  We study the propagation of Cerenkov photons generated by Very High Energy
gamma-rays and hadrons in the atmosphere. The photon production height
distributions are estimated from semi-empirical methods and compared with those
derived by standard simulation techniques. Incident spectra at various
observation altitudes are then derived after applying wavelength dependent
corrections due to photon attenuation in the atmosphere during the propagation
of photons from the height of production to the height of observation. These
are generated both for gamma- and hadron primaries of various energies. The
derived production height distributions agree very well with those generated by
the simulation package `CORSIKA' at all energies and for both gamma-$ray and
proton primaries. The incident photon spectra are found to be both altitude
dependent and primary energy dependent. The peak of the incident spectrum
shifts towards the shorter wavelength with increasing altitude of observation
for a given primary. Also the peak of the photon spectrum shifts towards the
shorter wavelength with increasing energy of the primary at given altitude. The
fraction of the UV component in the incident Cerenkov spectrum is estimated
both for gamma-ray and hadronic primaries at various observation altitudes and
energies. Hadron generated Cerenkov spectra are marginally richer in UV light
and the difference increases slightly at higher altitudes. The fraction of the
UV to the visible light in the Cerenkov spectrum could be a useful parameter to
separate gamma-rays from cosmic ray background only if one can measure this
fraction very accurately.
