National Readjustment Dale Pursell Observation and Analysis Division

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

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

NATIONAL SPATIAL REFERENCE SYSTEM • A component of the National Spatial Data Infrastructure (NSDI) http: //www. fgdc. gov/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

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.

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

NATIONAL READJUSTMENT WHAT WHY? HOW WHEN POST QUESTIONS

The NAD 83(86) Adjustment Team

NAD 83(86) DOPPLER STATIONS

COMPARISON OF DATUM ELEMENTS NAD 27 NAD 83 ELLIPSOID CLARKE 1866 a=6, 378, 206. 4 m 1/f = 294. 9786982 GRS 80 a=6, 378, 137 m 1/f = 298. 257222101 DATUM POINT Triangulation Station Meades Ranch, Kansas NONE Earth Mass Center ADJUSTMENT 25 k Stations few hundred Base lines few hundred Astro Az 250 k Stations 30 k EDMI base lines 5 k Astro Azimuths Doppler and VLBI

NAD 27 and NAD 83

Results of NAD 83(86) • Network Accuracy - 1 Meter • Local Accuracy – First-Order (1 part in 100, 000)

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

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) B-Order (8 mm + 1: 1, 000)

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. NAD 83(1991. 35)

HIGH ACCURACY REFERENCE NETWORK

NETWORK STATUS HPGN/HARN & STATEWIDE 1991 GPS 197 reos 7/96 GPS 1047 GPS 606 1994 GPS 404 GPS 412 1993 1992 GPS 376 1996 GPS 805 GPS 941 1995 GPS 887 1994 GPS 633 GPS 1048 1992 1997 GPS 1179 1991 GP S 291 1996 GPS 1121 1995 1997 GPS 882 1997 GPS 1178 GPS 725 1993 GPS 1150 reos-6/95 - GPS 904 1995 GPS 908 GPS 611 -GPS 120 1997 -1 9 G 9 P 2 199 S 1 GPS 3260 94 96 1993 GPS 610 1995 GPS 852 GPS 1133 1992 1994 1992 GPS 585 1992 GPS 1200 re os 19 GPS 730 GPS 419 1993 1994 reobs 9/97 reos 1/96 GPS 936 S 1 GPS 383 GPS 366 GPS 721 90 GPS 341 70 1991 1992 1996 1992 19 GPS 222 -G P GPS 450 1993 GPS 667 GPS & CLASSICAL ADJUSTMENTS COMPLETED. GPS ADJUSTMENT COMPLETED 1997 GPS 577

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

FBN/CBN SURVEYS 1998 GPS 1340 1998 GPS 1333 1999 GPS 1394 1999 GPS 1377 1999 GPS 1356 1999 GPS 1370 1998 GPS 1288 1999 GPS 1347 1999 GPS 1397 2002 GPS 1686 2002 GPS 1687 2000 GPS 1481 2001 GPS 1629 1999 GPS 1381 2003 GPS 1726 1999 GPS 1399 1998 GPS 1267 2000 GPS 1492 2001 GPS 1641 1997 GPS 1207 2003 GPS 1752 2000 GPS 1506 2000 2001 GPS 1596 GPS 1514 2001 GPS 1712 2000 2002 GPS 1731 2003 GPS 1851 2000 GPS 1411 2003 GPS 1463 GPS 1825 1850 2000 MEANS 2000 2002 GPS-1547 2003 GPS 1753 GPS 1462 GPS 1188 2000 GPS 1519 2000 GPS 1530 2001 GPS 1554 1997 1998 GPS 1250 GPS 1273 1998 GPS 1258 1999 GPS 1264 GPS 1378 GPS READJUSTMENT COMPLETED FBN GPS ADJUSTMENT COMPLETED 2003 GPS 1682 WILLIAMS

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

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

IMPROVING POSITIONAL ACCURACY NETWORK TIME SPAN NETWORK ACCURACY LOCAL ACCURACY NAD 27 1927 -1986 10 METERS (1 part in 100, 000) NAD 83(86) 1986 -1990 1 METER (1 part in 100, 000) HARN 1990 -1997 0. 1 METER CORS 1996 - 0. 01 meter B-order (1 part in 1 million) A-order (1 part in 10 million) 0. 01 meter

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

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

NATIONAL READJUSTMENT WHAT WHY HOW? WHEN POST QUESTIONS

NGS Adjustment Team (1986) (2005)

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

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

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

AIRPORT SURVEYS

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

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

The National Readjustment General Comments Ø The CORS/CGPS sites provided the control Ø Only GPS projects participated Ø 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. Ø Free adjustment analysis of each GPS project that contributed to the National Spatial Reference System.

