrographic surveys used in compiling the Craig DEMs....................................7

Table 5. Multibeam swath sonar surveys used in compiling the Craig DEMs.......................................14

Table 6. Topographic datasets used in compiling the Craig DEMs........................................................15

Table 7. Relationship between MHW and other vertical datums in the Craig region ............................19

Table 8. Data hierarchy used to assign gridding weight in MB-System..................................................21
Digital Elevation Models of Craig, Alaska:

Procedures, Data Sources and Analysis

1. Introduction

	 	 In October 2008, the National Geophysical Data Center (NGDC), an office of the National Oceanic and

Atmospheric Administration (NOAA), developed two integrated bathymetric–topographic digital elevation models 

(DEMs) centered on Craig, Alaska (Fig. 1) for the Pacific Marine Environmental Laboratory (PMEL) NOAA Center

for the Tsunami Research (http://nctr.pmel.noaa.gov/). The 1 arc-second1 and 1/3 arc-second coastal DEMs will be 

used as input for the Method of Splitting Tsunami (MOST) model developed by PMEL to simulate tsunami generation, 

propagation and inundation. The DEMs were generated from diverse digital datasets in the region (grid boundary and 

sources shown in Fig. 2) and designed to represent modern morphology. They 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 description of the data sources and 

methodology used to develop the Craig DEMs. 

1. In polar latitudes, longitude lines are spaced significantly closer together than latitude lines, approaching zero at the poles. While the DEMs

are built upon grids of square cells in geographic coordinates, they are not square cells when converted to meters. At the latitude of Craig, Alaska 

(55o28’35”N, 133o8’54”W) 1 arc-second of latitude is equivalent to 30.68 meters; 1 arc-second of longitude equals 17.42 meters.

Figure 1. Shaded-relief image 

of the Craig 1 arc-second DEM. 

Contour interval is 250 meters. 

Image is in Mercator projection.
Lim et al., 2009

2

2. Study Area

 Craig, Alaska is located at 55o28’35”N 133o8’54”W, on Craig Island, connected to the west coast of Prince 

of Wales Island. It is a part of the Alexander Archipelago and is approximately 56 miles northwest of Ketchikan and 

220 miles south of Juneau. The Prince of Wales Island spans an area of more than 2,600 square miles and covers 990 

miles of coastline. The islands in the area are the exposed peaks of submerged coastal mountains that rise steeply from 

the Pacific Ocean. The morphology is characterized by deep, fjord-like channels that separate the islands and cut them

off from the mainland. In addition, forested mountains, deep U-shaped valleys, streams, lakes, and bays are prevalent 

in the area. 

	 	 The town was named after Craig Miller who established a fish saltery on nearby Fish Egg Island in 1907 with

the assistance of the local Haida natives. He went on to construct a cold storage plant and packing company at the 

present site of Craig, Alaska. 

3. Methodology

 The Craig DEMs were 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) geographic 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 1a: PMEL specifications for the 1 arc-second Craig DEM.

Grid Area Craig, Alaska

Coverage Area 132.49 o to 134.31o W; 54.49o to 56.28o 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 ASCII raster grid

Table 1b: PMEL specifications for the 1/3 arc-second Craig DEM.

Grid Area Craig, Alaska

Coverage Area 133.00 o to 133.46o W; 55.30o to 55.63o N

Coordinate System Geographic decimal degrees

Horizontal Datum World Geodetic System of 1984 (WGS 84)

Vertical Datum MHW

Vertical Units Meters

Cell Size 1/3 arc-second

Grid Format ESRI ASCII raster 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 Models of Craig, Alaska

3

3.1 Data Sources and Processing

Shoreline, bathymetric, and topographic digital datasets (Fig. 2) were obtained from several U.S. federal and 

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

U.S. Fish and Wildlife Service (USFWS); the U.S. Geological Survey (USGS); and the U.S. Army Corps of Engineers 

(USACE). Safe Software’s FME data translation tool package was used to shift datasets to NAD 83 horizontal datum 

and to convert 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 also accomplished using FME, based upon 

data from the NOAA Craig tidal station, as no VDatum model software was available for this area. 

Figure 2. Source and coverage of datasets used in compiling the Craig DEMs. 

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.
Lim et al., 2009

4

3.1.1 Shoreline

Two digital coastline datasets of the Craig region were analyzed for inclusion in the Craig DEMs: NOAA 

ENC #17405 (1:40,000 scale) and USFWS statewide Alaska digital coastline. Comparisons between the two coastline 

datasets, NOS hydrographic surveys, Shuttle Radar Topography Mission (SRTM) topographic DEM and NOS 

hydrographic lidar showed that the USFWS coastline (Table 2) best fit the topographic and bathymetric data (Fig. 3)

and was edited to create a “combined coastline” for the Craig DEMs.

ENC #17405 provided an extracted coastline covering a 16 km2 area surrounding Craig. This coastline is at 

lower resolution and less complete than the SRTM topographic dataset and is not as accurate as the USFWS coastline. 

Therefore it was not used in building the Craig DEMs. 

 Table 2. Shoreline dataset used in compiling the Craig DEMs.

