noaa / NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

National Environmental Satellite,

Data, and Information Service

NOAA Technical Memorandum NESDIS NGDC-17

DIGITAL ELEVATION MODEL OF MONTAUK, NEW YORK:

PROCEDURES, DATA SOURCES AND ANALYSIS 

B.W. Eakins

L.A. Taylor

K.S. Carignan

R.R. Warnken

T. Sazonova 

D.C. Schoolcraft

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-17

DIGITAL ELEVATION MODEL OF MONTAUK, NEW YORK:

PROCEDURES, DATA SOURCES AND ANALYSIS

Barry W. Eakins1

Lisa A. Taylor2

Kelly S. Carignan1

Robin R. Warnken2

Tatiana Sazonova1

David C. Schoolcraft2

1

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

2

NOAA, National Geophysical Data Center, Boulder, Colorado

National Geophysical Data Center

Marine Geology and Geophysics Division 

Boulder, Colorado

March 2009
Eakins et al., 2009

ii

NOTICE

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

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

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

or advertising purposes is not authorized. 

Corresponding project contact:

Lisa A. Taylor

NOAA, National Geophysical Data Center

Marine Geology and Geophysics Division

325 Broadway, E/GC 3

Boulder, Colorado 80305

Phone: 303-497-6767

Fax: 303-497-6513

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

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

Also available from the National Technical Information Service (NTIS)

(http://www.ntis.gov)
Digital Elevation Model of Montauk, New York

iii

Contents

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

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

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

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

3.1.1 Shoreline................................................................................................................5

3.1.2 Bathymetry ............................................................................................................7

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

3.1.4 Bathymetry–Topography.....................................................................................15

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

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

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

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

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

3.3.2	 Surfacing of beach-profile data ...........................................................................18

3.3.3 Smoothing of bathymetric data ...........................................................................18

3.3.4 Gridding the data with MB-System.....................................................................19

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

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

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

3.4.3 Slope maps and 3-D perspectives........................................................................20

3.4.4	 Comparison with source data files.......................................................................21

3.4.5 Comparison with NGS geodetic monuments......................................................22

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

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

6. References........................................................................................................................................23

7. Data Processing Software ................................................................................................................23

List of Figures

Figure 1. Shaded-relief image of the Montauk, New York DEM ..............................................................1

Figure 2. Boulder-covered beach and moraine cliffs on Long Island’s Atlantic Ocean coast ...................2

Figure 3. Source and coverage of datasets used to compile the Montauk DEM........................................4

Figure 4. Digital coastline datasets in Montauk Harbor.............................................................................6

Figure 5. Spatial coverage of bathymetric datasets used to compile the Montauk DEM ..........................7

Figure 6. Digital NOS hydrographic survey coverage in the Montauk region ........................................10

Figure 7. NOS multibeam sonar survey H11250 .....................................................................................11

Figure 8. Coverage of USGS multibeam sonar survey offshore Georgica Pond, Long Island................12

Figure 9. Source and coverage of topographic datasets used to compile the Montauk DEM..................13

Figure 10. Source and coverage of bathymetric–topographic datasets used to compile the 

Montauk DEM...................................................................................................................15

Figure 11. Histogram of the differences between NOS hydrographic survey H10984 and the 

1 arc-second pre-surfaced bathymetric grid ......................................................................19

Figure 12. Slope map of the Montauk DEM..............................................................................................20

Figure 13. Perspective view from the southeast of the Montauk DEM .....................................................21

Figure 14.	 Histogram of the differences between one JALBTCX coastal LiDAR file and the

Montauk DEM...................................................................................................................21

Figure 15. Histogram of the differences between NGS geodetic monument elevations and the 

Montauk DEM...................................................................................................................22

Figure 16. Location of NGS geodetic monuments and NOAA tide stations in the Montauk region.........22
Eakins et al., 2009

iv

List of Tables

Table 1.	 PMEL specifications for the Montauk, New York DEM ............................................................3

Table 2. Shoreline datasets available in the Montauk, New York region .................................................5

Table 3. NOAA Electronic Navigational Charts in the Montauk region..................................................5

Table 4. NOAA Raster Nautical Charts in the Montauk region ...............................................................5

Table 5. Bathymetric datasets used in compiling the Montauk DEM ......................................................7

Table 6. Digital NOS hydrographic surveys used in compiling the Montauk DEM................................8

Table 7. NOAA Raster Nautical Charts from which NGDC digitized soundings..................................12

Table 8. Topographic datasets used in compiling the Montauk DEM....................................................13

Table 9. Bathymetric–topographic datasets used in compiling the Montauk DEM...............................15

Table 10. Relationship between Mean High Water and other vertical datums at the Montauk 

tide station, #8510560........................................................................................................17

Table 11. Data hierarchy used to assign gridding weight in MB-System.................................................19
Digital Elevation Model of Montauk, New York:

Procedures, Data Sources and Analysis

1. Introduction

In September 2007, the National Geophysical Data Center (NGDC), an office of the National Oceanic and

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

Montauk, New York (Fig. 1)—the northeastern end of Long Island—for the Pacific Marine Environmental Laboratory

(PMEL) NOAA Center for Tsunami Research (http://nctr.pmel.noaa.gov/). The 1/3 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. 3) and will be used for tsunami inundation modeling, as part of the tsunami forecast system 

SIFT (Short-term Inundation Forecasting for Tsunamis) 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 

Montauk DEM. 

Figure 1. Shaded-relief image of the Montauk, New York DEM.

1. The Montauk DEM is built upon a grid of cells that are square in geographic coordinates (latitude and longitude), however, the cells are not square 

when converted to projected coordinate systems, such as UTM zones (in meters). At the latitude of Montauk, New York (41°02.1′ N, 71°57.3′ W) 

1/3 arc-second of latitude is equivalent to 10.283 meters; 1/3 arc-second of longitude equals 7.786 meters.
Eakins et al., 2009

2

2. Study Area

The geologically young sediments that cover much of the U.S. Eastern Seaboard make up the Atlantic Coastal 

Plain, which includes Long Island, Fishers Island, Block Island, Martha’s Vineyard, Nantucket, and Cape Cod. These 

islands are parts of glacial moraines—long ridges of clay, sand, gravel, and boulders deposited at the edge of a 

continental glacier. On Long Island, the Ronkonkoma Moraine marks the southernmost advance of the glacier in this 

region. During the last ice age, the growing mass of ice on the continents depleted the ocean waters enough to lower 

sea level by 100 meters. As the ice melted, the rising sea made parts of these moraines into islands. Waves and currents 

have been modifying them ever since.

