Measuring GNSS ionospheric total electron content at Concordia, and application to L-band radiometers

In the framework of the project BIS - Bipolar Ionospheric Scintillation and Total Electron Content Monitoring, the ISACCO-DMC0 and ISACCO-DMC1 permanent monitoring stations were installed in 2008. The principal scope of the stations is to measure the ionospheric total electron content (TEC) and to monitor the ionospheric scintillations, using high-sampling-frequency global positioning system (GPS) ionospheric scintillation and TEC monitor (GISTM) receivers. The disturbances that the ionosphere can induce on the electromagnetic signals emitted by the Global Navigation Satellite System constellations are due to the presence of electron density anomalies in the ionosphere, which are particularly frequent at high latitudes, where the upper atmosphere is highly sensitive to perturbations coming from outer space. With the development of present and future low-frequency space-borne microwave missions (e.g., Soil Moisture and Ocean Salinity [SMOS], Aquarius, and Soil Moisture Active Passive missions), there is an increasing need to estimate the effects of the ionosphere on the propagation of electromagnetic waves that affects satellite measurements. As an example, how the TEC data collected at Concordia station are useful for the calibration of the European Space Agency SMOS data within the framework of an experiment promoted by the European Space Agency (known as DOMEX) will be discussed. The present report shows the ability of the GISTM station to monitor ionospheric scintillation and TEC, which indicates that only the use of continuous GPS measurements can provide accurate information on TEC variability, which is necessary for continuous calibration of satellite data

Mineral re-equilibration and P-T path of metagabbros, Sierra de San Luis, Argentina: insights into the exhumation of mafic-ultramafic belt

At La Melada, Sierra de San Luis, Argentina, two lenses of mafic-ultramafic rocks, mainly consisting of metagabbros, are made up of igneous and metamorphic minerals in varying combinations. These rocks are part of a narrow NNE-SSW trending belt along the eastern flank of the Sierra and were affected by Famatinian metamorphism and deformation followed by shear deformation. La Melada metagabbros show a wide variety of microstructures including actinolite + chlorite + quartz pseudomorphs, epidote coronas and epidote + quartz symplectites, actinolite + quartz intergrowths and calcite + chlorite aggregates. These microstructural characteristics witness a complex metamorphic history consisting of a progressive cooling and decompression associated with regional and shear deformation from M0 down to the M1 to M3 greenschist/sub- greenschist stage. Cooling from the M0 stage (T≈780°C and <6.5 < P < 8.0 kbar) led to destabilization of pyroxene with talc formation at the M1 stage (T = 650-670 °C, P < 6 kbar). Further cooling resulted in the formation of actinolite + chlorite + quartz pseudomorphs growing on igneous and metamorphic amphibole (M2 stage <600 < T < 625 °C and P ≈ 3.8 kbar). The third re-equilibration stage led to the formation of epidote coronas and epidote + quartz symplectite around igneous plagioclase (M3 stage< 420 < T < 470 °C and 2 < P < 4 kbar). Calcite + chlorite aggregates partially replacing actinolite are evidence of the last stage of mineral re-equilibration. As compared to P-T path previously reported in the literature, La Melada rocks indicate that mineral re-equilibration reached P-T conditions as low as ∼420-470 °C, with epidote development under (sub-)greenschist-facies P-T conditions. The resulting P-T path is in agreement with the P-T path reconstructed for the country rocks

Early stage evolution of the mafic-ultramafic belt at La Melada, Sierra de San Luis, Argentina: P-T constraints from metapyroxenite pseudosection modelling

At La Melada, Sierra de San Luis, Argentina, two lenses of mafic-ultramafic rocks, which underwent Famatinian metamorphism followed by shear deformation, form part of a NNE-SSW-trending belt along the eastern flank of the Sierra. Metapyroxenites from the lenses are granoblastic rocks made up of igneous and metamorphic minerals, with varying degrees of deformation and mylonitization. These rocks preserve evidence of post-magmatic re-equilibration that followed the emplacement of the mafic-ultramafic rocks. Microstructural investigation and P-T pseudosection modelling suggest that La Melada metapyroxenites experienced a temperature and pressure decrease from the M0 (800 °C < T < 920 °C; 0.7 GPa < P < 0.9 GPa) to the M1 stage (720 °C < T < 780 °C; 0.6 GPa < P < 0.7 GPa). Further re-equilibration led to the formation of talc + cummingtonite during the M2 stage and to the development of metamorphic plagioclase and dolomite in the post-M2 stage. The P-T segment reconstructed for La Melada metapyroxenites is consistent with a back-arc setting and with P-T paths previously reported in the literature

Evolucion metamorfica de las melagabronoritas coroniticas de El Arenal, faja mafica-ultramafica El Destino-Las Aguilas, Sierra de San Luis

The coronitic meta- melagabbronorites are part of the El Arenal bodies which belong to the El Destino-Las Aguilas mafic to ultramafic belt, outcroping on the eastern flank of the Sierra de San Luis. They are fine-grained rocks with corona microstructures around Mg-rich olivine and An-rich plagioclase which record three metamorphic stages of mineral crystallization developed under granulite, amphibolite and greenschist P-T conditions. The coronitic meta-melagabbros represent early, high Cr-Ni fractions, with [Mg++/Mg+++FeT ++] comprised between 0.72 and 0.75, derived from a low-Ti olivine tholeiitic magma which emplaced before the penetrative Famatinian deformation and the widespread coeval metamorphism. The subsequent uplift and the slow cooling of the deep-seated magma was possible because of the high P-T conditions of the crustal level, ca. amphibolite facies, and result in the development of the coronas after an early slightly deuteric alteration of the primary, now preserved as relics, igneous minerals. When granulite facies conditions were reached Mg-rich olivine and Ca-rich plagioclase became unstable and reacted to form orthopyroxene and symplectitic clinopyroxene + spinel around olivine. H2O-rich fluids necessary for the amphibole crystallization, which formed symplectite intergrowths with spinel and also replaced relic orthopyroxene during the amphibolite stage, were provided by dehydration of the adjacent country rocks caused by the development of metamorphic reactions. Minerals formed under greenschist P-T conditions were probably related with the final exhumation of the rocks, and are thought to represent the last part of the counterclockwise evolutionary path followed by the melagabbronites during the early Palaeozoic times

A simulator prototype of delay-doppler maps for GNSS reflections from bare and vegetated soils

When considering a bistatic system made up of GNSS satellites and a receiver, the power at the receiver is modeled taking into account the matched filtering of the incoming signal with the PRN code modulation and Doppler filtering. In this paper, the simulator developed in the framework of the LEIMON Project [1] supported by ESA, will be presented. The simulator is able to predict the power reflected by land taking as input the system and observation parameters, as well as the land surface parameters. The earth surface (represented by bare and vegetated soils) leaves its signature through the bistatic scattering coefficient which has been modeled by means of well established electromagnetic theories applicable at L-band. Experimental data collected during the LEIMON campaign will be compared with simulated data. © 2010 IEEE