SMOS L2 OS ATBD - ARGANS

113
ICM-CSIC
LOCEAN/SA/CETP
IFREMER
pp(
o,
o)
pq(
o,
o)
sin
odo
o.
SMOS L2 OS
Algorithm Theoretical
Baseline Document
4 cos
1
/2
2
p= s
0 0
d (5)
For a perfectly flat sea surface, this expression reduces to
2
2
(0) coss
sw(
S,
Ts)
| ( , , ) | =
sin s
R
hh
S Ts
s
2
coss
sw(
S,
Ts)
sin
s
2
2
(0) sw(
S,
Ts)
coss
sw(
S,
Ts)
| ( , , ) | =
sin s
Rvv
S Ts
s
2
sw(
S,
Ts)
coss
sw(
S,
Ts)
sin
s
2
2
(6)
Doc: SO-TN-ARG-GS-0007
Issue: 3 Rev: 9
Date: 25 January 2013
Page: 113
where sw( S,
Ts)
is the dielectric constant for seawater given by the Klein and Swift model. S
is the salinity and T s is the sea surface temperature. Note there is no cross-pol reflectivity in
the flat-surface case, and the reflected signal is
2
f
/2
2
(0)
seco
Tp ( s)
= | Rpp(
S,
Ts,
s)
| (
so,
s
o)
Tsky(
o,
o)
e sin
odod
o
(7)
0
which simplifies to
0
2
f (0)
sec
s
Tp
( s)
= | Rpp(
S,
Ts,
s)
| Tsky(
s,
s
)
e
(8)
For typical ocean values of SST (0-38 C) and SSS (20-40 psu), the sensitivity to SSS of the
flat sea surface reflectivity at L-band vary from about 0.5x10 -3 /psu to 3.5x10 -3 /psu and its
sensitivity to SST vary from about 0.2x10 -3 /°C to 2x10 -3 /°C, considering both linear
polarizations and all incidence angles between 0 and 60°. Despite some previously listed very
localized bright spots (Cassiopeia A, Orion A, Cygnus A, Taurus A, ...) for which the
downwelling signal can reach up to about 400 K, the sky brightness temperature at L-band
vary in general from 2.75 K to around 10 K. Assuming a 10 K bright source, the sensitivity of
the specularly reflected celestial brightness temperature signals to SSS and SST might reach
around 0.03 K/psu and 0.02 K/°C. These values are representative of an average worst case
scenario since the surface reflectivity drops significantly in presence of roughness. To make
possible the operational implementation of the sky glitter calculation, we nevertheless make
the assumption that the sky glitter results at non zero wind speed weakly depend on these two
surface parameters. We therefore selected ocean average values of T s=
15°C
and S = 35 psu.
For the flat sea surface cases, we however account for expected variations in these
parameters.
4.7.4. Transport to antenna level and Integration over the Antenna Pattern
Although the focus of that part of the ATBD is on representing the sky scattered signal at
surface level, we also discuss here issues related to the transport from the ground to the
antenna and to the integration over the antenna pattern, as different processing are required
wether the surface is rough or flat.
4.7.4.1. Tracing the galactic noise from surface to antenna level