The continental shelf, slope, and rise lie seaward of the Atlantic Coastal Plain. The continental shelf is nearly 

level; the continental slope has a slope of 2o to 4o; the continental rise slopes less than 1o. They are made of material 

eroded from the land, carried by rivers to the ocean, and distributed there by marine currents. During the period of low 

sea level, the continental shelf was exposed as part of the coastal plain, and rivers cut valleys across it to the shelf edge. 

Most of those valleys have since been filled with sediment, but a vestige of the Hudson Shelf Valley still remains. The

Hudson Canyon and other, large canyons are cut into the shelf edge and continental slope. Much of this canyon-cutting 

occurred when rivers, swollen with glacial meltwater and laden with glacial sediment, flowed across the exposed shelf

and met the sea at the top of the continental slope. The sediment that the rivers poured into the ocean at those points 

formed density currents. These currents cut the canyons into the slope (from Rogers et al., http://gretchen.geo.rpi.edu/

roecker/nys/nys_edu.pamphlet.html).

Figure 2. Boulder-covered beach and moraine cliffs on Long Island’s Atlantic Ocean coast. Montauk Lighthouse is in the 

distance. (Image taken from http://3dparks.wr.usgs.gov/nyc/parks/loc65.htm).
Digital Elevation Model of Montauk, New York

3

3. Methodology

The Montauk, NewYork DEM was constructed tomeet PMELspecifications(Table 1), based on inputrequirements

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 1983 (NAD 83) and Mean High Water (MHW), for modeling of maximum 

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

following subsections.

Table 1. PMEL specifications for the Montauk, New York DEM.

Grid Area Montauk, New York

Coverage Area 72.6o to 71.5o W; 40.6o to 41.4o N

Coordinate System Geographic decimal degrees

Horizontal Datum World Geodetic System 1984 (WGS 84)

Vertical Datum Mean High Water (MHW)

Vertical Units Meters

Grid Spacing 1/3 arc-second

Grid Format ESRI Arc ASCII grid

2. The horizontal difference between the North American Datum of 1983 (NAD 83) and World Geodetic System of 1984 (WGS 84) geographic 

horizontal datums is approximately one meter across the contiguous U.S., which is significantly less than the cell size of the DEM. Most GIS applications treat the two datums as identical, so do not actually transform data between them, and the error introduced by not converting between 

the datums is insignificant for our purposes. NAD 83 is restricted to North America, while WGS 84 is a global datum. As tsunamis may originate

most anywhere around the world, tsunami modelers require a global datum, such as WGS 84 geographic, for their DEMs so that they can model the 

wave’s passage across ocean basins. This DEM is identified as having a WGS 84 geographic horizontal datum even though the underlying elevation

data were typically transformed to NAD 83 geographic. At the scale of the DEM, WGS 84 and NAD 83 geographic are identical and may be used 

interchangeably.
Eakins et al., 2009

4

3.1 Data Sources and Processing

Shoreline, bathymetric, topographic, and bathymetric-topographic digital datasets (Fig. 3) were obtained from 

several U.S. federal, state and local agencies including: NOAA’s National Ocean Service (NOS), Office of Coast

Survey (OCS) and Coastal Services Center (CSC); the U.S. Geological Survey (USGS); and the U.S. Army Corps 

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

datasets to NAD 83 horizontal datum and to convert them into ESRI (http://www.esri.com/) ArcGIS shape files3. 

The shape files were then displayed with ArcGIS to assess data quality and manually edit datasets. Vertical datum

transformations to MHW were accomplished using FME, based upon conversion grids created by PMEL from the 

NOAA tide stations in the area. VDatum model software (http://nauticalcharts.noaa.gov/csdl/vdatum.htm) was used 

for the region south of Long Island. GMT (http://gmt.soest.hawaii.edu/) and MB-System (http://www.ldeo.columbia.

edu/res/pi/MB-System/) were used to grid the data and build the DEM.

Figure 3. Source and coverage of datasets used to compile the Montauk DEM.

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

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

83 datum transformations.
Digital Elevation Model of Montauk, New York

5

3.1.1 Shoreline

Coastline datasets of the Montauk region were obtained from NOAA’s Office of Coast Survey and Coastal

Services Center (Table 2).

Table 2. Shoreline datasets available in the Montauk, New York region.

Source Year Data Type Spatial 

Resolution

Original Horizontal 

Datum/Coordinate System

Original Vertical 

Datum URL

OCS ENCs and 

RNCs

2006-

2007 Coastline 1:10,000 to 1:80,000 WGS 84 geographic Mean High Water http://nauticalcharts.noaa.

gov/

NOAA CSC 2003

Vector 

shoreline of 

New York

Various NAD 83 geographic Mean High Water http://www.csc.noaa.gov/

shoreline/data.html

NOAA OCS 1994

Vector 

shoreline of 

U.S.

Avg. 

1:70,000 NAD 83 geographic NGVD29

1) NOAA Office of Coast Survey nautical charts

Four of the NOAA nautical charts in the vicinity of Montauk, NY have been released as Electronic 

Navigational Charts (ENCs) with chart features in digital form. These ENCs (Table 3) were downloaded from 

NOAA’s Office of Coast Survey website (http://nauticalcharts.noaa.gov/mcd/enc/index.htm). The ENCs are 

available in S-57 format and include coastline data at Mean High Water. Other nautical charts (Table 4) 

were available as georeferenced raster nautical charts (RNCs; digital images of the charts) and were used for 

digitizing coastline sections, and for quality control of bathymetric and topographic datasets.

Table 3. NOAA Electronic Navigational Charts in the Montauk region.

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

13205 US4CN21M BLOCK ISLAND SOUND AND APPROACHES 1:80,000 1999

13218 US4MA23M MARTHA’S VINEYARD TO BLOCK ISLAND 1:80,000 2001

12354 US4NY1GM LONG ISLAND SOUND-EASTERN PART CONN-NY 1:80,000 2000

13209 US5MA22M BLOCK ISLAND SOUND AND GARDINERS BAY 1:40,000 1999

Table 4. NOAA Raster Nautical Charts in the Montauk region.

