National Readjustment

1. National Readjustment DALE PURSELL ACSM 2006

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) 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

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. NATIONAL READJUSTMENT WHAT WHY? HOW WHEN POST QUESTIONS

7. The NAD83(86) Adjustment Team

9. NAD83(86) DOPPLER STATIONS

10. 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

11. NAD 27 and NAD 83

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

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

14. 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)

15. 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)

16. HIGH ACCURACY REFERENCE NETWORK

17. NETWORK STATUS 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 GPS419 1992 1995 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

18. 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

19. FBN/CBN Surveys Current Status: • Observations complete for 48 contiguous states and the District of Columbia • Additional major surveys in Alabama (reductions underway), California and Minnesota will be included-perhaps others • West Virginia still needs to be reprocessed (Leica SR399 antennas); possibly other states or portions of states (study underway)

20. Statewide GPS Readjustments • Complete (or unnecessary) for 43 of 48 States,+ DC, PR • Readjustment of EH’s and/or Positions (5cm tolerance) • Layered Adjustment Approach Used • States not Completed • CA-Requires special analysis-underway • MO, TN, KY-not started (4/18/05) • OH underway (4/18/2005)

21. 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 2003 GPS1753 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

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

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

25. 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

26. 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.

27. 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

28. NATIONAL READJUSTMENT WHAT WHY HOW? WHEN POST QUESTIONS

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

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

31. NAD 83 READJUSTMENT 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

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

33. AIRPORT SURVEYS

34. 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.

35. Project Adjustment Analysis • 3375 Projects complete • Free Adjustment • Residual Plot • Outliers Rejected • Connectivity to A/B Order Network Verified • Summary sheet with Project Information Created • 69117 stations

36. 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

37. The National Readjustment More Comments • Computation and database loading of scale factors for each project is underway. • Statewide GPS Readjustments are providing extra information about the network on a state by state basis.

38. Concept of Operation • Modified ADJUST, GPSCOM, LLSOLV software will be used plus new residual analysis software • Helmert Blocking strategy will be used. • Coordinates Produced and Published for both NAD83 (NSRS) and ITRF • Adjustment in NAD83-Transformed to ITRF • Canadian (Mexican?) Data Integrated at top layer • Network and Local Accuracies also Produced

39. Helmert Blocks • CORS provides control at top block • Canadian data • Each state will comprise a separate block of data

40. Helmert Blocking Strategy

41. 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

42. 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

43. 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

44. ANTICIPATED SHIFTS • Based on a preliminary adjustment of all FBN’s to the published values. < 5 cm. in the horizontal component with an average shift of 2.2 cm. < 10 cm. in the vertical component with an average shift of 4.6 cm.

45. NATIONAL READJUSTMENT WHAT WHY HOW WHEN? POST QUESTIONS

46. Time-line for National Readjustment Positions and Ellipsoid Heights • All projects guaranteed to be included in the adjustment must be loaded in the database no later than 06/01/2005 • Projects submitted after 06/01/2005 will be accepted and loaded into the database but will not be included in the readjustment • Anticipated completion by February 10, 2007 • Project Report • 3 months-February, 2007 through May, 2007

47. We will be celebrating our 200th anniversary on February 10, 2007

49. NATIONAL READJUSTMENT WHAT WHY HOW WHEN POST? QUESTIONS

50. 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. • A set of national transformation parameters for “classical” non-GPS stations and GPS stations that were excluded from the National Readjustment will be developed by NGS. • Because of the relatively small shifts anticipated, a model such as NADCON will not be developed.