GEODESY USING THE SWEDISH PERMANENT GPS NETWORK - EFFECTS OF SNOW ACCUMULATION ON ESTIMATES OF SITE POSITIONS

We have observed variations at the several centimeter level in estimat es of the vertical coordinate of site position. The estimates are obta ined from our analysis of data acquired from the Swedish permanent Glo bal Positioning System (GPS) network. The observed variations are stro ngly correlated with changes in the indirectly inferred accumulation o f snow, which we assume collects on the radomes and pillars; the GPS s ites could not be observed directly due to their remoteness. Numerical simulations which assume a simple geometry for the snow cover are use d to study the effects of snow accumulation on GPS phase observables a nd hence on estimates of the vertical coordinate of site position obta ined from these observables. Our results indicate that the variations in the vertical coordinate of site position can be fully explained by reasonable accumulations of snow which retard the GPS signals and enha nce signal scattering effects.