In this article, the possible use of synthetic-aperture radar (SAR), for measuring the moisture content and surface roughness is analyzed. Data have been acquired on the Melarchez subwatershed during ...the Orgeval '89 campaign from March to December 1989. Radar back-scattering measurements were provided by the French airborne scatterometer ERASME. Simultaneous ground measurements of soil moisture and roughness, leaf-area index, and water content of the canopy were conducted on 12 test fields. Using radar configurations close that of the ERS-1 SAR, the results clearly indicate that radar data cannot be easily converted into moisture estimates at field scale over a variety of bare soil, essentially due to the effect of roughness on radar response. Nevertheless, mean soil-moisture values measured within bare soil fields over the whole subwatershed, show a decrease in soil-surface moisture from March to October. The same feature is clearly obtained by averaged radar measurements over all bare-soil fields, indicating that ERS-1 could be used for monitoring the moisture state on a regional scale. Furthermore, the great variability of radar backscattering and radar-slope data, for a given soil practice, for example, ploughing or sowing, and for the same date of measurement over bare soil, suggests that, under natural field conditions, backscattering from a soil surface may not be sufficient to explain and understand the radar response and that volume scattering may have to be accounted for as well. Finally, concerning soil roughness, the standard deviation of surface-height slope discriminates the roughness states, which apparently is a pertinent parameter for analyzing the variation of the backscattering coefficient with incidence angle.
Fourier transform infrared (FTIR) spectroscopy and high-performance liquid chromatography (HPLC) were used to study the adsorption behavior of human serum albumin (HSA) onto a polymer-layer type ...anion exchanger, poly(vinylimidazole) (PVI) adsorbed and cross-linked on a porous silica support. The data are compared with previous results for HSA adsorbed on C6 alkyl chains grafted on the same silica matrix. For the adsorption onto the PVI support from a phosphate buffer solution of low ionic strength (pD 7.4), the FTIR experiments reveal only very weak structural and solvation changes. A large fraction of the protein remains irreversibly adsorbed and the amount retained at equilibrium is close to that observed for the adsorption on the reversed-phase support, although the structural effect of the stationary phase was much larger with the grafted C6 alkyl chains. Comparing to the solution state, only 2% of the HSA backbone is modified by adsorption on PVI, whereas 12% alterations are involved for the protein adsorbed on the reversed-phase support. When adsorbed from an eluent containing 20% acetonitrile, the amount of HSA retained by the PVI ion exchanger is about twice that measured with the buffer alone. This result is explained by a more compact structure of the protein when dissolved in the organoaqueous solvent. The presence of acetonitrile does not markedly affect the elution front of HSA adsorbed on the charged hydrophilic adsorbent. This result contrasts with the much lower apparent adsorption rate observed when HSA is adsorbed on the grafted alkyl chain support in the presence of acetonitrile in the buffer.
The gas chromatography–mass spectrometry (GC–MS) experiment using capillary and micropacked columns is one of the main instruments of the Huygens probe of the Cassini–Huygens mission launched in ...October 1997 for the in situ analysis of Titan’s atmosphere. Because of its composition and density the study of the atmosphere of Titan is of primary interest for understanding the prebiotic chemistry in the primitive Earth’s environment. We describe here the GC subsystem of the GC–MS instrument with a particular emphasis on its exobiological implications. The GC subsystem includes three columns which operate in parallel: a carbon molecular sieve micropacked column is used for the separation of CO, N
2 and other permanent gases; a capillary column will separate the light hydrocarbons up to C
3; a second capillary column with a cyanopropyl dimethyl polysiloxane stationary phase will analyze the C
4–C
8 hydrocarbons and the low-molecular mass nitriles up to C
4. These heavier compounds will mainly result from the pyrolysis of the aerosols present in the atmosphere of Titan by using the aerosol collector pyrolyser instrument.
