High AccuracyNationwide Differential

Global Positioning System(HA-NDGPS)

Jim ArnoldCGSIC New Orleans

July 2008

Problem and Program ObjectivesHA-NDGPS

• Examine ways to enable 3-D dynamic positioning at the centimeter level throughout the US,

• Coexist with existing infrastructure,• Minimize deployment costs.

Problem: Submeter resolution of vehicle position neededfor many advanced vehicle safety concepts.

Program Objective: Assess the implementation feasibility for improving the accuracy of the NDGPS service, usingexisting infrastructure, to meet the requirements of additionalapplications without decreasing availability and integrityand still meeting the needs of existing users.

GPS(13 meters)

Perspective on Accuracy Horizontal, Dynamic, 95%

NDGPS(1-2 meters)

HA-NDGPS(Dynamic)(.1 Meters)

HA-NDGPS(Static)(.01 Meters)

NDGPS• Nationwide network of GPS reference

stations• Provide real time code phase corrections for

diverse applications– Transportation– Agriculture– GIS

• Provides data for other users– NGS– UNAVCO– Etc.

Coverage

The Site

ATU

BUPG

Electronics

GSOS

HA-NDGPS Program Phases• Phase 1

Develop Modulator and Data Link ReceiversInterface System ModulesBroadcast Characterization and Optimization Single Site Concept Demonstration (Hagerstown, MD)

• Phase 2Pre-Broadcast Integrity AlgorithmMultiple Site/Baseline Concept Demonstration (Hawk Run, PA)Iono/Tropo PredictionApplication Development

Broadcast Site Configuration

TRANSMITTER

DIPLEXER

REFERENCE

STATION

DATA

FORMATTERMODULATOR

TRANSMITTERDGPS/NDGPS

HIGH ACCURACYDGPS

TO ANTENNA

OBSERVABLES

CORRECTIONS

Rack Mount PC

DSP/Analog Card

Data Formatter/Modulator Diplexor

Static Positioning at 50 kmActual Real-time Hydra plot of static

geodetic survey application performed at Dickerson, MD

47.8 km from reference station.

Reference Data Source – Hagerstown HA-NDGPS Broadcast

Long Range Single Baseline TestTangier Island HA-NDGPS Experiment

(250 km). Comparison of approximate “truth” geodetic coordinates of mail boatWith the real-time solution based upon the HA-NDGPS broadcast. Results are roughly 10-20 centimeters as expected at this great range.

Phase II• Hawk Run Installation Status

– Installed and Operating

• Testing– Report available

• http://www.navcen.uscg.gov/ndgps/HA-NDGPS.PhaseII.Report.July2004.four.pdf

• Application Development– Partnering with other agencies to develop applications– US Army Corps of Engineers

HA-NDGPS Coverage

Hagerstown, MD

Hawk Run, PA

Orbisonia , PA50 mile baselines

Multi-Station

“Accurate” SolutionNationwide RTK?

• What You Need:– Satellite Lock– Ground based system

broadcasting observables– Accurate Ephemeris– Accurate Clock data– Good ionosphere model– Good Troposphere model– Integrity Check– Multiple reference stations

at less than 200 mile baselines

• What You Get:– Initial .5 to 2 meter code

accuracy– Reduced search space for

integers– Very fast integer resolution

at long ranges

Code Differential Solution

500 100 150

50

0

100

150

Integer Resolution

500 100 150

50

0

100

150

Integer Resolution

500 100 150

50

0

100

150

Integer Resolution

500 100 150

50

0

100

150

Models - Total Electron Count

Wx Model-Derived Wet Signal Delay Over CONUS

Courtesy, Dr. Sunil Bisnath formally with USM, now at Harvard Smithsonian Astrophysical Observatory

Applications• Transportation

– Highway• Automated Road Construction• Intersection Collision Avoidance• Dynamic Mapping• Digital Highway Measurement Vehicle

– Railroad• Track Defect Monitoring

– Maritime• Under keel clearance

• USDA– Agriculture

• Precision Farming• Autonomous Farm Vehicles

– USFS• Logging boundaries• Infestation monitoring

• Interior– National Park Service

• Monitoring subsidence of critical monuments

• Real-time boundary marking

– Fish and Wildlife Service• Monitoring critical habitat• Biological Assessments

• EPA– Hazardous Material Spill

containment

• Etc.

