Towards large-scale stochastic refraction tomography: a comparison of three evolutionary algorithms     

Keurfon Luu  Mark Noble  Alexandrine Gesret  Philippe Thierry 《Geophysical Prospecting》2020,68(2):536-552

The main goal of this study is to assess the potential of evolutionary algorithms to solve highly non-linear and multi-modal tomography problems (such as first arrival traveltime tomography) and their abilities to estimate reliable uncertainties. Classical tomography methods apply derivative-based optimization algorithms that require the user to determine the value of several parameters (such as regularization level and initial model) prior to the inversion as they strongly affect the final inverted model. In addition, derivative-based methods only perform a local search dependent on the chosen starting model. Global optimization methods based on Markov chain Monte Carlo that thoroughly sample the model parameter space are theoretically insensitive to the initial model but turn out to be computationally expensive. Evolutionary algorithms are population-based global optimization methods and are thus intrinsically parallel, allowing these algorithms to fully handle available computer resources. We apply three evolutionary algorithms to solve a refraction traveltime tomography problem, namely the differential evolution, the competitive particle swarm optimization and the covariance matrix adaptation–evolution strategy. We apply these methodologies on a smoothed version of the Marmousi velocity model and compare their performances in terms of optimization and estimates of uncertainty. By performing scalability and statistical analysis over the results obtained with several runs, we assess the benefits and shortcomings of each algorithm.  相似文献   

Cobalt, manganese, and iron near the Hawaiian Islands: A potential concentrating mechanism for cobalt within a cyclonic eddy and implications for the hybrid-type trace metals   总被引：1，自引：0，他引：1  

Abigail E. Noble  Mak A. Saito  Kanchan Maiti  Claudia R. Benitez-Nelson 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1473

The vertical distributions of cobalt, iron, and manganese in the water column were studied during the E-Flux Program (E-Flux II and III), which focused on the biogeochemistry of cold-core cyclonic eddies that form in the lee of the Hawaiian Islands. During E-Flux II (January 2005) and E-Flux III (March 2005), 17 stations were sampled for cobalt (n=147), all of which demonstrated nutrient-like depletion in surface waters. During E-Flux III, two depth profiles collected from within a mesoscale cold-core eddy, Cyclone Opal, revealed small distinct maxima in cobalt at 100 m depth and a larger inventory of cobalt within the eddy. We hypothesize that this was due to a cobalt concentrating effect within the eddy, where upwelled cobalt was subsequently associated with sinking particulate organic carbon (POC) via biological activity and was released at a depth coincident with nearly complete POC remineralization [Benitez-Nelson, C., Bidigare, R.R., Dickey, T.D., Landry, M.R., Leonard, C.L., Brown, S.L., Nencioli, F., Rii, Y.M., Maiti, K., Becker, J.W., Bibby, T.S., Black, W., Cai, W.J., Carlson, C.A., Chen, F., Kuwahara, V.S., Mahaffey, C., McAndrew, P.M., Quay, P.D., Rappe, M.S., Selph, K.E., Simmons, M.P., Yang, E.J., 2007. Mesoscale eddies drive increased silica export in the subtropical Pacific Ocean. Science 316, 1017–1020]. There is also evidence for the formation of a correlation between cobalt and soluble reactive phosphorus during E-Flux III relative to the E-Flux II cruise that we suggest is due to increased productivity, implying a minimum threshold of primary production below which cobalt–phosphate coupling does not occur. Dissolved iron was measured in E-Flux II and found in somewhat elevated concentrations (0.5 nM) in surface waters relative to the iron depleted waters of the surrounding Pacific [Fitzwater, S.E., Coale, K.H., Gordon, M.R., Johnson, K.S., Ondrusek, M.E., 1996. Iron deficiency and phytoplankton growth in the equatorial Pacific. Deep-Sea Research II 43 (4–6), 995–1015], possibly due to island effects associated with the iron-rich volcanic soil from the Hawaiian Islands and/or anthropogenic inputs. Distinct depth maxima in total dissolved cobalt were observed at 400–600 m depth, suggestive of the release of metals from the shelf area of comparable depth that surrounds these islands.  相似文献   

An experimental approach to understanding the optical effects of space weathering   总被引：2，自引：0，他引：2  

