Bill Henning Senior Geodesist, PLS. 301-713-3196 x 111, william.henning@noaa

1. GREAT LAKES REGION HEIGHT MODERNIZATION CONSORTIUM NGS AND REAL TIME POSITIONING Bill Henning Senior Geodesist, PLS. 301-713-3196 x 111, william.henning@noaa.gov ftp://ftp.ngs.noaa.gov/dist/whenning/GLRHMC/

2. REAL-TIME ACTIVITIES AT THE NGS • OPERATE AN NTRIP CASTER. (Fed. Owned/operated – currently 8. RTCM 2.3 & 3.0, From Foundation CORS. NO CORRECTORS) • DEVELOP AND PUBLISH GUIDELINES DESCRIBING BEST PRACTICES IN RTK & RTN .(RTK Users draft, RTN Operators draft, etc.) • PARTICIPATE IN MEETINGS, FORUMS, WORKSHOPS, ETC., CONCERNING REAL-TIME NETWORKS. SEEK LEADERSHIP ROLES.(FIG, FGCS, ESRI, ACSM, RTCM, etc.) • RESEARCH PHENOMENA AFFECTING ACCURATE REAL-TIME POSITIONING. (Orbits, refraction, multipath, antenna calibration, geoid separations, gravity, crustal motion, etc.)

3. SINGLE-BASE USERS GUIDELINES • WHY/HOW? • Legacy equipment • Closest base networks • Areas with no cell coverage • Empirical methods • Source for background info. • Dynamic technology

4. SINGLE BASE GUIDELINES –MEANT AS A BEST METHODS AND ALSO AS A BACKGROUND REFERENCE FOR RT: • EQUIPMENT • GNSS SIGNAL BASICS • PRINCIPLES OF RT POSITIONING • ATMOSPHERIC ISSUES • PLANNING • BEST METHODS • ACCURACY/PRECISION • ATMOSPHERIC ISSUES • MULTIPATH • METADATA • COMMUNICATION • OFFICE CHECKS • RT GLOSSARY

5. 8400 MPH 8400 MPH SVN 31 SVN 8 SVN 14 8400 MPH SVN 23 EVERY EPOCH OF OBSERVATION MUST COMPUTE CHANGE IN POSITION DUE TO EARTH ROTATION, SATELLITE ORBIT CHANGE AND RELATIVITY! 8400 MPH 800 MPH +/- AT “C”, 1 NANOSECOND = 30 CM!

6. SUNSPOT CYCLE • Sunspots follow a regular 11 year cycle • We are just past the low point of the current cycle • Sunspots increase the radiation hitting the earth's upper atmosphere and produce an active and unstable ionosphere 2013 http://www.swpc.noaa.gov/

7. WWW.SWPC.NOAA.GOV

8. IONOSPHERIC EFFECTS ON POSITIONING AVERAGE IONO- NO NETWORK HIGH IONO- NO NETWORK 2D PRECISION/ACCURACY (CM) SINGLE BASE RTK @ 10 KM (2000-2002) (1994-1995) NETWORK SOLUTION @ 30 KM WITH NETWORK DISTANCE TO REFERENCE STATION (KM) (SOURCE-BKG- GERMANY)

9. IONO, TROPO, ORBIT CONTRIBUTE TO PPM ERROR REMEMBER GNSS EQUIPMENT MANUFACTURERS’ SPECS!

10. 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

11. DRAFT GUIDELINES- 95% CONFIDENCE

12. THE NGS AND REAL-TIME NETWORKS

13. REAL TIME NETWORKS (RTN)- A NEW INFRASTRUCTURE! • PERHAPS OVER 80 RTN EXIST IN THE USA WITH MANY IN THE PLANNING STAGES • HOW ARE THEY ESTABLISHED? • HOW ARE THEIR COORDINATES COMPUTED? ARE THEY CONSISTENT? • HOW IS THE NETWORK ADJUSTED? • **HOW DOES THE RTN ALIGN TO THE NSRS? • CAN USERS USE ANY MANUFACTURERS’ EQUIPMENT IN THE RTN? • DO OVERLAPPING NETWORKS GIVE THE SAME COORDINATES? • WHAT ARE THE FIELD ACCURACIES? ?

