The proportion reflected is not only determined by properties of the surface itself, but also by the spectral and angular distribution of solar radiation reaching the Earth's surface.
ðə pɹəpˈoːɹʃən ɹᵻflˈɛktᵻd ɪz nˌɑːt ˈoʊnli dɪtˈɜːmɪnd baɪ pɹˈɑːpɚɾiz ʌvðə sˈɜːfɪs ɪtsˈɛlf, bˌʌt ˈɔːlsoʊ baɪ ðə spˈɛktɹəl ænd ˈæŋɡjʊlɚ dˌɪstɹɪbjˈuːʃən ʌv sˈoʊlɚ ɹˌeɪdɪˈeɪʃən ɹˈiːtʃɪŋ ðɪ ˈɜːθz sˈɜːfɪs.