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REAL TIME POSITIONING

FGDC – FEDERAL GEODETIC CONTROL SUBCOMMITTEE METHODOLOGY WORK GROUP- JOE EVJEN CHAIR DEVELOPMENT OF USER GUIDELINES AND INVOLVEMENT OF THE NATIONAL GEODETIC SURVEY IN EMERGING REAL TIME GEODETIC POSITIONING METHODS WEDNESDAY FEBRUARY 13, 2007 BILL HENNING . REAL TIME POSITIONING. “ IT DEPENDS”.

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REAL TIME POSITIONING

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  1. FGDC – FEDERAL GEODETIC CONTROL SUBCOMMITTEEMETHODOLOGY WORK GROUP-JOE EVJEN CHAIRDEVELOPMENT OF USER GUIDELINES AND INVOLVEMENT OF THE NATIONAL GEODETIC SURVEY INEMERGING REAL TIME GEODETIC POSITIONING METHODSWEDNESDAY FEBRUARY 13, 2007BILL HENNING

  2. REAL TIME POSITIONING “ IT DEPENDS”

  3. REAL TIME POSITIONING • PDOP • MULTIPATH • SATELLITES • BASE ACCURACY • BASE SECURITY • REDUNDANCY, REDUNDANCY, REDUNDANCY • PPM – IONO, TROPO MODELS, ORBIT ERRORS • SPACE WEATHER- “K” INDECES • GEOID QUALITY • RTN- TIED TO NSRS • BUBBLE ADJUSTMENT • LATENCY, UPDATE RATE KNOWLEDGE OF ALL THE ABOVE = OPERATOR EXPERTISE

  4. 300 KM 80 KM

  5. SUNSPOT CYCLE • Sunspots follow a regular 11 year cycle • We are just past the peak of the current cycle • Sunspots increase the radiation hitting the earth's upper atmosphere and produce an active and unstable ionosphere http://www.spaceweather.com/

  6. IONOSPHERIC EFFECTS ON POSITIONING

  7. TROPOSPHERE DELAY The more air molecules, the slower the signal (dry delay) High pressure, Low temperature 90% of total delay relatively constant and EASY TO CORRECT FOR The more water vapor in the atmosphere the slower the signal (wet delay) High humidity 10% of total delay Highly variable and HARD TO CORRECT FOR Ionosphere troposphere 10 KM GREATER THAN 10 KM

  8. WHO USES REAL TIME POSITIONING ? • INTELLIGENT TRANSPORTATION • PRECISION AGRICULTURE • CONSTRUCTION & MACHINE CONTROL • SURVEYING & ENGINEERING • GIS – EMERGENCY PLANNING,INFRASTRUCTURE,ENVIRONMENTAL, PHOTOGRAMMETRIC CONTROL • SCIENCE & ACADEMIA- DEFORMATION STUDIES, EARTHQUAKE & SUBSIDENCE STUDIES, CRUSTAL MOVEMENT, ATMOSPHERIC STUDIES, ETC.

  9. WHY REAL TIME? • NO POST PROCESSING • FASTER THAN STATIC GPS, MORE ACCURATE THAN DGPS • NAVIGATION TO ANY COORDINATE – RECOVERY/VALIDATION • CONSTRUCTION STAKE OUT ON THE FLY • MACHINE CONTROL & AGRICULTURAL USES • FIELD CALIBRATION TO LOCAL OR NSRS CONTROL

  10. WHY REAL TIME? • TECHNICIAN KNOWS THE DATA IS COLLECTED • EASY TO BRING INTO CAD OR GIS • SEAMLESS FIELD INTEGRATION WITH OTHER SURVEY INSTRUMENTS • IT’S EASY TO ACHIEVE SURVEY GRADE ACCURACY

  11. WHY NETWORK RTK (RTN)? Because the requirement for a user base station is removed: • No reconnaissance/recovery of passive control • No time lost setting up and breaking down a base static • No base baby sitting, therefore labor cost is reduced No base means with two rovers the project is completed in half the time • = $$$ savings

