Laser ranging data analysis for a colocation campaign of French Transportable Laser Ranging System (FTLRS) in Tahiti

Tahiti is a unique geodetic site located in the south Pacific Ocean where few observatories exist nearby. The American mobile station MOBLAS-8 was installed in Tahiti in 1998, and GPS and DORIS systems were also deployed in its vicinity in order to develop this site into one of the fundamental colocated sites of the International Terrestrial Reference Frame. In order to make a new estimate of the colocation differences between the different techniques, a campaign of the French Transportable Laser Ranging System (FTLRS) was conducted in Tahiti between April and October 2011. The FTLRS was deployed close to the existing equipment. Observations for LAGEOS 1, LAGEOS 2 and Starlette were studied, and the solutions to the local ties between FTLRS, MOBLAS-8, DORIS and GPS were evaluated. Our results of the geodetic local-ties between laser stations and GPS agree well with the measurements made by the Institut National de l’Information Géographique et Forestière (IGN) during the campaign, with differences less than 2 mm in the vertical direction. The laser station range biases as a function of satellites are also presented, -3 ( ± 2) mm for MOBLAS-8 and 3 ( ± 3) mm for FTLRS, respectively. In addition, we investigated the role of time bias (ranging from a few hundreds of nanoseconds to one microsecond) given by the Time Transfer by Laser Link experiment, which shows a limited impact on the present SLR analysis. We also compared the coordinates of the three available techniques at Tahiti, i.e., laser, GPS and DORIS. We found the accuracy of laser solutions still needs to be improved, so that the SLR at Tahiti could contribute more effectively to the tracking of satellites and thus to the international reference frame. This study is useful in evaluating the SLR and other space techniques in order to prepare the deployment of new equipment in Tahiti in the near future.