1. PBO Frame Definition using SNARF Version 1.0 Tom Herring MIT

2. 11/16/2006SNARF 11/062 Construction of SNARF V1.0 Solution based on: –CBN_cumu_r98_v0.snx CBN input sinex file –NAR_cumu_r02_v0.snx NAR input sinex file –XVSOLFIN.SNX PUR input sinex file Sites used in at least two of these files carried forward GIA Model: snarf_NCP_gia_model.apr from J. Davis C program 77 sites used to align with the gia model velocities. SNARF V1.0 has additional 35 sites.

3. 11/16/2006SNARF 11/063 Sites in SNARF V00 77 Red sites used to align to GIA model (based on quality of time series) 35 additional sites that can be used for realization

4. 11/16/2006SNARF 11/064 Statistics of V1.0 WRMS differences (78 sites): from –GIA E 0.77 N 0.49 U 1.61 mm/yr –Zero E 0.74 N 0.61 U 2.71 mm/yr Square root chi2/f of differences –GIA E 3.27 N 2.34 U 2.51 –Zero E 3.12 N 2.93 U 4.17 Implication is that GIA model improves north and height fits but not east. Given locations of SNARF reference sites little GIA signal in east.

5. 11/16/2006SNARF 11/065 PBO SNARF Realization Velocity solution created with combined PBO results for Jan 2004-September 2006 (GPS Week 1392). Rotated, translated and scaled onto SNARF V1.0 using IGS core sites in North America: RMS Fits to 19 sites (includes Hawaii sites): E 0.60 N 0.69 U 2.15 mm/yr Similar RMS when all over lapping sites are used. From this frame 258 sites used daily to realize the PBO frame. Updates to PBO frame definition yearly, new sites added every quarter.

6. 11/16/2006SNARF 11/066 PBO and SNARF sites Red: PBO Blue: SNARF Currently not much overlap in mid- continent/East coast area. This will improve as PBO is fully deployed

7. 11/16/2006SNARF 11/067 PBO/SNARF Issues Some sites do not agree well (e.g., INVK is subsiding rapidly in SNARF and uplifting in PBO (-12 versus +2 ±2 mm/yr). Scale and scale rate between the CWU and NMT PBO solutions are quite different. Expected because of differences in satellite antenna offsets. Problem should be resolved with new IGS absolute phase center models. (Implemented in GAMIT, still some issues in GYPSY). In PBO alignment, Hawaii sites and Russian site (BILI) are used; ideally SNARF will include non-North American sites.