National Readjustment

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National Readjustment

• DALE PURSELL
• ACSM
• 2006

2
NATIONAL READJUSTMENT

• WHAT?
• WHY
• HOW
• WHEN
• POST
• QUESTIONS

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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) 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

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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.

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NATIONAL GEODETIC SURVEY

• WEB SITE
• http//www.ngs.noaa.gov

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NATIONAL READJUSTMENT

• WHAT
• WHY?
• HOW
• WHEN
• POST
• QUESTIONS

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The NAD83(86) Adjustment Team
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NAD83(86) DOPPLER STATIONS
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COMPARISON OF DATUM ELEMENTS

• NAD 27
  NAD 83
• ELLIPSOID CLARKE 1866
  GRS80
• a6,378,206.4 m
  a6,378,137 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

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NAD 27 and NAD 83
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Results of NAD83(86)

• Network Accuracy - 1 Meter
• Local Accuracy First-Order
• (1 part in 100,000)

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NAD 83(86) NETWORK PROBLEMS

• Not GPSABLE
• POOR STATION ACCESSIBILITY
• IRREGULARLY SPACED
• POSITIONAL ACCURACY

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HIGH ACCURACY REFERENCE NETWORKS

• GPSABLE
• Clear Horizons for Satellite Signal Acquisition
• EASY ACCESSIBILITY
• Few Special Vehicle or Property Entrance
  Requirements
• REGULARLY SPACED
• Always within 20-100 Km
• HIGH HORIZONTAL ACCURACY
• A-Order (5 mm 110,000,000)
• B-Order (8mm 11,000,000)

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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)

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HIGH ACCURACY REFERENCE NETWORK
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NETWORK STATUS
HARN STATEWIDE
1991
GPS222
1996
1992
1996
1991
GPS1048
GPS341
1991
GPS197
1996
GPS805
reos 7/96
GP S291
1993
1994
reos-1996
GPS941
GPS1047

reobs 9/97
1996
GPS730
1995
1994
GPS606
1992
1995
GPS1121
1997
1997
GPS887
GPS404
1994
GPS394
1991
GPS882
GPS260
GPS
GPS1178
1997
1997
1995
1993
1200

GPS633
1992
GPS908
1992
1993
GPS1150
GPS1179
GPS610
reos-6/95-GPS904

GPS412
GPS611
GPS419
1992
1995
1990
-GPS120
1997
GPS852
GPS376
1993
GPS1133

1993
1992
1994
GPS725
GPS366
GPS721
1992
GPS585

1990
1992
GPS383
reos 1/96 GPS936
-GPS170
GPS450
1993
GPS667
1997
.
GPS CLASSICAL ADJUSTMENTS COMPLETED

GPS ADJUSTMENT COMPLETED
GPS577
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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

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FBN/CBN Surveys

• Current Status
• Observations complete for 48 contiguous states
  and the District of Columbia
• Additional major surveys in Alabama (reductions
  underway), California and Minnesota will be
  included-perhaps others
• West Virginia still needs to be reprocessed
  (Leica SR399 antennas) possibly other states or
  portions of states (study underway)

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Statewide GPS Readjustments

• Complete (or unnecessary) for 43 of 48 States,
  DC, PR
• Readjustment of EHs and/or Positions (5cm
  tolerance)
• Layered Adjustment Approach Used
• States not Completed
• CA-Requires special analysis-underway
• MO, TN, KY-not started (4/18/05)
• OH underway (4/18/2005)

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FBN/CBN SURVEYS
1998
GPS1340
2000

2002
1999
GPS1492

2001
GPS1686
GPS1394

GPS1641

2000
1998
GPS1506
GPS1333

2002
1999
1997
2000
GPS1687

2001
1999
GPS1377
GPS1207

2001
GPS1514
GPS1596
GPS1397
GPS1712

2003

2000
2000
GPS1752
1999

2000
2003
GPS1481

2003
GPS1463

2002
1999
GPS1519
GPS1356
GPS
GPS1731
GPS1825
GPS1370
1850

2001


2000
2000
MEANS
GPS1629

2003

2000

2003

GPS1462
1998
GPS1530
GPS1188
GPS1851
2002
GPS1726
GPS1288
GPS-1547
1999

2001
2003 GPS1753
1999
2000
1999
GPS1399
GPS1554
GPS1347
GPS1411

GPS1381
1997
1998
GPS1250
1998
GPS1273
1998
GPS1258
1998
GPS1267
GPS1264
1999
GPS1378

2003
GPS READJUSTMENT COMPLETED
GPS1682
WILLIAMS
FBN GPS ADJUSTMENT COMPLETED
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http//www.ngs.noaa.gov/PROJECTS/FBN/
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http//www.ngs.noaa.gov/PROJECTS/FBN/
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IMPROVING POSITIONAL ACCURACY

• TIME NETWORK LOCAL
• NETWORK 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

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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.

