Digital Elevation Model for King Cove, Alaska:

Procedures, Data Sources and Analysis

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

Research by the NOAA National Geophysical Data Center (NGDC)

August 15, 2008

Taylor1, L.A., B.W. Eakins2, K.S. Carignan2, R.R. Warnken1, T. Sazonova 2, and D.C. Schoolcraft1

1. NOAA, National Geophysical Data Center, Boulder, Colorado

2. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder

Corresponding author contact:

Lisa A. Taylor

NOAA, National Geophysical Data Center

Marine Geology and Geophysics Division

325 Broadway, E/GC 3

Boulder, Colorado 80305

Phone: 303-497-6767

Fax: 303-497-6513

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

http://www.ngdc.noaa.gov/mgg/inundation/
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 2

CONTENTS

1. Introduction ............................................................................................................................................. 4

2. Study Area............................................................................................................................................... 5

3. Methodology ........................................................................................................................................... 5

3.1 Data Sources and Processing.......................................................................................................... 6

3.1.1 Shoreline.................................................................................................................... 7

3.1.2 Bathymetry.............................................................................................................. 10

3.1.3 Topography ............................................................................................................. 16

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 DEM with MB-System............................................... 21

3.4 Quality Assessment of the DEM.................................................................................................. 21

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

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

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

3.4.4 Comparison with source data files......................................................................... 23

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

4. Summary and Conclusions................................................................................................................... 25

5. Acknowledgments ................................................................................................................................ 25

6. References............................................................................................................................................. 25

7. Data Processing Software..................................................................................................................... 25

LIST OF FIGURES

Figure 1. Shaded-relief image of the King Cove, Alaska region ................................................................. 4

Figure 2. Source and coverage of datasets used to compile the King Cove, Alaska DEM........................ 6

Figure 3. Digital coastline datasets in the King Cove vicinity ..................................................................... 7

Figure 4. Example of modifications to coastline at King Cove Harbor....................................................... 9

Figure 5. Digital NOS hydrographic survey coverage in the King Cove region ...................................... 12

Figure 6. USACE survey data points and RNC #16549 inset for King Cove Harbor.............................. 13

Figure 7. 2006 high oblique photo of King Cove Harbor........................................................................... 13

Figure 8. NOS LiDAR dataset coverage in King Cove DEM.................................................................... 14

Figure 9. Detail of RNC #16547 at Sandman Reefs................................................................................... 15

Figure 10. Source and coverage of topographic datasets used to compile the King Cove DEM............... 16

Figure 11. Example of gaps in SRTM data coverage ................................................................................... 17

Figure 12. King Cove Harbor with USACE project overview image.......................................................... 18

Figure 13. Histogram of the difference between NOS soundings for survey H06586 and the 1 

arc-second NOS pre-surfaced bathymetric grid................................................................... 20

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

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

Figure 16. Histogram of the difference between the part of the SRTM dataset and the 1 arcsecond King Cove DEM. ...................................................................................................... 23

Figure 17. Histogram of the differences between the USGS topographic benchmarks elevations 

and the 1 arc-second King Cove DEM................................................................................. 24

Figure 18. Location of the USGS topographic benchmarks......................................................................... 24
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 3

LIST OF TABLES

Table 1. PMEL specifications for the 1 arc-second King Cove, Alaska DEM.......................................... 5

Table 2. Shoreline datasets used in compiling the King Cove, Alaska DEM............................................ 7

Table 3. Bathymetric datasets used in compiling the King Cove, Alaska DEM..................................... 10

Table 4. Digital NOS hydrographic surveys used in compiling the King Cove, Alaska DEM.............. 11

Table 5. Topographic datasets used in compiling the King Cove, Alaska DEM .................................... 16

Table 6. Relationship between Mean High Water and other vertical datums in the King Cove

region...................................................................................................................................... 19

Table 7. Data hierarchy used to assign gridding weight in MB-System.................................................. 21
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 4

Digital Elevation Model for King Cove, Alaska:

Procedures, Data Sources and Analysis

1. INTRODUCTION

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

Administration (NOAA), has developed a revised bathymetric–topographic digital elevation model (DEM) centered 

on King Cove, Alaska (Fig. 1) for the Pacific Marine Environmental Laboratory (PMEL) NOAA Center for 

