The Snow Water Equivalent (SWE) describes the amount of water stored in snow. The SWE is a key parameter for various applications including meteorological information systems, run-off predictions for hydro power plants, and roof load monitoring. The SWE as well as the snow height and liquid water content can be determined with Global Navigation Satellite System (GNSS) signals. The set-up consists of two GNSS antennas where as one antenna is placed on the ground below the snow and the second one is placed on a pole above the snow, and serves as reference antenna. The differential GNSS signals are affected by the relative position between the antennas, the snow and the GNSS carrier phase ambiguities. The GNSS signals are refracted at the air-snow interface, and attenuated and delayed in the snow pack. The contribution of this talk is three-fold: First, we have extended our snow parameter estimation [2,3] from a single-frequency, dual constellation (GPS + Galileo) solution to a multi-frequency, triple-constellation (GPS + Galileo + Beidou) solution [1]. Secondly, we have used a Kalman filter to continuously estimate the SWE and carrier phase ambiguities [1] instead of a least-squares estimation. Third, the float ambiguity estimates are now fixed to integer numbers with the Least-Squares Ambiguity Decorrelation Adjustment (LAMBDA) method. The first results are very promising and indicate that the measurement period for snow parameter estimation can be reduced from several hours to less than 30 minutes. References: [1] Julian Weiss: “Snow Parameter Estimation with Multi-Frequency and Multi-Constellation GNSS”, Master thesis, Techn. Univ. Muenchen, Germany, 2021. [2] Patrick Henkel, Franziska Koch, Florian Appel, Heike Bach, Monika Prasch, Lino Schmid, Juerg Schweizer, and Wolfram Mauser: “Snow Water Equivalent of Dry Snow Derived from GNSS Carrier Phases“, in: IEEE Transactions on Geoscience and Remote Sensing, vol. 56, issue 6, pp. 3561 – 3572, Jun. 2018. [3] Franziska Koch, Patrick Henkel, Florian Appel, Lino Schmid, Heike Bach, Markus Lamm, Monika Prasch, Juerg Schweizer, and Wolfram Mauser: “Retrieval of snow water equivalent, liquid water content, and snow height of dry and wet snow by combining GPS signal attenuation and time delay“, in Water Resources Research, vol. 55, issue 5, pp. 4465 – 4487, May 2019.