A Sequentially Estimated Terrestrial Reference Frame: JTRF2020

JPL's newly developed software for determining terrestrial reference frames, known as SREF (Square-root REference Frame filter), has been used to produce JTRF2020, a combined terrestrial reference frame determined from the input SINEX files submitted by the IVS, IGS, ILRS, and IDS for ITRF2020. SREF, being based upon a square-root information filter and smoother, determines the reference frame sequentially from the input station position time series. Incorporating process noise in SREF, determined from geophysical fluid loading models, allows the observed station positions to be smoothed between discontinuities caused by earthquakes and equipment changes. Reference frames determined by SREF, like JTRF2020, are represented by this set of smoothed station position time series. SREF also fits a model (consisting of a piecewise linear trend, annual and semi-annual periodic terms, and a sum of exponential terms to represent postseismic motion) to the station's observations and uses the model to fill gaps in the station's observing history, to forecast the position of the station after it stopped observing, and to hindcast its position before it started observing. The result of using SREF to determine JTRF2020 will be presented.