Tsunami Research (http://nctr.pmel.noaa.gov/). The 1 arc-second1 coastal DEM will be used as input for the Method 

of Splitting Tsunami (MOST) model developed by PMEL to simulate tsunami generation, propagation and 

inundation. The DEM was generated from diverse digital datasets in the region (grid boundary and sources shown in 

Fig. 2) and will be used for tsunami inundation modeling as part of the tsunami forecast system Short-term 

Inundation Forecasting for Tsunamis (SIFT) currently being developed by PMEL for the NOAA Tsunami Warning 

Centers. This report provides a summary of the data sources and methodology used in developing the King Cove

DEM.

Figure 1. Shaded relief image of the King Cove 

DEM. Contour interval is 100 meters. Image is in 

Mercator projection.

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

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

Alaska (55°3′42′′ N, 160°18′37′′ W) 1 arc-second of latitude is equivalent to 30.92 meters; 1 arc-second of longitude equals 17.75 meters.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 5

2. STUDY AREA

King Cove is located on the south side of the Alaska Peninsula, on a sand spit fronting Deer Passage and 

Deer Island. It is 18 miles southeast of Cold Bay and 625 miles southwest of Anchorage at 55.06167° North 

Latitude and 162.31028° West Longitude. King Cove lies in the maritime climate zone with temperatures averaging

25 to 55 F, with extremes from -9 to 76 F. Snowfall averages 52 inches, and total annual precipitation is 33 inches.

King Cove was founded in 1911 when Pacific American Fisheries built a salmon cannery there. Early settlers were 

Scandinavian, European, and Unangan fishermen.

3. METHODOLOGY

The King Cove DEM was developed to meet PMEL specifications (Table 1), based on input requirements 

for the MOST inundation model. The best available digital data were obtained by NGDC and shifted to common 

horizontal and vertical datums: World Geodetic System 1984 (WGS84) and Mean High Water (MHW), for 

modeling of “worst-case scenario” flooding, respectively. Data processing and evaluation, and DEM assembly and 

assessment are described in the following subsections.

Table 1: PMEL specifications for the 1 arc-second King Cove, Alaska DEM.

Grid Area King Cove, Alaska

Coverage Area 161.8 o to 162.8o W; 54.45o to 55.35o N

Coordinate System Geographic decimal degrees

Horizontal Datum World Geodetic System 1984 (WGS84)

Vertical Datum Mean High Water (MHW)

Vertical Units Meters

Grid Spacing 1 arc-second

Grid Format ESRI ASCII raster grid
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 6

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 National Geospatial-Intelligence Agency (NGA); the U.S. Fish and Wildlife Service (FWS); the U.S. 

Geological Survey (USGS); the U.S. Army Corps of Engineers (USACE); and Scripps Institution of Oceanography 

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

WGS84 horizontal datum and to convert into ESRI (http://www.esri.com/) ArcGIS shape files. The shape files 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 King Cove tidal station, as no VDatum 

model software (http://nauticalcharts.noaa.gov/csdl/vdatum.htm) was available for this area. 

Figure 2. Source and coverage of datasets used to compile the King Cove, Alaska DEM. White 

areas denote data gaps.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 7

3.1.1 Shoreline

Four digital coastline datasets of the King Cove region were analyzed for inclusion in the King Cove DEM: 

NOAA OCS electronic navigational charts #16520 and #16549; National Geospatial-Intelligence Agency (NGA)

High Water Line; USGS geologic map derived shoreline; and U.S. Fish and Wildlife Service (FWS) statewide 

Alaska digital coastline. Comparisons between the different coastline datasets, NOS hydrographic surveys, SRTM 

topographic DEM, and raster nautical charts showed that the NGA and FWS coastlines (Table 2) best fit the 

topographic and bathymetric data (Fig. 3 and 4) and were used to create a ‘combined coastline’ for the King Cove 

DEM.

Table 2. Shoreline datasets used in compiling the King Cove, Alaska DEM.

Source Year Data Type Spatial Resolution

Original Horizontal 

Datum/Coordinate 

System

Original 

Vertical Datum URL

NGA 2000

Satellite 

derived High 

Water Line

1:75,000 or smaller WGS84 geographic ~ High Water 

Line See footnote 2

U.S. FWS 2006 Compiled 

coastline Various WGS84 geographic Undefined

Figure 3. Digital coastline datasets in the King Cove vicinity shown with SRTM topographic data.

