Comparison of lamp and detector-based integrating sphere radiance calibrations using the NASA GSFC Filter Radiometer Monitoring System (FRMS)

The NASA GSFC Filter Radiometer Monitoring System (FRMS) was used to compare lamp-based and detector-based spectral radiance calibration of an integrating sphere. The FRMS is a telecentric, filter radiometer employing two apertures, a filter wheel, and a detector. The FRMS uses nine filters at specific wavelengths from 360 to 2400 nm. The lamp-based calibration used a National Institute of Standards and Technology (NIST) calibrated irradiance standard lamp to calibrate the irradiance responsivity of a scanning spectroradiometer. The spectroradiometer was then used to transfer its irradiance calibration to an integrating sphere. The lamp-based spectral radiance calibration of the sphere was calculated using the sphere irradiance, the sizes of the sphere exit and spectroradiometer entrance apertures, and the distance between those apertures. The detector-based calibration of the sphere used NIST calibrated absolute radiance Si photodiode detector to determine the absolute spectral radiance responsivity of the FRMS with the NASA GSFC Automated Laser Tuned Advanced Radiometry (ALTAR) laser system as the source. The absolute spectral radiance responsivity of the FRMS was measured at the following channels: 380, 410, 640, and 840, nm. The FRMS measured the integrating sphere to make a direct determination of its absolute radiance at those channels. Analysis of lamp-based and detector-based radiance measurements of the integrating sphere at four wavelength bands will be presented.