Source Year Data Type Spatial Resolution Original Horizontal Datum/

Coordinate System

Original 

Vertical Datum

USFWS 2006 Compiled 

coastline Various WGS 84 geographic Undefined

Figure 3. Digital coastline datasets surrounding Craig Harbor. The ENC coastline is of lower 

resolution and is less accurate than the SRTM topographic data. It was not used in building the 

Craig DEMs.
Digital Elevation Models of Craig, Alaska

5

1) U.S. Fish and Wildlife Service coastline

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 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; the horizontal datum of the compiled USFWS coastline is WGS 84. The USFWS coastline 

provides complete coverage of the DEM areas.

To obtain the best digital MHW coastline, NGDC manually edited the USFWS coastline into a combined 

coastline (Fig. 3). The USFWS coastline was chosen over the ENC due to its full coverage of the DEMs. The 

USFWS coastline was edited to be consistent with the SRTM topography, NOS hydrographic survey data, 

and NOS hydrographic lidar. The coastline around Craig Harbor was manually adjusted to fit recent USACE

survey data and to represent two breakwaters off the southeast tip of Craig Island (Fig. 4). The combined 

coastline was sub-sampled to 10-meter spacing using NGDC’s GEODAS software and converted to point 

data for use in the gridding process. It was also used as a coastal buffer for the bathymetric pre-surfacing 

algorithm (see Sec. 3.3.2) to ensure that interpolated bathymetric values reached “zero” at the coast. The 

combined coastline was used to clip the SRTM and National Elevation Dataset (NED) topographic DEMs, 

which contained elevation values, typically zero, over the open ocean (see Sec. 3.1.3).

Figure 4. Coastline in Craig Harbor (black line) shown with USACE hydrographic data and 

USACE project overview map.
Lim et al., 2009

6

3.1.2 Bathymetry

Bathymetric datasets used in the compilation of the Craig DEMs included: NOS hydrographic surveys, 

one recent USACE harbor survey, NOAA ENC chart soundings, two NOS hydrographic lidar surveys, and NGDC 

multibeam swath sonar surveys (Table 3). Datasets were originally referenced to mean lower low water (MLLW) or 

mean sea level (MSL).

Table 3. Bathymetric datasets used in compiling the Craig DEMs.

Source Year Data Type Spatial Resolution

Original 

Horizontal 

Datum/

Coordinate 

System

Original 

Vertical 

Datum

URL

NGDC

1909 

to 

2003

NOS 

hydrographic 

survey 

soundings

Ranges from 10 meters 

to 1.5 kilometers (varies 

with scale of survey, depth, 

traffic and probability of

obstructions)

NAD 27, 

NAD 83, Early 

Alaskan Datum, 

Undefined Datum

MLLW

(meters)

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

bathymetry/hydro.html

USACE 2003 Harbor 

survey

~2 to 10 meters

Alaska State 

Plane, zone 1, 

NAD 83 feet

MLLW

(feet)

http://www.poa.usace.army.mil/en/

hydro/King%20Cove/2006/

NOAA 

ENCs 2008

NOAA 

digitized 

nautical chart 

soundings

~500 to 1200 meters WGS 84 

geographic

MLLW 

(meters)

http://nauticalcharts.noaa.gov/

mcd/enc/

NOS 2005 Hydrographic 

lidar surveys 5 meters NAD 83 geographic

MLLW 

(meters)

NGDC 2007

Multibeam 

swath sonar 

surveys

Raw sonar files gridded to

1 arc-second

WGS 84 

geographic

Assumed

MSL 

(meters)

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

bathymetry/multibeam.html

1) National Ocean Service hydrographic survey data

A total of 158 NOS hydrographic surveys conducted between 1909 and 2003 were used in the Craig 

DEM development (Table 4; Fig. 5). The hydrographic survey data were originally vertically referenced to 

MLLW and horizontally referenced to NAD 27 or NAD 83 geographic and Early Alaska, or “undetermined” 

datums. 

Data point spacing for the surveys ranged from about 10 to 60 meters in shallow water to 1.5 kilometers 

in deep water. All surveys were extracted from NGDC’s NOS Hydrographic Survey Database (http://www.

ngdc.noaa.gov/mgg/bathymetry/hydro.html) in their original datums (Table 4). The data were then converted 

to NAD 83 using FME software, an integrated collection of spatial extract, transform, and load tools for 

data transformation; some NOS surveys were manually shifted in ArcGIS to fit the combined coastline. The

surveys were subsequently clipped to a polygon 0.05 degrees (~5%) larger than the 1 arc-second gridding 

area to support data interpolation across DEM boundaries.

After converting 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 compared to the NED 

and SRTM topographic data and the combined coastline. 

NOS survey #H11237 had incorrect bathymetry values, determined when checked against the 

smoothsheet and overlapping datasets. Further investigation revealed that the original soundings had been 

converted from fathoms to meters twice. FME was used to change each sounding in survey #H11237 to the 

correct value by multiplying the elevations by .5468 (1 meter = .5468 fathoms). NOS was contacted and they 

are in the process of revising the survey. 
Digital Elevation Models of Craig, Alaska

7

Table 4. Digital NOS hydrographic surveys used in compiling the Craig DEMs.

