ALBERT

Description: In both AVIRIS and ISM data, through the use of mixing models, geological boundaries of the Ronda massif are identified with respect to the surrounding rocks. We can also yield first-order vegetation maps. ISM and AVIRIS instruments give consistent results. On the basis of endmember fraction images, it is then possible to discard areas highly vegetated or not belonging to the peridotite massif. Within the remaining part of the mosaic, spectro-mixing analysis reveals spectral variations in the peridotite massif between the well-exposed areas. Spatially organized units are depicted, related to differences in the relative depth of the absorption band at 1 micron, and it may be due to a different pyroxene content. At this stage, it is worth noting that, although mineralogical variations observed in the rocks are at a sub-pixel scale for the airborne analysis, we see an emerging spatial pattern in the distribution of spectral variations across the massif which might be prevailingly related to mineralogy. Although it is known from fieldwork that the Ronda peridotite massif exhibits mineralogical variations at local scale in the content of pyroxene, and at regional scale in different mineral facies, ranging from garnet-, to spinel- to plagioclase-lherzolites, no attempt has been done yet to produce a synoptic map relating the two scales of analysis. The present work is a first attempt to reach this objective, though a lot more work is still required. In particular, for the purpose of mineralogical interpretation, it is critical to relate the airborne observation to field work and laboratory spectra of Ronda rocks already obtained, with the use of image endmembers and associated reference endmembers. Also, the pretty rough linear mixing model used here is taken as a 'black-box' process which does not necessarily apply correctly to the physical situation at the sub-pixel level. One may think of using the ground-truth observations bearing on the sub-pixel statistical characteristics (texture, structural pattern, surface distribution and vegetation contribution (grass,..)) to produce a more advanced mixing model, physically appropriate to the geologic and environmental contexts.

Description: Ultramafic rocks are relatively rare at the Earth's surface but constitute the vast majority of the Earth by volume. Exposures of ultramafic bodies are therefore crucial for deducing many important processes that occur in the Earth's mantle. An important science question regarding the spatial distribution, abundance, and composition of mafic minerals in ultramafic bodies that can be examined with advanced sensor data is the melting process. When a lherzolite melts, clinopyroxene (cpx) melts first and therefore variations in the modal amount of cpx remaining in the mantle are a reflection of the amount of fractional melting that has occurred. Fe goes preferentially into the melt during melting but a 20 percent batch melting (i.e. closed system) acquires less Fe relative to 20 percent fractional melting (i.e. open system). Since the strength and wavelength of diagnostic absorptions is a strong function of Fe content, it is possible to make maps of the variation in Fe:Mg ratios which can be related to the general melting process. Accurate ground-truth information about local mineralogy provides internal calibration and consistency checks. Investigations using imaging spectrometer are very complementary to field studies because advanced sensor data can provide a synoptic view of modal mineralogy and chemical composition whereas field studies focus on detailed characterization of local areas. Two excellent exposures of ultramafic lithologies are being investigated with visible to mid-infrared imaging spectrometer data: the Ronda peridotite near Ronda, Spain and the Beni Bousera ophiolitic fragment in northern Morocco. Although separated by the Alboran Sea, these bodies are thought to be related and represent fertile sub-continental mantle. The Ronda peridotite is predominantly spinel lherzolite but grades into harzburgite and shows considerable variation in major and trace element compositions. Mafic layering and dykes (i.e. olivine gabbro) are also observed. This indicates some sections of the peridotite have experienced greater degrees of partial melting. The Beni Bousera peridotite also contains mafic layers and dykes and grades into harzburgite representing similar fundamental shifts in the bulk chemistry of this ultramafic body probably related to an episode of partial melting. The specific mode of emplacement of these bodies is controversial and important for understanding the tectonic evolution of this region. Our investigations are not necessarily designed to help resolve this controversy. Rather, these exposures provide excellent and unusual examples of fertile mantle which have undergone variable degrees of partial melting.

Description: Previous studies have compared the global topographic distribution of both planets by means of differential hypsometric curves. For the purpose of comparison, the terrestrial oceanic load was removed, and a reference base level was acquired. It was chosen on the basis of geometric considerations and reflected the geometric shape of the mean dynamical equilibrium figure of the planetary surface in both cases. This reference level corresponds to the well-known sea level for the Earth; for Venus, given its slow rate of rotation, a sphere of radius close to the mean, median and modal values of the planetary radii distribution were considered and the radius value of 6051 km arbitrarily taken. These studies were based on the low resolution (100 x 100 sq km) coverage of Venus obtained by the Pioneer Venus altimeter and on the 1 deg x 1 deg terrestrial topography. But, apart from revealing the distinct contrast existing between the Earth's bimodal and Venus' strong unimodal topographic distribution, the choice of such a reference level is inadequate and even misleading for the comparative geophysical understanding of the planetary relief distribution. The present work reinvestigates the comparison between Earth and Venus hypsometric distribution on the basis of the high-resolution data provided, on one hand, by the recent Magellan global topographic coverage of Venus' surface, and on the other hand, by the detailed NCAR 5 x 5 ft. grid topographic database currently available for the Earth's surface.

Description: On the base of laboratory results and telescopic data it is shown that the spectropolarization ratio P(sub max(sup B))/P(sub max(sup R)) for blue and red spectral regions is a remote sensing parameter of lunar soil maturity. It correlates with value of maturity index derived from morphological or ferromagnetic methods of exposure age determination. This parameter is equal to 0.315 for Reiner-gamma formation. So Reiner-gamma area is covered by immature soil. An extensive spectral mapping of the Reiner-gamma formation with high spatial resolution (0.2 km/pixel) was produced. This result was obtained at the 2-meter aperture telescope of Pic-du-Midi (France). The data sets consist in repeated runs comprising 10 selected narrow-band images (from 0.4 to 1.05 micron). The analysis of these data suggests that such a type of immature material includes not more than 28% of agglutinattes. We find the model grain size of fine fraction to be 40 micrometers grain size, of more immature soil 400-500 micrometers, and of the formation soil 120-150 micrometers. The exposure age of the Reiner-gamma immature soil is equal about 10 x 10(exp 6) years.