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High Accuracy Nationwide Differential Global Positioning System (HA-NDGPS) Jim Arnold CGSIC New Orleans July 2008
Problem and Program Objectives HA-NDGPS Problem: Submeter resolution of vehicle position needed for many advanced vehicle safety concepts. Program Objective: Assess the implementation feasibility for improving the accuracy of the NDGPS service, using existing infrastructure, to meet the requirements of additional applications without decreasing availability and integrity and still meeting the needs of existing users. • Examine ways to enable 3 -D dynamic positioning at the centimeter level throughout the US, • Coexist with existing infrastructure, • Minimize deployment costs.
Perspective on Accuracy Horizontal, Dynamic, 95% HA-NDGPS(Dynamic) (. 1 Meters) HA-NDGPS(Static) (. 01 Meters) NDGPS (1 -2 meters) GPS (13 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.
BUPG The Site Electronics ATU GSOS
HA-NDGPS Program Phases • Phase 1 ü Develop Modulator and Data Link Receivers ü Interface System Modules ü Broadcast Characterization and Optimization ü Single Site Concept Demonstration (Hagerstown, MD) • Phase 2 ü Pre-Broadcast Integrity Algorithm ü Multiple Site/Baseline Concept Demonstration (Hawk Run, PA) ü Iono/Tropo Prediction ü Application Development
Broadcast Site Configuration REFERENCE STATION OBSERVABLES DATA MODULATOR FORMATTER CORRECTIONS DSP/Analog Card Rack Mount PC TRANSMITTER DGPS/NDGPS DIPLEXER TRANSMITTER HIGH ACCURACY DGPS TO ANTENNA
Data Formatter/Modulator Diplexor
Static Positioning at 50 km Actual 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 Test Tangier Island HA-NDGPS Experiment (250 km). Comparison of approximate “truth” geodetic coordinates of mail boat With 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. Phase. II. Report. July 2004. four. pdf • Application Development – Partnering with other agencies to develop applications – US Army Corps of Engineers
HA-NDGPS Coverage Orbisonia , PA 50 mile baselines Hagerstown, MD Hawk Run, PA
“Accurate” Solution Nationwide 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 0 50 100 150
Integer Resolution 0 50 100 150
Integer Resolution 0 50 100 150
Integer Resolution 0 50 100 150
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 • • • Interior Automated Road Construction Intersection Collision Avoidance Dynamic Mapping Digital Highway Measurement Vehicle – Railroad • Track Defect Monitoring – National Park Service • Monitoring subsidence of critical monuments • Real-time boundary marking – Fish and Wildlife Service • Monitoring critical habitat • Biological Assessments – Maritime • Under keel clearance • USDA – Agriculture • Precision Farming • Autonomous Farm Vehicles – USFS • Logging boundaries • Infestation monitoring • 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 Arnold Federal Highway Administration Turner-Fairbank Highway research Center Mc. Lean, VA 22101 (202)493 -3265 Phase I Test Report http: //www. tfhrc. gov/its/ndgps/02110/index. htm Phase II Test Report http: //www. tfhrc. gov/its/pubs/05034/index. htm
HIGH ACCURACY - NDGPS Robinson Pt l Fort Stevens l l Whidbey Is Wenatchee n n Spokane n Polson n Edinburg n Great Falls n Appleton n Seneca n Klamath Falls Cape Mendocino l Billings s Weiser s INEL n Chico n Austin ª Lincoln Clark n Whitney Omaha l n Goodland s Point Loma l Iowa City n n St Mary’s l Rock n ª Island l Flagstaff Sallisaw l n Albuquerque Memphis l Bobo Summerfield Tucson s Hartsville Dandridge Hackleburg Grady n Millers Ferryl Caretaker Sites New Site Coast Guard Site Green - Operating Red – Planned Dark Blue – HA-NDGPS Installed Light Blue – HA-NDGPS Planned s Odessa s New Bern Ashville l Charleston n s Munday Vicksburgl s El Paso s n Kensington n n Driver n l Cape Henry s Martinsville s Greensboro n l Fort Macon Monterey s n è è n. Annapolis Henlopen l Cape Louisville n Fayetteville Acushnet l Moriches Cincinnati s St. Mary’s s l St Louis n l Sandy Hook Hawk Run Hagerstown l Reedy Point Onondaga Kansas èl City Topeka n Canton s l Medford Pueblo n n Essex n Saginaw Hudson l l Bay Falls Youngstownn Detroit Elmira n Milwaukee l Middlebury l Brunswick s l Portsmouth n Sturgeon Bayl n Kanab Point Arquello l Pine River n l Whitefish Pt l Neebish Island l Cheboygan l Ledyard n Pigeon Point ª Bakersfield l St. Paul l Rawlinss Myton n s Jackson Jack s Creek Wisconsin Point n n Medora n s Pattern Penobscot Upper Keweenaw n Macon n Savannah l Mobile English Turnl Point s Langtry Galveston l l Cape Canaveral Egmont Keyl l Miami l Aransas Pass Key West l
The Broadcast • Broadcast Code and Carrier Phase Data • Capability to broadcast all observables (L 1, L 2 C, L 5, and others) contained in less than 1000 bits • Data rates - 1 KBPS • Initially L 1 and L 2 -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.