Remote sensing of potential lunar resources: 2. High spatial resolution mapping of spectral reflectance ratios and implications for nearside mare TiO₂ content

High spatial resolution maps illustrating variations in spectral reflectance 400/560 nm ratio values have been generated for the following mare regions: (1) the border between southern Mare Serenitatis and northern Mare Tranquillitatis (including the MS‐2 standard area and Apollo 17 landing site), (2) central Mare Tranquillitatis, (3) Oceanus Procellarum near Seleucus, and (4) southern Oceanus Procellarum around Flamsteed. We have also obtained 320–1000 nm reflectance spectra of several sites relative to MS‐2 to facilitate scaling of the images and provide additional information on surface composition. Inferred TiO 2 abundances for these mare regions have been determined using an empirical calibration which relates the weight percent TiO 2 in mature mare regolith to the observed 400/560 nm ratio. Mare areas with high TiO 2 abundances are probably rich in ilmenite (FeTiO 3 ) a potential lunar resource. The highest potential TiO 2 concentrations we have identified in the nearside maria occur in central Mare Tranquillitatis. Inferred TiO 2 contents for these areas are >9 wt % and are spatially consistent with the highest‐TiO 2 regions mapped previously at lower spatial resolution. We note that the morphology of surface units with high 400/560 nm ratio values increases in complexity at higher spatial resolutions. New telescopic spectra of landing sites successfully reproduce the Charette relation, although we find that the 400/560 nm value is strongly a fimction of the sample area size. The increased spectral contrast of the 400/730 nm ratio over the 400/560 nm ratio demonstrates the potential increased precision with which the 400/730 nm ratio might be used to estimate TiO 2 abundances. Comparisons have been made with previously published geologic maps, Lunar Orbiter IV, and ground‐based images, and some possible morphologic correlations have been found between our mapped 400/560 nm ratio values and volcanic landforms such as lava flows, mare domes, and collapse pits.