angles

Solar and observation zenith and azimuth angles

Initialized

variable	user
`tts` `tto, psi` -> directional_angles	`calc_brdf()`
`tto, psi`	`RTMt_planck()` `RTMt_sb()`
`tts, tto, psi`	`RTMf()` `RTMo()` `RTMz()`
`tts`	`output_data()`

Fields initialized in select_input() (read from input_data.xlsx)

variable	units	type	default	description
tts	deg	double	30.0	solar zenith angle
tto	deg	double	0.0	observer zenith angle
psi	deg	double	90.0	azimuthal difference between solar and observation angle relative azimuth angle