GEODETIC PROGRAMS NEEDS OF 

LOUISIANA AND WISCONSIN

Report to Congress

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Ocean Service

National Geodetic Survey

August 2001
Donald L. Evans

Secretary

U.S. DEPARTMENT OF COMMERCE

Scott B. Gudes

Acting Under Secretary of Commerce for Oceans and Atmosphere

and Administrator of 

National Oceanic and Atmospheric Administration

Margaret A. Davidson

Acting Assistant Administrator for Ocean Services and Coastal Zone Management

National Ocean Service

Charles W. Challstrom

Director

National Geodetic Survey

August 2001
i

TABLE OF CONTENTS

TABLE OF CONTENTS.................. i

EXECUTIVE SUMMARY . . . . . . . . . . . . . . . . . ii

GEODETIC PROGRAM NEEDS OF LOUISIANA AND WISCONSIN . . 1

REQUIREMENT FOR THE REPORT................1

INTRODUCTION.......................1

LOUISIANA ........................6

Background .....................6

Needs........................8

Potential Benefits . . . . . . . . . . . . . . . . 11

Recommendations . . . . . . . . . . . . . . . . . . 14

WISCONSIN . . . . . . . . . . . . . . . . . . . . . . . 17

Background . . . . . . . . . . . . . . . . . . . . 17

Needs . . . . . . . . . . . . . . . . . . . . . . . 19

Potential Benefits . . . . . . . . . . . . . . . . 20

Recommendations . . . . . . . . . . . . . . . . . . 24

GLOSSARY OF TERMS AND ACRONYMS . . . . . . . . . . 25
1 U.S. Department of Commerce, June 1998, National Height

Modernization Study, Report to Congress.

ii

EXECUTIVE SUMMARY

DIRECTION FROM CONGRESS

This document was prepared in response to the direction contained

in House Report 107-139 (to accompany H.R. 2500 - Departments of

Commerce, Justice, and State, the Judiciary, and Related Agencies

Appropriations Bill, Fiscal Year 2002) that the National Oceanic

and Atmospheric Administration (NOAA) “... is directed to work with

the states of Louisiana and Wisconsin to assess their requirements

for similar [NOAA Geodesy] programs and report back to the

Committee by September 15, 2001.” This report assesses the

requirements and potential benefits of Louisiana and Wisconsin

participating in the National Height Modernization System and

geodetic spatial reference programs.

OVERVIEW

Height Modernization Study to Height Modernization System

Height modernization is an effort, led by the National Geodetic

Survey (NGS), to enhance the vertical component of the National

Spatial Reference System (NSRS). NSRS is a consistent national

reference framework that specifies latitude, longitude, height

(elevation), scale, gravity, and orientation throughout the United

States, as well as how these values change with time. NSRS

provides accurate knowledge of the size, shape, and position of our

environment, as seen daily in the construction and safety of roads

and buildings, the transportation of goods and people by car, ship

or plane, as well as in the monitoring and protecting of our

environment. Height modernization includes a series of activities

designed to advance and promote the determination of high accuracy

elevations through the use of Global Positioning System (GPS)

surveying, rather than by classical line-of-sight leveling.

In 1998, the United States Congress directed NGS, an office within

the National Ocean Service of NOAA, to conduct a National Height

Modernization Study1 to determine the effectiveness of height

modernization in California and North Carolina. Major findings of

the study concluded that the height modernization needs that could

benefit all states are:
2

Louisiana Coastal Wetlands Conservation and Restoration

Task Force and Wetlands Conservation and Restoration Authority,

1998, Coast 2050: Toward a Sustainable Coastal Louisiana,

Executive Summary, Louisiana Department of Natural Resources.

iii

 A reliable, cost-effective, standardized, legally established

national vertical reference datum (i.e., North American

Vertical Datum of 1988 (NAVD 88)) and the infrastructure

(i.e., NSRS) through which to access and utilize it.

 The capability to easily interrelate the many vertical datums

currently in existence, but particularly with respect to a

standardized national vertical reference datum (coordinate

system).

 National technical standards and guidelines for using GPS to

determine heights.

The study addressed the national need for and benefits to be

derived from enhancing the vertical component of NSRS, while

focusing specifically on the states of California and North

Carolina. In Fiscal Year (FY) 2000, NGS received funding “for

initial planning of the National Height Modernization System

Demonstration, based on the recommendations contained in the

National Height Modernization Study, in California and North

Carolina.” NGS received additional funding in FY 2001 in support

of height modernization activities in California and North

Carolina. In California, the California Reference Spatial Center

(CSRC) was created. The CSRC offers a state-of-the-art position

and height system to aid public health and safety, preservation of

valuable resources, and improved business productivity. In North

Carolina, four urban areas will soon receive height modernization

surveys, conducted through contracts with the private sector, that

will modernize their transportation, land survey, and emergency

response systems. This funding has led to the implementation of

the National Height Modernization Study and the development of a

height modernization system in these states.

Assessment of Louisiana and Wisconsin

Rapid land loss and continuous elevation (height) changes in

Louisiana require a well-managed and monitored federal/state

geodetic control network to protect the environment, ensure safety

of its citizens, and enhance prosperity within the state.

Currently, 25 to 35 square miles of wetland per year are lost in

Louisiana due to ground subsidence (sinking of the land) and

coastal erosion.2 Cities and cultures are at risk of losing their
iv

land and having to relocate. Flooding and sea level rise threaten

the coastal region, most of which is only three feet above sea

level. Flood plain models and evacuation plans, developed using

outdated elevations, put the citizens of the low-lying areas at

great risk during heavy rains. The current available geodetic

control does not support the state’s needs to evaluate and manage

the changes in its environment and the impact on its economy and

ecosystem. Problems with historic surveys, land movement, and sea

level rise have made the current vertical geodetic control in

Louisiana obsolete, inaccurate, and unable to ensure safety.

In Wisconsin, the existing federal/state geodetic control network

simply does not support today’s design and construction projects.

Land in Wisconsin is susceptible to frost heave (uplifting of land)

and post-glacial rebound (rising of the Earth’s surface). As the

land moves, often the survey monuments move, making the previously

determined height information for the points inaccurate.

Additionally, in most parts of the state, 50 percent or more of all

bench marks have been destroyed due to construction and land

development activities. The critical nature of the shortfall of

accurate geodetic control, especially vertical control, prompted

the Wisconsin Land Information Board to establish a State Elevation

Data Task Force to assess the needs and uses for vertical control

and directly address the deficiencies. National, state, and local

agencies, as well as the private sector, need consistent and

accurate geodetic control for use in highway and land development,

monitoring and modeling of shoreline and flood plains, and safe and

economical transportation of goods.

Process of Assessment

This report identifies and documents the user requirements in

Louisiana and Wisconsin for height information, including those

requirements utilizing both horizontal and vertical data. To

identify and document this information, a two-step process was

followed. First, the NGS state advisor and NOAA program

coordinator in Louisiana and the NGS state advisor in Wisconsin

contacted the users within their state and documented their input.