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

H03042* 1909 20,000 MLLW Undetermined horizontal datum

H03042A* 1909 40,000 MLLW Undetermined horizontal datum

H03416* 1912/13 20,000 MLLW Undetermined horizontal datum

H03417* 1912 20,000 MLLW Undetermined horizontal datum

H03427* 1912 10,000 MLLW Undetermined horizontal datum

H03427I* 1912 20,000 MLLW Undetermined horizontal datum

H03539* 1913 10,000 MLLW Undetermined horizontal datum

H03540* 1913 20,000 MLLW Undetermined horizontal datum

H03547* 1913 10,000 MLLW Undetermined horizontal datum

H03666* 1914 10,000 MLLW Undetermined horizontal datum

H03678* 1914 20,000 MLLW Undetermined horizontal datum

H03679* 1914 10,000 MLLW Undetermined horizontal datum

H03680* 1914 10,000 MLLW Undetermined horizontal datum

H03691* 1914 20,000 MLLW Undetermined horizontal datum

H03692* 1914 20,000 MLLW Undetermined horizontal datum

H03692A* 1914/25 20,000 MLLW Undetermined horizontal datum

H03795* 1915 10,000 MLLW Undetermined horizontal datum

H03818* 1915 20,000 MLLW Undetermined horizontal datum

H03819A* 1916 120,000 MLLW Undetermined horizontal datum

H03819B* 1920 120,000 MLLW Undetermined horizontal datum

H03880* 1915 20,000 MLLW Undetermined horizontal datum

H03912* 1916 20,000 MLLW Undetermined horizontal datum

H03930* 1916 10,000 MLLW Undetermined horizontal datum

H03931* 1916 40,000 MLLW Undetermined horizontal datum

H03932* 1916 20,000 MLLW Undetermined horizontal datum

H03932A* 1917 20,000 MLLW Undetermined horizontal datum

H03932I* 1916 10,000 MLLW Undetermined horizontal datum

H03933* 1916 20,000 MLLW Undetermined horizontal datum

H03940* 1916 20,000 MLLW Undetermined horizontal datum

H04009* 1917 20,000 MLLW Undetermined horizontal datum

H04191* 1920 20,000 MLLW Undetermined horizontal datum

H04192* 1920 20,000 MLLW Undetermined horizontal datum

H04203* 1921 20,000 MLLW Undetermined horizontal datum

H04204* 1921 10,000 MLLW Undetermined horizontal datum

H04208A* 1921 120,000 MLLW Undetermined horizontal datum

H04208B* 1921 60,000 MLLW Undetermined horizontal datum

H04209* 1921 20,000 MLLW Undetermined horizontal datum

H04209I1* 1921 10,000 MLLW Undetermined horizontal datum

H04209I2* 1921 10,000 MLLW Undetermined horizontal datum

H04251* 1922 20,000 MLLW Undetermined horizontal datum

H04259* 1922 20,000 MLLW Undetermined horizontal datum

H04260* 1922 20,000 MLLW Undetermined horizontal datum

H04261A* 1922/23 120,000 MLLW Undetermined horizontal datum

H04261B* 1922/23 60,000 MLLW Undetermined horizontal datum

H04264* 1922 20,000 MLLW Undetermined horizontal datum

H04273* 1922 20,000 MLLW Undetermined horizontal datum

H04274* 1922 50,000 MLLW Undetermined horizontal datum
Lim et al., 2009

8

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

H04325* 1923 20,000 MLLW Undetermined horizontal datum

H04326* 1923 20,000 MLLW Undetermined horizontal datum

H04330* 1923 10,000 MLLW Undetermined horizontal datum

H04441* 1924 10,000 MLLW Undetermined horizontal datum

H04515* 1925 20,000 MLLW Undetermined horizontal datum

H04516* 1925 40,000 MLLW Undetermined horizontal datum

H04517A* 1925 20,000 MLLW Undetermined horizontal datum

H04534* 1925 10,000 MLLW Undetermined horizontal datum

H04535* 1925 20,000 MLLW Undetermined horizontal datum

H04536* 1925 40,000 MLLW Undetermined horizontal datum

H04594* 1925 20,000 MLLW Undetermined horizontal datum

H04622A* 1926 20,000 MLLW Undetermined horizontal datum

H04626A* 1926 40,000 MLLW Undetermined horizontal datum

H04626AI* 1926 20,000 MLLW Undetermined horizontal datum

H04761A* 1927 10,000 MLLW Undetermined horizontal datum

H04773* 1927 10,000 MLLW Undetermined horizontal datum

H04774* 1927 10,000 MLLW Undetermined horizontal datum

H06283* 1937 20,000 MLLW Early Alaska Datums

H06284* 1937 20,000 MLLW Early Alaska Datums

H06285* 1937 20,000 MLLW Early Alaska Datums

H06358* 1938 10,000 MLLW Early Alaska Datums

