Spectrometers based on acousto-optic tunable filters for in-situ lunar surface measurement

Abstract

The lunar surface consists of rocks of varying sizes and shapes, which are made of minerals, such as pyroxene, plagioclase, olivine, and ilmenite, that exhibit distinctive spectral characteristics in the visible and near-infrared (VIS–NIR) and short-wave infrared (SWIR) regions. To analyze the composition of the lunar surface minerals, several spectrometers based on acousto-optic tunable filters (AOTFs) have been developed to detect lunar surface objects and to obtain their reflectance spectra and geometric images. These spectrometers, including the VIS–NIR imaging spectrometer onboard China’s Chang’e 3/4 unmanned lunar rovers and the Lunar Mineralogical Spectrometer onboard the Chang’e 5/6 lunar landers, use AOTFs as dispersive components. Both are equipped with a VIS/NIR imaging spectrometer, one or several SWIR spectrometers, and a calibration unit with dust-proofing functionality. They are capable of synchronously acquiring the full spectra of the lunar surface objects and performing in-situ calibrations. We introduce these instruments and present a brief description of their working principle, implementation, operation, and major specifications, in addition to the initial scientific achievement of lunar surface exploration.