14. NGS RT WEB PAGES – OPERATIONAL PROTOTYPE CURRENT POLICY: NGS WILL NOT RESTREAM RT DATA FROM NON-FEDERAL SITES

15. RADIO TECHNICAL COMMISSION FOR MARITIME SERVICESDIFFERENTIAL GNSS POSITIONING= RTCM SC-104 • INTERNATIONAL STANDARDS BY ORGANIZATIONS- non-profit scientific, professional and educational, governmental and non-governmental • RTCM format is OPEN SOURCE, GENERIC • RECOMMENDED STANDARDS FOR DIFFERENTIAL GNSS POSITIONING • ALL MAJOR RT GNSS GEAR CAN USE THIS FORMAT • IN USA, MEMBERS INCLUDE: FCC, USCG, NGS, MAJOR GNSS MANUFACTURERS • NTRIP STANDARDS (An application-level protocol that supports streaming (GNSS) data over the Internet)

16. NGS RTCM 3.X STREAMS

17. “FOUNDATION” CORS CONCEPT (SHOWN AT NOMINAL 500 KM SPACING)

18. DEVELOPING COOPERATIVE PARTNERS USCG 86 TOTAL -38 INLAND (DOT)

19. USCG DGPS TEST SITES DRIVER, VA UPPER KEWANEE, MI NEW BERN, NC MORICHES, NY ANNAPOLIS, MD ENGLISH TURN, LA CARD SOUND, FL TAMPA, FL KODIAK, AK PENOBSCOT, ME

20. PBO STATIONS • BINEX, RTCM 2.4, RTCM 3.0 • 0.6 to 2.0 seconds latency • SERVER IN BOULDER, CO • 97 RT STATIONS +/- http://pboweb.unavco.org/?pageid=107

21. PBO RT STREAMS

22. http://www.ntrip.org/ 155 STREAMS TO http://www.igs-ip.net/home

23. Position Time Series (long-term) earthquake 2002 2003 2004 2005 2006 2007 2008 2002 2003 2004 2005 2006 2007 2008 seasonal variation 2002 2003 2004 2005 2006 2007 2008

24. EXAMPLE OF WHY RTN REFERENCE STATIONS SHOULD BE MONITORED SUBSIDENCE ≈ 6 MM / YEAR ENGLISH TURN CORS

25. POSSIBLE REASONS FOR CYCLICAL MOVEMENT • FLUID WITHDRAWAL/INFUSION • OCEAN LOADING • ATMOSPHERIC LOADING • RECEIVERS • PROCESSING • IONO MODELING • VOLCANIC “BREATHING” • INTERMITTENT ELECTRICAL INTERFERENCE • SNOW

26. DRAFT

27. PURPOSE OF RTN GUIDELINES Promote consistency of RTN-generated coordinates with current realizations of both the North American Datum of 1983 (NAD 83) and the International Terrestrial Reference System (ITRS). Note that NAD 83 is the official spatial reference system for geometric positioning in the United States.

28. OPERATING A RTN- CHAPTER ONE DRAFT #1 Include a subnetwork of the RTN into the National CORS network. This would be three stations If RTN has less than 30 stations, 10% of RTN with greater than 30 stations. #2 Align all RTN reference stations coordinates to the CORS network at 2-cm horizontal and 4-cm vertical #3 For each reference station in the RTN, use the Online Positioning User Service (OPUS) at http://www.ngs.noaa.gov/OPUS/ to test for the continued consistency of its adopted positional coordinatesand velocity on a daily basis, and revise the station’s adopted coordinates and/or velocity if the tests reveal a need to do so.

