National Readjustment

Dale PursellObservation and Analysis Division

National Geodetic Survey

FGCS Workgroup MeetingFebruary 14, 2007

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

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

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 part in 1 million)

A-order (1 part in 10 million)

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

NGS Adjustment Team (1986)NGS Adjustment Team (2005)

NAD 83 READJUSTMENT

ONLY GPS DATA WAS USED

CONTINUOUSLY OPERATING REFERENCE STATIONS

FEDERAL BASE NETWORKCOOPERATIVE BASE NETWORK

USER DENSIFICATION NETWORKAIRPORT SURVEYS

Project Adjustment Analysis

3436 ProjectsFree AdjustmentResidual Plot Outliers RejectedConnectivity to A/B Order Network

VerifiedSummary sheet with Project Information

Created67693 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 HPGN 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 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 provided control at the top blockCGPS coordinates were determined by Scripps’ Sector utility projected to the 2007.0 epoch.

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 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 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

(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

AVERAGE SHIFTS

• 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 will not be 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 = 851073No. of constrained parameters = 3No. of unknown parameters = 203,076Degrees 0f Freedom = 647997Standard error of unit weight = 1.276619

Constrained adjustment (486 National CORS and 195 CGPS sites)

No. of Observations = 851073No. of constrained parameters = 2055No. of unknown parameters = 203,076Degrees 0f Freedom = 650049Standard error of unit weight = 1.375490

www.ngs.noaa.gov/NationalReadjustment

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 will be accepted and loaded into the database but will not be included in the readjustment

Completed February 8, 2007 Project Report

6 months-February, 2007 through July, 2007

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.

Post National Readjustment

New adjustment procedures will be developed that incorporate local and network accuracies.

Design and Publish new data sheets.

Provide error ellipses for every station

A reference frame maintenance strategy (NAD83, ITRF, either or both) will be developed.

Important Facts

– COMPLETION DATE – February 08, 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