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21.
Arnon Karnieli Dr. 《GeoJournal》1990,22(4):391-398
The classical methods for interpolating and spatial averaging of precipitation fields fail to quantify the accuracy of the estimate. On the other hand, kriging is an interpolation method for predicting values of regionalized variables at points (punctual kriging) or average values over an area (block kriging).This paper demonstrates the use of the kriging method for mapping and evaluating precipitation data for the State of Arizona. Using 158 rain gauge stations with 30 years or more of record, the precipitation over the state has been modeled as a realization of a two dimensional random field taking into consideration the spatial variability conditions.Three data sets have been used: (1) the mean annual precipitation over the state; (2) the mean summer rainy season; and (3) the mean winter rainy season. Validation of the empirical semi-variogram for a constant drift case indicated that the exponential model was appropriate for all the data sets. In addition to a global kriging analysis, the data have been examined under an anisotropic assumption which reflects the topographic structure of the state. 相似文献
22.
The effect of the overlying water velocity on ammonium (NH4+) uptake by benthic biofilms was studied in a recirculating laboratory flume (260 cm long, 29 cm wide), packed with 5 cm of silica sand arranged into bedforms. NH4+ uptake was determined as the reduction in NH4+ concentration in the water at average overlying water velocities of 0.8, 2, 4 and 8 cm s?1. NH4+ uptake was relatively constant under laminar flow conditions but increased when the flow regime became turbulent (>4 cm s?1). This pattern was observed for two biofilms differing in their total biomass and in the abundance of the ammonia‐oxidizing bacteria, thus indicating that NH4+ uptake was strongly controlled by mass‐transfer processes. The near stoichiometric relationship between the rates of NH4+ uptake and nitrate (NO3?) accumulation suggests that aerobic nitrification was the main route for NH4+ uptake. Microelectrode measurements showed a sharp decline of oxygen concentrations and pH values within the biofilms, thus supporting strong nitrification activity within the surficial section of the benthic biofilms. The results of this study highlight the key role of hydrodynamic conditions in regulating NH4+ uptake in the transition from laminar to turbulent flow conditions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
23.
Ibrahim Ozdemir Arnon Karnieli 《International Journal of Applied Earth Observation and Geoinformation》2011
Estimation of forest structural parameters by field-based data collection methods is both expensive and time consuming. Satellite remote sensing is a low-cost alternative in modeling and mapping structural parameters in large forest areas. The current study investigates the potential of using WordView-2 multispectral satellite imagery for predicting forest structural parameters in a dryland plantation forest in Israel. The relationships between image texture features and the several structural parameters such as Number of Trees (NT), Basal Area (BA), Stem Volume (SV), Clark-Evans Index (CEI), Diameter Differentiation Index (DDI), Contagion Index (CI), Gini Coefficient (GC), and Standard Deviation of Diameters at Breast Heights (SDDBH) were examined using correlation analyses. These variables were obtained from 30 m × 30 m square-shaped plots. The Standard Deviation of Gray Levels (SDGL) as a first order texture feature and the second order texture variables based on Gray Level Co-occurrence Matrix (GLCM) were calculated for the pixels that corresponds to field plots. The results of the correlation analysis indicate that the forest structural parameters are significantly correlated with the image texture features. The highest correlation coefficients were calculated for the relationships between the SDDBH and the contrast of red band (r = 0.75, p < 0.01), the BA and the entropy of blue band (r = 0.73, p < 0.01), and the GC and the contrast of blue band (r = 0.71, p < 0.01). Each forest structural parameter was modeled as a function of texture measures derived from the satellite image using stepwise multi linear regression analyses. The determination coefficient (R2) and root mean square error (RMSE) values of the best fitting models, respectively, are 0.38 and 109.56 ha−1 for the NT; 0.54 and 1.79 m2 ha−1 for the BA; 0.42 and 27.18 m3 ha−1 for the SV; 0.23 and 0.16 for the CEI; 0.32 and 0.05 for the DDI; 0.25 and 0.06 for the CI; 0.50 and 0.05 for the GC; and 0.67 and 0.70 for the SDDBH. The leave-one-out cross-validation technique was applied for validation of the best-fitted models (R2 > 0.50). In conclusion, cross-validated statistics confirmed that the structural parameters including the BA, SDDBH, and GC can be predicted and mapped with a reasonable accuracy using the texture features extracted from the spectral bands of WorldView-2 image. 相似文献
24.
