Abstract

Surface downward shortwave radiation (DSR) and photosynthetically active radiation (PAR), its visible component, are key parameters needed for many land process models and terrestrial applications. Most existing DSR and PAR products were developed for climate studies and therefore have coarse spatial resolutions, which cannot satisfy the requirements of many applications. This paper introduces a new global high-resolution product of DSR (MCD18A1) and PAR (MCD18A2) over land surfaces using the MODIS data. The current version is Collection 6.0 at the spatial resolution of 5 km and two temporal resolutions (instantaneous and three-hour). A look-up table (LUT) based retrieval approach was chosen as the main operational algorithm so as to generate the products from the MODIS top-of-atmosphere (TOA) reflectance and other ancillary data sets. The new MCD18 products are archived and distributed via NASA’s Land Processes Distributed Active Archive Center (LP DAAC). The products have been validated based on one year of ground radiation measurements at 33 Baseline Surface Radiation Network (BSRN) and 25 AmeriFlux stations. The instantaneous DSR has a bias of −15.4 W/m2 and root mean square error (RMSE) of 101.0 W/m2, while the instantaneous PAR has a bias of −0.6 W/m2 and RMSE of 45.7 W/m2. RMSE of daily DSR is 32.3 W/m2, and that of the daily PAR is 13.1 W/m2. The accuracy of the new MODIS daily DSR data is higher than the GLASS product and lower than the CERES product, while the latter incorporates additional geostationary data with better capturing DSR diurnal variability. MCD18 products are currently under reprocessing and the new version (Collection 6.1) will provide improved spatial resolution (1 km) and accuracy.

Highlights

  • Solar radiation, mainly in the shortwave spectrum, is the primary energy resource of the Earth system and, affects many processes of the system [1]

  • Two other global Downward shortwave radiation (DSR) products (Clouds and the Earth’s Radiant Energy System (CERES) and Global LAnd Surface Satellite (GLASS)) were validated using the same data set of ground measurements and the results were compared with the MCD18A1 product

  • The current Collection 6.0 MCD18 products are produced at 5 km resolution and the forthcoming Collection 6.1 data sets will be available at the improved resolution of 1 km

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Summary

Background

Mainly in the shortwave spectrum, is the primary energy resource of the Earth system and, affects many processes of the system [1]. Downward shortwave radiation (DSR) that reaches the land surface is of particular importance to the terrestrial ecosystem and human society because of its role in surface radiation and energy budget and because it is the driving force of many land processes [2]. It affects the weather and climate processes through regulating exchanges of energy, carbon, water, other matter, and momentum between the surface and the atmosphere [3].

Algorithm Description
Data Processing and Product Generation
Field Data and Processing
Validation of Instantaneous Product
Validation of 3-h and Daily Products
Comparison with Other DSR Products
Validation of PAR Product
Findings
Summary and Future Plans
Full Text
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