Wavelength Calibration for the LIBS Spectra of the Zhurong Mars Rover

China's first Mars rover, Zhurong, landed on the southern region of Utopia Planitia, Mars, on 14 May 2021 (UTC). Zhurong is equipped with the Mars Surface Composition Detection Package (MarSCoDe), which analyzes the Martian surface's material composition. Composed of laser-induced breakdown spectroscopy (LIBS), short-wave infrared spectroscopy (SWIR), and a microimaging camera, MarsCoDe can work at a distance of 1.6-7 m to analyze element abundance and the mineralogy of targets on the Martian surface. Analysis shows that the wavelengths of MarSCoDe onboard LIBS spectra acquired within the same probe period will have different degrees of drift, leading to deviation in qualitative and quantitative elemental analysis. This paper finds that the spectrum drift follows a quadratic function relationship with the CCD temperature of the MarSCoDe spectrometer, based on which a wavelength calibration method is established. According to the function, the drift of a certain channel is calculated by the corresponding CCD temperature, and then the wavelength of the spectrum is calibrated by the drift. The accuracy of this calibration method for the position of peak wavelength in the LIBS spectrum can reach about 1/5 of the apparatus spectral width, and the cross-validation analysis using a norite standard sample shows that it is comparable to the wavelength calibration accuracy of the ChemCam onboard data product.

Automated summary

China's first Mars rover, Zhurong, successfully landed in the southern region of Utopia Planitia on May 14, 2021. Equipped with MarSCoDe, Zhurong is able to analyze the material composition of the Martian surface using LIBS, SWIR, and a microimaging camera. However, analysis shows that the spectra acquired by MarSCoDe's LIBS experience wavelength drift, which affects the accuracy of elemental analysis. This paper establishes a wavelength calibration method based on a quadratic function relationship between the drift and CCD temperature of the MarSCoDe spectrometer.