Implementation of the dynamic Allan variance for the Galileo System Test Bed V2

The dynamic Allan variance (DAVAR) method has been recently proposed as an extension of the classical Allan variance, with the aim of defining the instantaneous stability of an atomic clock. It is in fact known that atomic clocks may undergo sudden failures, are influenced by environmental factors, and they eventually age and stop working. Hence the stability of an atomic clock may vary with time, and in some demanding applications, such as navigation systems, a quick identification of clock failures is of the utmost importance. Working on the first preliminary data coming from the Galileo System Test Bed (GSTB) V2, some criticalities were encountered in the DAVAR evaluation and its graphical representation, when dealing with long periods of missing data. A new estimation method has been developed, allowing to evaluate the DAYAR in case of missing data, not equally spaced data and with large periods of missing observation. The new estimation method is presented here. The experimental results obtained by applying the improved DAVAR on the Galileo experimental satellite are also shown. Also experimental data obtained by using the two-way satellite time and frequency rransfer (TWSTFT) method are analyzed and discussed.