JTRF2020: Results and Next Steps

JPL's newly developed software for determining terrestrial reference frames, known as SREF (Square-root Reference frame Estimation 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 on a square-root information filter and smoother, determines the reference frame sequentially from the input station position time series. For JTRF2020, 525 GNSS, 194 DORIS, 116 SLR, and 96 VLBI, or a total of 931, station position time series were used. 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 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. For JTRF2020, the model consists of a piecewise linear trend, an annual periodic term, and a sum of exponential terms to represent postseismic motion for those stations that experience postseismic motion. The result of using SREF to determine JTRF2020 will be presented.