improvements to the national spatial reference system
DESCRIPTION
Improvements to the National Spatial Reference System. Marti Ikehara : [email protected] 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 - PowerPoint PPT PresentationTRANSCRIPT
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Improvements to the National Spatial Reference System
Marti Ikehara: [email protected] Geodetic Advisor
CLSA Webinar, 11/30/11
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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
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Rationale for Updating the NSRS• Definition starts with a global RF: ITRF##• No fixed tectonic plate results in velocities
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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
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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
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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
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rotation introduces angle changes for time difference of single difference (TDSD) phase
observables
Relative vs. Absolute GNSS Antenna CalibrationABSOLUTE
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NGS Calibrations compared to IGS type mean
Mm
L1 PCV’s
http://www.ngs.noaa.gov/ANTCALAzimuthal, as well as elevation, differences
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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
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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
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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
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• 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)
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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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
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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
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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
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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