Nautical Chart # Region Scale Ed. Date

12352 SHINNECOCK BAY TO MORICHES BAY LONG ISLAND NY Various 2006-03-01

12353 SHINNECOCK LIGHT TO FIRE ISLAND LIGHT 1:80,000 2003-11-01

12358 NEW YORK LONG ISLAND SHELTER ISLAND SOUND AND PECONIC 

BAYS 1:40,000 2002-09-01

12372 LONG ISLAND SOUND - RI CONN 1:40,000 2006-11-01

12374 NORTH SHORE OF LONG ISLAND SOUND-DUCK ISLAND TO 

MADISON REEF 1:20,000 2000-10-28

12375 CONNECTICUT RIVER LONG ISLAND SOUND TO DEEP RIVER 1:20,000 2001-02-17

12377 CONNECTICUT RIVER-DEEP RIVER TO HIGGANUM CREEK 1:20,000 2001-01-13

13211 NORTH SHORE OF LONG ISLAND SOUND - NIANTIC BAY VICINITY 1:20,000 2004-09-01

13212 APPROACHES TO NEW LONDON HARBOR 1:20,000 2005-11-01

13213 NEW LONDON HARBOR AND VICINITY 1:10,000 2004-03-01

13214 FISHERS ISLAND SOUND 1:20,000 2006-04-01

13215 BLOCK ISLAND SOUND-PT JUDITH TO MONTAUK PT CONN-RI-NY 1:40,000 2004-08-01

13217 BLOCK ISLAND RI 1:15,000 2006-11-01

13219 PT JUDITH HARBOR RI 1:15,000 2001-10-06
Eakins et al., 2009

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2) NOAA Coastal Services Center coastline of New York 

A statewide coastline of New York was downloaded from NOAA’s Coastal Services Center. These 

shoreline data represent a vector conversion of a set of NOS raster shoreline maps (often called t-sheet 

or tp-sheet maps). These vector data were created by contractors to NOS who vectorized georeferenced 

raster maps using Environmental Systems Research Institute, Inc. (ESRI) ArcInfo’s(r) ArcScan(r) software to 

create individual ArcInfo coverages. The individual coverages were ultimately edge-matched and appended 

together to form this statewide coverage. The CSC New York shoreline includes man-made features, such as 

piers (e.g., Fig. 4).

3) NOAA Office of Coast Survey U.S. coastline

National Oceanic and Atmospheric Administration’s (NOAA) Medium Resolution 1:70,000 scale 

Digital Vector Shoreline is a high-quality, Geographic Information System-ready, general-use digital vector 

data set containing the coastline of the contiguous United States of America. It was created by the Strategic 

Environmental Assessments (SEA) Division of NOAA’s Office of Ocean Resources Conservation and

Assessment. Compiled from hundreds of NOAA coast charts, this product comprises over 75,000 nautical 

miles of coastline (nearly 2.5 million vertices). The shoreline was created from data captured (digitized 

from scanned images of the master separates of the NOS Charts) from over 270 National Ocean Service 

Navigation Charts and spans some 80,000 nautical miles at an average map scale of 1:70,000. This coastline 

is at lower resolution than the other NOAA coastlines (e.g., Fig .4).

NGDC extracted the coastlines from the four ENCs available in the Montauk area (Table 3), then digitized 

sections of coastline from higher-resolution, larger-scale RNCs (Table 4) that do not exist in ENC form. Modifications

to the “Montauk” coastline included adjustments to fit the most recent topographic and topographic–bathymetric lidar

data and removal of manmade features such as piers. Digitization and coastline modification were done using ArcMap

editing tools.

Figure 4. Digital coastline datasets 

in Montauk Harbor. Blue–lowresolution OCS shoreline of the U.S.; 

Green–CSC shoreline of New York, 

which includes manmade features 

such as piers; Purple–ENC shoreline 

from Chart 13209; Red–final 

‘Montauk’ coastline derived from 

NOAA ENCs and RNCs
Digital Elevation Model of Montauk, New York

7

3.1.2 Bathymetry

Bathymetric datasets used in the compilation of the Montauk DEM include 78 NOS hydrographic surveys, recent 

NOS and USGS multibeam sonar surveys, and soundings from NOAA nautical charts (Table 5; Fig. 5).

Table 5. Bathymetric datasets used in compiling the Montauk DEM.

Source Year Data Type Spatial Resolution

Original Horizontal 

Datum/Coordinate 

System

Original 

Vertical Datum URL

 NOS 

1883 

to 

2000

Hydrographic 

survey 

soundings

Ranges from 10 m to 1 

km (varies with scale 

of survey, depth, traffic,

and probability of 

obstructions)

NAD 27 or NAD 83 

geographic

Mean Low 

Water or Mean 

Lower Low 

Water

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

mgg/bathymetry/hydro.html

NOS 2003 Multibeam 

sonar survey 2 meters NAD 83 geographic Mean Lower Low Water

USGS 2006 Multibeam 

sonar survey 3 meters WGS 84 geographic

Inferred Mean 

Lower Low 

Water

NOAA 

ENCs 2007 Digital chart soundings 250 to 2000 meters WGS 84 geographic Mean Lower Low Water http://nauticalcharts.noaa.gov/

NOAA 

RNCs 2007

NGDCdigitized 

soundings

50 to 300 meters WGS 84 geographic Mean Lower 

Low Water http://nauticalcharts.noaa.gov/

Figure 5. Spatial coverage of bathymetric datasets used to compile the Montauk DEM.
Eakins et al., 2009

8

1) NOS hydrographic survey data

A total of 78 NOS hydrographic surveys conducted between 1883 and 2000 were utilized in developing 

the Montauk DEM (Table 6; Fig. 6). The digital hydrographic survey data were originally vertically referenced 

to Mean Lower Low Water (MLLW) or Mean Low Water (MLW) and horizontally referenced to either NAD 

27 or NAD 83 datums.

