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Improvements to the National Spatial Reference System. Marti Ikehara : California Geodetic Advisor CLSA Webinar, 11/30/11. Topics. New Coordinates and Epoch for CORS (done) Consequent Adjustment of 80K Passive Stations Subsequent Development of GEOID12

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improvements to the national spatial reference system

Improvements to the National Spatial Reference System

Marti Ikehara:

California Geodetic Advisor

CLSA Webinar, 11/30/11

  • New Coordinates and Epoch for CORS (done)
  • Consequent Adjustment of 80K Passive Stations
  • Subsequent Development of GEOID12
  • ..and a new Datasheet format to show you
  • DSWorld: viewing control in Google Earth, and multiple ‘reports’ submission tools
  • Free-for-all—any topic-- Q/A
rationale for updating the nsrs
Rationale for Updating the NSRS
  • Definition starts with a global RF: ITRF##
  • No fixed tectonic plate results in velocities
rationale cont
Rationale (cont)
  • NSRS’s global frame was ITRF00 epoch 1997.00. Projecting 13 yrswas unrealistic because of velocities; NAD 83(CORS96) epoch 2002.00 projecting 8 yrs was becoming a problem
  • Coordinates and velocities were a mixture from last reprocessing (1994-2002) and adjustments using 8 to 3 IGS ref. sites
  • Mixture of Computed and HTDP velocities
  • Assumed NAD83 vertical vel. = 0 mm/yr
  • Change fr Relative to Absolute antenna phase center values in ITRF definition
  • Metadata issues, eg, discontinuities/offsets
  • Significant software changes since 2002
multi year cors solution mycs
Multi-year CORS Solution: MYCS
  • “Multiyear” effort began 6 years ago
  • IGS proposed re-processing all data to re-compute station coordinates, orbits, and EOPs (earth orientation parameters) fr 1994-present
  • NGS began with a revision of PAGES software and processing strategy driven by weak NGS orbit contributions to IGS
  • 860 weekly (full history) CORS+ ~230 global SINEX files containing X,Y,Z positions and full variance-covariance information
  • Coordinates published (online) on Sept 6, 2011

Relative vs. Absolute GNSS Antenna Calibration


Corbin, VA

Variations were compared to AOA antenna as ‘standard’

PCV was only related to vertical variations

rotation introduces angle changes for time difference of single difference tdsd phase observables
rotation introduces angle changes for time difference of single difference (TDSD) phase observables

Relative vs. Absolute GNSS Antenna Calibration


ngs calibrations compared to igs type mean
NGS Calibrations compared to IGS type mean

L1 PCV’s

Azimuthal, as well as elevation, differences


so what s different about the cors coordinates
So, what’s different about the CORS coordinates?
  • Change to absolute antenna calibrations
    • Use absolute cal. in your processing: DON’T MIX!
  • Better because 8 more years of:
    • International CGPS sites
    • CORS data: about 1600 total, ~1000 w/ >2.5 yrs
    • Orbit determination sophistication
    • CORS velocity data
  • Better HTDP modeling for those w/ <2.5 yrs
  • Better processing algorithms
how do i find the coordinates
How do I find the coordinates?
  • Individual CORS Coordinate page, as before
  • On CORS page, Data Products, Coordinates Explained, Table 1, left column hotlinks

  • TWO basic divisions:
    • One with COMPUTED velocities, one MODELED
  • TWO basic Ref Frames: IGS08, NAD83
  • Two types of coordinates/vel for each of those:
    • X,Y,Z ANDlat/long/ht (N,E,U)
  • Recommend using only CORS w/ computed velocities
lists of cors
Lists of CORS
  • Tables on webpage are ASCII because others have scripts that read those lists
  • I made spreadsheets of the lists and sorted by state; intend to post them to CGAR website:

  • Culled Decommissioned, separate worksheet
  • Next sort is by Operational or Non-Op (next slide)
  • Besides daily monitoring, stacking/computation to be done perhaps bimonthly; status updated
  • Show spreadsheets
marti answered questions maq
Marti-Answered Questions (MAQ)
  • Q. You’ve been saying NGS has adopted “IGS08” as the basis of the current realization; why not “ITRF08”?
  • NGS realized that, because the NSRS is defined by GPS ‘observations’ at CORS but not using the other space-based techniques, the RF name should not be ITRF##.
  • Q. What is the criteria for publishing new coordinates?

A. 2cm H, 4cm V, but if 1 changes, both are re-done


  • Q. What is the magnitude of the changes?

