Specifying GEOSEG flags a scan to be converted into a geodetic segment. See the section on insertion of geodetic segments for more details about this capability. The argument of GEOSEG is the total time for the geodetic segment. The duration of each scan in the segment is specified with DWELL. The scan to be converted should have a source specified to keep various checking routines happy, but it is not important what that source is, or even whether it is up. In the construction of the segment, it will be ignored.
Geodetic segments will likely need to be 30 to 40 minutes long to have good coverage at all antennas with multiple low elevation scans. They could be even longer if slow antennas are included. Note that not all antennas will be in all scans.
The sources used for the geodetic segments are specified with GEOSRCS.