SMOS L2 Ocean Salinity
L2OS QWG #4: RFI
7-9 March 2011
ARGANS & L2OS ESL
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SMOS L2 Ocean Salinity
RFI over the ocean
DEW line RFI prevents successful salinity retrieval North Pacific & Atlantic
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SMOS L2 Ocean Salinity
Outliers & RFI
Transect at 45N +-1
Dg_num_outliers
SM_TEST_MIR_OSDAP2_20110209T064251_20110209T073653_317_001_8
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SMOS L2 Ocean Salinity
Outliers & RFI
From CH/JLV/JB TN: typical N. Atlantic RFI pattern in salinity (left),
typical oscillations in TBs (right)
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Outlier detection SMOS
in L2OSPP
and itsSalinity
usefulness in RFI detection and correction –
L2 Ocean
HENOCQ et al, SMOS L2OS technical note, 28/02/11
Outliers & RFI
Some Tests close to Greenland
New algorithm more consistent and effective (below
0317 outlier detection algorithm
outliers=filled points)
With L2OSPP v3.17
With new algorithm
for pol = 0 to 3 /* Stokes 1..4 */
A
for each measurement
A
if abs((Tbsmos[pol] – Tbmodel[pol]) – correction[pol])
> 5 * σTB
B
then
Refinements:
outlier[pol, meas] = TRUE
- If no RFI, 3 sigma sorting
may discard good
where
measurements
:
 Add
a first step
at
correction
= median
(Tbmeas - Tbmodel)
B
gridpointσTB
level
identifying
2 + σTBmodel2 )
= √for
(σTB_radiometric_noise
the risk of outliers (see TN)
Future work:
-use « up and down
evolution » of (Btmeas–
BTmodel) over a dwell to
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detect
RFI
SMOS L2 Ocean Salinity
Outliers & RFI
0318 new 2 step RFI outlier detection algorithm based on reducing outlier threshold if
high probability of RFI detected
for pol = 0 to 3 /* Stokes 1..4 */
if std(TBmodel[pol] - TBsmos[pol]) > 1.2 * std_theory then
rfi_outlier_risk[pol] = TRUE
if rfi_outlier_risk[pol] then
for each measurement
if abs(TBmodel[pol] - TBsmos[pol]) > 3 * rad_noise then
rfi_outlier[pol, meas] = TRUE
where
std_theory = √ ((TB_radiometric_noise2 + TBmodel2 ) / nMeas)
factor of 1.2 is 99% confidence with 100 measurements (1 + 0.18)
nsig is reduced from 5 (non-RFI outlier detection threshold) to 3
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SMOS L2 Ocean Salinity
Outliers & RFI
0318 new RFI outlier detection algorithm disabled
SM_OPER_MIR_SCSF1C_20110209T064251_20110209T073653_346_001_1
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SMOS L2 Ocean Salinity
Outliers & RFI
0318 new RFI outlier detection algorithm enabled
SM_OPER_MIR_SCSF1C_20110209T064251_20110209T073653_346_001_1
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SMOS L2 Ocean Salinity
Outliers & RFI
Fg_ctrl_suspect_RFI = RFI outliers > 50%
Danger of false positives?
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delta SSS1 (RFI off – on)
Impact on non-RFI retrieval?
SMOS L2 Ocean Salinity
Outliers & RFI
RFI outlier detection algorithm disabled (left)
enabled (right)
SM_OPER_MIR_SCSF1C_20100802T153816_20100802T163215_344_001_1
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SMOS L2 Ocean Salinity
Outliers & RFI
RFI outlier detection algorithm disabled (left)
enabled (right)
SM_OPER_MIR_SCSF1C_20100802T153816_20100802T163215_344_001_1
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SMOS L2 Ocean Salinity
Outliers & RFI – L1PP 350
0318 new RFI outlier detection algorithm enabled
SM_TEST_MIR_SCSF1C_20100315T080748_20100315T090119_350_001_0
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SMOS L2 Ocean Salinity
Outliers & RFI – L1PP 350
Any correlation between L1 & L2 RFI flagging?
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SMOS L2 Ocean Salinity
Outliers & RFI
Other possible RFI detection approaches
Detecting RFI induced oscillations in dwell line TBs (eg using fft) – see TN from Claire,
Jacqueline & Jean-Luc (oscillations seem higher in VV?):
Using L1c RFI flags?
Using AUX_RFILST?
CATDS use one month data in 5 degree bins per grid point...
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