An Insight on Scale Definition in JTRF2020

JTRF2020 is the latest TRF solution computed at JPL by assimilating frame input data submitted by the IVS, IGS, ILRS, and IDS for ITRF2020. Determined with SREF (Square-root Reference frame Estimation Filter), a computational code based on a square-root information filter and Dyer-McReynolds smoother algorithm, JTRF2020 adopts a time-series based representation: Its daily time series determined from observations of a multi-technique space-geodetic network of 931 stations describe, through their Cartesian coordinates, the deformation of solid Earth as a function of time. Such coordinates are inherently expressed in Earth’s Center of Mass as sensed by SLR and give access to the quasi-instantaneous scale implied by the underlying frame.  JTRF2020, like its predecessor JTRF2014, traditionally adopts a scale relying on VLBI and SLR observations only. In this presentation, we will guide the readers through the process we adopted to define and construct the scale of JTRF2020, from the determination and analysis of the scale differences between VLBI and SLR to the way in which the time-variable scale bias between VLBI and SLR is handled within the J2020 assimilation.