A new debiased Seas surface Salinity map from LOCEAN

Category : CATDS, Cal/Val, L2, Ocean

New info from Jacqueline Boutin!

A new version (version 3) of debiased SMOS SSS L3 maps generated by the
LOCEAN CATDS expertise center is available at CATDS.

This third version of Level 3 SMOS SSS corrected from systematic biases
uses an improved ‘de-biasing’ technique: with respect to version 2, the
adjustment of the long term mean SMOS SSS in very dynamical areas, like
in river plumes, and the bias correction at high latitudes have been
improved. See more information and data link HERE

These products will be presented at IGARSS next week (poster 3447).

SMOS retrieves salinity closer to the coast line

Category : L2, L3, Ocean

From J Boutin, and colleagues from LOCEAN

Salinity observing satellites have the potential to monitor river fresh-water plumes mesoscale spatio-temporal variations better than any other observing system. In the case of the SMOS mission, this capacity was hampered due to the contamination of SMOS data processing by strong land-sea emissivity contrasts.

JB-blog3-1

With the new systematic error mitigation, SMOS SSS becomes more consistent with the independent SMAP SSS close to land, for instance capturing consistent spatio-temporal variations of low salinity waters in the Bay of Bengal and Gulf of Mexico (see Figure 1 below). The standard deviation of the differences between SMOS and SMAP weekly SSS is less than 0.3 pss in most of the open ocean. The standard deviation of the differences between 18-day SMOS SSS and 100-km averaged ship SSS is 0.20 pss (0.24 pss before correction) in the open ocean (see Figure 2 below). Even if this standard deviation of the differences increases closer to land, the larger SSS variability yields a more favorable signal-to-noise ratio, with r2 between SMOS and SMAP SSS larger than 0.8. The correction also reduces systematic biases associated with man-made Radio Frequency Interferences (RFI), although SMOS remains more impacted by RFI than SMAP. This newly-processed dataset will allow the analysis of SSS variability over a larger than 8 years period in regions previously heavily influenced by land-sea contamination, such as the Bay of Bengal or the Gulf of Mexico.

The new SMOS SSS products are available at CATDS (’CEC LOCEAN debias v2′ produced by LOCEAN/ACRI expertise center and ‘CPDC L3Q’ produced by the near real time CATDS chain). The paper is available here (the link is freely active during 2 months).

JB-blog3-2

Figure 1: SMOS SSS corrected according to (a,d) Kolodziejczyk et al. (2016) methodology, (b, e) the method described in this paper (CEC); (c, f) SMAP SSS, in two areas : (a, b, c) : Bay of Bengal - August 21st 2015; (d, e, f) : Gulf of Mexico – August18th 2015.SMOS and SMAP SSS is averaged over a SMOS repetitive orbit sub-cycle (18 days) and two SMAP repetitive orbit cycles (16 days) respectively. Striking fresh SSS features in better agreement with SMOS (new version) and SMAP are indicated with white arrows.

JB-blog3-3

Figure 2: Statistics of ship comparisons (May 2010-August 2016) binned as a function of the distance from the nearest coast: top) mean difference; bottom) standard deviation of the differences; the black line indicates the standard deviation of ship SSS in each class. Ship and SMOS SSS are integrated over 100 km. Orange: monthly SMOS L3P SSS (without error mitigation) ; pink : monthly SMOS L3Q (with error mitigation; near real time processing); light blue : 18-day SMOS CEC (with error mitigation; LOCEAN/ACRI expertise center processing); green : ISAS (Argo optimal interpolation).

Research Engineer in Remote Sensing: Characterising Uncertainties in Satellite Sea Surface Salinity

Category : Ocean, position opening

A research engineer position is open at the Laboratoire d’Océanographie et du Climat – Expérimentation et Approches Numériques (LOCEAN)/ Institut Pierre Simon Laplace (IPSL), PARIS, starting as soon as possible. The position is open for one year, renewable for 2 years depending on the candidate performance.

Context:

The SMOS (Soil Moisture and Ocean Salinity) mission is the first Earth-observing satellite mission carrying an L-band radiometer interferometer. Since its launch at the end of 2009, it has acquired more than 8 years of data that demonstrate the feasibility of the sea surface salinity retrieved by satellite with remarkable spatial resolution compared to other techniques. It has also opened new research perspectives. This unique 8-year salinity time series has permitted unique analyses of salinity variability, linked to oceanic meso-scale and to El Niño type events. Two other satellite missions, Aquarius (2011-2015, CONAE/NASA) and SMAP (2015-, NASA), also based on L-band radiometry, have been providing complementary synoptic salinity measurements leading to an unprecedented spatial coverage. Nevertheless, uncertainties on retrieved salinities differ depending on the radiometer type, the observation geometry, the calibration method, and on the direct and inverse models.

The LOCEAN team is involved since 1999 in the definition of the direct and inverse models applicable to SMOS and in the calibration-validation of the SMOS measurements. It is recognized as SMOS expert support laboratory by the European Spatial Agency (ESA) and by the Centre Aval de Traitement des Données SMOS funded by Centre National d’Etudes Spatiales (CNES). The selected candidate will join the LOCEAN team involved in the physics of the L-band radiometry, in the satellite salinity validation and in the understanding of responsible processes for the observed differences between satellites and in situ measurements, in particular those associated with air-sea interactions, vertical stratification and small-scale variability (www.locean-ipsl.upmc.fr/smos/ and siss.locean-ipsl.upmc.fr).

