A reflectance calibration method for Multispectral Camera (MSCam) on the Zhurong rover

The Multispectral Camera (MSCam) onboard the Zhurong rover, collecting eight band images in the visible and near-infrared wavelengths, aims to investigate the morphological characteristics and mineralogic properties of the Martian surface. Due to the perturbation of Martian atmosphere, accurate reflectance calibration for the MSCam data is crucial for the further spectral interpretation. Here, we proposed a reflectance calibration method to convert the MSCam radiance to reflectance factor using the MSCam calibration target. This study begins with the laboratory multi-angle measurements to characterize the photometric properties of the MSCam calibration target. Based on these photometric characteristics, a reflectance model consisting of a directional reflection term and a specular reflection term is developed. The constructed reflectance model achieves a high precision, the root mean square errors (RMSEs) between the modeled and measured reflectance factor are <1.5% and the determination coefficients (R2) are >99.3% in all cases. We then applied this reflectance model to the in-flight observations to derive the reflectance of the Martian surface. The validations indicate that the in-flight derived reflectance factors of the calibration target are consistent with the laboratory measurements, and the derived reflectance spectra of the Martian surface are comparable to the spectra captured by the other mission.