Parametrizing surface wave tomographic models with harmonic spherical splines     

Abel Amirbekyan  Volker Michel  Frederik J. Simons † 《Geophysical Journal International》2008,174(2):617-628

We present a mathematical framework and a new methodology for the parametrization of surface wave phase-speed models, based on traveltime data. Our method is neither purely local, like block-based approaches, nor is it purely global, like those based on spherical harmonic basis functions. Rather, it combines the well-known theory and practical utility of the spherical harmonics with the spatial localization properties of spline basis functions. We derive the theoretical foundations for the application of harmonic spherical splines to surface wave tomography and summarize the results of numerous numerical tests illustrating the performance of a practical inversion scheme based upon them. Our presentation is based on the notion of reproducing-kernel Hilbert spaces, which lends itself to the parametrization of fully 3-D tomographic earth models that include body waves as well.  相似文献   

Late slowdown of the Atlantic Meridional Overturning Circulation during the Last Glacial Inception: New constraints from sedimentary (231Pa/230Th)     

Abel Guihou  Sylvain Pichat  Sìlvia Nave  Aline Govin  Laurent Labeyrie  Elisabeth Michel  Claire Waelbroeck 《Earth and Planetary Science Letters》2010,289(3-4):520-529

Our study gives new constraints on the response of Atlantic Meridional Overturning Circulation (AMOC) export to various forcings during the Last Glacial Inception. The decay corrected excess sedimentary (²³¹Pa/²³⁰Th) activity ratio (hereafter referred to as (Pa/Th)) has been measured over that period in two deep cores from the Western (SU90-11, 44°04′N, 40°01′W, 3645 m) and Eastern (MD01-2446, 39°03′N, 12°37′W, 3547 m) basins of the North Atlantic. Both records display significant changes despite the relatively short half-life of ²³¹Pa (～ 32 kyr) compared to the period we investigate. The (Pa/Th) variability does not correlate to changes in local opal flux normalized to ²³⁰Th. Moreover, the (Pa/Th) profiles display a high degree of coherency with indirect proxies of AMOC activity such as the benthic foraminifera δ¹³C and the mid-latitude summer Sea Surface Temperature in nearby reference cores. These additional pieces of evidence support our interpretation of the (Pa/Th) as reflecting AMOC export. The (Pa/Th) repeatedly underwent rapid changes during the Last Glacial Inception associated with the extension of ice rafted detritus in the North Atlantic, highlighting the control of ice-sheet dynamics through freshwater forcing on AMOC export. AMOC export remains large during periods of ice-sheet growth and its decreases lag the Northern Hemisphere summer insolation forcing. AMOC modulation appears driven by ice-sheet dynamics, itself driven by the seasonal insolation gradient between low and high Northern Hemisphere latitudes and the associated intensity of the meridional oceanic and atmospheric circulation.  相似文献   

Soil temperature and CO2 degassing,SO2 fluxes and field observations before and after the February 29, 2016 new vent inside Nyiragongo crater     

Charles M. Balagizi  Mathieu M. Yalire  Honoré M. Ciraba  Vicky B. Kajeje  Abel S. Minani  Annie B. Kinja  Marcellin M. Kasereka 《Bulletin of Volcanology》2016,78(9):64

  相似文献   

Modelling blue and green water availability under climate change in the Beninese Basin of the Niger River Basin,West Africa          下载免费PDF全文

Djigbo Félicien Badou  Bernd Diekkrüger  Evison Kapangaziwiri  Mamadou L. Mbaye  Yacouba Yira  Emmanuel A. Lawin  Ganiyu T. Oyerinde  Abel Afouda 《水文研究》2018,32(16):2526-2542

