In 1995 as a part of a company-funded research program we designed and developed the Seismic Detection of Tornadoes (SDT) Instrument Package which we nicknamed "Snail". This portable package is designed to measure the three components of the short-period seismic signal, plus atmospheric pressure fluctuations, in the vicinity of a tornado. The external appearance of the Snail resembles the National Severe Storm Lab (NSSL) meteorological instrument package (commonly referred to as the "Turtle") in size, shape, and weight. By such an approach, experience gained in the handling and deployment of Turtles can be applied to the handling and deployment of Snails. As shown in the figure, the one distinct difference in appearance between the Snail and the NSSL Turtle is that, to measure the three components of the short-period seismic signal, the Snail has the geophone component, attached by a cable to the hemispherical shell containing the electronics package. The pressure transducer to measure atmospheric pressure fluctuations is housed within the hemispherical shell.
Recently one of the original Snails has been modified to allow for the measurement of two components of the long-period seismic signal by means of a tiltmeter assembly. This modified instrument package has been designated a "Supersnail", as shown in the figure.
All Snails have been transferred to VorTek LLC for further seismic data collection.
