Paul G. Lucey

Mapping the FeO and TiO2 content of the lunar surface with multispectral imagery

The derivation of quantitative elemental concentrations from multispectral imaging of the Moon has long been a goal of lunar remote sensing. Concentration maps at the spatial resolutions available from the recent Clementine mission would provide a revolutionary new tool for understanding the origin and evolution of the lunar crust. Lucey et al. [1995] presented a method for extracting the concentration of Fe from multispectral imaging of the Moon. This paper examines and quantifies important aspects ofthat technique left unexamined by Lucey et al. which had the potential to severely limit its utility. These aspects include the effects of maturity, grain size, mineralogy, shading due to topography, and the presence of glass. We also present a new algorithm for derivation of TiO2 from multispectral imaging of both mare and highland units. We find that both techniques are only weakly sensitive to maturity and that they have about 1 wt % accuracy based on examination of the spectral properties and compositions of resolved lunar sampling stations presented by Blewett et al. [1997]. We also discuss these findings in the context of two contrasting views of the effect of composition on lunar spectral properties presented by Pieters and coworkers and Hapke and coworkers. We find the view of Hapke and coworkers to be more consistent with our observations. Using a global mosaic of Clementine multispectral data and these element derivation algorithms, we find that the global modal abundance of FeO is 4.5 wt %±1 wt % and the global modal abundance of TiO2 is 0.45 wt %±1 wt. %.

Initial observations from the Lunar Orbiter Laser Altimeter (LOLA)

As of June 19, 2010, the Lunar Orbiter Laser Altimeter, an instrument on the Lunar Reconnaissance Orbiter, has collected over 2.0 × 10^9 measurements of elevation that collectively represent the highest resolution global model of lunar topography yet produced. These altimetric observations have been used to improve the lunar geodetic grid to ~10 m radial and ~100 m spatial accuracy with respect to the Moons center of mass. LOLA has also provided the highest resolution global maps yet produced of slopes, roughness and the 1064-nm reflectance of the lunar surface. Regional topography of the lunar polar regions allows precise characterization of present and past illumination conditions. LOLAs initial global data sets as well as the first high-resolution digital elevation models (DEMs) of polar topography are described herein.

Iron abundances on the lunar surface as measured by the Lunar Prospector gamma‐ray and neutron spectrometers

[i] Global measurements of iron abundances on the lunar surface are presented using data from the Lunar Prospector (LP) Gamma-Ray Spectrometer (GRS) and Neutron Spectrometer (NS). In this study, we derive relative iron abundances from the low-altitude, high spatial resolution (∼(45 km) 2 ) LP data using the 7.6 MeV neutron capture gamma-ray doublet. As part of the LP-GRS analysis, we demonstrate the importance of accounting for variations in neutron number density across the lunar surface by measuring neutron fluxes using LP-NS data. In a first step of comparing the LP-GRS data with previously published iron abundances inferred from Clementine Spectral Reflectance (CSR) data, we show that the existing CSR FeO data are nonlinear with respect to the LP relative iron abundances. We use the LP data to linearize the relationship between the CSR and the relative iron values then recalibrate the CSR data to iron abundance using returned soil abundances. We then correlate the CSR data, except for major anomalies, with the LP relative iron measurements to convert the LP data to absolute iron abundances. When we compare the LP-GRS and revised CSR data sets, we find a very good correspondence. There are two locations (Mare Tranquillitatis and South Pole-Aitken (SPA) basin) that show major discrepancies, suggesting that the CSR data are locally overestimating iron abundances. In both these regions, the discrepancies identified by the LP-GRS/CSR comparison are possibly explained by mineralogical differences that are not accounted for in the CSR to FeO calibration. In regards to our understanding of the Moon, the LP data have found the following: (I) There exist large expanses of mare basalt in the western mare regions that have very high iron abundances (22-23 wt.% FeO) that are underrepresented but not absent from the returned sample collection and are highly unusual for mare soils, which typically contain a significant amount of highlands contamination. (2) The low iron abundances in the lunar highlands (∼5 FeO wt.%) are consistent with a previous analysis using thermal and epithermal neutrons and with the idea that the lunar crust formed by a relatively simple magma ocean process. (3) The comparison of LP and CSR derived iron abundances suggests that the material within SPA basin is similar to a norite-type rock without an enriched mantle FeO signature. (4) A comparison of LP and CSR data at Tycho Crater shows a large discrepancy such that the CSR data show moderate iron abundances of 8-9 wt.% FeO while the LP data show very low iron abundances of 3-4 wt.% FeO. This discrepancy cannot yet be easily explained by any known process.

