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\begin{document}

\title{ITRF2020: The International Laser Ranging Service (ILRS) Contribution}



\author[1]{Erricos Pavlis}%
\author[2]{Vincenza Luceri}%
\author[3]{Antonio Basoni}%
\author[3]{David Sarrocco}%
\author[1]{Magda Kuzmicz-Cieslak}%
\author[4]{Keith Evans}%
\author[5]{Giuseppe Bianco}%
\affil[1]{Joint Center for Earth Systems Technology}%
\affil[2]{e-GEOS S.p.A.}%
\affil[3]{e-GEOS S.p.A., ASI/CGS}%
\affil[4]{University of Maryland Baltimore County}%
\affil[5]{Agenzia Spaziale Italiana}%


\vspace{-1em}



  
  \date{June 18, 2024}


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\begin{abstract}
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 \textasciitilde{}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.%
\end{abstract}%



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