noaa / NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

National Environmental Satellite,

Data, and Information Service

NOAA Technical Memorandum NESDIS NGDC-59

DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST:

PROCEDURES, DATA SOURCES AND ANALYSIS 

M.R. Love

C.J. Amante

B.W. Eakins

L.A. Taylor

National Geophysical Data Center

Marine Geology and Geophysics Division

Boulder, Colorado

August 2012

UNITED STATES

DEPARTMENT OF COMMERCE

Rebecca Blank

Acting Secretary

NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

Mary M. Glackin

Under Secretary for Oceans

and Atmosphere/Administrator

National Environmental Satellite,

Data, and Information Service

Mary E. Kicza

Assistant Administrator

NOAA Technical Memorandum NESDIS NGDC-59

DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST:

PROCEDURES, DATA SOURCES AND ANALYSIS 

Matthew R. Love1 

Christopher J. Amante1, 2

Barry W. Eakins2

Lisa A. Taylor3

1. Earth Resources Technology, Inc., Annapolis Junction, Maryland

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

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

Funded by the American Recovery and Reinvestment Act (ARRA) of 2009.

National Geophysical Data Center

Marine Geology and Geophysics Division 

Boulder, Colorado

August 2012
NOTICE 

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

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

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

or advertising purposes is not authorized. 

Corresponding project contact:

Lisa A. Taylor

NOAA National Geophysical Data Center

Marine Geology and Geophysics Division

325 Broadway, E/GC 3

Boulder, Colorado 80305

Phone: 303-497-6767

Fax: 303-497-6513

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

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

Also available from the National Technical Information Service (NTIS)

(http://www.ntis.gov)

ii
Contents

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

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

3. Source Elevation Data................................................................................................ 3

3.1 Data Sources And Processing ................................................................................. 3

3.1.1 Coastline............................................................................................... 3

3.1.2 Bathymetry ............................................................................................ 5

3.1.3 Topography ............................................................................................ 8

3.1.4 Bathymetry–Topography ............................................................................. 11

3.2 Establishing Common Datums ................................................................................ 14

3.2.1 Vertical datum transformations ....................................................................... 14

3.2.2 Horizontal datum transformations.................................................................... 14

3.2.3 Verifying consistency between datasets .............................................................. 14

4. Structured DEM Development ...................................................................................... 15

4.1 Smoothing of bathymetric data................................................................................ 15

4.2 Building the NAVD 88 Structured DEM ..................................................................... 16

4.3 Building the MHW Structured DEM ......................................................................... 18

4.3.1 Developing the conversion grid ...................................................................... 18

4.3.2 Assessing the accuracy of conversion grid........................................................... 18

4.3.3 Creating the MHW Structured DEM................................................................. 19

4.4 Quality Assessment of the Structured DEMs................................................................. 21

4.4.1 Horizontal accuracy ................................................................................... 21

4.4.2 Vertical accuracy ...................................................................................... 21

4.4.3 Slope maps and 3D perspectives ..................................................................... 21

4.4.4 Comparison with National Geodetic Survey geodetic monuments ................................. 21

4.4.5 Comparison with source data files ................................................................... 21

5. Summary and Conclusions .......................................................................................... 26

6. Acknowledgements .................................................................................................. 26

7. References ............................................................................................................ 26

8. Data Processing Software ............................................................................................ 27

Appendix A. NOS Hydrographic Surveys.............................................................................. 28

Appendix B. Electronic Navigational Charts .......................................................................... 42

List of Figures

Figure 1. Shaded-relief image of the Northern Gulf Coast NAVD 88 DEM ...................................... 1

Figure 2. Extents of the Northern Gulf Coast project area and the states located within ......................... 2

Figure 3. Portion of coastline dataset used in the development of the Northern Gulf Coast DEMs. ............. 4

Figure 4. Bathymetric data sources available in the Northern Gulf Coast region. ................................ 5

Figure 5. NOS digital hydrographic survey coverage in the Northern Gulf Coast region. ....................... 6

Figure 6. OCS ENC bathymetric datasets available in the Northern Gulf Coast region. ......................... 7

Figure 7. Topographic data sources in the Northern Gulf Coast region. .......................................... 8

Figure 8. USGS NED 1-arc second DEMs used in the development of the Northern Gulf Coast DEMs ....... 9

Figure 9. FDEM data sources used in the development of the Northern Gulf Coast DEMs ..................... 10

Figure 10. Bathymetric/Topographic data sources used in compiling the Northern Gulf Coast DEMs ........... 12

Figure 11. Pre-surface bathymetric grid of the Northern Gulf Coast ............................................... 15

Figure 12. Histogram of the differences between the NOS hydrographic soundings and the Northern Gulf

Coast bathymetric surface. ................................................................................ 16

Figure 13. Data density of the Northern Gulf Coast DEMs. ........................................................ 17

Figure 14. Available VDatum Project Areas (P.A.) in the Northern Gulf Coast DEM region...................... 18

Figure 15. Elevation conversion values of ’NAVD-88-to-MHW’ conversion grid derived from VDatum. ....... 19

Figure 16. Histogram of the differences between the conversion grid and xyz difference files using NOS hydrographic survey data..................................................................................... 20

iii
Figure 17. Slope map of the Northern Gulf Coast NAVD 88 DEM. ................................................ 22

Figure 18. Perspective view from the southwest of the Northern Gulf Coast NAVD 88 DEM. ................... 23

Figure 19. Comparison with NGS geodetic monuments, locations and histogram. ................................ 24

Figure 20. Hisograms of the differences between individual datasets and the Northern Gulf Coast NAVD 88

DEM........................................................................................................ 25

List of Tables

Table 1. Specifications for the Northern Gulf Coast DEMs ........................................................ 2

Table 2. Coastline datasets used in compiling the Northern Gulf Coast DEMs ................................... 3

Table 3. Bathymetric datasets used in compiling the Northern Gulf Coast DEMs................................ 5

Table 4. Topographic Datasets Used in Compiling the Northern Gulf Coast DEM............................... 8

Table 5. Bathymetric/Topographic Datasets Used in Compiling the Northern Gulf Coast DEMs ............... 11

Table 6. Data hierarchy used to assign gridding weight in MB-System ........................................... 16

Table A-1. NOS Hydrographic datasets used in building the Northern Gulf Coast DEMs.......................... 28

Table B-2. ENC datasets used in building the Northern Gulf Coast DEMs .......................................... 42

iv
Digital Elevation Models of the Northern Gulf Coast:

Procedures, Data Sources and Analysis

1. INTRODUCTION

In December 2010, the National Geophysical Data Center (NGDC), an office of the National Oceanic and Atmospheric Administration (NOAA), has developed two bathymetric–topographic digital elevation models (DEMs) of

the Northern Gulf Coast (Figure 1). The DEMs were developed for NOAA’s Coast Survey Development Laboratory

(CSDL) through the American Recovery and Reinvestment Act (ARRA) of 20091to evaluate the utility of the Vertical

Datum Transformation tool (VDatum), developed jointly by NOAA’s Office of Coast Survey (OCS), National Geodetic

Survey (NGS), and Center for Operational Oceanographic Products and Services (CO-OPS) (http://vdatum.noaa.gov/).

The 1 arc-second DEM2referenced to North American Vertical Datum of 1988 (NAVD 88) was carefully developed and evaluated. A NAVD 88 to mean high water (MHW) 1/3 arc-second conversion grid derived from VDatum

project areas was then created to model the relationship between NAVD 88 and MHW in the Gulf of Mexico region.

NGDC combined the NAVD 88 DEM and the conversion grid to develop a 1/3 arc-second MHW DEM. The NAVD 88

DEM was generated from diverse digital datasets in the region (grid boundary and sources shown in Figures 2, 4 and

7) and the DEMs will be used for storm surge inundation and sea level rise modeling. This report provides a summary

of the data sources and methodology used in developing the two Northern Gulf Coast DEMs.