Data point spacing for the NOS surveys varied by collection date. In general, earlier surveys had greater 

point spacing than more recent surveys. All surveys were extracted from NGDC’s online NOS hydrographic 

database (http://www.ngdc.noaa.gov/mgg/bathymetry/hydro.html). The data were then converted to NAD 83 

geographic and MHW using FME software, an integrated collection of spatial extract, transform, and load 

tools for data transformation (http://www.safe.com). The surveys were subsequently clipped to a polygon 

0.05 degree (~5%) larger than the Montauk DEM area to support data interpolation along grid edges. 

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

ArcMap and reviewed for digitizing errors against scanned original survey smooth sheets and edited as 

necessary. The surveys were also compared to the topographic, bathymetric, and topographic–bathymetric 

datasets, the Montauk coastline, and NOS raster nautical charts (RNCs). In some areas, significant coastal

change has occurred, causing the shallow-water soundings in particular to be inaccurate.

Table 6. Digital NOS hydrographic surveys used in compiling the Montauk DEM.

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

H01603B 1883 10,000 mean low water undetermined

H01603C 1883 10,000 mean low water undetermined

H04893 1928 10,000 mean low water NAD 1913

H05322 1933 20,000 mean low water NAD 27

H05323 1933 10,000 mean low water NAD 27

H05324 1933 20,000 mean low water NAD 27

H05325 1933 20,000 mean low water NAD 27

H05326 1933 5,000 mean low water NAD 27

H05344 1933 20,000 mean low water NAD 27

H05378 1933 10,000 mean low water NAD 27

H05379 1933 10,000 mean low water NAD 27

H05380 1933/35 10,000 mean low water NAD 27

H05381 1933 10,000 mean low water NAD 27

H05382 1933 10,000 mean low water NAD 27

H05383 1933 20,000 mean low water NAD 27

H05513 1934 10,000 mean low water NAD 27

H05514 1934 20,000 mean low water NAD 27

H05515 1934 20,000 mean low water NAD 27

H05516 1934 10,000 mean low water NAD 27

H06328 1938 40,000 mean low water NAD 27

H06329 1938 40,000 mean low water NAD 27

H06330 1938 40,000 mean low water NAD 27

H06331 1938 80,000 mean low water NAD 27

H06347 1938 120,000 mean low water NAD 27

H06442 1939 10,000 mean low water NAD 27

H06443 1939 40,000 mean low water NAD 27

H06444 1939 40,000 mean low water NAD 27

H06668 1941 5,000 mean low water NAD 27

H06828 1943 5,000 mean low water NAD 27

H07640 1948 10,000 mean low water NAD 27

H08315 1958 12,500 mean low water NAD 27
Digital Elevation Model of Montauk, New York

9

H08615 1961 10,000 mean low water NAD 27

H08616 1961/62 10,000 mean low water NAD 27

H08708 1962 10,000 mean low water NAD 27

H08709 1961/62 20,000 mean low water NAD 27

H08908 1966 10,000 mean low water NAD 27

H08926 1966/68 10,000 mean low water NAD 27

H08936 1967 10,000 mean low water NAD 27

H08996 1968 10,000 mean low water NAD 27

H08997 1968/69 10,000 mean low water NAD 27

H09051 1969 10,000 mean low water NAD 27

H09059 1969 10,000 mean low water NAD 27

H09087 1969 20,000 mean lower low water NAD 27

H09088 1969 20,000 mean low water NAD 27

H09089 1969 20,000 mean low water NAD 27

H09093 1969 10,000 mean low water NAD 27

H09170 1970 10,000 mean low water NAD 27

H09181 1970/71 20,000 mean low water NAD 27

H09212 1971 20,000 mean low water NAD 27

H09550 1975 40,000 mean low water NAD 27

H09551 1975 40,000 mean low water NAD 27

H09554 1975 40,000 mean low water NAD 27

H09555 1975 80,000 mean low water NAD 27

F00264 1984 20,000 mean lower low water NAD 27

D00102 1989 40,000 mean lower low water NAD 83

F00340 1989 10,000 mean lower low water NAD 83

F00341 1989 10,000 mean lower low water NAD 83

D00103 1990 40,000 mean lower low water NAD 83

F00343 1990 10,000 mean lower low water NAD 83

F00345 1990 10,000 mean lower low water NAD 83

F00348 1990 10,000 mean lower low water NAD 83

H10339 1990 10,000 mean lower low water NAD 83

H10350 1990 10,000 mean lower low water NAD 83

D00111 1991 20,000 mean lower low water NAD 83

F00363 1991 10,000 mean lower low water NAD 83

F00364 1991 10,000 mean lower low water NAD 83

F00365 1991 10,000 mean lower low water NAD 83

H10378 1991 10,000 mean lower low water NAD 83

H10424 1991/92 10,000 mean lower low water NAD 83

F00377 1992 10,000 mean lower low water NAD 83

H10659 1995/96 10,000 mean lower low water NAD 83

H10788 1997 10,000 mean lower low water NAD 83

H10795 1997/99 10,000 mean lower low water NAD 83

H10900 1999 10,000 mean lower low water NAD 83

H10930 1999 10,000 mean lower low water NAD 83

H10914 1999/2000 10,000 mean lower low water NAD 83

H10984 2000 10,000 mean lower low water NAD 83
Eakins et al., 2009

10

Figure 6. Digital NOS hydrographic survey coverage in the Montauk region. DEM boundary in 

purple; Montauk coastline in red.
Digital Elevation Model of Montauk, New York

11

2) NOS multibeam sonar survey

NOS, in cooperation with USGS, conducted a detailed multibeam sonar survey, H11250 in 2003, in the 

channel between Plum and Fishers Islands (Fig. 7) for geologic mapping purposes. NOS is still reviewing 

the survey so it has not been publicly released, though USGS did provide a preliminary grid of the data to 

NGDC for use in building the Montauk DEM. The bathymetric grid was in WGS 84 geographic coordinates, 

and undefined vertical datum, assumed to be MLLW. Cell size was ~2 meters. Survey results were published

in USGS Open File Report 2007-1012 “Geologic Interpretation and Multibeam Bathymetry of the Sea Floor 

in the Vicinity of the Race, Eastern Long Island Sound” (Poppe et al, 2007; http://woodshole.er.usgs.gov/

pubs/of2007-1012/).

