Assessment of the EUMETSAT Multi Decadal Land Surface Albedo Data Record from Meteosat Observations

Alessio Lattanzio,Marie Doutriaux-Boucher,Rob Roebeling,Jörg Schulz,Michael Grant

doi:10.3390/rs13101992

Abstract

Surface albedo, defined as the ratio of the surface-reflected irradiance to the incident irradiance, is one of the parameters driving the Earth energy budget and it is for this reason an essential variable in climate studies. Instruments on geostationary satellites provide suitable observations allowing long-term monitoring of surface albedo from space. In 2012, EUMETSAT published Release 1 of the Meteosat Surface Albedo (MSA) data record. The main limitation effecting the quality of this release was non-removed clouds by the incorporated cloud screening procedure that caused too high albedo values, in particular for regions with permanent cloud coverage. For the generation of Release 2, the MSA algorithm has been replaced with the Geostationary Surface Albedo (GSA) one, able to process imagery from any geostationary imager. The GSA algorithm exploits a new, improved, cloud mask allowing better cloud screening, and thus fixing the major limitation of Release 1. Furthermore, the data record has an extended temporal and spatial coverage compared to the previous release. Both Black-Sky Albedo (BSA) and White-Sky Albedo (WSA) are estimated, together with their associated uncertainties. A direct comparison between Release 1 and Release 2 clearly shows that the quality of the retrieval improved significantly with the new cloud mask. For Release 2 the decadal trend is less than 1% over stable desert sites. The validation against Moderate Resolution Imaging Spectroradiometer (MODIS) and the Southern African Regional Science Initiative (SAFARI) surface albedo shows a good agreement for bright desert sites and a slightly worse agreement for urban and rain forest locations. In conclusion, compared with MSA Release 1, GSA Release 2 provides the users with a significantly more longer time range, reliable and robust surface albedo data record.

Highlights

Land surface albedo is one of the Essential Climate Variables (ECVs) defined by the Global Climate Observing System (GCOS) [1]
Surface albedo has been retrieved exploiting imagery acquired by instruments on board several platforms, both polar and geostationary satellites [5], such as for instance Moderate Resolution Imaging Spectroradiometer (MODIS) [6,7], Multi-angle Imaging SpectroRadiometer (MISR) [8], AVHRR [9,10] and Meteosat Second Generation (MSG) [11]
Models the Bidirectional Reflectance Distribution Function (BRDF) as a product of angular functions and a reflectance level ρ0 [13]. These angular functions depend on the satellite and sun position and three model parameters, i.e., the empirical surface parameter ρc to characterize the hot-spot, and k, Θ to account for surface anisotropy controlling the shape of the surface bidirectional reflectance factors (BRF) [14]

Summary

Introduction

Land surface albedo is one of the Essential Climate Variables (ECVs) defined by the Global Climate Observing System (GCOS) [1]. Surface albedo has been retrieved exploiting imagery acquired by instruments on board several platforms, both polar and geostationary satellites [5], such as for instance MODIS [6,7], MISR [8], AVHRR [9,10] and Meteosat Second Generation (MSG) [11]. Observations acquired by geostationary satellites have the advantages of offering both a long-term dataset and an angular sampling of the surface, as well as providing diurnal sampling of key Remote Sens.

Methods

Results

Conclusion