In-flight calibration of the HIFI diplexers     

Michael Mueller  Willem Jellema  Bertrand Delforge  David Teyssier  Martin Eggens  Robert Huisman  Geert Keizer 《Experimental Astronomy》2014,37(2):369-379

HIFI is a heterodyne spectrometer aboard the Herschel Space Observatory, providing high-spectral-resolution capabilities. Of its seven frequency bands, four (bands 3, 4, 6, and 7) employ Martin-Puplett diplexers to combine sky signal and local oscillator at the two linear polarizations H and V, prior to feeding them into the mixers (receivers). The optical path difference in each of these 8 diplexers must be tuned to the observed frequency. The required actuator currents were determined in flight before the start of routine science observations. We here report on regular (roughly quarterly) engineering test observations to validate the repeatability of the HIFI diplexers during the routine phase of Herschel operations. We find the optical path difference to be stable to within 0.4 % of the relevant wavelength, typically at the sub-micron level. We conclude that the repeatability and precision of the diplexer tuning mechanism are so high that science data are in no way negatively affected. With the diplexer calibration established and validated, this line of reasoning can be reversed, and the diplexers can be used as relative spectrometers to measure the local-oscillator frequency, i.e., to check the spectral purity of the local oscillator across the diplexer bands. This was done from before launch out to the last months of cryogenic operations in space.  相似文献   

The effect of sideband ratio on line intensity for Herschel/HIFI     

Ronan Higgins  David Teyssier  Colin Borys  Jonathan Braine  Claudia Comito  Bertrand Delforge  Frank Helmich  Michael Olberg  Volker Ossenkopf  John Pearson  Russell Shipman 《Experimental Astronomy》2014,37(2):433-452

The Heterodyne Instrument for the Far Infrared (HIFI) on board the Herschel Space Observatory is composed of a set of fourteen double sideband mixers. We discuss the general problem of the sideband ratio (SBR) determination and the impact of an imbalanced sideband ratio on the line calibration in double sideband heterodyne receivers. The HIFI SBR is determined from a combination of data taken during pre-launch gas cell tests and in-flight. The results and some of the calibration artefacts discovered in the gas cell test data are presented here along with some examples of how these effects appear in science data taken in orbit.  相似文献   

Correlation of reefal Oxfordian episodes and climatic implications in the eastern Paris Basin (France)     

Cdric Carpentier  Bertrand Martin‐Garin  Bernard Lathuilire  Serge Ferry 《地学学报》2006,18(3):191-201

Oxfordian reefal episodes of Lorraine and Burgundy have a long time been considered as contemporaneous. Biostratigraphic data and sequential evolutions peculiar to each region indicate their structural autonomy during Oxfordian times. A north‐south‐oriented well‐logging transect shows that, during the Middle Oxfordian, a shallow reefal platform developed in Lorraine while thin deeper deposits occurred in Burgundy. In spite of their different ages, reefal episodes of Middle Oxfordian in Lorraine and Upper Oxfordian in Burgundy exhibit a broadly similar vertical evolution of coral communities. During the Late Oxfordian, the contemporaneous occurrence of a diversified assemblage in the Burgundy region, a colder coral assemblage characterized by eurytopic genera and the decrease in seawater isotopic temperatures in Lorraine can be explained by a shift in trophic conditions, a climatic change related to structural rearrangements in this strategic place and a modification of oceanic circulations between the arctic and the Tethyan regions.  相似文献   

