Using remotely sensed solar radiation data for reference 1 evapotranspiration estimation at a daily time step
نویسندگان
چکیده
16 Solar radiation is an important climatic variable for assessing reference evapotranspiration 17 (E0), but it is seldom available in weather station records. Meteosat satellite images processed 18 with the Heliosat-2 method provide the HelioClim-1 database, which displays spatialized 19 solar radiation data at a daily time step for Europe and Africa. The aim of the present work 20 was to investigate the interest of satellite-sensed solar radiation for E0 calculation, where air 21 temperature is the sole local weather data available. There were two study areas in Southern 22 France. One (Southwest, SW) is characterized by oceanic climate and the other (Southeast, 23 SE) by Mediterranean climate. A data set of daily values for 19 weather stations spanning five 24 years (2000-2004) was used. First, a sensitivity analysis of the Penman-Monteith formula to 25 climate input variables was performed, using the Sobol’ method. It shows that E0 is mainly 26 governed by solar radiation during summer, and by wind speed during winter. Uncertainties 27 of HelioClim-1 solar radiation data and their repercussions on E0 formulae were evaluated, 28 using the FAO-56 Penman-Monteith formulae (PM) and radiation-based methods (Turc, TU; 29 Priestley-Taylor, PT and Hargreaves-Radiation, HR). It was shown that HelioClim-1 data 30 slightly underestimate solar radiation and provide relative RMSE (root mean squared error) of 31 20% of the mean annual value for SW and 14% for SE. The propagation of HelioClim-1 data 32 uncertainties is small in PM but considerable in radiation methods. Four estimation methods 33 were then compared to PM data: the 1985 Hargreaves formula (HT) based on air temperature 34 only; TU, PT and HR, based on air temperature and satellite sensed solar radiation. Radiation 35 methods were more precise and more accurate than HT, with RMSE ranging from 0.52 mm to 36 0.86 mm against 0.67 mm to 0.96 mm. These results suggest that using satellite-sensed solar 37 radiation may improve E0 estimates for areas where air temperature is the only available 38 record at ground level. 39 40
منابع مشابه
Using remotely sensed solar radiation data for reference evapotranspiration estimation at a daily time step
16 Solar radiation is an important climatic variable for assessing reference evapotranspiration 17 (E0), but it is seldom available in weather station records. Meteosat satellite images processed 18 with the Heliosat-2 method provide the HelioClim-1 database, which displays spatialized 19 solar radiation data at a daily time step for Europe and Africa. The aim of the present work 20 was to inve...
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