Work details :

- Characterization of uncertainties of satellite salinity products based on intercomparisons of the various satellite products and comparisons with in situ measurements. This work will be based on existing tools that the selected engineer will adapt to focus on case studies allowing the identification of the uncertainties origin. It will be performed in strong collaboration with researchers and engineers of the LOCEAN SMOS team.

- SMOS data processor development assessment in collaboration with the engineers and researchers in charge of its evolution. Participation to regular progress meetings (teleconferences) of CATDS (2-3 per year).

- Support to users (in French and English)

-Writing of technical papers and participation to scientific papers is possible, depending on the obtained results.

Required Skills:

-       Physics of satellite measurement

-       Data statistical analysis and critical interpretation of the results

-       Autonomy and team collaborative working

-       Python / Matlab ; LINUX

-       Interest in team software development: object-oriented programming, code refactoring & automated testing (e.g. pytest), version control (e.g. Git), code documentation.

Appreciated Skills:

-       Optimization for large dataset processing

-       Interest for environmental science

-       French and English

Level: Research Engineer (PhD thesis or equivalent). Master 2 in remote sensing will also be considered.

Address : LOCEAN, Sorbonne Université, Tour 45-55, 5E, 4, place Jussieu, 75005 PARIS, FRANCE.

Salary : about 1900E monthly net, commensurable with qualification and experience of the candidate (CNRS salary grid)

Candidates should send a statement of interest, CV and coordinates of 2 referees to  Jacqueline Boutin (jb@locean-ipsl.upmc.fr) and Dimitry Khvorostyanov (dimitry.khvorostyanov@locean.upmc.fr ).

Soon 8 candles for SMOS!!!!! (5/8)

Category : CATDS, L2, L3, Model, Ocean

Another post from Jacqueline…and Jérôme

Water cycle in the Bay of Bengal

J. Vialard , S. Marchand et al. (LOCEAN)

The Bay of Bengal receives large amounts of freshwater from the Ganges-Brahmaputra river and monsoonal rainfall. The associated very low surface salinities induce a very stable stratification that inhibits vertical mixing of heat and nutrients. This has strong consequences for the climatological rainfall, intensification of tropical cyclones and ocean productivity in this region.

Available climatologies based on in situ data (e.g. World Ocean Atlas, top row) do not resolve the very strong horizontal gradients in this region. SMOS data (middle row) reveal that the narrow, coastal-trapped East-Indian Coastal Current transport the freshwater plume of Ganges-Brahmaputra along the Indian coast from October to December, resulting in large horizontal gradients (typically ~5 pss between coastal and offshore waters). The 8 years-long time series reveals a strong inter-annual variability of the freshwater plume southward extent, which can be related to Indian Ocean climate variability.


blogJB2-1

Caption: World ocean atlas (derived from in situ data, top row) and SMOS (middle row) (SSS climatology (altimeter-derived surface current climatology are overlaid on both panels). (Bottom row) Latitude-time section of SMOS SSS along the east coast of India. The southward extent of the freshwater plume varies depending on Indian Ocean climate variability associated with the Indian Ocean Dipole (Akhil et al. in prep.). (SMOS CATDS CPDC L3Q SSS)

To know more about associated work:

Akhil, V.P., F. Durand, M. Lengaigne, J. Vialard, M.G. Keerthi, V.V. Gopalakrishna, C. Deltel, F. Papa and C. de Boyer Montégut, 2014: A modeling study of the processes of surface salinity seasonal cycle in the Bay of Bengal, J. Geophys. Res. Oceans, 119, doi:10.1002/2013JC009632.

Akhil, V. P., M. Lengaigne, J. Vialard, F. Durand, M. G. Keerthi, A. V. S. Chaitanya, F. Papa, V. V. Gopalakrishna, and C. de Boyer Montégut, 2016a: A modeling study of processes controlling the Bay of Bengal sea surface salinity interannual variability, J. Geophys. Res. Oceans, 121, 8471–8495, doi:10.1002/2016JC011662.

Akhil, V.P., M. Lengaigne, F. Durand, J. Vialard, V.V. Gopalakrishna, C. de Boyer Montégut and J. Boutin, 2016b: Validation of SMOS and Aquarius remotely-sensed surface salinity in the Bay of Bengal, IJRS, 37,  doi: 10.1080/01431161.2016.1145362

Boutin, J., J.L. Vergely, S. Marchand, F. D’Amico, A. Hasson, N. Kolodziejczyk, N. Reul, G. Reverdin (2017), Revised mitigation of systematic errors in SMOS sea surface salinity: a Bayesian approach, Remote Sensing of Environment, in revision.

Chaittanya, A.V.S., M. Lengaigne, J. Vialard, V.V. Gopalakrishna, F. Durand, Ch. Krantikumar, V. Suneel, F. Papa and M. Ravichandran, 2014: Fishermen-operated salinity measurements reveal a “river in the sea” flowing along the east coast of India, Bull. Am. Met. Soc., 95, 1897-1908.

Fournier, S., J. Vialard, M. Lengaigne, T. Lee, M.M. Gierach, A.V.S. Chaitanya, Unprecedented satellite synoptic views of the Bay of Bengal “river in the sea”, 2017: J. Geophys. Res., in (minor) revision.

download wordpress themes