The RESSAC radar system, used from aircraft platforms for measuring directional spectra of ocean waves in the gravity domain (wavelengths from 30 to 400 m), is presented. The instrument consists of a ...C-band (5.35-GHz) FM/CW radar system. The transmitting and receiving antennas look toward the surface at a low incidence angle ( approximately=14 degrees for the center of the antenna beam) and rotate around a vertical axis. When the data are processed, the known antenna gain pattern is removed from the recorded signal, making it possible to estimate the sea surface slope variance, which in turn is used to determine the tilt modulation transfer function, without the need of any external wind measurement. Fully normalized spectra obtained from RESSAC are compared to other data sets.< >
In the near future, space probes will be used to investigate Titan and the P/Wirtanen comet because they are of interest for the fields of planetology and exo/astrobiology. One of the main objectives ...of these probes is to characterize the chemical composition of these extraterrestrial environments. The scientific payload of the probes will carry gas chromatography (GC) as one of the main experiments focused on this characterization through the separation and identification of the many species present in these environments. Despite the development of proper instrumentation for space applications, limitations and instrumental constraints imposed by the space environment prevent optimal separation of the analyzed species. Therefore, complex chromatograms are obtained from in situ space analysis and a mathematical approach is required to decode the signals and interpret all the data recovered by the space instruments. This paper describes a chemometric approach based on Fourier analysis and applications specifically developed to interpret the complex chromatograms that will be collected during space missions. This approach can be used to determine the number of species present in the chromatogram and other analytical properties, but can also be used to find repeated structures in the retention pattern, representative of common chemical features between the chromatographic peaks and the corresponding compounds. Therefore, within the framework of experiments for the calibration of the Cassini-Huygens GC-MS and ACP experiments, this approach was applied to the interpretation of data related to GC analysis of Titan's tholins produced in the laboratory. The procedure was also directly applied to isothermal chromatograms simulating the GC analyses of complex samples, obtained with standard species, which could be operated by the Rosetta Lander probe to investigate the nucleus of the comet P/Wirtanen (COSAC experiments). It is thus demonstrated that this method is helpful both in the chemical characterization of analogues of extraterrestrial matter produced in laboratory simulation aimed at calibrating space instruments and in the interpretation of data collected during space missions.
The kinetic behavior of human serum albumin (HSA) adsorbed on a reversed-phase support was studied. With a phosphate buffer eluent (pH 7.4), the sharp elution front characterizes a fast kinetic ...adsorption process with a high apparent adsorption rate. In presence of 20% acetonitrile added to the eluent the apparent adsorption rate is about 60 times as low as that found for the first adsorption step in pure buffer. The largest column capacity is found with 20% acetonitrile in buffer; for larger organic solvent contents, a decrease of both the apparent adsorption rate and the column capacity are observed with increasing amounts of acetonitrile in the buffer. In order to better understand the chromatographic behavior of HSA on this type of support, we studied the stuctural infrared characteristics of the protein in solution. Fourier transform infrared spectra show that acetonitrile induces some structural changes of the protein in solution and competes with alkyl chains for the interaction with HSA explaining the slow adsorption kinetic process observed in presence of the organic solvent in the eluent. The more compact protein structure found with 20% acetonitrile is correlated with the larger amount of protein adsorbed at this aqueous buffer–organic solvent composition.
