Methods & Instruments
| The crests of tsunami waves may be more than a hundred kilometers or more away from each other. Therefore, passengers on boats at sea, or far away from shore where the water is deep, will not feel or see the tsunami waves as they pass by underneath at high speeds. The tsunami may be perceived as nothing more than a gentle rise and fall of the sea surface. Therefore, the best method for detecting tsunamis is to precisley measure the pressure of the water at the bottom of the ocean. Envirtech has developed an instrument that uses a pressure depth sensor, and a computer with an acoustic modem to communicate this information to a surface buoy. The data are then relayed via Inmarsat-C satellite link to Land stations, which forward the signals for immediate dissemination to Warning Centers. Each deep sea station is designed to detect and report tsunamis on its own, without instructions from land. The tsunami detection algorithm in the instrument's software works by first estimating the amplitudes of the pressure fluctuations within the tsunami frequency band and then testing these amplitudes against a threshold value.The high accuracy of measurment is due to a quartz crystal resonator whose frequency of oscillation varies with the pressure. |
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