Photosynthetically active radiation from Clouds and the Earth’s Radiant Energy System (CERES) products

[1] We describe a method that retrieves surface photosynthetically active radiation (PAR) and its direct and diffuse components from the Surface and Atmospheric Radiation Budget (SARB) product of Clouds and the Earth’s Radiant Energy System (CERES). The shortwave spectrum in the SARB Edition 2 is calculated in 15 bands, 4 of which are used to develop the PAR, in conjunction with the look-up tables described in this paper. We apply these look-up tables to existing CERES Terra Edition 2 products. The new retrieved surface PAR is validated with LI-COR PAR measurements at seven Surface Radiation Budget Network (SURFRAD) sites using data from March 2000 to June 2005. The relative bias of retrieved all-sky PAR at the SURFRAD sites is 4.6 % (positive sign indicating retrieval exceeds measurement), and 54 % of the all-sky samples are within the ±10 % uncertainty of the LI-COR PARmeasurements. The satellite field-of-view (FOV) is more representative of the ground instrument FOV under clear conditions, so 89 % of clear-sky retrievals are within the uncertainty of the LI-COR PARmeasurements at SURFRAD sites with positive biases at most sites. The retrieved PAR is also validated at the Atmospheric Radiation Measurement (ARM) Southern Great Plains Central Facility (CF) site using data fro