ken@Miranda ~/c/_/tmp
$ cat gravity
2010-10-01 00:00:03 lat1 long1 grav1
2010-10-02 00:00:05 lat2 long2 grav2
2010-10-03 00:00:07 lat3 long3 grav3

ken@Miranda ~/c/_/tmp
$ cat magnetics
2010-10-02 00:00:05 lat2 long2 mag1
2010-10-03 00:00:07 lat3 long3 mag2
2010-10-04 00:00:09 lat4 long4 mag3

ken@Miranda ~/c/_/tmp
$ cat bathymetry
2010-10-03 00:00:07 lat3 long3 bath1
2010-10-04 00:00:09 lat4 long4 bath2
2010-10-05 00:00:01 lat3 long3 bath3