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1.
Potential evapotranspiration (PET) is a key input to hydrological models. Its estimation has often been via the Penman–Monteith (P–M) equation, most recently in the form of an estimate of reference evapotranspiration (RET) as recommended by FAO‐56. In this paper the Shuttleworth–Wallace (S–W) model is implemented to estimate PET directly in a form that recognizes vegetation diversity and temporal change without reference to experimental measurements and without calibration. The threshold values of vegetation parameters are drawn from the literature based on the International Geosphere–Biosphere Programme land cover classification. The spatial and temporal variation of the LAI of vegetation is derived from the composite NOAA‐AVHRR normalized difference vegetation index (NDVI) using a method based on the SiB2 model, and the Climate Research Unit database is used to provide the required meteorological data. All these data inputs are publicly and globally available. Consequently, the implementation of the S–W model developed in this study is applicable at the global scale, an essential requirement if it is to be applied in data‐poor or ungauged large basins. A comparison is made between the FAO‐56 method and the S–W model when applied to the Yellow River basin for the whole of the last century. The resulting estimates of RET and PET and their association with vegetation types and leaf area index (LAI) are examined over the whole basin both annual and monthly and at six specific points. The effect of NDVI on the PET estimate is further evaluated by replacing the monthly NDVI product with the 10‐day product. Multiple regression relationships between monthly PET, RET, LAI, and climatic variables are explored for categories of vegetation types. The estimated RET is a good climatic index that adequately reflects the temporal change and spatial distribution of climate over the basin, but the PET estimated using the S–W model not only reflects the changes in climate, but also the vegetation distribution and the development of vegetation in response to climate. Although good statistical relationships can be established between PET, RET and/or climatic variables, applying these relationships likely will result in large errors because of the strong non‐linearity and scatter between the PET and the LAI of vegetation. It is concluded that use of the implementation of the S–W model described in this study results in a physically sound estimate of PET that accounts for changing land surface conditions. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

2.
During a three year-period, the participants of a NATO Science for Peace project performed ambient noise measurements inside buildings in four European countries. This paper reports the results relevant to reinforced concrete (RC) buildings with height in the range 1–20 floors. The total number of such buildings surveyed is 244. The most striking feature is the similarity of the height-period relationships in the four countries, which allowed the treatment of the all measurements as a single database. We found no significant correlation with other variables, and calculated a regression that is very similar to other empirical height-period relationships and quite different from code provisions and theoretical models.  相似文献   

3.
In this paper all important results on laboratory measurements of electrical properties of rocks and minerals for the last four years are presented. Although basic results from all over world are reviewed, East European and U.S.S.R. works are described more extensively. Only D.C. conductivity results are considered, however all principal conclusions hold in similar form for both D.C. and A.C. conductivities. At the end the most important areas of further study and measurement are depicted and the main problems of the future are outlined.  相似文献   

4.
中国岩石圈三维结构数值模拟数据库   总被引：1，自引：5，他引：1  
应总结中国岩石圈三维结构研究成果的需要，本文介绍了数值模拟数据库的建设，它系国土资源部中国岩石圈三维结构数据库下属子库之一．该数据库在Windows2000环境中开发，以Visual Basic6．0和Arc／Info的二次开发工具Mapobject作为应用系统开发平台，分别用Microsoft Access 2000和SQL Server2000作为数据库平台，并利用Arc／Info的Desktop版本建立空间数据和元数据．最终实现了一个具有从空间数据、属性数据、元数据等多角度查询功能的系统．文中详细介绍了平台选取、数据库建立、系统结构、系统功能等问题．  相似文献   

