A correlation study based on Al/Si x-ray fluorescence data from Southwestern part of mare serenitatis

The Tacquet Formation in southwestern Mare Serenitatis has unusually low visible albedos for the Al/Si intensity ratios measured by the Apollo 15 X-ray fluorescence experiment. This is a contradiction of the demonstrated good correlation between Al/Si and visible albedo data. To understand why this situation exists, a correlation study has been undertaken. This study is based on Al/Si intensity ratios and includes such other remote sensing data as visible and near IR spectral reflectance, color-difference and color-ratio photography, and broad spectrum visible albedo measurements. The Tacquet unit appears to have: (1) an average Al/Si intensity which is intermediate between mare and highland values (=0.21); (2) visible albedos equivalent to the two darkest mare units in the Tranquillitatis-Serenitatis area; (3) a low titanium content; and (4) a relatively high glass-to-crystal ratio. The evidence indicates that the discrepancy between visible albedos and Al/Si intensities in the vicinity of the Tacquet Formation might be due primarily to the addition of highland-type ejecta from the crater, Menelaus, onto a low albedo mare unit. The possibility that the formation consists of dark, high Al material such as spinel, perhaps extruded from the Menelaus Rilles, cannot be excluded, although no such material has been sampled by the lunar missions.     

Explaining NDVI trends in northern Burkina Faso

Many studies have shown a ‘greening of the Sahel’ on the basis of analysis of time series of satellite images and this has shown to be, at least partly, explained by changes in rainfall. In northern Burkina Faso, an area stands out as anomalous in such analysis, since it is characterized by a distinct spatial pattern and strongly dominated by negative trends in Normalized Difference Vegetation Index (NDVI). The aim of the paper is to explain this distinct pattern. When studied over the period 2000–2012, using NDVI data from the MODIS sensor the spatial pattern of NDVI trends indicates that non-climatic factors are involved. By relating NDVI trends to landscape elements and land use change we demonstrate that NDVI trends in the north-western parts of the study area are mostly related to landscape elements, while this is not the case in the south-eastern parts, where rapidly changing land use, including. expansion of irrigation, plays a major role. It is inferred that a process of increased redistribution of fine soil material, water and vegetation from plateaus and slopes to valleys, possibly related to higher grazing pressure, may provide an explanation of the observed pattern of NDVI trends. Further work will focus on testing this hypothesis.