Stand-off Raman spectroscopic detection of minerals on planetary surfaces

We have designed and developed two breadboard versions of stand-off Raman spectroscopic systems for landers based on a 5-in. Maksutov-Cassegrain telescope and a small (4-in. diameter) Newtonian telescope receiver. These systems are capable of measuring the Raman spectra of minerals located at a distance of 4.5-66 m from the telescope. Both continuous wave (CW) Ar-ion and frequency doubled Nd:YAG (532 nm) pulsed (20 Hz) lasers are used as excitation sources for measuring remote Raman spectra of rocks and minerals. We have also made complementary measurements on the same rock samples with a micro-Raman system in 180 and 135 degrees geometry for evaluating the system performance and for estimating effect of grain size and laser-induced heating on the spectra of minerals using alpha-quartz as a model mineral. A field portable remote pulsed Raman spectroscopic system based on the 5-in. telescope and an f/2.2 spectrograph has been developed and tested. We have also demonstrated a prototype of a combined Raman and laser-induced breakdown spectroscopy (LIBS) system, capable of providing major element composition and mineralogical information on both biogenic and inorganic minerals at a distance of 10 m from the receiver.

Thermal infrared spectroscopy of experimentally shocked anorthosite and pyroxenite: Implications for remote sensing of Mars

We performed shock recovery experiments at JSC (17-63 GPa) on samples of Stillwater pyroxenite and anorthosite and acquired their thermal infrared spectra (3-50 micron) to investigate the degradation of spectral features at high pressures. Additional information is contained in the original extended abstract.

A combined remote Raman and LIBS instrument for characterizing minerals with 532 nm laser excitation.

The authors have developed an integrated remote Raman and laser-induced breakdown spectroscopy (LIBS) system for measuring both the Raman and LIBS spectra of minerals with a single 532 nm laser line of 35 mJ/pulse and 20 Hz. The instrument has been used for analyzing both Raman and LIBS spectra of carbonates, sulfates, hydrous and anhydrous silicates, and iron oxide minerals in air. These experiments demonstrate that by focusing a frequency-doubled 532 nm Nd:YAG pulsed laser beam with a 10x beam expander to a 529-microm diameter spot on a mineral surface located at 9 m, it is possible to measure simultaneously both the remote Raman and LIBS spectra of calcite, gypsum and olivine by adjusting the laser power electronically. The spectra of calcite, gypsum, and olivine contain fingerprint Raman lines; however, it was not possible to measure the remote Raman spectra of magnetite and hematite at 9 m because of strong absorption of 532 nm laser radiation and low intensities of Raman lines from these minerals. The remote LIBS spectra of both magnetite and hematite contain common iron emission lines but show difference in the minor amount of Li present in these two minerals. Remote Raman and LIBS spectra of a number of carbonates, sulfates, feldspars and phyllosilicates at a distance of 9 m were measured with a 532-nm laser operating at 35 mJ/pulse and by changing photon flux density at the sample by varying the spot diameter from 10 mm for Raman to 530 microm for LIBS measurements. The complementary nature of these spectra is highlighted and discussed. The combined Raman and LIBS system can also be re-configured to perform micro-Raman and micro-LIBS analyses, which have applications in trace/residue analysis and analysis of very small samples in the nano-gram range.