Next, NGS conducted user forums on August 8 in Madison, Wisconsin,

and on August 13 in Baton Rouge, Louisiana, to obtain further

insights and recommendations from state and local governments, the

private sector, and the academic community. Due to the short time

frame for completing the report, NGS believes Louisiana and

Wisconsin are in general agreement with our assessments, however,

the states did not have the opportunity to review and comment on

the report.
v

FINDINGS

Based on the above information which was analyzed by NGS, it has

been determined that participation by Louisiana and Wisconsin in

the National Height Modernization System could result in:

 improved disaster preparedness;

 accurate digital elevation models, enabling better flood plain

analysis and determination of flood plain needs;

 improved coastal and harbor navigation, enabling safer and

more cost-effective shipment of goods;

 improved aircraft navigational aids, and safer approach and

landing procedures;

 accurate determination of coastal erosion rates and flood

plain boundaries;

 advanced surface transportation control and monitoring;

 improved land and marine geographic information systems (GIS)

and assessment of environmental effects on regions influenced

by water level changes;

 enhanced agricultural practices resulting in reduced run-off

water pollution;

 more efficient fish farming, including crawfish farming;

 infrastructure monitoring of subsidence and erosion;

 better management of natural resources through the use of

reliable GIS;

 improved understanding of tectonic movement; and

 significant time and cost savings in field surveying.

Both Louisiana and Wisconsin require improved vertical geodetic

control that would make possible the applications and benefits

listed above. They each have unique geophysical situations that

represent problems specific to their regions that would be improved

through participation in the National Height Modernization System.

RECOMMENDATIONS

The report clearly identified the need for height modernization in

Louisiana and Wisconsin. Based on our assessment of their needs,

NGS provides the following recommendations:

Louisiana

1. Perform additional GPS measurements and leveling on bench

marks to establish the basic framework of survey points needed

to support height modernization in Louisiana as recommended in

the 1998 National Height Modernization Study. The framework,

designed specifically to meet Louisiana’s needs, would be

funded through outside sources and grants and would provide
vi

accurate, reliable, and consistent height information

referenced to NAVD 88 to be included in NSRS.

2. Expand the current network of CORS and explore the use of

additional height monitoring stations (i.e, Port-A-Measures

(PAMs) and extensometers) in Louisiana. The combination of

CORS throughout the state and mobile and stationary height

monitoring stations concentrated in subsidence areas together

provide an accurate statewide height monitoring system

referenced to the highly accurate National CORS network.

3. Establish a Louisiana Spatial Reference Center (LASRC). Like

California, Louisiana does not have a state agency

coordinating efforts to improve the geodetic reference frame

and requires a Spatial Reference Center to work in conjunction

with NGS to support height modernization within the state.

Wisconsin

1. Accelerate the Wisconsin Height Modernization Program (WI-HMP)

from ten to five years. Analyze data collected in the early

phases of the WI-HMP to determine possible modifications to

field procedures and the design of the program. Specifically,

assess the amount of leveling to be completed and the current

specifications and guidelines of the field observations to

ensure accurate, yet economic, development of height

modernization.

2. Promote Wisconsin as a role model and trainer in height

modernization. Since Wisconsin’s height modernization effort

is already underway, the state would be in a position to

advise neighboring states in the development and uses of

height modernization. Transfer of technology through NGS with

Wisconsin as a regional leader could help address the entire

region’s economic and environmental issues.

3. Investigate opportunities for additional funding for the

height modernization in Wisconsin. Additional resources would

result in more outsourcing opportunities, as well as

technology transfer, to private surveyors.
1

GEODETIC PROGRAM NEEDS OF

LOUISIANA AND WISCONSIN

REQUIREMENT FOR THE REPORT

This report was prepared in response to the direction contained in

House Report 107-139, to accompany H.R. 2500, Departments of

Commerce, Justice, and State, the Judiciary, and Related Agencies

Appropriations Bill for Fiscal Year 2002, that the National Oceanic

and Atmospheric Administration (NOAA) “... is directed to work with

the states of Louisiana and Wisconsin to assess their requirements

for similar [NOAA Geodesy] programs and report back to the

Committee by September 15, 2001.” This report assesses the

requirements and potential benefits of Louisiana and Wisconsin

participating in the National Height Modernization System and

geodetic spatial reference programs.

INTRODUCTION

The National Geodetic Survey (NGS), an office within the National

Ocean Service of NOAA, is responsible for managing the National

Spatial Reference System (NSRS), a consistent national reference

framework that specifies latitude, longitude, height, scale,

gravity, and orientation throughout the United States, as well as

how these values change with time. NSRS provides accurate

knowledge of the size, shape, and position of our environment, as

seen daily in the construction and safety of roads and buildings,

the transportation of goods and people by car, ship or plane, as

well as in the monitoring and protecting of our environment.

Prior to 1983, NGS relied on classical line-of-sight survey

measurements to establish the national reference framework.

Full-scale development of the Global Positioning System (GPS) which

began with the launching of four satellites in 1979, enabled

positioning without the need to see between the points being

surveyed. Today, GPS is a constellation of 24 satellites that

transmit signals to GPS receivers all over the world. Using GPS,

a survey that once took days to complete now can be done in a few

hours at a much lower cost. Modern technology and “real-time”

positioning techniques are continuously being developed for modern

day challenges and applications.

NGS, through the use of GPS, has completed the major portion of the

horizontal (latitude/longitude) component of NSRS. The vertical
2

component of NSRS still requires better accuracy and modernization

through the use of GPS technology.

Height modernization is an effort, led by NGS, to enhance the

vertical component of NSRS. Height modernization includes a series

of activities designed to advance and promote the precise

determination of heights (elevations) of the land through the use

of GPS surveying. These activities include:

 research and development activities seeking to improve the

determination of heights (elevations) by GPS surveys;

 improvements in the accuracy of geoid heights [Geoid models

are derived from measurements of the Earth’s gravity field and

are important in translating GPS heights to orthometric

heights (heights above mean sea level)];

 the development of technical standards and guidelines for

using GPS to determine heights;

 technical advice, aid with planning GPS height surveys,

workshops, and other training forums to educate the surveying

community; and

 funds provided by Congress for grants to appropriate partners

that wish to implement height modernization in their

jurisdictions.

In 1998, the United States Congress directed NGS, an office within

the National Ocean Service to conduct a National Height

Modernization Study to determine the effectiveness of height

modernization in California and North Carolina. Major findings of

the study concluded that the height modernization needs that could

benefit all states are:

 A reliable, cost-effective, standardized, legally established

national vertical reference datum (i.e., North American

Vertical Datum of 1988 (NAVD 88)) and the infrastructure

(i.e., NSRS) through which to access and utilize it.

 The capability to easily interrelate the many vertical datums

currently in existence, but particularly with respect to a

standardized national vertical reference datum (coordinate

system).

