UV surface albedo snow and non-snow climatology for CTMs, Version 13, 13.June 2005
Thomas Laepple and Martin Schultz, MPI for Meteorology; Hamburg, National Center for Atmospheric
Research, Boulder.
tlaepple@awi-bremerhaven.de

Description of the data processing:
(for more details and data validation, please see [Laepple 05] )

Data basis is the MODIS43C1 product that provides a 16-day composite of the albedo on a
0.25ƒ grid as well as quality flags and the snow coverage percentage for each pixel
Data from January 2001 to December 2002 were used, with a gap in June 2001 due to
instrumental problems.  One 0.25ƒ x 0.25ƒ snow albedo climatology map was created for
 each month by merging (or averaging if multiple maps show snow cover) all the pixels
in this timeframe in which the snow flag indicates 100% coverage. Missing pixels and
pixel which were derived from less than four MODIS pixel were filled with snow pixels
 from neighbouring months. The threshold of four input pixel is a trade off between
providing seasonal variability of the albedo and producing representative data. From
these maps the specific albedo for each landtype were calculated by linear regression
using MODIS fractional landtype data. In this   version only one set of
specific albedo coefficients was calculated (no time and latitude dependence)
The albedo of the remaining missing pixels was modelled as linear combination of the
specific albedos and landtype fractions. A similar merging procedure was performed for
 no-snow pixels to get a monthly no-snow albedo climatology.


Wavelength correction:

The ratio of the landtype specific albedos of GOME Band 5 (463nm) and GOME Band 2 (380nm) were calculated.
Band 1 (335nm) was not used because the values are probably to high [Koehlemeijer 2003].

The correction values are consistent with spectral reflectance measurements from
[Pinker, 95].

Correction was applied to the following landtypes which had ratios significant larger
than 1 and cover significant areas :

Ratio <Albedo of Landtype BAND5> / <Albedo of Landtype BAND2>
Landtype 7, Open Shrublands: 1.12
Landtype 8, Woody Savannas   1.21
Landtype 9, Savannas         1.36
Landtype 10, Grasslands      1.47
Landtype 12, Cropland        1.18
Landtype 16, Barren          1.60


Version 11: In the snow-free albedo maps, the pixels of landtype 15 (snow and ice) where no measurements exist where set to the albedo value 0.05 which corresponds to an average snow free albedo

Version 12: The albedo on the Antarctic Plateau was set to 0.98 as described in the paper

Version 13: The land albedo was extended 3 degree around the continents to avoid problems with slightly different landmasks. The extrapolation was done by 1.) removing the outside pixels around the continents where the MODIS albedo is generally too low due to influence of the zero albedo sea pixels. 2.) adding 12 pixels around the continents with the albedo values of the nearest land pixels.

Reference:
T. Laepple, M. Schultz, J. F. Lamarque, S. Madronich, R. E. Shetter, B. L. Lefer, M.G. Schultz and E. Atlas Improved Albedo Formulation for Chemistry-Transport Models based on satellite observations and assimilated snow data and its impact on tropospheric photochemistry, Journal of Geophysical Research, VOL. 110, D11308, doi:10.1029/2004JD005463, 2005