5.
In the period up to about 1965 the stations of the Soviet seismic network distributed throughout the regions of the U.S.S.R. had increased in number to in excess of one hundred. In order that the data provided by such stations could be applied to the study of the earth's structure rather than merely regional problems, and to the determination of the seismic character of the territory of the U.S.S.R. as a whole, it became necessary to institute the Unified System of Seismic Observations (USSO) of the U.S.S.R. The standardization of data and organization of the stations into a system of base and regional stations and also into zonal networks, covering specific seismic zones of the U.S.S.R., has been effected within the USSO. Currently the USSO consists of 215 stations mostly equipped with high-sensitivity instruments with magnifications of 20–50,000 and dynamic ranges of 35–40 dB. To exploit the large volume of observational data obtained through the system it is necessary to devise a programme for the transmission, processing and storage of data on the necessary scale. In the present paper we describe the methods which have been adopted and those which are in the course of development for such a programme in the U.S.S.R.  相似文献   

6.
By combining AVHRR data from the NOAA satellites with information from a database of in situ measurements, large-scale maps can be generated of the microphysical parameters most immediately significant for the modelling of global circulation and climate. From the satellite data, the clouds can be classified into cumuliform, stratiform and cirrus classes and then into further sub-classes by cloud top temperature. At the same time a database of in situ measurements made by research aircraft is classified into the same sub-classes and a statistical analysis is used to derive relationships between the sub-classes and the cloud microphysical properties. These two analyses are then linked to give estimates of the microphysical properties of the satellite observed clouds. Examples are given of the application of this technique to derive maps of the probability of occurrence of precipitating clouds and of precipitating water content derived from a case study within the International Cirrus Experiment (ICE) held in 1989 over the North Sea.  相似文献   

7.
New experimental data depicting equatorial spread-F were taken during an HF radar sounding campaign in Korhogo (Ivory Coast, 9°24N, 5°37W, dip 4°S). Range-time-intensity maps of the radar echoes have been analyzed to identify the signatures of density depletions and bottomside spread-F. Density depletions are well known features of equatorial spread-F, and are believed to emerge after the development of a Rayleigh-Taylor instability on the bottomside F-layer. A simple model is developed and used to simulate the flow of density depletions over the radar field of view. The simulation permits an interpretation of the data that yields the zonal flow velocity as a function of local time. Comparisons with previous measurements are undertaken to assess the consistency of the computational results, and qualitative arguments are presented to identify bottomside spread-F. Using the computational results as reference, a morphological study of ionograms showing spread-F is undertaken which reveals the specific signature of bottomside spread-F on ionograms recorded just after sunset.  相似文献   

8.
Abstract

Soil erosion vulnerability and extreme rainfall characteristics over the Mediterranean semi-arid region of Tunisia are crucial input for estimation of siltation rate in artificial reservoirs. A comprehensive high-resolution database on erosive rainfall, together with siltation records for 28 small reservoirs, were analysed for this region, the Tunisian Dorsal (the easternmost part of the Atlas Mountains). The general life-span of these reservoirs is only about 14 years. Depending on the soil degradation in the different catchments, the corresponding reservoirs display a wide range of soil erosion rates. The average soil loss was 14.5 t ha?1 year?1 but some catchments display values of up to 36.4 t ha?1 year?1. The maximum 15-min duration rainfall intensity was used to determine the spatial distribution of rainfall erosivity. The northwestern parts of the Tunisian Dorsal display the most extreme rainfall erosivity. Spatial erosion patterns are to some extent similar; however, they vary greatly according to their location in the “soil degradation cycle”. This cycle determines the soil particle delivery potential of the catchment. In general, the northwestern parts of the Dorsal display modest soil erosion patterns due to the already severely degraded soil structure. Here, the soil surface is often the original bedrock. However, the greatest soil erosion occurs in the mid-eastern parts of the Dorsal, which represents the “degradation front”. The latter corresponds to the area with highest erosion, which is continuously progressing westward in the Dorsal. The large variation between the erosive rainfall events and the annual soil loss rates was explained by two important factors. The first relates to the soil degradation cycle. The second factor corresponds to the degradation front with the highest soil loss rates. At present this front is located at 300 m altitude and appears to be moving along an 80-km westward path starting from the east coast. A better understanding of the above can be used to better manage soils and soil covers in the Tunisian Dorsal area and, eventually, to decrease the soil erosion and reservoir siltation risk.