Figure 1. Shaded-relief image of the Northern Gulf Coast NAVD 88 DEM

1On Feb. 13, 2009, Congress passed the American Recovery and Reinvestment Act of 2009 at the urging of President Obama, who signed it into

law four days later. A direct response to the economic crisis, the Recovery Act’s three goals are to create new jobs as well as save existing ones,

spur economic activity and invest in long-term economic growth and foster unprecedented levels of accountability and transparency in government

spending (http://www.recovery.gov/Pages/home.aspx).

2The Northern Gulf Coast 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 Mobile, AL, 1/3 arc-second of

latitude is equivalent to 10.2641 meters; 1/3 arc-second of longitude equals 8.9371 meters
Love, et al. 2012

2. STUDY AREA

The Northern Gulf Coast DEMs cover the area from New Orleans, Louisiana in the west to Panama City, Florida

in the east, including portions of Louisiana, Mississippi, Alabama, and Florida (Figure 2). The Northern Gulf Coast

region is made of many inlets, bays, and lagoons and is intersected by numerous rivers, the largest of which is the

Mississippi River, which drains into the Gulf of Mexico in Louisiana. Much of the land along the Northern Gulf

Coast is, or was, marshland. Ringing the Gulf Coast is the Gulf Coastal Plain which stretches from Southern Texas

to the western Florida Panhandle. The central part of the Gulf Coast, from eastern Texas through Louisiana, consists

primarily of marshland. The eastern part of the Gulf Coast, predominantly Florida, is dotted with many bays and inlets.

Due to the proximity of the Gulf to the subtropical waters of the Gulf of Mexico, the Northern Gulf Coast region is

vulnerable to hurricanes as well as floods and severe thunderstorms.

Table 1. Specifications for the Northern Gulf Coast DEMs

Grid Area Northern Gulf Coast

Coverage Area -90.75 ◦, 31.25 ◦, -85.0

◦, 28.5◦

Coordinate System Geographic decimal degrees

Horizontal Datum World Geodetic System 1984 (WGS 84)

Vertical Datum North American Vertical Datum of 1988 (NAVD 88)

Vertical Units Meters

Grid Spacing 1/3 arc-second

Grid Format ESRI Arc ASCII grid

Figure 2. Extents of the Northern Gulf Coast project area and the states located within

2
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

3. SOURCE ELEVATION DATA

The best available digital data were obtained by NGDC and shifted to common horizontal and vertical datums:

North America Datum 1983 (NAD 83)3and NAVD 88. NGDC developed a conversion grid derived from VDatum

project areas to transform the Northern Gulf Coast DEM in its entirety from NAVD-88-to-MHW, for modeling of

maximum flooding (Section 3.3.4 & 3.3.5). Data were gathered in an area slightly larger (∼5%) than the DEM extents.

This ’data buffer’ ensures that gridding occurs across rather than along the DEM boundaries to prevent edge effects.

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

3.1 Data Sources And Processing

Coastline, bathymetric, and topographic digital datasets (Tables 2, 3, and 4) were obtained from several U.S.

federal agencies: NOAA’s NGDC, OCS and Coastal Services Center (CSC); the United States Geological Survey

(USGS); and the United States Army Corps of Engineers (USACE). The datasets were displayed with Earth Systems

Research Institute (ESRI) ArcGIS, ESRI Imagery World 2D Online World Imagery 2D, and Applied Imagery Quick

Terrain Modeler software (QT Modeler) to assess data quality and manually edit datasets. Vertical datum transformations to MHW were accomplished using NOAAâA ̆ Zs Vertical Datum Transformation (  ́ VDatum)

4

software, and ESRI

ArcGIS, based upon data from NOAA tide stations (see Section 3.2.1).

3.1.1 Coastline

Coastline datasets of the Northern Gulf Coast region were obtained from a variety of sources, including OCS

and NGDC. The coastline dataset used in developing a combined detailed coastline was the NGDC world vector

shoreline (Table 2, Figure 3). This dataset provided a detailed MHW coastline for the entire Northern Gulf Coast

coverage area. NGDC did not use a coastline dataset over areas where pre-built DEMs were available (Section 3.1.4).

See sections 3.2.1 and 3.2.2 for horizontal and vertical datum transformation specifics, respectively.

Table 2. Coastline datasets used in compiling the Northern Gulf Coast DEMs

Source Year Data Type Spatial

Resolution

Original Horizontal

Datum/Coordinate

System

Original Vertical

Coordinate System URL

NOAA

NGDC NOS 1994

Composite

vectorized

coastline

2.0 mm at

1:250,000 WGS 84 geographic MHW http://rimmer.ngdc.noaa.gov/

3The horizontal difference between 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. Many 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 waveâA ̆ Zs 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.

4VDatum is a free software tool being developed jointly by NOAA’s NGS, OCS, and CO-OPS. VDatum is designed to vertically transform geospatial

data among a variety of tidal, orthometric and ellipsoidal vertical datums.

3
Love, et al. 2012

Figure 3. Portion of coastline dataset used in the development of the Northern Gulf Coast DEMs.

4
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

3.1.2 Bathymetry

Bathymetric datasets available in the Northern Gulf Coast region included 322 National Oceanic Survey

(NOS) hydrographic surveys, and 33 ENCs (Table 3; Figure 4). NGDC reviewed but did not use 10 multibeam surveys.

See sections 3.2.1 and 3.2.2 for horizontal and vertical datum transformation specifics, respectively.

Table 3. Bathymetric datasets used in compiling the Northern Gulf Coast DEMs

Source Year Data Type Spatial

Resolution

Original Horizontal

Datum/Coordinate

System

Original Vertical

Coordinate System URL

NOS-CSDL 1888 to

2001

Hydrographic

survey

soundings

Ranges from

1:5,000 to

1:80,000

NAD 83 geographic MLLW or MLW

http://www.

nauticalcharts.

noaa.gov/csdl/

welcome.htm

ENC/OCS Hydrographic

point data

Ranges from

1:20,000 to

1:458,596

(varies by chart)

WGS 84 geographic MLLW

http://www.

nauticalcharts.

noaa.gov

Figure 4. Bathymetric data sources available in the Northern Gulf Coast region.

5
Love, et al. 2012

1) NOS Hydrographic Surveys

A total of 322 NOS hydrographic surveys conducted between 1873 and 2003 were available for use in the

development of the Northern Gulf Coast DEMs (Figure 5). CSDL provided NGDC with a non-superceded database

of NOS hydrographic surveys. The database excluded NOS survey data if there were more recent NOS survey data

at the same location. NGDC also manually edited older NOS hydrographic survey data that were inconsistent with

USACE soundings in more recently dredged channels. The data were vertically referenced to mean lower low water

(MLLW) or mean low water (MLW) and horizontally referenced to NAD 83 geographic. Survey data were used in

an area 0.05 degree (∼5%) larger than the Northern Gulf Coast DEM extent to support data interpolation across

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

point spacing than more recent surveys. NOS survey data were clipped to bathymetric–topographic datasets using

Python5and transformed from MLLW or MLW to NAVD 88 using VDatum. 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 various topographic and bathymetric data, the final coastline, and OCS

Raster Navigational Charts (RNCs). See Sections 3.2.1 and 3.2.2 for horizontal and vertical datum transformation

specifics, respectively.

Figure 5. NOS digital hydrographic survey coverage in the Northern Gulf Coast region. Some soundings from earlier surveys were not used as

they have been superseded by more recent surveys.

5Python is an interpreted, general-purpose high-level programming language whose design philosophy emphasizes code readability. Python is free

and open source software. http://www.python.org/

6
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

2) OCS Electronic Navigational Charts

Thirty-three ENC bathymetric datasets were available from OCS in the Northern Gulf Coast coverage

area (Figure 6). The ENCs were downloaded from the OCS web site (http://www.nauticalcharts.noaa.gov), and

were horizontally referenced to NAD 83 geographic and vertically referenced to MLLW. The data were reviewed

and compared to the coastline and to the corresponding RNCs. See Sections 3.2.1 and 3.2.2 for horizontal and

vertical datum transformation specifics, respectively.

Figure 6. OCS ENC bathymetric datasets available in the Northern Gulf Coast region.