H07095* 1946 2,500 MLLW Early Alaska Datums

H07098* 1946 5,000 MLLW Early Alaska Datums

H07987* 1957 10,000 MLLW Early Alaska Datums

H08036* 1953 10,000 MLLW Early Alaska Datums

H08037* 1953 10,000 MLLW Early Alaska Datums

H08038* 1953 10,000 MLLW Early Alaska Datums

H08064* 1953 20,000 MLLW Early Alaska Datums

H08065A 1953/54 10,000 MLLW NAD 27

H08065B 1953/54 10,000 MLLW NAD 27

H08067* 1953/54 10,000 MLLW Early Alaska Datums

H08112 1960 20,000 MLLW NAD 27

H08127* 1954 10,000 MLLW Early Alaska Datums

H08128* 1954 10,000 MLLW Early Alaska Datums

H08130* 1954 10,000 MLLW Early Alaska Datums

H08131* 1954 10,000 MLLW Early Alaska Datums

H08132* 1954 10,000 MLLW Early Alaska Datums

H08133 1954 10,000 MLLW Early Alaska Datums

H08134* 1954 20,000 MLLW Early Alaska Datums

H08149 1954 10,000 MLLW Early Alaska Datums

H08150* 1954 10,000 MLLW Early Alaska Datums

H08151* 1955 10,000 MLLW Early Alaska Datums

H08230 1945/55 10,000 MLLW Early Alaska Datums

H08231 1955 10,000 MLLW Early Alaska Datums

H08232 1955 10,000 MLLW Early Alaska Datums

H08244 1955 10,000 MLLW Early Alaska Datums

H08245 1955 10,000 MLLW Early Alaska Datums

H08286 1956 10,000 MLLW Early Alaska Datums

H08287 1956 10,000 MLLW Early Alaska Datums
Digital Elevation Models of Craig, Alaska

9

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

H08288* 1956 10,000 MLLW Early Alaska Datums

H08289* 1956 10,000 MLLW Early Alaska Datums

H08290 1956 10,000 MLLW Early Alaska Datums

H08325 1955 10,000 MLLW NAD 27

H08326 1956/58 5,000 MLLW Early Alaska Datums

H08359* 1957 10,000 MLLW Early Alaska Datums

H08391 1957 10,000 MLLW early Alaska Datums

H08392* 1957 10,000 MLLW Early Alaska Datums

H08393 1957 10,000 MLLW NAD 27

H08443 1958 10,000 MLLW Early Alaska Datums

H08444 1958 40,000 MLLW NAD 27

H08455* 1958/60 10,000 MLLW NAD 27

H08456* 1958 10,000 MLLW NAD 27

H08457 1958 10,000 MLLW NAD 27

H08458 1958 10,000 MLLW Early Alaska Datums

H08466* 1959 10,000 MLLW Early Alaska Datums

H08531 1960 10,000 MLLW Early Alaska Datums

H08532 1960 10,000 MLLW Early Alaska Datums

H08533 1963 10,000 MLLW Early Alaska Datums

H08604 1961 20,000 MLLW Early Alaska Datums

H08605 1961 20,000 MLLW Early Alaska Datums

H08640 1962 10,000 MLLW Early Alaska Datums

H08653 1962 10,000 MLLW Early Alaska Datums

H08654 1962 10,000 MLLW Early Alaska Datums

H08688* 1965 10,000 MLLW Early Alaska Datums

H08769 1963 10,000 MLLW Early Alaska Datums

H08945 1967/71 10,000 MLLW Early Alaska Datums

H08946* 1967/71 10,000 MLLW Early Alaska Datums

H09084 1969 10,000 MLLW Early Alaska Datums

H09085 1969 10,000 MLLW Early Alaska Datums

H09092 1969 20,000 MLLW NAD 27

H09192 1971 10,000 MLLW NAD 27

H09193 1971 5,000 MLLW NAD 27

H09194 1971 20,000 MLLW NAD 27

H09215 1971 10,000 MLLW Early Alaska Datums

H09216* 1971 10,000 MLLW Early Alaska Datums

H09220 1971 10,000 MLLW Early Alaska Datums

H09222 1971 5,000 MLLW Early Alaska Datums

H09269 1972 10,000 MLLW NAD 27

H09309 1972 10,000 MLLW Early Alaska Datums

H09401 1973 10,000 MLLW Early Alaska Datums

H09402 1973 10,000 MLLW NAD 27

H09403 1973 10,000 MLLW NAD 27

H09754 1978 5,000 MLLW Early Alaska Datums

H09756* 1978 5,000 MLLW Early Alaska Datums

H09757 1978 10,000 MLLW Early Alaska Datums

H10818 1998 10,000 MLLW NAD 83

H10949 2000 20,000 MLLW NAD 83

H10950 2000 20,000 MLLW NAD 83
Lim et al., 2009

10

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

H10951 2001 20,000 MLLW NAD 83

H10959 2000 20,000 MLLW NAD 83

H11058 2001 10,000 MLLW NAD 83

H11099 2002 10,000 MLLW NAD 83

H11160 2002 10,000 MLLW NAD 83

H11161 2002 10,000 MLLW NAD 83

H11162 2002 10,000 MLLW NAD 83

H11163 2002 10,000 MLLW NAD 83

H11164 2002 20,000 MLLW NAD 83

H11165 2002 10,000 MLLW NAD 83

H11237 2003 10,000 MLLW NAD 83

H11238 2003 10,000 MLLW NAD 83

H11240 2003 10,000 MLLW NAD 83

* Geographic position manually adjusted in ArcGIS to fit combined coastline.

