High count seismic data collection and transmission through analog time

Abstract

A data collection and transmission system for gathering high count vertical seismic data is disclosed using a sequence of vertically aligned seismic receivers, the analog outputs from which are sequentially analog sampled and time multiplexed onto a common pair of data conductors in the support and transmission cable. The data is time demultiplexed at the surface and appears substantially as digital data because of the relatively short sampling times. Such data is converted into analog data with conventional digital-to-analog converter means. A clock signal activates counters for establishing non-overlapping data gates in the respective sondes, the operation of the gates supplying the cable with the respective receiver analog signals in a sequence from bottom to top, simultaneously switching off previously gated signals until a clock reset pulse resets the entire sonde string. Borehole engaging means are locally powered at each sonde and are controlled for engagement and disengagement from above using appropriate control signals therefor. The appropriate coupling by the engagement means at each sonde is monitored by examining the change in motor voltage reflected on the data lines. Alternatively, a shaker may be employed for generating geophone receiver signals for comparison purposes with an appropriate standard.