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Tang G.,CAS Institute of Geographical Sciences and Natural Resources Research | Tang G.,University of Chinese Academy of Sciences | Xiang B.,Chinese Research Academy of Environmental Sciences | Liang S.,CAS Shenzhen Institutes of Advanced Technology | And 2 more authors.
2012 5th International Congress on Image and Signal Processing, CISP 2012 | Year: 2012

Cloud clutter is the most important noise in NDVI time series data signal; hence to remove the cloud noise is prerequisite for the normal use of NDVI data. In this paper, the MODIS NDVI data of Second Songhua River Basin and Songhua River Trunk Stream Basin is adopted as the experimental region, to conduct a comparative analysis of noise reduction effect for the HANTS algorithm, the Moving Average method and the Asymmetric Gaussian function fitting method. The results show that the HANTS algorithm and the Asymmetric Gaussian function fitting method can effectively remove the noise, while the denoising effect of the Moving Average method is inferior. In general, the HANTS algorithm can provide the best denoising effect, but the algorithm is more difficult in setting parameters. © 2012 IEEE. Source

Li J.,Sichuan Agricultural University | Wang Y.,Sichuan Agricultural University | Gao P.,Sichuan Provincial Water Conservancy Research Institute
Huanjing Kexue Xuebao/Acta Scientiae Circumstantiae | Year: 2015

This study used indoor culture method to investigate the damaging effect of hydrogen peroxide (H2O2) on Microcystis aeruginosa. Results showed that the toxic effect increased with increasing H2O2 concentrations. The number of algal cells, the content of chlorophyll a, carotenoid and protein, and T-AOC of Microcystis aeruginosa reduced rapidly after 24 hours, while the content of MDA increased significantly. Meanwhile, the H2O2 content in culture medium also reduced rapidly. Toxic effect also increased gradually with the processing time. The value of each index reduced to a very low level after 72 hours, the content of MDA increased to the maximum, and the H2O2 was consumed and decomposed gradually, implying that a maximum damage effect of algal cells was achieved. At 50 mg·L-1, H2O2 can effectively remove algal cells, and exert a strong damaging effect on the physiological indexes and anti-oxidizing capacity of algal. ©, 2015, Science Press. All right reserved. Source

Lou Y.,China Agricultural University | Kang S.,China Agricultural University | Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | And 2 more authors.
Sichuan Daxue Xuebao (Gongcheng Kexue Ban)/Journal of Sichuan University (Engineering Science Edition) | Year: 2014

Connotation of water-saving irrigation was elaborated, and the factors of water-efficient irrigation developing were analyzed. Three items of sub-indices of engineering, agriculture and management water-saving were adopted. Firstly, main ingredients with thirty-three indices of the sub-indices were extracted to reduce the number of evaluation indices and establish index system of regional water-saving irrigation developing level evaluation model. Secondly, combination weights were formed from both of objective weight determined by entropy weight method and subjective weight determined by analytic hierarchy process method. Finally, the set pair analysis was selected for analysis. The evaluations showed that two regions are of general, seven regions are of relatively poor, twelve regions are of poor, and the rations of them in all regions are 9%, 33% and 58%, respectively. The results indicated that water-efficient irrigation developing level of every region is still lower, and the overall of Sichuan province is evaluated with level of poor. Therefore, the model has a strong practicality to evaluate the water-saving irrigation development in different regions. Source

Feng Y.,University of Sichuan | Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | Wei X.,University of Sichuan | And 2 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2014

