ott sensitivity study and sun correction impact j. gourrion and the smos-bec team

OS-ESL meeting, Barcelona, February 21-22nd, 2011

OTT sensitivity study

and

Sun correction impact

J. Gourrion and the SMOS-BEC team

SMOS-BEC, ICM/CSIC


OTT sensitivity

DPGS OTT

Impact on OTT quality of different factors:

1. Galactic signals

2. Number of snapshots used

3. Apparent drift (or temporal integration window width)

Experiments designed to remove inter-dependence

OTT quality criterion: stability, level of dependence on the subset of data


OTT sensitivity

Force independence of factor 2 (constant number of snapshots N) and 3 (use a 12-days period)

Galactic potential contamination detection: threshold on the incident field (3.5 to 8 K)

For each threshold value, N snapshots are randomly selected, and an OTT computed

Using the lowest threshold value as reference, we compute the OTT rms increase due to increasing galactic contamination

Impact of galactic contamination


Force independence of factor 1 (strict galactic filter) and 3 (use a 12-days period)

For three different periods, the reference situation is given by the overall number of available snapshots after filtering.

the number of snapshots is progressively reduced, snapshots are randomly selected and corresponding OTTs are computed

OTT rms increase is computed as a function of snapshot number reduction factor and averaged over the 3 datasets (consistency checked)

OTT sensitivity

Impact of number of snapshots


Force independence of factor 1 (strict galactic filter) and 2 (constant number of snapshots N)

The temporal window width is increased from 6 days to 48 days

In each case, N snapshots are randomly selected, and an OTT computed

Using the shortest temporal window as reference, we compute the OTT rms increase due to increasing data inconsistency

OTT sensitivity

Impact of apparent drift


As expected, the number of snapshots used to compute the OTT should be kept as high as possible, the upper limit being set by other constraints

Galaxy presence in the snapshots used to compute the OTT may induce large errors in the characterization of systematic instrument/reconstruction biases (up to 0.4 K rms at X- and Y-pol)

Apparent instrumental drift can induce significant errors. If not canceled, numbers provided should help defining the OTT recomputation period.

OTT sensitivity

Summary


Direct sun correction impact

Using DPGS file :

SM_OPER_MIR_SC_F1B_20100803T131914_20100803T141314_340_001_0



Using DPGS file :


* 0.1-0.2 K shift

* no impact on latitudinal variations



Using DPGS file :




Using DPGS file :


1K impact on latitudinal variations


Summary

Variability of the distribution of observed geophysical conditions inside the FOV, when computing the OTT, may introduce inconsistencies in the modified brightness temperatures

Adequate snapshot selection procedure enables to reduce consequent biases in the retrieved salinities. The procedure requires much more data than one half-orbit.

The residual SSS anomalies are highly reduced when using a roughness-improved forward model (IQR divided by 2, Y-pol)

In terms of salinity, X-pol is much noisier than Y-pol.

To further reduce the SSS errors:

work on the roughness description and more generally on the forward model improve the inversion method from the present linear approach

ott sensitivity study and sun correction impact j. gourrion and the smos-bec team

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