National Readjustment

1. National Readjustment Dale Pursell Observation and Analysis Division National Geodetic Survey ACSM St. Louis, Mo. March 11, 2007

2. NATIONAL READJUSTMENT • WHAT? • WHY • HOW • WHEN • POST • QUESTIONS

3. NATIONAL SPATIAL REFERENCE SYSTEM • A component of the National Spatial Data Infrastructure (NSDI) - http://www.fgdc.gov/nsdi/nsdi.html • Contains all geodetic control contained in the National Geodetic Survey (NGS) Integrated Data Base: • Horizontal and vertical control points • Geoid models such as GEOID 03 • Gravity • Precise GPS orbits • Continuously Operating Reference Stations (CORS) • National Shoreline data as observed by NGS • Standards and Specifications for data submittal

4. NATIONAL SPATIAL REFERENCE SYSTEM • MULTIPURPOSE – Supports Geodesy, Geophysics, Land Surveying, Navigation, Mapping, Charting and GIS • ACTIVE – Accessible through Continuously Operating Reference Stations (CORS) and derived products • INTEGRATED – Related to International services and standards (e.g. International Earth Rotation Service, International GPS Service etc.) • DOCUMENTED – Complete metadata is provided for elements.

5. NATIONAL GEODETIC SURVEY WEB SITE http://www.ngs.noaa.gov

6. NATIONALREADJUSTMENT WHAT WHY? HOW WHEN POST QUESTIONS

8. The NAD83(86) Adjustment Team

10. NAD83(86) DOPPLER STATIONS

11. COMPARISON OF DATUM ELEMENTS NAD 27NAD 83 ELLIPSOID CLARKE 1866 GRS80 a=6,378,206.4 m a=6,378,137 m 1/f = 294.9786982 1/f = 298.257222101 DATUM POINT Triangulation Station NONE Meades Ranch, Kansas Earth Mass Center ADJUSTMENT 25k Stations 250k Stations few hundred Base lines 30k EDMI base lines few hundred Astro Az 5k Astro Azimuths Doppler and VLBI

12. NAD 27 and NAD 83

13. Results of NAD83(86) • Network Accuracy - 1 Meter • Local Accuracy – First-Order (1 part in 100,000)

14. NAD 83(86) NETWORK PROBLEMS Not “GPSABLE” POOR STATION ACCESSIBILITY IRREGULARLY SPACED POSITIONAL ACCURACY

15. HIGH PRECISION GPS NETWORKS “GPSABLE” Clear Horizons for Satellite Signal Acquisition EASY ACCESSIBILITY Few Special Vehicle or Property Entrance Requirements REGULARLY SPACED Always within 20-100 Km HIGH HORIZONTAL ACCURACY A-Order (5 mm + 1:10,000,000) B-Order (8mm + 1:1,000,000)

16. HARN/HPGN ADJUSTMENT A-Order Adjusted to VLBI-Existing FBN-CORS B-Order Adjusted to A-Order Existing Horizontal (Conventional & GPS) Readjusted to A/B-Order New Adjustment Date Tag e.g. NAD83(1991.35)

17. HIGH ACCURACY REFERENCE NETWORK

18. NETWORK STATUS HPGN/HARN & STATEWIDE 1991 GPS222 1996 1992 1996 1991 GPS1048 GPS341 1991 GPS197 1996 GPS805 reos 7/96 GP S291 1993 1994 reos-1996 GPS941 GPS1047 reobs 9/97 1996 GPS730 GPS606 1994 1995 1992 1995 GPS1121 1997 1997 GPS404 GPS887 1994 1991 GPS394 GPS882 GPS GPS260 GPS1178 1997 1997 1995 1993 1200 GPS633 1992 GPS908 1992 1993 GPS1150 GPS1179 GPS610 reos-6/95-GPS904 GPS412 GPS611 1995 GPS419 1992 1990 -GPS120 1997 GPS852 1993 GPS376 GPS1133 1993 1994 1992 GPS725 GPS366 GPS721 1992 GPS585 1990 1992 GPS383 reos 1/96 GPS936 -GPS170 GPS450 1993 GPS667 1997 . GPS & CLASSICAL ADJUSTMENTS COMPLETED GPS ADJUSTMENT COMPLETED GPS577

19. FEDERAL BASE NETWORK NGS FUNDED NGS MARK MAINTENANCE MINIMUM 100 KM STATION SPACING A and B-ORDER HORIZONTAL ACCURACY FIRST-ORDER CLASS II ORTHOMETRIC HEIGHTS or SECOND-ORDER CLASS I ORTHOMETRIC HEIGHTS SECOND-ORDER CLASS I ELLIPSOIDAL HEIGHTS REVISIT EVERY 3 TO 5 YEARS