Uplift and heat flow following the injection of magmas into the lithosphere     

Jean-Claude Mareschal 《Geophysical Journal International》1983,73(1):109-127

Summary. The thermal effect of a rapid injection of hot magmas into the lower part of the lithosphere is modelled as an increase in heat production through the invaded region. The change in surface heat flow and the uplift resulting from the thermal expansion are determined in three-dimensional axially symmetric geometry: they are expressed as the space time convolutions of a Green's function with the anomalous heat production.
The anomalies with shorter wavelength (compared to the lithospheric thickness) are attenuated. This filtering affects the surface uplift more than the heat flow anomaly; the attenuation effect is larger when only the lower part of the lithosphere is invaded.
The uplift time constant is of the same order as the heat conduction time if the lower lithosphere is invaded by magmas at a moderate rate (i.e. the rate of injection does not exceed the equivalent of 0.1 per cent of the lithospheric volume in 10⁶yr). Fifty per cent of the total uplift takes place in about 80 × 10⁶yr for a lithosphere 100 km thick. The uplift is slightly faster when the whole lithosphere is invaded. The heat flow anomaly is delayed when the lower part of the lithosphere is invaded.
The spatial extent and the timing of the uplift and heat flow anomalies are critical in determining the mechanism's feasibility. Magma injections explain rapid uplifts [> 100 m (10⁶ yr)⁻¹] only if the magma is supplied at a very high rate (i.e. at least 10 per cent of the lithosphere volume per 10⁶yr). It is a feasible mechanism for uplifts that occur over longer periods of time (≊ 30 × 10⁶yr) such as those that seem to have occurred when the African plate came to rest with respect to the mantle.  相似文献   

Trip making, induced travel demand, and accessibility   总被引：2，自引：1，他引：1  

Jean-Claude Thill  Marim Kim 《Journal of Geographical Systems》2005,7(2):229-248

Traditional transportation planning practice rests on the premise that the demand for transportation is derived. On the other hand, economic theory advances that enhancement to the transportation system leads to lower travel cost and hence to induced demand. Such an argument lends support to the view that the rate at which trips are generated is linked to the ease of making trips to potential destinations. Rather conflicting evidence has so far come out of aggregate trip generation modeling applications. This paper revisits this issue with proper characterization of integral accessibility. Poisson regression models of automobile trip generation by trip purpose are estimated on travel survey data in Minneapolis–St. Paul, MN. Alternative measures of accessibility are tested for statistical significance. Conclusions are drawn on the role of accessibility in trip making and on the comparison of integral accessibility measures.The first author gratefully acknowledges the financial support of NSF grant SBR- 9308394. We are particularly indebted to Rick Gelbmann, Robert Paddock, and Mark Philippi at the Metropolitan Council, Minneapolis–St. Paul, and William Barrett at the Office of Transportation Data Analysis, Minnesota Department of Transportation for their availability to answer all our data-related questions.  相似文献   

Some considerations from the direct comparison between the observations and the theory of solar disk polarization     

Jean-Claude Pecker 《Solar physics》1970,15(1):88-96

Simple considerations of observed variation with wavelength of polarization on the solar disc, computed continuum polarization, and estimated line polarization have led to the following simple conclusions (more qualitative than quantitative); (a) The metal abundances in the photosphere are five times larger than the classical values adopted in the BCA model of the solar photosphere. (b) The depolarization factor k in lines is an increasing function of wavelength. (c) Assuming that k varies as ², an additional polarization (which can be either solar or instrumental) has to be taken into account.  相似文献   

Characterization of potential zones of dust generation at eleven stations in the southern Sahara   总被引：2，自引：0，他引：2  

I. Clark  P. Assamoi  J. Bertrand  F. Giorgi 《Theoretical and Applied Climatology》2004,77(3-4):173-184

Summary Synoptic wind data for multi-decadal periods at eleven stations located in the southern Sahara region (Agadez, Atar, Bilma, Dori, Gao, Kayes, Nema, Niamey, Nouadhibou, Ouagadougou and Tessalit) are used to study the monthly dust deflation power over the region. We found that, regardless of the conditions of the soil, the deflation power (or wind efficiency) is not sufficient to generate significant amounts of aerosols south of 15°N. North of this latitude, the deflation power is much larger, with potential zones of either very strong deflation (Nouadhibou and Bilma) or severe deflation (Gao, Tessalit, Nema, Atar, Agadez). Stations in the Sahel region such as Gao, Agadez and Tessalit are characterized by a gradual reinforcement of the deflation power between 1970 and 1984 in correspondence of increasing desertification over the region. During this same period, Bilma, a well know region of dust source, experienced a major reduction in deflation power due to shifts in large scale wind patterns.  相似文献   

Metasomatism and melting history of a Variscan lithospheric mantle domain: evidence from the Puy Beaunit xenoliths (French Massif Central)     

