Rapid Computation of Occultation Lightcurves using Fourier Decomposition

Calculation of a stellar occultation lightcurve from an assumed refractivity profile involves the integral of the refractivity or its derivatives along the line of sight through an atmosphere. For the general case, normal numerical integration can be time consuming for least-squares fitting with a modest number of free parameters, or for calculation at a fine grid for comparison with local refocusing (“spikes”) in a lightcurve. A new method, based on the Fourier decomposition of the refractivity profile, can rapidly calculate the line-of-sight integrals needed for occultations. The method is formulated for small planets, to be applicable to Pluto and Triton. The Fourier decomposition method may have applicability to a wider range of atmospheric studies.