20. FBN/CBN SURVEYS 1998 GPS1340 2000 2002 1999 GPS1492 2001 GPS1686 GPS1394 GPS1641 2000 1998 GPS1506 GPS1333 2002 1999 1997 2000 GPS1687 2001 GPS1377 1999 GPS1207 2001 GPS1514 GPS1596 GPS1397 GPS1712 2003 2000 2000 GPS1752 1999 2003 2000 2003 GPS1481 GPS1463 2002 1999 GPS1519 GPS1356 GPS GPS1825 GPS1731 GPS1370 1850 2001 2000 2000 MEANS GPS1629 2003 2000 2003 GPS1462 1998 GPS1530 GPS1851 2002 GPS1188 GPS1726 GPS1288 GPS-1547 1999 2003GPS1753 2001 1999 2000 GPS1399 1999 GPS1554 GPS1347 GPS1411 GPS1381 1997 1998 GPS1250 1998 GPS1273 1998 GPS1258 1998 GPS1267 1999 GPS1264 GPS1378 2003 GPS READJUSTMENT COMPLETED GPS1682 WILLIAMS FBN GPS ADJUSTMENT COMPLETED

21. http://www.ngs.noaa.gov/PROJECTS/FBN/

22. http://www.ngs.noaa.gov/PROJECTS/FBN/

23. IMPROVING POSITIONAL ACCURACY TIME NETWORK LOCAL NETWORK SPAN ACCURACY ACCURACY NAD 27 1927-1986 10 METERS (1 part in 100,000) NAD83(86) 1986-1990 1 METER (1 part in 100,000) HARN 1990-1997 0.1 METER B-order (1 part in 1 million) A-order (1 part in 10 million) CORS 1996 - 0.01 meter 0.01 meter

24. Reasons for Readjustment • Multiple epoch dates • Inconsistencies between states • Need to be Consistent with CORS • Compute Network and Local accuracies September 24, 2003 NGS Executive Steering Committee approved a plan for the readjustment of the horizontal positions and ellipsoid heights for GPS stations in the contiguous United States. Orthometric Height adjustment will not be attempted

25. What about Orthometric Heights? • Decision was made not to perform a National Readjustment of orthometric heights at this time • Control = NAVD 88 not the CORS • Since no change in control most orthometric elevations would not change significantly • Network & Local Accuracy numbers for the orthometric heights would be the primary reason for readjustment • Would require relevant network accuracies for the NAVD 88 network-This would require a complete analysis of the NAVD 88 network

26. NATIONAL READJUSTMENT WHAT WHY HOW? WHEN POST QUESTIONS

27. NGS Adjustment Team (2005) NGS Adjustment Team (1986)

28. NAD 83 READJUSTMENT ONLY GPS DATA WAS USED CONTINUOUSLY OPERATING REFERENCE STATIONS FEDERAL BASE NETWORK COOPERATIVE BASE NETWORK USER DENSIFICATION NETWORK AIRPORT SURVEYS

29. COOPERATIVE BASE NETWORK STATE/LOCAL FUNDED STATE/LOCAL MARK MAINTENANCE 25 TO 30 KM STATION SPACING B-ORDER HORIZONTAL ACCURACY THIRD-ORDER CLASS I ORTHOMETRIC HEIGHT THIRD-ORDER CLASS I ELLIPSOIDAL HEIGHT REVISIT AS NEEDED

30. USER DENSIFICATION NETWORK STATE/LOCAL FUNDED STATION SPACING AS REQUIRED GPS OBSERVATIONS ONLY (HORIZONTAL) FIRST-ORDER HORIZONTAL ACCURACY REVISIT AS NEEDED

31. AIRPORT SURVEYS

32. Project Adjustment Analysis • 3436 Projects • Free Adjustment • Residual Plot • Outliers Rejected • Connectivity to A/B Order Network Verified • Summary sheet with Project Information Created • 67693 stations

33. TRASH Projects Not Recommended for Inclusion • Currently 149 Projects with 9903 stations • Many Third Order FAA Projects from 1980’s • Some Projects that have no ties to the Network • Original TN HARN (Macrometer Data) • Original Eastern Strain Network Project

34. The National Readjustment General Comments • The CORS/CGPS sites provided the control • Only GPS projects participated • The FBN/CBN Surveys were a key element since these were high accuracy (2 cm) surveys that tied the HARN to the CORS throughout the contiguous United States and provided more accurate values for the ellipsoid heights of most HARN stations. • Free adjustment analysis of each GPS project that contributed to the National Spatial Reference System.

35. The National Readjustment More Comments • Computation and database loading of scale factors for each project was completed. • Statewide GPS Readjustments provided extra information about the network on a state by state basis.