 National technical standards and guidelines for using GPS to

determine heights.

The study addressed the national need for and benefits to be

derived from enhancing the vertical component of NSRS, while

focusing specifically on the states of California and North

Carolina. In Fiscal Year (FY) 2000, NGS received funding “for
3

initial planning of the National Height Modernization System

Demonstration, based on the recommendations contained in the

National Height Modernization Study (NHMS), in California and North

Carolina.” NGS received additional funding in FY 2001 in support

of height modernization activities in California and North

Carolina. This funding has led to the implementation of the

National Height Modernization Study and the development of a height

modernization system in these states.

In California, the California Reference Spatial Center (CSRC) was

created. The CSRC offers a state-of-the-art position and height

system to aid public health and safety, preservation of valuable

resources, and improved business productivity. The CSRC has

established a Coordinating Council, adopted a constitution and

bylaws, and currently is developing a master plan to design and

document the proposed development of the California Spatial

Reference System geodetic control network. Current projects of the

CSRC include:

 development of a full-service data portal for Continuously

Operating Reference Station (CORS) data;

 provision of NAVD 88 heights for all California CORS;

 addition of a real-time GPS infrastructure to the existing San

Francisco Bay Height Modernization demonstration project

network; and

 exploration of the use of Interferometric Synthetic Aperture

Radar for monitoring land subsidence (sinking of land).

In North Carolina, four urban areas will soon receive height

modernization surveys, conducted through contracts with the private

sector, that will modernize their transportation, land survey, and

emergency response systems. Contractor selection is currently

underway. In addition, the initial groundwork for the height

modernization surveys is complete with the incorporation of four

additional CORS into the National CORS system and the conclusion of

the field observations for the Federal Base Network

(FBN)/Cooperative Base Network (CBN) survey in North Carolina.

This report focuses on the states of Louisiana and Wisconsin and

their requirements for similar programs to advance and promote the

enhancement of NSRS, focusing on the vertical component, through

the use of GPS technology.

Geodetic control is a highly accurate, consistent, and reliable set

of information about the locations (latitude/longitude), heights

(relative to a common point), and characteristics of points

(stations) within an area. NSRS is the Nation’s geodetic control

framework. It is this geodetic control (precisely determined
4

positions) that serves as the basis for all other mapping,

construction, transportation, agricultural, and public safety

industries. Without geodetic control, correct locations,

distances, and directions between places are impossible.

Ground subsidence and the resulting loss of land are critical

issues in Louisiana and other states along the Gulf of Mexico.

Subsidence, the sinking of land primarily caused by the withdrawal

of groundwater from below the Earth’s surface, can fracture roads

and building foundations and can burst water, sewer, and gas lines.

It is of particular concern to coastal areas where sea level rise

is a real threat. Without accurate monitoring of subsidence, it is

impossible to accurately gauge sea level rise and its potential

impacts. Establishing a modernized NSRS in Louisiana would assist

in coastal restoration, transportation and public safety, not just

in Louisiana, but for similar actions in other Gulf Coast states.

Wisconsin and states in the Great Lakes region have vertical

problems associated with frost heave, post-glacial rebound, and

other unique geologic features. Wisconsin is taking the lead in

addressing these problems resulting from vertical movement, having

already initiated a statewide Height Modernization Program to

strengthen its geodetic control system.

Louisiana and Wisconsin are focusing on the 1998 National Height

Modernization Study and use of GPS technology to establish, monitor

and develop a highly accurate, vertical federal/state geodetic

control network to enhance their economies, ensure safety of life

and property, and protect their unique environments.

This report identifies and documents the user requirements in

Louisiana and Wisconsin for height information, including those

requirements utilizing both horizontal and vertical data. To

identify and document this information, a two-step process was

followed. First, the NGS state advisor and NOAA program

coordinator in Louisiana and the NGS state advisor in Wisconsin

contacted the users within their state and documented their input.

Next, NGS conducted user forums on August 8 in Madison, Wisconsin,

and on August 13 in Baton Rouge, Louisiana, to obtain further

insights and recommendations from state and local governments, the

private sector, and the academic community. Due to the short time

frame for completing the report, NGS believes Louisiana and

Wisconsin are in general agreement with our assessments, however,

the states did not have the opportunity to review and comment on

the report.

Participants in the user forum held in Madison, Wisconsin, on

August 8, included representatives from: Department of
5

Administration (Office of Land Information Services); Wisconsin

Department of Natural Resources; Wisconsin Department of

Transportation; University of Wisconsin; and the Minnesota

Department of Transportation. Participants in the user forum held

in Baton Rouge, Louisiana, on August 13, included representatives

from: United States Army Corps of Engineers (USACE); Louisiana

Department of Transportation; Louisiana Department of Natural

Resources; Louisiana Professional Engineer and Professional Land

Surveyor Licensing Board; Department of Public Works for Baton

Rouge; Amite River Basin Commission; Mid-Continent Oil and Gas

Association; Louisiana State University (LSU); University of

Louisiana at Lafayette (ULL); Baffle and Baffle Consultants; C.L.

Jack Stelly and Associates, Inc.; Meyer, Meyer, LaCroix & Hixson;

3001, Inc.; T. Baker Smith, Inc.; Morris P. Hebert, Inc.; and

N.E.I.

Based on the above information which was analyzed by NGS, it has

been determined that participation by Louisiana and Wisconsin in

the National Height Modernization System could result in:

 improved disaster preparedness;

 accurate digital elevation models (DEM), enabling better flood

plain analysis and determination of flood plain needs;

 improved coastal and harbor navigation, enabling safer and

more cost-effective shipment of goods;

 improved aircraft navigational aids, and safer approach and

landing procedures;

 accurate determination of coastal erosion rates and flood

plain boundaries;

 advanced surface transportation control and monitoring;

 improved land and marine geographic information systems (GIS)

and assessment of environmental effects on regions influenced

by water level changes;

 enhanced agricultural practices resulting in reduced run-off

water pollution;

 more efficient fish farming, including crawfish farming;

 infrastructure monitoring of subsidence and erosion;

 better management of natural resources through the use of

reliable GIS;

 improved understanding of tectonic movement; and

 significant time and cost savings in field surveying.

Both Louisiana and Wisconsin require improved vertical geodetic

control (height or elevation reference) that would make possible

the applications and benefits listed above. Each state has unique

geophysical situations that represent problems specific to its

region that would be improved through participation in the National

Height Modernization System.
6

1993 2020

LOUISIANA

Background

Louisiana’s land is moving. Subsidence, the sinking of the land,

is occurring at a rate of up to one inch every three years in some

areas of the state. Most of the vertical elevations (heights) used

by surveyors and engineers have not been calibrated, or checked,

since 1988 and may currently be in error of one foot or more. The

state’s southern region, affected over the years by the changing

courses of the Mississippi River, currently is undergoing the

largest loss of land in the nation because of subsidence and

erosion, especially in the New Orleans area. Currently, 25 to 35

square miles of marsh are lost each year. While many projects

exist to examine, monitor, prevent, and restore land that is lost

due to settling, the key element to understanding the true

relationship of the ongoing processes is a common, accurate

federal/state network of elevations. This can be done through

highly accurate GPS technology. The next generation of information

based on this technology is needed to better guide the massive

public investments that are foreseeable in upcoming decades in the

areas of coastal restoration, transportation infrastructure, and

public safety.

