Toward the effective geodetic observation network

(Guest post by Toshimichi Otsubo)

Satellite Laser Ranging (SLR; Photograph) is a precise technique to measure the distance between a ground station and an artificial satellite. It is being used for a wide range of geodetic purposes. About 40 stations all over the world are currently operational and the majority of them has now attained sub-centimeter precision. However, they are not uniformly distributed and there are some gaps remaining on the globe.

Figure: Simulated improvement rate of three translation parameters of a terrestrial reference frame when one laser-tracking station (one of the colored circles) is added to the existing laser-tracking network (white triangles; large ones are high productive stations with > 2000 normal points during the March-April 2015 period).
Figure: Simulated improvement rate of three translation parameters of a terrestrial reference frame when one laser-tracking station (one of the colored circles) is added to the existing laser-tracking network (white triangles; large ones are high productive stations with > 2000 normal points during the March-April 2015 period).

Otsubo et al. (2016) ran a unique simulation to find the optimal place of a future SLR station. Realistic numbers of SLR observations for a new station are numerically simulated, based on its location and the actual data acquisition statistics of the existing stations. The estimated errors are compared between the cases with and without a new station.

A station in the southern hemisphere is found to be useful in general. This is clearly due to the fact that there are only 7 existing stations in the southern hemisphere. More importantly, it is revealed that the most effective place differs according to the geodetic parameter. This study looks into the estimated errors of the geocenter (the gravity center of the Earth; the result shown in the figure) and the low-degree terms of Earth’s gravity field. The X and Y components of the geocenter and the sectoral terms of the Earth’s gravity field are remarkably improved by a station in the polar regions. A middle latitude station best contributes to the tesseral gravity terms, and, to a lesser extent, a low latitude station best performs for the Z component of the geocenter and the zonal gravity terms.

This study is being used to seek a strategic expansion of the global geodetic network.

Photograph: Satellite Laser Ranging in Koganei, Japan, provided by National Institute of Information and Communications Technology.

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