Algorithm Theoretical Based Document (ATBD) - CESBIO

SO-TN-ESL-SM-GS-0001
Issue 1.a
Date: 31/08/2006
SMOS level 2 processor
Soil moisture ATBD
We now consider a specific DGG node, and the WA DFFG which surrounds the DGG node being considered (as defined
in section 3.2.2.5).
3.2.3.2.1 Content of DFFG pixels
An initial land cover classification surface fractions on the DFFG is given by a LUT described in TGRD. This LUTis
fixed and has been generated once and for all for a given DFFG resolution from the aggregation of the ECOCLIMAP
detailed classification, high resolution water information and topography (see TGRD generation methods for details).
Let’s consider a given DFFG pixel cell that belongs to WA DFFG . This pixel contains a list of sub-pixel surface fractions
(%) that correspond to the list of FM complementary classes presented in Table 14. Each FM class is also associated
with a detailed landcover classification code that will be used later as an index to the LAND_COVER_CLASSES LUT
to access surface properties for computing reference values. One then refers to those classes as complementary, in the
sense that together they cover the whole surface of the DFFG pixel.
Besides, this list is completed by the topography features of the DFFG cell: fractions of moderate and strong
topography, FTM and FTS. Opposite to the previous fractions, FTM and FTS are considered as supplementary, in the
sense that in order to introduce them, one has to override the previous complementary fractions in such a way that the
resulting set becomes complementary.
3.2.3.2.2 Accounting for external conditions to update the DFFG pixel content
The initial aggregated classes and surface fractions describe the fixed features of WA DFFG . These features are subject to
change due to eventual non permanent (NPE) surface conditions. We handle this situation with the three following
actions:
• First, we need to complete the intial classes with categories corresponding to frozen and snow covered zones
since they are handled with specific models. As for topography, NPE fractions are considered as
supplementary.
• Next, we eventually need to reallocate fractions and/or need to change other surface properties depending on
the above events and possible others. For example, if the temperature drops under a certain level, FWP
becomes FEI, if the low vegetation becomes frozen then its optical thickness is forced to 0, …
In certain cases some actions have also to be taken on reference values
• Always satisfy the constraint that all the final fractions of the DFFG pixel are complementary.
The next subsections indicate the actions to be performed and the triggers that activate them. It is important to follow
the order of the subsections.
3.2.3.2.2.1 Soil to frozen
Trigger: ISTL1 < TH_SOIL_FRZ
Actions on reference values: TAU_FRZ=(FNO*TAU_FNO+FFO*TAU_FFO+FEU*TAU_FEU+FEB*TAU_FEB)
/(FNO + FFO + FEU + FEB)
Actions on fractions values: FRZ = FNO + FFO + FEU + FEB; FNO=FFO=FEU=FEB=0
3.2.3.2.2.2 Pure water to ice
Trigger: (LSM