A system for analyzing three-dimensional seismic data includes a plurality
of digitizer units, each with a configuration of geophones, a data
recording and control center, a base GPS receiver with an associated
antenna with a substantially unrestricted view of the sky and at the
respective digitizer units low-power slave GPS receivers that acquire and
track GPS satellite signals using tracking assistance information
provided by the base GPS receiver. The slave GPS receivers use the
tracking assistance information to acquire and track GPS satellite
signals from which the slave GPS receivers produce associated range
information. The system batch processes the range information provided by
the slave GPS receivers over an extended period of time to determine the
precise positions of the respective slave GPS receivers. The system
provides the position information to the slave GPS receivers, and the
receivers locally produce associated timing signals that are based on the
GPS codes. If a particular slave GPS receiver cannot, at a given time,
track any GPS satellite signals, a nearby slave GPS receiver supplies
timing information required for the geophone data gathering operations.