Spatial and temporal scaling behavior of surface shortwave downward radiation based on MODIS and in situ measurements

In this letter, a new Moderate Resolution Imaging Spectroradiometer (MODIS)-based 5-km surface shortwave downward (SWD) radiation data set is used to examine the spatial scaling behavior of the surface radiative fluxes. In situ measurements of SWD radiation at time scales from 5 to 55 min from the Oklahoma MesoNet and the Baseline Surface Radiation Network sites over the U.S. are employed to examine the temporal scaling behavior of surface downward radiation and to evaluate the estimates based on MODIS observations from both Terra and Aqua platforms. Analysis reveals that the surface SWD radiation derived from MODIS Terra is in better agreement with ground observations than those from MODIS Aqua. Spatial scaling behavior is investigated based on the MODIS-derived SWD radiation at scales varying from 5 to 100 km. The root mean square difference and the mean standard deviation are found to be highly correlated with the scale exhibiting a strong log-linear relationship. This is a first study on the scaling behavior for surface SWD. Such information is expected to provide linkage between different satellite-based radiation data sets including those derived from geostationary satellites usually of coarser spatial resolutions.