Abstract
Downward shortwave radiation (DSR) is an essential parameter in the terrestrial radiation budget and a necessary input for models of land-surface processes. Although several radiation products using satellite observations have been released, coarse spatial resolution and low accuracy limited their application. It is important to develop robust and accurate retrieval methods with higher spatial resolution. Machine learning methods may be powerful candidates for estimating the DSR from remotely sensed data because of their ability to perform adaptive, nonlinear data fitting. In this study, the gradient boosting regression tree (GBRT) was employed to retrieve DSR measurements with the ground observation data in China collected from the China Meteorological Administration (CMA) Meteorological Information Center and the satellite observations from the Advanced Very High Resolution Radiometer (AVHRR) at a spatial resolution of 5 km. The validation results of the DSR estimates based on the GBRT method in China at a daily time scale for clear sky conditions show an R2 value of 0.82 and a root mean square error (RMSE) value of 27.71 W·m−2 (38.38%). These values are 0.64 and 42.97 W·m−2 (34.57%), respectively, for cloudy sky conditions. The monthly DSR estimates were also evaluated using ground measurements. The monthly DSR estimates have an overall R2 value of 0.92 and an RMSE of 15.40 W·m−2 (12.93%). Comparison of the DSR estimates with the reanalyzed and retrieved DSR measurements from satellite observations showed that the estimated DSR is reasonably accurate but has a higher spatial resolution. Moreover, the proposed GBRT method has good scalability and is easy to apply to other parameter inversion problems by changing the parameters and training data.
Highlights
Downward shortwave radiation (DSR) is a key parameter in the land-atmosphere interaction, which largely controls human life and ecosystems due to its important role in energy cycles [1,2], the hydrological cycle [3,4], the carbon cycles [5,6], and solar energy utilizations [7,8,9,10,11,12,13]
A number of gridded global DSR products exist from remote sensing, reanalysis, and general circulation models (GCMs)
A critical quality control procedure was performed to the ground measurements from the China Meteorological Administration (CMA) before they were used in this study
Summary
Downward shortwave radiation (DSR) is a key parameter in the land-atmosphere interaction, which largely controls human life and ecosystems due to its important role in energy cycles [1,2], the hydrological cycle [3,4], the carbon cycles [5,6], and solar energy utilizations [7,8,9,10,11,12,13]. Knowledge of DSR is essential for improving our understanding of the Earth’s climate and potential climatic changes [14]. A number of gridded global DSR products exist from remote sensing, reanalysis, and general circulation models (GCMs). Satellite remote sensing is one of the most practical ways to derive DSR measurements with relatively higher spatial resolution and accuracy. DSR data can be obtained in three ways. The first is through collection from ground measurements. This method is characterized by high precision and uneven geographic distribution
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