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) - 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

NATIONAL READJUSTMENT WHAT WHY? HOW WHEN POST QUESTIONS

The NAD83(86) Adjustment Team

NAD83(86) DOPPLER STATIONS

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 = /f = 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

NAD 27 and NAD 83

Results of NAD83(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 Km HIGH HORIZONTAL ACCURACY A-Order (5 mm + 1:10,000,000) B-Order (8mm + 1:1,000,000)

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. NAD83( )

HIGH ACCURACY REFERENCE NETWORK

GPS & CLASSICAL ADJUSTMENTS COMPLETED GPS ADJUSTMENT COMPLETED GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS197 GPS GPS908 GPS GPS725 HPGN/HARN & STATEWIDE NETWORK STATUS GPS404 GPS GPS GP S291 reobs 9/ GPS721 reos 7/96 GPS1047 reos 1/96 GPS GPS1133 reos-6/95-GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS1150 reos-1996

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 GPS ADJUSTMENT COMPLETED FBN/CBN SURVEYS GPS READJUSTMENT COMPLETED 1999 GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS GPS 1850 MEANS 2003 GPS1682 WILLIAMS 2003 GPS GPS-1547

IMPROVING POSITIONAL ACCURACY TIMENETWORKLOCAL NETWORKSPANACCURACYACCURACY NAD METERS(1 part in 100,000) NAD83(86) METER(1 part in 100,000) HARN METER B-order (1 part in 1 million) A-order (1 part in 10 million) CORS meter0.01 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?  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

NATIONAL READJUSTMENT WHAT WHY HOW? WHEN POST QUESTIONS

NGS Adjustment Team (1986) NGS Adjustment Team (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  3436 Projects  Free Adjustment  Residual Plot  Outliers Rejected  Connectivity to A/B Order Network Verified  Summary sheet with Project Information Created  stations

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

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 HARN stations.  Free adjustment analysis of each GPS project that contributed to the National Spatial Reference System.

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.

Concept of Operation  Helmert Blocking strategy was used.  NETSTAT- New Helmert Blocking software developed for the entire adjustment process incorporated 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

Helmert Blocks  CORS/CGPS provided control at the top block  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.

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

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

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

NEW STANDARDS FOR GEODETIC CONTROL ( 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

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 ITRF2005 were not 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.

FINAL STATISTICS Free adjustment No. of Observations = No. of constrained parameters = 3 No. of unknown parameters = 203,076 Degrees 0f Freedom = Standard error of unit weight = Constrained adjustment (out of 689 possible CORS constraints, 678 were totally constrained, 7 totally freed up, 4 heights only freed) No. of Observations = No. of constrained parameters = 2055 No. of unknown parameters = 203,076 Degrees 0f Freedom = Standard error of unit weight =

Statement regarding control used for the NAD 83(NSRS2007) Control for the NAD 83(NSRS2007) 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 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 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 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 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(NSRS2007) 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 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.full description of RDF Must have Acrobat Reader to access this file. Down free reader herereader Read this policy statement before using any NAD83(NSRS 2007) data present here Click here to get the re-adjusted NAD 83 (NSRS 2007) data in RDF format.policy statementNAD 83 (NSRS 2007) data in RDF format

NATIONAL READJUSTMENT WHAT WHY HOW WHEN? POST QUESTIONS

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 were accepted and loaded into the database but were not included in the readjustment  Completed February 8, 2007  Project Report  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  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.

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(NSRS2007) datasheet availability In the interim before data sheets with the NAD 83(NSRS2007) 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  New adjustment procedures will be developed that incorporate local and network accuracies.  Design and Publish new data sheets. A reference frame maintenance strategy (NAD83, ITRF, either or both) will be developed.

Important Facts –COMPLETION DATE – February 08, 2007 –NEW DATUM TAG - NAD 83(NSRS2007) For the latest information- visit the national readjustment webpage at: (

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?