Citation Jebari, S., Berndtsson, R., Bahri, A. & Boufaroua, M. (2010) Spatial soil loss risk and reservoir siltation in semi-arid Tunisia. Hydrol. Sci. J. 55(1), 121–137.  相似文献   

9.
本文研究了量规函数、台站方位、台基以及不同测量方法对测定震级 ML 的影响.结果表明:1)得到了一个新的量规函数 R3（△）,它比原有的 R1（△）和 R2（△）更适合于我国西南地区:2)由于地震波辐射的方向性,处在不同方位的台站震级差可达0.3——0.5级.用 P 波与S 波的某种组合可消除一些方向性影响;3)基岩台基的校正值不大.某些较大的台基校正值可能是仪器放大倍数没测准的影响;4)除用 S 波的水平分量求震级外,S 波的垂直分量以及 P 波的水平分量和垂直分量乘以适当的倍数后,都可用来求震级 ML.求得的结果与常规方法的结果之间几乎没有什么差别.   相似文献   

10.
Sensitivity of seismic waves to structure   总被引：2，自引：0，他引：2  
We study how the perturbations of a generally heterogeneous isotropic or anisotropic structure manifest themselves in the wavefield, and which perturbations can be detected within a limited aperture and a limited frequency band. A short-duration broad-band incident wavefield with a smooth frequency spectrum is considered. In-finitesimally small perturbations of elastic moduli and density are decomposed into Gabor functions. The wavefield scattered by the perturbations is then composed of waves scattered by the individual Gabor functions. The scattered waves are estimated using the first-order Born approximation with the paraxial ray approximation. For each incident wave, each Gabor function generates at most 5 scattered waves, propagating in specific directions and having specific polarisations. A Gabor function corresponding to a low wavenumber may generate a single broad-band unconverted wave scattered in forward or narrow-angle directions. A Gabor function corresponding to a high wavenumber usually generates 0 to 5 narrow-band Gaussian packets scattered in wide angles, but may also occasionally generate a narrow-band P to S or S to P converted Gaussian packet scattered in a forward direction, or a broad-band S to P (and even S to S in a strongly anisotropic background) converted wave scattered in wide angles. In this paper, we concentrate on the Gaussian packets caused by narrow-band scattering. For a particular source, each Gaussian packet scattered by a Gabor function at a given spatial location is sensitive to just a single linear combination of 22 values of the elastic moduli and density corresponding to the Gabor function. This information about the Gabor function is lost if the scattered wave does not fall into the aperture covered by the receivers and into the legible frequency band.  相似文献   

11.
Direct measurements of the Earth's magnetic field in Italy since 1640 a.d. have been used to check the remanence directions derived from historically dated volcanic rocks of Etna and Vesuvius. Direct measurements consist of the records of L’Aquila and Pola geomagnetic observatories, the repeat stations of the Italian Magnetic Network and the data base of the Historical Italian Geomagnetic Data Catalogue. All have been relocated to the same reference site (Viterbo — lat. 42.45°N, long. 12.03°E) in order to draw a reference secular variation (SV) curve. The direction of the Earth's field at Viterbo has also been calculated from the historical records (2000-1600) of ref. [Jackson, A., Jonkers, A.R.T., Walker, M.R., 2000. Four centuries of geomagnetic secular variation from historical records. Phil. Trans. R. Soc. London, Ser. A 358, 957-990] database. The remanence directions from Etna show a general agreement with the trend of the SV curve, although their inclination is usually lower than that from the direct measurement. The directions from Vesuvius are more scattered. Large discrepancies occur at both volcanoes and in some cases have been ascribed in the literature to poor geographic information, making it difficult to identify the flows actually emplaced during the eruptions reported in the chronicles. Closer examination shows that the great majority of the best-defined remanence directions (semi-angle of confidence α95 < 2.5°) deviate significantly from the geomagnetic direction measured at the time of the emplacement, the angle between the two directions being larger than the α95 value. The value of 2.5-3.0° can thus be regarded as a conservative evaluation of the error when dealing with dating Etna and Vesuvius lava flows older than 17th century, even when the accuracy attained in remanence measurements is higher. In default of a SV curve for Italy derived from archaeological artefacts, a further error in dating is introduced when reference is made to SV curves of other countries, even if well-established, as these are from regions too far from Italy (>600 km) to confidently relocate magnetic directions.  相似文献   

