Renji Remesan

Daily Pan Evaporation Modeling in a Hot and Dry Climate

Evaporation plays a key role in water resources management in arid and semiarid climatic regions. This is the first time that an artificial neural network (ANN) model is applied to estimate evaporation in a hot and dry region (BWh climate by the Koppen classification). It has been found that ANN works very well at the study site and, further, an integrated ANN and autoregressive with exogeneous inputs can have an improved performance over the traditional ANN. Both models significantly outperformed the two empirical methods. It has been demonstrated that the important weather factors to be included in the model inputs are wind speed, saturation vapor pressure deficit, and relative humidity. This result is different from all those reported in the literature and is interestingly linked with a 1936 study by Anderson, who emphasized the importance of saturation vapor pressure deficit. As evaporation is a nonlinear dynamic process, the selection of suitable input weather variables has been a complicated and tim...

Error Correction Modelling of Wind Speed Through Hydro-Meteorological Parameters and Mesoscale Model: A Hybrid Approach

Accurate estimation of wind speed is essential for many hydrological applications. One way to generate wind velocity is from the fifth generation PENN/NCAR MM5 mesoscale model. However, there is a problem in using wind speed data in hydrological processes due to large errors obtained from the mesoscale model MM5. The theme of this article has been focused on hybridization of MM5 with four mathematical models (two regression models- the multiple linear regression (MLR) and the nonlinear regression (NLR), and two artificial intelligence models – the artificial neural network (ANN) and the support vector machines (SVMs)) in such a way so that the properly modelled schemes reduce the wind speed errors with the information from other MM5 derived hydro-meteorological parameters. The forward selection method was employed as an input variable selection procedure to examine the model generalization errors. The input variables of this statistical analysis include wind speed, temperature, relative humidity, pressure, solar radiation and rainfall from the MM5. The proposed conjunction structure was calibrated and validated at the Brue catchment, Southwest of England. The study results show that relatively simple models like MLR are useful tools for positively altering the wind speed time series obtaining from the MM5 model. The SVM based hybrid scheme could make a better robust modelling framework capable of capturing the non-linear nature than that of the ANN based scheme. Although the proposed hybrid schemes are applied on error correction modelling in this study, there are further scopes for application in a wide range of areas in conjunction with any higher end models.

ANFIS and NNARX based rainfall-runoff modeling

Modeling of non-linearity and uncertainty associated with rainfall-runoff process has received a lot of attention in the past years. Recently artificial intelligence techniques are used for hydrological time series modelling. Earlier studies showed this approach is effective, still there are concerns about how these techniques perform efficiently to predict the run-off with high standard of accuracy. To this end, this paper explores the ability of two artificial intelligence techniques, namely neural network auto regressive with exogenous input (NNARX) and adaptive neuro-fuzzy inference system, to model the rainfall-runoff phenomenon effectively from antecedent rainfall and runoff information. Specifically, to illustrate applicability of these techniques, two year (1994-1995) rainfall-runoff data from Brue catchment of The United Kingdom were used. The models having various input structures were constructed and the best structure was investigated with help of the proposed technique, called gamma test. Training data length selection and best input combination were carried out prior to modeling with help of gamma test. The performance of the ANFIS model in training and testing sets were compared with that of NNARX model with help of several statistical parameters. The results of the study have shown that both ANFIS and NNARX could work efficiently in rainfall-runoff modeling and can provide high accuracy and reliability in runoff prediction.

GA-based optimization of a fourth-order sigma-delta modulator for WLAN

Over-sampling sigma-delta analogue-to-digital converters (ADCs) are one of the key building blocks of state of the art wireless transceivers. In the sigma-delta modulator design the scaling coefficients determine the overall signal-to-noise ratio. Therefore, selecting the optimum value of the coefficient is very important. To this end, this paper addresses the design of a fourth-order multi-bit sigma-delta modulator for wireless local area networks (WLAN) receiver with feed-forward path and the optimum coefficients are selected using genetic algorithm (GA)-based search method. In particular, the proposed converter makes use of low-distortion swing suppression SDM architecture which is highly suitable for low oversampling ratios to attain high linearity over a wide bandwidth. The focus of this paper is the identification of the best coefficients suitable for the proposed topology as well as the optimization of a set of system parameters in order to achieve the desired signal-to-noise ratio. GA-based search engine is a stochastic search method which can find the optimum solution within the given constraints.