AUSGeoid93 has been completely superseded by AUSGeoid98. AUSGeoid93 should only be needed for very specific purposes.
AUSGeoid93 was the second in the series of national geoid models produced by Geoscience Australia. It consisted of a 10' by 10' grid (approximately 20km) of geoid-ellipsoid separations (N values) in terms of the WGS84 ellipsoid.
These values were computed for the Australian region using:
Specific Purposes for AUSGeoid93
Where a project joins heights previously derived using AUSGeoid93, re-create the previous heights using your archived ellipsoidal heights and the new AUSGeoid98. If you no longer have the original ellipsoidal heights or AUSGeoid93 N values, you may have to re-create the ellipsoidal heights by requesting interpolated AUSGeoid93 N values from the off-line archive.
NOTE: It is strongly recommended that GPS determined heights should be stored as ellipsoidal values, so they can be reduced at any time using the latest N value.