Solar Spectral Irradiance Measured from 11.58 km with a Leiss Monochromator and a Photoelectric Filter Radiometer.

Solar spectral irradiance measurements were made from NASA's Convair 990 research aircraft using a Leiss double prism monochromator and a GSFC modified Eppley Mark V radiometer. Six flights were made over the Pacific and western United States at an altitude of 11.58 km. Excellent agreement is noted between the two instruments through a wavelength range of 0.3-1.1 micro, even though they are optically and electronically dissimilar. Instrument calibrations were performed in flight using an NBS type quartz-iodine standard of spectral irradiance. Extrapolation to zero air mass was facilitated by the fact that at 11.58 km the aircraft was above 80% of the permanent gases of the atmosphere and more importantly above 99.9% of the water vapor and all the atmospheric pollutants. The resulting solar spectral curves differ significantly from Johnson's in several regions. Solar constant measurements made with other flight instruments resulted in a value of 0.1351 W cm(-2), which is about 3.3% less than Johnson's, but is in good agreement with recently published values of Drummond, Laue, and others.