The state of Louisiana is in need of a statewide, reliable,

vertical federal/state geodetic control network. Historic survey

measurements, made by pre-GPS, classical line-of-sight leveling

techniques, show that existing bench marks (vertical geodetic

control marks, consisting of metal disks or rods that monument

Dark areas indicate wetland loss - past and near future.
7

NAVD 88 control in Louisiana

points on land) throughout the southern portion of the state have

undergone dramatic changes in elevation, making existing height

information unusable. Quality survey work with reliable accuracy

is a major challenge for surveyors in the southern part of the

state. In addition, the central portion of the state has very few

known elevations based on NAVD 88 (see figure below). [NAVD 88 is

the latest vertical coordinate system for consistently defining

heights and is similar to defining an elevation relative to mean

sea level.] Problems with adjustments and lack of vertical

geodetic control have kept the data from being loaded into the NSRS

data base. [Adjustments “change” or “fit” the survey data to

improve the final results of the survey.] The earliest estimates

of having the Louisiana leveling data readjusted is three to five

years from now.
8

Another unique problem for Louisiana due to its subsidence and poor

historical data, is the use of several vertical datums (coordinate

systems) within the state. In areas of severe subsidence, such as

the New Orleans area, several adjustments of survey monuments have

been performed to update heights (elevations) for a particular

year. Often these adjustments rely on the elevation of only one

station, rather than on a network of stations. If the elevation on

the one station is in error, the error will affect all the stations

being adjusted resulting in inaccurate elevations on several survey

monuments.

Needs

Examples of specific uses of height modernization identified by

Louisiana are indicated in the following text boxes, according to

the general need they describe. Based on the information obtained

from the state, the major needs (and supporting information)

identified are:

1. A reliable, cost-effective, standardized, legally established

national vertical reference datum (i.e., NAVD 88) and the

infrastructure (NSRS) through which to access and use it.

A standard, reliable vertical federal/state geodetic

control network does not exist in Louisiana. An

example of this is in the area near New Iberia. The

Port of Iberia recently contacted NGS asking for

technical services and support to establish vertical

control along the coast and the Port of Iberia access

routes. The Port of Iberia, which recently underwent

an expansion, serves as a major hub for the

construction, oil and gas industries, coastal

exploration and production activities. Future studies

are underway to deepen access channels to the port to

support an increase in shipping and marine operations.

Accurate vertical control would enable precise

positioning of the dredges as well as efficient use of

the dredged material. The Port of Iberia, as well as

other ports in Louisiana, needs vertical control

established to efficiently modernize access to its

facilities.

Port of Iberia
3

Chartuk, Robert, July 2001, “Tropical Storm Allison is

Nation’s Costliest Ever,” NOAA Report, Volume IX, No. 7, p. 2.

9

3

2. The capability to easily interrelate the many vertical datums

currently in existence, but particularly with respect to a

standardized national vertical reference datum (i.e.,

NAVD 88).

Elevations used in current evacuation plans are based

on unreliable vertical control. Louisiana is impacted

by more flooding and storm-induced damage to

communities and housing than any other state. In June

2001, Tropical Storm Allison hit Louisiana. “A state

of emergency was declared in 25 parishes as a week’s

worth of rain generated more than two feet of water.

Freshwater submerged U.S. Highway 90 [the primary

evacuation route in southern Louisiana] for over 12

hours.”3 About 90 percent of the coast of Louisiana is

less than three feet above sea level. Because of the

inaccuracies of surveys and models, the “true” heights

in this region are only known to within a foot.

Inaccurate heights lead to inaccurate flood plain

models and unreliable evacuation plans. The state

needs an established, consistent vertical control

system to accurately assess flooding and its threat to

coastal populations.

Development of evacuation plans

USACE stream gauge data is often erroneous, citing

that streams run north when actually they are running

south. Gauge data and datums need to be referenced to

NAVD 88. Tide and water level gauges managed by USACE

are in the process of being switched over to NAVD 88.

Gauge data

Exposed pipelines and capped wellheads pose a hazard

for navigation and the environment. To prevent

disasters such as pipeline bursts and marine

accidents, accurate positioning and identification of

pipes and wellheads in coastal waters, especially in

areas of subsidence and coastal erosion, are needed.

Pipeline and wellhead mapping
4

Rogers, Al, July 27, 2001, “Dead Zone Now Called Largest

Ever,” RodnReel.com featured article.

10

4

In Louisiana, an established vertical federal/state

geodetic control network that relates to various

industries is needed to promote business and reduce

environmental hazards.

Gulf coast fishery harvests (principally Louisiana)

provide about 40 percent of the nation’s annual

seafood supply in tonnage and value. Forty percent of

all coastal wetlands in the country are found in

Louisiana. Extensive hypoxia (low oxygen) events,

referred to as the “Dead Zone,” have very large

impacts on the state and the fisheries in the Gulf of

Mexico.

This “Dead Zone” off the Louisiana coast covers an

estimated 8,000 square mile area and is being called

the largest ever hypoxic area on record. Heavy rains

from Tropical Storm Allison fueled this lifeless

moving area in the Gulf of Mexico as storm run-off

along the Mississippi River carried nutrients down

river into the Gulf of Mexico. The most prevalent

run-off nutrients include fertilizer from farms and

industrial and urban wastes from the 32 states in the

river’s watershed.

A consistent vertical control network is needed to

allow the agricultural industry to better manage the

fertilizers used on fields and to allow better

monitoring and assessment of run-off and its affect on

the wetlands and fishing industry.

Agriculture and the watershed4
5

Center for GeoInformatics, Louisiana State University,

“Establishment of subsidence rates, net surface changes, and

relative sea-level rise rates between 2001 and 2006, Barataria

Hydrologic Basin,” Draft proposal.

11

5

3. National technical standards and guidelines for using GPS to

determine heights.

Potential Benefits

The benefits of height modernization to the state of Louisiana,

categorized by area of industry and described with examples in text

boxes, include:

The National Geodetic Survey is working with the state

and LSU to create a comprehensive monitoring of

processes in the Barataria Hydrologic Basin, combining

the need for height modernization with the monitoring

of coastal subsidence and sea level rise.

The Barataria basin is currently losing approximately

12 square miles of wetlands annually, making it among

the most rapidly disappearing estuaries on Earth.

