Abstract
Net radiation is an important component of the earth’s surface energy balance, which plays a vital role in the evolution of regional climate or climate change. The estimation of this component at regional or global scales is critical and challenging due to the sparse and limited ground-based observations. This paper made an attempt to analyze the feasibility of a remote sensing-based surface energy balance model using satellite (TERRA/MODIS) data to derive the net radiation (Rn). In the present study, MODIS data at 15 different days of the year (DOY) were utilized to visualize the spatial pattern of net radiation flux over three versatile and heterogeneous ecohydrological land surfaces (upstream, midstream, and downstream) of northwest China (Heihe river basin). The results revealed that the estimated net radiation from the satellite data agrees well with the ground-based measurements over three different surfaces, with a mean relative error of 9.33% over the upstream superstation (grasslands), 13.95% over the middle stream superstation (croplands), and 11.63% over the downstream superstation (mixed forests), where the overall relative error was 11.64% with an overall rmse of 29.36 W/m2 in the study area. The regional distribution of net radiation over the versatile land surfaces was validated well at a large scale during the five-month period and over different land surfaces. It was also observed that the spatial pattern of net radiation varies spatially over three different landscape regions during four different days of the year, which might be associated with different climatic conditions and landscape features in these regions. The overall findings of this study concluded that satellite-derived net radiation can rationally be obtained using a single-source remote sensing model over different land surfaces.
Highlights
Net radiation (Rn ) is the balance between the total incoming solar radiations towards the Earth’s surface and outgoing solar radiation fluxes, which mainly influences other surface energy balance components through evapotranspiration, photosynthesis, and heating of air and soil
Numerous studies have used several possible methods and models [6,7] for estimating net radiation along with other components based on satellite remote sensing data, namely: Surface Energy Balance Index (SEBI) [8], Simplified-SEBI (S-SEBI) [9], Surface Energy Balance System (SEBS) [10], Surface Energy Balance Algorithm for Land (SEBAL) [11], Mapping Evapotranspiration at High Resolution with Internalized Calibration) (METRIC) [12,13], Vegetation Index/Temperature
The validation and estimation of satellite-derived surface fluxes are crucial and highly challenging, due to different land surface characteristics, which played a significant role in the estimation and validation processes [20]
Summary
Net radiation (Rn ) is the balance between the total incoming solar radiations towards the Earth’s surface and outgoing solar radiation fluxes, which mainly influences other surface energy balance components through evapotranspiration, photosynthesis, and heating of air and soil. The principle and model parameterizations, variations are involved in process-based source conditions (single or double), input requirements, assumptions, dependency on ground measurements and applications These criteria demonstrated the degree of suitability of the methods over different surfaces at local and regional scales. The validation and estimation of satellite-derived surface fluxes are crucial and highly challenging, due to different land surface characteristics, which played a significant role in the estimation and validation processes [20] In these circumstances, the present study has made an attempt to demonstrate the net radiation with the SEBS model using MODIS images over three different landscape regions of study areas such as the upstream, midstream, and downstream regions of the Heihe river basin in northwest China. The key purposes of this paper are two-fold: (i) to examine the regional distribution of net radiation (Rn ) using TERRA-MODIS images over different ecohydrological land surfaces, and (ii) to validate the estimated Rn with the 4-component net radiometer measurements over three superstations in the study area
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