9. a ground-based radiometer operating at a wavelength of 0.45 µm is used to measure the solar radiance reaching the radiometer, io. for a solar zenith angle of 30°, it measures an io = 1.74 x 107 wm-2 µm-1 sr-1 . for a solar zenith angle of 60° it measures an io = 1.14 x 107 wm-2 µm-1 sr-1 . from this information, determine the solar radiance that’s normally incident at the top-of-atmosphere and the atmospheric optical depth.