12.
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13.
《Journal of Geodynamics》2010,49(3-5):305-309
A new database for absolute gravity (AG) measurements has been implemented at BGI and BKG and is operational now for storing absolute gravity data either in the form of metadata or as detailed measurement results. The database development was proposed by the IGFS (International Gravity Field Service) and is expected to have a great importance for the GGOS (Global Geodetic Observing System) initiative. This database will provide an overview about AG stations and observations and by this improve the cooperation between gravity groups and foster the combination with other geodetic observation techniques. The international community of absolute gravimeter users is asked to contribute to this database.In addition to its primary purposes, demonstration of the global site distribution and information about available observations, the database could also provide an important contribution to the Global Geodynamics Project (GGP). Precise repeated absolute gravity measurements at the superconducting gravimeter (SG) sites are necessary for the determination of SG drift parameters and can be used for checking SG instrument calibration factors. The AGrav database is capable of storing the necessary AG observations at the SG location in detail up to the “single drop level” and provides this information for the combination with SG time series. An example for a selected station is presented. It is proposed to establish an interface between the AGrav and GGP databases.  相似文献   

14.
Although pesticides are primarily degraded in the topsoil, significant attenuation can be expected in groundwater systems where the transit time of pesticides usually are orders of magnitude longer than in the soil. Because degradation and transport processes in the subsurface take place at time scales of months to years or even decades, direct measurements of natural attenuation are hampered by practical and logistical limitations (for instance the limited duration of sampling or a correct estimation of the pesticide flux into groundwater). Indirect methods such as measuring the changes in the ratio of degradation product to parent compound as a function of transit time in the aquifer, along a flow line provide a possible alternative. This paper presents a simple mathematical formulation of the relationship between transit time in the subsurface and changes in that ratio, and allows estimating the transformation rate of both parent compound and degradation product. The applicability of the method is illustrated in a case study investigating atrazine attenuation in a fractured sandstone aquifer.  相似文献   

15.
A worldwide database of liquefaction-induced sand blows has been compiled to generate empirical relationships between earthquake parameters and sand blow geometries. Curves resulting from these empirical relationships can be used afterwards for the study of historic and pre-historic earthquakes that formed sand blows. This database only incorporates instrumental earthquakes inducing sand blows, characterised in terms of magnitude (Mw), hypocentral location and focal mechanism solution. Two relationships are herein presented. The first curve, minimum likelihood of liquefaction occurrence (magnitude/epicentral distance), displays a logarithmic behaviour, as others already proposed. The second curve of sand-blow diameter vs epicentral distance is the first proposal of this kind, whose shape follows a negative power-law. Magnitude estimations of (pre-)historic earthquakes then may be attempted through these empirical relationships. Resulting magnitudes derived from these curves should be mostly considered as underestimated. The curves will reflect actual magnitudes only if, correspondingly, the farthest and largest blow has ever been reported during the after-earthquake survey. Following the same principle, a magnitude estimation resulting from the measuring of a sand blow can only be considered as minimal because it is almost impossible to ascertain that the measured feature is the biggest one produced by the earthquake under evaluation. Finally, these results call for thorough surveys of induced effects after every future moderate-to-large earthquake, as any empirical relationship simply improves by incorporating new data.  相似文献   

