1. NATIONAL READJUSTMENT WHAT WHY HOW WHEN NAD83(NSRS)

3. NAD27 to NAD83

4. COMPARISON OF DATUM ELEMENTS NAD 27 NAD 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

6. NAD83(86) DOPPLER STATIONS

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

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

9. HARN HIGH ACCURACY REFERENCE 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)

10. HIGH ACCURACY REFERENCE NETWORK

11. HARN 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(1995)

12. 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 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

13. Adjustment Tags Different statewide adjustments Different years (epochs) Needed to distinguish between adjustments so….. The Adjustment tag was created NAD83(1995)----NC’s original HARN adjustment

14. FEDERAL BASE NETWORK (FBN ) Reobserve the FBN to better connect the HARNs to the CORS -MINIMUM 100 KM STATION SPACING -2cm local horizontal accuracy -2cm ellipsoid heights Also: observed concurrently -CBN Cooperative Base Network -User Densification Network

15. 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

16. Reasons for NEW 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.

17. What about Orthometric Heights?  No National Orthometric height Readjustment at this time  Ortho Control = NAVD 88 not the CORS  Since no change in control most orthometric elevations would not change significantly

18. 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

19. NAD 83 READJUSTMENT ONLY GPS DATA WILL BE USED -CONTINUOUSLY OPERATING REFERENCE STATIONS -FEDERAL BASE NETWORK -COOPERATIVE BASE NETWORK -USER DENSIFICATION NETWORK -HARN -NGS AIRPORT SURVEYS

20. The National Readjustment General Comments  The CORS will provide the control  Only GPS projects will participate  The FBN/CBN Surveys are a key element since these are high accuracy (2 cm) surveys that tie the HARN to the CORS throughout the contiguous United States and provide more accurate values for the ellipsoid heights of most HARN stations.  The required free adjustment analysis of each GPS project that contributes to the National Spatial Reference System is complete.

21. 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

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. 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

24. IMPROVING POSITIONAL ACCURACY TIMENETWORK LOCAL NETWORK SPANACCURACY ACCURACY _ NAD 27 1927-198610 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 meter 0.01 meter

25. Important Facts DEADLINE for data submittal June 1, 2005 COMPLETION DATE – February 10, 2007 NEW DATUM TAG - NAD83(NSRS) For the latest information- visit the national readjustment webpage at: (www.ngs.noaa.gov/NationalReadjustment/)

26. GEODETIC CONTROL DATA SHEET Station NameNorthing (m)Easting (m)Diff. Northing 83/86 – 83/95 Diff. Easting 83/86 – 83/95 Smithport 83/86 199354.569665067.183 Smithport 83/95 199354.397665067.5130.172 (m)-0.330 m) Smithport 83/20010.013 (m) 0.010 (m) Smithport 83/NSRS ??? < 0.010(m) ??? < 0.010(m)

27. http://www.ngs.noaa.gov/NationalReadjustment/

29. NC Constrained Horizontal residuals

30. NC Horz Constrained Adjustment Ellip HT residuals

32. The NAD83(86) Adjustment Team

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

34. NAD83(NSRS)