Lambertian Surface Albedo Climatology at 360 nm from TOMS Data Using Moving Time-Window Technique


Satellite retrieval algorithms, including estimation of the surface UV irradiance, require accurate knowledge of the surface albedo. At UV wavelengths the surface albedo is often low, some 3-8%, but snow or ice cover can increase the surface albedo up to 95%. Therefore, the surface albedo of polar regions has high annual variation which complicates accurate estimation of the surface UV irradiance from satellite data. Previously, the surface albedo climatologies have been constructed assuming that the seasonal surface albedo cycle is identical from year to year [Herman et al. 1997, Koelemeijer et al. 2003]. At high latitudes this assumption leads to substantial underestimation of the surface albedo during snow cover transition periods.The aim of this work was to construct a global UV range albedo climatology with fine spatial and temporal resolution and realistic high-latitude values.

Climatology Construction Method

The moving time-window (MTW) method [Tanskanen et al. 2003] is based on the assumption that the reflectivity values within a certain time-window around the day of interest form a sample of the reflectivity distribution whose lower tail corresponds to the clear sky case. An estimate of the surface albedo is obtained by fitting a linear function to the lower tail of the cumulative distribution of the sample. The wider the time-window is, the more information is available about the reflectivity distribution. However, use of a very wide time-window leads to underestimation of the surface albedo in case the surface albedo experiences a transient within the time-window. In order to account for the surface albedo transients the MTW algorithm aims at choosing an optimum time-window by narrowing and shifting the window during transients. The MTW algorithm was applied to the TOMS 360 nm Lambertian Equivalent Reflectivity (LER) time-series to construct daily surface albedo estimates for the Nimbus-7 period. Prior to the use of the MTW method the LER data were gridded to a 1 by 1 degree regular grid defining the grid cell value as the daily minimum LER value. Finally, the surface albedo climatology was constructed by averaging the resulting surface albedo estimates for the years 1979-1992.

Climatology Example Figures

Comparison with the MLER Climatology

Download climatology

The surface albedo climatology can be downloaded as a zipped tar package (7.2 MB). The climatology is stored as 360x180x365 elements of 1 byte binary data with no additional delimiters nor any metadata. The data set can be considered as a 3-dimensional array varying in longitude, latitude and day of the year. The structure of the file is such that longitude is the fastest varying dimension, latitude is the second fastest, while day of the year is the slowest varying dimension. The longitude dimension runs from West to East  with 1 degree step starting from -179.5E. Accrodingly, the latitude dimension runs from South to North with one degree step starting from -89.5N. The download package contains some documentation and a Fortran example of how to use the climatology.

Download climatology

When the climatological UV albedo data is used in a publication or presentation, the source of data should be acknowledged by referring to the appropriate publication [Tanskanen 2004].


Herman, J. R., E. A. Celarier, Earth surface reflectivity climatology at 340--380 nm from TOMS data, J. Geophys. Res., 102, 28003--28011, 1997.

Koelemeijer, R. B. A., J. F., de Haan, P. Stammes, A database of spectral surface reflectivity in the range 335--772 nm derived from 5.5 years of GOME observations, J. Geophys. Res., 105, 5059--5067, 1997.

Tanskanen, A., A. Arola, J. Kujanpää, Use of the moving time-window technique to determine surface albedo from the TOMS reflectivity data, In: Proc. SPIE Vol. 4896, p. 239--250, 2003.

Tanskanen, A. Lambertian Surface Albedo Climatology at 360 nm from TOMS Data Using Moving Time-Window Technique. In: Proceedings of the XX Quadrennial Ozone Symposium, 1-8 June 2004, Kos, Greece.

Aapo Tanskanen, November 5th, 2004