Figure 5. Digital NOS hydrographic survey coverage in the Craig region. Red denotes boundary of 1 arc-second DEM;. 

green denotes boundary of 1/3 arc-second DEM; coastline in black.
Digital Elevation Models of Craig, Alaska

11

2) U.S. Army Corps of Engineers harbor survey

The USACE conducted a high-resolution hydrographic harbor survey of Craig Harbor in 2003 (Figs. 6 

and 7). The survey was originally referenced to NAD 83 Alaska State Plane coordinates (feet) and MLLW 

vertical datum (feet). The resolution of the survey ranges from ~2 to 10 meters and the depth ranges from 

-1.1 to -11.3 meters at MHW.

Figure 6. USACE project layout image for Craig Harbor. 

(http://www.poa.usace.army.mil/CO/CoOrg/PnI_New)
Lim et al., 2009

12

Figure 7. An oblique photo of Craig taken on Apri 28, 2005 from the west. Provided by the USACE AK District web site.

(http://www.poa.usace.army.mil/CO/CoOrg/PnI_New/craig%20hbr%20south%20cove%20R&H%2005.jpg)
Digital Elevation Models of Craig, Alaska

13

3) NOAA Electronic Navigational Chart soundings

Nautical charts #16016 and #17404 were available from OCS in Electronic Navigational Chart (ENC) 4

format and, as no bathymetric survey data were available for these areas, sounding data were extracted from 

these charts using FME. 

ENC chart #16016 covers the area from Dixon Entrance to Cape St. Elias. Soundings range from ~3 

kilometers to 6.5 kilometers apart, and depths range from -2166.24 meters to -6.44 meters. The scale for this 

dataset is 1:300,000.

ENC chart #17404 coverage stretches eastward from San Christoval Channel to Cape Lynch. Soundings 

range from ~20 meters to ~1200 meters apart, and depths range from -3.14 meters to -277.14 meters at MHW. 

The scale for this dataset is 1:40,000.

4) National Ocean Service hydrographic lidar surveys

NOS provided NGDC with two recent hydrographic lidar surveys located in the eastern and central part 

of the Craig 1 arc-second DEM (Fig. 8). The lidar surveys are referenced to NAD 83 geographic and MLLW. 

These surveys range from -.01 to -38.86 meters in elevation with a point spacing of 5 meters. The elevations 

on or near the shoreline were generally inconsistent with the SRTM dataset and were not used in building the 

Craig 1 arc-second DEM.

Figure 8. NOS hydrographic lidar surveys in the Craig region. #H11209 is located on the north eastern border and 

#H11208 is in the central portion of the 1 arc-second Craig DEM.

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/]
Lim et al., 2009

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5) Multibeam swath sonar files

Two multibeam swath sonar surveys (Table 5; Fig. 2) were available from the NGDC multibeam sonar 

bathymetry database (http://www.ngdc.noaa.gov/mgg/bathymetry/multibeam.html) for use in the 1 arcsecond Craig DEM. This database is comprised of the original swath sonar files of surveys conducted mostly

by the U.S. academic fleet. Most of the multibeam swath sonar surveys offshore were transits rather than

dedicated sea-floor surveys. Both surveys have a horizontal datum of WGS 84 geographic and an undefined

vertical datum, assumed to be equivalent to MSL. 

The downloaded data were gridded to 1 arc-second resolution using MB-System. MB-System is an 

NSF-funded free software application specifically designed to manipulate multibeam swath sonar data. The

gridded data were converted to shapefiles and transformed to MHW using FME.

Table 5. Multibeam swath sonar surveys used in compiling the Craig DEMs.

Cruise ID Ship Year Original Vertical 

Datum

Original Horizontal 

Datum Institution

F0CI93 Surveyor 1993 Assumed MSL WGS 84 geographic NOAA

KMO514 Kilo Moana 2005 Assumed MSL WGS 84 geographic University of New 

Hampshire
Digital Elevation Models of Craig, Alaska

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3.1.3 Topography

Topographic datasets in the Craig region were obtained from the USGS: NED 2 arc-second gridded 

topography and 1 arc-second SRTM (Fig. 9; Table 6). NGDC also digitized harbor features not represented in either 

topographic dataset.

Table 6. Topographic datasets used in compiling the Craig DEMs.

