A comparison of the calculated and measured spectral radiances of the atmosphere toward the zenith

Helicopter-borne direct spectrophotometric measurements of the zenith-directed characteristic radiation of the atmosphere are compared to the predictions of a 9-input-parameter Schwarzschild-Eddington-type radiative-transfer model. Data were obtained over forest and water in 4-min observations in six bands from 460 to 870 nm at 15-3200 m. Input data for the model were derived from radiosonde temperature and humidity profiles, solar-altitude and scattering-angle determinations, and global-radiation and atmospheric-transmission measurements made on the ground using 34 narrower channels with the same type of spectrophotometer as employed for the airborne observations. The measured and calculated results are presented in tabular and graphic form and found to agree to within 5 percent, a value comparable to the measurement error of the system. The model is thus considered useful in correcting for zenith-directed atmospheric radiance effects on remote-sensing devices of similar precision.