National Readjustment

1. National Readjustment Dale Pursell Observation and Analysis Division National Geodetic Survey FGCS Workgroup Meeting February 14, 2007

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

4. 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)

5. 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)

6. HIGH ACCURACY REFERENCE NETWORK

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

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

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

15. Project Adjustment Analysis • 3436 Projects • Free Adjustment • Residual Plot • Outliers Rejected • Connectivity to A/B Order Network Verified • Summary sheet with Project Information Created • 67674 stations

16. 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

17. 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 HPGN stations. • Free adjustment analysis of each GPS project that contributed to the National Spatial Reference System.

18. 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.

19. Concept of Operation • Helmert Blocking strategy was used. • NETSTAT- New Helmert Blocking software developed for the entire adjustment process incorporating 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

20. Helmert Blocks • CORS/CGPS provided control at the top block CGPS coordinates were determined by Scripps’ Sector utility projected to the 2007.0 epoch. • 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.

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

22. 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

23. 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

24. 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

25. AVERAGE SHIFTS • 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.

26. ISSUES New realization of the CORS coordinates based on ITRF2005 will not be 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.

27. 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 (486 National CORS and 195 CGPS sites) 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

28. www.ngs.noaa.gov/NationalReadjustment

32. Time-line for National Readjustment Positions and Ellipsoid Heights • All projects loaded in the NGS database prior to November 15, 2005 were included in the National Readjustment • Projects submitted after 11/15/2005 will be accepted and loaded into the database but will not be included in the readjustment • Completed February 8, 2007 • Project Report • 6 months-February, 2007 through July, 2007

33. For Stations not Included • NGS recommends that NAD 83 data that is NOT part of the NSRS readjustment be readjusted by contractor/user with the original observations. • Because of the relatively small shifts anticipated, a model such as NADCON will not be developed between previously determined GPS coordinates.

34. Post National Readjustment • New adjustment procedures will be developed that incorporate local and network accuracies. • Design and Publish new data sheets. Provide error ellipses for every station • A reference frame maintenance strategy (NAD83, ITRF, either or both) will be developed.

35. Important Facts • COMPLETION DATE – February 08, 2007 • NEW DATUM TAG - NAD83 (NSRS2007) For the latest information- visit the national readjustment webpage at: (http://www.ngs.noaa.gov/NationalReadjustment

36. OTHER ISSUES • We will streamline the process of project acceptance and database loading • OPUS DB • Require that all projects (submitted after the November 15, 2005 deadline) be tied to CORS • Accept/require more data in digital format-e.g.. reports, logs… • Photographs