Source Year Data Type Spatial Resolution

Original Horizontal 

Datum/Coordinate 

System

Original Vertical 

Datum URL

USGS 

NED 2006 Topographic DEM 2 arc-second grid NAD 27 geographic NGVD29(meters) http://ned.usgs.gov/

NASA

SRTM 2000 Topographic DEM 1 arc-second grid WGS 84 geographic WGS 84/EGM96 Geoid (meters) http://srtm.usgs.gov/

Figure 9. Source and coverage of topographic datasets used in compiling the Craig DEMs.
Lim et al., 2009

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1) U.S. Geological Survey National Elevation Dataset topography

USGS’s NED provides complete 2 arc-second coverage of Alaska5. Data are in NAD 27 Alaska 

geographic coordinates and North American Vertical Datum of 1929 (NGVD29) vertical datum (meters), 

and are available for download as raster DEMs. The extracted bare-earth elevations have a vertical accuracy 

of +/- 7 to 15 meters depending on source data resolution (see the USGS Seamless web site for specific source

information: http://seamless.usgs.gov). The dataset was derived from USGS quad maps and aerial photos 

based on surveys conducted in the 1970s and 1980s. The NED data were used only to fill in gaps within the

SRTM data (e.g., Fig. 9). In addition, the NED data had values over the open oceans that were deleted by 

clipping to the coastline.

Figure 10. Coverage of NED 2 arc-second topographic data in the Craig DEMs. Note: White areas denote data gaps.

5. The USGS National Elevation Dataset (NED; http://ned.usgs.gov/) has been developed by merging the highest-resolution, best quality elevation data available across the United States into a seamless raster format. NED is the result of the maturation of the USGS effort to provide 

1:24,000-scale Digital Elevation Model (DEM) data for the conterminous U.S. and 1:63,360-scale DEM data for Alaska. The dataset provides 

seamless coverage of the United States, HI, AK, and the island territories. NED has a consistent projection (Geographic), resolution (1 arc-second), 

and elevation units (meters). The horizontal datum is NAD 83, except for AK, which is NAD 27. The vertical datum is NAVD88, except for AK, 

which is NGVD29. NED is a living dataset that is updated bimonthly to incorporate the “best available” DEM data. As more 1/3 arc-second (10 m) 

data covers the U.S., then this will also be a seamless dataset. [Extracted from USGS NED web site]
Digital Elevation Models of Craig, Alaska

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2) NASA Space Shuttle Radar Topography Mission

The NASA SRTM obtained elevation data on a near-global scale to generate the most complete highresolution digital topographic database of Earth6

. 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, edited to define the coastline, and 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 Craig, there are numerous 

small areas with “no data” values necessitating the use of the lower-resolution NED topographic data in these 

areas (Fig. 11). The SRTM DEM also contains values over the open ocean, which were deleted by clipping 

to the combined coastline.

Figure 11. Example of gap (white area) in the SRTM data coverage. Gaps were filled with topographic data from the NED DEM. 

Edited coastline in black. Blue represents zero values over the open ocean.

6. 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]
Lim et al., 2009

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3) NGDC digitized harbor features

Using a USACE project overview image as a reference, NGDC digitized a point shapefile to represent

two main harbor features at Craig. The breakwater that forms the southeastern barrier of Craig Island and the 

breakwater that forms the barrier to the south of the Craig Harbor entrance were given elevation values of 1 

meter, estimated from aerial photographs (e.g., Fig. 7).

Figure 12. Detail of Craig Harbor with USACE project overview georeferenced image underlying SRTM topographic data.
Digital Elevation Models of Craig, Alaska

19

3.2 Establishing Common Datums

3.2.1 Vertical datum transformations

Datasets used in the compilation and evaluation of the Craig DEMs were originally referenced to a number 

of vertical datums including: MLLW, MSL, WGS 84/EGM96 Geoid, and NGVD29. All datasets were transformed to 

MHW to provide the maximum flooding for inundation modeling.

1) Bathymetric data

The NOS hydrographic surveys, the USACE survey data, NOS lidar surveys, and the nautical chart 

soundings were transformed from MLW and MLLW to MHW, using FME software, by adding a constant 

offset measured at the NOAA Craig tidal station (Table 7). The multibeam swath sonar grid was transformed 

from MSL to MHW by adding a constant offset of -1.215 meters (Table 7).

2) Topographic data

The NED and SRTM DEMs were originally referenced to NGVD29 and WGS 84/EGM96 Geoid vertical 

datums, respectively. There are no survey markers in the vicinity of Craig that relate these two geodetic 

datums to the local tidal datums. Thus, it was assumed that both datums are essentially equivalent to MSL in 

this area (Table 7). Conversion to MHW, using FME software, was accomplished by adding a constant value 

of -1.215 meters.

Table 7. Relationship between MHW and other vertical datums in the Craig region.*

Vertical datum Difference to MHW

MTL -1.212

NGVD29 + -1.215

WGS 84/EGM96 Geoid + -1.215

MSL -1.215

MLW -2.424

MLLW -2.842

* Datum relationships determined by tidal station #9451600 at Craig, Alaska.

+ Assumed to be equivalent to MSL.

3.2.2 Horizontal datum transformations

Datasets used in compiling the Craig DEMs were originally referenced to Early Alaska, “undetermined”, 

and NAD 27, NAD 83, or WGS 84 geographic horizontal datums. The relationships and transformational equations 

between the geographic horizontal datums are well established. The NAD 27 geographic data were converted to 

a horizontal datum of NAD 83 geographic using FME software. The NOS surveys referenced to Early Alaska or 

“undetermined” horizontal datums were manually shifted in ArcGIS to fit the combined coastline.
Lim et al., 2009

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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

ESRI ArcMap and Quick Terrain Modeler 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:

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

automated clipping to the combined coastline.