 2. The NGA Office of Global Navigation, Maritime Division is in the process of developing a new version of World Vector Shoreline (WVS®) 

and in support of this effort has acquired a prototype Global Shoreline Data set. This new shoreline is an approximation of the High Water Line; 

it is NOT a Mean High Water Line since the source data have not been tide coordinated (http://www.nga.mil/portal/site/nga01/index.jsp?epicontent=GENERIC&itemID=9328fbd8dcc4a010VgnVCMServer3c02010aRCRD&beanID=1629630080&viewID=Article). The prototype 

Global Shoreline Data set (satellite derived High Water Line) in work at NGA has been acquired from orthorectified NASA, 2000 era, 

LANDSAT GeoCover (multi-spectral imagery). [Extracted from metadata]
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 8

1) National Geospatial-Intelligence Agency High Water Line

The NGA Office of Global Navigation, Maritime Division developed the Global Shoreline Data set

from digitized orthorectified NASA, 2000 era, LANDSAT GeoCover (multi-spectral imagery). This new 

shoreline is an approximation of the High Water Line with a resolution of 1:75,000 or smaller. The NGA 

coastline provided coverage of the DEM area excluding the area east of Belkofski Bay and had gaps in 

King Cove Harbor (Fig. 3). In the Cold Bay region the NGA coastline provided more detail than the FWS 

coastline.

2) U.S. Fish and Wildlife Service

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

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

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

Alaska Department of Natural Resources. This dataset was graciously provided to NGDC by Bret 

Christensen, U.S. Fish and Wildlife Service. 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 FWS coastline; the horizontal datum of the compiled FWS coastline is WGS84. The FWS 

coastline provides complete coverage of the DEM area and included features in King Cove Harbor that 

were not resolved in the NGA coastline (Fig. 3 and 4).

3) NOAA OCS electronic navigational chart #16520 and #16549 extracted coastlines

Electronic navigational chart (ENC) #16520 provided an extracted coastline covering the western 

portion of the DEM to Belkofski Bay. When compared to the SRTM topographic dataset, this coastline at a 

scale of 1 to 300,000, is not as detailed as the NGA and the FWS coastlines. The OCS coastline is also 

shifted 100 to 300 meters to the north as compared to the SRTM dataset. The smaller scaled nautical chart 

#16549, while providing more detail of harbor features, did not represent all features in the harbor and also 

varied from the topographic data by as much as 100 meters (Fig. 3). These data was not used in building 

the combined coastline for the DEM.

4) USGS geologic map derived shoreline

The USGS developed a shoreline captured from geologic coverages, digitized from 1:63,360 

topographic maps for parts of Cold Bay and 1:250,000-scale topographic maps. While providing complete 

coverage of the DEM area, the USGS coastline is less detailed than either the FWS or the NGA coastlines 

and is offset from the SRTM dataset and nautical chart #16549 in varying directions exceeding 500 meters. 

This dataset was not used in building the combined coastline for the DEM.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 9

To obtain the best digital MHW coastline, NGDC combined the NGA and FWS coastlines into a 

‘combined coastline’. Where overlap occurred, the NGA coastline was usually excised, as the FWS coastline was 

typically more consistent with the NOS hydrographic survey data and SRTM topography. This ‘combined coastline’ 

was manually adjusted to fit the recent USACE surveys and project overview image at King Cove harbor

(http://www.poa.usace.army.mil/CO/CoOrg/PnI_New/p&ione_2007.html#Kin) to reflect the north breakwater and

in South Harbor to reflect both north and south breakwaters (Fig. 4). North of the town of Cold Bay the NGA

coastline was used as it more closely represented small inlet features shown on nautical chart #16549. The edits 

were done using ArcGIS. The combined coastline was subsampled to 10-meter spacing 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 

Section 3.3.2) to ensure that interpolated bathymetric values reached “zero” at the coast. The combined coastline 

was also used to clip the SRTM topographic DEM, which contained elevation values, typically zero, over the open 

ocean (Section 3.1.3).