16.
In this study, the correction problem of mean‐field bias of radar rain rate was investigated using the concept of linear regression. Three different relationships were reviewed for their slopes to be used as the bias correction factor: Relationship 1 (R1) is based on the conventional linear regression, relationship 2 (R2) is forced to pass the origin and relationship 3 (R3) is the line whose slope is the G/R ratio. In other words, R1 is the regression line connecting the intercept and the mass centre of measurement pairs, R2 is the regression line forced to pass the origin, and R3 is the line connecting the origin and the mass centre. The slopes of all three relationships were reviewed analytically to compare them, and thereby, the effect of zero measurements could be evaluated. Additionally, the effect of using switched independent and dependent variables on the derived slopes was also evaluated. The theoretically derived results were then verified by analysing the rainfall event on 10–11 August 2010 in Korea. Finally, the difference between the bias‐corrected radar rain rate and the rain gauge rain rate was quantified by root mean square error and mean error so that it could be used as a measure for the evaluation of bias correction factors. In conclusion, the slope of R2 was found to be the best for the bias correction factor. However, when deciding the slope of this R2, the radar rain rate should be used as the independent variable in the low rain rate region, and the rain gauge rain rate in the high rain rate region above a certain threshold. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

17.
IntroductionSeismicity analysis is an important branch of seismology, which focuses statistically on the study of time, space and magnitude distribution of a group of earthquakes (FU, 1997). Earthquakes as instability phenomena of the lithosphere, however, involve very complicated mechanics. The seismic activity level is not steady, but fluctuating time by time, which shows the alternative change of periods of quiescence and activity (FU, 1986; Mogi, 1984; ZHANG, 1987). Because of such com…  相似文献   

18.
—?A neural network module has been implemented in the Prototype International Data Centre (PIDC) for automated identification of the initial phase type of seismic detections. Initial training of the neural networks for stations of the International Monitoring System (IMS) requires considerable effort. While there are many seismic phases in the analyst-reviewed database that can be assumed as the ground-truth resource of the initial phase type of Teleseism (T), Regional P (P), and Regional S (S), no ground-truth database of noise (N) is available. To reduce analyst effort required in building a ground-truth database, an “Adaptive Training Approach” is proposed in this paper. This approach automatically selects training patterns to take advantage of the learning ability of neural networks and information on the accumulated observation database. Using this approach, neural networks were trained on the data provided by station STKA, Australia. The performance of automated phase identification has been improved significantly by the retrained neural networks. This approach is also validated by comparison with the performance using the ground-truth noise database.  相似文献   

19.
地震活动性参数的变尺度（Rem>/Sem>）分析   总被引：7，自引：0，他引：7       下载免费PDF全文
李娟  陈颙 《地震学报》2001,23(2):143-150
将改变时间标度的方法应用于地震活动性分析中，选择具有不同空间尺度范围、时间范围和地震活动背景的现代仪器地震目录作为研究对象，分析了几个地震活动性参数——地震频度和地震发生时间间隔与时间标度的关系．这些地震活动性参数的极差和均方差之比与时间标度呈现出幂指数变化方式，且幂指数都大于0.5，表明地震的发生并非无记忆的泊松过程，而是具有随机和规律的双重特性．犎指数偏离0.5的程度可以衡量随机与规律成分所占比重，偏离越大，该序列的规律性成分越多，反之则越少．通过时间标度变换，可以较短时间的观测为基础，对变量未来的发生情况做出保守的估计．   相似文献   

20.
Strong motion data recorded by the Turkish national strong motion network has been compiled and processed systematically for the first time, together with detailed geophysical and geotechnical site measurements for all of its stations. The catalog information of 18 seismological agencies and other sources were examined to obtain reliable source, geometry, and distance parameters for each event. The high quality digital and analog strong motion data was processed by a uniform methodology to remove the high- and low-frequency noise. Currently, the seismological and spectral information of 4,607 strong motion records are available for use by earth scientists and earthquake engineers. In this article, we present the fundamental features of this database and explain our methodology in their calculation. We present several comparisons of our database with other related studies to verify our approach during the computational stage of the seismological parameters. The results confirm the reliability of our calculations. The database has also enabled us to derive empirical magnitude conversion relationships to estimate moment magnitude in terms of different magnitude scales. The article ends with a discussion of the likely improvements in the European accelerometric data through contributions from this strong motion database applicable for seismically active shallow-crust regions. The findings of this article emphasize the necessity of global strong motion databases in Europe for better estimation of seismic hazard in regions of similar seismotectonic environment.  相似文献   

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