Hydrophone Measurement of Sea-Bed Pressure and Temperature Fluctuations Up to Tidal Period

摘要

A conventional hydrophone, connected without pre-amplifier to several miles of underwater cable, has been used to measure sea-bed pressure fluctuations. Fluctuation periods extended to the tidal period. This was possible owing to the high leakage resistance of both the lead zirconate titanate sensitive element and the hydrophone cable. The hydrophone signals can be due to changes in either pressure or temperature, and can amount to several tens of volts. The pressure fluctuations of several seconds period due to the sea surface waves were observed. The fluctuations of several minutes period were of relatively low level, and probably caused in part by internal waves. The fluctuations of tidal period are mainly due to the tidal-height pressure variations in winter, but in summer the temperature variations are more important. This is confirmed by thermistor data, in addition all the records regularly show very much larger swings at springs than at neaps. 'Hydrophones' could be made responsive only to pressure or only to temperature, and have some advantages as sensors. (Author)