Absolute calibration of the Chang’E-1 IIM camera and its preliminary application

Abstract

The interference imaging spectroradiometer (IIM) onboard the first lunar satellite of China “Chang’E-1” can now provide approximately global high spectral and spatial resolution reflectance spectra of the Moon. It is the essential instrument with which to accomplish one of the four missions of the first lunar satellite of China. As the current data provided by the Lunar Exploration Program Center and National Astronomical Observatories (NAOC) are not reflectance and the sensor response is inhomogeneous in the line direction, users can not use the current data directly. Moreover, due to the narrow band range, IIM data cannot cover the absorption peak of the mafic minerals of the Moon completely, which limits its ability for identifying minerals. The main objective of this study is to describe the methods for absolute calibration, correction and acquiring the absorption center of minerals for IIM data. The results from our study show that in the space domain the sensor response decreases toward the left, and in the spectral domain the response of the longer bands is more inhomogeneous than that of the shorter bands. After the calibration and correction, the reflectance of IIM matches the earth-based telescopic spectra well, which suggests the possible use of the processed data in the geological research. A high correlation was found between the absorption center and the wavelength at which the first derivative equals 0, i.e., the so-called Stagnation Point in the mathematical sense. In the end, we show a preliminary applied study of the two craters with diameter larger than 35 km using the calibrated data. The spectra of IIM data show that the lunar crust has compositional diversity within the km scale. Pure anorthosite may be found on the wall and floor of the Aristarchus crater with the map of absorption center, which indicates that anorthosite is ubiquitously present within the lunar crust. IIM, with its capacity to acquire lunar composition at the regional and global scale, will contribute to the research of lunar origin and evolution.