Surface albedo and toc-r 300 m products from PROBA-V instrument in the framework of Copernicus Global Land Service

Abstract

PROBA-V instrument launched in 2013 is offering a global daily coverage at pixel resolutions of 333 m and 1 km in three spectral bands (BLUE, RED, NIR) and 600 m for shortwave infrared (SWIR). The PROBA-V mission is the follow-on of the VEGETATION program started in 2000, which allowed generating long-term series at 1 km pixel resolution. The PROBA-V products belong to the Copernicus Global Land Service portfolio (http://land.copernicus.eu/global/). The sensor design of PROBA-V with oriented cameras offers a wide field of view (FOV) for sampling the BRDF (Bidirectional Reflectance Distribution Function). This paper details the methodology implemented at the premises of VITO (Flemish Institute for Technological Research) with the aim to disseminate routinely from PROBA-V daily observations for both surface albedo (SA) and top-of-canopy corrected reflectance (TOC-R) products. The method classically operates a selection of cloudless scenes, performs atmospheric corrections, and finally applies a correction of directional effects on a pixel per pixel basis. The synthesis period is the decade and the composite period is 20 days. Such choice is a pointwise sampling as being a trade-off between the availability of clear scenes and the timescale for phenology. Regarding the albedo catalogue, a narrow-band to broadband conversion is stipulated. A recurrent technique serves for gap-filling based on the spread of weighed a priori data. Additional information concerns the quality flag and the age of the product. Preliminary accuracy assessment is performed through a comparison with the Moderate Imaging Spectroradiometer (MODIS) Collection 6. Dependable spatial consistency is reached except for wintertime with deviations in terms of rmse (root mean square errors) about 0.03 for visible and shortwave domains, and 0.04 for near infrared. Besides, both PROBA-V and MODIS C6 exhibit close time profiles, marked by smoothness or rapid transitions. Results over 10 confidence sites reveals rmse values of 0.032 and bias of 0.01 over the 2014 full annual cycle.