One of the possible applications of satellite radar remote sensing is to estimate surface soil moisture. To evaluate the capacity of ERS 1/synthetic aperture radar (SAR), a European Space Agency ...(ESA) pilot project has been set up. The test site is a small agricultural watershed situated in the central part of French Brittany. During 1992 and 1993, almost all possible SAR images were acquired together with two types of ground truths: intensive ground measurements during 14 field campaigns and point automatic measurements over the entire period. From the comparison of those ground truth data with the ERS 1 images, the following results are obtained. On a field scale the relation between the radar signal and the surface soil moisture depends strongly on the type of culture: Correlation is poor for the different cultures except for wheat. On a basin scale, it is shown that during the period of low vegetation density, there is a linear correlation between the mean radar data and the point automatic measurements. This last result is very encouraging and could open the way to hydrological applications
Mass is one of the most important parameters for determining the true nature of an astronomical object. Yet, many published exoplanets lack a measurement of their true mass, in particular those ...detected thanks to radial velocity (RV) variations of their host star. For those, only the minimum mass, or \(m\sin i\), is known, owing to the insensitivity of RVs to the inclination of the detected orbit compared to the plane-of-the-sky. The mass that is given in database is generally that of an assumed edge-on system (\(\sim\)90\(^\circ\)), but many other inclinations are possible, even extreme values closer to 0\(^\circ\) (face-on). In such case, the mass of the published object could be strongly underestimated by up to two orders of magnitude. In the present study, we use GASTON, a tool recently developed in Kiefer et al. (2019) & Kiefer (2019) to take advantage of the voluminous Gaia astrometric database, in order to constrain the inclination and true mass of several hundreds of published exoplanet candidates. We find 9 exoplanet candidates in the stellar or brown dwarf (BD) domain, among which 6 were never characterized. We show that 30 Ari B b, HD 141937 b, HD 148427 b, HD 6718 b, HIP 65891 b, and HD 16760 b have masses larger than 13.5 M\(_\text{J}\) at 3-\(\sigma\). We also confirm the planetary nature of 27 exoplanets among which HD 10180 c, d and g. Studying the orbital periods, eccentricities and host-star metallicities in the BD domain, we found distributions with respect to true masses consistent with other publications. The distribution of orbital periods shows of a void of BD detections below \(\sim\)100 days, while eccentricity and metallicity distributions agree with a transition between BDs similar to planets and BDs similar to stars about 40-50 M\(_\text{J}\).
The fresnel interferometric imager Koechlin, Laurent; Serre, Denis; Deba, Paul ...
Experimental astronomy,
03/2009, Letnik:
23, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The Fresnel Interferometric Imager has been proposed to the European Space Agency (ESA) Cosmic Vision plan as a class L mission. This mission addresses several themes of the CV Plan:
Exoplanet study
...,
Matter in extreme conditions
, and
The Universe taking shape
. This paper is an abridged version of the original ESA proposal. We have removed most of the technical and financial issues, to concentrate on the instrumental design and astrophysical missions. The instrument proposed is an ultra-lightweight telescope, featuring a novel optical concept based on diffraction focussing. It yields high dynamic range images, while releasing constraints on positioning and manufacturing of the main optical elements. This concept should open the way to very large apertures in space. In this two spacecraft formation-flying instrument, one spacecraft holds the focussing element: the Fresnel interferometric array; the other spacecraft holds the field optics, focal instrumentation, and detectors. The Fresnel array proposed here is a 3.6 ×3.6 m square opaque foil punched with 10
5
to 10
6
void “subapertures”. Focusing is achieved with no other optical element: the shape and positioning of the subapertures (holes in the foil) is responsible for beam combining by diffraction, and 5% to 10% of the total incident light ends up into a sharp focus. The consequence of this high number of subapertures is high dynamic range images. In addition, as it uses only a combination of vacuum and opaque material, this focussing method is potentially efficient over a very broad wavelength domain. The focal length of such diffractive focussing devices is wavelength dependent. However, this can be corrected. We have tested optically the efficiency of the chromatism correction on artificial sources (500 <
λ
< 750 nm): the images are diffraction limited, and the dynamic range measured on an artificial double source reaches 6.2 10
− 6
. We have also validated numerical simulation algorithms for larger Fresnel interferometric arrays. These simulations yield a dynamic range (rejection factor) close to 10
− 8
for arrays such as the 3.6 m one we propose. A dynamic range of 10
− 8
allows detection of objects at contrasts as high as than 10
− 9
in most of the field. The astrophysical applications cover many objects in the IR, visible an UV domains. Examples are presented, taking advantage of the high angular resolution and dynamic range capabilities of this concept.
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