Improvements to the National Spatial Reference System

Marti Ikehara: marti.ikehara@noaa.govCalifornia 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• ..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• Definition starts with a global RF: ITRF##• No fixed tectonic plate results in velocities

Rationale (cont)• NSRS’s global frame was ITRF00 epoch 1997.00.

Projecting 13 yrs was 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• “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

Geodetic Reference Framespast and present

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Relative vs. Absolute GNSS Antenna CalibrationRELATIVE

Variations were compared to AOA antenna as ‘standard’PCV was only related to vertical variations

Corbin, VA

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

observables

Relative vs. Absolute GNSS Antenna CalibrationABSOLUTE

NGS Calibrations compared to IGS type mean

Mm

L1 PCV’s

http://www.ngs.noaa.gov/ANTCALAzimuthal, as well as elevation, differences

So, what’s different about the CORS coordinates?

• Change to absolute antenna calibrations– Use absolute cal. in youryour 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?• Individual CORS Coordinate page, as before• On CORS page, Data Products, Coordinates

Explained, Table 1, left column hotlinkshttp://www.ngs.noaa.gov/CORS/coords.shtml• 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 AND lat/long/ht (N,E,U)

• Recommend using only CORS w/ computed velocities

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:http://www.dot.ca.gov/hq/row/landsurveys/geodetic/geodetic_control.html

• 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

• Q. You’ve been saying NGS has adopted “IGS08” as the basis of the current realization; why not “ITRF08”?

A. 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

YOUR QUESTIONS??• Q. What is the magnitude of the changes?A1. at the same epoch, so just changes in ‘base’ RFA2. from previous official epoch to current epoch

Marti-Answered Questions (MAQ)

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:http://www.ngs.noaa.gov/CORS/coord_info/myear_FAQ.shtmlFor CA: Northern, Central, Southern groupings

QUESTIONS?TIP: Lots of useful info found by navigating here:Data Products, CORS Coordinates EXPLAINEDEg, access to ALL 60-day and Long term plots

and now on to PASSIVE STATIONS

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

• 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

• 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?

• 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

• 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• Surveys tab, near bottom, National Adjustment or

Quick link in left column, main page. FAQ page:

http://www.ngs.noaa.gov/web/surveys/NA2011/NA2011_FAQ.shtml

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• 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

Second news story; won’t migrate for awhileCan sign up for announcements (news subscription service) via emails; not an RSS;Front page, bottom Right column

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• http://www.ngs.noaa.gov/web/surveys/

datasheet/AC6803_htmod.pdf

DSWorld: mapping tool and more• Need to have Google Earth installed• Tools, Download PC Software, USER-CONTRI-

BUTED SOFTWARE, DSWorld• http://www.ngs.noaa.gov/• 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

Demonstration

MappingCounty example, Toggle between V & V-88onlyCORS: Tools/Options/4char; OPUS-DBAll NGSIDB: color represents CONDITION

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

Marti.ikehara@noaa.gov