Mapping iron in the lunar mare: An improved approach

[1] Previous methods for mapping iron (Lucey et al., 1995, 1998, 2000a) give inconsistent results in terms of suppressing the effects of maturity, making it difficult to distinguish true units of contrasting iron from regions that simply show the residual effects of incomplete separation of maturity. These methods rely on an assumption that materials of similar iron content but varying maturity form radial trends on a plot of VIS reflectance versus NIR/VIS ratio. Recently, the assumption of radial behavior of maturity trends in mare regions has been called into question by Staid and Pieters (2000). They observed trends in the mare that appeared more parallel in nature. In this work we study nearly 10,000 craters in six mare regions and model the effects of maturity with radiative transfer theory to quantify and better understand the spectral behavior of maturity variations in the mare. We confirm that the maturity trends in mare regions are more parallel than radial, and we exploit this fact to develop a new algorithm for determination of iron content in mare regions. This new mare iron algorithm better compensates for maturity than previous methods, and uncertainties due to maturity variations are less than 0.5 wt% FeO. Absolute uncertainties are similar to previous algorithms (1.5 wt% FeO). Results from this work provide the ability to detect iron anomalies in the ejecta of craters and as a result more confidently map vertical stratigraphy in the lunar mare in terms of iron composition.

Remote sensing studies of the Orientale Region of the Moon: A pre‐Galileo view

We have acquired both an extensive data base of visible and near-infrared spectra and multispectral images (ultraviolet and visible) of the Orientale region of the Moon. Our results show that the eastern Inner Rook Mountains are composed of anorthosite. Portions of the main ring of the Humorum basin and the inner ring of Grimaldi are also composed of anorthosite. Other deposits within the Orientale basin and the major ejecta unit outside the basin are dominated by noritic anorthosites; mature surfaces have spectra nearly identical to those taken of areas in the vicinity of the Apollo 16 site. Thus, it appears that Orientale ejecta are more mafic than materials that are thought to have originated at depth (i.e., the anorthosites in the Inner Rook Mountains). There are large areas that have mare basalt signatures mixed with highland rock types, indicating the existence of ancient, pre-Orientale mare volcanism. Present mare surfaces in the Orientale region contain basalts of intermediate to very low TiO2 content.

Remote sensing studies of the terrain northwest of Humorum Basin

We have used near-infrared reflectance spectra and Earth-based radar data to investigate the composition and origin of the various geologic units northwest of Humorum basin as well as the stratigraphy of the Humorum pre-impact target site. The results of our spectral analysis indicate that at least a portion of the inner, mare-bounding ring is composed of pure anorthosite. Other highlands units in the region are dominated by noritic anorthosite. The anorthosites on the inner ring may have been derived from a layer of anorthosite that exists at depth beneath a more pyroxene-rich unit. Both Gassendi G and F craters expose mare material from beneath a highlands-rich surface unit that was emplaced as a result of the Letronne, Gassendi, and other impact events. This ancient basalt unit was emplaced after the formation of Humorum basin but prior to the Orientale impact.

Spectroscopic observations of bright and dark emission features on the night side of venus.

Near-infrared spectra of a bright and a dark thermal emission feature on the night side of Venus have been obtained from 2.2 to 2.5 micrometers (�m) at a spectral resolution of 1200 to 1500. Both bright and dark features show numerous weak absorption bands produced by CO2, CO, water vapor, and other gases. The bright feature (hot spot) emits more radiation than the dark feature (cold spot) throughout this spectral region, but the largest contrasts occur between 2.21 and 2.32 �m, where H2SO4 clouds and a weak CO2 band provide the only known sources of extinction. The contrast decreases by 55 to 65 percent at wavelengths longer than 2.34 �m, where CO, clouds, and water vapor also absorb and scatter upwelling radiation. This contrast reduction may provide direct spectroscopic evidence for horizontal variations in the water vapor concentrations in the Venus atmosphere at levels below the cloud tops.