Full-waveform topographic lidar: State-of-the-art

Airborne laser scanning (ALS) is an active remote sensing technique providing range data as 3D point clouds. This paper aims at presenting a survey of the literature related to such techniques, with emphasis on the new sensors called full-waveform lidar systems. Indeed, an emitted laser pulse interacts with complex natural and man-made objects leading to a temporal distortion of the returned energy profile. The new technology of full-waveform laser scanning systems permits one to digitize the complete waveform of each backscattered pulse. Full-waveform lidar data give more control to an end user in the interpretation process of the physical measurement and provide additional information about the structure and the physical backscattering characteristics of the illuminated surfaces. In this paper, the theoretical principles of full-waveform airborne laser scanning are first described. Afterwards, a review of the main sensors as well as signal processing techniques are presented. We then discuss the interpretation of full-waveform measures with special interest on vegetated and urban areas.     

Analysis of energetic electron drop-outs in the upper atmosphere of Titan during flybys in the dayside magnetosphere of Saturn

We discuss the high energy electron absorption signatures at Titan during the Cassini dayside magnetospheric encounters. We use the electron measurements of the Low Energy Measurement System of the Magnetospheric Imaging Instrument. We also examine the mass loading boundary based on the ion data of the Ion Mass Spectrometer sensor of the Cassini Plasma Spectrometer. The dynamic motion of the Kronian magnetopause and the periodic charged particle flux and magnetic field variations – associated with the magnetodisk of Saturn – of the subcorotating magnetospheric plasma creates a unique and complex environment at Titan. Most of the analysed flybys (like T25–T33 and T35–T51) cluster at similar Saturn Local Time positions. However the instantaneous direction of the incoming magnetospheric particles may change significantly from flyby to flyby due to the very different magnetospheric field conditions which are found upstream of Titan within the sets of encounters.The energetic magnetospheric electrons gyrate along the magnetic field lines of Saturn, and at the same time bounce between the mirror points of the magnetosphere. This motion is combined with the drift of the magnetic field lines. When these flux tubes interact with the upper atmosphere of Titan, their content is depleted over approximately an electron bounce period. These depletion signatures are observed as sudden drop-outs of the electron fluxes. We examined the altitude distribution of these drop-outs and concluded that these mostly detected in the exo-ionosphere of Titan and sometimes within the ionosphere.However there is a relatively significant scatter in the orbit to orbit data, which can be attributed to the which can be attributed to the variability of the plasma environment and as a consequence, the induced magnetosphere of Titan. A weak trend between the incoming electron fluxes and the measured drop-out altitudes has also been observed.     

Thermomagnetic analysis of magnetite parts of serpentinite samples and results of other investigations

Summary The normal type of serpentinites consists of chrysotile. The magnetite parts are essential parts of the structure of chrysotile serpentinites (primary magnetite). Chrysotile is changed to antigorite by mechanical deformations. The magnetite parts of rock structure are lost and they sat down in the veins of serpentinite rocks (secondary magnetite). In this paper the thermomagnetic diagrams and the results of X-ray investigations of secondary and primary magnetite are described. Some results of susceptibility measurements are given. The secondary magnetite is characterized by a region of oxydation in the interval 280–400° C (secondary magnetite-Fe₂O₃-Fe₂O₃). The oxydation to -Fe₂O₃ is remarkably. On the thermomagnetic diagrams of primary magnetite no typical oxydation region is to be seen. The oxydation: primary magnetite-Fe₂O₃ is very small. The interval of measured susceptibility values amounts to (10–1500)·10^–6 cgs units. The essential variability of the main parts of serpentinite samples is characterized by the great changes of susceptibility values from point to point.The determined values of specific saturation magnetization (Gauss. cm³ g^–1), the X-ray powder data, and some results on remanent magnetization are given.

