Reference Frame Theory and Practice Kristine Larson University of Colorado

Reference Frame Theory and Practice I’m only going to talk about practice, with an emphasis on education & outreach! There is a strong need for continued education about the reference frame, i.e SNARF. With PBO, there will be more users than ever - users without a geodetic background.

Lessons learned from ITRF2000 Frame should be developed by a broad group (which this committee represents). Multiple groups from multiple techniques (SLR, VLBI, DORIS, GPS) all contributed solutions. Evaluation of outlier sites important - and time consuming. Multiple software analyses and comparisons are key.

Lessons learned from ITRF2000 ITRF2000 had limitations because we needed contributions from SLR and VLBI which had long time histories at non-optimal sites. Altamimi et al. published ITRF2000 in JGR. Frame station positions and velocities available by anonymous ftp. The ITRF2000 group wrote a general article about reference frames for EOS.

Lessons learned from ITRF2000 When all is said and done, almost all GPS users end up realizing ITRF2000 from the IGS orbits. So realizing the frame becomes linked to the issue of making sure users implement the IGS orbits (and antenna eccentricities) in their softwares correctly. SNARF is a different kind of frame, but we need to consider how users will implement it.

Lessons learned from ITRF2000 Models (e.g. ocean loading, phase centers) used in computing solutions should be as consistent as possible. The ITRF2000 group did not provide software to help users implement and translate between different frames. We should do this.

Lessons learned as GRL editor Many people trying to use GPS to study tectonic problems do not understand the frame they are using (which can be ok if the software properly uses the IGS orbits and the IGS doesn’t change their frame!). Nevertheless, many users fail to properly describe their frame, making it impossible to properly assess their results.

Lessons learned as GRL editor Linking PBO products (SNARF) to past frames will facilitate comparisons that users will want to make for their research projects. I routinely force authors to use a proper (refereed journal article) reference to describe their frame. Thus, I believe we are obligated to publish SNARF in a journal.

How do we reach people? Technical descriptions of the frame are, of course, required. But (I think) there needs to be a parallel effort to summarize the frame (SNARF) for non- geodesists. Something like the “GIPSY cartoon book” that Gregorius wrote. Another forum for this information would be an on-line format.

Different Users Users (1) of PBO products which will depend on SNARF. Users (2) of SNARF that continue to analyze data with GAMIT, GIPSY, NGS, Bernese softwares.

Reference Frames for Dummies Excellent websites describing reference frame concepts already exist (I’m thinking of the NGS website). But, I often wonder if the reason I think they are good is because I already understand what they are trying to say. We need non-experts to “test-drive” our education efforts.

Now that I know I’m summarizing station selection criteria ;-) What are we using as our basis for monument descriptions? Are we content with what is available on-line?