Standardizing Reference Frame Terms in Heliophysics

Standardizing Reference Frame Terms in Heliophysics We describe an effort by IVOA and Heliophysics representatives to develop a standard for reference frames and reference system terms. The objective of this effort is to provide a proposal for additions to the existing IVOA standard for reference frames. Bob Weigel, Baptiste Cecconi, Brian Thomas, Bobby Candey, Rebecca Ringuette, Albert Shih, Scott Turner, Grant Stephens, Ivar Christopher, and Steven Petrinec Small NASA/HDRL-supported IHDEA working group project; started in October 2023. Result of HDRL Conclave break-out session in January, 2023. Space Time Coordinate Transform (STCT) Standards Working Group ○Meeting Notes ○Email list: https://groups.io/g/hdrl-stct/ ○Contact [email protected] for bi-weekly (Thursday @ noon) telecon invite Background Background IVOA has Reference Frames Many other similar lists exist: ●SPASE ●TREPS ●Papers Background Primary objective 1. Develop a standard (IVOA chosen) for reference frames and reference system terms. Draft at tinyurl.com/stct-ivoa This is needed and will be useful, but impediments will still exist for widespread adoption including the need for it to enable reproducibility. Secondary objective: 2. Address these impediments. Recommendations given in JGR paper to be submitted in November: tinyurl/stct-draft. Feedback welcome. Why IVOA instead of SPASE SPASE has CoordinateSystem with children of CoordinateRepresentation (e.g., Cartesian, Spherical) and CoordinateSystemName (e.g., GSE, GSM). Stand-alone IVOA standard has advantages ●SPASE version can change but CoordinateSystem part does not ●Easier to reference in other standards (in HAPI, we want to point to a external standard for interpretation of a reference frame acronym; avoids pointing to the full SPASE schema when only a small part is needed.) IVOA has other advantages ●Will help in bridging two communities (Heliophysics and Astronomy) ●Many existing tools understand IVOA metadata (e.g., Astropy, VOTables) Primary Objective Challenges Many challenges for developing a standard. ●Ambiguous terminology: ○“Coordinate System” used in Heliophysics. “Reference System” and “Reference Frame” used in SPICE, Astronomy, and Earth Science. ○GCI, GEI, GEI2000, J2000 all could mean the same thing (or not). Similar issues with other reference systems (e.g., MAG, etc.) ●Reference Frames (implementations of reference systems) are needed for reproducibility (e.g., ICRS = reference system; ICRF1, 2, 3 = reference frame). ●Long history of usage of some terms in Heliophysics. ●Historical assumption is that differences in implementations are not significant relative to measurement uncertainty. Examples on “Historical Assumption” What follows is not a criticism of data providers They are providing results consistent with historical assumption Examples on “Historical Assumption” Geotail location from SSCWeb and CDAWeb MMS-2 location from SSCWeb and JPL/Horizons (JPL is using SPICE kernel that does not account for maneuvers.) ExamplesExamples on “Historical Assumption”