Olivier?FéméniasEmail author  Nicolas?Coussaert  Julien?Berger  Jean-Claude?C.?Mercier  Daniel?Demaiffe 《Contributions to Mineralogy and Petrology》2004,148(1):13-28

Mantle xenoliths from Puy Beaunit (French Massif Central) are compositionally varied, ranging from relatively fertile spinel lherzolites to refractory spinel dunites. Fertile peridotites have registered a modal (amphibole-bearing lherzolites) and cryptic metasomatic event that took place before the last Permian (257 Ma) melting episode. Depletion processes have been constrained by chemical modelling: the depletion is related to different degrees of partial melting, but two major melt extraction episodes are needed to explain the range of major element composition. The second event was responsible for the local large-scale dunitification of former residues. The first melting event (F25%) and metasomatic enrichment are attributed to an ancient fluid and/or liquid infiltration that could be related to a pre-Variscan regional subduction (located to the north of the Beaunit area). Texture acquisition and major deformation of the mantle xenoliths were sub-contemporaneous of the subduction and would result from lithospheric delamination. The second melting event (F17%) produced high-Mg basalts with calc-alkaline trace element signature that gave rise to the Permian underplating episode recognised in western Europe.  相似文献   

Non-conservative behavior of bromide in surface waters and brines of Central Andes: A release into the atmosphere?     

François Risacher  Bertrand Fritz 《Geochimica et cosmochimica acta》2006,70(9):2143-2152

The transfer of reactive bromine into the atmosphere was recently observed by Hönninger et al. [Hönninger, G., Bobrowski, N., Palenque, E.R., Torrez, R., Platt, U., 2004. Reactive bromine and sulfur emission at salar de Uyuni, Bolivia. Geophys. Res. Lett.31, doi:10.1029/2003GL018818] in a large salt pan of the Bolivian Altiplano: the salar de Uyuni. However, bromide is considered to be an excellent conservative tracer, which leads to the questioning of its actual conservation in surficial geochemical processes. The relation between bromide and lithium, thought to be a conservative component in waters and brines of the Central Andes, points to a depletion of Br relative to Li in Uyuni brines of about 50-300 kg/day, a flux close to that measured by Hönninger et al. (2004): ?200 kg/day. Such values are very low in regard to the size of the salar (5-30 g/km²/day). Salt efflorescences have a much higher surface area than a flat salt crust, which should enhance the release of bromine. Leach solutions of salt efflorescences in closed basins of northern Chile are compared to their parent waters. Conservative components should have the same concentration ratios in both solutions. Actually, a strong depletion in Br is observed in the leach solutions, which could suggest a significant release of Br from the salt into the atmosphere. During the rainy season, efflorescences are leached and their dissolved components brought in saline lakes and salars. Evaporative profiles show a slight but noticeable fractionation between Li and Br which could be due to the contribution of Br-depleted leach solutions of salt efflorescences. Therefore, bromide does not behave conservatively in surface waters and brines of the Central Andes. If the loss of Br is really due to its transfer into the atmosphere, then the flux would be much higher than that estimated for the salar de Uyuni alone. Numerous salt pans, saline lakes, and widespread efflorescences covering large land surfaces would contribute significantly more reactive bromine into the atmosphere.  相似文献   

Application of a semi-spectral cloud water parameterization to cooling tower plumes simulations     

Emmanuel Bouzereau  Luc Musson Genon  Bertrand Carissimo 《Atmospheric Research》2008,90(1):78-90

In order to simulate the plume produced by large natural draft cooling towers, a semi-spectral warm cloud parameterization has been implemented in an anelastic and non-hydrostatic 3D micro-scale meteorological code. The model results are compared to observations from a detailed field experiment carried out in 1980 at Bugey (location of an electrical nuclear power plant in the Rhône valley in East Central France) including airborne dynamical and microphysical measurements. Although we observe a slight overestimation of the liquid-water content, the results are satisfactory for all the 15 different cases simulated, which include different meteorological conditions ranging from low wind speed and convective conditions in clear sky to high wind and very cloudy. Such parameterization, which includes semi-spectral determination for droplet spectra, seems to be promising to describe plume interaction with atmosphere especially for aerosols and cloud droplets.  相似文献