7
Love, et al. 2012

3.1.3 Topography

The topographic datasets used to build the Northern Gulf Coast DEMs include: USGS National Elevation

Dataset (NED) 1 arc-second DEMs (Table 4; Figure 7). See Sections 3.2.1 and 3.2.2 for horizontal and vertical datum

transformation specifics, respectively.

Table 4. Topographic Datasets Used in Compiling the Northern Gulf Coast DEM

Source Year Data Type Spatial

Resolution

Original Horizontal

Datum/Coordinate

System

Original Vertical

Coordinate System URL

USGS 1999 Bare-earth lidar 1 - 5 meters WGS 84 geographic NAVD 88 (meters) http:

//ned.usgs.gov/

FDEM 2009 Bare-earth

contours

2 feet NAD 83 HARN NAVD 88 (feet)

http://www.

floridadisaster.org/

gis

Figure 7. Topographic data sources in the Northern Gulf Coast region.

8
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

1) USGS NED

The USGS NED provided complete 1 arc-second bare-earth DEM (NED 1 DEM) coverage of the Northern

Gulf Coast region6(Figure 8). The NED 1 DEM was utilized in gridding the Northern Gulf Coast DEMs. The

extracted bare-earth elevations from the NED 1 DEM have a reported vertical accuracy of +/- 7 to 15 meters

depending on source data resolution. The NED 1 DEM was derived from USGS quadrangle maps and aerial

photographs based on topographic surveys, and has been revised using data from 1999 to 2009. The NED DEMs

were converted to xyz for gridding using Python and GDAL. See Sections 3.2.1 and 3.2.2 for horizontal and vertical

datum transformation specifics, respectively.

Figure 8. USGS NED 1-arc second DEMs used in the development of the Northern Gulf Coast DEMs

6The 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 NAVD 88, except for AK, which is NGVD29. NED is a living

dataset that is updated bimonthly to incorporate the “best available” DEM data. As more 1/3 arc second (10 m) data covers the U.S., then this will

also be a seamless dataset. [Extracted from USGS NED web site]

9
Love, et al. 2012

2) FDEM contoured lidar

The topographic lidar datasets used in compiling the Northern Gulf Coast DEM were collected in 2006

and 2009 for a variety of organizations, including FDEM, the Florida Water Management Districts, the Florida

Fish and Wildlife Conservation Commission, the Florida Department of Environmental Protection, the USACE

Jacksonville District, and other state and federal agencies. The ultimate goal of this project was to use the lidar data

as new elevation inputs for updated Sea, Lake, and Overland Surges from Hurricanes (SLOSH) data grids, resulting in updates of the Regional Hurricane Evacuation Studies (RHES; http://www.saw.usace.army.mil/floodplain/

Hurricane%20Evacuation.htm) for the state.

FDEM coastal lidar for Franklin County, FL (Figure 9) were downloaded by NGDC from the FDEM

GIS portal (http://www.floridadisaster.org/gis) as 2ft vector contours. The 2009 coastal lidar data were horizontally

referenced to NAD 83 HARN and vertically referenced to NAVD 88. The vector contours were converted to xyz

points to be used in the final gridding process using Python and GDAL. See Sections 3.2.1 and 3.2.2 for horizontal

and vertical datum transformation specifics, respectively.

Figure 9. FDEM data sources used in the development of the Northern Gulf Coast DEMs

10
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

3.1.4 Bathymetry–Topography

The combined bathymetric–topographic datasets used to build the Northern Gulf Coast DEMs include:

NGDC’s Southern Louisiana DEM, NGDC’s New Orleans, LA DEM, NGDC’s Mobile, AL DEM, NGDC’s Biloxi,

MS DEM and NGDC’s Panama City, FL DEM (Table 5; Figure 10). See Sections 3.2.1 and 3.2.2 for horizontal and

vertical datum transformation specifics, respectively.

Table 5. Bathymetric/Topographic Datasets Used in Compiling the Northern Gulf Coast DEMs

Source Year Data Type Spatial

Resolution

Original Horizontal

Datum/Coordinate

System

Original Vertical

Coordinate System URL

NGDC

Southern

Louisiana

DEM

2010 Digital

Elevation Model 1/3 arc-second WGS 84 geographic NAVD 88 (meters)

http://wwwdev.

ngdc.noaa.gov/

mgg/inundation/

hurricane/hfip.

html

NGDC New

Orleans, LA

DEM

2009 Digital

Elevation Model 1/3 arc-second WGS 84 geographic NAVD 88 (meters)

http://www.ngdc.

noaa.gov/mgg/

inundation/

vdatum/vdatum.

html

NGDC

Biloxi, MS

DEM

2007 Digital

Elevation Model 1/3 arc-second WGS 84 geographic MHW (meters)

http://www.ngdc.

noaa.gov/mgg/

inundation/

tsunami/

NGDC

Mobile, AL

DEM

2009 Digital

Elevation Model 1/3 arc-second WGS 84 geographic NAVD 88 (meters)

http://www.ngdc.

noaa.gov/mgg/

inundation/

vdatum/vdatum.

html

NGDC

Panama City,

FL DEM

2009 Digital

Elevation Model 1/3 arc-second WGS 84 geographic NAVD 88 (meters)

http://www.ngdc.

noaa.gov/mgg/

inundation/

vdatum/vdatum.

html

11
Love, et al. 2012

Figure 10. Bathymetric/Topographic data sources used in compiling the Northern Gulf Coast DEMs

12
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

1) NGDC Southern Louisiana DEM

A 1/3 arc-second NAVD 88 DEM of Southern Louisiana [Love, et al., 2010] was downloaded from the

NGDC for use in the development of the Northern Gulf Coast DEM (Table 5 Figure 10). The DEM was developed

for the Hurricane Forecast Improvement Project (HFIP), with the purpose of developing a new methodology for

building companion structured and unstructured DEMs. The Southern Louisiana DEM was contructed to meet the

CSDL specifications, based on storm surge and sea level rise modeling requirements. The DEM was subsampled

to 1 arc-second and converted to xyz format for gridding using GMT, Python and GDAL.

2) NGDC New Orleans, LA DEM

A 1/3 arc-second NAVD 88 DEM of New Orleans, Louisiana [Love, et al., 2009] was downloaded from the

NGDC for use in the development of the Northern Gulf Coast DEM (Table 5 Figure 10). The DEM was developed

for NOAA’s CSDL through the ARRA of 2009 to evaluate the utility of VDatum, developed jointly by NOAA’s

OCS, NGS, and CO-OPS (http://vdatum.noaa.gov/). The DEM was subsampled to 1 arc-second and converted to

xyz format for gridding using GMT, Python and GDAL.

3) NGDC Biloxi, MS DEM

A 1/3 arc-second NAVD 88 DEM of Biloxi, Mississippi [Taylor, et al., 2007] was downloaded from

the NGDC for use in the development of the Northern Gulf Coast DEM (Table 5 Figure 10). The DEM was

developed for the Pacific Marine Environmental Laboratory (PMEL) NOAA Center for Tsunami Research (http:

//nctr.pmel.noaa.gov/). The DEM was subsampled to 1 arc-second and converted to xyz format for gridding using

GMT, Python and GDAL.

4) NGDC Mobile, AL DEM

A 1/3 arc-second NAVD 88 DEM of Mobile, Alabama [Amante, et al., 2009] was downloaded from the

NGDC for use in the development of the Northern Gulf Coast DEM (Table 5 Figure 10). The DEM was developed

for NOAA’s CSDL through the ARRA of 2009 to evaluate the utility of VDatum, developed jointly by NOAA’s

OCS, NGS, and CO-OPS (http://vdatum.noaa.gov/). The DEM was subsampled to 1 arc-second and converted to

xyz format for gridding using GMT, Python and GDAL.

5) NGDC Panama City, FL DEM

A 1/3 arc-second NAVD 88 DEM of Panama City, Florida [Amante, et al.,2009] was downloaded from the

NGDC for use in the development of the Northern Gulf Coast DEM (Table 5 Figure 10). The DEM was developed

for NOAA’s CSDL through the ARRA of 2009 to evaluate the utility of VDatum, developed jointly by NOAA’s

OCS, NGS, and CO-OPS (http://vdatum.noaa.gov/). The DEM was subsampled to 1 arc-second and converted to

xyz format for gridding using GMT, Python and GDAL.

