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/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

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QUESTIONS

The NAD83(86) Adjustment Team

NAD83(86) DOPPLER STATIONS

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

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/

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

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 NETWORKCOOPERATIVE BASE NETWORK

USER DENSIFICATION NETWORKAIRPORT SURVEYS

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

REVISIT AS NEEDED

AIRPORT SURVEYS

Project Adjustment Analysis

3436 Projects Free 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 stationsMany Third Order FAA Projects from 1980’sSome Projects that have no ties to the NetworkOriginal 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 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 SHIFTSUSA 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 = 851073

No. of constrained parameters = 3

No. of unknown parameters = 203,076

Degrees 0f 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 0f Freedom = 650049

Standard error of unit weight = 1.375490

www.ngs.noaa.gov/NationalReadjustment

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 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(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 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 NAD83(NSRS 2007) data present here   Click here to get the re-adjusted NAD 83 (NSRS 2007) data in RDF format.

NATIONAL READJUSTMENT

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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 200th anniversary on February 10,

2007

NATIONAL READJUSTMENT

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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:

(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

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HOW

WHEN

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QUESTIONS?