  The Radiative Transfer Model (RTM) and the retrieval algorithm, incorporated
in the SCIATRAN 2.2 software package developed at the Institute of Remote
Sensing/Institute of Enviromental Physics of Bremen University (Germany),
allows to simulate, among other things, radiance/irradiance spectra in the
2400-24 000 {\AA} range. In this work we present applications of RTM to two
case studies. In the first case the RTM was used to simulate direct solar
irradiance spectra, with different water vapor amounts, for the study of the
water vapor content in the atmosphere above Sierra Nevada Observatory.
Simulated spectra were compared with those measured with a spectrometer
operating in the 8000-10 000 {\AA} range. In the second case the RTM was used
to generate telluric model spectra to subtract the atmospheric contribution and
correct high-resolution stellar spectra from atmospheric water vapor and oxygen
lines. The results of both studies are discussed.