13
Love, et al. 2012

3.2 Establishing Common Datums

3.2.1 Vertical datum transformations

Datasets used in the compilation and evaluation of the Northern Gulf Coast DEMs were originally referenced

to several vertical datums including MLLW, MLW, MLG and NAVD 88. All datasets were transformed to NAVD 88

using VDatum. Where no VDatum coverage existed (Figure 14) datasets were transformed to NAVD 88 using the

Northern Gulf Coast conversion grid (Section 4.3.1) which was derived from the existing VDatum project areas.

• Bathymetric Data All hydrographic surveys used in the compilation of the Northern Gulf Coast DEMs were

transformed from MLLW, MLW or MLG to NAVD 88, using VDatum.

• Topographic Data All topographic datasets used in the compilation of the Northern Gulf Coast DEMs originated in NAVD 88 vertical datum. No further vertical transformations were required for these datasets.

• Bathymetric–Topographic Data Bathymetric-topographic datasets used in the compilation of the Northern

Gulf Coast DEMs either originated in NAVD 88 vertical datum or were transformed from MHW to NAVD 88

using VDatum.

3.2.2 Horizontal datum transformations

Datasets used to build the Northern Gulf Coast DEMs were downloaded or received referenced to WGS 84

geographic, NAD 83 geographic, NAD 83 Louisiana State Plane (feet) and NAD 83 UTM Zone 16 or 15 N horizontal

datums. The relationships and transformational equations between these horizontal datums are well established. Data

were converted to a horizontal datum of NAD 83 geographic using Proj4 and VDatum.

7

3.2.3 Verifying consistency between datasets

After horizontal and vertical transformations were applied, the ascii xyz files were reviewed for consistency

between datasets. Problems and errors were identified and resolved before proceeding with subsequent gridding steps.

7Proj4 (a free standard Unix filter function which converts geographic longitude and latitude coordinates into cartesian coordinates, (λ, φ) → (x, y),

by means of a wide variety of cartographic projection functions) was used to horizontally transform datasets that originated in a State Plane datum

before vertical transformations were performed using VDatum, which did not support state plane transformations at the time of development.

14
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

4. STRUCTURED DEM DEVELOPMENT

4.1 Smoothing of bathymetric data

The NOS hydrographic survey data are generally sparse relative to the resolution of the 1 arc-second Northern

Gulf Coast DEMs. This is especially true deep for water surveys in the Gulf of Mexico and shallow water surveys

in lakes and bayous where data have point spacing up to 350 meters apart. In order to reduce the effect of artifacts

created in the DEM by the low-resolution NOS datasets, and to provide effective interpolation in the deep water and

into the coastal zone, a 1 arc-second pre-surface bathymetric grid (Figure 11) was generated using Generic Mapping

Tools (GMT)8. The coastline elevation value was set at 0 meters to ensure a bathymetric surface below zero in areas

where data are sparse or non-existent.

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

0.05 degrees (∼5%) larger than the Northern Gulf Coast gridding region. The GMT command ’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 to an ESRI Arc ASCII grid file, and clipped to the final coastline (to eliminate data interpolation into

land areas) using GDAL. The resulting surface was compared with original NOS soundings to ensure grid accuracy

(Figure 12), and then exported as an xyz file for use in the final gridding process (Table 6).

Figure 11. Pre-surface bathymetric grid of the Northern Gulf Coast

8GMT is an open source collection of ∼60 tools for manipulating geographic and Cartesian data sets (including filtering, trend fitting, gridding,

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

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

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

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

http://gmt.soest.hawaii.edu/ [Extracted from GMT web site.]

15
Love, et al. 2012

Figure 12. Histogram of the differences between the NOS hydrographic soundings and the Northern Gulf Coast bathymetric surface.

4.2 Building the NAVD 88 Structured DEM

MB-System9 was used to create the 1 arc-second Northern Gulf Coast NAVD 88 DEM. The MB-System

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

data. The data hierarchy used in the ’mbgrid’ gridding algorithm, as relative gridding weights, is listed in Table 6. The

resulting binary grid was converted to an Arc ASCII grid using the MB-System tool mbm_grd2arc to create the final 1

arc-second Northern Gulf Coast NAVD 88 DEM. Figure 13 illustrates cells in the DEM that have interpolated values

(shown as white) versus data contributing to the cell value (shown as black).

Table 6. Data hierarchy used to assign gridding weight in MB-System

Dataset Relative Gridding Weight

NGDC Northern Gulf Coast DEMs 75

NOS hydrographic surveys 75

USGS NED 60

FLDEM Franklin Co. contours 60

ENC hydrographic data 20

Pre-surfaced bathymetric grid 1

9MB-System is an open source software package for the processing and display of bathymetry and backscatter imagery data derived from multibeam,

interferometry, and sidescan sonars. The source code for MB-System is freely available (for free) by anonymous ftp (point and access through these

web pages). A complete description is provided in web pages accessed through the web site. MB-System was originally developed at the LamontDoherty Earth Observatory of Columbia University (L-DEO) and is now a collaborative effort between the Monterey Bay Aquarium Research

Institute (MBARI) and L-DEO. The National Science Foundation has provided the primary support for MB-System development since 1993.

The Packard Foundation has provided significant support through MBARI since 1998. Additional support has derived from SeaBeam Instruments

(1994–1997), NOAA (2002–2004), and others. URL: http://www.ldeo.columbia.edu/res/pi/MB-System/ [Extracted from MB-System web site.]

16
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

Figure 13. Data density of Northern Gulf Coast DEMs; Areas where source data were available are depicted in black; areas where grid interpolation

was necessary are depicted in white. Areas of sparse data density are difficult to see at the current scale.

17
Love, et al. 2012

4.3 Building the MHW Structured DEM

The MHW DEM was created by adding the ’NAVD-88-to-MHW’ conversion grid to the NAVD 88 DEM.

4.3.1 Developing the conversion grid

Using extents slightly larger (∼5%) than the Northern Gulf Coast project area, an initial xyz file was created

that contained the coordinates of the four bounding vertices and midpoint of the larger extents. The elevation value

at each of the points was set to zero. The GMT command ’surface’ applied a tension spline to interpolate cell values

making a zero-value 3 arc-second grid. This zero-grid was then converted to an intermediate xyz file using the GMT

command ’grd2xyz’. Conversion values from NAVD-88-to-MHW at each xyz point were generated using VDatum and

the null values were removed.

The median-averaged xyz file was then interpolated with the GMT command ’surface’ to create the 1 arcsecond ’NAVD-88-to-MHW’ conversion grid with the extents of the Northern Gulf Coast project area. NGDC then

used the GMT command ’surface’ to interpolate values that represented the differences between the two datums

onshore to the DEM extents (Figure 15) and offshore areas where no VDatum project areas were available (Figure

14).

Figure 14. Available VDatum Project Areas (P.A.) in the Northern Gulf Coast DEM region.

4.3.2 Assessing the accuracy of conversion grid

The ’NAVD-88-to-MHW’ conversion grid was assessed using the NOS survey data. For testing of this

methodology, the NOS hydrographic survey data were transformed from MLW and MLLW to NAVD 88 using VDatum. The resultant xyz files were filtered to remove any null values and then were merged together to form a single

xyz file of the NOS hydrographic survey data with a vertical datum of NAVD 88. A second xyz file of NOS data was

created with a vertical datum of MHW using the same method. Elevation differences between the MHW and NAVD

88 xyz files were computed.

To verify the conversion grid methodology, the difference xyz file was used to generate a histogram using

18
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

Figure 15. Elevation conversion values of ’NAVD-88-to-MHW’ conversion grid derived from VDatum. Values equal the difference between NAVD

88 and MHW.