Restoration, monitoring, and analysis projects such as

a coast-wide network of monitoring stations,

monitoring stations for the Davis Pond diversion

project, and the development of a comprehensive

hydrodynamic model will soon be in place. These

studies will document the dynamics of vegetative

communities, fish and wildlife assemblages,

bathymetry, and comprehensive hydrology of the basin.

Collectively, they will bridge the gap from a

project-level understanding to a more systems-level

understanding, strengthening the ability to forecast

future scenarios and allowing for better planning

strategies.

A methodology will also be developed in conjunction

with Louisiana Department of Natural Resources

personnel that will allow for reproducible

measurements of marsh heights during the duration of

the project. Real-time kinematic (RTK) GPS surveying

methods will be used to measure marsh heights at the

centimeter level.

Barataria Hydrologic Basin5
12

Safety/Flooding

 Improved emergency response routes:

S improve time models and routes for evacuation;

S decrease number of people stranded; and

S improve models for river flood stage predictions as well

as measurements.

 More accurate models of storm surges, coastal erosion, and

trajectories of oil and chemical spills that enable better

response to these hazards.

 Accurate digital elevation models, enabling better flood plain

analysis and determination of flood insurance needs.

 Improved flood control and the cost/benefit ratio for USACE

projects, including levee and subsidence projects and

development of hurricane protection systems.

Navigation/Ports

 Improved coastal and harbor navigation, enabling safer and

more cost-effective shipment of goods.

 Precise positioning of dredges and dredge materials.

Height modernization would provide accurate,

standardized, vertical geodetic control for the flood

management program of Amite River Basin Commission.

Additionally, it would improve the flood plain models

used by the Federal Emergency Management Agency.

Flood plain management

Critical care, special needs patients are at heightened

risk during large evacuations, due to the potential for

long travel times with limited or no access to medical

facilities. A study sponsored by Jefferson Parish and

conducted by the LSU Hurricane Center is underway to

assess the capacity of midrise hospital buildings in

the New Orleans area to be used for special needs

shelters. Storm surge flood modeling, building systems

assessments, and future modifications to hospital

utilities and infrastructure are highly dependent on

accurate elevation data.

Hurricane sheltering in hospitals
13

 Determination of the “true” rate of sea level rise aside from

the vertical subsidence along the coast.

Agriculture/Aquaculture

 Real-time positioning of farm equipment and reduction of

production costs.

 More efficient fish farming, including crawfish farming.

 Better management of natural resources through the use of

reliable GIS.

 Decreased run-off of contaminants as a result of controlled

applications of water, fertilizers, and pesticides in

precision farming.

Scientific

 Improved understanding of tectonic movement.

 Improved modeling of the geoid (equipotential surface of the

Earth’s gravity field which best fits mean sea level).

Land Survey

 More accurate horizontal and vertical geodetic control for

public and private sector users.

 Ability to achieve greater accuracy in parcel mapping efforts.

 Remote sensing and shoreline mapping support.

In addition to mapping and monitoring the wetland,

height modernization will contribute to the reduction

of fertilizers and pesticides introduced into the

coastal wetland ecosystem through the use of precision

farming. In precision farming, computers mounted in

farm equipment are guided by GPS and regulate the use

of water, seeds, fertilizers, and pesticides precisely

to their fields to within a foot, thus decreasing

production cost and contaminate run-off.

Precision farming

The Port of Iberia and other ports and waterways in

Louisiana would benefit from the cost effective

methods of determining accurate depths and elevations

resulting from height modernization.

Modernization of ports and waterways
14

Recommendations

Based on our assessment of the needs of Louisiana, NGS provides the

following recommendations:

1. Perform additional GPS measurements and leveling on bench

marks to establish the basic framework of survey points needed

to support height modernization in Louisiana as recommended in

the 1998 Height Modernization Study. The establishment of the

framework would be funded through outside sources and grants

and completed within five years. The framework, designed

specifically to meet Louisiana’s needs, would provide

accurate, reliable, and consistent height information

referenced to NAVD 88 to be included in NSRS. With NGS

oversight, state and local agencies would work with the

private sector to perform the geodetic survey projects.

Rapid land loss and continuous elevation (height) changes in

Louisiana require a well-managed and monitored federal/state

geodetic control network to protect the environment, ensure

safety of its citizens, and enhance prosperity within the

state. Currently, 25 to 35 square miles of wetland per year

are lost in Louisiana due to ground subsidence (sinking of the

land) and coastal erosion. Cities and cultures are at risk of

losing their land and having to relocate. Flooding and sea

level rise threaten the coastal region, most of which is only

three feet above sea level. Flood plain models and evacuation

plans, developed using outdated elevations, put the citizens

of the low-lying areas at great risk during heavy rains. The

current available geodetic control does not support the

state’s needs to evaluate and manage the changes in its

In the Grand Isle and Port Fourchon area of coastal

Louisiana, a collaborative effort between NOAA, the

United States Geological Survey (USGS), and ULL is

underway that will merge bathymetric and topographic

data to develop a prototype elevation surface that

can be used by coastal communities, planners, and

managers for a wide range of coastal projects. The

demonstration project uses accurate geodetic control

for its kinematic GPS techniques, airborne data

collection using Light Detection and Ranging (LIDAR),

and data transformation tools.

Grand Isle - Port Fourchon

topographic/bathymetric demonstration project
15

Photograph of a PAM

environment and the impact on its economy and ecosystem.

Problems with historic surveys, land movement, and sea level

rise have made the current vertical geodetic control in

Louisiana obsolete, inaccurate, and unable to ensure safety.

Adequate spacing of high accuracy GPS measurements coinciding

with current existing height information, from classical lineof-sight surveys, also improves the geoid model(model derived

from measurements of the Earth’s gravity), which relates GPS

heights to orthometric heights (leveling elevations). This

results in more efficient and economic applications of GPS

technology to determine elevations.

2. Expand the current network of CORS and explore the use of

Port-A-Measures (PAMs) and extensometers in Louisiana. The

combination of CORS throughout the state and mobile and

stationary height monitoring stations concentrated in

subsidence areas together provide an accurate statewide height

monitoring system referenced to the highly accurate National

CORS network. To serve as the essential framework for height

modernization, special emphasis is required in the southern

part of the state.

PAMs are mobile monitoring systems that use GPS to determine

height changes to monitor subsidence. Extensometers are

permanent devices for measuring small changes in the distance

between two points on the Earth, and are used to detect

subsidence without the use of GPS. Continuous monitoring by

use of CORS across the state would allow for accurate

information of subsidence at the ground level. Plans are

already underway for expansion of the National CORS network in
16

the state, but additional state and local CORS are needed in

the southern part of the state undergoing the most serious

land loss. [National CORS is a nationwide network of hundreds

of CORS which have been positioned so that their elevations

are assumed to have zero errors relative to the center of the

Earth. CORS provide data for high accuracy GPS postprocessing of elevation data. Some of the CORS are also radio

beacons that instantaneously transmit differential GPS

corrections for users with RTK GPS applications.]

