Stefanie Tompkins

Character and Spatial Distribution of OH/H2O on the Surface of the Moon Seen by M3 on Chandrayaan-1

Lunar Water The Moon has been thought to be primarily anhydrous, although there has been some evidence for accumulated ice in permanently shadowed craters near its poles (see the Perspective by Lucey, published online 24 September). By analyzing recent infrared mapping by Chandrayaan-1 and Deep Impact, and reexamining Cassini data obtained during its early flyby of the Moon, Pieters et al. (p. 568, published online 24 September), Sunshine et al. (p. 565, published online 24 September), and Clark et al. (p. 562, published online 24 September) reveal a noticeable absorption signal for H2O and OH across much of the surface. Some variability in water abundance is seen over the course of the lunar day. The data imply that solar wind is depositing and/or somehow forming water and OH in minerals near the lunar surface, and that this trapped water is dynamic. Space-based spectroscopic measurements provide evidence for water or hydroxyl (OH) on the surface of the Moon The search for water on the surface of the anhydrous Moon had remained an unfulfilled quest for 40 years. However, the Moon Mineralogy Mapper (M3) on Chandrayaan-1 has recently detected absorption features near 2.8 to 3.0 micrometers on the surface of the Moon. For silicate bodies, such features are typically attributed to hydroxyl- and/or water-bearing materials. On the Moon, the feature is seen as a widely distributed absorption that appears strongest at cooler high latitudes and at several fresh feldspathic craters. The general lack of correlation of this feature in sunlit M3 data with neutron spectrometer hydrogen abundance data suggests that the formation and retention of hydroxyl and water are ongoing surficial processes. Hydroxyl/water production processes may feed polar cold traps and make the lunar regolith a candidate source of volatiles for human exploration.

Optimization of endmembers for spectral mixture analysis

Abstract Linear spectral mixture analysis can be used to model the spectral variability in multi- or h yperspectral images and to relate the results to the physical abundance of surface constituents represented by the spectral endmembers. The most difficult step in. this analytical approach lies in the selection of spectral endmembers, which are chosen to represent surface components. A new approach to endhnember selection is presented here, which may be used to augment existing methods, in which the endmembers are derived -mathematically from the image data subject to a set of user-defined constraints. The constraints take the form of a starting -model and allowable deviations from that starting model, which incorporate any a priori knowledge of the data and physical properties of the scene. These constraints are applied to the basic mixing equations, which are then- solved iteratively to derive a set of spectral endmembers that t inintize the residual error. Because the input to the model is quantitative, the derivation. process is repeatable, and endmembers derived with different sets of constraints may be compared to each other directly. Three examples are presented, in which spectral endmembers are derived according to this nwdel for a series of images: a synthetic image cube whose endmembers are already known a natural terrestrial scene, and a natural lunar scene. Detailed analysis of the model inputs and results reveal that this modified approach to endinernber selection provides physically realistic spectral endmembers that in many cases represent purer components than could be found in any pixel in. the image scene.

A Sharper View of Impact Craters from Clementine Data

The ultraviolet-visible camera on the Clementine spacecraft obtained high-spatial resolution images of the moon in five spectral channels. Impact craters mapped with these multispectral images show a scale of lithologic diversity that varies with crater size and target stratigraphy. Prominent lithologic variations (feldspathic versus basaltic) occur within the south wall of Copernicus (93 kilometers in diameter) on the scale of 1 to 2 kilometers. Lithologic diversity at Tycho (85 kilometers in diameter) is less apparent at this scale, although the impact melt of these two large craters is remarkably similar in this spectral range. The lunar surface within and around the smaller crater Giordano Bruno (22 kilometers in diameter) is largely dominated by the mixing of freshly excavated material with surrounding older soils derived from a generally similar feldspathic lithology.

Mineralogy of the mafic anomaly in the South Pole-Aitken Basin: Implications for excavation of the lunar mantle

The mineralogy of South Pole-Aitken Basin [SPA] (the largest confirmed impact basin on the Moon) is evaluated using five-color images from Clementine. Although olivine-rich material as well as basalts rich in clinopyroxene are readily identified elsewhere on the farside, the dominant rock type observed across the interior of SPA is of a very noritic composition. This mineralogy suggests that lower crust rather than the mantle is the dominant source of the mafic component at SPA. The lack of variation in observed noritic composition is probably due to basin formation processes, during which extensive melting and mixing of target materials are likely to occur.