Gnuplot10 to evaluate the performance of the 1 arc-second conversion grid by comparing ’NAVD-88-to-MHW’ conversion grid to the combined difference xyz files from the VDatum project area (Fig. 16). Errors in the vertical datum

conversion method will reside for the most part in the ’NAVD-88-to-MHW’ conversion grid, as the topographic data

are already referenced to NAVD 88. Errors in the source datasets will require rebuilding just the NAVD 88 DEM.

4.3.3 Creating the MHW Structured DEM

Once the NAVD 88 structured DEM was completed and assessed for errors, the conversion grid was added to

it using the GMT command ’grdmath’. The resulting MHW structured DEM was reviewed and assessed using RNCs,

USGS topographic maps, and ESRI World 2D imagery.

10Gnuplot is an open-source command-driven interactive function plotting program. It can be used to plot functions and data points in both two- and

three-dimensional plots in many different formats. It is designed primarily for the visual display of scientific data.

19
Love, et al. 2012

Figure 16. Histogram of the differences between the conversion grid and xyz difference files using NOS hydrographic survey data.

20
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

4.4 Quality Assessment of the Structured DEMs

4.4.1 Horizontal accuracy

The horizontal accuracy of topographic and bathymetric features in the Northern Gulf Coast DEMs are dependent upon the datasets used to determine corresponding DEM cell values and the cell size of the DEM. The

horizontal accuracy is 10 meters where topographic lidar datasets contribute to the DEM cell value. The horizontal

accuracy is 0.75 meters at 1 sigma where only bathymetric–topographic lidar-derived data contributes to the DEM cell

value. 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 sub aerial 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 the morphologic change that occurs in this dynamic region.

4.4.2 Vertical accuracy

Vertical accuracy of the Northern Gulf Coast DEMs are also highly dependent upon the source datasets

contributing to DEM cell values. Topographic lidar has an estimated RMSE of 13.9 to 20 cm. Bathymetric–topographic

lidar-derived data have a vertical accuracy of 0.20 meters at 1 sigma. 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.

4.4.3 Slope maps and 3D perspectives

GMT was used to generate a slope grid from the Northern Gulf Coast NAVD 88 DEM to allow for visual

inspection and identification of artificial slopes along boundaries between datasets (Figure 17). The DEM was transformed to UTM Zone 15 North coordinates (horizontal units in meters) in GDAL 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 QTModeler. Analysis of preliminary grids revealed suspect data

points, which were corrected before recompiling the DEM. Figure 18 shows a perspective view image of the 1 arcsecond Northern Gulf Coast NAVD 88 DEM in its final version.

4.4.4 Comparison with National Geodetic Survey geodetic monuments

The elevations of 80948 NOAA NGS geodetic monuments (Figure 19a) were extracted from online shapefiles of NGS Geodetic 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 NAVD 88 (in meters). Monument elevations were

compared with elevations of the Northern Gulf Coast NAVD 88 DEM. Differences between the DEM elevations and

the NGS geodetic monument elevations range from -109.5 to 77.5 meters, with the majority of them being within

+/-1 meter (Figure 19b). Negative values indicate that the monument elevation is less than the DEM elevation. After

examination, it was determined that those monuments with the largest deviations do not represent ground surface as

they are located on top of an observation tower, light house, at the apex of other structures, or are receded into the

ground.

4.4.5 Comparison with source data files

To ensure grid accuracy, the Northern Gulf Coast NAVD 88 DEM was compared to source data files. All

bathymetric and topographic source data were compared to the DEM using Python, GDAL and Gnuplot. Histograms

of the differences between individual datasets and the DEM are shown in Figure 20. The largest differences between

source datasets and the DEM resulted from the averaging of multiple topographic source datasets where data coverage

overlapped, particularly in regions of steep slopes.

21
Love, et al. 2012

Figure 17. Slope map of the Northern Gulf Coast NAVD 88 DEM. Flat-lying slopes are white; dark shading denotes steep slopes. The coastline is drawn in blue

22
DIGITAL

ELEVATIONMODELS OF THENORTHERNGULFCOAST

Figure 18. Perspective view from the southwest of the Northern Gulf Coast NAVD 88 DEM. Fifteen times vertical exaggeration.

23
Love, et al. 2012

(a) Locations of NGS monuments used in the evaluation of the Northern Gulf Coast DEMs.

(b) Histogram of the differences between the NGS monument elevation values and the

Northern Gulf Coast DEM

Figure 19. Comparison with NGS geodetic monuments, locations and histogram.

24
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

(a) Histogram of the differences between the FDEM lidar

dataset and the Northern Gulf Coast NAVD 88 DEM

(b) Histogram of the differences between the NED 1 DEM

dataset and the Northern Gulf Coast NAVD 88 DEM

(c) Histogram of the differences between the ENC hydrographic dataset and the Northern Gulf Coast NAVD 88

DEM

(d) Histogram of the differences between the NOS hydrographic dataset and the Northern Gulf Coast NAVD 88

DEM

Figure 20. Hisograms of the differences between individual datasets and the Northern Gulf Coast NAVD 88 DEM.

25
Love, et al. 2012

5. SUMMARY AND CONCLUSIONS

Two bathymetric–topographic digital elevation models of the Northern Gulf Coast region, with cell spacing of 1

arc-second, and vertical datums of NAVD 88 and MHW, respectively, were developed for CSDL through the ARRA

of 2009. The DEMs were developed to validate the utility of NOAA’s OCS, NGS, and CO-OPS jointly developed

VDatum tool and will be used for storm surge inundation and sea level rise modeling. The best available digital data

from U.S. federal, state and local 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, GMT, MB-System, QT Modeler, GDAL, Proj4 and Gnuplot software. VDatum was utilized throughout the

development of the Northern Gulf Coast DEMs to transform data to common vertical datums. Furthermore, NGDC

developed a conversion grid derived from the VDatum project areas that transformed the Northern Gulf Coast NAVD

88 DEM to MHW, and allowed for vertical transformation of source datasets where no VDatum coverage area existed.

Recommendations to improve the Northern Gulf Coast DEMs, based on NGDCâA ̆ Zs research and analysis, are  ́

listed below:

• Conduct topographic lidar surveys for all near-shore regions.

• Conduct NOS hydrographic surveys in hydrographic data gaps and in estuary bays and rivers.

• Conduct topographic surveys of coastal marsh-lands.

6. ACKNOWLEDGEMENTS

The creation of the Northern Gulf Coast DEMs was funded by the ARRA of 2009. The authors thank Jay Ratcliff

of the USACE for supplying otherwise unavailable bathymetric surveys. The authors also thank Cuong Hoang and

Maureen Kenny (NOAA CSDL) for providing NGDC with the NOS survey non-superceded database.

7. REFERENCES

Amante, C.J., Love, M.R., Eakins, B.W., Taylor, L.A., 2009: Digital Elevation Models of Mobile, Alabama: Procedures, Data Sources and Analysis.

Amante, C.J., Love, M.R., Eakins, B.W., Taylor, L.A., 2009: Digital Elevation Models of Panama City, Florida:

Procedures, Data Sources and Analysis.

Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix A, 2003. Federal Emergency Management Agency, Flood Hazard Mapping Program.

Love, M.R., Amante, C.J., Eakins, B.W., Taylor, L.A., 2009: Digital Elevation Models of New Orleans, Louisiana:

Procedures, Data Sources and Analysis.

Love, M.R., Amante, C.J., Eakins, B.W., Taylor, L.A., 2010: Digital Elevation Models of Southern Louisiana: Procedures, Data Sources and Analysis.

Taylor, L.A., Eakins, B.W., Carignan, K.S., Warnken, R.R., Sazonova, T., Schoolcraft, D.C., 2007: Digital Elevation

Models of Biloxi, Mississippi: Procedures, Data Sources and Analysis.

