1. n. [Geophysics]

A line joining base stations whose transmissions are synchronized during surveying.

See: base station,  survey

2. n. [Geophysics]

A reference line, such as a "shale baseline," a line representing the typical value of a given measurement for a shale on a well log, or the zero-amplitude line of a seismic trace.

See: bias

3. n. [Geophysics]

The original survey of a set of surveys covering the same area but acquired over a period of time. In four-dimensional seismic data, it is the first seismic survey, which is then compared to subsequent surveys.