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Zusammenfassung Die Normaltypserpentinite bestehen aus Chrysotil. Der Magnetit ist Bestandteil der Struktur der Chrysotilserpentinite (primärer Magnetit). Unter dem Einfluß mechanischer Deformationen geht Chrysotil in Antigorit über. Die Magnetitanteile der Gesteinsstruktur gehen verloren und scheiden sich auf Klüften ab (sekundärer Magnetit). In der vorliegenden Arbeit werden die thermomagnetischen Abhängigkeiten und die Ergebnisse von Röntgenuntersuchungen des sekundären und primären Magnetits beschrieben. Es werden einige Ergebnisse der Suszeptibilitätsmessungen angeführt. Der sekundäre Magnetit wird durch einen Oxydationsbereich im Temperaturintervall 280–400° C charakterisiert (sekundärer Magnetit-Fe₂O₃-Fe₂O₃). Die Oxydation zu -Fe₂O₃ ist beträchtlich. Die thermomagnetischen Diagramme des primären Magnetits zeigen keinen typischen Oxydationsbereich. Die Oxydation: primärer Magnetit-Fe₂O₃ ist sehr gering. Das Intervall der gemessenen Suszeptibilitätswerte beträgt (10–1500)·10^–6 CGS-Einheiten. Die starke Veränderlichkeit der Hauptbestandteile der Serpentinitproben wird durch die großen Änderungen der Suszeptibilitätswerte von Punkt zu Punkt gekennzeichnet.Die gemessenen Werte der Sättigungsmagnetisierung (Gauss.cm³ g^–1), der Röntgenuntersuchungen und einige Ergebnisse über die remanente Magnetisierung werden gegeben.

     

The use of transplanted cultured tropical oysters (Saccostrea commercialis) to monitor Cd levels in North Queensland coastal waters (Australia)

Bivalves are commonly used to detect metal pollution in the marine environment. Commercially cultured Milky oysters (Saccostrea commercialis) were transplanted in various sites along the North Queensland coast and analyzed for two metals of potentially anthropogenic origin (Cd, Zn). To provide additional information, naturally occurring Black Lip oysters (Saccostrea echinata) were also collected at the transplantation sites. The study demonstrated that the oysters species transplanted are good bioindicators of these metal concentrations in tropical waters, sensitive to variations in the environment at concentrations which are much smaller than pollution signals commonly reported for temperate waters. Three transplant experiments were carried out from May 1999 to February 2000. Milky oysters transplanted to offshore areas (Orpheus Is., Kelso Reef) accumulated Cd in the soft parts whereas oysters sampled from cages placed in Ross Creek and the Herbert River estuaries showed a decrease in Cd concentration, which resulted from an increase in dry weight. Dry weight appeared to be an important covariant affecting Cd concentration in the oysters whereas it does not unambiguously affect Zn concentrations. For the duration of the experiments, oysters sampled from the Magnetic Is. reference site showed effectively constant Cd concentrations and total Cd contents which indicates that any seasonal cycle affecting metal concentration is weak. It was found that Cd accumulation in oysters increased as ambient dissolved Cd concentration decreased, from which it was concluded that for these oysters, the predominant source of Cd was from the particulate phase rather than the dissolved phase.     

Surface area, porosity and water adsorption properties of fine volcanic ash particles

