function cosscatang, cossza, cosvza, phi ;+ ; NAME: ; COSSCATANG ; ; PURPOSE: ; Return the scattering angle of the incident and emerging rays. ; NOTE: the scattering angle is defined as 180 degrees when ; sza = vza = 0 and phi = 180. ; ; CALLING SEQUENCE: ; cos_omega = cosscatang(cossza, cosvza, phi) ; ; INPUTS: ; cossza cosine of solar (or incident) zenith angle ; cosvza cosine of viewing (or emergin or satellite) zenith angle ; phi relative azimuth angle; this is defined as the difference ; between the solar azimuth angle and the viewing azimuth ; angle; when sat, sun are in the same position in ; the sky, phi = 0 ; ; OPTIONAL INPUTS: ; ; OUTPUTS: ; The scattering angle is returned. ; ; EXAMPLE: ; IDL> print,acosd(cosscatang(cosd(60),cosd(60),0)) ; 0.00000 ; IDL> print,acosd(cosscatang(cosd(60),cosd(60),180)) ; 120.000 ; ; PROCEDURE ; ; COMMON BLOCKS: ; None. ; ; NOTES ; ; REFERENCES ; ; AUTHOR and DATE: ; Jeff Hicke Earth Space Research Group, UCSB 1/04/94 ; ; MODIFICATION HISTORY: ; ;- ; radian_phi = phi * !dtor return, cossza*cosvza + $ sin(acos(cossza))*sin(acos(cosvza))*cos(radian_phi) end