Figure 7. NOS multibeam sonar survey H11250. 
Eakins et al., 2009

12

3) USGS multibeam sonar survey

USGS conducted a multibeam sonar survey offshore Georgica Pond, Long Island in 1996 (Fig. 8). Survey 

results were published in USGS Open File Report 00-243 “Seafloor Sediment Distribution Off Southern

Long Island, New York” (Schwab et al, 2000; http://pubs.usgs.gov/of/2000/of00-243/). The bathymetric data 

were provided to NGDC by Jane Denny, USGS, Woods Hole in xyz format, WGS 84 geographic and MLLW 

datums. Data point spacing is about 3 meters.

Figure 8. Coverage of USGS multibeam sonar survey offshore Georgica Pond, Long Island.

4) NOAA ENCs

There are several regions in the Montauk area without digital NOS hydrographic soundings. NGDC 

extracted the soundings from NOAA Electronic Navigational Charts in the area (Fig. 5; Table 3) for use in 

building the Montauk DEM. Soundings were in meters, referenced to MLLW and WGS 84 datums.

5) NGDC-digitized soundings from NOAA RNCs

Remaining gaps in the bathymetry were filled by directly digitizing soundings (Fig. 5) from the largestscale NOAA Raster Nautical Charts (RNCs) for each area (Table 7). The RNCs are georeferenced to NAD 

83, with soundings displayed in meters at MLLW. Soundings were digitized using ESRI ArcMAP 9.2. 

Table 7. NOAA Raster Nautical Charts from which NGDC digitized soundings.

Nautical Chart # Region Scale Ed. Date

12352 SHINNECOCK BAY TO MORICHES BAY LONG ISLAND NY Various 2006-03-01

12358 NEW YORK LONG ISLAND SHELTER ISLAND SOUND AND 

PECONIC BAYS 1:40,000 2002-09-01

12372 LONG ISLAND SOUND - RI CONN 1:40,000 2006-11-01

12374 NORTH SHORE OF LONG ISLAND SOUND-DUCK ISLAND TO 

MADISON REEF 1:20,000 2000-10-28

12375 CONNECTICUT RIVER LONG ISLAND SOUND TO DEEP RIVER 1:20,000 2001-02-17

13212 APPROACHES TO NEW LONDON HARBOR 1:20,000 2005-11-01

13213 NEW LONDON HARBOR AND VICINITY 1:10,000 2004-03-01

13214 FISHERS ISLAND SOUND 1:20,000 2006-04-01

13217 BLOCK ISLAND RI 1:15,000 2006-11-01
Digital Elevation Model of Montauk, New York

13

3.1.3 Topography

Topographic datasets in the Montauk region were obtained from NOAA’s Coastal Services Center (CSC), and the 

U.S. Geological Survey (USGS; Table 8; Fig. 9). 

Table 8. Topographic datasets used in compiling the Montauk DEM.

Source Year Data Type Spatial 

Resolution

Original Horizontal 

Datum/Coordinate System

Original 

Vertical Datum URL

NOAA CSC 2000 Coastal LiDAR ~6 meters NAD 83 geographic NAVD88 

(meters)

http://maps.csc.noaa.

gov/TCM/

NOAA CSC 2004

Bare-earth 

LiDAR DEMs 

of CT

~2 meters NAD 83 geographic NAVD88 

(meters)

http://maps.csc.noaa.

gov/TCM/

USGS 1999-

2000 NED DEM 1/3 arcsecond NAD 83 geographic NAVD88(meters) http://ned.usgs.gov/

Figure 9. Source and coverage of topographic datasets used to compile the Montauk DEM.
Eakins et al., 2009

14

1) Coastal Services Center coastal topographic LiDAR

A fall 2000 coastal LiDAR survey4 of the southern coasts of Rhode Island and Connecticut (Fig. 9) was 

downloaded from NOAA’s Coastal Services Center (CSC) web site (http://maps.csc.noaa.gov/TCM/). Data 

were collected as part of the Airborne LIDAR Assessment of Coastal Erosion (ALACE) project, a partnership 

between NOAA, NASA, and USGS. Survey data are in NAD 83 geographic horizontal datum and NAVD88 

vertical datum. The data were downloaded at 5-meter point spacing, and mostly follow the coastline though 

they also contain elevation values from over the open ocean, which were deleted by NGDC. These data were 

not processed to bare earth, so some manmade features such as buildings are present in the data. Data were in 

NAD 83 geographic and NAVD88 datums. Horizontal accuracy is 80 cm, and vertical accuracy is estimated 

at 15 cm.

2) CSC topographic LiDAR survey of Connecticut

A 2004 topographic LiDAR survey5 of southern Connecticut (Fig. 9) was also downloaded from NOAA’s 

Coastal Services Center (CSC) web site (http://maps.csc.noaa.gov/TCM/). The LiDAR data are available as 

“first return” and “bare earth”. NGDC downloaded the bare-earth data at 5-meter point spacing. Data were in

NAD 83 geographic and NAVD88 datums. Horizontal accuracy is 50 cm, and vertical accuracy is estimated 

at 5.7 cm for bare-earth data.

3) USGS NED topographic DEM

The USGS National Elevation Dataset (NED; http://ned.usgs.gov/) provides complete 1/3 arc-second 

coverage of the Montauk region6

. Data are in NAD 83 geographic coordinates and NAVD88 vertical datum 

(meters), and are available for download as raster DEMs. The 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 quadrangle maps and 

aerial photographs based on topographic surveys; it has been revised using data collected in 1999 and 2000. 

The NED DEM included “zero” elevation values over the open ocean, which were removed from the dataset 

by clipping to the Montauk coastline.

