NATIONAL READJUSTMENT

•WHAT

•WHY

•HOW

•WHEN

NAD83(NSRS)

NAD83(NSRS)

NAD27 to NAD83

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

NAD83(86) DOPPLER STATIONS

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

HARN

HIGH ACCURACY REFERENCE 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)

HIGH ACCURACY REFERENCE NETWORK

HARN 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(1995)

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

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

Adjustment Tags

• Different statewide adjustments • Different years (epochs)

• Needed to distinguish between adjustments so…..

• The Adjustment tag was created

• NAD83(1995)----NC’s original HARN adjustment

FEDERAL BASE NETWORK (FBN )

Reobserve the FBN to better connect the HARNs to the CORS-MINIMUM 100 KM STATION SPACING-2cm local horizontal accuracy-2cm ellipsoid heights

Also: observed concurrently -CBN Cooperative Base Network-User Densification Network

FBN GPS ADJUSTMENT COMPLETED

FBN/CBN SURVEYS

GPS READJUSTMENT COMPLETED

1999GPS1347

1998GPS1273

1997GPS1250

1998GPS1267 1998

GPS1264

1998GPS1258

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

Reasons for NEW 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.

What about Orthometric Heights?

No National Orthometric height Readjustment at this time

Ortho Control = NAVD 88 not the CORS Since no change in control most orthometric

elevations would not change significantly

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

NAD 83 READJUSTMENT

ONLY GPS DATA WILL BE USED

-CONTINUOUSLY OPERATING REFERENCE STATIONS-FEDERAL BASE NETWORK-COOPERATIVE BASE NETWORK-USER DENSIFICATION NETWORK-HARN-NGS AIRPORT SURVEYS

The National Readjustment General Comments

The CORS will provide the control Only GPS projects will participate 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 HARN stations.

The required free adjustment analysis of each GPS project that contributes to the National Spatial Reference System is complete.

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

Network Accuracy

Network accuracy of a control pointA 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

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

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

Important Facts

• DEADLINE for data submittal June 1, 2005• COMPLETION DATE – February 10, 2007• NEW DATUM TAG - NAD83(NSRS)

For the latest information- visit the national readjustment webpage at: (www.ngs.noaa.gov/NationalReadjustment/)

GEODETIC CONTROL DATA SHEET

Station Name Northing (m) Easting (m) Diff. Northing 83/86 – 83/95

Diff. Easting 83/86 – 83/95

Smithport 83/86

199354.569 665067.183

Smithport 83/95

199354.397 665067.513 0.172 (m) -0.330 m)

Smithport83/2001

0.013 (m) 0.013 (m)

0.010 (m)

Smithport83/NSRS

???< 0.010(m)

???< 0.010(m)

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

NC Constrained Horizontal residuals

NC Horz Constrained AdjustmentEllip HT residuals

The NAD83(86) Adjustment Team

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

NAD83(NSRS)