National Readjustment

Donald.Mulcare@noaa.gov

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) - http://www.fgdc.gov/nsdi/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 NAD83(86) Adjustment Team

NAD83(86) DOPPLER STATIONS

Guess who …

COMPARISON OF DATUM ELEMENTS

NAD 27 NAD 83ELLIPSOID 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

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 ACCESSIBILITYFew Special Vehicle or Property Entrance

Requirements

REGULARLY SPACEDAlways within 20-100 Km

HIGH HORIZONTAL ACCURACYA-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(1991.35)

HIGH ACCURACY REFERENCE NETWORK

GPS & CLASSICAL ADJUSTMENTS COMPLETED

GPS ADJUSTMENT COMPLETED

1990

-GPS1

70

1990-GPS120

1991GPS222

1992GPS366

1997GPS11791992

GPS412

1992 GPS3831992

GPS450

1992GPS419

1992GPS394

1992GPS341

1993

1993

GPS585

1993 GPS667

1992GPS376

1995GPS887

1997.

GPS577

1991GPS197

GPS2601991

1995GPS908

GPS610

1993

GPS725

HPGN/HARN & STATEWIDE NETWORK STATUS

1993

1994GPS404

GPS611

1994GPS633

1991 GP S291 reobs 9/97

1994 GPS721

reos 7/96 GPS1047

reos 1/96 GPS936

1997GPS1133

reos-6/95-GPS904

1995GPS852

1995GPS882

1993GPS606

1996GPS1048 1996

GPS8051996GPS941 1994

GPS7301996GPS1121

1997GPS1178

1997 GPS 12001997

GPS1150

reos-1996

Official policy FEDERAL BASE NETWORK

NGS funded and MaintainedMinimum 100 KM station spacing

Local ACCURACIES

Horizontal: 1-cm.Ellipsoid height: 2-cm

NAVD 88: 3-cmGravity: 50 micro-gals

REVISIT EVERY 3 TO 5 YEARS

FEDERAL BASE NETWORK

NGS FUNDEDNGS MARK MAINTENANCE

MINIMUM 100 KM STATION SPACINGA and B-ORDER HORIZONTAL ACCURACY

FIRST-ORDER CLASS II ORTHOMETRIC HEIGHTS or

SECOND-ORDER CLASS I ORTHOMETRIC HEIGHTSSECOND-ORDER CLASS I ELLIPSOIDAL HEIGHTS

REVISIT EVERY 3 TO 5 YEARS

FBN GPS ADJUSTMENT COMPLETED

FBN/CBN SURVEYS

GPS READJUSTMENT COMPLETED

1999GPS1347

1998GPS1273

1997GPS1250

1998GPS1267 1998

GPS1264

1998

GPS1258

1999GPS1394

1999GPS1397

1997GPS1207

1999GPS1378

1999GPS1370

1999GPS1356

1998GPS1288

1998GPS1333

1998GPS1340

1999GPS1377

1999GPS1381

1999GPS1399

2000GPS1411

2001 GPS1629

2000 GPS1463

2000

GPS1462

2000 GPS1481

2000 GPS1492

2000 GPS1506

2000 GPS1514

2000 GPS1519

2000 GPS1530

2000 GPS1188

2001 GPS1712

2001GPS1554

2001GPS1641

2001 GPS1596

2002 GPS1686

2002 GPS1687

2002 GPS1731

2003 GPS1752

2003

GPS1825

2003 GPS1851

2003 GPS1753

2003 GPS 1850 MEANS

2003 GPS1682WILLIAMS

2003 GPS1726 2002

GPS-1547

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

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

NGS Map version

Old Datasheet format

Difference is:

DN = -0.644 (m)

DE = +0.712 (m)

DU = 1.195 (m)

IMPROVING POSITIONAL ACCURACY

TIME NETWORK LOCALNETWORK 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 (1.0 ppm) A-order (0.1 ppm)

CORS 1996 - 0.01 meter 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?

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

http://tsrc.cbi.tamucc.edu/THM/HomePage

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

http://www.csr.utexas.edu/grace/

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 FUNDEDSTATE/LOCAL MARK MAINTENANCE

25 TO 30 KM STATION SPACINGB-ORDER HORIZONTAL ACCURACY

THIRD-ORDER CLASS I ORTHOMETRIC HEIGHTTHIRD-ORDER CLASS I ELLIPSOIDAL HEIGHT

REVISIT AS NEEDED

USER DENSIFICATION NETWORK

STATE/LOCAL FUNDEDSTATION 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.

PHASE I PLANNING - RECONPHASE I OBSERVEDPHASE I PROCESSEDPHASE II OBSERVEDPHASE II PROCESSEDPHASE II RELEASEDPHASE III PLANNEDPHASE III PHOTOPHASE III OBSERVEDPHASE III PROCESSEDPHASE III RELEASED

ANA STATUS 10/31/2004

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 69117 stations

TRASH

Projects Not Recommended for Inclusion Currently 149 Projects with 9903 stations

Many Third Order FAA Projects from 1980’sSome Projects that have no ties to the NetworkOriginal TN HARN (Macrometer Data in 1990) Original Eastern Strain Network Project

Texas Projects eliminated

• 17407• GPS078• GPS088• GPS1138• GPS1170/4• GPS146• GPS158• GPS288• GPS304• GPS407

GPS482GPS577GPS577/DGPS582GPS584GPS586GPS849/193

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 2007.0 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 3

HB 4

HB 5

HB8HB 9

HB16HB 17

FLGA AL MS

HB 18

NC SC

HB 19

HB 32

HB 33

HB10

HB11

HB 20

HB 21

HB 22

HB 23

HB 6

HB 7

HB 12

HB 13

HB 24

HB 25

HB 26

HB 27

HB 14

HB15

HB28

HB 29

HB 30

HB 31

HB 34

HB 35

HB 36

HB 37

HB 38

HB 39

HB 40

HB 41

HB 42

HB 43

HB 44

HB 45

HB 46

HB 47

HB 48

HB 49

HB 50

HB 51

OR WA CA AK PR VQ

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

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

(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• 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 (ATA)-1

X = ATWA-1*ATWL

V = A*X-L

σ2 = (VTWV)/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 = 851,073No. of constrained parameters = 2055No. of unknown parameters = 203,076Degrees 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 = 0.70

2400 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.

www.ngs.noaa.gov/NationalReadjustment

http://www.ngs.noaa.gov/NationalReadjustment/StatusReports/Statistics.final/NewBB/tx.newbb.txt

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

http://www.unavco.org/research_science/workinggroups_projects/snarf/snarf.html

Velocities in ITRF

Vertical velocities dominated by GIA

We celebrated our 200th 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:

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

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?