Sarah K. Noble  Carl M. Pieters  Lindsay P. Keller 《Icarus》2007,192(2):629-642

The creation and accumulation of nanophase iron (npFe⁰) is a principal mechanism by which spectra of materials exposed to the space environment incur systematic changes referred to as “space weathering.” Since there is no reason to assume that cumulative space weathering products throughout the Solar System will be the same as those found in lunar soils, these products are likely to be very dependent on the specific environmental conditions under which they were produced. We have prepared a suite of analog soils to explore the optical effects of npFe⁰. By varying the size and concentration of npFe⁰ in the analogs we found significant systematic changes in the Vis/NIR spectral properties of the materials. Smaller npFe⁰ (<10 nm in diameter) dramatically reddens spectra in the visible wavelengths while leaving the infrared region largely unaffected. Larger npFe⁰ (>40 nm in diameter) lowers the albedo across the Vis/NIR range with little change in the overall shape of the continuum. Intermediate npFe⁰ sizes impact the spectra in a distinct pattern that changes with concentration. The products of these controlled experiments have implications for space-weathered material throughout the inner Solar System. Our results indicate that the lunar soil continuum is best modeled by npFe⁰ particles with bulk properties in the 15–25 nm size range. Larger npFe⁰ grains result in spectra that are similar in shape to the Mercury continuum. The continuum of S-type asteroid spectra appear to be best represented by low abundances of npFe⁰. The size of asteroidal npFe⁰ is similar to that of lunar soils, but slightly smaller on average (10–15 nm).  相似文献   

On Selection of Analog Volcanoes     

Armando Rodado  Mark Bebbington  Alasdair Noble  Shane Cronin  Gill Jolly 《Mathematical Geosciences》2011,43(5):505-519

Estimating the occurrence probability of volcanic eruptions with VEI ??3 is challenging in several aspects, including data scarcity. A?suggested approach has been to use a simple model, where eruptions are assumed to follow a Poisson process, augmenting the data used to estimate the eruption onset rate with that from several analog volcanoes. In this model the eruption onset rate is a random variable that follows a gamma distribution, the parameters of which are estimated by an empirical Bayes analysis. The selection of analog volcanoes is an important step that needs to be explicitly considered in this model, as we show that the analysis is not always feasible due to the required over-dispersion in the resulting negative binomial distribution for the numbers of eruptions. We propose a modification to the method which allows for both over-dispersed and under-dispersed data, and permits analog volcanoes to be chosen on other grounds than mathematical tractability.  相似文献   

Dynamics of initial ecosystem development at the artificial catchment Chicken Creek, Lusatia, Germany   总被引：1，自引：1，他引：0  

Michael Elmer  Werner Gerwin  Wolfgang Schaaf  Markus K. Zaplata  Karin Hohberg  Rossen Nenov  Oliver Bens  Reinhard F. Hüttl 《Environmental Earth Sciences》2013,69(2):491-505

In autumn 2005, the artificial catchment Chicken Creek was completed in an open-cast lignite mine in Lusatia, Germany. The 6 ha area has been constructed as a two-layer system consisting of a clay aquiclude and a sandy aquifer at the top. After construction, the site was left to an unrestricted and unmanaged succession. A comprehensive environmental monitoring program started immediately after the site was completed. Time series of essential environmental parameters were recorded with high temporal and spatial resolution. This paper presents selected time series of the past 6-year ecosystem development. Important changes registered in this period allow for the definition of distinctive phases of the still ongoing initial ecosystem evolution. A primary, short, but pronounced geo-phase—characterized by surface runoff, excessive erosion and sedimentation as well as very rapid immigration of biota—was followed by a hydrological dominated phase with processes, such as groundwater recharge. At the end of the study period, biotic processes became more evident. It can be concluded that the artificial catchment offers unique opportunities for interdisciplinary research on the establishment of an ecological system with rapidly growing complexity. The highly dynamic development of the Chicken Creek catchment provides the possibility to observe manifold changes within short time and to detect feedbacks and their modifications between different ecosystem compartments.  相似文献   

Space Weathering on Mercury: Implications for Remote Sensing     

Noble  S. K.  Pieters  C. M. 《Solar System Research》2003,37(1):31-35

By applying our understanding of lunar space weathering processes, we can predict how space weathering will effect the soil properties on Mercury. In particular, the extreme temperature range on Mercury may result in latitudinal variations in the size distribution of npFe₀, and therefore the spectral properties of the soil.  相似文献   

The conceptual and practical challenges to technology categorisation in the preparation of technology needs assessments     