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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

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NATIONAL READJUSTMENT

• WHAT
• WHY
• HOW?
• WHEN
• POST
• QUESTIONS

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NGS Adjustment Team (1986)
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NAD 83 READJUSTMENT

• ONLY GPS DATA WILL BE USED
• CONTINUOUSLY OPERATING REFERENCE STATIONS
• FEDERAL BASE NETWORK
• COOPERATIVE BASE NETWORK
• USER DENSIFICATION NETWORK
• AIRPORT SURVEYS

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NAD 83 READJUSTMENT

• 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

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USER DENSIFICATION NETWORK

• STATE/LOCAL FUNDED
• STATION SPACING AS REQUIRED
• GPS OBSERVATIONS ONLY (HORIZONTAL)
• FIRST-ORDER HORIZONTAL ACCURACY
• REVISIT AS NEEDED

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AIRPORT SURVEYS
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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.

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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

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TRASH

• Projects Not Recommended for Inclusion
• Currently 149 Projects with 9903 stations
• Many Third Order FAA Projects from 1980s
• Some Projects that have no ties to the Network
• Original TN HARN (Macrometer Data)
• Original Eastern Strain Network Project

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The National Readjustment More Comments

• Computation and database loading of scale factors
  for each project is underway.
• Statewide GPS Readjustments are providing extra
  information about the network on a state by state
  basis.

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Concept of Operation

• Modified ADJUST, GPSCOM, LLSOLV software will be
  used plus new residual analysis software
• Helmert Blocking strategy will be used.
• Coordinates Produced and Published for both NAD83
  (NSRS) and ITRF
• Adjustment in NAD83-Transformed to ITRF
• Canadian (Mexican?) Data Integrated at top layer
• Network and Local Accuracies also Produced

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Helmert Blocks

• CORS provides control at top block
• Canadian data
• Each state will comprise a separate block of data

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Helmert Blocking Strategy
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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

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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

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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

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ANTICIPATED SHIFTS

• Based on a preliminary adjustment of all FBNs to
  the published values.
• lt 5 cm. in the horizontal component with an
• average shift of 2.2 cm.
• lt 10 cm. in the vertical component with
• an average shift of 4.6 cm.

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NATIONAL READJUSTMENT

• WHAT
• WHY
• HOW
• WHEN?
• POST
• QUESTIONS

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Time-line for National Readjustment Positions
and Ellipsoid Heights

• All projects guaranteed to be included in the
  adjustment must be loaded in the database no
  later than 06/01/2005
• Projects submitted after 06/01/2005 will be
  accepted and loaded into the database but will
  not be included in the readjustment
• Anticipated completion by February 10, 2007
• Project Report
• 3 months-February, 2007 through May, 2007

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We will be celebrating our 200th anniversary on
February 10, 2007
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NATIONAL READJUSTMENT

• WHAT
• WHY
• HOW
• WHEN
• POST?
• QUESTIONS

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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.

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Post National Readjustment

• Areas outside the US may need to be readjusted
  (e.g. Hawaii, Puerto Rico, Pacific Islands).
• New adjustment procedures will be developed that
  incorporate local and network accuracies.
• A reference frame maintenance strategy (NAD83,
  ITRF, either or both) needs to be developed.
• Design and Publish new data sheets.

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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
• (http//www.ngs.noaa.gov/????

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OTHER ISSUES

• We will streamline the process of project
  acceptance and database loading
• Require that all projects (submitted after the
  June 1, 2005 deadline) be tied to CORS
• Accept/require more data in digital format-e.g..
  reports, logs
• Photographs???

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NATIONAL READJUSTMENT

• WHAT
• WHY
• HOW
• WHEN
• POST
• QUESTIONS?

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