Influence of shadow on the thermal and optical snow indices and their interrelationship

The mean values of different snow indices exhibit significant difference between the sunlit and shadow test sites with Z-values ranging between 68.92 and 1220.39 (p < 0.0001). Shadow significantly increases correlation of the thermal snow indices with the optical snow cover indices with r ≥ 0.81, while r-values lie below 0.29 in the sunlit test site (Student's t-test, p < 0.0001). On the other hand, thermal snow indices exhibit low correlation with both optical snow cover characteristic indices in either site; however, shadow induces negative correlation between them (r = − 0.37 to − 0.62, p < 0.0001). The results ascertain the varying influence of shadow on the optical and thermal snow indices and their interrelationship, which could be significantly helpful for accurate radiative transfer modelling of snow in the light of the seasonal variation in the earth-sun geometry.