29. REFERENCE STATION COORDINATE DERIVATION: ALL CORS FIXEDALL CORS WEIGHTEDOPUSOPUS + HARNBEST FIT TO ONE MASTER STATION

30. Suggestions for Determining RTN Station Coordinates Option 1: Submit 24 hours of GPS data from each station to OPUS for each of at least 10 days and compute the arithmetic mean of the daily OPUS-generated coordinates. Option 2: Process at least 10 days of GPS data from all RTN stations using a simultaneous network adjustment while “constraining” several CORS coordinates with weights of 1 cm in each horizontal dimension and 2 cm in the vertical dimension. NGS recommends Option 2.

31. Suggestions for Determining Velocities for RTN Stations • Use the HTDP (Horizontal Time-Dependent Positioning) software to predict velocities for new RTN stations. (The predicted vertical velocity will be zero.) • After 3 years, use GPS data from the RTN station to produce a time series of the station’s coordinates, then use this time series to estimate a velocity for the RTN station.

32. “OPUS-LIKE” GENERATED GRAPHIC OF RTN STATIONS- SIMILAR TO CORS 60-DAY PLOT

33. BEST METHODS FORPOSITIONING WITH RT

34. BEST METHODS FROM THE GUIDELINES:THE 7 “C’s” http://www.ngs.noaa.gov/ SEARCH: CLASSICAL REAL TIME • CHECK EQUIPMENT • COMMUNICATION • CONDITIONS • CONSTRAINTS(OR NOT) • COORDINATES • COLLECTION • CONFIDENCE THE CONTROL IS AT THE POLE

35. FROM NGS SINGLE BASE DRAFT GUIDELINES CHAPTER 5 - FIELD PROCEDURES, AND USERS CHAPTER OF RTN GUIDELINES: RT = single base, either active or passiveB = Both Single base and RTN ACHIEVING ACCURATE, RELIABLE POSITIONS USING GNSS REAL TIME TECHNIQUES

36. CHECK EQUIPMENT • B BUBBLE- ADJUSTED? • RT BATTERY- BASE FULLY CHARGED 12V? • B BATTERY – ROVER SPARES? • RT USE PROPER RADIO CABLE (REDUCE SIGNAL LOSS) • RT RADIO MAST HIGH AS POSSIBLE? (5’ = 5 MILES, 20’ = 11 MILES, DOUBLE HEIGHT=40% RANGE INCREASE). LOW LOSS CABLE FOR >25’. • RT DIPOLE (DIRECTIONAL) ANTENNA NEEDED? • RT REPEATER? • RT CABLE CONNECTIONS SEATED AND TIGHT? • B“FIXED HEIGHT” CHECKED? • RT BASE SECURE?

37. COMMUNICATION • RT UHF FREQUECY CLEAR? • B CDMA/CELL - STATIC IP FOR COMMS? • B CONSTANT COMMS WHILE LOCATING • RT BATTERY STRENGTH OK? • B CELL COVERAGE?

38. CONDITIONS • RT WEATHER CONSISTENT? • B CHECK SPACE WEATHER? • B CHECK PDOP/SATS FOR THE DAY? • RT OPEN SKY AT BASE? • RT MULTIPATH AT BASE? • B MULTIPATH AT ROVER? • B USE BIPOD?

39. CONSTRAINTS (OR NOT) • B ≥ 4 H & V, KNOWN & TRUSTED POINTS? • B CALIBRATION RESIDUALS-OUTLIERS? • B DO ANY PASSIVE MARKS NEED TO BE HELD? • RT BASE WITHIN CALIBRATION? • B SAME OFFICE & FIELD CALIBRATION USED?

