Analysis Working Group

The prime objective of ILRS' Analysis Working Group (AWG) is the exploitation of the tracking data collected by ILRS and the generation of a number of scientific data products, based on these Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) observations. At present, the most commonly available products include station coordinates and velocities, Earth Orientation Parameters (EOP), reference frame (RF) realizations based exclusively on SLR data, time series of vector variations of the RF origin with respect to the geocenter (commonly referred to as "geocenter motion"), time series of SINEX files (typically of weekly resolution) with position and EOP estimates and their covariance, time series of low degree harmonic variations, satellite orbits in SP3c formatted files, contributions to lunar ephemerides, and many others.

Historically, ILRS Analysis Centers provided SLR station coordinates to the International Earth Rotation and Reference Systems Service (IERS) individually. During the last two decades, with many new geodetic observation techniques coming to fruition (e.g. GPS, DORIS, GLONASS), it became apparent that a better organization of the contributions to IERS was necessary. This led to the establishment of the IAG Services, one of which is the ILRS. Since the organization of the ILRS and its AWG, the data and products dissemination process has been streamlined and it is maintained under strict configuration control. The AWG currently coordinates eight Analysis Centers (AC) operated by analysts of various international institutions, all of which have completed successfully a benchmark process that guarantees the quality and consistency of their contributions to ILRS, and eventually IERS. In addition to the eight AC, the AWG has established a primary and a back up Combination Center (CC), which combine the AC products and deliver a single official ILRS product to IERS. The ILRS products are primarily used in the definition of the origin and absolute scale of the International Terrestrial Reference Frame (ITRF), a unique contribution of the laser ranging technique.

The official weekly Position+EOP SINEX contribution series commenced its operations in June 2004. In addition to that, a similar product based on weekly arcs that are analyzed daily (7-day arcs sliding by one day) is generated in a pilot project mode and delivered daily to IERS' NEOS service for improved EOP forecasting operations. At the moment, the orbital product, the "geocenter motion" and the low degree harmonic series products are also operating in the pilot project mode. It is expected that most of these projects will turn operational in the very near future. During the last two developments of the ITRF, ITRF2005 and ITRF2008, the AWG made major efforts to extend its products to the years prior to its institution. For ITRF2005 the AWG contributed a complete weekly series of SINEX files covering the period 1993 to 2005. During the current process for the establishment of ITRF2008, the effort was extended to include the historical LAGEOS data from 1983 on. It is planned that in the near future the AWG will generate additional products that can be used to establish new and improved versions of ITRF.

Responsible Government Official: Carey Noll
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