Summary• HA-NDGPS signal successfully broadcast from

multiple locations– State-of-the-Art modulation– Reliable diplexing technology

• Developed new atmospheric modeling approaches

• Accuracy better than 10 cm horizontally, 95%• Availability above 99.9%• Implementation cost <$100,000 per site

Contact Information

Jim ArnoldFederal Highway Administration

Turner-Fairbank Highway research CenterMcLean, VA 22101

(202)493-3265

Phase I Test Reporthttp://www.tfhrc.gov/its/ndgps/02110/index.htm

Phase II Test Reporthttp://www.tfhrc.gov/its/pubs/05034/index.htm

Applications

The End

HIGH ACCURACY - NDGPS

Caretaker Sites New Site Coast Guard Site Green - Operating Red – Planned Dark Blue – HA-NDGPS Installed Light Blue – HA-NDGPS Planned

Hawk RunHawk Run

MaconMacon

GradyGrady

HackleburgHackleburg BoboBobo

GoodlandGoodland

TopekaTopeka

OnondagaOnondaga

MedfordMedford

EdinburgEdinburg

MedoraMedora

BillingsBillings

Great FallsGreat Falls

PolsonPolson SpokaneSpokane

AppletonAppleton

Klamath FallsKlamath Falls

AustinAustin

BakersfieldBakersfield

EssexEssex FlagstaffFlagstaff

AlbuquerqueAlbuquerque

SummerfieldSummerfield

PuebloPueblo

HudsonHudson FallsFalls

Whidbey IsWhidbey Is

Robinson PtRobinson Pt

Fort StevensFort Stevens

Cape Cape MendocinoMendocino

Pigeon PointPigeon Point

Point ArquelloPoint Arquello

Point LomaPoint Loma

Aransas PassAransas Pass

GalvestonGalveston

English TurnEnglish Turn

MobileMobilePointPoint

Egmont KeyEgmont Key

Key WestKey West

MiamiMiami

Cape CanaveralCape Canaveral

Fort MaconFort Macon

Cape HenryCape Henry

Cape HenlopenCape Henlopen

Sandy HookSandy Hook

MorichesMoriches

Millers FerryMillers Ferry VicksburgVicksburg

MemphisMemphis SallisawSallisaw

KansasKansasCityCity

St LouisSt Louis

RockRockIslandIsland

St. PaulSt. Paul

WisconsinWisconsin Point Point

UpperUpperKeweenawKeweenaw

Whitefish PtWhitefish PtNeebish IslandNeebish IslandCheboyganCheboygan

Sturgeon BaySturgeon Bay

DetroitDetroit

SaginawSaginawBayBay

MilwaukeeMilwaukee

YoungstownYoungstown

TucsonTucson MundayMunday

JacksonJackson

MytonMyton

El PasoEl Paso

INELINEL

DandridgeDandridge

CincinnatiCincinnati

MontereyMonterey

LangtryLangtry

RawlinsRawlins

WeiserWeiser

KanabKanab

HagerstownHagerstown

AshvilleAshville

MartinsvilleMartinsville

MiddleburyMiddlebury

Jack Jack CreekCreek

OdessaOdessa

GreensboroGreensboro

OmahaOmaha

Pine Pine RiverRiver

St. Mary’sSt. Mary’s

LouisvilleLouisville

ElmiraElmira

KensingtonKensington

FayettevilleFayettevilleNew BernNew Bern

AnnapolisAnnapolis

Canton Canton

Iowa CityIowa City

St Mary’sSt Mary’s

LedyardLedyard

SenecaSeneca

LincolnLincoln

WenatcheeWenatchee

WhitneyWhitney

ClarkClark

ChicoChico

PenobscotPenobscot

CharlestonCharleston

SavannahSavannah

HartsvilleHartsville

Reedy PointReedy Point

DriverDriver

PortsmouthPortsmouth

BrunswickBrunswick

AcushnetAcushnet

Pattern Pattern

The Broadcast• Broadcast Code and Carrier Phase Data

• Capability to broadcast all observables (L1,L2C,L5, and others) contained in less than 1000 bits

• Data rates - 1KBPS• Initially L1 and L2-P(Y) observables are broadcast

• Utilize an Advanced Broadcast Link• Data synchronized to GPS time• Carrier calibrated with GPS to sub-hertz levels• Spectrally efficient modulation (raised cosine MSK)• “One second data” in compact mode

Add Ons• National Geodetic Survey:

– Replacing Brass Survey Markers– Continuosly Operating Reference Station

• GPS in Weather:– Troposphere and Ionisphere Delays– Troposphere delay correlated Atmospheric Water

Vapor,

• Plate Boundary Observatory:– Used to measure plate movement.

• Etc.