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Chapter 19
Land surface albedo quantifies the energy reflected back into the
atmosphere by the surface. It defines the radiometric lower boundary for
any short-wave radiative transfer problem in the atmosphere, linking
surface vegetation, soils and topography radiometrically to the
meteorological system, and influencing the top-of-atmosphere energy
balance, cloud formation and precipitation, feedback loops operating
through atmospheric convective patterns, and general atmospheric
circulation.
Where the surface is vegetated, the value of albedo quantifies the shortwave solar energy input into the biosphere, its main source of energy. It
influences the land surface energy balance through influencing the latent
heat flux due to evapotranspiration from vegetation.
Albedo is largely determined by the optical and structural properties of
vegetated and non-vegetated surfaces. In vegetated areas, it may
therefore potentially be used as an indicator of vegetation conditions,
and changes in albedo may be related to changes in the vegetation, both
structurally and in terms of green matter, quantified for example through
the Leaf Area Index (LAI). The three-dimensional structural properties
of vegetated and non-vegetated surfaces are of particular interest for an
estimation of surface roughness length, which drives energy and
momentum exchanges between the surface and the dynamic
meteorological processes in the atmosphere.
In spite of this importance of land surface albedo in the global system,
currently no global albedo data set approaching kilometer-scale resolution is
available. Global circulation models use static data sets mostly driven by
land cover type and derived from a variety of sources of often unknown
quality and based on various modeling assumptions, or compute albedo from
vegetation physiological parameters using very simple radiative models.
However, space sensors are now becoming available that allow the
routine production of global albedo products in the very near future. These
are the European POLDER, MSG and MERIS, and the American MODIS
and MISR instruments. The algorithmic basis for deriving albedo from these
sensors exploits new methods making use of the observed bidirectional
reflectance distribution functions of the Earth’s surface. With a few
compromises on calibration, geolocation and accuracy of the atmospheric
correction, these methods are also applicable to the AVHRR, which is
especially important in view of the long data record available from that
instrument.
Chapter 19
Land surface albedo quantifies the energy reflected back into the
atmosphere by the surface. It defines the radiometric lower boundary for
any short-wave radiative transfer problem in the atmosphere, linking
surface vegetation, soils and topography radiometrically to the
meteorological system, and influencing the top-of-atmosphere energy
balance, cloud formation and precipitation, feedback loops operating
through atmospheric convective patterns, and general atmospheric
circulation.
Where the surface is vegetated, the value of albedo quantifies the shortwave solar energy input into the biosphere, its main source of energy. It
influences the land surface energy balance through influencing the latent
heat flux due to evapotranspiration from vegetation.
Albedo is largely determined by the optical and structural properties of
vegetated and non-vegetated surfaces. In vegetated areas, it may
therefore potentially be used as an indicator of vegetation conditions,
and changes in albedo may be related to changes in the vegetation, both
structurally and in terms of green matter, quantified for example through
the Leaf Area Index (LAI). The three-dimensional structural properties
of vegetated and non-vegetated surfaces are of particular interest for an
estimation of surface roughness length, which drives energy and
momentum exchanges between the surface and the dynamic
meteorological processes in the atmosphere.
In spite of this importance of land surface albedo in the global system,
currently no global albedo data set approaching kilometer-scale resolution is
available. Global circulation models use static data sets mostly driven by
land cover type and derived from a variety of sources of often unknown
quality and based on various modeling assumptions, or compute albedo from
vegetation physiological parameters using very simple radiative models.
However, space sensors are now becoming available that allow the
routine production of global albedo products in the very near future. These
are the European POLDER, MSG and MERIS, and the American MODIS
and MISR instruments. The algorithmic basis for deriving albedo from these
sensors exploits new methods making use of the observed bidirectional
reflectance distribution functions of the Earth’s surface. With a few
compromises on calibration, geolocation and accuracy of the atmospheric
correction, these methods are also applicable to the AVHRR, which is
especially important in view of the long data record available from that
instrument.