The quality analysis of GNSS satellite positioning data
Focused on the Beidou satellite system (BDS), dual satellite system (GPS/GLONASS) and three satellite system (BDS/GPS/GLONASS), the parameters influencing the quality of static and real-time dynamic positioning date of the GNSS systems, such as the multipath effect, ionospheric delay, data utilization rate and signal-to-noise ratio, number of satellites and accuracy factor PDOP value, have been comparatively analyzed in this paper. The results of tests have shown that compared to the single satellite system BDS the average multipath errors (mp1 and mp2) of multi satellite system fusion decreased by 18 and 8% respectively, due to the increase in the number of visible satellites in multi-satellite fusion, it is possible to compensate each other to a certain extent, thus weakening the influence of the multipath effect on the positioning results. When the cut-off angle is greater than 40°, the single system cannot meet the need of navigation and positioning, however having more visible satellites than the single system it is possible for multi satellite system fusion to maintain lower and more stable PDOP value for high precision positioning services.
Geomatic Techniques Applied to the Dynamic Study (2001–2019) of the Rock Glacier in the Veleta Cirque (Sierra Nevada, Spain)
During the Little Ice Age (LIA), Corral del Veleta (Sierra Nevada) housed a small glacier of which relict glacial ice and permafrost still remain under packets of ice blocks. Currently, it is considered the southernmost rock glacier in Europe. The analysis and results of monitoring carried out on this rock glacier reveal it to be in an accelerated process of immobilization and that the relict glacial ice blocks and permafrost on which it lies are in a continual process of degradation. The rock glacier was monitored from 2001 to 2019 using diverse geomatic techniques, to which geophysical and thermal techniques were added. The results obtained during the observation period shed light on the dynamic of the rock glacier (morpho-topographic movements and deformations) as well as the physical state of the underlying frozen bodies (volumetric reduction and spatial distribution). The changes observed are related to variations in the dominant high-mountain climate of Sierra Nevada, particularly since the end of the 20th century, the general tendencies of which are increasing temperatures, decreasing annual snowfall, and a shorter duration of snow on the ground.
Suppressed Light Emission of the Reaction Zone in Detonation
THE detonation of high explosives in water can be photographed with an open camera and a flash light as the explosive gases do not emit light. The method has been used1 to investigate the spread of shock waves and explosive gases, and to investigate the initiation by shock waves2. We have found that it can be used also in certain gases such as butane and propane. The method is not suitable, on the other hand, for explosives with two levels of detonation velocity in the case of low velocity. A great part of the reaction then occurs after the reaction zone has passed and the expanding explosive gases are very luminous even in water.