  The motion of our solar system relative to the CMB rest frame leads to subtle
distortions in the observed CMB sky map due to the aberration effect. Usually
the corresponding peculiar velocity is determined from the CMB dipole but
neglecting intrinsic dipole contributions. Here it is investigated whether
certain invariant scalar measures, which are derived from first and second
order covariant derivatives on the sphere, can detect the distortions caused by
the aberration effect at high multipoles. This would in principle allow to
disentangle the Doppler from intrinsic dipole contributions providing an
independent method for the determination of our peculiar velocity. It is found
that the eigenvalues of the Hessian matrix of the temperature field are well
suited for that task.
