Estimating daily global radiation from air temperature and rainfall measurements (original) (raw)
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Estimating Daily Net Radiation over Vegetation Canopy through Remote Sensing and Climatic Data
Journal of Irrigation and Drainage Engineering, 2007
Net radiation ͑R n ͒ϭkey variable in hydrological studies. Measured net radiation data are rarely available and are often subject to error due to equipment calibration or failure. In addition, point measurements of net radiation do not represent the diversity of the regional net radiation values which are needed for large scale evapotranspiration mapping. A procedure has been developed to estimate daily net radiation using canopy temperature, albedo, short wave radiation and air temperature. This procedure makes it possible to estimate R n by combining information from satellite and local weather stations. Three different methodologies are presented to estimate net radiation. Comparisons between net radiation using the three methods resulted in average error ranging from 1 to 30% and standard error of estimate ranging from 1.06 to 5.34 MJ/ m 2 / day.
European Journal of Agronomy, 2003
RadEst3.00 estimates and evaluates daily global solar radiation values at given latitudes. Radiation is calculated as the product of the atmospheric transmissivity of radiation times the radiation outside the earth atmosphere. Four models estimate the atmospheric transmissivity, based on the daily temperature range. Model parameters can be fitted over one or more years of data by iterative procedures. Graphical and statistical evaluations of the estimates are presented. Reports of the analysis can be exported in a variety of formats. Penman Á/Monteith or Priestley Á/Taylor reference evapotranspiration is estimated, using both measured and estimated radiation. Utilities are provided to process numerous files, or correct possible constant biases in the data. Samples of data for tropical and temperate sites are supplied with the software. #
Agricultural and Forest Meteorology, 1999
We present a reformulation of the Bristow±Campbell model for daily solar radiation, developed using daily observations of radiation, temperature, humidity, and precipitation, from 40 stations in contrasting climates. By expanding the original model to include a spatially and temporally variable estimate of clear-sky transmittance, and applying a small number of other minor modi®cations, the new model produces better results than the original over a wider range of climates. Our method does not require reparameterization on a site-by-site basis, a distinct advantage over the original approach. We do require observations of dewpoint temperature, which the original model does not, but we suggest a method that could eliminate this dependency. Mean absolute error (MAE) for predictions of clear-sky transmittance was improved by 28% compared to the original model formulation. Aerosols and snowcover probably contribute to variation in clear-sky transmittance that remains unexplained by our method. MAE and bias for prediction of daily incident radiation were about 2.4 MJ m À2 day À1 and 0.5 MJ m À2 day À1 , respectively. As a percent of the average observed values of incident radiation, MAE and bias are about 15% and 4%, respectively. The lowest errors and smallest biases (percent basis) occurred during the summer. The highest prediction biases were associated with stations having a strong seasonal concentration of precipitation, with underpredictions at summerprecipitation stations, and overpredictions at winter-precipitation stations. Further study is required to characterize the behavior of this method for tropical climates. #
International Journal of …, 2011
A new model for collectable solar energy estimation via air temperature data is proposed. The model (to be called SEAT) runs in the standard way: first global solar irradiance is computed, and then a cloud cover correction is applied, to end with the summing up of the results for daily global solar irradiation. To address the issue that air temperature-based models are sensitive to their origin location, an adaptive algorithm is reported. Comparison of SEAT forecast with measured data from 15 European stations, located between 40 and 501 northern latitudes and altitudes lower than 500 m, shows an acceptable level of accuracy of the new model. The relative root mean square of monthly mean of daily global solar irradiation has been found between 0.055 and 0.112 for continental sites and between 0.064 and 0.156 for seacoast sites. The way of embedding cloudiness into the solar irradiance procedure calculation and the method of relating daily mean cloudiness with daily air temperature extremes are the main novelty features of SEAT. The approach for SEAT is described en detail to guide potential users either to further develop more complex similar models or to simplify them by particularization.