The aim of this study was to quantify climate change impact on future blue water (BW) and green water (GW) resources as well as the associated uncertainties for 4 subbasins of the Beninese part of the Niger River Basin. The outputs of 3 regional climate models (HIRHAM5, RCSM, and RCA4) under 2 emission scenarios (RCP4.5 and RCP8.5) were downscaled for the historical period (1976–2005) and for the future (2021–2050) using the Statistical DownScaling Model (SDSM). Comparison of climate variables between these 2 periods suggests that rainfall will increase (1.7% to 23.4%) for HIRHAM5 and RCSM under both RCPs but shows mixed trends (?8.5% to 17.3%) for RCA4. Mean temperature will also increase up to 0.48 °C for HIRHAM5 and RCSM but decrease for RCA4 up to ?0.37 °C. Driven by the downscaled climate data, future BW and GW were evaluated with hydrological models validated with streamflow and soil moisture, respectively. The results indicate that GW will increase in all the 4 investigated subbasins, whereas BW will only increase in one subbasin. The overall uncertainty associated with the evaluation of the future BW and GW was quantified through the computation of the interquartile range of the total number of model realizations (combinations of regional climate models and selected hydrological models) for each subbasin. The results show larger uncertainty for the quantification of BW than GW. To cope with the projected decrease in BW that could adversely impact the livelihoods and food security of the local population, recommendations for the development of adequate adaptation strategies are briefly discussed.  相似文献   

An investigation into robust spectral indices for leaf chlorophyll estimation   总被引：2，自引：0，他引：2  

Russell Main  Moses Azong Cho  Renaud Mathieu  Martha M. O’Kennedy  Abel Ramoelo  Susan Koch 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(6):751-761

Quantifying photosynthetic activity at the regional scale can provide important information to resource managers, planners and global ecosystem modelling efforts. With increasing availability of both hyperspectral and narrow band multispectral remote sensing data, new users are faced with a plethora of options when choosing an optical index to relate to their chosen or canopy parameter. The literature base regarding optical indices (particularly chlorophyll indices) is wide ranging and extensive, however it is without much consensus regarding robust indices. The wider spectral community could benefit from studies that apply a variety of published indices to differing sets of species data. The consistency and robustness of 73 published chlorophyll spectral indices have been assessed, using leaf level hyperspectral data collected from three crop species and a variety of savanna tree species. Linear regression between total leaf chlorophyll content and bootstrapping were used to determine the leafpredictive capabilities of the various indices. The indices were then ranked based on the prediction error (the average root mean square error (RMSE)) derived from the bootstrapping process involving 1000 iterative resampling with replacement. The results show two red-edge derivative based indices (red-edge position via linear extrapolation index and the modified red-edge inflection point index) as the most consistent and robust, and that the majority of the top performing indices (in spite of species variability) were simple ratio or normalised difference indices that are based on off-chlorophyll absorption centre wavebands (690–730 nm).  相似文献   

Towards integrated geographical information processing     

David J. Abel  Beng Chin Ooi  Kian-Lee Tan  Soon Huat Tan 《International journal of geographical information science》2013,27(4):353-371

Many geographical applications access data from multiple disparate repositories such as file systems, Geographical Information Systems and database management systems which contain data able to be interrelated. Existing approaches that either built a single repository that contain all the required data or simply interconnect these repositories have not been well received. In this paper, we present the design of the Virtual GIS, a system for distributed spatial data processing in heterogeneous environments. The Virtual GIS is an integrated system that provides all the essential facilities for integrating and retrieving data from multiple component systems.The system isparticularly aimed at extensibility and scalability through distributing the processing load across the component systems and a global frontend. The object-oriented data model is adopted as a common data model to ensure meaningful data sharing. We also employ the fivelevel schema architecture of Sheth and Larson as the framework for system integration. Finally, queries are processed using a five-phase query processing approach.  相似文献   

Reliable Determination of Ge in Solid Environmental Samples Using a Chemical Preparation Procedure Developed for Si Isotopes and ICP‐MS Analysis          下载免费PDF全文

Camille Delvigne  Bernard Angeletti  Abel Guihou  Isabelle Basile‐Doelsch  Jean‐Dominique Meunier 《Geostandards and Geoanalytical Research》2018,42(1):139-149

Germanium (Ge) exists at trace levels in the Earth's crust and is a powerful geochemical tracer of the silicon (Si) cycle. This study proposes a simple and reliable method for determining Ge contents in environmental samples using ICP‐MS. As Si and Ge have very similar chemical properties, we investigated the applicability of the chemical preparation procedure developed for Si isotopes for the determination of Ge in environmental samples. Advantages of this procedure are as follows: (a) efficient removal of the matrix and main interferences affecting Ge determinations by ICP‐MS, (b) a low limit of detection (6 ng l^?1), (c) relative repeatability of approximately 3% obtained on ⁷⁴Ge and (d) robustness and accuracy based on agreement within errors with the published Ge values for rock reference materials (BHVO‐2, AGV‐2 and BCR‐2). This procedure allowed revision of the Ge values of three soil reference materials (1.67 ± 0.09 μg g^?1, 2.41 ± 0.18 μg g^?1, 1.89 ± 0.10 μg g^?1 for GBW 07401, GBW 07404 and GBW 07407, respectively) and proposal of a value for the plant reference material ERM‐CD281 (70 ± 3 μg g^?1). This method provides a convenient procedure for determining Ge mass fractions in environmental samples and opens the possibility of coupling two tracers of the Si biogeochemical cycle with a single measurement procedure.  相似文献   

