A detection algorithm of frequency jumps for GNSS satellite clocks
As the frequency and time reference of space satellites, satellite clock has a direct influence on GNSS service performance. Any anomaly of the atomic clock behavior on board the satellites causes errors for user position. Therefore, it is necessary to detect clock anomaly. Frequency jumps are one of the most common anomalies in atomic clocks of on-board satellites, which appear due to space radiation, temperature change and other factors. In this paper, a detection algorithm of frequency jumps based on the batch least squares residues is proposed. Performance of the new algorithm is analyzed and verified by numerical simulation. The detection algorithm of frequency jumps for satellite clocks proposed in this paper is helpful to GNSS satellite clock autonomous integrity monitoring.
Application of the Dynamic Allan Variance for the Characterization of Space Clock Behavior
Due to their stability atomic clocks represent the core of navigation systems such as GPS and the future European Galileo system. To identify possible anomalies, it is fundamental to detect when the clock stability varies with time. The dynamic Allan variance (DAVAR) makes this monitoring process possible. We extend the DAVAR to the case of a time series with missing data, and we analyze the presence of periodic behaviors, two common phenomena in space clocks.
Google Earth: Mathematical Art Forms
We trace the development of Google Earth and consider various artifacts, natural and anthropogenic, ancient and modern. These artifacts are only obvious from high elevations and some have a mathematical form and artistic appeal. We also illustrate how Google Earth's high-altitude imagery can be fruitful inspiration for mathart and provide some example.