RNAAC combinations in the IGS

1
RNAAC combinations in the IGS

• Thomas Herring, tah_at_mit.edu,
• Department of Earth Atmospheric and Planetary
  Sciences, MIT

2
OVERVIEW

• Regional densification SINEX files generated
  since GPS week 860 (June 96). (Global SINEX
  since week 819 (September 95).
• Up to eight different regional analyses have been
  submitted ASI (Spain), AUS (Australia), GIA
  (Alaska), GSI (Japan), SIR (S. America), NAR
  (NAREF), EUR (EUREF), PGC (Canada)
• Analysis Procedure
• Comparison with PBO analysis mehod
• Future developments.

3
Procedures

• RNAAC solutions are run with a 4-week
  (originally), then 5-week and most recently
  6-week delay after generation of IGS final
  products (these lags have become a problem)
• Most common contributors have been EURef, SIRGAS
  and GSI. Recently on GSI coming in on time.
• Largest contributor was NAREF but they stopped
  after week 1400 due to phase-center model
  implementation.
• GNAAC is IGS AC combination (compared with Remi
  Ferlands official combination). All sites
  included.
• RNAAC is regional solutions combined with GNAAC
  solution.

4
Method

• Most recent (since week 1396).
• SINEX indicates that only loose constraints
  applied (GSI, EUR and SIR) so we add rotation and
  translation covariance to loosen solution
• Each center is combined with GNAAC solution and
  chi-squared/f of combined used to determine scale
  factor for covariance matrix. This method can
  have problems when only a small number of common
  stations. Rescaling factors are closer to unity
  than GNAAC solutions.
• RNAAC solutions are combined with GNAAC and
  system aligned to IGS05.
• RMS of change in the position of the stations in
  the GNAAC solution computed to see impact of
  RNAAC
• SINEX file of combined solution submitted to
  CDDIS with summary file.

5
RNAAC Stations (Red), GNAAC (Black)
Certain areas are still not be densified.
6
Number of sites in solutions
7
RNAAC Impact
RMS of change in global sites when RNAAC
solutions added
8
Recent impact (post week 1400)
Figure also shows recent lose of contributing
solutions
9
PBO GPS Data Analysis

• ACs (NMT and CWU) are routinely generating PBO
  GPS data products
• Rapid Sinex files 24 hour latency
• Final Sinex files 6-13 day latency, weekly run
  started after IGS final products become available
• Supplemental Sinex files 12-week latency, weekly
  run. Includes missed sites and a 3-4 tie sites
  from final runs to link network. Tests show
  performance similar to finals. Bias fixing not
  quite so good due typically to wider site
  spacing.
• Supplemental runs also add sites to original
  final submission (until re-processing generates
  new set of final runs).
• SINEX and RMS files ftpd to MIT
• Recently campaign processing (Bob Smith) added to
  processing first as an additional run similar to
  the supplemental runs and once caught up,
  included in the supplementals.
• Added USGS processing of SCIGN sites (SCEC
  funding). Results appear in combined product.

10
PBO Combination Analysis

• ACC
• Rotates, translates, and scales each AC to PBO
  SNARF reference frame check and correct meta
  data (when possible)
• Combine AC results and transforms combined
  product to PBO SNARF (Stable North America
  Reference Frame)
• Outlier checks and report generated that is
  emailed to pbo_acs_at_chandler.mit.edu
• SINEX and time-series files sent to UNAVCO via
  LDM
• The PBO realization of SNARF is updated about
  once-per-year Requires re-submission of all
  frame defined sinex files and time series files.
  Latest version 20070919173418. At 6-month
  intervals updates are made for new stations.
  (Reference frame sites are not updated in these
  incremental updates and thus the time series and
  SINEX do not need release.

11
PBO SNARF Reference Frame
Red IGS reference sites Yellow PBO/Nucleus
sites Here we align to IGS rather than merge with
GNAAC(Time scale difference PBO daily not
weekly).
254 sites used to estimate daily rotation,
translation and scale onto the North America
Frame. Outlier detection during estimation.
12
WRMS daily scatter PBO Sites
Results from 2004 to present Linear trends
removed. Total 691 sites

• Daily RMS Scatters Combined solution for PBO
  Sites
• Median North 1.1 mmMedian East 1.4
  mmMedian Height 3.9 mm

13
RNAAC Statistics
Results are for post-Week 1400 Total 352
sites (need at least 50 weeks)

• Weekly WRMS Scatters Regional solution
• Median North 1.5 mmMedian East 1.5
  mmMedian Height 5.9 mm

14
GNAAC Statistics
Results post week 1400 Total sites 275 (need at
least 50 weeks)

• Weekly WRMS Scatters Global solution
• Median North 1.2 mmMedian East 1.4
  mmMedian Height 4.1 mm

15
RMS scatters for Nucleus sites (purple) and PBO
sites (yellow), RMS scatter gt 3 mm (black,
1mm).Red circle shows 1 mm RMS scatter
16
Prospects

• Recently few RNAAC solutions being submitted.
  Maybe for regional centers access to IGS
  reference through orbits and local IGS stations
  is adequate.
• This procedure adopted by PBO and allows
  common-mode error to be reduced in regional time
  series.
• PBO generates and makes openly available SINEX
  files of solutions which can be merged with
  global GPS networks if desired.
• Maybe there is no need for IGS to generate weekly
  RNAAC solution (operators can do themselves)
• There is a need for availability of
  non-constrained SINEX files from regional
  analysis that can be merged for densification of
  ITRF.