Improving estimation of hourly, daily, and monthly solar radiation by importing global data sets
Agricultural and Forest Meteorology, 2006
Surface solar radiation is an important parameter in hydrological models and crop yield models. This study developed a model to estimate solar radiation from sunshine duration. The model is more accurate and more general than traditional Å ngström-Prescott models. It can explicitly account for radiative extinction processes in the atmosphere. Moreover, global data sets that describe the spatial and temporal distribution of ozone thickness and Å ngström turbidity were introduced in the model to enhance its universal reliability and applicability. The model was calibrated in lowland and humid sites and validated at a number of sites in various climate and elevation regions. The new model shows overall better performances than three Å ngström-Prescott models. Because this model follows the simple form of the Å ngström-Prescott model, and its inputs (sunshine duration, air temperature, and relative humidity) are accessible from routine surface meteorological observations, it can be easily applied to hydrological and agricultural studies. The source code and the auxiliary data of the model are available from the authors upon request. #
Journal of Applied Meteorology and Climatology , 2012
Photosynthetically active radiation (PAR) is absorbed by plants to carry out photosynthesis. Its estimation is important for many applications such as ecological modeling. In this study, a broadband transmittance scheme for solar radiation at the PAR band is developed to estimate clear-sky PAR values. The influence of clouds is subsequently taken into account through sunshine-duration data. This scheme is examined without local calibration against the observed PAR values under both clear-and cloudy-sky conditions at seven widely distributed Surface Radiation Budget Network (SURFRAD) stations. The results indicate that the scheme can estimate the daily mean PAR at these seven stations under all-sky conditions with root-mean-square error and mean bias error values ranging from 6.03 to 6.83 W m 22 and from 22.86 to 1.03 W m 22 , respectively. Further analyses indicate that the scheme can estimate PAR values well with globally available aerosol and ozone datasets. This suggests that the scheme can be applied to regions for which observed aerosol and ozone data are not available.
Satellite-based estimation of daily average net radiation under clear-sky conditions
Advances in Atmospheric Sciences, 2014
Daily average net radiation (DANR) is an important variable for estimating evapotranspiration from satellite data at regional scales, and is used for atmospheric and hydrologic modeling, as well as ecosystem management. A scheme is proposed to estimate the DANR over large heterogeneous areas under clear-sky conditions using only remotely sensed data. The method was designed to overcome the dependence of DANR estimates on ground data, and to map spatially consistent and reasonably distributed DANR, by using various land and atmospheric data products retrieved from MODIS (Moderate Resolution Imaging Spectroradiometer) data. An improved sinusoidal model was used to retrieve the diurnal variations of downward shortwave radiation using a single instantaneous value from satellites. The downward shortwave component of DANR was directly obtained from this instantaneous value, and the upward shortwave component was estimated using satellite-derived albedo products. Four observations of air temperature from MOD07 L2 and MYD07 L2 data products were used to derive the downward longwave component of DANR, while the upward longwave component was estimated using the land surface temperature (LST) and the surface emissivity from MOD11 L2. Compared to in situ observations at the cropland and grassland sites located in Tongyu, northern China, the root mean square error (RMSE) of DANR estimated for both sites under clear-sky conditions was 37 W m −2 and 40 W m −2 , respectively. The errors in estimation of DANR were comparable to those from previous satellite-based methods. Our estimates can be used for studying the surface radiation balance and evapotranspiration.
Estimating solar irradiation sums from sunshine and cloudiness observations
Solar Energy, 1980
Abstraet--A method is presented that offers the possibility of estimating solar irradiation sums on the basis of sunshine and cloudiness observations only. Its application requires the knowledge of the local hourly sums of global and diffuse solar irradiation by clear weather as well as the hourly sums of diffuse solar irradiation due to clouds. These quantities were determined for the actual radiation climate in Lisbon. Effective daily amount of sunshine and cloudiness are defined and compared with the usual daily sunshine and cloudiness concepts; the relationship between daily relative amount of sunshine and cloudiness is established for Lisbon.