Optical calibration of the Global Ultraviolet Imager (GUVI)

The Global Ultraviolet Imager (GUVI) of the NASA Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics (TIMED) mission has been calibrated at the Optical Calibration Facility of the Applied Physics Laboratory. This spectrographic imager has a 0.74 degrees x11.6 degrees field-of-view, a 140 degrees x11.6 degrees field-of-regard and collects data in 176 wavelength bins in the spectral range from 120-180 nm. The calibration of this far ultraviolet instrument requires continuously variable wavelengths and angles within a high-vacuum system from the light source to the instrument. An optical calibration facility has been developed providing a bright, uniform, wavelength-selectable, collimated light beam, which is mapped in situ to correct for intensity drifts in the lamp. The facility design and the calibration procedure are discussed.