•	 Lack of good bathymetric data in the southern quarter of the 1 arc-second DEM.

•	 Lack of good bathymetric data near the coastline.

•	 Positional uncertainty of NOS surveys with Early Alaska or “undetermined” horizontal datums.

3.3.2 Smoothing of bathymetric data

The NOS hydrographic surveys are generally sparse at the resolution of the 1 arc-second grid in both deep 

water and near shore; the NOS survey data have point spacing up to 1.5 kilometers apart. In order to reduce the effect 

of artifacts in the form of lines of “pimples” in the 1 arc-second DEM due to this low resolution dataset, and to provide 

effective interpolation into the coastal zone, a 1 arc-second-spacing “pre-surface” or 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 combined with the USACE surveys, ENC sounding, 

NOS hydrographic lidar, and NGDC multibeam swath sonar bathymetry data into a single file. Points extracted every

10 meters from the combined coastline were also included and assigned negative values of -1 meter to ensure 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 3 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”. Conversion of 

this Arc ASCII grid file into an Arc raster permitted clipping of the grid with the combined coastline (to eliminate data

interpolation into land areas). The resulting surface was compared with the original soundings to ensure grid accuracy 

(e.g., Fig. 13), converted to a shapefile, and then exported as an xyz file for use in the final gridding process (see

Table 8). The statistical analysis of the differences between the 1 arc-second bathymetric surface and one of the NOS 

surveys showed that the majority of the NOS soundings are in good agreement with the bathymetric surface. The few 

exceptions where the difference reached a few meters are attributed to rugged bathymetry where two or more closely 

positioned points were averaged to obtain the elevation of one grid cell.

Figure 13. Histogram of the difference between NOS hydrographic survey H03547 and the 1 arc-second pre-surfaced 

bathymetric grid. 
Digital Elevation Models of Craig, Alaska

21

3.3.3 Building the 1 arc-second and 1/3 arc-second DEMs with MB System

MB-System was used to create 1 arc-second and 1/3 arc-second DEMs of Craig, Alaska. The MB-System

tool “mbgrid” applied a tight spline tension to the xyz data, and interpolated values for cells without data. The data 

hierarchy used in the “mbgrid” gridding algorithm, as relative gridding weights, is listed in Table 8. Greatest weight 

was given to the high-resolution USACE and NOS hydrographic lidar datasets. Least weight was given to the presurfaced 1 arc-second bathymetric grid.

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

Dataset Relative Gridding Weight

SRTM topographic DEM 10

USACE surveys 1000

NOS hydrographic surveys 10

Final coastline at 0 meters elevation 1

USGS NED topographic DEM 100

ENC soundings 100

NOS lidar surveys 1000

NGDC hydrographic sonar multibeam 10

NGDC digitized features 10

Pre-surfaced bathymetric grid 1

3.4 Quality Assessment of the DEMs

3.4.1. Horizontal accuracy

The horizontal accuracy of topographic and bathymetric features in the Craig DEMs are dependent upon the 

datasets used to determine corresponding DEM cell values. Topographic features in island interiors have an estimated 

horizontal accuracy of 50 to 75 meters, based on the documented accuracy of the NED and SRTM DEMs. Bathymetric 

features in areas covered by early 20th century NOS hydrographic soundings—along the margins of the DEM—are 

resolved only to within a few tens of meters in shallow water, and hundreds of meters in deep-water areas; their 

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

navigated (e.g., GPS) NOS hydrographic surveys.

3.4.2 Vertical accuracy

Vertical accuracy of elevation values for the DEMs are also highly dependent upon the source datasets 

contributing to grid cell values. Island interiors have vertical accuracies of between 10 and 15 meters, derived from the 

NED topographic data (estimated vertical accuracy of 10 meters) and the SRTM topographic data (vertical accuracy 

better than 16 meters but typically about 10 meters). Bathymetric values are derived from a wide range of input data, 

consisting of single and multibeam sounding measurements from the early 20th centuries to recent: modern NOS 

standards are 0.3 m in 0 to 20 m of water, 1.0 m in 20 to 100 m of water, and 1% of the water depth in 100 m of water. 

Gridding interpolation to determine bathymetric values between sparse, poorly located NOS soundings degrades the 

vertical accuracy of elevations in deep water to about 5% of water depth.
Lim et al., 2009

22

3.4.3 Slope map and 3-D perspectives

ESRI ArcCatalog was used to generate a slope grid from the 1 arc-second Craig DEM to allow for visual 

inspection and identification of artificialslopes along boundaries between datasets(Fig. 14).The DEM wastransformed

to UTM zone 8N coordinates (horizontal units in meters) in ArcCatalog for derivation of the slope grid; equivalent 

horizontal and vertical units are required for effective slope analysis. Three-dimensional viewing of the DEMs (Figs. 

15 and 16) was accomplished using POV Ray. Analysis of preliminary grids revealed suspect data points, which were 

corrected before recompiling the DEM. 

