Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | SNARF Ver 2.0 Construction: Current Status Thomas Herring, Department of Earth Atmospheric and Planetary Sciences, MIT Cambridge, MA

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | Overview Analysis of GPS solutions submitted for SNARF Version 2.0 –Initial Vers 2.0 generated using stations which appear in at least two analyses. –There are 465 total sites, 283 unique locations. –Height rate sigmas: 222 sites < 5 mm/yr; 213 < 4 ; 200 < 3 ; 167 < 2 and 59 < 1 mm/yr Motions in the SNARF realization. Iteration now needed to generate GIA model for use in final alignment. 10/25/2015SNARF TAH2

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | 10/25/2015SNARF TAH3 Submissions to SNARF Ver 2.0 Code AC File Stat UStat Rew CBN CBN/NRCAN CBN06P30v4uc.snx NAR NAREF/NRCAN NAR06P44v6uc.snx PUR EC/Purdue calais_nov06.snx UAF JF/UAF UAF_SNARF.stacov UNR GB/UNR UNR_SNARF_0208.stacv Stat -- number of stations in solution. Multiple entries for stations with breaks. Ustat -- number of unique stations Rew -- Multiplier of covariance matrix to make velocity sigmas realistic. Reweighting factors were determined from the square root of chi^2-per-degree of freedom (normalized root mean square scatter, NRMS) of the differences between the velocity estimates and IGS05 North America reference stations

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | Analysis Method Each center is converted from SINEX or STACOV to Globk binary format. Centers which have frame constrained have ±10 mas and ±1 m rotation and translation covariance added. Variance scaling factors are determined by velocity RMS fit to IGS05. During combination of results, rotations, translation and scale values and rates are estimated. At end of combination, reference frame is realized by rotation/translation and scale onto reference system (could be SNARF V 1.0 GIA, IGS05 or SNARF V 2.0 (for comparing analysis center results). In current combination, UAF analysis is not used due to numerical stability problems. Final version of SNARF will use a GIA model derived from preliminary version. Velocities at collated sites are equated. 10/25/2015SNARF TAH4

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | 10/25/2015SNARF TAH5 RMS Velocity difference between contributions and combined Ver. 2.0 Code # WRMS (mm/yr) V02 NRMS V02 N E U N E U CBN NAR PUR UAF UNR The reweighting coefficients were set to make the average NRMS from the IGS05 comparison be approximately unity. All sites here should appear in at least 2 analyses but not always with equal sigmas.

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | 10/25/2015SNARF TAH6 RMS Position differences between analyses and SNARF Ver 2.0 Code # WRMS (mm) NRMS N E U N E U CBN NAR PUR UAF UNR There is variability here possibly due to antenna height problems. 76 site renames were needed. Positions do not agree as well as velocities in general.

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | SNARF Ver 1.0 GIA Model 10/25/2015SNARF TAH7

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | SNARF Version 2.0 Preliminary Figures that follow show vertical and horizontal motions for SNARF Ver. 2.0 and the contributing solutions. In these figures, all sites with vertical rate sigmas < 6.5 mm/yr are shown and sigmas are used to weight the vertical interpolations Sites with horizontal velocity sigmas less than 1.0 mm/yr are shown with 95% confidence ellipses. 10/25/2015SNARF TAH8

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | Preliminary Version 2.0 aligned with SNARF Ver 1.0 GIA Model 10/25/2015SNARF TAH9

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | Velocities aligned with IGS05 10/25/2015SNARF TAH10

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | CNB contribution 10/25/2015SNARF TAH11

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | NAR contribution 10/25/2015SNARF TAH12

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | PUR contribution 10/25/2015SNARF TAH13

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | UAF contribution 10/25/2015SNARF TAH14

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | UNR Contribution 10/25/2015SNARF TAH15

Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F | 10/25/2015SNARF TAH16 Summary With height errors accounted for, rigorous combination of analyses is possible (except UAF). 47 sites have significant height errors and there could be problems at other sites. Noise models could be improved. There are large variance re-scaling factors which compensate from correlated noise at stations. Development of site specific noise models would improve the overall reliability of the final solution New model needs to be incorporated into the GIA ensemble model for the final frame alignment. Consistency of horizontal and vertical motions could be a problem. Numerical stability problems when UAF analysis is included which needs to be resolved. Some small remaining editing of sites needed. Results so far are all pre-absolute phase center models and so frame will need to re-done when IGS re-processing is complete.