  We present new grids of transmission spectra for hot-Jupiters by solving the
multiple scattering radiative transfer equations with non-zero scattering
albedo instead of using the Beer-Bouguer-Lambert law for the change in the
transmitted stellar intensity. The diffused reflection and transmission due to
scattering increases the transmitted stellar flux resulting into a decrease in
the transmission depth. Thus we demonstrate that scattering plays a double role
in determining the optical transmission spectra -- increasing the total optical
depth of the medium and adding the diffused radiation due to scattering to the
transmitted stellar radiation. The resulting effects yield into an increase in
the transmitted flux and hence reduction in the transmission depth. For a
cloudless planetary atmosphere, Rayleigh scattering albedo alters the
transmission depth up to about 0.6 micron but the change in the transmission
depth due to forward scattering by cloud or haze is significant throughout the
optical and near-infrared regions. However, at wavelength longer than about 1.2
$\mu$m, the scattering albedo becomes negligible and hence the transmission
spectra match with that calculated without solving the radiative transfer
equations. We compare our model spectra with existing theoretical models and
find significant difference at wavelength shorter than one micron. We also
compare our models with observational data for a few hot-Jupiters which may
help constructing better retrieval models in future.
