A broadband photometer experiment is being prepared for the Atmosphere Explorer-C, -D, and -E missions to record the solar irradiance in seven wavelength bands in the range from 40 to 1250 Å. The experiment contains four spiral electron multipliers located behind a moving eight-position filter wheel. Six of the eight sections of this wheel contain metallic filters used to spectrally isolate the solar irradiance. In addition, three Al2O3 diodes, two with filters, are being used to record the solar irradiance over the full range of orbital altitudes including those at which operation of multipliers with high voltages on open structures would be unsafe. A principal goal of the experiment will be to measure time dependence of the solar irradiance.
Photometric calibration will be based on preflight exposure to a storage-ring synchrotron light source which has been calibrated by combining synchrotron theory with the absolute values of irradiance at 4000 Å obtained from comparison with the best available standard of irradiance.
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