Systematic Error Monitoring and Modeling in ILRS Data and Products for ITRF2020 Development

The International Laser Ranging Service (ILRS) has completed the second re-analysis of the complete modern-era data set (1993 to present), based on the improved modeling of the data and the newly adopted approach that ensures the results are free of systematic errors in the underlying data. Over the past three years the ILRS Analysis Standing Committee (ASC), devoted almost entirely its efforts to develop, evaluate and implement the new approach to continuously monitor the systematic errors at all ILRS sites in the network. Initially, the execution of a 4-year Pilot Project (PP) demonstrated the robust estimation of persistent systematic errors at the millimeter level. In a subsequent step the new approach is used in the re-analysis of the entire SLR data set from 1993 to present and for all five targets that will contribute data for the development of the next ITRF2020: LAGEOS 1 & 2, Etalon 1 & 2, and LARES. This re-analysis incorporates an improved "target signature" model (the so-called center-of-mass offset) which allows a better separation of true systematic error of each tracking system from the errors in the model describing the target satellites. The improved modeling results in improved TRF attributes that are reflected in the resulting new time series of the TRF origin and scale. The ILRS ASC is now using the new approach in the development of its operational products and we are using this as a tool to monitor station performance and to extend the history of systematics at each station. The new approach will be used with each re-analysis for all future ITRF model developments. Following these developments, the ILRS operational products form now a seamless extension of the re-analysis series, providing a continuous product based on our best knowledge of the ground system behavior and performance. The presentation will demonstrate the level of improvement with respect to the previous ILRS product series and a glimpse of what we should expect after the development of ITRF2020.