We investigated the effectiveness of combining gauge observations and satellite-derived precipitation on flood forecasting. Two data merging processes were proposed: the first one assumes that the individual precipitation measurement is non-bias, while the second process assumes that each precipitation source is biased and both weighting factor and bias parameters are to be calculated. Best weighting factors as well as the bias parameters were calculated by minimizing the error of hourly runoff prediction over Wu-Tu watershed in Taiwan. To simulate the hydrologic response from various sources of rainfall sequences, in our experiment, a recurrent neural network (RNN) model was used.
The results demonstrate that the merged method used in this study can efficiently combine the information from both rainfall sources to improve the accuracy of flood forecasting during typhoon periods. The contribution of satellite-based rainfall, being represented by the weighting factor, to the merging product, however, is highly related to the effectiveness of ground-based rainfall observation provided gauged. As the number of gauge observations in the basin is increased, the effectiveness of satellite-based observation to the merged rainfall is reduced. This is because the gauge measurements provide sufficient information for flood forecasting; as a result the improvements added on satellite-based rainfall are limited. This study provides a potential advantage for extending satellite-derived precipitation to those watersheds where gauge observations are limited. 相似文献
Statistical methods are widely applied in visibility forecasting. In this article, further improvements are explored by extending
the standard probabilistic neural network approach. The first approach is to use several models to obtain an averaged output,
instead of just selecting the overall best one, while the second approach is to use deterministic neural networks to make
input variables for the probabilistic neural network. These approaches are extensively tested at two sites and seen to improve
upon the standard approach, although the improvements for one of the sites were not found to be of statistical significance. 相似文献
Numerical simulations of variable-density flow and solute transport have been conducted to investigate dense plume migration for various configurations of 2D fracture networks. For orthogonal fractures, simulations demonstrate that dispersive mixing in fractures with small aperture does not stabilize vertical plume migration in fractures with large aperture. Simulations in non-orthogonal 2D fracture networks indicate that convection cells form and that they overlap both the porous matrix and fractures. Thus, transport rates in convection cells depend on matrix and fracture flow properties. A series of simulations in statistically equivalent networks of fractures with irregular orientation show that the migration of a dense plume is highly sensitive to the geometry of the network. If fractures in a random network are connected equidistantly to the solute source, few equidistantly distributed fractures favor density-driven transport. On the other hand, numerous fractures have a stabilizing effect, especially if diffusive transport rates are high. A sensitivity analysis for a network with few equidistantly distributed fractures shows that low fracture aperture, low matrix permeability and high matrix porosity impede density-driven transport because these parameters reduce groundwater flow velocities in both the matrix and the fractures. Enhanced molecular diffusion slows down density-driven transport because it favors solute diffusion from the fractures into the low-permeability porous matrix where groundwater velocities are smaller. For the configurations tested, variable-density flow and solute transport are most sensitive to the permeability and porosity of the matrix, which are properties that can be determined more accurately than the geometry and hydraulic properties of the fracture network, which have a smaller impact on density-driven transport. 相似文献
By taking advantage of the close relationship between quality and quantity of water, we investigated the potential improvements of the in-reservoir water quality through the optimization of reservoir operational strategies. However, the few available techniques for optimization of reservoir operational strategies present some limitations, such as restrictions on the number of state/decision variables, the impossibility considering stochastic characteristics and difficulties for considering simulation/prediction models. One technique which presents great potential for overcoming some of these limitations is applied here and investigated for the first time in such complex system. The method, named stochastic fuzzy neural network (SFNN), can be defined as a fuzzy neural network (FNN) model stochastically trained by a genetic algorithm (GA) based model to yield a quasi optimal solution. The term “stochastically trained” refers to the introduction of a new loop within the training process which accounts for the stochastic variable of the system and its probabilities of occurrence. The SFNN was successfully applied to the optimization of the monthly operational strategies considering maximum water utilization and improvements on water quality simultaneous. Results showed the potential improvements on the water quality through means of hydraulic control. 相似文献
Slope instability studies appear to recognize a number of potential superficial slide-producing agents, which may be directly
detected and monitored with Earth Observation (EO) data. The main objective of this work is to use conventional EO data and
automatic techniques for providing land-use change maps useful in landslide prevention. The idea is to use the detection of
changes in areas already involved in landslide events as a precursory sign of variations in the equilibrium status of the
slope, independently from other natural triggering events, such as rain and seismic events. Attention is focused on man-induced
surface changes, such as deforestation, urban expansion and construction of artificial structures.
A historical set of 20 multi-temporal Landsat TM images, covering the period 1987–2000, was analyzed using a supervised change
detection technique on a test site affected by slope instability phenomena located in the Abruzzo region in Southern Italy.
A change image is obtained by comparing year-specific thematic map pairs. It contains useful information not only on the place
where a transition occurred, but also on the specific classes involved in the transitions between two different years. The
full set of change images is used to extract class-conditional transition probabilities, to evaluate variations in specific
class distribution and the total number of changed pixels in time. Four classes and their transitions were considered in the
analysis: (1) arboreous land, (2) agricultural land, (3) barren land, and (4) artificial structures.
The quantitative analysis of the class-joint transition probability values of some specific class-transitions that may worsen
slope stability showed that in an area prone to landslides the probability of landslide re-activation or first activation
is higher where changes have occurred. Although based on a limited number of known events, such a result encourages extensive
experimentation of the proposed technique on better documented landslide test sites. 相似文献
ABSTRACTThe evaluation of a new method for forecasting freeze-up at the eastern end of the Northwest Passage, a principal gateway into the Canadian High Arctic, is presented. The technique uses real-time data from a novel ocean observatory that combines acoustic, cable, and satellite communications technology to provide year-round bihourly data. The basis for the predictive capability comes from a previous analysis of a decade-long time series of instrumented mooring data collected in the area, which demonstrated a strong link between late summer upper ocean salinity and the timing of freeze-up there. Using real-time data from the observatory and this previously established relationship, accurate predictions of the timing of freeze-up in 2012 and 2013 with lead times of four weeks and two weeks, respectively, are presented. This unique forecasting capability points to the enhanced value of real-time data systems when these systems are located where previously collected long time series monitoring has revealed key relationships in the marine environment. 相似文献