The SOLSTICE preflight/ground calibrations included unit level calibrations in the LASP/CU calibration laboratory and system level calibrations primarily at the NIST Synchrotron Ultraviolet Radiation Facility (SURF) III. Many of the calibration techniques for the SOLSTICE instruments are similar to those used for the UARS SOLSTICE calibration program [Woods et al., 1993] and for LASP’s TIMED and suborbital solar EUV irradiance program [Woods and Rottman, 1990]. Unit level calibrations included characterization of individual optical and instrument elements, including gratings, detectors, and mirrors.
The LASP/CU Calibration and Test Equipment 2 (CTE-2) was primarily used for these measurements. The radiometric calibration for the CTE-2 uses photodiodes that are calibrated at NIST. Many of the CTE-2 characterization tests, including the reflection and grating efficiency measurements, only require relative calibrations using two detectors, usually photon-counting photomultiplier tubes (PMTs). The calibration uncertainties for the CTE-2 measurements typically range from 10-20%. The scattered light properties of the diffraction gratings were also analyzed using the equipment and procedures described by Woods et al. .
The system level calibrations for SOLSTICE included detailed wavelength and photometric calibrations of the fully assembled instrument. Wavelength calibration uses platinum and mercury lamps that provide well spaced line emissions. The primary photometric calibration occurred at the NIST SURF III. BL-2 is dedicated for NASA instrumentation and provides a vacuum tank and gimbal system large enough to accommodate the SOLSTICE instrument. Photometric calibrations at SURF included mapping instrument responsivity over the field-of-view (a 5 × 5 gridded map over its 1.0° × 1.0° FOV along with a more detailed cruciform along two measurement strips through the center for the FOV with 0.1° resolution). Both the SOLSTICE instruments and calibration equipment at SURF are controlled by computers; therefore, the calibration tasks and analysis are largely automated; and all calibration data are electronically archived.