USING GPS MULTIPATH FOR SNOW DEPTH SENSING - FIRST EXPERIENCE WITH DATA FROM PERMANENT STATIONS IN SLOVAKIA

Analysis of multipath reflections of GPS satellite signals at permanent GPS stations allows deducing the height of GPS antenna above the horizontal reflecting surface. If the effective height of the reflector is varying, e.g. due to change of snow cover in the vicinity of GPS antenna monumentation, the multipath characteristics are affected, namely the period of the harmonic oscillations of the reflected signal. We analyzed three types of GPS observables influenced by multipath: signal-to-noise ratio SNR1 and SNR2 related to L1 and L2 carrier phases respectively, and L4, the geometry-free linear combination of carrier phases. The GPS multipath snow sensing is demonstrated on two GNSS permanent stations in Slovakia – Ganovce (GANP) and Liesek (LIE1), where the snow cover during winter season reaches up to 40 cm and the snow depth manual measurements are regularly performed. Due to terrain topography, buildings, structures and other obstacles in the vicinity of pillar where the GPS antenna is mounted only narrow azimuthal sectors in these sites are suitable for analyzing reflected signals from ground. Comparisons of series of manual snow depth sensing with data resulting from GPS multipath analyses generally shows consistency better than 5 cm, however some periods where the biases are at 10 cm level were recognized. ARTICLE INFO