Inflight Radiometric Calibration of New Horizons' Multispectral Visible Imaging Camera (MVIC)

TL;DR

This paper presents two validated in-flight radiometric calibration techniques for New Horizons' MVIC camera, enabling accurate conversion of observed data into physical units and addressing detector gain drift issues.

Contribution

It introduces two semi-independent calibration methods validated against each other, improving in-flight radiometric calibration accuracy for the MVIC instrument.

Findings

Calibration techniques agree within 7%

Stellar calibration covers all detectors

Calibration keywords enable conversion to physical units

Abstract

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.