Figure 4. ‘Combined coastline’ (black dashed line) shown with USACE data and USACE project

overview image.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 10

3.1.2 Bathymetry

Bathymetric datasets used in the compilation of the King Cove DEM include 45 NOS hydrographic 

surveys, two recent USACE harbor surveys, NOS hydrographic LiDAR surveys, electronic navigational chart 

soundings, and a subset extracted from the Global Measured and Estimated Seafloor Topography (MEST) DEM

(Table 3).

Table 3. Bathymetric datasets used in compiling the King Cove, Alaska DEM.

Source Year Data Type Spatial Resolution

Original 

Horizontal 

Datum/Coordinat

e System

Original 

Vertical 

Datum URL

NOS

1901

to 

1956

Hydrographic 

survey 

soundings

Ranges from 10 meters to 

1.5 kilometers (varies with 

scale of survey, depth, 

traffic and probability of 

obstructions)

NAD27, Early 

Alaskan Datum, 

Undefined Datum

MLLW

(meters)

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

mgg/bathymetry/hydro.html

USACE 2006 Harbor survey ~2 to 10 meters

Alaska State 

Plane, Zone 7, 

NAD83 feet

MLLW

(feet)

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

mil/en/hydro/King%20Cove/

2006/

OCS ENC

#16549 2003

NGDC 

digitized 

nautical chart 

soundings

~500 to 1200 meters WGS84 

geographic

MLLW

(meters)

http://chartmaker.ncd.noaa.g

ov/MCD/enc/index.htm

NOS 2005

Hydrographic 

LiDAR 

surveys

5 meters NAD83

geographic

MLLW

(meters)

SIO 2007

Altimetryderived 

seafloor 

estimate

1 arc-minute WGS84 

geographic MSL http://topex.ucsd.edu/marine_topo/

1) NOS hydrographic survey data

A total of 45 NOS hydrographic surveys conducted between 1901 and 1956 were used in the King 

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

referenced to Mean Lower Low Water (MLLW) and horizontally referenced to either “Early Alaska”,

“Unalaska”, or “undetermined” datums. Frequently, in creating digital versions of early 20th century 

surveys, NOS was unable to determine the horizontal datum of the original survey. In the digitizing process 

these surveys were adjusted to a more current ‘datum of records’, frequently NAD27, by NOS 

(http://www.ngdc.noaa.gov/mgg/dat/geodas/docs/hyd93.txt).

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 online database 

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

then converted to WGS84 using FME software, an integrated collection of spatial extract, transform, and 

load tools for data transformation (http://www.safe.com); some NOS surveys were manually shifted in 

ArcGIS to fit the combined coastline. The surveys were subsequently clipped to a polygon 0.05 degree

(~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 Section 3.2.1), the data were displayed in ESRI 

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

the NED and SRTM topographic data and the combined coastline. Survey #H06702 was found to have two 

soundings digitized with incorrect depth values when compared to the corresponding smooth sheet and 

were corrected using ArcMap.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 11

Table 4. Digital NOS hydrographic surveys used in compiling the King Cove, Alaska DEM.