An object-based approach for mapping forest structural types based on low-density LiDAR and multispectral imagery     

Luis Ángel Ruiz  Jorge Abel Recio  Pablo Crespo-Peremarch  Marta Sapena 《国际地球制图》2018,33(5):443-457

Mapping forest structure variables provides important information for the estimation of forest biomass, carbon stocks, pasture suitability or for wildfire risk prevention and control. The optimization of the prediction models of these variables requires an adequate stratification of the forest landscape in order to create specific models for each structural type or strata. This paper aims to propose and validate the use of an object-oriented classification methodology based on low-density LiDAR data (0.5 m^?2) available at national level, WorldView-2 and Sentinel-2 multispectral imagery to categorize Mediterranean forests in generic structural types. After preprocessing the data sets, the area was segmented using a multiresolution algorithm, features describing 3D vertical structure were extracted from LiDAR data and spectral and texture features from satellite images. Objects were classified after feature selection in the following structural classes: grasslands, shrubs, forest (without shrubs), mixed forest (trees and shrubs) and dense young forest. Four classification algorithms (C4.5 decision trees, random forest, k-nearest neighbour and support vector machine) were evaluated using cross-validation techniques. The results show that the integration of low-density LiDAR and multispectral imagery provide a set of complementary features that improve the results (90.75% overall accuracy), and the object-oriented classification techniques are efficient for stratification of Mediterranean forest areas in structural- and fuel-related categories. Further work will be focused on the creation and validation of a different prediction model adapted to the various strata.  相似文献   

Enhanced Atlantic Meridional Overturning Circulation supports the Last Glacial Inception     

Abel Guihou  Sylvain Pichat  Aline Govin  Silvia Nave  Elisabeth Michel  Jean-Claude Duplessy  Philippe Telouk  Laurent Labeyrie 《Quaternary Science Reviews》2011,30(13-14):1576-1582

The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the climate system. However, its role during climate change is still poorly constrained particularly during an Interglacial to Glacial climate transition and the associated global cooling. We present here the first reconstruction of the evolution of the vertical structure of the rate of the AMOC from the Last Interglaciation to the subsequent glaciation (128,000–60,000 years ago) based on sedimentary (²³¹Pa/²³⁰Th) records. We show a deep AMOC during the interglacial warmth Marine Isotope Stage (MIS) 5.5 and a shallower glacial one during glacial MIS 4. The change between these two patterns occurred mostly during the glacial inception, i.e. the transition from MIS 5.5 to MIS 5.4. Our data show that AMOC was enhanced during this latter transition as a consequence of a large increase of the overturning rate of the Intermediate Waters, above 2500 m. We suggest that this AMOC pattern required a reinforced Gulf Stream-North Atlantic Current system that ultimately supported ice-sheet growth by providing heat and moisture to the Northern high latitudes. From MIS 5.4 to MIS 5.1, the AMOC was broadly continuous below 2000 m and supported periods of ice-sheet growth. As a result, a glacial AMOC is triggered at the beginning of MIS 4 due to the extension of ice-sheet and the subsequent reorganization of deep-water formation. This study highlights the role of intermediate waters as a major player during climate change.  相似文献   

Colouration Phenomena of Mediterranean Blennies (Pisces,Blenniidae)     

Erich F. Abel 《Marine Ecology》1993,14(4):291-312

Abstract. The blennies of the Mediterranean Sea were observed in nature by snorkeling and SCUBA diving. Particular attention was paid to their changeable basic patterns and colouring alternations as effected by ecological and ethological factors. Additionally, the tendency for colour change was tested in differently coloured tanks. These experiments failed to demonstrate the striking adaptations seen in the natural environment, except for a remarkable reaction to black and white. The summary of all known reports is supported by colour illustrations; the problems of the colouring alternations are discussed.  相似文献