Spherical geometry in montecarlo radiative transfer solver. If mc_spherical is selected mc_backward is switched on automatically. Viewing direction and sun position are defined with respect to the sensor position specified by ZOUT. For details about the implementation of spherical geometry please refer to (Emde and Mayer, 2007).
Emde, C., & Mayer, B., (2007), "Simulation of solar radiation during a total solar eclipse: A chal-lenge for radiative transfer." Amospheric Chemistry and Physics. Vol. 112, pp. 2259‒ 2270.