3. Establish a Louisiana Spatial Reference Center (LASRC). Like

California, Louisiana does not have a state agency

coordinating efforts to improve the geodetic reference frame

and requires a Spatial Reference Center to work in conjunction

with NGS to support height modernization within the state.

[With assistance and grants from NGS, the California Spatial

Reference Center was established to better address

California’s geodetic control needs.] The creation of a LASRC

would serve as a regional center for height modernization and

foster technology transfer not only between NGS and the state,

but also between Louisiana and its neighboring states.

Louisiana’s active coastal wetlands and shorelines create

unique referencing issues that cannot be addressed solely by

the national program. The coastal processes and monitoring

programs, including remote sensing and shoreline mapping, that

examine subsidence and shoreline retreat require more timely

action that can be done more effectively at the state and

local level. NOAA is currently engaging in a partnership

agreement with Louisiana State University to enhance NSRS in

Louisiana. The LASRC would provide an Internet link to the

NSRS data base, develop specifications and guidelines for GPS

surveys not otherwise available at the national level, and

educate users on spatial data referencing issues and

applications.
17

NAVD 88 control in Wisconsin

WISCONSIN

Background

Before GPS, the vertical federal/state geodetic control network

consisted of orthometric heights (vertical heights relative to mean

sea level). The vertical control stations (bench marks) were

surveyed using classical leveling to differentially determine the

height between bench marks. In Wisconsin, the vertical

federal/state geodetic control network established by NGS was

conducted primarily in the 1920's and 1930's, with additional

control established by USGS in the 1950's. The figure below

indicating NAVD 88 control in Wisconsin represents elevation

(height) information currently in the NSRS data base.

Much of the NAVD 88 control information is outdated, however, since

many of the stations have not been revisited or surveyed in recent

years and may no longer be useable. When NGS updated Wisconsin’s

vertical control to NAVD 88 in 1991, there were 7400 vertical

control monuments (points with precisely determined heights).

Today, fewer than half of these monuments can be found. Many of
18

the monuments were destroyed during construction and development

projects. Of the remaining monuments, many cannot be tied to the

GPS network because overhead obstructions such as trees, buildings,

and utility lines block GPS signals, and many others are unstable

with substantial discrepancies between published elevations and

current measurements. A recent report from the Wisconsin

Department of Transportation (WisDOT) states that out of the

vertical control marks searched for to support their statewide

height modernization effort, only about 15 percent of the most

stable quality marks (coded in the NSRS data base as A- or Bstability) were found useable.

The current vertical federal/state geodetic control network in

Wisconsin is insufficient. Most of the bench marks are old and

subject to environmental disturbances, namely frost heave and postglacial rebound. Frost heave occurs when water-saturated soil is

deformed and uplifted during periods of freezing. Post-glacial

rebound is the rising of the Earth’s surface which occurs in land

that was compressed by glaciers during the last ice age. The land

is still rebounding in the Great Lakes region today. Additionally,

in most parts of the state, 50 percent or more of all bench marks

have been destroyed due to construction and land development

activities.

In 1991, Wisconsin was one of the first states to establish a High

Accuracy Reference Network (HARN). The HARN was a nationwide

effort led by NGS to upgrade the horizontal positions and GPS

(ellipsoid) heights of the national geodetic control network using

GPS techniques. In 1997, with continuing improvements in GPS

technologies coupled with the development of the very highly

accurate CORS network, NGS launched a new effort - the Federal Base

Network (FBN) campaign. The FBN is a very high accuracy network of

high accuracy network of monumented stations (points) with 100-km

nominal spacing throughout the United States and its territories.

The FBN, observed and managed by NGS, also contains additional

stations as needed in areas of subsidence, crustal motion, or

special interest. NGS recognized that the state and local

governments, as well as the private sector, were interested in a

network of geodetic control with less distance between stations.

While establishing the FBN, NGS invited all interested parties to

simultaneously observe additional stations, known as the

Cooperative Base Network (CBN). The CBN is a very high accuracy

network of monumented stations with 25- to 30-km nominal spacing,

established and maintained through cooperative agreements with

other Federal, state, and local government agencies. The focus of

the FBN/CBN surveys was to cooperatively reobserve the HARN

stations as either FBN or CBN stations with personnel from NGS,

state and local communities. The FBN and CBN stations would then
6

NGS vertical adjustment of WI-HMP, Phase 1.

19

be positioned relative to the highly accurate CORS, dramatically

improving the GPS vertical component of NSRS.

WisDOT and NGS have a history of cooperative effort in the use of

GPS technology to improve both the horizontal and vertical control

data within the state. Even with these efforts however, there are

still gaps and need for improvement in the state’s geodetic

network.

Needs

In Wisconsin, the existing federal/state geodetic control network

simply does not support today’s design and construction projects.

The critical nature of the shortfall of accurate geodetic control,

especially vertical control, prompted the Wisconsin Land

Information Board in April 2001, to establish a State Elevation

Data Task Force to assess the needs and uses for vertical control

and directly address the deficiencies. National, state, and local

agencies, as well as the private sector, need consistent and

accurate geodetic control for use in highway and land development,

monitoring and modeling of shoreline and flood plains, and safe and

economical transportation of goods.

Wisconsin was one of the first states to realize it needed to

enhance its vertical height system. As a result, in 2000, WisDOT

and NGS agreed to collaborate on the Wisconsin Height Modernization

Program (WI-HMP). The agencies drew from the 1998 National Height

Modernization Study in formulating a 10-phase plan to improve

elevation data throughout the state. The goal of the WI-HMP is to

eliminate inconsistencies between horizontal and vertical control

data, supplement control where marks have been destroyed, and

create a network that can use GPS technologies as a cost-effective

positioning tool in place of conventional equipment and procedures.

While the HARN and FBN/CBN campaigns provided highly accurate

horizontal and GPS ellipsoid heights to the state, the WI-HMP will

provide highly accurate and precise primary vertical control

(orthometric heights), as well as densify (add more stations to)

the federal/state geodetic control network, to all of Wisconsin.

Of the 43 bench marks with published NAVD 88 heights

leveled to in Phase I of the WI-HMP, only 19 (44%) could

be constrained in the final NGS vertical adjustment. The

other 24 (56%) had elevation changes ranging from

-20.4 cm (-8.0 inches) to 19.2 cm (+7.5 inches) from the

published NAVD 88 heights.6
20

Planned as a 10-year effort, but more practical and cost-efficient

as a five-year plan, the WI-HMP will establish a three-dimensional

federal/state geodetic network using GPS and conventional leveling

techniques throughout the state. Accuracies of 2 cm are expected

in the horizontal and vertical components. The plan follows NGS

guidelines and calls for the submission of all data collected and

processed to be submitted to NGS for inclusion in NSRS.