Figure 14. Slope map of the 1 arc-second Craig DEM in the vicinity of Craig, Alaska. Flat-lying 

slopes are white; dark shading denotes steep slopes; combined coastline in red.
Digital Elevation Models of Craig, Alaska

23

Figure 15. Perspective view from the southeast of the 1 arc-second Craig DEM. Vertical exaggeration–times 2.

Figure 16. Perspective view from the southeast of the 1/3 arc-second Craig DEM. Vertical exaggeration–times 2.
Lim et al., 2009

24

3.4.4	 Comparison with source data files

To ensure grid accuracy, the 1/3 arc-second Craig 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. A histogram of the difference 

between selected SRTM data points and the 1/3 arc-second Craig DEM is shown in Figure 17. 

Figure 17. Histogram of the difference between the SRTM topographic dataset and the 1/3 arc-second Craig DEM. 

3.4.5 Comparison with USGS topographic elevations

Topographic elevations were obtained from the USGS topographic Craig quadrangle (http://agdc.usgs.gov/

data/usgs/to_geo.html). The quadrangle gives positions and elevations in NAD 83 and NGVD29 vertical datum (in 

feet) and has a scale of 1:63,360 with a 100-foot contour interval. 

To be consistent with the USGS Craig quadrangle, the 1/3 arc-second Craig DEM was converted from meters 

into feet. A contour map with a 100-foot interval was created of San Juan Bautista Island (Fig. 18B). The contour 

map was then compared against the USGS topographic quadrangle (Fig. 18A). Although the figures show that minor

differences exist between the 1/3 arc-second Craig DEM and the USGS topographic elevations, the morphology of the 

island is accurately captured in the DEM.

Topographic elevations at localized high points in the DEM are lower than USGS topographic quadrangle 

elevations (Fig. 18). These differences may be attributable to the fact that the SRTM and NED topographic data, used 

to constrain the subaerial parts of the DEM, represent averages of land elevations over 30 × 30 meter, and 60 × 60 

meter square areas, respectively, while the topographic quadrangle elevations represent local maxima.
Digital Elevation Models of Craig, Alaska

25

Figure 18. Comparison between USGS topography contours and the 1/3 arc-second Craig DEM topographic contours. 

A) Brown lines and numbers represent 100 ft. contours from the USGS topographic map. B) Red lines and purple numbers 

represent 100 ft. contours from the 1/3 arc-second Craig DEM.
Lim et al., 2009

26

4. Summary and Conclusions

 Two integrated topographic–bathymetric DEMs of the Craig, Alaska area, with cell size of 1 arc-second and 

1/3 arc-second, were developed for the PMEL NOAA Center for Tsunami Research. The best available digital data 

from U.S. federal 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 ArcGIS, FME, GMT, 

Quick Terrain Modeler, and MB-System software. 

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

•	 Conduct bathymetric surveys in the southern quarter of the 1 arc-second DEM area.

•	 Obtain more recent data in the area immediately around Craig.

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

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

5. Acknowledgments

 The creation of the DEMs were funded by NOAA Center for Tsunami Research at PMEL. The authors thank 

Nazila Meratia and Vasily Titov (PMEL), Bret Christensen (USFWS), and Gary Nelson and Brooke McMahon (NOS 

Pacific Hydrographic Branch).

6. References

Electronic Navigational Chart #16016, 7th Edition, 2007. Dixon Entrance to Cape St. Elias. Scale 1:300,000. U.S. 

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

Electronic Navigational Chart #17404, 10th Edition, 2008. San Christoval Channel to Cape Lynch. Scale 1:40,000. 

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

Nautical Chart #17403, 14th Edition, 2006. Davidson Inlet and Sea Otter Sound. Scale 1:40,000. U.S. Department of 

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17404, 13th Edition, 2006. San Christoval Channel to Cape Lynch. Scale 1:40,000. U.S. Department 

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

Nautical Chart #17405, 15th Edition, 2006. Ulloa Channel to San Christoval Channel. Scale 1:40,000. U.S. Department 

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

Nautical Chart #17406, 7th Edition, 2004. Bakers Noyes and Lulu Islands. Scale 1:40,000. U.S. Department of 

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17407, 15th Edition, 2003. Northern Part of Tlevak Strait and Ulloa Channel. Scale 1:40,000. U.S. 

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

Nautical Chart #17408, 8th Edition, 2003. Central Dall Island and Vicinity. Scale 1:40,000. U.S. Department of 

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17426, 15th Edition, 2006. Kasaan Bay Prince of Wales Island. Scale 1:40,000. U.S. Department of 

Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #17431, 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.
Digital Elevation Models of Craig, Alaska

27

7. Data Processing Software

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

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

http://www.safe.com/

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

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

GMT v. 4.3.0 – Generic Mapping Tools, shareware developed and maintained by Paul Wessel and Walter Smith, 

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

MB-System v. 5.1.0, 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/

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

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

Quick Terrain Modeler v.6.0.1, developed by Johns Hopkins University Applied Physics Laboratory, licensed by 

Applied Imagery, Silver Spring, Maryland, http://www.appliedimagery.com/