The ILRS contribution to ITRF2020 is a time series of weekly/bi-weekly SINEXs with station position estimates and EOP, from 7-day arcs (1993.0 – 2021.0) and 15-day arcs over 1983.0- 1993.0. Each solution was obtained as the combination of loosely constrained individual solutions from the seven ILRS Analysis Centers: ASI, BKG, DGFI, ESA, GFZ, JCET and NSGF. Everyone followed strict standards agreed within the ILRS Analysis Standing Committee (ASC) and used SLR data from LAGEOS, LAGEOS-2, Etalon-1 and Etalon-2, (LAGEOS-only from 1983 to 1992). The ILRS ASC devised an innovative approach in handling systematic errors in the network, never before utilized. After a 5-year pilot-project documented in Luceri et al., (2019). The Station Systematic Error Monitoring PP (SSEM), delivered a series of long-term mean bias estimates for each station, the time intervals of applicability and their statistics. They were derived from freely adjusted station position and EOP solutions for the period 1993.0 to 2020.5, using the latest satellite CoG model. The simultaneous estimation of the station heights and measurement biases resulted in a self-consistent set of weekly bias estimates for each site. Breaks and “jumps” were used to decne the periods of applicability and to calculate the mean bias and its standard deviation. The mean biases were pre-applied in the re- analysis, limiting the remaining jitter of the bias to negligible level. This approach strengthened the estimation process without a compromise of the cnal results’ accuracy. As a result, the ILRS contribution to ITRF2020 minimized the scale difference between SLR and VLBI to below 2 mm (ITRF2014 ~9 mm). We present an overview of the procedures, models, the improvement over previous ILRS products, focusing especially on the Core ILRS sites, and an overview of how the new model has been implemented in support of the ILRS ogcial products.

Geodetic network infrastructure has evolved with increasing pace the past decade with remarkable additions of modern hardware, replacing aging, '80s vintage equipment throughout the globe. The Satellite Laser Ranging-SLR network is the slowest in making changes designed and planned more than a decade ago [Pearlman et al., 2019a]. This is in part due to the voluntary nature of establishing such installations and to a greater part the high cost and limited availability of the one-of-a-kind equipment. NASA, partners and international agencies, embarked on updates with standardization will help in the long term [Merkowitz et al., McGarry et al., Wilkinson, et al., 2019]. SLR needs more than updating the network to deliver the accuracy required today. New "targets" must also be used that support mm-accuracy. LAGEOS was conceived and built in the early '70s with a ~5 mm accuracy in mind [Pearlman et al., 2019b]. This limitation forced analysts to develop approaches of data analysis to ensure that even with such data one can reach the required 1-mm accuracy [Luceri et al., 2019]. Along with the network updates a parallel effort was thus initiated to modernize the space segment as well. Initially with the design and launch of LARES in 2012 [Pavlis et al., 2015] and following that, the design of LARES-2 [Ciufolini et al., 2017, Paolozzi et al., 2019], which was successfully launched on July 13, 2022 [https://www.nature.com/articles/d41586-022-02034-x]. The new mm-accurate target was quickly acquired first by the Matera, Italy station only three days after launch and although very early in the mission, the data were of remarkably high quality and insignificant bias. This prompted a quick evaluation and a test inclusion of this target in the limited list of SLR targets supporting the ITRF development. With an orbit nearly identical to LAGEOS (with supplementary inclination), taking full advantage of all the appropriate models designed and applied to LAGEOS, we achieved 7-day orbital fits of 3-5 mm even without a tuned target signature correction! We will present an overview of the initial analysis of LARES-2 data focusing on comparing them to contemporaneously taken LAGEOS data, we will show results from our initial inclusion of LARES-2 in developing ILRS products for ITRF development and discuss the ILRS plans for its full integration. Ciufolini, Phys. Rev. Lett (1986) Ciufolini, Int. J. of Mod. Phys. A (1989) Pearlman et al., J Geod 93, 2161-2180 (2019a). https://doi.

The ILRS completed the reanalysis of the entire period of useful data from geodetic spherical targets spanning 1983 to end of 2020. The combined products were submitted to ITRS for the development of the ITRF2020. The main period that is supported by all four target satellites (LAGEOS, LAGEOS-2 and the two Etalons) was already used in a preliminary release of an ITRF2020 model in May 2021. For the period 1983-1993 with only LAGEOS data the reduction was in of 15-day arcs with 3-day averaged EOP. Due to the lack of a priori estimated mean biases for the 1983-1993 period, we adjusted a 15-day average bias at all stations to accommodate systematic and target signature errors. Otherwise the reanalysis used the same improved modeling of the 1993-2020 data. The adoption of predetermined mean biases ensured the results are minimally affected by systematic errors in the data. The 2021 ILRS contribution to ITRF2020 minimized the scale difference between SLR and VLBI below 2 mm (ITRF2014 ~9 mm). The reanalysis incorporates an improved “target signature” model (CoG) for better separation of true systematic errors from errors in describing the target’s signature. The ILRS Analysis Standing Committee—ASC devoted its efforts on developing the new analysis approach over the past 5 years. The robust estimation of persistent systematic errors at the millimeter level, while still considering information provided by the stations, permitted the adoption of a consistent series of long-term mean corrections for each station for the period 1993-2020, that are now pre-applied. The use of this approach for this reanalysis led to improved results, reflected in the new time series of the TRF origin and especially in its scale. Seven official ILRS Analysis Centers contributed to the weekly time series and six ACs contributed to the 15-day series for 1983-1993, all computed according to the ILRS ASC guidelines. The series were combined by the ILRS Combination Center to obtain the official ILRS product contribution to ITRF2020 spanning a 38-year period. The presentation will provide an overview of the analysis procedures and models, and it will demonstrate the level of improvement with respect to the previous ILRS product series; the stability and consistency of the solution are discussed for the individual AC contributions and the combined SLR time series.