Studio e realizzazione di un protocollo di compressione dati per reti di sensori sismici

Abstract

Abstract Permanent seismic network management, in a country defined by active volcanoes, as well as a tectonic faults network, involve evaluating a great number of working and efficiency parameters, especially when risks are of a different nature and can cause economic damage to the local region. One example is the Permanent Seismic Net managed by the Istituto Nazionale di Geofisica e Vulcanologia(INGV), Catania Section, in Italy, which comprises about sixty seismic stations, using analogical and digital technology, located around Mt. Etna, the Peloritani and Hyblean areas, southern Calabria and in the Aeolian archipelago. Digital technology enables increasing management performance, signal to noise ratio and firmness, allowing gradual upgrades from analogical to digital stations. On the other hand, it introduces some new problems such as the small capacity of the transmission channel (available bandwidth), which is hard to manage and causes data acquisition delays. The seismic signals, in particular, after digitization, are compressed to make better use of the available channel. The use of a lossless compression algorithm causes variable efficiency that depends, generally, on the kind of signal to compress. We know that signals that change frequently in a time window, and that have a high RMS amplitude, are more difficult to compress with lossless compression, and hence need more bandwidth. Instead, signals with a low RMS amplitude and that change little in a time window, are better compressed with lossless compression and require smaller space channels. Various active volcanic phenomenology in eruption phases, could cause a big variation in some seismic signal parameters like RMS amplitude, this variation causes channel bandwidth consumption increase. This implies an efficiency evaluation of the Nanometrics® transmission protocol and compression algorithm used by the remote station instruments, especially in critical stages as when a volcano is preparing to erupt. Alternative protocols are proposed to increase the global evaluation quality of the Nanometrics® protocol and compression algorithm used by the RSP instrumentation. Comparisons between solutions are made by studying the relationship between seismic signal RMS amplitude and its bandwidth consumption. Studying the compression algorithm and researching potential optimization, helps build a plausible evaluation of the bandwidth needed in the critical stages that are typical in active volcanoes like Etna.