Implementation of the WI-HMP consists of:

 researching and recovering existing NSRS bench marks;

 plotting high accuracy GPS and bench marks;

 densifying GPS at three different levels;

- primary base stations at 25 kilometer (km) spacing;

- secondary base stations at 12-14 km spacing;

- local network stations at 6-8 km spacing;

 creating new level lines incorporating high accuracy GPS and

existing bench marks;

 locating new bench marks at 2 km spacing along level lines;

 performing conventional leveling on bench marks, HARNs, and

primary base stations;

 performing GPS on all levels of GPS stations to transfer

elevations;

 processing, analysis and adjustment of GPS and leveling data;

and

 submitting adjusted data to NGS for review and inclusion in

the NSRS data base.

Potential Benefits

The benefits of height modernization to the state of Wisconsin,

categorized by industry and described by examples in the text

boxes, include:

Safety

 Improved emergency response routes:

S improve time models and routes for evacuation;

S decrease number of people stranded; and

S improve models for river stage predictions as well as

measurements.

 More accurate models of storm surges, coastal erosion, and

trajectories of oil and chemical spills that enable better

response to these hazards.

 Accurate digital elevation models, enabling better flood plain

analysis and determination of flood insurance needs.
21

Navigation/Transportation

 Improved coastal and harbor navigation, enabling safer and

more cost-effective shipment of goods.

 Combined bathymetric and vertical height information in

shoreline models.

Highway Construction and Improvement

 More accurate vertical data for preliminary highway design.

 Improved ability to delineate drainage basins for bridge and

culvert sizing.

 Improved data quality to provide more accurate, more detailed

digital elevation models.

 Nearby bench marks for use in highway design and construction

which are more reliable and cost effective.

Agriculture

 Real-time positioning of farm equipment and reduction of

production costs.

WisDOT used RTK GPS to verify both the horizontal and

vertical positions of a group of photogrammetric

targets that had been placed in the field for a

highway design/mapping project. Using the current

method of static GPS and conventional leveling took

280 staff-hours to complete. With WI-HMP completed,

the RTK GPS method took only 30 staff-hours, more

than nine times faster than the current methods

employed. Again, these savings will continue to

accrue for WisDOT and other local and state agencies

as the WI-HMP expands.

WI-HMP and RTK GPS method success

The Wisconsin Department of Natural Resources is

responsible for the analysis of more than 20,000 dams.

Accurate vertical heights are needed to show downstream

flooding that would occur if a dam failed. Many of

these dams are old and dam burst analysis is critical

for the protection of human life.

Dam burst analysis
22

 Decreased run-off of contaminants as a result of controlled

applications of water, fertilizers, and pesticides in

precision farming.

Property Description

 Expedited gathering of information for flood plain

determination.

 Allow incorporation of topographic files as part of tax parcel

maps to provide more detailed information about property

parcels.

Land Surveying

 Facilitated registration of Public Land Survey System data in

the computer aided design environment.

 Greater accuracy in parcel mapping efforts.

 More accurate horizontal and vertical geodetic control for

public and private sector users.

The Central Sands area of Wisconsin, a major producer

of vegetables, relies heavily on irrigation and the

use of fertilizers and pesticides. Improved height

information and the use of precision farming

techniques will reduce run-off and reduce production

costs in this agricultural region.

Central Sands agricultural region

A recent problem with elevations occurred in a project

mapped by WisDOT for a high speed rail project.

Because of a lack of accurate heights, GPS-derived

heights were miscalculated, resulting in over 100 hours

of additional survey work, a three-month delay in the

project, and an additional 50 hours of mapping work to

correct the problem. Improved and consistent heights

would have prevented these costly errors and delays.

High speed rail project

Digital elevation models of agricultural areas would

allow crop dusters to fly their fields without

requiring manual flagging of the fields, thus reducing

costs.

Crop dusting
23

Land Information Systems

 Greater accuracy for field checks on digital orthophotos

(digital version of a rectified (corrected) aerial

photograph).

 Provided field reference points for verifying accuracy of

resource grade GPS collected data.

 Improved data quality for more detailed terrain modeling and

three-dimensional visualization activities.

Land Conservation

 Better determination of wetland boundaries.

 Better determination of Great Lakes erosion and lake level

rise.

 Soil erosion assessments.

 Increased data visualization and three-dimensional modeling.

Land Use Planning

 Better determination of slope gradients.

 Better determination of elevations for flood plain

delineations.

Dodge County conducts substantial amounts of

photogrammetry each year. As part of the quality

control program, the digital orthophoto products are

checked for accuracy. Before the WI-HMP was in place,

it took 24 hours to conduct field checks necessary to

verify horizontal and vertical positions of check

points in a single 36 square mile Public Land Survey

System Township. With WI-HMP completed, RTK GPS

procedures make it possible to complete the

verification in four hours. This 6:1 savings

translates into hundreds of thousands of dollars

annually for Dodge County, when taking into account the

many highway projects for which they are responsible.

Verification of orthophoto products

Topographic surveys are used for proper site selection

of dairy operations. Sites with a slope of 2 to 6

percent allow for drainage without erosion.

Dairy modernization
24

 Facilitate evaluation of property characteristics for permits,

petitions, and parcel combinations.

Scientific

 Improved understanding of tectonic movement (post-glacial

rebound).

 Improved modeling of the geoid.

Recommendations

Based on our assessment of the needs of Wisconsin, NGS provides the

following recommendations:

1. Accelerate the Wisconsin Height Modernization Program (WI-HMP)

from ten to five years. Analyze data collected in the early

phases of the WI-HMP to determine possible modifications to

field procedures and the design of the program. Specifically,

assess the amount of leveling to be completed and the current

specifications and guidelines of the field observations to

ensure accurate, yet economic, development of height

modernization.

The potentially substantial economic benefits to the state and

nation through the transportation, agriculture, construction,

and public safety industries realized five years sooner would

make Wisconsin a prototype for height modernization for the

region, as well as the country. NGS acknowledges the

tremendous effort underway by the WisDOT to complete its

10-year WI-HMP, but cautions that technology will outpace the

effort unless the work is accelerated through modified

procedures and guidelines.

2. Promote Wisconsin as a role model and trainer in height

modernization. Since Wisconsin’s height modernization effort

is already underway, the state would be in a position to

advise neighboring states in the development and uses of

height modernization. Transfer of technology through NGS with

Wisconsin as a regional leader could help address the entire

region’s economic and environmental issues.

3. Investigate opportunities for additional funding for the

height modernization in Wisconsin. Additional resources would

result in more outsourcing opportunities, as well as

technology transfer, to private surveyors. Funding would

also ensure that the efforts of the state are recognized as it

has developed and implemented a valuable resource for all

users of spatial data.
25

GLOSSARY OF TERMS AND ACRONYMS

ADJUSTMENT

The process of finding a set of “best” values from a set of

redundant survey observations. An adjustment changes, or

fits, the survey data to improve the final results of a

survey.