4. This data set was collected with a LIDAR (LIght Detection And Ranging) instrument designed and developed by the Observational Sciences 

Branch (OSB) of NASA at the Wallops Flight Facility in Virginia. The instrument, originally designed for mapping ice sheets in Greenland, is called 

the Airborne Topographic Mapper or ATM. The ATM II (the latest version), operates with a Spectra Physics laser transmitter, which provides a 7 

nanoseconds long, 250 microjoules pulse at a frequency-doubled wavelength of 523 nanometers in the blue-green spectral region. The laser transmitter can function at pulse rates from 2 to 10 kilohertz (kHz). The laser system with a separate cooling unit weighs approximately 45 kilograms 

(kg) and requires approximately 15 amperes of power at 115 volts. The transmitted laser pulse is reflected to the surface of the earth with the aid of

a small folding mirror mounted on the back of a secondary mirror of a rotating scan mirror assembly mounted directly in front of the telescope. The 

scan mirror, which is rotated at 20 hertz, is comprised of a section of round aluminum stock, machined to a specific off-nadir angle. A scan mirror

with the off-nadir angle of 15 degrees was utilized, producing an elliptical scan pattern with a swath width equal to 50 percent of the approximately 

700-meter aircraft altitude. The reflected laser pulse is transmitted to a photo-multiplier assembly that consists of a lens, a narrow bandpass filter,

and a single photomultiplier tube. [Extracted from metadata.]

5. LiDAR data collection was performed using a LH Systems ALS50 Light Detection And Ranging (LiDAR) system, 41 flight lines of high density (submeter ground sample distance) data were collected over areas in coastal Connecticut (approximately 300 square kilometers). Two returns 

were recorded for each laser pulse along with an intensity value for each return. The data acquisition occurred in one (1) mission on October 8, 

2004. Three (3) airborne global positioning system (GPS) base stations were used to support the LiDAR data acquisition: Moriches 1 continuously 

operating reference station (CORS) ARP, NGS point P36, and one station Woolpert located using static GPS positioning methods, Madison CP. In 

addition, twenty-two control points were surveyed through fast-static GPS methods to support the final accuracy analysis and tied into the National

Geodetic Survey (NGS) points Moriches CORS and P36. [Extracted from metadata.]

6. 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 Georgia. 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 website]
Digital Elevation Model of Montauk, New York

15

3.1.4 Bathymetry–Topography

Two bathymetric–topographic datasets were available for Long Island, New York: Joint Airborne LiDAR 

Bathymetry Technical Center of Expertise (JALBTCX) coastal LiDAR survey and USACE beach profiles (Fig 10;

Table 9).

Table 9. Bathymetric–topographic datasets used in compiling the Montauk DEM.

Source Year Data Type Spatial Resolution Original Horizontal 

Datum/Coordinate System

Original Vertical 

Datum

JALBTCX 

LiDAR 2005 Coastal LiDAR < 5 meters WGS 84 geographic MLLW (meters)

USACE 2001–

2005

Beach 

profiles

profiles up to 650 meters long, spaced

150 to 650 meters apart, with point 

spacing of 1.5 to 6 meters

NAD 83 New York State 

Plane, Long Island (feet) NGVD29 (ffet)

Figure 10. Source and coverage of bathymetric–topographic datasets used to 

compile the Montauk DEM.
Eakins et al., 2009

16

1) JALBTCX coastal LiDAR

The Joint Airborne Lidar Bathymetry Technical Center of Expertise conducted a bathymetric–topographic 

LiDAR survey of the southern coast of Long Island in 2005 using the Compact Hydrographic Airborne 

Rapid Total Survey (CHARTS) system7. These data are published on the NOAA CSC web site (http://maps.

csc.noaa.gov/TCM/) and were downloaded at 5-meter point spacing in NAD 83 geographic and NAVD88 

datums. Horizontal accuracy is 3 m, and vertical accuracy is estimated at 30 cm. These data have not been 

processed to bare earth, so buildings and trees are represented in the data. NGDC manually removed elevations 

derived from returns off of the top of the Montauk Lighthouse (Fig. 2) so that that part of the Montauk DEM 

approximates bare earth. Bathymetric values represent only a few percent of the elevations in this dataset.

2) USACE beach profiles

The U.S. Army Corps of Engineers (USACE) conducts beach monitoring programs of Long Island, New 

York (Morang, 2002). Data from these monitoring programs were provided to NGDC by Diane Rahoy and 

John Mraz, USACE, NewYork District office. Data included beach and bathymetric profiles at Montauk Point,

Lake Montauk, W. Shinnecock Bay and the entrance to Mattituck Creek (Fig. 10), as well as topographic 

measurements and contours. Data were collected between 2001 and 2005 and referenced to NAD 83 New 

York State Plane, Long Island (feet) and NGVD29 (feet). At the entrance to Lake Montauk, the data consists 

primarily of bathymetric profiles across the harbor entrance spaced 10 to 20 meters apart, with elevations

every .3 m. Along the coast at Mattituck and Shinnecock, the beach profiles are 500–650 meters long and

spaced 150–650 meters apart, with elevations every 1.5–6 meters. 

7. Acquisition data were acquired using a SHOALS-1000T. Sensor orientation was measured using a POS AV 410, while images were acquired at 

1Hz using a Duncantech DT4000 digital camera. Prior to survey PDOP was checked and missions planned to avoid PDOP greater than 3.5. During 

survey the plane was always within 30km of a GPS ground control point, to provide a good quality position solution. Final positions were determined using a post-processed inertially aided Kinematic GPS (KGPS) solution. GPS ground control data were acquired at 1Hz. Data received by 

the airborne system were continually monitored for data quality during acquisition operations. Display windows showed coverage and information 

about the system status. In addition, center waveforms at 5Hz were shown. All of this information allowed the airborne operator to assess the quality of data being collected. Data were processed in the field to verify coverage and data quality. Data were processed using the SHOALS Ground

Control System (GCS). The GCS includes links to Applanix POSPac software for GPS and inertial processing, and IVS Fledermaus software for 

data visualization, 3D editing and tie-line analysis. Data were processed in NAD 83 horizontal and vertical datum. Data were later converted to 

the NAVD88 vertical datum using the GEOID03 model. Fugro in-house utilities were used to extract XYZ data from the native LIDAR files and

split the data in to pre-defined boxes, each covering approximately 5km of shoreline. ASCII files include Longitude Latitude Elevation Date Time

Intensity (Topo) or Depth Confidence (Hydro). [Extracted from metadata.]
Digital Elevation Model of Montauk, New York

17

3.2 Establishing Common Datums

3.2.1 Vertical datum transformations

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

vertical datums including Mean Lower Low Water (MLLW), Mean Low Water (MLW), National Geodetic Vertical 

Datum of 1929 (NGVD29), and North American Vertical Datum of 1988 (NAVD88). All datasets were transformed 

to MHW to provide the maximum flooding for inundation modeling. Units were converted from feet to meters as

appropriate. PMEL provided NGDC with conversion grids for MLLW to MHW, MLW to MHW and NAVD88 to MHW. 

