    normally either of the corrections

                  'LT+S'
                  'CN+S'

               should be used. These and the other supported options
               are described below. `abcorr' may be any of the
               following:

                  'NONE'     No aberration correction.

               Let `lt' represent the one-way light time between the
               observer and the input surface point `spoint' (note: NOT
               between the observer and the target body's center)