26
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

8. DATA PROCESSING SOFTWARE

ArcGIS 9.3 - developed and liscensed by ESRI, Redlands, California, http://www.esri.com

ESRI World Imagery - ESRI ArcGIS Resource Centers, http://www.esri.com

GEODAS v. 5 - Geophysical Data System, free software 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, free software 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 - free software developed and maintained by David W. Caress and Dale N. Chayes, funded by

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

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

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

GDAL v. 1.7.1 - Geographic Data Abstraction Library is a translator library maintained by Frank Warmerdam,

http://gdal.org

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

org/proj/

VDatum v. 2.3 developed and maintained by NOAAs National Geodetic Survey (NGS), Office of Coast Survey

(OCS), and Center for Operational Oceanographic Products and Services (CO-OPS), http://vdatum.noaa.gov/

27
Love, et al. 2012

APPENDIX A. NOS HYDROGRAPHIC SURVEYS

Table A-1. NOS Hydrographic datasets used in building the Northern Gulf Coast DEMs

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

Datum

H01184 1873 Undetermined 1:40,000 Undetermined

H01991 1876 Undetermined 1:4800 Undetermined

H01909 1888 Undetermined 1:5,000 Undetermined

H01910 1888 Undetermined 1:5,000 Undetermined

H01911 1888 Undetermined 1:5,000 Undetermined

H01912 1888 Undetermined 1:5,000 Undetermined

H01913 1888 Undetermined 1:5,000 Undetermined

H01914 1888 Undetermined 1:5,000 Undetermined

H01915 1888 Undetermined 1:5,000 Undetermined

H01916 1888 Undetermined 1:5,000 Undetermined

H01917 1888 Undetermined 1:5,000 Undetermined

H02072 1891 Undetermined 1:20,000 Undetermined

H02295 1897 Undetermined 1:20,000 Undetermined

H02341 1898 Undetermined 1:20,000 Undetermined

H02342 1898 Undetermined 1:20,000 Undetermined

H02380 1899 Undetermined 1:20,000 Undetermined

H02381 1899 Undetermined 1:20,000 Undetermined

H04000 1917 MLW 1:40,000 Undetermined

H04021 1917 MLW 1:40,000 Undetermined

H03961 1917 Undetermined 1:40,000 Undetermined

H04139 1919 Undetermined 1:80,000 Undetermined

H04171 1920 MLW 1:80,000 Undetermined

H04212 1921 Undetermined 1:80,000 Undetermined

H04219 1922 Undetermined 1:80,000 Undetermined

H04223 1922 Undetermined 1:80,000 Undetermined

H05024 1930 Undetermined 10,000 Undetermined

28
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

Table A-1 – Continued

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

Datum

H05033 1930 Undetermined 20,000 Undetermined

H05115 1930 Undetermined 40,000 Undetermined

H05113 1931 Undetermined 80,000 Undetermined

H05491 1933 Undetermined 20,000 Undetermined

H05667 1934 Undetermined 10,000 Undetermined

H05668 1934 Undetermined 10,000 Undetermined

H05723 1934 Undetermined 10,000 Undetermined

H05478 1934 Undetermined 20,000 Undetermined

H05479 1934 Undetermined 20,000 Undetermined

H05480 1934 Undetermined 20,000 Undetermined

H05481 1934 Undetermined 20,000 Undetermined

H05482 1934 Undetermined 20,000 Undetermined

H05490 1934 Undetermined 20,000 Undetermined

H05492 1934 Undetermined 20,000 Undetermined

H05493 1934 Undetermined 20,000 Undetermined

H05494 1934 Undetermined 20,000 Undetermined

H05495 1934 Undetermined 20,000 Undetermined

H05496 1934 Undetermined 20,000 Undetermined

H05497 1934 Undetermined 20,000 Undetermined

H05537 1934 Undetermined 20,000 Undetermined

H05539 1934 Undetermined 20,000 Undetermined

H05541 1934 Undetermined 20,000 Undetermined

H05669 1935 Undetermined 10,000 Undetermined

H05705 1935 Undetermined 10,000 Undetermined

H05706 1935 Undetermined 10,000 Undetermined

H05707 1935 Undetermined 10,000 Undetermined

H05729 1935 Undetermined 10,000 Undetermined

H05780 1935 Undetermined 10,000 Undetermined

29
Love, et al. 2012

Table A-1 – Continued

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

Datum

H05781 1935 Undetermined 10,000 Undetermined

H05782 1935 Undetermined 10,000 Undetermined

H05783 1935 Undetermined 10,000 Undetermined

H05791 1935 Undetermined 10,000 Undetermined

H05792 1935 Undetermined 10,000 Undetermined

H05793 1935 Undetermined 10,000 Undetermined

H05796 1935 Undetermined 10,000 Undetermined

H05797 1935 Undetermined 10,000 Undetermined

H05805 1935 Undetermined 10,000 Undetermined

H05806 1935 Undetermined 10,000 Undetermined

H05817 1935 Undetermined 10,000 Undetermined

H05823 1935 Undetermined 10,000 Undetermined

H05538 1935 Undetermined 20,000 Undetermined

H05730 1935 Undetermined 20,000 Undetermined

H05794 1935 Undetermined 20,000 Undetermined

H05812 1935 Undetermined 20,000 Undetermined

H05818 1935 Undetermined 20,000 Undetermined

H05822 1935 Undetermined 20,000 Undetermined

H05833 1935 Undetermined 20,000 Undetermined

H05835 1935 Undetermined 20,000 Undetermined

H05836 1935 Undetermined 20,000 Undetermined

H05869 1935 Undetermined 20,000 Undetermined

H06172 1936 Undetermined 20,000 Undetermined

H06174 1936 Undetermined 20,000 Undetermined

H06154 1936 Undetermined 40,000 Undetermined

H06155 1936 Undetermined 40,000 Undetermined

H06156 1936 Undetermined 40,000 Undetermined

H06157 1936 Undetermined 40,000 Undetermined

30
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

Table A-1 – Continued

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

Datum

H06173 1936 Undetermined 40,000 Undetermined

H06184 1936 Undetermined 80,000 Undetermined

H06185 1936 Undetermined 80,000 Undetermined

H06448 1939 Undetermined 10,000 Undetermined

H06449 1939 Undetermined 10,000 Undetermined

H06450 1939 Undetermined 10,000 Undetermined

H06451 1939 Undetermined 10,000 Undetermined

H06452 1939 Undetermined 10,000 Undetermined

H06492 1939 Undetermined 20,000 Undetermined

H06513 1939 Undetermined 20,000 Undetermined

H06633 1940 Undetermined 10,000 Undetermined

H06547 1940 Undetermined 160,000 Undetermined

H06548 1940 Undetermined 160,000 Undetermined

H06634 1940 Undetermined 20,000 Undetermined

H06635 1940 Undetermined 20,000 Undetermined

H06636 1940 Undetermined 20,000 Undetermined

H06637 1940 Undetermined 20,000 Undetermined

H06638 1940 Undetermined 20,000 Undetermined

H06551 1940 Undetermined 40,000 Undetermined

H06552 1940 Undetermined 40,000 Undetermined

H06553 1940 Undetermined 40,000 Undetermined

H06554 1940 Undetermined 40,000 Undetermined

H06555 1940 Undetermined 40,000 Undetermined

H06549 1940 Undetermined 80,000 Undetermined

H06550 1940 Undetermined 80,000 Undetermined

H06656 1940 Undetermined 80,000 Undetermined

H06685 1941 Undetermined 20,000 Undetermined

H06686 1941 Undetermined 20,000 Undetermined

31
Love, et al. 2012

Table A-1 – Continued

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

Datum

H06693 1941 Undetermined 20,000 Undetermined

H06694 1941 Undetermined 20,000 Undetermined

H06687 1941 Undetermined 40,000 Undetermined

H06688 1941 Undetermined 40,000 Undetermined

H06689 1941 Undetermined 40,000 Undetermined

H06690 1941 Undetermined 40,000 Undetermined