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

H02557* 1901 10,000/20,000 mean lower low water undetermined

H03305* 1911 40,000 mean lower low water undetermined

H03305A 1911 20,000 mean lower low water undetermined

H03305I 1925 20,000 mean lower low water Unalaska Datum

H03654 1913/39 100,000 mean lower low water undetermined

H04301* 1923/25 60,000 mean lower low water undetermined

H04314* 1923/24 20,000 mean lower low water undetermined

H04374* 1924 20,000 mean lower low water undetermined

H04375* 1923/24 20,000 mean lower low water undetermined

H04380* 1924 20,000 mean lower low water undetermined

H04490* 1925 20,000 mean lower low water undetermined

H04491* 1925 40,000 mean lower low water undetermined

H04496 1925 20,000 mean lower low water undetermined

H06143* 1936 40,000 mean lower low water early Alaska Datum

H06280* 1937 10,000 mean lower low water early Alaska Datum

H06281* 1937/39 20,000 mean lower low water early Alaska Datum

H06384* 1938 10,000 mean lower low water early Alaska Datum

H06385* 1938 20,000 mean lower low water early Alaska Datum

H06437* 1939 20,000 mean lower low water early Alaska Datum

H06482* 1939 10,000 mean lower low water early Alaska Datum

H06484* 1938/39 40,000 mean lower low water Unalaska Datum

H06485* 1940 40,000 mean lower low water early Alaska Datum

H06486* 1939/40 80,000 mean lower low water early Alaska Datum

H06487* 1940 20,000 mean lower low water early Alaska Datum

H06488* 1939/40 20,000 mean lower low water early Alaska Datum

H06586* 1940 40,000 mean lower low water early Alaska Datum

H06587* 1940 20,000 mean lower low water early Alaska Datum

H06588* 1940/42 20,000 mean lower low water early Alaska Datum

H06589* 1940 20,000 mean lower low water early Alaska Datum

H06590 1940 20,000 mean lower low water early Alaska Datum

H06591 1940 20,000 mean lower low water early Alaska Datum

H06592 1940 10,000 mean lower low water early Alaska Datum

H06593* 1940 20,000 mean lower low water early Alaska Datum

H06699 1941 40,000 mean lower low water early Alaska Datum

H06702* 1941 20,000 mean lower low water early Alaska Datum

H06703* 1941 20,000 mean lower low water early Alaska Datum

H06704* 1941 5,000 mean lower low water early Alaska Datum

H06716 1941 10,000 mean lower low water early Alaska Datum

H06767* 1942 20,000 mean lower low water early Alaska Datum

H06768* 1942 20,000 mean lower low water early Alaska Datum

H06769* 1942 20,000 mean lower low water early Alaska Datum

H06772 1942 20,000 mean lower low water early Alaska Datum

H07030* 1945 5,000 mean lower low water early Alaska Datum

H07031* 1945 5,000 mean lower low water early Alaska Datum

H08301* 1956 20,000 mean lower low water early Alaska Datum

* Geographic position manually adjusted in ArcGIS to fit combined coastline.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 12

Figure 5. Digital NOS hydrographic survey coverage in the King Cove region. Red denotes boundary of 1 arc-second 

DEM with the combined coastline in black.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 13

2) USACE harbor surveys

USACE conducted or contracted harbor surveys in King Cove Harbor and in South Harbor in 2006

(Figs. 6 and 7). The two surveys contain both bathymetric and topographic data. The surveys were 

originally referenced to NAD83 Alaska State Plane coordinates and MLLW vertical datum. The resolution 

of the two surveys range from ~2 to 10 meters and from 2.7 to -22.2 meters in depth at MHW.

Figure 6. USACE survey 

data points and RNC #16549 

inset for King Cove Harbor. 

Combined coastline shown 

in blue.

Figure 7. A 2006 highly oblique photo of King Cove Harbor

taken from USACE AK District website.

(http://www.poa.usace.army.mil/CO/CoOrg/PnI_New/p&ion

e_2007.html#Kin).
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 14

3) OCS Electronic Navigational Chart soundings

OCS nautical chart #16549 was available in electronic navigation chart format and, as no bathymetric 

survey data was available for the area, sounding data was extracted from this chart using FME. Coverage 

stretches eastward from Cold Bay through Deer Passage, including King Cove and King Cove Lagoon, east 

to Pavlof Islands. Soundings range from ~20 meters to ~1200 meters apart, and depths range from -1.96 

meters to -148.16 meters at MHW.

4) NOS Hydrographic LiDAR

NOS provided NGDC with six recent hydrographic LiDAR surveys located in the eastern part of the 

DEM (Fig. 8). The LiDAR surveys are referenced to NAD83 and MLLW. These surveys range from -63 to 

47 meters in elevation and have point spacing of 5 meters. The elevations on and near the shoreline are 

generally consistent with the SRTM dataset, higher elevations are less accurate.

Figure 8. NOS hydrographic LiDAR surveys located on the eastern border of the King Cove DEM (boundary shown in red).
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 15

5) Measured and Estimated Seafloor Topography (MEST)

Two areas within the DEM boundary where no survey data were available are located southeast of 

Deer Island in the Sandman Reefs (Fig. 2). Figure 9 shows the western most of the two un-surveyed areas 

surrounded by NOS soundings. Bathymetric values for these areas, approximately 18 square kilometers, 

were extracted from the ‘Measured and Estimated Seafloor Topography’ 1-minute DEM (Smith and 

Sandwell, 1997; http://topex.ucsd.edu/marine_topo/).