A1. at the same epoch, so just changes in ‘base’ RF

A2. from previous official epoch to current epoch

notes about velocities
Notes about velocities
  • Pacific plate: at 5cm/yr (right at the San Andreas fault), in 20 years, that’s 100cm or 1m!
  • In 8 yrs, those NW arrows’ max is ~40cm
  • Sites experiencing significant vertical crustal motion may also shift horizontally
  • MYCS FAQ #6 provides plots of State-scale changes:

For CA: Northern, Central, Southern groupings



TIP: Lots of useful info found by navigating here:

Data Products, CORS Coordinates EXPLAINED

Eg, access to ALL 60-day and Long term plots

and now on to PASSIVE STATIONS

a cryptic evolution of nad 83
A Cryptic Evolution of NAD 83
  • Original realization completed in 1986
    • Consisted (almost) entirely of classical (optical) observations
  • “High Precision Geodetic Network” (HPGN) and “High Accuracy Reference Network” (HARN) realizations
    • Most done in 1990s, essentially state-by-state
    • Based on GPS data but classical stations included in adjustments
    • Did NOT use CORS as constraints
  • Partial HARN/FBN Obs, late 1990’s
    • Used CORS as control, but not statewide adjustment; in CA, only ~200 stns
  • National Re-Adjustment of 2007
    • ITRF00 and NAD 83(CORS96) basis for CORS constraints and (NSRS2007) for passive
    • Simultaneous nationwide adjustment, first since 1986; no classical stations
need for a new national adjustment na2011 project for passive geodetic stations
NEED for a new national adjustment, NA2011 project, for passive geodetic stations
  • Optimally align passive control with CORS
  • >1000 projects submitted since 2007 NatlReadj
    • Number of stations increased by 1/3 in just 5 years!
    • Plus Observations for Hawaii & other Pacific islands
  • More consistent results in tectonically active areas
    • Longer time series for CORS as well as
    • More current data for passive, and better tectonic modeling
benefits of a new national adjustment for passive geodetic stations
Benefits of a new national adjustment for passive geodetic stations
  • Network and local accuracies on stations
    • Including future submitted projects
    • But not for excluded (rejected) stations
  • Better computations and analysis techniques
    • Improved outlier detection
    • Incorporation of lessons learned from previous national adjustment
what are some of the checking and cleaning techniques and processing
What are some of the checking and cleaning techniques and processing?
  • Unexclude previous no-check stations if new data came in
  • Exclude no-check stations
  • Exclude PIDs for L1PC when antenna replaced at a CORS
  • Caution in subsidence areas because no model for vertical velocity; disclude earlier project(s) or obs when multiple obs made
current status of na2011 mid nov 2011
Current status of NA2011, mid-Nov 2011
  • Cutoff date for projects was Sept 2011
  • Minimal constraint adjs have run successfully
  • 4152 projects and 79,107 stations; includes 954 CORS w/ >2.5 yrs data
  • 371,962 enabled vectors (+42,493 rejected = 414,455 total vectors)
  • Standard error of unit weight = 1.26
  • Starting constrained adjustments, using errors from CORS solution (not ‘perfect’, not 0 error)
detailed info about na2011 on website
Detailed info about NA2011 on website
  • Surveys tab, near bottom, National Adjustment or Quick link in left column, main page. FAQ page:

next steps 2012
Next steps, 2012
  • NA2011 Adjustment thought to be completed, fully published in/by February
  • Testing network accuracy calcs for subsequent submitted projects and database procedures
  • Until NA2011 Adjustment is complete and ready to be published:
    • OPUS solutions will continue to produce coordinates in both former and current ref frames
    • New DS format will not go into effect
    • Next Geoid model cannot be finalized
geoid12 development
GEOID12 Development
  • Model will be based on ellipsoid heights published from NA2011 project
  • Proposed stations, different than for GEOID09, for inclusion/exclusion just distributed to geodetic advisors for review
  • Currently being developed using preliminary NA2011 “results”
  • NOTE: Two months after GEOID12 released, project submissions must use NAD83(2011)

QUESTIONS? then Datasheet format changes

updating the datasheet format
Updating the DataSheet Format

Second news story; won’t migrate for awhile

Can sign up for announcements (news subscription service) via emails; not an RSS;

Front page, bottom Right column

change highlights
Change highlights
  • Better grouping of geometric elements, eg, ellipsoid height and epoch date
  • CLARITY about geoid model usage, including for superceded ortho height data
  • Note: earlier this year, NGS started publishing superceded GPS-derived ortho heights
  • Inclusion (hyperlink) to Local Ties & Accuracies
dsworld mapping tool and more
DSWorld: mapping tool and more
  • Need to have Google Earth installed
  • Tools, Download PC Software, USER-CONTRI-BUTED SOFTWARE, DSWorld
  • FIRST: Tools, Update program to 4.10.16
  • Enhancement enables you to distinguish VERTCON NAVD88 from other(control) NAVD88
  • (My) firewall settings preclude easy updates


County example, Toggle between V & V-88only

CORS: Tools/Options/4char; OPUS-DB

All NGSIDB: color represents CONDITION


Recovery Notes, incl Destroyed; Photo Naming Convention, Editing Tools; Correct County, Photo