H06691 1941 Undetermined 80,000 Undetermined

H06692 1941 Undetermined 80,000 Undetermined

H06786 1942 Undetermined 20,000 Undetermined

H06787 1942 Undetermined 20,000 Undetermined

H06788 1942 Undetermined 20,000 Undetermined

H06784 1942 Undetermined 40,000 Undetermined

H06785 1942 Undetermined 40,000 Undetermined

H06789 1943 Undetermined 20,000 Undetermined

H07173 1947 Undetermined 10,000 Undetermined

H07603 1947 Undetermined 200,000 Undetermined

H07631 1947 Undetermined 40,000 Undetermined

H07632 1947 Undetermined 40,000 Undetermined

H07633 1947 Undetermined 40,000 Undetermined

F00077 1948 MLW 40,000 North American Datum

1927

H07723 1948 Undetermined 1:100,000 Undetermined

H07604 1948 Undetermined 200,000 Undetermined

H07679 1949 Undetermined 100,000 Undetermined

H08524 1960 Undetermined 10,000 Undetermined

H08525 1960 Undetermined 10,000 Undetermined

H08526 1960 Undetermined 10,000 Undetermined

H08560 1960 Undetermined 10,000 Undetermined

32
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

Table A-1 – Continued

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

Datum

H08561 1960 Undetermined 10,000 Undetermined

H08562 1960 Undetermined 10,000 Undetermined

H08573 1960 Undetermined 10,000 Undetermined

H08574 1960 Undetermined 10,000 Undetermined

H08575 1960 Undetermined 10,000 Undetermined

H08592 1960 Undetermined 10,000 Undetermined

H08563 1960 Undetermined 20,000 Undetermined

H08586 1961 Undetermined 10,000 Undetermined

H08587 1961 Undetermined 10,000 Undetermined

H08588 1961 Undetermined 10,000 Undetermined

H08589 1961 Undetermined 10,000 Undetermined

H08590 1961 Undetermined 10,000 Undetermined

H08591 1961 Undetermined 10,000 Undetermined

H08633 1961 Undetermined 10,000 Undetermined

H08634 1961 Undetermined 10,000 Undetermined

H08635 1961 Undetermined 10,000 Undetermined

H08636 1961 Undetermined 10,000 Undetermined

H08642 1961 Undetermined 10,000 Undetermined

H08643 1961 Undetermined 10,000 Undetermined

H08644 1961 Undetermined 10,000 Undetermined

H08645 1961 Undetermined 10,000 Undetermined

H08646 1961 Undetermined 10,000 Undetermined

H08647 1961 Undetermined 20,000 Undetermined

H08648 1961 Undetermined 20,000 Undetermined

H08584 1961 Undetermined 5,000 Undetermined

H08585 1961 Undetermined 5,000 Undetermined

H08649 1962 Undetermined 10,000 Undetermined

H08650 1962 Undetermined 10,000 Undetermined

33
Love, et al. 2012

Table A-1 – Continued

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

Datum

H08651 1962 Undetermined 10,000 Undetermined

H08652 1962 Undetermined 10,000 Undetermined

H08923 1966 MLW 10,000 North American Datum

1927

H08922 1966 MLW 10,000 Undetermined

H08925 1967 MLW 10,000 North American Datum

1927

H08924 1967 MLW 20,000 Undetermined

H08970 1968 MLW 10,000 North American Datum

1927

H08971 1968 MLW 20,000 Undetermined

H09004 1968 Undetermined 20,000 Undetermined

H09156 1970 MLW 10,000 North American Datum

1927

H09177 1970 MLW 10,000 North American Datum

1927

H09109 1970 MLW 20,000 North American Datum

1927

H09118 1970 MLW 20,000 North American Datum

1927

H09028 1970 Undetermined 20,000 Undetermined

H09199 1971 MLW 10,000 North American Datum

1927

H09262 1971 MLW 10,000 North American Datum

1927

H09263 1971 MLW 10,000 North American Datum

1927

H09200 1971 MLW 20,000 North American Datum

1927

H09261 1971 MLW 20,000 North American Datum

1927

H09279 1972 MLW 10,000 North American Datum

1927

H09347 1972 Unknown 20,000 North American Datum

1927

H09354 1973 MLW 20,000 North American Datum

1927

34
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

Table A-1 – Continued

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

Datum

H09466 1974 MLW 40,000 North American Datum

1927

H09734 1977 GCLWD 20,000 North American Datum

1927

H09735 1977 GCLWD 20000 North American Datum

1927

H09761 1978 GCLWD 20,000 North American Datum

1927

H09781 1978 GCLWD 20,000 North American Datum

1927

H09797 1978 GCLWD 20,000 North American Datum

1927

H09803 1978 GCLWD 20,000 North American Datum

1927

H09755 1978 GCLWD 20000 North American Datum

1927

H09786 1978 GCLWD 40,000 North American Datum

1927

H09804 1979 GCLWD 20,000 North American Datum

1927

H09861 1979 GCLWD 20000 North American Datum

1927

H09798 1979 GCLWD 40,000 North American Datum

1927

H09832 1979 GCLWD 50,000 North American Datum

1927

H09846 1979 MLLW 40000 North American Datum

1927

H09915 1980 GCLWD 20000 North American Datum

1927

H09883 1980 GCLWD 40000 North American Datum

1927

H09924 1980 MLLW 10000 North American Datum

1927

H09925 1980 MLLW 10000 North American Datum

1927

H09989 1981 MLLW 10,000 North American Datum

1927

H09968 1981 MLLW 10000 North American Datum

1927

35
Love, et al. 2012

Table A-1 – Continued

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

Datum

H09928 1981 MLLW 20,000 North American Datum

1927

H09943 1981 MLLW 20,000 North American Datum

1927

H09971 1981 MLLW 20,000 North American Datum

1927

H09954 1981 MLLW 40,000 North American Datum

1927

H09996 1982 MLLW 10,000 North American Datum

1927

H09995 1982 MLLW 10000 North American Datum

1927

H10005 1982 MLLW 10000 North American Datum

1927

H10069 1982 MLLW 10000 North American Datum

1927

H10041 1982 MLLW 20000 North American Datum

1927

H10001 1982 MLLW 40,000 North American Datum

1927

H10053 1982 MLLW 40000 North American Datum

1927

H10122 1983 MLLW 10,000 North American Datum

1927

H10114 1983 MLLW 20000 North American Datum

1927

H10113 1983 MLLW 40000 North American Datum

1927

H10166 1984 MLLW 10000 North American Datum

1927

H10168 1984 MLLW 10000 North American Datum

1927

D00078 1984 Undetermined 40000 Undetermined

D00065 1984 Undetermined 80000 Undetermined

H10170 1985 MLLW 10,000 North American Datum

1927

H10172 1985 MLLW 10000 North American Datum

1927

H10207 1985 MLLW 10000 North American Datum

1927

36
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

Table A-1 – Continued

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

Datum

H10179 1985 MLLW 20000 North American Datum

1927

H10208 1985 MLLW 20000 North American Datum

1927

H10180 1985 MLLW 40000 North American Datum

1927

H10206 1985 MLLW 40000 North American Datum

1927

H10209 1986 MLLW 10000 North American Datum

1927

H10210 1986 MLLW 10000 North American Datum

1927

H10235 1986 MLLW 10000 North American Datum

1927

H10226 1986 MLLW 20000 North American Datum

1927

F00288 1986 MLLW 40000 North American Datum

1927

H10236 1987 MLLW 10000 North American Datum

1927

H10237 1987 MLLW 10000 North American Datum

1927

H10259 1987 MLLW 10000 North American Datum

1927

H10260 1987 MLLW 10000 North American Datum

1927

H10262 1987 MLLW 10000 North American Datum

1927

H10247 1987 MLLW 20000 North American Datum

1927

H10261 1987 MLLW 20000 North American Datum

1927

B00136 1988 MHW 50,000 North American Datum

1983

H10266 1988 MLLW 10000 North American Datum

1927

H10267 1988 MLLW 10000 North American Datum

1927

H10292 1988 MLLW 10000 North American Datum

1983

37