Our understanding on how ash particles in volcanic plumes react with coexisting gases and aerosols is still rudimentary, despite the importance of these reactions in influencing the chemistry and dynamics of a plume. In this study, six samples of fine ash (<100 m) from different volcanoes were measured for their specific surface area, a_s, porosity and water adsorption properties with the aim to provide insights into the capacity of silicate ash particles to react with gases, including water vapour. To do so, we performed high-resolution nitrogen and water vapour adsorption/desorption experiments at 77 K and 303 K, respectively. The nitrogen data indicated a_s values in the range 1.1–2.1 m²/g, except in one case where a a_s of 10 m²/g was measured. This high value is attributed to incorporation of hydrothermal phases, such as clay minerals, in the ash surface composition. The data also revealed that the ash samples are essentially non-porous, or have a porosity dominated by macropores with widths >500 Å. All the specimens had similar pore size distributions, with a small peak centered around 50 Å. These findings suggest that fine ash particles have relatively undifferentiated surface textures, irrespective of the chemical composition and eruption type. Adsorption isotherms for water vapour revealed that the capacity of the ash samples for water adsorption is systematically larger than predicted from the nitrogen adsorption a_s values. Enhanced reactivity of the ash surface towards water may result from (i) hydration of bulk ash constituents; (ii) hydration of surface compounds; and/or (iii) hydroxylation of the surface of the ash. The later mechanism may lead to irreversible retention of water. Based on these experiments, we predict that volcanic ash is covered by a complete monolayer of water under ambient atmospheric conditions. In addition, capillary condensation within ash pores should allow for deposition of condensed water on to ash particles before water reaches saturation in the plume. The total mass of water vapour retained by 1 g of fine ash at 0.95 relative water vapour pressure is calculated to be ~10^–2 g. Some volcanic implications of this study are discussed.Editorial responsibility: J. Gilbert     

The LMDZ4 general circulation model: climate performance and sensitivity to parametrized physics with emphasis on tropical convection

The LMDZ4 general circulation model is the atmospheric component of the IPSL–CM4 coupled model which has been used to perform climate change simulations for the 4th IPCC assessment report. The main aspects of the model climatology (forced by observed sea surface temperature) are documented here, as well as the major improvements with respect to the previous versions, which mainly come form the parametrization of tropical convection. A methodology is proposed to help analyse the sensitivity of the tropical Hadley–Walker circulation to the parametrization of cumulus convection and clouds. The tropical circulation is characterized using scalar potentials associated with the horizontal wind and horizontal transport of geopotential (the Laplacian of which is proportional to the total vertical momentum in the atmospheric column). The effect of parametrized physics is analysed in a regime sorted framework using the vertical velocity at 500 hPa as a proxy for large scale vertical motion. Compared to Tiedtke’s convection scheme, used in previous versions, the Emanuel’s scheme improves the representation of the Hadley–Walker circulation, with a relatively stronger and deeper large scale vertical ascent over tropical continents, and suppresses the marked patterns of concentrated rainfall over oceans. Thanks to the regime sorted analyses, these differences are attributed to intrinsic differences in the vertical distribution of convective heating, and to the lack of self-inhibition by precipitating downdraughts in Tiedtke’s parametrization. Both the convection and cloud schemes are shown to control the relative importance of large scale convection over land and ocean, an important point for the behaviour of the coupled model.     

Analysis of the institutional and social responses to the eruption and the lahars of Mount Pinatubo volcano from 1991 to 1998 (Central Luzon, Philippines)

Mount Pinatubo volcano erupted in June 1991 in the main island of Luzon belonging to the Philippines archipelago. Huge economic losses and population exodus have followed. This major crisis has been relayed with other crises due to rain-fed lahars which have been supplied with eruption deposits. These lahars have occurred every year since 1991 during the rainy season. They will probably last until 2005. After a brief presentation of the Philippine official response system to disasters, this paper draws up a critical analysis of the different kinds of institutional and social responses deployed to manage the different crisis and post-crisis phases of this event. Based on three viewpoints: from population, media and other actors, this analysis attempts to point out the strengths and weaknesses of the official management system, especially by studying the efficiency and the range of the solutions taken. So, it appears that the management of the June 1991 main crisis (eruption) was a success. On the other hand, difficulties have occurred with lahars risk management. Indeed, these lahars have obliged the authorities to protect and relocate thousands of people. In spite of persistent problems, the management system (monitoring/warning/evacuation) of lahar crises improves year after year. Failures appear especially within the rehabilitation program (protection/rehousing). Many direct (lack of means, preparedness, coordination, dialog, etc.) and indirect (politico-administrative, socio-economic, cultural contexts) factors come together to lock the wheels of the institutional response system. They defer the socio-economic start of this vital northern Philippines area. This revised version was published online in July 2006 with corrections to the Cover Date.