  12. WHY NETWORK RTK (RTN)? • RTNS CAN BE SEAMLESSLY CONNECTED TO THE NSRS – This means: • Regional inter-GIS compatibility • Continual accuracy and integrity monitoring • Easy datum adjustment/change updates • In other words - “Everything fits together” NSRS

  13. WHY NETWORK RTK (RTN)? • NO DISTANCE CORRELATED ERROR - Atmospheric, ephemeris corrections for the site of survey Data degrade gracefully outside of the network or if a reference station is down • RTN RTK is easier than single base RTK

  14. RTK PPM ERROR VS. BASELINE LENGTH

  15. THE ROLE OF THE NGS IN SUPPORT OF RTN • The NGS should provide real time RAW data streams (via NTRIP) from a subset of the National CORS network- perhaps in a 200 Km spacing grid. These data streams will aid in the establishment, validation and monitoring of the RTNs by network administrators. NO CORRECTORS • The NGS could assess and accredit proposed or even current RTN reference station sites for obstructions, multipath, positional integrity - in short, for anything that might affect optimal performance of the RTN. • Additionally, NOAA/NGS could stream satellite ephemerides, satellite clock parameters, iono and tropo models and even crustal motion models for public use. • The NGS, continuing its role in support of accurate, reliable positioning, would study temporal macro variations in positions (seasonal, daily, ocean loading, atmospheric loading, subsidence, tectonic, etc.) and would study phenomena affecting accurate positioning (satellite orbits, refraction, multipath, antenna phase centers, geoid, etc.)

  16. THE ROLE OF THE NGS IN SUPPORT OF RTN • Since there are no sanctioned guidelines for establishing an RTN, the NGS should strongly encourage that aREPRESENTATIVE SAMPLING of the RTN stations become a National CORS or Coop CORS • ORIGINAL coordinate derivations for any RTN start up should be reviewed by the NGS to ensure compatibility with the NSRS at the datum tie level (2-cm Horizontal , 4-cm vertical). • The NGS should monitor or review areas where RTNs are merging or overlapping with others- perhaps managed by separate entities- to ensure coordinate compatibility. This will reduce liability and add to the general public welfare for work done based upon these RTNs.

  17. THE ROLE OF THE NGS IN RTN • The NGS should monitor and archive data and metadata from the RTN master stations. Each RTN station should provide a periodic OPUS solution, perhaps weekly, to the NGS where it could be integrated through OPUS-DB. These data and metadata should be a part of the NSRS at some level and therefore accessible to the public. • Metadata specs should be developed. These might include pictures, dates, station details, etc.- similar to the National CORS network.

  18. THOUGHTS TO PONDER • With or without NGS involvement and support services, RTN will blanket the USA. • There exists no cohesive national policy, guidelines, standards, specifications, metadata archiving nor database management for RTN. • The public deserves independent QA/QC on this new utility of the GNSS that impacts their lives.

  19. THE ROLE OF THE NGS IN REAL TIME POSITIONING • Testing for TEC cut-offs • Testing for baseline lengths • Minimum field conditions • Minimum field procedures • Positional Accuracy goals – 95% confidence of achieving 2-cm H, 4-cm V DYNAMIC DOCUMENTS: = 1. “NGS User Guidelines for Single Base GNSS Real Time Positioning” 2. “NGS User Guidelines for GNSS Real Time Positioning in RTN” 3. “NGS Guidelines for GNSS RTN Administrators”

  20. EXPECTED GNSS DERIVED NSRS ORTHOMETRIC HEIGHT ACCURACIES • DGPS = 1-2 METERS, CODE PHASE, L1 SMOOTHING • SINGLE BASE RTK = 2-5 CM (3-D), AVERAGE OF REDUNDANT POSITIONS ≤ 10-15 KM • RTN = 2-7 CM (3-D), WITHIN NETWORK • OPUS = 2-5 CM, ≥ 4-HOURS OF DATA • OPUS-RS = 5 CM H, 10 CM V, ≥ 15 MIN. DATA • STATIC GPS = 2 CM LOCALLY USING GUIDELINES EXPECTED CLASSICAL LEVELING NSRS ORTHOMETRIC HEIGHT ACCURACIES • GEODETIC LEVELING = ≤ 1 CM IN 10 KM (3RD ORDER)

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