Reference crop evapotranspiration (ET0) is of importance to estimate crop water requirement and make plans of irrigation scheme. Research on temporal and spatial variation of ET0 is important for regional agricultural water management and regional water allocation. The purpose of this study was to make a better understanding of the variation characteristics of ET0 in hilly area of central Sichuan where the agricultural water mostly depends on irrigation. Penman-Monteith equation recommended by Food and Agriculture Organization (FAO) in 1998 was applied to calculate the daily ET0 for 13 meteorological stations within 52 years (1961-2012). Kriging of GIS was introduced to draw the maps of ET0 that could present a clear spatial distribution of ET0. Mann-Kendall trend test was used to analyze temporal distribution characteristics of ET0, and the causes of ET0 change were manifested by sensitivity analysis based on path analysis method. The results showed that: annual ET0 change had a conspicuous decreasing trend in hilly area of central Sichuan in the past 52 years, especially in Langzhong,Yibin and Ziyang station where ET0 decreased significantly (α=0.05). However, in Mianyang station, ET0 increased within 52 years; The temporal distribution characteristics indicated that, during 1961-1979, ET0 increased gradually then decreased until 2003. The trend of ET0 change in a year was a single peak curve, and the change accounting for 85.82% of the year was mostly between March and October. The maximum of ET0 was 3.46 mm/d in July and the minimum was 0.79 mm/d in December. The spatial distribution of ET0 revealed that ET0 decreased gradually from northeast and southeast to the center. During 1961-1970 and 1981-1990, there were several sudden changes in spatial distribution. Compared with the average value within 52 years, the ET0 was smaller in Bazhong station but bigger in Ziyang and Neijiang station. Considering the uneven distribution of ET0 within a year and the sudden changes, the conclusion could be attained that the variation characteristics of ET0 in hilly area of central Sichuan was influenced by the change of weather greatly. The path analysis between meteorological factors and ET0 revealed that the path coefficient of sunshine duration (n), wind speed (u2), relative humidity (RH) and temperature (T) were 0.61, 0.37, -0.25 and 0.019, respectively. Their overall contribution to R2 were 0.48, 0.28, 0.13 and 0.001, respectively. When n, u2, RH and T were removed respectively in sensitivity analysis, R2 values were reduced from 0.89 to 0.596, 0.81,0.84 and 0.88, respectively. R2 had the biggest change when n was removed, and thus ET0 was more sensitive to n and n was the key meteorological factor affecting ET0 in hilly area of central Sichuan. The coefficient of determination between actual and estimated ET0 in four quarters was 0.93, 0.97, 0.96 and 0.94, respectively, when average quarter temperature instead of T was used to estimate ET0, which indicated that it was reasonable to use average quarter temperature to calculate ET0 when meteorological data in hilly areas of central Sichuan was lacking. This research provided information for agricultural production in hilly area of central Sichuan. Source

Feng Y.,University of Sichuan | Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | Gong D.,Chinese Academy of Sciences | And 2 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2015

Reference crop evapotranspiration (ET0) is an essential parameter of water resource planning and management. Accurate estimation of ET0 becomes vital in planning and optimizing irrigation schedules and irrigation systems management. Numerous methods have been proposed for estimating ET0, among which Penman-Monteith (P-M) model recommended by Food and Agriculture Organization of the United Nations (FAO) in 1998 is the best one. FAO accepted the P-M model as the standard and sole equation for ET0 estimation since it provided the most accurate results across the world wherever in an arid or humid environment. But the main problems for computing ET0 by the P-M model are its complicated nonlinear process and requirements of many climatic variables. Thus, it is urgent to develop a simpler and more appropriate model in areas with limited data especially in developing countries like China. In the current study, the applicability of extreme learning machine (ELM) in ET0 modeling based on limited data was assessed in the humid environment in hilly area of central Sichuan, China. In addition, four climate-based models (Hargreaves, Priestley-Taylor, Makkink and Irmark-Allen) and the ELM model were tested against the P-M model to study their performance by using three commonly used criteria: root mean square error (RMSE), coefficient of determination (R2) and efficiency coefficient (Ens). From the statistical results, the ELM model performed well in expressing the nonlinear relationship between ET0 and meteorological factors; when based on temperature data, the ELM model performed better than Hargreaves model which is an empirical temperature-based model. When radiation and temperature data were introduced in the ELM model, the error decreased significantly, and it was much more accurate than the Priestley-Taylor, Makkink and Irmark-Allen model. It was found that the ELM model, which required maximum air temperature, minimum air temperature and sunshine duration input variables, had the best accuracy and was the optimal approach to estimate ET0 when the complete weather data required by the P-M model were not available. The further assessment of ELM was conducted and it was confirmed that the model could provide a powerful tool in estimating ET0 in the humid environment like hilly area of central Sichuan when lack of meteorological data. The research could provide a reference to accurate ET0 estimation in hilly area of central Sichuan. ©, 2014, Chinese Society of Agricultural Engineering. All right reserved. Source

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