Estimation Of Land Surface Incident Solar Radiation And Photosynthetically Active Radiation

Solar Radiation is the only energy source of the earth. Thus, estimation of incident solar radiation (DSSR) and photosynthetically active radiation (PAR) at surface has great significances. Because the downward surface solar radiation is one of the most important variables to estimate radiation budget and is also one of the most important input datasets in many climate and atmosphere models. Moreover, the incident PAR controls the speed of photosynthesis actions of the vegetations, and finally, influences the vegetation’s growth, development, and so on. Meanwhile, the estimation of the downward surface shortwave radiation and PAR has significant impacts on estimation of global radiation balance and global primary production.PAR is always calculated by multiplying the photosynthetic coefficients to the incident solar radiation. And the global available PAR products have coarse spatial resolution, temporal resolution and products precisions. As a result, these products cannot meet our requirements. The corresponding DSSR data has fine temporal resolution, but coarse spatial resolution as PAR products. The usefulness of the currently available PAR products is constricted by their limited spatial and temporal resolution. Moreover, climate change is one of the hot topics in the science community. It is hard to say "Global Dimming" or "Global Brightening" is at dominated position during the past decades. To verify it, it is urgent and important to estimate the DSSR and PAR with high precisions and spatial and temporal resolutions globally.This paper starts the research based on the multiple data source. First, we introduce the parameterization methods to estimate the DSSR and PAR. Then analyze their advantages and disadvantages. The applicability of the existing parameterization algorithms for deriving PAR using remotely sensed data are limited by their requirements for external atmospheric information. Then we present an improved Look-up table method to estimate the DSSR and PAR and implement it to polar-orbiting and geostationary satellites. This algorithm utilizes the advantages of the spatial coverage of polar-orbiting satellites and the advantages of the temporal resolution of the geostationary satellites. The new PAR algorithms differ from existing algorithms in that the new algorithms derive surface properties and atmospheric optical properties using time-series of at-sensor radiance without external atmospheric information. To assess the effectiveness of the newly developed PAR algorithms, validation efforts have been made using ground measurements made at different surface radiation networks. The validations indicate that the new PAR algorithms for MODIS, GOES, MSG, MTSAT and FY2C are capable of reaching reasonably high accuracy with no need for external atmospheric information. Finally, the global DSSR and PAR products are derived by integrating of the radiation products from the satellites we selected.The main contents of this paper are as follows:1. Give a general review on the algorithms to estimate the DSSR and PAR. And point out the existed problems in these methods and the research objectives.2. Describe the basic principles and algorithms to estimate the DSSR and PAR such as the definition of solar radiation, solar constant, and so on. The solar radiation software: MODTRAN are also fully introduced.3. Introduce the parameterization schedule to estimate the DSSR and PAR. The parameterization methods include the broadband, spectral models under clear-sky and cloudy-sky conditions and also other conventional methods, such as regression and sunshine-hour index based methods. All results are validated on SURFRAD sites.4. Depict the physical principle of Look-up Table method, and implement this algorithm to the polar-orbiting and geostationary satellite. Moreover, the sensitivity analyses of Look-up Table method have been presented, and the most important factors influence the algorithm has been pointed out.5. Validate the retrieved results using different surface radiation networks such as SURFRAD, BSRN, Aeronet, and CarbonEurope. The algorithm to get the global radiation products from multiple radiation data sources has been designed.6. Finally, Present the conclusions and ongoing research works need to be done.In one word, estimation of the DSSR and PAR based on Look-up table method has clear physical principles, and can be implemented using different satellites’data with simple input requirements. Thus, this algorithm can be used to estimate the DSSR and PAR globally, which match the basic requirements for radiation products.