National Readjustment Geodesist, Texas State Advisor National Geodetic Survey Texas Society of Professional Surveyors October 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

Guess who …

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

Official policy FEDERAL BASE NETWORK NGS funded and Maintained Minimum 100 KM station spacing Local ACCURACIES Horizontal: 1-cm. Ellipsoid height: 2-cm NAVD 88: 3-cm Gravity: 50 micro-gals REVISIT EVERY 3 TO 5 YEARS

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

NGS Map version

Old Datasheet format

Difference is: DN = (m) DE = (m) DU = (m)

IMPROVING POSITIONAL ACCURACY TIMENETWORKLOCAL NETWORKSPANACCURACYACCURACY NAD METERS(1 part in 100,000) NAD83(86) METER(1 part in 100,000) HARN METER B-order (1.0 ppm) A-order (0.1 ppm) 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

Heights h – H – N = 0 + errors in components

Tectonic Plates NUVEL-1A

Geoid Modeling Issues The new ellipsoid heights will be used in the next hybrid geoid model. Future efforts will center on improvements to our gravity data. NGS has acquired an airborne gravity meter. We plan a comprehensive set of observations to capture gravity throughout the United States and our possessions. Airborne gravity data supplements terrestrial and satellite based gravity.

Gravity Recovery And Climate Experiment

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 (started in 1994) FEDERAL BASE NETWORK (A & B) COOPERATIVE BASE NETWORK (B) USER DENSIFICATION NETWORK (First) AIRPORT SURVEYS (B & First)

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 This data was observed, reduced and adjusted by outside entities. NGS reviewed the projects for ties, adjustment constraints, over-all results. Until recently, they were not required to tie to CORS.

AIRPORT SURVEYS

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  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 in 1990)  Original Eastern Strain Network Project

Texas Projects eliminated GPS078 GPS088 GPS1138 GPS1170/4 GPS146 GPS158 GPS288 GPS304 GPS407 GPS482 GPS577 GPS577/D GPS582 GPS584 GPS586 GPS849/193

Points in rejected projects.

The National Readjustment General Comments  The CORS/CGPS sites were the control  Only GPS projects participated  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 HPGN stations.  The required free adjustment analysis of each GPS project that contributes to the National Spatial Reference System is complete.

More Comments  Computation and database loading of scale factors for each project.  Statewide GPS Readjustments provided extra information about the network on a state-by-state basis.

Concept of Operation  Helmert Blocking strategy 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.

Helmert Blocks CORS/CGPS provides control at top block CGPS coordinates were determined by Sector projected to the epoch. Each state comprised a separate block of data except  California which was broken into two blocks (North and South)

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 were 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

Note that this position was formerly order “B” (1-ppm)

Computations of accuracies This is an extract from an OPUS extended solution.

Annoying details A is a design matrix L is a matrix of observations W is a weight matrix X is the vector of unknowns Q is the variance- covariance matrix (A T A) -1 X = A T WA -1 *A T WL V = A*X-L σ2 = (V T WV)/DF Accuracy of a quantity is determined by multiplying standard deviation of variances by diagonal element of the Q matrix.

SHIFTS (National results) < 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.

ISSUES New realization of the CORS coordinates will not be available-we are recommending the use of 2002 coordinates as published. The new Policy statement is posted on the NSRS Readjustment webpage.. To be decided-will another adjustment be run after the next CORS realization (2005) is released and new CORS coordinates published.

ITRF and WGS 84

ITRF to NAD 83 (????)

NSRS 2007 adjustment  Four free iterations completed with decreasing numbers of residuals over 5 cm and with decreasing variances in each block and overall. Analysis of each block continues. No. of Observations = 851,073 No. of constrained parameters = 2055 No. of unknown parameters = 203,076 Degrees 0f Freedom = 650,049  Constraints in adjustment: 471 National CORS, 3 Canadian CACS, 1 Mexican CORS and 213 California CGPS sites

TEXAS STATISTICS Total # of Stations: 2400 Max Horizontal Shift:0.208 (m) Average Hz Shift:0.016 (m) Max Vertical Shift:0.250 (m) Average Vt. Shift:0.018 (m)

Texas NAD 83(NSRS 2007) Adjustment Statistics Texas Final Free Adjustment: Variance = stations and 813 rejected vectors Texas Final Constrained Adjustment: Variance = 1.38 Note the sole constraint for the national free adjustment (CORS site GAIT) and the 678 CORS/CGPS sites for the constrained adjustment.

Station position (lat, long, ell height) Network Accuracy (lat, long, Hz correlation, ell height) at one-sigma. Units are centimeters Local Accuracy (lat, long, correlation, ell hght) Re-adjustment Distribution Format

Same data in datasheet format

Superseded values will also be shown

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 adjustment by February 10, 2007 deadline New Datasheets including new positions and network accuracies available NOW. Project Report (pending)

SNARF – Stable North American Reference Frame

narf/snarf.html

Velocities in ITRF

Vertical velocities dominated by GIA

We celebrated 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.  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 between previously determined GPS coordinates.

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 10, 2007 –NEW DATUM TAG - NAD83(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?