Abstract
The Goddard Laser for Absolute Measurement of Radiance (GLAMR) has been used to provide spectral and radiometric calibration data for several earth science instruments, including the Joint Polar Satellite System (JPSS) -2 and -3 Visible and Infrared Radiometer Suite (VIIRS). Analysis of data collected by both VIIRS instruments has suggested the presence of fluorescence emitted from the GLAMR integrating sphere when illuminated by visible and ultraviolet light. This takes the form of an unexpected out of band response below 550 nm in several VIIRS bands that is in addition to interband electronic crosstalk. The VIIRS spectral response is also characterized by a monochromator which does not replicate the higher out-of-band response but has reduced dynamic range.
As a result of the VIIRS data analysis, additional characterization of the GLAMR integrating sphere have been performed specifically to check for fluorescence in the visible and near infrared range by illuminating the sphere with visible and near ultraviolet monochromatic light. The broad band spectrum of radiance generated by the integrating sphere is measured using a calibrated spectroradiometer at 3 nm spectral resolution with high SNR at a factor of 10-4 of the radiance of the primary illumination wavelength. This allows for out of band characterization down to the noise floor of previous VIIRS testing. This spectrum is correlated with the VIIRS data sets as well as other instruments calibrated using the same integrating sphere. Prior instrument data also allows some check of the stability of the fluorescence signal over time.
The characterization of the fluorescence will allow it to be accounted for in analysis of flight instrument spectral responses and improve the overall accuracy of the GLAMR characterization.
Characterization of Fluorescence from the GLAMR 30” Integrating Sphere
The Goddard Laser for Absolute Measurement of Radiance (GLAMR) has been used to provide spectral and radiometric calibration data for several earth science instruments, including the Joint Polar Satellite System (JPSS) -2 and -3 Visible and Infrared Radiometer Suite (VIIRS). Analysis of data collected by both VIIRS instruments has suggested the presence of fluorescence emitted from the GLAMR integrating sphere when illuminated by visible and ultraviolet light. This takes the form of an unexpected out of band response below 550 nm in several VIIRS bands that is in addition to interband electronic crosstalk. The VIIRS spectral response is also characterized by a monochromator which does not replicate the higher out-of-band response but has reduced dynamic range.
As a result of the VIIRS data analysis, additional characterization of the GLAMR integrating sphere have been performed specifically to check for fluorescence in the visible and near infrared range by illuminating the sphere with visible and near ultraviolet monochromatic light. The broad band spectrum of radiance generated by the integrating sphere is measured using a calibrated spectroradiometer at 3 nm spectral resolution with high SNR at a factor of 10-4 of the radiance of the primary illumination wavelength. This allows for out of band characterization down to the noise floor of previous VIIRS testing. This spectrum is correlated with the VIIRS data sets as well as other instruments calibrated using the same integrating sphere. Prior instrument data also allows some check of the stability of the fluorescence signal over time.
The characterization of the fluorescence will allow it to be accounted for in analysis of flight instrument spectral responses and improve the overall accuracy of the GLAMR characterization.