Grid has 1 minute cell size with data in WGS84 geographic coordinates and MSL. These data are 

exceptionally coarse at the resolution of the 1 arc-second King Cove DEM; however, they provide the only 

digital constraints on the bathymetry in the Sandman Reefs region. Extracted bathymetric data are generally 

shallower than overlapping measured bathymetric values (e.g., NOS hydrographic soundings and 

multibeam swath sonar survey data) and are considered to be of low accuracy.

Figure 9. NOS hydrographic survey sounding data, shown as multicolored points, surrounding unsurveyed western Sandman Reefs area as 

shown on RNC #16547.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 16

3.1.3 Topography

Topographic datasets for King Cove were obtained from the U.S. Geological Survey: National Elevation 

Dataset 2 arc-second gridded topography, and 1 arc-second NASA space shuttle radar topography (Fig. 10, Table 5).

NGDC also digitized harbor features not represented in either topographic dataset.

Table 5. Topographic datasets used in compiling the King Cove, Alaska DEM.

Source Year Data Type Spatial Resolution

Original 

Horizontal 

Datum/Coordinate 

System

Original 

Vertical Datum URL

USGS 

NED 2006 Topographic DEM 2 arc-second grid NAD27 geographic

NGVD29

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

NASA

SRTM 2000 Topographic DEM 1 arc-second grid WGS84 geographic

WGS84/EGM96 

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

NGDC 2008 digitized harbor 

features 10 meter point spacing WGS84 geographic MHW

Figure 10. Source and coverage of topographic 

datasets used in compiling the King Cove DEM.

1) USGS NED topography

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

provides complete 2 arc-second coverage of Alaska3. Data are in NAD27 Alaska geographic coordinates 

and NGVD29 vertical datum (meters), and are available for download as raster DEMs. The extracted bareearth 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 was used only to fill in gaps within the SRTM data (e.g. Fig. 10).

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

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

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

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

(meters). The horizontal datum is NAD83, except for AK, which is NAD27. The vertical datum is NAVD88, except for AK, which is NGVD29. 

NED is a living dataset that is updated bimonthly to incorporate the "best available" DEM data. As more 1/3 arc second (10 m) data covers the 

U.S., then this will also be a seamless dataset. [Extracted from USGS NED website]
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 17

2) NASA space shuttle radar topography

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

to generate the most complete high-resolution digital topographic database of Earth4. 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 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 WGS84/EGM96 Geoid. 

While providing near complete coverage of the Aleutian Islands in the vicinity of King Cove, there are 

numerous small areas with “no data” values (e.g., Fig. 11), necessitating use of the lower-resolution NED 

topographic data in these areas. The SRTM DEM also contains values over the open ocean, which were 

deleted by clipping to 

the combined coastline.

Figure 11. 

Example of gaps

(white areas) in 

SRTM data 

coverage. Gaps 

were filled with 

topographic data 

from the NED 

DEM. Combined 

coastline in red.

 4. 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]
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 18

3) NGDC digitized harbor features

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

represent the two main harbor features at King Cove. The breakwater that forms the southern barrier of 

King Cove Lagoon entrance, the rock groin just south of the breakwater at the anchorage harbor, and the 

southern most breakwater at the mooring basin (referred to as Babe Newman in USACE documents, Fig. 

12). Elevations applied to points were obtained from the USACE project overview image. 

Figure 12. Detail of King Cove Harbor with USACE project overview georeferenced image underlying SRTM topographic data.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 19

3.2 Establishing Common Datums

3.2.1 Vertical datum transformations

Datasets used in the compilation and evaluation of the King Cove DEM were originally referenced to a 

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

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

the worst-case scenario for inundation modeling.

1) Bathymetric data

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

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

measured at the NOAA King Cove tidal station (see Table 6).

2) Topographic data

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

respectively. There are no survey markers in the vicinity of King Cove that relate these two geodetic 

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

equivalent to MSL in this area (Table 6). Conversion to MHW, using FME software, was accomplished by 

adding a constant value of -0.747 meters.

Table 6. Relationship between Mean High Water and other vertical datums in the King Cove region.*

Vertical datum Difference to MHW

MTL -0.73

NGVD29 + -0.747

MSL -0.747

MLW -1.46

MLLW -1.869

* Datum relationships determined by tidal station #9459881 at King Cove, Alaska.