Tsiolkovsky crater: A window into crustal processes on the lunar farside

Mineralogy and distribution of rock types in the Tsiolkovsky region of the lunar farside are evaluated in terms of crustal stratigraphy and evolution. Calibrated multispectral images from five orbits of Clementine data provide compositional information at a scale that allows diverse geologic features to be analyzed and compared. The entire region is seen to be highly anorthositic, with outcrops of relatively pure anorthosite quite common. The crater itself has excavated blocks of anorthosite and noritic anorthosite from the near-surface highland crust, often in a mixed jumble. The central peaks of Tsiolkovsky, which have exhumed much deeper material, however, are composed of relatively pure anorthosite with olivine-rich zones concentrated near the ridge crests. Boundaries between the anorthosite and olivine-rich zones are sharp, but spatial relations suggest the coherent olivine-rich zone is relatively thin (<1 km). The composition of the mare material filling Tsiolkovsky is shown to be low-titanium basalt. Smaller exposures of mare basalt occur about one crater radius from the rim. The crustal structure to ∼25 km in this region prior to the Tsiolkovsky impact appears to be (top to bottom) a few kilometers of anorthositic breccias comprising the megaregolith, a zone of crystalline anorthosite with pockets of noritic anorthosite, a zone of anorthosite devoid of iron-bearing minerals, and a zone of relatively pure anorthosite containing olivine-rich material, possibly emplaced as intrusions.

Emerging opportunities for localization and tracking [Guest Editorial]

GPS has been a phenomenal success. Simply consider as examples its use in car navigation systems or walking around city streets with the help of a smart phone. However, GPS is unavailable inside buildings, in urban canyons, underground, and underwater. Developing complementary location and tracking technologies for these environments would unleash the use of such capabilities in many applications in the military, public safety, and commercial arenas. Within residences and nursing homes, for example, there is an increasing need for indoor geolocation systems to track people with special needs, the elderly, and children to relieve the need for around-the-clock visual monitoring. Other applications include systems to assist the visually impaired, locate instrumentation and other equipment in hospitals, and track specific items in warehouses. In first responder/public safety and military applications, indoor geolocation systems are needed to monitor inmates in prisons, locate miners trapped in mines, and track/guide first responders and soldiers inside buildings. Given the growing interest in sensor networks and radio frequency identification (RFID) technologies, one can also envision wider-ranging applications such as locating unwanted chemical, biological, or radioactive materials using sensor networks, and tracking specific items such as controlled pharmaceuticals in their containers using RFID tags.

Special Section Guest Editorial: Gradient Index Optics

In the past century, every component of an optical system has become lighter and smaller, except the lenses. Typical lenses have too few degrees of freedom—just the refractive index, and the front and back surface shapes—to meet the demands of the vast array of modern optical systems which collect, project, or otherwise manipulate light. (Even in imaging systems, where computational power has the potential to eliminate the tight coupling between lenses and performance, more capable lenses would increase the trade space that optical designers have available to them).

Landcover Change over Central Virginia: Comparison of Endmember Fractions in Hyperspectral Data

A spectral mixture analysis (SMA) based change detection approach has been applied to hyperspectral image (HSI) data collected by the HyMap sensor. As a first step in extending this approach from multispectral to HSI data, an HSI change pair featuring a forested region in central Virginia in the fall of 1999 and 2000 was modeled via SMA as a linear combination of three main endmember materials: green vegetation, non-photosynthetic vegetation, and shade. The fractional abundance images resulting from the SMA are compared quantitatively to assess the level of detail with which change can be detected and understood from the HSI data. Alternatives to the simple three SMA endmember solution are discussed as well, including the use of additional endmembers to account for seasonal change or multiple vegetation species. The utility of SMA-based change detection for mapping subpixel changes in materials is demonstrated, as is the increased interpretability over traditional change detection approaches.