Journal Article

MoonIndex, an Open‐Source Tool to Generate Spectral Indexes for the Moon From M3 Data

Carli, Cristian, Nodjoumi, Giacomo, Suárez‐Valencia, Javier Eduardo, Zambon, Francesca, Rossi, Angelo Pio

2024

Overview

Spectral indexes are tools widely used to analyze the composition of planetary surfaces. Many indexes have been formulated over the years to map the lunar surface, but there is no unified database for them. In this work we describe an Open‐Source Python package called MoonIndex, that recreates 38 indexes compiled from the literature, using data from the Moon Mineralogy Mapper (M3). The processing started with the filtering of the data cubes to reduce the noise, the continuum of the spectrum was then removed using a convex hull or a second‐and‐first‐order fit method. Later, the indexes were calculated, following as possible the original formulations. The results on spectral indexes calculated before the continuum removal were similar to those of the original formulations. Conversely, the results obtained for spectral indexes calculated after the continual removal were not always coherent. Some indexes, like the band depth, are especially sensitive to the removal method, as well as the derived band areas and asymmetries. We also recreated RGB composite maps, our results highlight the compositional patterns in a similar way as the ones in the literature, even if the color ramps can differ. The products of MoonIndex are open, ready for interpretation, versatile, consistent, and cross‐comparable. Plain Language Summary Spectral indexes are parameters defined from the characteristics of reflectance spectra, and they are useful to investigate the spectral properties of a surface and to retrieve mineralogical properties of a planetary body. They can reveal the presence of specific minerals in rocks, indicate mineralogical variations from different units, highlight physical properties of a surface, or show the effect of the exposure to the space environment. For the Moon, several spectral indexes have been formulated over time using data from many spacecraft, but no unified database is available. In this work, we created an open‐source Python package called MoonIndex, which recreates 38 indexes to study the lunar surface. The indexes were collected from the literature, and our results achieved various levels of fidelity. Some of the indexes we calculated exactly reproduce those found in the literature, while in other cases, index calculations differ due to processing constraints or due to missing information in the original formulations, such as the continuum removal method used, or the band operations conducted to create the indexes. MoonIndex is a reliable and versatile tool to approach the compositional analysis of the lunar surface. Key Points MoonIndex is an open‐source tool that successfully recreates spectral indexes for the Moon taken from the literature The continuum‐removal method has a major impact in the resulting indexes, so its selection should be considered when interpreting the data The indexes obtained with MoonIndex are consistent whit the results of previous authors, which usually used licensed software

• Publisher: John Wiley & Sons, Inc,American Geophysical Union (AGU)
• Subject: geology / hyperspectral / Mineralogy / Minerals / Moon / Moon Mineralogy Mapper / Python / Remote sensing