On SMOS SSS biases in 2012 ... SMOS – In situ comparisons in SPURS region

On SMOS SSS biases in 2012 ... SMOS – In situ comparisons in SPURS region

J. Boutin*, N. Martin*, O. Hernandez*, G. Reverdin*

*LOCEAN

Mean SSS in OTT region(2012: real time SSS; OTT not well phased)

N. Martin e al. 2012

2012

What differences between:- using a bias correction method based on observed SSS biases in

the ‘OTT region’ wrt to updating OTT

- using WOA climatology as reference or ISAS (interpolated in situ measurements) and using whole ‘OTT area’ (45°S-5°S) or a reduced area (30°S-5°S)

Mean SSS in OTT region(2012: real time SSS; OTT not well phased)

2012

Before the catch-up reprocessing, we test an adhoc correction (OCOR):

For each point in the OTT area (140W-95W; 45S-55S):DSSS=SSSsmos-SSSwoa => DTb(DSSS, SSS, SST, WS) => <DTb>ott

In each ocean pixel:DSSS=f(<DTb>ott, SSS, SST, WS)

Adhoc correction (OCOR):

For each point in the OTT area (140W-95W; 45S-55S):DSSS=SSSsmos-SSSwoa => DTb(DSSS, SSS, SST, WS) => <DTb>ott

In each ocean pixel:DSSS=f(<DTb>ott, SSS, SST, WS)

Daily <DTb>ott Ascending orbits

5 day running mean of <DTb>ott Ascending orbits

Various curves using WOA SSS or ISAS SSS, 5S-30S or 5S-45S as reference=> weak differences (<0.1K but not completely negligible)

Daily <DTb>ott very noisy => we use 5day running means computed on ascending and descending orbits separetly and using WOA as reference

WOA, 5S-45SISAS, 5S-45SWOA, 5S-30SISAS, 5S-30S

Adhoc correction (OCOR):

For each point in the OTT area (140W-95W; 45S-55S):DSSS=SSSsmos-SSSwoa => DTb(DSSS, SSS, SST, WS) => <DTb>ott

In each ocean pixel:DSSS=f(<DTb>ott, SSS, SST, WS)

Daily <DTb>ott Descending orbits

5 day running mean of <DTb>ott Descending orbits

Various curves using WOA SSS or ISAS SSS, 5S-30S or 5S-45S as reference

Daily <DTb>ott very noisy => we use 5day running means computed on ascending and descending orbits separetly and using WOA as refernce

WOA, 5S-45SISAS, 5S-45SWOA, 5S-30SISAS, 5S-30S

BIASES on monthly SSS maps with respect to ISAS SSSAscending orbits Descending orbits

OTT Area

45°N-45°S

Less variable biases with OCOR than with REPR because of daily correction

‘Global’ biases very different from biases in OTT region!!

REPR-ISASWOA-ISAS

OCOR-ISAS

Different biases in OTT region and other regions......

STD of (SMOSOCOR SSS - SMOSREPR SSS)Ascending orbits Descending orbits

45°N-45°S

The temporal variation of biases within 15days + the variation of the biases in the FOV => std >0.1 on monthly 1° maps!!!

Almost no difference between applying a mean daily bias (OCOR_1day) or a 5 days running mean (OCOR_5days)

STD of (SMOS SSS - ISAS SSS) for OCOR and OTT_Repr correctionsAscending orbits Descending orbits

OTT Area

45°N-45°S Although OTT_REPR correction is not daily, std (SMOS-

ISAS) is equivalent (or even smaller) for REPR than for OCOR => a mean correction is less efficient than a varying OTT correction (at least with uncorrect galactic map!)

OCOR-ISAS

REPR-ISAS

October 2012 Desc.

Over 45S-45N :OCOR-ISAS : -0.17 (std=0.47)

REPR-ISAS : 0.28 (std=0.45)

SummaryA correction deduced from mean SSS bias over ‘OTT area’ corrects a large part of biases but remains less efficient than updating OTT

Needs for updating OTT more frequently than every 2 weeks will improve

But

Large north-south biases remain

In ‘OTT region’ : North-south variations of biases and SSS variations wrt climatology responsible for uncertainty in OTT <0.1K

SPURS area

Large scale bias between SMOS & AQUARIUS averaged over SPURS area

We first correct for a mean bias between SMOS & WOA or AQUARIUS & WOA

Comparisons SMOS-Toucan & Colibri(+/-9jours, +/-50km)

Mean and standard deviation of SSS SMOS – SSS TSG for each campaign (Colibri and Toucan). Correction of bias B1 is applied. In green: colocalisations in October 2011

Mean negative bias because WOA SSS often lower than in situ SSS

SSS in October 2011 in SPURS regionSMOS SSS theoretical error

SSS in October 2011 in SPURS region

SSS in August 2012 during the STRASSE campaign

Boutin et al., AGU 2012

All data

R2 =0.78n = 30896 mean = -0.06 std = 0.2median = -0.04 RMSE = 0.21

Error < 0.4 PSS-78

R2 =0.81n = 23835 mean = -0.03 std = 0.18median = -0.02 RMSE = 0.19

Summary of SPURS comparisons

Once large scale seasonal bias has been corrected, rms error of SMOS SSS ~0.2; SMOS allows a good monitoring of SSS spatial structures at 50-100km scale