40. CALIBRATIONS/VERTICAL LOCALIZATIONS

41. COORDINATES • B TRUSTED SOURCE? • B WHAT DATUM/EPOCH ARE NEEDED? • RT GIGO • B ALWAYS CHECK KNOWN POINTS. • B PRECISION VS. ACCURACY • B GROUND/PROJECT VS. GRID/GEODETIC • B GEOID MODEL QUALITY • B LOG METADATA

42. COLLECTION • B CHECK ON KNOWN POINTS! • B SET ELEVATION MASK • B ANTENNA TYPES ENTERED OK? • B SET COVARIANCE MATRICES ON (IF NECESSARY). • B RMS SHOWN IS TYPICALLY 68% CONFIDENCE (BRAND DEPENDENT) • B H & V PRECISION SHOWN IS TYPICALLY 68% CONFIDENCE • B TIME ON POINT? QA/QC OF INTEGER FIX • B MULTIPATH? DISCRETE/DIFFUSE • B BUBBLE LEVELED? • B PDOP? • B FIXED SOLUTION? • B USE BIPOD? • B COMMS CONTINUOUS DURING LOCATION? • B BLUNDER CHECK LOCATION ON IMPORTANT POINTS.

43. MULTIPATH θ θ = EXTRA DISTANCE

44. MULTIPATH = NOISESPECULAR(DISCRETE) & DIFFUSE INSIDE GNSS NOVEMBER-DECEMBER 2008 “MULTIPATH-MITIGATION TECHNIQUES USING MAXIMUM-LIKELIHOOD PRINCIPLE” MOHAMED SAHMOUDI AND RENE JR. LANDRY WWW.INSIDEGNSS.COM

45. CONFIDENCE • B CHECK KNOWN BEFORE, DURING, AFTER SESSION. • B NECESSARY REDUNDANCY? • B WHAT ACCURACY IS NEEDED? • RT REMEMBER PPM • RT BASE PRECISION TO NEAREST CALIBRATION POINT • B AVERAGE REDUNDANT SHOTS – PRECISION DIFFERENCE WITHIN NEEDS OF SURVEY • B BE AWARE OF POTENTIAL INTERFERENCE (E.G., HIGH TENSION TOWER LINES)

46. Two Days/Same Time -10.254 -10.251 THE IMPORTANCE OF REDUNDANCY > -10.253 Difference = 0.3 cm “Truth” = -10.276 Difference = 2.3 cm Two Days/ Different Times -10.254 > -10.275 -10.295 Difference = 4.1 cm “Truth” = -10.276 Difference = 0.1 cm

47. DRAFT GUIDELINES- 95% CONFIDENCE

48. METADATA ! • BESIDES ATTRIBUTE FIELDS, THE RT PRACTICIONER MUST KEEP RECORDS OF ITEMS NOT RECORDED IN THE FIELD,FOR INSTANCE: • WHAT IS THE SOURCE OF THE DATA? • WHAT IS THE DATUM/ADJUSTMENT/EPOCH? • WHAT ARE THE FIELD CONDITIONS? • WHAT EQUIPMENT WAS USED, ESPECIALLY- WHAT ANTENNA? • WHAT FIRMWARE WAS IN THE RECEIVER & COLLECTOR? • WHAT REDUNDANCY, IF ANY, WAS USED?

49. QUICK FIELD SUMMARY: • Set the base at a wide open site • Set rover elevation mask between 12° & 15° • The more satellites the better • The lower the PDOP the better • The more redundancy the better • Beware multipath • Beware long initialization times • Beware antenna height blunders • Survey with “fixed” solutions only • Always check known points before, during and after new location sessions • Keep equipment adjusted for highest accuracy • Communication should be continuous while locating a point • Precision displayed in the data collector can be at the 68 percent level (or 1σ), which is only about half the error spread to get 95 percent confidence • Have back up batteries & cables • RT doesn’t like tree canopy or tall buildings

50. THE QUICK SUMMARY BOILED DOWN: • COMMUNICATIONS: THE KEY TO SUCCESS • CHECK SHOT: FIRST BEFORE NEW WORK • REDUNDANCY: FOR CONFIDENCE ≥200 RTN WORLDWIDE ≥80 RTN IN THE USA ≥35 DOT WITH STATEWIDE NETWORKS PLANNED ?