Stardust-NExT NAVCAM Calibration and Performance
By Ken Klaasen, Co-Investigator
|NAVCAM calibration data processing pipeline logic flow; related functions are grouped by different shading colors View larger image|
Significant improvements in the calibration of the Stardust-NExT NAVCAM have been realized through the acquisition of new calibration data during the NExT mission as well as reanalysis of prime mission data. Substantial improvements in the NAVCAM calibration were achieved in the areas of geometric correction, spatial resolution, and radiometric calibration (in particular, zero-exposure signal levels, shutter time offsets, absolute radiometric response, noise, and scattered light characterization).
The camera PSF was characterized down to an unprecedented level of nearly 10^-6 of the total point-source star signal. Star images were used to monitor the effectiveness of CCD heating in removing recurring contamination from the detector. Shutter performance was calibrated as a function of image line number and shutter blade movement direction to an accuracy of <0.1 ms.
Models for estimating the bias and dark current levels as functions of CCD temperature and time since the CCD heater was last powered off were developed that allow reasonably accurate radiometric calibration of windowed images, which do not return the overclocked pixel values that explicitly provide the bias level. Absolute radiometric response calibration conversion constants were derived from images of photometric standard stars. Residual contamination patterns were tracked to assess their impact on flat-field calibrations. The dependence of scattered light levels on Sun-illumination direction and scan mirror position was determined for many geometries.
The data processing pipeline has been updated to incorporate these improved calibrations and will be used to generate archival NAVCAM data records for both the NExT (new) and the primary Stardust mission (upgrade), which will be delivered to the Planetary Data System