| 摘要 |
<p num="1"><br/><br/>A system for analyzing three-dimensional seismic data includes a plurality of <br/>digitizer <br/>units (7), each with a configuration of geophones (8), a data recording and <br/>control center <br/>(12), a base GPS receiver with an associated antenna (5) with a substantially <br/>unrestricted <br/>view of the sky and at the respective digitizer units (7) low-power slave GPS <br/>receivers<br/>(6) that acquire and track GPS satellite (9) signals using tracking assistance <br/>information <br/>provided by the base GPS receiver. The slave GPS receivers (6) use the <br/>tracking <br/>assistance information to acquire and track GPS satellite signals that may be <br/>relatively <br/>weak at the receivers, due to conditions at the site, such as foliage canopies <br/>(11) and so <br/>forth. The system processes range information provided by the slave GPS <br/>receivers (6) <br/>over an extended period of time. In this way, the precise positions of the <br/>respective slave <br/>GPS receivers (6), and thus, the digitizer units, can be calculated, even if <br/>the slave GPS <br/>receivers (6) are able to observe and collect data from sets of two or more <br/>satellites (9) <br/>for only three or four relatively short time intervals at various sky <br/>positions during the <br/>extended period. The slave GPS receivers (6) then locally produce for the <br/>digitizer units<br/>(7) timing signals that are based on the GPS codes and synchronized across the <br/>system. If <br/>a given slave GPS receiver (6) cannot, at a given time, track any GPS <br/>satellite signals, a <br/>nearby slave GPS receiver (6) supplies the timing information required for the <br/>geophone <br/>data gathering operations.<br/>
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