The International DORIS Service: genesis and early achievements

All space-geodetic techniques are now organized as separate services of the International Association of Geodesy (IAG), supporting the first pilot project “Global Geodetic Observing System (GGOS)”. The International DORIS (Détermination d’Orbite et Radiopositionnement Intégrés par Satellite) Service (IDS) was created in mid-2003 to organize a DORIS contribution to this project and to foster a larger international cooperation on this topic. The goal of this paper is to summarize the key steps that were taken to create this structure and to present its current organization and recent results. At present, more than 50 groups from 35 different countries participate in the IDS at various levels, including 43 groups hosting DORIS stations in 32 countries all around the globe. Four Analysis Centres (ACs) provide results, such as estimates of weekly or monthly station coordinates, geocentre variations or Earth polar motion, that will soon be used to generate IDS-combined products for geodesy and geodynamics. As a first test, a preliminary combination was performed for all the 2004 data from these four ACs. Three of them show RMS of weighted station residuals with respect to this combination solution between 1 and 2 cm. The main topic under investigation is a discrepancy in the scale factor of the terrestrial reference frame (TRF) to map the individual solutions into the combination solution, which reaches 6 cm (multiplying the unit-less scale factor by the Earth radius to get convert scale to millimetre in vertical at the Earth’s surface). Finally, foreseen improvements of the DORIS technology are discussed as well as future improvements concerning the service organization itself and the accuracy and reliability of its scientific products.     

Two-dimensional PP/PS-stereotomography: P- and S-waves velocities estimation from OBC data

We present the extension of stereotomography to P - and S -wave velocity estimation from PP - and PS -reflected/diffracted waves. In this new context, we greatly benefit from the use of locally coherent events by stereotomography. In particular, when applied to S -wave velocity estimation from PS -data, no pairing of PP - and PS -events is a priori required. In our procedure the P -wave velocity model is obtained first using stereotomography on PP -arrivals. Then the S -wave velocity model is obtained using PS -stereotomography on PS -arrivals fixing the P -wave velocity model. We present an application to an 'ideal' synthetic data set demonstrating the relevance of the approach, which allows us to recover depth consistent P - and S -waves velocity models even if no pairing of PP - and PS -events is introduced. Finally, results to a real data set from the Gulf of Mexico are presented demonstrating the potential of the method in a noisy data context.     

Importance of borehole deviation surveys for monitoring of hydraulic fracturing treatments

During seismic monitoring of hydraulic fracturing treatment, it is very common to ignore the deviations of the monitoring or treatment wells from their assumed positions. For example, a well is assumed to be perfectly vertical, but in fact, it deviates from verticality. This can lead to significant errors in the observed azimuth and other parameters of the monitored fracture‐system geometry derived from microseismic event locations. For common hydraulic fracturing geometries, a 2° deviation uncertainty on the positions of the monitoring or treatment well survey can cause a more than 20° uncertainty of the inverted fracture azimuths. Furthermore, if the positions of both the injection point and the receiver array are not known accurately and the velocity model is adjusted to locate perforations on the assumed positions, several‐millisecond discrepancies between measured and modeled SH‐P traveltime differences may appear along the receiver array. These traveltime discrepancies may then be misinterpreted as an effect of anisotropy, and the use of such anisotropic model may lead to the mislocation of the detected fracture system. The uncertainty of the relative positions between the monitoring and treatment wells can have a cumulative, nonlinear effect on inverted fracture parameters. We show that incorporation of borehole deviation surveys allows reasonably accurate positioning of the microseismic events. In this study, we concentrate on the effects of horizontal uncertainties of receiver and perforation positions. Understanding them is sufficient for treatment of vertical wells, and also necessary for horizontal wells.     

