Estimation of daily average net radiation from MODIS data and DEM over the Baiyangdian watershed in North China for clear sky days

摘要: Daily average net radiation (DANR) is a critical variable for estimation of daily evapotranspiration (ET) from remote sensing techniques at watershed or regional scales, and in turn hydrological modeling water resources management. This study attempts to comprehensively analyze physical mechanisms governing the variation each component DANR during day, with objective improve parameterization schemes shortwave (DANSR) longwave (DANLR) using MODIS (MODerate Resolution Imaging Spectroradiometer) data products, DEM, minimum meteorological order map spatially consistent reasonably distributed scales clear sky days. First, geometric model simulating direct solar by accounting effects terrain factors (slope, azimuth elevation) on availability sloping land surfaces adopted. Specifically, magnitudes sunrise sunset angles, frequencies surface being illuminated as well potential sunshine duration given are computed basis. The applied Baiyangdian North China, showing capability distinctly characterize spatial pattern surfaces. DANSR can then be successfully derived simulated means characteristics nearly invariant diffuse daytime conjunction MCD43A1 albedo products. Second, four observations Terra-MODIS Aqua-MODIS temperature (LST) emissivities band 31 32 MOD11A1, MYD11A1 MOD11_L2 products six days April September year 2007, utilized simulate LST accuracy estimates DANLR. Comparisons DANLR proposed observation-based method that an existing one method, against Penmen equation solely routine indicates capable more accurately than method. Using Penman reference, results show overall has bias 2.7 W m(-2) root mean square error (RMSE) 12.8 m(-2), whereas -33.3 RMSE 39.6 across 18 weather stations tested In general, shown reasonable over entire result improvement resulting would serve linking instantaneous evaporative fraction Er primarily remotely sensed data. (C) 2010 Elsevier B.V. All rights reserved.