Theses grids were derived from vertical datum relationships established at tide stations in the Montauk region.

1) Bathymetric data

The NOS hydrographic surveys, the ENC and RNC soundings, and the USGS and NOS multibeam sonar 

surveys were transformed from MLLW and MLW to MHW, using FME software, by adding the appropriate 

conversion grid.

2) Topographic data

The USGS NED 1/3 arc-second DEM and the CSC LiDAR data were originally referenced to NAVD88. 

Both datasets were transformed from NAVD88 to MHW, using FME software, by adding the NAVD88-toMHW conversion grid.

3) Bathymetric–topographic data

The JALBTCX bathymetric-topographic LiDAR data were transformed from NAVD88 to MHW 

by adding the NAVD88-to-MHW conversion grid using FME. The USACE beach profile data were first

transformed from NGVD29 to NAVD88 by adding a constant offset of -0.288 (the difference between these 

two datums as measured at the Montauk tide station, #8510560). This difference is roughly equivalent with 

other tide stations in the region. The data were then transformed to MHW using the NAVD88-to-MHW 

conversion grid. All transformations were performed using FME.

Table 10. Relationship between Mean High Water and other vertical datums at the Montauk tide station, #8510560.

Vertical datum Difference to MHW

NAVD88 -0.286 meters

MSL -0.306 meters

NGVD29 -0.574 meters

MLW -0.631 meters

MLLW -0.683 meters

3.2.2 Horizontal datum transformations

Datasets used to compile the Montauk DEM were originally referenced to NAD 83 New York State Plane Long 

Island (feet), NAD 83 geographic, NAD 27 geographic, or WGS 84 geographic horizontal datums. The relationships 

and transformational equations between these horizontal datums are well established. All data were converted to a 

horizontal datum of NAD 83 geographic using FME software.
Eakins et al., 2009

18

3.3 Digital Elevation Model Development

3.3.1 Verifying consistency between datasets

After horizontal and vertical transformations were applied, the resulting ESRIshape files were checked inArcMap

for consistency between datasets. 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:

•	 Presence of piers in the ENC coastlines, which had to be removed.

•	 Lack of existing high-resolution coastline files for most of the area, which necessitated digitizing of coastline

segments from large-scale NOAA nautical charts.

•	 Data values over the ocean and rivers in the NED and CSC LiDAR topographic data. The NED dataset 

required automated clipping to the Montauk coastline. The CSC LiDAR datasets were manually clipped to 

the coastline.

•	 The older NOS hydrographic surveys were digitized, under contract, from the original survey sheets. The 

digital files contained many errors that were recognized and corrected by NGDC during data evaluation, by

comparison with the survey sheets.

•	 Coastal area without digital bathymetric values. NGDC hand-digitized soundings in these areas from largescale NOAA nautical charts.

•	 The two coastal LiDAR datasets (JALBTCX bathymetric–topographic and CSC topographic) had not been 

processed to bare earth. NGDC only removed elevation values that represented the Montauk Lighthouse at 

Montauk Point. Other elevations representing the tops of buildings and trees were left in the datasets.

3.3.2	 Smoothing of beach-profile data

The USACE beach-profile data at Shinnecock Bay and the entrance to Mattituck Creek have high resolution along

the profiles (1.5 to 6 meters), but the profiles are spaced some distance apart (150 to 650 meters), much greater than the

1/3 arc-second (~10 meter) resolution required for the Montauk DEM. NGDC gridded these profiles at 1/3 arc-second

to create interpolated values between the profiles. Interpolation was performed using the ‘triangulate’ command in

GMT, an NSF-funded share-ware software application designed to manipulate data for mapping purposes (http://gmt.

soest.hawaii.edu/).

3.3.3 Smoothing of bathymetric data

The NOS hydrographic survey data are generally sparse at the resolution of the 1/3 arc-second Montauk DEM: 

in both deep water and in some areas close to shore, the NOS survey data have point spacing up to 1900 m apart. In 

order to reduce the effect of artifacts in the form of lines of “pimples” in the DEM due to this low resolution data, 

and to provide effective interpolation into the coastal zone, a 1 arc-second-spacing ‘pre-surface’ bathymetric 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 ENC and RNC soundings, and the USGS 

and NOS multibeam sonar data into a single file, along with points extracted from the Montauk coastline—to provide

a buffer along the entire coastline. The coastline points were assigned a -0.5 elevation value so that interpolation into 

coastal bays without bathymetric values would produce negative elevation values of ~-0.5 meters.

The point data were median-averaged using the GMT tool ‘blockmedian’ to create a 1 arc-second grid 0.05

degrees (~5%) larger than the Montauk DEM gridding region. The GMT tool ‘surface’ was then used to apply a tight

spline tension to interpolate elevations for cells without data values. The GMT grid created by ‘surface’was converted

into an ESRI Arc ASCII grid file, and clipped to the Montauk coastline (to eliminate data interpolation into land areas).

The resulting surface was compared with original soundings to ensure grid accuracy (e.g., Fig. 11), converted to a 

shape file, and then exported as an xyz file for use in the final gridding process (see Table 11).
Digital Elevation Model of Montauk, New York

19

Figure 11. Histogram of the differences between NOS hydrographic survey H10984 and the 1 arc-second pre-surfaced 

bathymetric grid.

3.3.4 Gridding the data with MB-System

MB-System (http://www.ldeo.columbia.edu/res/pi/MB-System/) was used to create the 1/3 arc-second Montauk 

DEM. MB-System is an NSF-funded share-ware software application specifically designed to manipulate submarine

multibeam sonar data, though it can utilize a wide variety of data types, including generic xyz data. The MB-System 

tool ‘mbgrid’ was used to apply a tight spline tension to the xyz data, and interpolate values for cells without data.

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

weight was given to the LiDAR and multibeam sonar data. Least weight was given to the pre-surfaced 1 arc-second 

bathymetric grid. Gridding was performed in quadrants, and the resulting Arc ASCII grids were seamlessly merged in 

ArcCatalog to create the final 1/3 arc-second Montauk DEM.