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

Concept of Operation Ø Helmert Blocking strategy was used. Ø NETSTAT- New Helmert Blocking software developed for the entire adjustment process incorporated more quality control and significant time saving features. Ø Coordinates Produced and Published for both NAD 83 (NSRS) and ITRF Ø Adjustment in NAD 83 -Transformed to ITRF Ø Network and Local Accuracies Produced

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

HELMERT BLOCKING STRATEGY HB 1 HB 2 HB 3 HB 4 HB 5 HB 9 HB 8 HB 17 HB 16 GA AL HB 1 0 HB 19 HB 18 FL MS NC SC HB 6 HB 32 HB 1 1 HB 20 HB 33 HB 34 HB 21 HB 35 HB 36 HB 12 HB 22 HB 37 HB 38 HB 23 HB 39 HB 7 HB 40 HB 13 HB 24 HB 41 HB 42 HB 25 HB 43 HB 44 HB 14 HB 26 HB 45 HB 46 HB 27 HB 48 HB 2 8 HB 49 HB 50 HB 1 5 HB 29 HB 51 OR HB 30 WA CA VA WV MD PA DC DE NY NJ CT MA ME NH RI VT LA AR TN KY MO IL IN OH MI WI MN IA ND SD NE KS OK TX NM AZ CO UT NV ID MT WY This is how each state fits into the National Readjustment HB 31 AK PR VQ

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

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

NEW STANDARDS FOR GEODETIC CONTROL (http: //fgdc. er. usgs. gov/standards/status/swgstat. html) • • • local accuracy -------network accuracy ----- adjacent points 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

AVERAGE SHIFTS USA 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.

ISSUES New realization of the CORS coordinates based on ITRF 2005 were not available- The published NAD 83(CORS 96) coordinates based on ITRF 2000 will define the new NAD 83 (NSRS 2007) 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.

FINAL STATISTICS Free adjustment No. of Observations = 851073 No. of constrained parameters = 3 No. of unknown parameters = 203, 076 Degrees 0 f 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 0 f Freedom = 650049 Standard error of unit weight = 1. 375490

www. ngs. noaa. gov/National. Readjustment

Statement regarding control used for the NAD 83(NSRS 2007) • Control for the NAD 83(NSRS 2007) 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).

Announcement concerning the publication of the NAD 83(NSRS 2007) 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 NAD 83(NSRS 2007) data present here Click here to get the re-adjusted NAD 83 (NSRS 2007) data in RDF format.

NATIONAL READJUSTMENT WHAT WHY HOW WHEN? POST QUESTIONS

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

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

NATIONAL READJUSTMENT WHAT WHY HOW WHEN POST? QUESTIONS

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

Policy regarding the readjustment of submitted projects but not included in the National Readjustment NGS has not made any commitment as to whether resources will be available to readjust projects submitted after the 2005 cutoff date. • It is suggested that the submitting agency readjust the project and submit the results to NGS for database entry. Only the output of ADJUST, the bfile with the final coordinates and ellipsoid heights and a very short report addendum detailing any problems or comments need be submitted. • NGS has not determined at this time the mechanism for computing the local and network accuracies for individual projects so there is no requirement for their submission.

• Policy regarding submission of future projects to NGS prior to NAD 83(NSRS 2007) datasheet availability In the interim before data sheets with the NAD 83(NSRS 2007) coordinates are available, use one of the following options: • 1. From the Web page listings, manually enter the new position coordinates to use for control in the adjustments and proceed with the required adjustments as previously performed. The project may be submitted to NGS but will not be entered into the database until the National Readjustment is loaded. NGS has not determined how local and network accuracies will be computed so there is no requirement for their submission at this time. • 2. Submit the project using the currently published control. It will be entered in the database and published relative to the currently published control values. A readjustment to determine 2007 values will need to be completed at some future time. (For information about readjustments of projects to the 2007 values, click on the policy statement).

Post National Readjustment Ø New adjustment procedures will be developed that incorporate local and network accuracies. Ø Design and Publish new data sheets. A reference frame maintenance strategy (NAD 83, ITRF, either or both) will be developed.

Important Facts – COMPLETION DATE – February 08, 2007 – NEW DATUM TAG - NAD 83(NSRS 2007) For the latest information- visit the national readjustment webpage at: (http: //www. ngs. noaa. gov/National. Readjustment

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

NATIONAL READJUSTMENT WHAT WHY HOW WHEN POST QUESTIONS?