  We use numerical simulations to investigate effect of turbulent velocity on
the power spectrum of \HI intensity from external galaxies when (a) all
emission is considered, (b) emission with velocity range smaller than the
turbulent velocity dispersion is considered. We found that for case (a) the
intensity fluctuation depends directly only on the power spectrum of the column
density, whereas for case (b) it depends only on the turbulent velocity
fluctuation. We discuss the implications of this result in real observations of
\HI fluctuations.
