SMOS L2 OS ATBD - ARGANS

IV
ICM-CSIC
LOCEAN/SA/CETP
IFREMER
SMOS L2 OS
Algorithm Theoretical
Baseline Document
Doc: SO-TN-ARG-GS-0007
Issue: 3 Rev: 9
Date: 25 January 2013
Page:A2- IV
total contribution (atmospheric + cosmic background) ranges from 5.5K at nadir to 7K at 50°
incidence angle. This contribution is not strongly affected by atmospheric parameters, in the
absence of heavy rain.
Galactic Noise
In contrast to atmospheric emission and cosmic background emission (2.7K), which are
homogeneous in space and time, galactic noise emissions are very inhomogeneous and they
generate a signal reflected by the sea surface that may strongly vary inside the SMOS swath.
Galactic noise reaching the sea surface are computed using a model developed at CETP
(Delahaye, Golé et al. 2002). It makes use of Reich and Reich charts for the galactic sources
at 0.25° resolution (Reich and Reich, pers. comm.). This map was weighted by weighted by
an average of the synthetic antenna lobe weighting functions over the alias free field of view
(Boutin, Font et al. 2004).
For this angular resolution, galactic sources vary from about 0.7K to more than 15K close to
the galactic centre. These signals are reflected at the sea surface assuming a flat sea.
Retrieval of a pseudo-dielectric constant
As shown in (Waldteufel, Vergely et al. 2004), simultaneous retrieval of the real, ', and
imaginary part, ", of dielectric constant from SMOS Tb is an ill posed problem as the cost
function, rather than a single minimum, exhibit a minimum valley, that can be represented
analytically using a modified cardioid model (Figure 2, left)). After carrying out the
following change of variable:
' = A_card (1 + cos(U_card) ) cos (U_card) + B_card
" = A_card (1 + cos(U_card) ) sin (U_card)
which is equivalent to:
A_card = m_card 2 / (m_card + ' – B_card) U_card = tan -1 ("/('-B_card) )
with: m_card = ( ('-B_card) 2 + " 2 ) 1/2
Eqn. 1
Eqn. 2