RNAAC combinations in the IGS

RNAAC combinations in the IGS Thomas Herring, tah@mit.edu, Department of Earth Atmospheric and Planetary Sciences, MIT

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. IGS ACWS TAH RNAAC

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 Ferland’s official combination). All sites included. • RNAAC is regional solutions combined with GNAAC solution. IGS ACWS TAH RNAAC

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. IGS ACWS TAH RNAAC

Certain areas are still not be densified. RNAAC Stations (Red), GNAAC (Black) IGS ACWS TAH RNAAC

Number of sites in solutions IGS ACWS TAH RNAAC

RMS of change in global sites when RNAAC solutions added RNAAC Impact IGS ACWS TAH RNAAC

Figure also shows recent lose of contributing solutions Recent impact (post week 1400) IGS ACWS TAH RNAAC

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 ftp’d 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. PBO seminar

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@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. PBO seminar

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. PBO seminar

WRMS daily scatter: PBO Sites Daily RMS Scatters Combined solution for PBO Sites Median North 1.1 mmMedian East 1.4 mmMedian Height 3.9 mm Results from 2004 to present Linear trends removed. Total 691 sites PBO seminar

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 IGS ACWS TAH RNAAC

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 IGS ACWS TAH RNAAC

RMS scatters for Nucleus sites (purple) and PBO sites (yellow), RMS scatter > 3 mm (black, 1mm).Red circle shows 1 mm RMS scatter PBO seminar

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. IGS ACWS TAH RNAAC

RNAAC combinations in the IGS