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

Dataset Relative Gridding Weight

JALBTCX bathymetric-topographic coastal LiDAR 10000

CSC topographic bare-earth LiDAR 10000

NOS multibeam sonar survey 10000

USGS multibeam sonar survey 10000

CSC topographic coastal LiDAR 1000

NOS hydrographic surveys: bathymetric soundings 1000

USGS NED topographic DEM 100

Montauk coastline 100

NOAA ENC and RNC soundings 10

Pre-surfaced bathymetric grid 1
Eakins et al., 2009

20

3.4 Quality Assessment of the DEM

3.4.1. Horizontal accuracy

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

datasets used to determine corresponding DEM cell values. Topographic features have an estimated accuracy of up to 

10 meters: CSC and JALBTCX LiDAR data have an accuracy of a few meters or less; NED topography is accurate 

to within about 10 meters. Bathymetric features are resolved only to within a few tens of meters in deep-water areas. 

Shallow, near-coastal regions, rivers, and harbor surveys have an accuracy approaching that of subaerial topographic 

features. Positional accuracy is limited by the sparseness of deep-water soundings, potentially large positional 

uncertainty of pre-satellite navigated (e.g., GPS) NOS hydrographic surveys, and by coastal morphologic change that 

occurs in this dynamic region.

3.4.2 Vertical accuracy

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

contributing to DEM cell values. Topographic areas have an estimated vertical accuracy between 0.1 to 0.3 meters 

for JALBTCX and CSC LiDAR data, and up to 7 meters for NED topography. Bathymetric areas have an estimated 

accuracy of between 0.1 meters and 5% of water depth. Those values were derived from the wide range of input data 

sounding measurements from the early 20th century to recent, GPS-navigated sonar surveys. Gridding interpolation to 

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

water.

3.4.3 Slope maps and 3-D perspectives

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

identification of artificial slopes along boundaries between datasets (e.g., Fig. 12). The DEM was transformed to UTM

Zone 18 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 

was accomplished using ESRI ArcScene (e.g., Fig. 13). Analysis of preliminary grids revealed suspect data points, 

which were corrected before recompiling the DEM. Figure 1 shows a color image of the 1/3 arc-second Montauk 

DEM in its final version.

Figure 12. Slope map of the Montauk DEM. Flat-lying slopes are white; dark shading denotes steep 

slopes; Montauk coastline in red.
Digital Elevation Model of Montauk, New York

21

Figure 13. Perspective view from the southeast of the Montauk DEM. Vertical 

exaggeration–times 10.

3.4.4	 Comparison with source data files

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

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

significantly overlap other data files with comparable weight). A histogram of the differences between one JALBTCX

coastal LiDAR survey file, 5-meter point spacing, and the Montauk DEM is shown in Figure 14. Differences cluster

around zero, with only a handful of values, in regions where buildings are present and several elevation values are 

averaged, exceeding 2-meter discrepancy from the DEM.

Figure 14. Histogram of the differences between one JALBTCX coastal LiDAR file and the Montauk DEM.
Eakins et al., 2009

22

3.4.5 Comparison with NGS geodetic monuments

The elevations of 1459 NOAA NGS geodetic monuments were extracted from online shape files of monument

datasheets (http://www.ngs.noaa.gov/cgi-bin/datasheet.prl), which give monument positions in NAD 83 (typically 

sub-mm accuracy) and elevations in NAVD88 (in meters). Elevations were shifted to MHW vertical datum (see 

Section 3.2.1) for comparison with the Montauk DEM (see Fig. 16 for monument locations). Differences between the 

Montauk DEM and the NGS geodetic monument elevations range from -50 to 14 meters, with the majority of them 

being within + 5 meters. Negative values indicate that the DEM is less than the monument elevation (Fig. 15). Large 

discrepancies from the DEM are from monuments located on the tops of buildings and other such manmade features. 

Many discrepancies are due to large uncertainties in monument locations (6 arc-seconds/~180 meters).

Figure 15. Histogram of the differences between NGS geodetic monument elevations and the Montauk DEM. 

Figure 16. Location of NGS geodetic monuments and NOAA tide stations in the Montauk region. 

NGS monument elevations were used to evaluate the DEM.
Digital Elevation Model of Montauk, New York

23

4. Summary and Conclusions

A bathymetric-topographic digital elevation model of the Montauk, New York region, with cell spacing of 1/3 

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, and MB-System software. 

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

•	 Conduct bathymetric-topographic LiDAR surveys of the northern coast of Long Island, New York and coastal 

bays and estuaries.

•	 Conduct hydrographic surveys for near-shore areas without digital sounding data, mostly around Block 

Island.

•	 Conduct complete topographic LiDAR surveying of Long Island, New York.

•	 Process CSC and JALBTCX coastal LiDAR data to bare earth.

5. Acknowledgments

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

authors thank Chris Chamberlin and Vasily Titov (PMEL), Diane Rahoy and John Mraz (USACE, New York District), 

and Bill Schwab and Jane Denny (USGS, Woods Hole).

6. References

Morang, Andrew, 2002, Atlantic Coast of New York Monitoring Program: Cross-Shore Profiles, Quality-Control 

Procedures, Monumentation, and Data Archiving, USACE Report ERDC/CHL TR-02-16.

Poppe, L.J., M.L. DiGiacomo-Cohen, E.F. Doran, S.M. Smith, H.F. Stewart, and N.A. Forfinski, 2007, Geologic 

Interpretation and Multibeam Bathymetry of the Sea Floor in the Vicinity of the Race, Eastern Long Island Sound, 

USGS Open File Report 2007-1012, http://woodshole.er.usgs.gov/pubs/of2007-1012/.

William B. Rogers, W.B., Y.W. Isachsen, T.D. Mock, and R.E. Nyahay, Overview of New York Geology, http://gretchen.

geo.rpi.edu/roecker/nys/nys_edu.pamphlet.html

Schwab, W.C., E.R. Thieler, J.F. Denny, W.W. Danforth, and J.C. Hill, 2000, Seafloor Sediment Distribution Off 

Southern Long Island, New York, USGS Open File Report 00-243, http://pubs.usgs.gov/of/2000/of00-243/

7. Data Processing Software

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

FME 2007 ESRI Edition – 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. 4.1.4 – 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/