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Inflight Radiometric Calibration of New Horizons' Multispectral Visible Imaging Camera (MVIC)
We discuss two semi-independent calibration techniques used to determine the
in-flight radiometric calibration for the New Horizons' Multi-spectral Visible
Imaging Camera (MVIC). The first calibration technique compares the observed
stellar flux to modeled values. The difference between the two provides a
calibration factor that allows the observed flux to be adjusted to the expected
levels for all observations, for each detector. The second calibration
technique is a channel-wise relative radiometric calibration for MVIC's blue,
near-infrared and methane color channels using observations of Charon and
scaling from the red channel stellar calibration. Both calibration techniques
produce very similar results (better than 7% agreement), providing strong
validation for the techniques used. Since the stellar calibration can be
performed without a color target in the field of view and covers all of MVIC's
detectors, this calibration was used to provide the radiometric keywords
delivered by the New Horizons project to the Planetary Data System (PDS). These
keywords allow each observation to be converted from counts to physical units;
a description of how these keywords were generated is included. Finally,
mitigation techniques adopted for the gain drift observed in the near-infrared
detector and one of the panchromatic framing cameras is also discussed