Using N -body simulations with a large set of massless test particles, we compare the predictions of two theories of violent relaxation, the well-known Lynden-Bell theory and the more recent theory by Nakamura. We derive 'weakened' versions of both the theories in which we use the whole equilibrium coarse-grained distribution function as a constraint instead of the total energy constraint. We use these weakened theories to construct expressions for the conditional probability Ki (τ) that a test particle initially at the phase-space coordinate τ would end-up in the i th macro-cell at equilibrium. We show that the logarithm of the ratio Rij (τ) ≡ Ki (τ)/ Kj (τ) is directly proportional to the initial phase-space density f 0 (τ) for the Lynden-Bell theory and inversely proportional to f 0 (τ) for the Nakamura theory. We then measure Rij (τ) using a set of N -body simulations of a system undergoing a gravitational collapse to check the validity of the two theories of violent relaxation. We find that both the theories are at odds with the numerical results, both qualitatively and quantitatively. 相似文献
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26.
We explore the possibility that the diffuse gamma-ray background radiation (GBR) at high Galactic latitudes could be dominated by inverse Compton scattering of cosmic ray (CR) electrons on the cosmic microwave background radiation and on starlight from our own galaxy. Assuming that the mechanisms accelerating Galactic CR hadrons and electrons are the same, we derive simple and successful relations between the spectral indices of the GBR above a few MeV and the CR electrons and CR nuclei above a few GeV. We reproduce the observed intensity and angular dependence of the GBR, in directions away from the Galactic disc and centre, without recourse to hypothetical extragalactic sources. 相似文献
27.
Predicting gully initiation at catchment scale was done previously by integrating a geographical information system (GIS) with physically based models, statistical procedures or with knowledge‐based expert systems. However, the reliability and validity of applying these procedures are still questionable. In this work, a data mining (DM) procedure based on decision trees was applied to identify areas of gully initiation risk. Performance was compared with the analytic hierarchy process (AHP) expert system and with the commonly used topographic threshold (TT) technique. A spatial database was used to test the models, composed of a target variable (presence or absence of initial points) and ten independent environmental, climatic and human‐induced variables. The following findings emerged: using the same input layers, DM provided better predictive ability of gully initiation points than the application of both AHP and TT. The main difference between DM and TT was the very high overestimation inherent in TT. In addition, the minimum slope observed for soil detachment was 2°, whereas in other studies it is 3°. This could be explained by soil resistance, which is substantially lower in agricultural fields, while most studies test unploughed soil. Finally, rainfall intensity events >62.2 mm h‐1 (for a period of 30 min) were found to have a significant effect on gully initiation. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
28.
Political geography in general and military geography in particular have paid little attention to the creation of security landscapes. Distinctive elements of the security landscape are identified at the macro-, the meso- and the microscales and applied to the development of Israel's security landscape since 1948, particularly in the Golan Heights and the Negev. The landscape intensifies from the core toward the periphery, expands with technological advances, and changes most at the micro-level. 相似文献
29.
Arkin Yaacov Karnieli Arnon Issar Arie Mtz.-Esparza Javier Diaz 《Environmental Geology》1986,8(4):185-192
Accelerated erosion of a desert cliff due to uncontrolled sewage water disposal was investigated at the Sede Boqer Campus
in the Negev, Israel An erosional cirque formed by this water was studied as a model simulating natural processes. The cliffs
consist of loess and conglomerate underlain by soft marl, clay, and chalk.
The rate of erosion is of the order of 5%–8% of the volume of water discharged. The rate of incision ranges from 10 2 to 13.3
m/yr and is several orders higher than that expected under normal rainfall conditions
The introduction of this new hydrological factor resulted in a severe disturbance of the morphological balance in the vicinity
of the cliffs, accelerated erosion, and generated circular slides 相似文献