+ Assumed to be equivalent to MSL.

3.2.2 Horizontal datum transformations

Datasets used to compile the King Cove DEM were originally referenced to Early Alaska, Unalaska, 

NAD27, NAD83, and WGS84 horizontal datums. The relationships and transformational equations between these 

horizontal datums are well established, with the exception of the Unalaska datum. All data were converted to a 

horizontal datum of WGS84 using FME software, with the exception of many of the NOS surveys, which were 

manually shifted in ArcGIS to fit the combined coastline.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 20

3.3 Digital Elevation Model Development

3.3.1 Verifying consistency between datasets

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

ESRI ArcMap 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 shape files were then 

converted to xyz files in preparation for gridding. Problems included:

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

automated clipping to the combined coastline.

• Lack of good bathymetric data in the southeastern part of the DEM and in the vicinity of the Sandman

Reefs

• Lack of good bathymetric data near the coastline.

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 3 arc-second-spacing ‘pre-surface’ or grid was generated 

using GMT, an NSF-funded share-ware software application designed to manipulate data for mapping purposes 

(http://gmt.soest.hawaii.edu/).

The NOS hydrographic point data, in xyz format, were combined with the USACE surveys, ENC 

soundings, and the estimated seafloor topography data into a single file, along with points extracted every 10 meters 

from the combined coastline—to provide a slightly negative (-2 meters) buffer along the entire coastline. The 

negative values of -2 meters were assigned to the coastline to make sure that the offshore elevations remain

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 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 

shape file, and then exported as an xyz file for use in the final gridding process (see Table 7). The statistical analysis 

of the differences between the 3 arc-second bathymetric surface and one of the NOS surveys (see Fig. 13) showed 

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

where the difference reached tens of meters are attributed to the rugged terrain when two or more closely positioned 

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

Figure 13. Histogram of the difference between NOS hydrographic survey H06586 and the 1 arc-second NOS pre-surfaced 

bathymetric grid. 
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 21

3.3.3 Building the 1 arc-second DEM with MB System

MB-System was used to create a 1 arc-second King Cove DEM. 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 7. Greatest weight was given to the highresolution topographic SRTM and NGDC harbor feature datasets. Least weight was given to the pre-surfaced 3 arcsecond bathymetric grid.

Table 7. Data hierarchy used to assign gridding weight in MB-System.

Dataset Relative Gridding Weight

SRTM topographic DEM 1,000

USACE surveys 100

NOS hydrographic surveys 10

Combined coastline at 0 meters elevation 100

USGS NED topographic DEM 1

ENC #16549 soundings 1

NOS LiDAR surveys 1

MEST bathymetric DEM 1

NGDC digitized features 1000

Pre-surfaced bathymetric grid 0.1

3.4 Quality Assessment of the DEM

3.4.1. Horizontal accuracy

The horizontal accuracy of topographic and bathymetric features in the King Cove DEM is 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 to a few hundred 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 DEM is 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, which have an estimated vertical accuracy of 10 meters; the SRTM topographic data, 

which have a vertical accuracy better than 16 meters but are typically about 10 meters. Gridding interpolation to 

determine bathymetric values between sparse, poorly located, early 20th-century NOS hydrographic soundings 

degrades the vertical accuracy of elevations in deep water, to about 5% of water depth. Bathymetry vicinity of 

Sandman Reefs, derived largely from the low-resolution estimated seafloor topography, is shoal biased by several 

meters.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 22

3.4.3 3-D perspective and slope map

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

visual inspection and identification of artificial slopes along boundaries between datasets (e.g., Fig. 14). The DEM 

was transformed to UTM Zone 4 coordinates (horizontal units in meters) in ArcCatalog for derivation of the slope 

grid; equivalent horizontal and vertical units are required for effective slope analysis. Three-dimensional viewing of 

the UTM-transformed DEM (e.g., Fig. 15) was accomplished using ESRI ArcScene. Analysis of preliminary grids 

revealed suspect data points, which were corrected before recompiling the DEM. 