Prélèvement et analyses des condensats de fumerolles sur volcans actifs: Soufrière de la Guadeloupe (1976–1977) et Pouzzoles et Vulcano (Italie) (1978)

The cooling of volcanic gases generates sublimates, condensates and gases. Condensates were sampled and analysed on different volcanoes: On Guadeloupe, phreatic eruptions occur when pH of condensates has maintained higher than 4 to 5 for 3 to 7 days. After the phreatic eruption, pH decreases to 1.5 to 2. At Pozzuoli and Vulcano it is possible to distinguish between gases washed by superficial waters (low mineral contents and high pH) and gases less affected by condensation and dissolution in the ground (high mineral contents and low pH).     

Some problems of the projection of chemical data into mineralogical classifications

The obvious need to be able to predict, on a routine basis, the name of an igneous rock from its chemistry is examined in the light of some multivariate statistical methods. Discriminant analysis is ruled out for general use, due to its inability to distinguish an unknown that does not belong to any of the groups set up by the analysis, and the complexities of the decision-making logic with large number of groups.The best method appears to be classification procedure which predicts the probabilities of an unknown belonging to a particular group. The two methods are illustrated using samples of basalts, andesites, dacites and rhyolites.     

Observing water-level variations from space-borne high-resolution Synthetic Aperture Radar (SAR) image correlation

The potential of correlating high-resolution Synthetic Aperture Radar images to estimate local water-level variations is analysed based on observing the motions of floating structures. By computing range and azimuth offsets on a COSMO-SkyMed multi-temporal data-set in an area of the French Atlantic Coast, displacement signatures were detected in several harbours of the region. They can be associated with specific floating structures, whose vertical motion is mostly driven by tides. Although the image resolution is not the best achievable for the COSMO-SkyMed sensor, comparison with ground-based tide information revealed that the obtained space-borne measurements are consistent with the tide gauges to a decimetric accuracy. Even if the requirements for traditional users of tidal data are not met by the current revisit time of the COSMO-SkyMed constellation, the method proposed here provides complementary measures, which are already well aligned to requirements of users concerned with long-term sea-level variation and river or lake water stocks.     

添加γ-聚谷氨酸对冬菠菜土壤温度的影响特性研究

为了探究添加γ-聚谷氨酸(γ-PGA)对冬菠菜种植中土壤温度的影响,设计施用不同γ-PGA浓度的单因素试验,对冬菠菜不同生育期和不同土壤深度的土壤温度进行了监测和分析,研究结果表明:施用γ-PGA增大了地表以下5 cm处日最高土壤温度,但日最高土壤温度与γ-PGA施用量并非正相关;在大气温度变化较大的冬菠菜发芽期和生长期,γ-PGA施用量较多的地表以下5cm处土壤日温度变化幅度较大;另外,γ-PGA施用量增大时,相同土层深度最高温度和最低温度均呈先增大后减小趋势,其中添加0.3%γ-PGA的土壤最高温度和最低温度明显相对最高。因此,施用适量的γ-聚谷氨酸可以有效起到保墒和保温的作用,可为冬菠菜的生长提供良好的生长环境。     

Surrogate-based parameter inference in debris flow model

This work tackles the problem of calibrating the unknown parameters of a debris flow model with the drawback that the information regarding the experimental data treatment and processing is not available. In particular, we focus on the evolution over time of the flow thickness of the debris with dam-break initial conditions. The proposed methodology consists of establishing an approximation of the numerical model using a polynomial chaos expansion that is used in place of the original model, saving computational burden. The values of the parameters are then inferred through a Bayesian approach with a particular focus on inference discrepancies that some of the important features predicted by the model exhibit. We build the model approximation using a preconditioned non-intrusive method and show that a suitable prior parameter distribution is critical to the construction of an accurate surrogate model. The results of the Bayesian inference suggest that utilizing directly the available experimental data could lead to incorrect conclusions, including the over-determination of parameters. To avoid such drawbacks, we propose to base the inference on few significant features extracted from the original data. Our experiments confirm the validity of this approach, and show that it does not lead to significant loss of information. It is further computationally more efficient than the direct approach, and can avoid the construction of an elaborate error model.