Ivan Nygaard  Ulrich Elmer Hansen 《Climatic change》2015,131(3):371-385

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Regional climate model simulation of the AMMA Special Observing Period #3 and the pre-Helene easterly wave     

Leonard M. Druyan  Matthew Fulakeza  Patrick Lonergan  Erik Noble 《Meteorology and Atmospheric Physics》2009,105(3-4):191-210

The study examines results of dynamic downscaling of two global analyses: the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis II and the Global Forecast System final analysis (FNL). Downscaling to a 0.5° grid over West Africa and the adjacent Atlantic Ocean is accomplished by each of two regional models, the Regional Model, version 3 (RM3) of the Center for Climate Systems Research and the Weather, Research and Forecasting model (WRF). Simulations are for September 2006, the African Monsoon Multidisciplinary Analysis (AMMA) Special Observing Period #3 (SOP-3). The aim of this study is to exploit the increased spatial detail in the simulations and representations of climate fields by the regional models to analyze meteorological systems within the SOP-3 area of interest and time frame. In particular, the paper focuses on the regional models’ representations of the structure and movement of a prominent easterly wave during September 10–13th, the precursor of Tropical Storm/Hurricane Helene. It describes the RM3 simulated structure of the developing storm in terms of circulation, precipitation, vertical motion, cumulus heating rates, and cross-sections of wind and geopotential height anomalies. Simulated cumulus heating rates within the wave’s main precipitation area imply a lowering of the bases of active cumulus in the transition from the African continent to the Atlantic, indicating that the ocean environment promotes greater upward latent heat flux that in turn intensifies overlying storms. RM3 circulation, precipitation patterns, and storm trajectory are reasonably consistent with observational evidence. Experiments show that precipitation rates near 6°N over the eastern North Atlantic are sensitive to vertical thermal stability, such that they are enhanced by warmer in situ sea-surface temperatures (SSTs) and diminished by colder SSTs. However, prescribing colder SST causes increases in precipitation north of 9°N within areas of large scale upward vertical motion where rainfall rates are less sensitive to in situ SSTs. The evaluation of WRF indicates that its storm propagation is too fast over West Africa, where associated WRF precipitation rates are exaggerated, but its performance is improved over the Atlantic.  相似文献   

Calcification rate influence on trace element concentrations in aragonitic bivalve shells: Evidences and mechanisms     

Matthieu Carré  Ilhem Bentaleb  Elmer Ordinola  Michel Fontugne 《Geochimica et cosmochimica acta》2006,70(19):4906-4920

Trace elements in calcareous organisms have been widely used for paleoclimatic studies. However, the factors controlling their incorporation into mollusc shells are still unclear. We studied here the Sr, Mg, Ba and Mn serial records in the shells of two aragonitic marine bivalve species: Mesodesma donacium and Chione subrugosa from the Peruvian Coast. The elemental concentrations were compared to local temperature and salinity records. The relationships with crystal growth rate G were investigated thanks to well defined periodic growth structures providing a precise shell chronology. Our results show that for both species, environmental parameters only have minor influence, whereas crystal growth rate strongly influences trace elements concentrations, especially for Sr (explaining up to 74% of the variance). The relationship between G and Sr/Ca exhibits variability among the shells as well as inside the shells. For a same growth rate value, Sr/Ca values are higher in more curved shell sections, and the growth rate influence is stronger as well. We show that intercellular and Ca²⁺-pump pathways cannot support the calcification Ca²⁺ flux, leading us to propose an alternative mechanism for ionic transport through the calcifying mantle, implying a major role for calcium channels on mantle epithelial cell membranes. In this new calcification model, Sr/Ca shell ratios is determined by Ca²⁺-channel selectivity against Sr²⁺, which depends (i) on the electrochemical potential imposed by the crystallisation process and (ii) on the Ca²⁺-channel density per surface unit on mantle epithelia.  相似文献   

An image converter-intensifier detector for high-resolution astronomical spectroscopy in the balloon ultraviolet     

B. Bates  R. E. L. Bankhead  D. J. McCartney  J. A. McQuoid  S. M. C. Noble 《Astrophysics and Space Science》1980,68(1):151-157

A rugged and compact image converter-intensifier camera has been developed for a balloon-borne spectrograph used in a programme of UV astronomical interference spectroscopy. Details are given of the construction of this new detector and of relevant performance characteristics in comparison with direct photography.  相似文献