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

Flat-lying slopes are white; dark shading denotes steep slopes; combined coastline in red.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 23

Figure 15. Perspective view from the southeast of the 1 arc-second King Cove DEM. Combined coastline in 

blue; vertical exaggeration–times 2.

3.4.4 Comparison with source data files

To ensure grid accuracy, the 1 arc-second King Cove 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 King Cove DEM is shown in Figure 16. The largest 

differences occur in regions of highly variable, steep coastal relief where multiple, closely spaced points were 

averaged to a single cell value.

Figure 16. Histogram of the difference between part of SRTM topographic dataset and the 1 arc-second King Cove DEM. 

The largest differences occur in regions of highly variable, steep coastal relief where multiple, closely spaced points were 

averaged to a single cell value.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 24

3.4.5 Comparison with USGS topographic elevations

Topographic elevations were extracted from online digital images of USGS topographic quadrangles at 

TopoZone (http://www.topozone.com) which give position and elevation in WGS84 and NGVD29 vertical datum 

(in feet). Elevations were converted to meters and shifted to MHW vertical datum (see Table 8) for comparison with 

the 1 arc-second King Cove DEM (see Fig. 16 for locations). Significant differences exist between the King Cove

DEM and the USGS topographic elevations: from -254 to -8.5 meters, with a negative value indicating that the 

DEM is less than the topographic quadrangle elevation (Fig. 17). Much of the difference results from horizontal 

offsets between the poorly resolved positional information taken from the online quadrangles, and the corresponding 

feature in the DEM. Such offsets range up to 254 meters. 

From a vertical perspective, topographic elevations, typically at localized high points though 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 sub aerial 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 maximum heights.

Figure 17. Histogram of the differences between the USGS topographic benchmarks elevations and the 1 arc-second King 

Cove DEM. The pronounced negative values (DEM less than topographic elevations) result partly from horizontal offsets 

of features, typically local highs, but may also result from comparing average elevation over an area with a local 

maximum.

Figure 18. Location of USGS 

topographic benchmarks used in quality 

assessment of King Cove DEM.
DIGITAL ELEVATION MODEL FOR KING COVE, ALASKA 25

4. SUMMARY AND CONCLUSIONS

A combined topographic–bathymetric digital elevation model of the King Cove, Alaska area, with cell 

spacing of 1 arc-second, was developed for the Pacific Marine Environmental Laboratory (PMEL) NOAA Center 

for Tsunami Research. The best available digital data from U.S. federal agencies were obtained by NGDC, shifted to 

common horizontal and vertical datums, and evaluated and edited before DEM generation. The data were quality 

checked, processed and gridded using ESRI ArcGIS, FME, GMT, Quick Terrain Modeler, and MB-System 

software. 

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

• Conduct bathymetric surveys in the region to the north of the Deer Island, at the entrance to King Cove, 

and in the Sandman Reefs area which currently have no digital measured bathymetric data.

• Obtain digital versions of NOAA nautical chart #16547 that has not yet been digitized.

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

5. ACKNOWLEDGMENTS

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

authors thank Chris Chamberlin and Vasily Titov (PMEL), Bret Christensen (U.S. Fish and Wildlife Service), Gary 

Nelson and Brooke McMahon (NOS Pacific Hydrographic Branch), David Scharff (NOS), Jeff Freymueller 

(University of Alaska, Fairbanks) and Greg Lee (USGS).

6. REFERENCES

Electronic Navigational Chart #16549, 3rd Edition, 2008. Alaska Peninsula Cold Bay and Approaches. Scale 

1:80,000. U.S. Department of Commerce, NOAA, National Ocean Service, Coast Survey.

Nautical Chart #16547, 9th Edition, 2004. Sanak Island and Sandman Reefs. Scale 1:81,326. U.S. Department of 

Commerce, NOAA, National Ocean Service, Coast Survey.

Electronic Navigational Chart #16520, 3rd Edition, 2007. Unimak and Akutan Passes. Scale 1:300,000. U.S. 

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

Smith, W. H. F., and D. T. Sandwell, Global seafloor topography from satellite altimetry and ship depth soundings, 

Science, v. 277, p. 1957-1962, 26 Sept., 1997.

Coast Pilot 9, 25th Edition, 2007. Alaska Peninsula. U.S. Department of Commerce, NOAA, National Ocean 

Service.

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

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

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

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

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/index.html