The Solar Constant Based on New Spectral Irradiance Data from 310 to 530 Nanometers

Abstract

Measurements made at an altitude of 11,150 ft on Mauna Loa in Hawaii with instrumentation recently developed at the National Bureau of Standards have yielded new solar spectral irradiance values (outside the atmosphere) within the region 310?530 nm. With two independent polar-axis-mounted instruments, a double-quartz-prism spectroradiometer, and a photoelectric filter radiometer, each incorporating integrating spheres, closely agreeing spectral data were obtained on several days during August 1966. The short-wavelength solar curve thus obtained agrees closely with the Johnson curve near 525 nm, but averages approximately 10% lower than the Johnson curve at shorter wavelengths. With the use of a new solar curve embodying the Smithsonian data without change as tabulated by Johnson at wavelengths above 525 nm and our data at wavelengths up to 525 nm, integration of the area under this curve results in a value of the solar constant of 0.136 W cm?2, or 1.95 cal cm?2 min.?1