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

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

10. IMPROVING POSITIONAL ACCURACY TIMENETWORKLOCAL NETWORKSPANACCURACYACCURACY NAD 271927-198610 METERS(1 part in 100,000) NAD83(86)1986-19901 METER(1 part in 100,000) HARN1990-19970.1 METER B-order (1 part in 1 million) A-order (1 part in 10 million) CORS1996 -0.01 meter0.01 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 (1986) NGS Adjustment Team (2005)

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. HB 1 HB 2 HB 4 HB8 HB1 6 FL GA HB 17 ALMS HB 9 HB 18 NCSC HB 19 HB 32 VAWV HB 33 MDPA HB 5 HB1 0 HB 20 HB 34 DCDE HB 35 NYNJ HB 21 HB 36 CTMA HB 37 MENH HB1 1 HB 22 HB 38 RIVT HB 39 LAAR HB 23 HB 40 TNKY HB 41 MOIL HB 3 HB 6 HB 12 HB 24 HB 42 INOH HB 43 MIWI HB 25 HB 44 MNIA HB 45 NDSD HB 13 HB 26 HB 46 NEKS HB 47 OKTX HB 27 HB 48 NMAZ HB 49 COUT HB 7 HB 14 HB2 8 HB 50 NVID HB 51 MTWY HB 29 ORWA HB1 5 HB 30 CAAK HB 31 PRVQ 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