Love, et al. 2012

Table A-1 – Continued

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

Datum

F00314 1988 MLLW 20000 North American Datum

1983

F00315 1988 MLLW 20000 North American Datum

1983

B00122 1988 MLLW 50,000 North American Datum

1983

B00124 1988 MLLW 50,000 North American Datum

1983

B00125 1988 MLLW 50,000 North American Datum

1983

B00130 1988 MLLW 50,000 North American Datum

1983

B00133 1988 MLLW 50,000 North American Datum

1983

B00138 1988 MLLW 50,000 North American Datum

1983

B00139 1988 MLLW 50,000 North American Datum

1983

D00100 1988 Undetermined 10000 Undetermined

D00077 1988 Undetermined 20000 Undetermined

D00079 1988 Undetermined 20000 Undetermined

H10294 1989 MLLW 10000 North American Datum

1927

F00324 1989 MLLW 20000 North American Datum

1983

F00329 1989 MLLW 20000 North American Datum

1983

F00335 1989 MLLW 20000 North American Datum

1983

B00183 1989 MLLW 50,000 North American Datum

1983

B00189 1989 MLLW 50,000 North American Datum

1983

B00190 1989 MLLW 50,000 North American Datum

1983

B00191 1989 MLLW 50,000 North American Datum

1983

B00193 1989 MLLW 50,000 North American Datum

1983

38
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

Table A-1 – Continued

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

Datum

B00194 1989 MLLW 50,000 North American Datum

1983

B00197 1989 MLLW 50,000 North American Datum

1983

B00198 1989 MLLW 50,000 North American Datum

1983

B00199 1989 MLLW 50,000 North American Datum

1983

B00258 1990 MLLW 50,000 North American Datum

1983

B00259 1990 MLLW 50,000 North American Datum

1983

H10387 1991 MLLW 10000 North American Datum

1983

H10394 1991 MLLW 10000 North American Datum

1983

H10403 1991 MLLW 10000 North American Datum

1983

H10375 1991 MLLW 20000 North American Datum

1983

H10393 1991 MLLW 20000 North American Datum

1983

B00290 1991 MLLW 50,000 North American Datum

1983

B00291 1991 MLLW 50,000 North American Datum

1983

B00294 1991 MLLW 50,000 North American Datum

1983

B00295 1991 MLLW 50,000 North American Datum

1983

F00361 1991 Undetermined 20000 Undetermined

H10383 1991 Undetermined 20000 Undetermined

H10410 1992 MLLW 10000 North American Datum

1983

H10418 1992 MLLW 10000 North American Datum

1983

H10423 1992 MLLW 10000 North American Datum

1983

H10427 1992 MLLW 10000 North American Datum

1983

39
Love, et al. 2012

Table A-1 – Continued

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

Datum

H10428 1992 MLLW 10000 North American Datum

1983

H10448 1992 MLLW 10000 North American Datum

1983

H10449 1992 MLLW 10000 North American Datum

1983

H10450 1992 MLLW 10000 North American Datum

1983

H10451 1992 MLLW 10000 North American Datum

1983

F00362 1992 Undetermined 20000 Undetermined

H10452 1993 MLLW 10000 North American Datum

1983

H10453 1993 MLLW 10000 North American Datum

1983

H10454 1993 MLLW 10000 North American Datum

1983

H10455 1993 MLLW 10000 North American Datum

1983

H10457 1993 MLLW 10000 North American Datum

1983

H10460 1993 MLLW 10000 North American Datum

1983

H10485 1993 MLLW 10000 North American Datum

1983

H10492 1993 MLLW 10000 North American Datum

1983

H10497 1993 MLLW 10000 North American Datum

1983

H10521 1993 MLLW 10000 North American Datum

1983

H10522 1993 MLLW 10000 North American Datum

1983

F00356 1993 Undetermined 10000 Undetermined

F00384 1993 Undetermined 10000 Undetermined

F00390 1993 Undetermined 10000 Undetermined

F00393 1993 Undetermined 10000 Undetermined

H10523 1994 MLLW 10000 North American Datum

1983

40
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

Table A-1 – Continued

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

Datum

H10525 1994 MLLW 10000 North American Datum

1983

H10526 1994 MLLW 10000 North American Datum

1983

H10527 1994 MLLW 10000 North American Datum

1983

H10528 1994 MLLW 10000 North American Datum

1983

F00397 1994 Undetermined 10000 Undetermined

F00398 1994 Undetermined 10000 Undetermined

F00401 1994 Undetermined 10000 Undetermined

F00476 2001 LWRP 1993 10,000 North American Datum

1983

H11082 2002 MLLW 10,000 North American Datum

1983

H11179 2002 MLLW 20,000 North American Datum

1983

H11228 2003 MLLW 10,000 North American Datum

1983

41
Love, et al. 2012

APPENDIX B. ELECTRONIC NAVIGATIONAL CHARTS

Table B-2. ENC datasets used in building the Northern Gulf Coast DEMs

Chart Title Edition Edition Date Scale

US4FL69M Apalachee Bay 6.0 2010-09-01 1:80000

US4FL68M Apalachicola Bay to Cape San Blas 4.1 2006-11-28 1:80000

US3GC04M Approaches to Mississippi River 43.0 2010-11-26 1:250000

US5LA24M Baptiste Collette Bayou to Mississippi River Gulf Outlet;Baptiste

Collette Bayou Extension 34.0 2010-07-29 1:40000

US4LA32M Barataria Bay and approaches 28.0 2010-12-02 1:80000

US3GC05M Cape St. George to Mississippi Passes 32.2 2010-05-17 1:456394

US4LA34M Chandeleur and Breton Sounds 22.1 2010-07-28 1:80000

US4FL74M Choctawhatchee Bay 4.1 2010-05-26 1:80000

US5FL64M Intracoastal Waterway Apalachicola Bay to Lake Wimico 8.1 2010-05-20 1:40000

US5FL65M Intracoastal Waterway Carrabelle to Apalachicola Bay;Carrabelle

River 15.0 2010-06-15 1:40000

US5MS11M Intracoastal Waterway Dog Keys Pass to Waveland 39.0 2010-11-22 1:40000

US5FL63M Intracoastal Waterway Lake Wimico to East Bay 12.0 2010-06-23 1:40000

US5LA36M Intracoastal Waterway Waveland to Catahoula Bay 18.0 2010-11-23 1:40000

US5FL62M Intracoastal Waterway West Bay to Santa Rosa Sound 18.0 2010-11-24 1:40000

US4LA25M Isles Dernieres to Point au Fer 11.0 2010-06-21 1:80000

US4MS10M Lake Borgne and approaches Cat Island to Point aux Herbes 11.1 2010-06-22 1:80000

US4LA39M Lakes Pontchartrain and Maurepas 12.0 2010-05-06 1:80000

US5LA41M Loop Deepwater Port Louisiana Offshore Oil Port 11.0 2010-11-04 1:50000

US4LA30M Mississippi River Delta;Southwest Pass;South Pass;Head of Passes 19.1 2010-06-23 1:80000

US4LA33M Mississippi River Delta;Southwest Pass;South Pass;Head of Passes 21.1 2010-09-07 1:80000

US5LA51M Mississippi River-New Orleans to Baton Rouge 24.1 2010-07-16 1:40000

US3GC03M Mississippi River to Galveston 37.0 2010-11-29 1:458596

US4LA35M Mississippi River-Venice to New Orleans 33.1 2010-11-18 1:80000

US5LA37M New Orleans Harbor Chalmette Slip to Southport 18.1 2010-09-15 1:15000

US5MS22M Pascagoula Harbor 23.1 2010-10-05 1:20000

US5FL72M Pensacola Bay 19.1 2010-05-10 1:30000

42
DIGITAL ELEVATION MODELS OF THE NORTHERN GULF COAST

Table B-2 – Continued

Chart Title Edition Edition Date Scale

US4FL71M Pensacola Bay and approaches 7.2 2010-04-05 1:80000

US5FL73M Pensacola Bay Entrance 9.0 2010-05-14 1:10000

US5LA26M Port Fourchon and Approaches 17.5 2010-06-22 1:20000

US5FL67M St. Andrew Bay - Bear Point to Sulpher Point 9.0 2010-07-06 1:5000

US4FL60M St Joseph and St Andrew Bays 8.0 2010-07-06 1:80000

US3GC06M Tampa Bay to Cape San Blas 13.1 2010-05-25 1:456394

US4LA29M Timbalier and Terrebonne Bays 11.1 2009-10-22 1:80000

US4LA31M Timbalier and Terrebonne Bays 23.0 2010-11-09 1:80000

43
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