A high resolution oxygen A-band and 820 nm water vapor band spectrometer has been developed and deployed in a field campaign at the ARM SGP site. The resolution of this instrument is 0.025 nm with out of band rejection better than 10^-5. Given the performance of the instrument, we retrieved the photon pathlength distributions in both bands. The joint statistics of photon pathlength moments (mean and variance) and cloud optical properties has been studied. Preliminary results demonstrate that information derived from photon pathlength distributions is a powerful diagnostic tool for sky homogeneity and can provide constraints for radiative transfer calculation in cloudy atmospheres. Furthermore, the role of cloud and aerosol on scattering and absortion processes in the atmosphere can be studied by using simultaneous high resolution measurements from oxygen A-band and 820 nm water vapor band.