Investigation of temperature and velocity fluctuations through the solar photosphere with the NaI D lines

In this work we explore the diagnostic properties of the Na I D resonance lines by calculating the response functions of their line profiles to temperature and velocity perturbations in the atmosphere. We propose a method to transform spectral line intensity fluctuations measured at several wavelengths into temperature and velocity disturbances at different height levels. Results from tests done with several theoretical models of perturbations are discussed. Perturbations that vary as linear functions of depth are efficiently reproduced. The method also provides good estimations for exponential models. As an example we present an application to solar granulation data obtained with Multichannel Subtractive Double Pass (MSDP) spectroscopy.