BENCH MARK

A bench mark is a vertical (elevation) geodetic control mark,

consisting of a metal disk or rod, that monuments a point on

land.

CBN

The Cooperative Base Network is a very high accuracy network

of monumented stations with 25- to 30-km nominal spacing,

established and maintained through cooperative agreements with

other Federal, state, and local government agencies.

CLASSICAL LEVELING

Classical, or conventional, line-of-sight leveling required

crews of surveyors to walk and carry survey equipment, taking

geodetic survey measurements approximately every 100 yards, to

establish and maintain a national coordinate system of

extremely accurate heights (elevations). The survey equipment

required that the points being measured were visible to one

another.

CONVENTIONAL LEVELING

Conventional, or classical, line-of-sight leveling required

crews of surveyors to walk and carry survey equipment, taking

geodetic survey measurements approximately every 100 yards, to

establish and maintain a national coordinate system of

extremely accurate heights (elevations). The survey equipment

required that the points being measured were visible to one

another.

CORS

Continuously Operating Reference Stations provide GPS data for

high accuracy GPS post-processing of elevation data. Some

CORS are also radio beacons that instantaneously transmit

differential GPS corrections for users with RTK GPS

applications.
26

CSRC

California Spatial Reference Center

DATUM

A datum is a set of values used as a reference or basis for a

coordinate system.

DEM

A digital elevation model is a digital cartographic

representation of the elevation of the land.

DEPARTMENT OF COMMERCE

The U.S. Department of Commerce is the parent organization of

NOAA. Its mission statement includes promotion of job

creation, economic growth, sustainable development, and

improved living standards by working in partnership with

business, universities, communities, and workers.

DIGITAL ORTHOPHOTO

A digital orthophoto the digital version of a rectified

(corrected) aerial photograph.

ELLIPSOID HEIGHT

An ellipsoid height is based on an ellipsoid model of the

surface of the Earth. A geoid height value must be applied to

compute an elevation (height) relative to mean sea level.

EXTENSOMETER

An extensometer is a permanent and highly accurate device used

for measuring small changes in height over time on the Earth.

Extensometers, which do not use GPS, are used to detect

subsidence.

FBN

The Federal Base Network is a very high accuracy network of

monumented stations with 100-km nominal spacing throughout the

United States and its territories. The FBN also contains

additional stations in areas of subsidence or crustal motion,

or as needed in support of Federal aircraft navigational

requirements.

FROST HEAVE

Frost heave is the uplifting of land which occurs when

water-saturated soil is deformed and uplifted during periods

of freezing.
27

GEODESY

Geodesy is a branch of applied mathematics concerned with the

determination of the size and shape of the Earth and the exact

positions of points on its surface, with a description of its

gravity field.

GEODETIC CONTROL

Geodetic control is a highly accurate, consistent, and

reliable set of information about the locations (latitude and

longitude), heights (relative to a specific point), and

characteristics of points within an area.

GEOID

The geoid is the equipotential surface of the Earth’s gravity

field which best fits mean sea level.

GEOID HEIGHT

Geoid height is the difference between a GPS height (ellipsoid

height) and an orthrometric height (elevation relative to mean

sea level).

GEOID MODEL

A geoid model is derived from measurements of the Earth’s

gravity field and is important in translating GPS heights to

orthometric heights.

GIS

Geographic Information Systems are computer systems used for

integrating, manipulating, analyzing, and displaying data

related to the positions on the Earth’s surface. The data may

be represented on different layers where each layer contains

data about a particular kind of feature.

GPS

The Global Positioning System is a satellite based positioning

system funded and operated by the Department of Defense, but

available to civilian users. GPS provides very accurate and

economical positioning.

HARN

High Accuracy Reference Network is a nationwide effort by NGS

to upgrade the horizontal positions and ellipsoid heights of

the national geodetic control network using GPS techniques.
28

HEIGHT MODERNIZATION

Height modernization is an effort, led by NGS, to enhance the

vertical component of NSRS, by promoting the precise

determination of heights through the use of GPS surveying.

LASRC

Louisiana Spatial Reference Center

LIDAR

Light Detection and Ranging is an aircraft-mounted laser

measuring system that uses a laser to transmit and receive

optical pulses for water surface and sea bottom detection to

determine sea water depth.

LSU

Louisiana State University

NATIONAL CORS

National CORS is a nationwide network of hundreds of CORS,

managed by NGS, which have been positioned so well that their

elevations are assumed to have zero errors relative to the

center of the Earth.

NATIONAL OCEAN SERVICE

The National Ocean Service, one of NOAA’s five line offices,

provides a wide range of products and services, established on

a scientific basis, for the protection of life, property, and

the environment.

NAVD 88

North American Vertical Datum of 1988 is the latest vertical

coordinate system for consistently defining heights and is

similar to defining an elevation relative to mean sea level.

NGS

The National Geodetic Survey is an office within the National

Ocean Service, which is a subset of the National Oceanic and

Atmospheric Administration. NGS’s role is to ensure that the

United States has a consistent, high accuracy geodetic

reference framework to support mapping, surveying, and other

infrastructure applications.

NOAA

The National Oceanic and Atmospheric Administration’s role is

to describe and predict changes in the Earth’s environment and

conserve and manage the Nation’s coastal and marine resources

to ensure sustainable economic opportunities.
29

NSRS

The National Spatial Reference System is the national

reference framework that specifies latitude, longitude,

height, scale, gravity, and orientation throughout the Nation,

as well as how these values change with time.

ORTHOMETRIC HEIGHT

An orthometric height, or elevation, is a height relative to

mean sea level.

PAM

A Port-A-Measure is a mobile monitoring system which uses GPS

to monitor ellipsoid height changes to monitor subsidence.

PORT-A-MEASURE

A Port-A-Measure, or PAM, is a mobile monitoring system which

uses GPS to monitor ellipsoid height changes to monitor

subsidence.

POST-GLACIAL REBOUND

Post-glacial rebound is the rising of the Earth’s surface

which occurs in land which was compressed by glaciers during

the last ice age.

PRECISION FARMING

In precision farming, computers mounted in farm equipment are

guided by GPS and regulate the use of water, seeds,

fertilizers, and pesticides to the foot, not to the field,

thus decreasing production cost and the run-off of

contaminants.

RTK GPS

Real-time kinematic GPS is a technique used to provide GPS

positioning. The technique involves tracking the carrier

phase of the GPS signals and requires a GPS base station close

to the user.

SUBSIDENCE

Subsidence is the sinking of land, often caused by the

withdrawal of groundwater from below the Earth’s surface.

ULL

University of Louisiana at Lafayette

USACE

United States Army Corps of Engineers
30

USGS

United States Geological Survey

WI-HMP

The Wisconsin Height Modernization Program is a program

developed by WisDOT and NGS, drawing from the National Height

Modernization Study recommendations, which utilizes GPS and

leveling techniques to improve elevation data throughout the

state.

WisDOT

Wisconsin Department of Transportation