S. Emamifar; A. Alizadeh
Abstract
Estimation the amount of radiation reaching the Earth's surface (Rs) is an important factor in the energy balance models simulation of plant growth and evapotranspiration estimation. Most Estimation models to radiation reaching the Earth's surface use satellite data and they are based on land surface ...
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Estimation the amount of radiation reaching the Earth's surface (Rs) is an important factor in the energy balance models simulation of plant growth and evapotranspiration estimation. Most Estimation models to radiation reaching the Earth's surface use satellite data and they are based on land surface temperatures. In this study, the Accuracy of solar radiation estimation is investigated Using four different models of neural networks (with the names of ANN1,ANN2, ANN3, ANN4) with the inputs Including products land surface temperature MODIS sensor (models 1 and 2 , and models 3 and 4 are based on MOD11A1 MYD11A1 products, respectively), extraterrestrial radiation (Ra) and relative sunshine (n / N). The results show that four neural network models are able to estimate the amount of radiation reaching the Earth's surface with good correlation (R2>. 85). However, models based on MOD11A1 products have a higher accuracy than models based on MYD11A1 products. Neural network model of ANN1 (based on MOD11A1 products, relative sunshine and extraterrestrial radiation (Ra)) with the coefficient of determination (R2) equal to .9332 and the root mean square error (RMSE) equal to 1.4448 MJ per square meter per day is more accurate on the estimation of solar radiation than other models. The results also showed that the Neural network model ANN2, comparing with Hargreaves and Samani models based on air temperature and extraterrestrial radiation, is More accurate in estimating of solar radiation.
M. Erfanian; S. Babaei Hesar
Abstract
Short wavelength of solar radiation that reaches the ground used as one of the key parameters in most models those estimate the potential Evapotranspiration, such as FAO Penman-Monteith. Despite the importance of amount of radiation, its measurement is done only in small number of stations in the country. ...
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Short wavelength of solar radiation that reaches the ground used as one of the key parameters in most models those estimate the potential Evapotranspiration, such as FAO Penman-Monteith. Despite the importance of amount of radiation, its measurement is done only in small number of stations in the country. Empirical radiation models, such as Angstrom- Prescott, despite the simplicity, require calibration and their coefficients must be properly estimated. In the present study a relatively simple physical model that called hybrid model was used to estimate daily solar radiation in 10 synoptic stations, Esfahan, Bojnourd, Bandar Abbas, Tabriz, Tehran, Ramsar, Zahedan, Kerman, Kermanshah and Mashhad and the results were compared with modified Daneshyar & Sabagh models those were proposed for various climatic conditions in previous researches. using a relatively small number of meteorological parameters include temperature, relative humidity, pressure and sunshine hours, Hybrid model estimated amount of radiation with reasonable accuracy. To compare the three models, mean error (ME), mean absolute error (MAE), root mean square error (RMSE) and mean percentage error (MPE) statistical criteria were used. Average of each error criteria in Hybrid model, respectively are, -0.27, 1.27, 1.59 and 2.01 and in the modified Daneshyar model are, -0.19, 2.64, 3.15 and 3.42. Also in modified Sabagh model these criteria are achieved equal to 0.91, 2.87, 3.93 and 11.20. Small amount of error criteria for Hybrid model represents the relatively high performance of this model in the estimation of solar radiation in daily scale.