36. Concept of Operation • Helmert Blocking strategy was used. • NETSTAT- New Helmert Blocking software developed for the entire adjustment process incorporated more quality control and significant time saving features. • Coordinates Produced and Published for both NAD83 (NSRS) and ITRF • Adjustment in NAD83-Transformed to ITRF • Network and Local Accuracies Produced

37. Helmert Blocks • CORS/CGPS provided control at the top block • An attempt was made to create a separate block of data for each state to minimize the number of junction observations between blocks. • California, Florida, Minnesota, North and South Carolina were broken into multiple blocks because of the number of stations located in these blocks.

38. HELMERT BLOCKING STRATEGY This is how each state fits into the National Readjustment

39. Network Accuracy • Network accuracy of a control point • A value that represents the uncertainty of its coordinates with respect to the geodetic datum at the 95-percent confidence level • Datum is considered to be best expressed by the Continuous Operating Reference Stations (CORS) • Local and Network accuracy values at CORS sites are considered to be infinitesimal (approach zero) • These accuracies will be implemented with the National Readjustment

40. Local Accuracy • Local Accuracy of a control point: • A value that represents the uncertainty of its coordinates relative to other directly connected, adjacent control points at the 95-percent confidence level • An approximate average of the individual local accuracy values between this control point and other observed control points used to establish its coordinates

41. NEW STANDARDS FOR GEODETIC CONTROL (http://fgdc.er.usgs.gov/standards/status/swgstat.html) • local accuracy -------------- adjacent points • network accuracy ---------- relative to CORS • Numeric quantities, units in cm (or mm) • Both are relative accuracy measures • Will not use distance dependent expression • Order/Class codes will no longer be used

42. AVERAGE SHIFTSUSA Wide • Based on the final adjusted results from the original published positions and ellipsoid heights < Average horizontal shift: 2.5 cm. < Average ellipsoid height shift: 2.7 cm.

44. ISSUES New realization of the CORS coordinates based on ITRF2005 were not available- The published NAD83(CORS96) coordinates based on ITRF2000 will define the new NAD83 (NSRS2007) coordinate system. This new Policy statement is posted on the NSRS Readjustment webpage. To be decided-will another adjustment be run after the next CORS realization (20??) is released and new CORS coordinates published.

45. FINAL STATISTICS Free adjustment No. of Observations = 851073 No. of constrained parameters = 3 No. of unknown parameters = 203,076 Degrees 0f Freedom = 647997 Standard error of unit weight = 1.276619 Constrained adjustment (out of 689 possible CORS constraints, 678 were totally constrained, 7 totally freed up, 4 heights only freed) No. of Observations = 851073 No. of constrained parameters = 2055 No. of unknown parameters = 203,076 Degrees 0f Freedom = 650049 Standard error of unit weight = 1.375490

46. www.ngs.noaa.gov/NationalReadjustment

48. Statement regarding control used for the NAD 83(NSRS2007) • Control for the NAD 83(NSRS2007) adjustment was provided by the CORS. . For all states except AZ, CA, OR, WA, NV and AK, the values used were the NAD 83 epoch 2002.0 values currently published by NGS. • In California, the NAD 83 values used for the California CORS and the National CORS were provided by the CSRC in epoch 2007. These values are currently published by CSRC and available from their website- • For AZ, OR, WA, NV and AK, HTDP was used to convert the currently published NAD 83 positions of the CORS to epoch 2007.0 • For all stations on the stable North American plate, no epoch date will be shown – as is currently the practice. For the other states, an epoch date of 2007.0 will be shown. In those states, except CA, HTDP can be used with the currently published CORS to determine the proper value to use. In CA, the values as currently published on the CSRS website can be used with HTDP (if necessary).

49. Announcement concerning the publication of the NAD 83(NSRS2007) coordinates. • NGS recognizes that the primary method by which NSRS monument coordinates are accessed is via the NGS datasheet format.  However, the software for making the re-adjusted coordinates and their associated local and network accuracies is not yet ready for public use.  Rather than provide a sub-standard service to its stakeholders, NGS has decided to release the re-adjusted coordinates with local and network accuracies in a simple text-based format for immediate use.  NGS expects this data to be available on datasheets before the end of March 2007.  An announcement will be made on the NGS home page when this service becomes active. The text format NGS has chosen for dissemination of the re-adjusted coordinates is known as Re-adjustment Distribution Format (or “RDF”).  While there are some similarities between this format and the well-known NGS “Blue Book” format, it must be emphatically stated that */_this is not Blue Book format_/*. Click here for a full description of RDF. Must have Acrobat Reader to access this file. Down free reader here Read this policy statement before using any NAD83(NSRS 2007) data present here Click here to get the re-adjusted NAD 83 (NSRS 2007) data in RDF format.