Soon 8 candles for SMOS!! (4/8)

Category : CATDS, Cal/Val, Data, L2, Non classé, ground measurements

Today let’s have a look back on what was done over land… but remember: it is only a quick summary of part of the findings!!

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Of course all the emphasis at the beginning was on the soil moisture retrievals over what as called « nominal surfaces », which meant land surface with moderate vegetation cover (fallow, crop land, savannah etc..) with all the cal val efforts related to it. For this in particular, several sites were dedicated to Cal Val (VAS in Spain, UDB in Germany, AACES/COSMOS/NAFE in Australia, and later HOBE in Denmark, with also sites in France, Poland, Finland, Tibet, etc…). We also relied heavily on the USDA so called « Watershed sites » and various sparse networks. Actually it is for SMOS that ESA and NASA decided to start the International Soil moisture Network.

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Various pictures SMOSREX, AACES, VAS, Crolles, Mysore, Sodankylä …

Surprisingly enough we obtained good results almost immediately. But this was only the beginning as, in parallel, both level 1 and level 2 made significant progresses, leading to always improved retrievals. Actually with such fast progresses, it has always been a bit of a frustration to see people use not up to date products, as publications looking at SMOS data tended – for obvious reasons – to be a couple of version old (but generally failed to stipulate which version they were looking at!).

The most striking features of these always improved retrievals was, to me, the fact that the range of validity tended to regularly increase. Low to medium topography did not seem to a be a limitation, we managed to make sense in case of flooded areas (see for instance Mississipi floods) and we could get information in case of dense vegetation. The Tor Vergata University for instance related very quickly the vegetation depth to tree height and performed soil moisture retrievals under rainforest. No so accurate of course, but the tendencies are well depicted.

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SMOS opacity vs tree height from ICESat for two season (Rahmoune et al)

The only trouble we had was that the vegetation optical depth was not as satisfactory as we would have expected. It remained noisy in spite of significant overall progresses. To address this problem and also to keep on improving our retrievals (parametrisations) INRA and CESBIO worked on a different approach, the so called SMOS-IC and, lo and behold, first results are rather amazing! We believe we have again struck gold. More about this in the near future!

To finish with the surface soil moisture and vegetation opacity retrievals, we were faced with the fact that the retrieval algorithm is not so fast and thus tests or re-processings are a lengthy and tedious. This was another motivation for SMOS-IC but we also wanted to go a step further and, as soon as enough data was acquired, we developed a global neural network retrieval scheme. It has since been implemented in ECMWF and delivers Soil moisture fields less than 3 hours of sensing, paving the way to many applications…. to be summarised soon: stay tuned!

Further reading

Fernandez-Moran, R.; Al-Yaari, A.; Mialon, A.; Mahmoodi, A.; Al Bitar, A.; De Lannoy, G.; Rodriguez-Fernandez, N.; Lopez-Baeza, E.; Kerr, Y.; Wigneron, J.-P. SMOS-IC: An Alternative SMOS Soil Moisture and Vegetation Optical Depth Product. Remote Sens. 2017, 9, 457.

Kerr, Y. H., et al. (2012), The SMOS Soil Moisture Retrieval Algorithm, IEEE Transactions on Geoscience and Remote Sensing, 50(5), 1384-1403, doi:10.1109/tgrs.2012.2184548.

Rahmoune, R., Ferrazzoli, P., Singh, Y., Kerr, Y., Richaume, P., Al Bitar,  A. SMOS Retrieval Results Over Forests: Comparisons With Independent Measurements. J-STARS ,2014

Rodriguez-Fernandez, N.J., Aires, F., Richaume, P., Kerr, Y.H., Prigent, C., Kolassa, J., Cabot, F., Jimenez, C., Mahmoodi, A., & Drusch, M. (2015). Soil Moisture Retrieval Using Neural Networks: Application to SMOS. Ieee Transactions on Geoscience and Remote Sensing, 53, 5991-6007

Vittucci, C., Ferrazzoli, P., Kerr, Y., Richaume, P., Guerriero, L., Rahmoune, R., & Laurin, G.V. (2016). SMOS retrieval over forests: Exploitation of optical depth and tests of soil moisture estimates. Remote Sensing of Environment, 180, 115-127

Soon 8 candles for SMOS!! (3/8)

Category : Non classé

Jacqueline Boutin, with Audrey Hasson, sent me this contribution, as part of our series of blog stories, to illustrate each day using a new case example, how it reveals, with unprecedented details, the influence of large scale climate events, like ENSO, Indian Ocean Dipole … on the two key hydrological cycle variables. Actually,the 2010-2017 SMOS measurements time series has allowed an unprecedented and unique monitoring of Sea Surface Salinity (SSS) and Soil Moisture (SM) and Cryosphere using L-band radiometry. here is one example!

The signature of ENSO on equatorial and extra-equatorial SSS in the Pacific Ocean

A. Hasson, J. Boutin and S. Marchand (LOCEAN, Paris)

Nearly 8 years of Sea Surface Salinity retrieved from the SMOS mission has enabled the observation of inter-annual variations associated with the El Niño Southern Oscillation. SMOS was launched just in time for a great two-year long La Niña event from mid 2010 to early 2012. Followed in 2014 a small El Niño event that prepared the Pacific Ocean for a large event from mid 2015 to mid 2016.

1- The equatorial SSS variability:

In the Western Pacific Ocean, a large body of fresh waters called the fresh-pool swings along the equator together with the El Niño Southern Oscillation as observed from in situ observations. SMOS measurements enables the much more precise description of the fresh-pool displacement and its previously unknown extension. In 2011, the equatorial western Pacific fresh pool retracts all the way to the western edge of the Pacific Ocean whereas in 2015 the fresh waters extend well east of the dateline.

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Caption: 2010-2017 longitude-time plot of SMOS SSS averaged between 2ºS and 2ºN. The NINO3.4 index is displayed on top, centered on the dateline, blue during La Niña and red during El Niño https://www.esrl.noaa.gov/psd/gcos_wgsp/Timeseries/Data/nino34.long.anom.data. (SMOS CATDS CPDC L3Q products)

To know more about associated work:

A. Hasson, M. Puy, J. Boutin and E. Guilyardi; Northward Propagation across the Tropical North Pacific Ocean Revealed by Surface Salinity: How El Niño Anomalies Reach Hawaii?, submitted to JGR-Oceans

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.


2- The eastern Pacific fresh-pool:

Heavy rain from the Inter-tropical Pacific Convergence Zone is associated with a large area of low surface salinity in the eastern Pacific Ocean. In this very under sampled region of the ocean, SMOS gives us great insight in the ocean variability.

Since launch, an extension of the eastern Pacific freshwaters is observed as shown around 18ºN. Fresh waters are trapped east of 110ºW during the 2011 La Niña and extend to the dateline following the 2015 El Niño.

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Caption: 2010-2017 longitude-time plot of SMOS SSS averaged between 16º and 20ºN. The NINO3.4 index is displayed on top, centred on the dateline, blue during La Niña and red during El Niño https://www.esrl.noaa.gov/psd/gcos_wgsp/Timeseries/Data/nino34.long.anom.data. (SMOS CATDS CPDC L3Q products)

To know more about associated work:

A. Hasson, M. Puy, J. Boutin and E. Guilyardi; Northward Propagation across the Tropical North Pacific Ocean Revealed by Surface Salinity: How El Niño Anomalies Reach Hawaii?, submitted to JGR-Oceans

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.

Guimbard S., N. Reul, B. Chapron, M. Umbert and C. Maes, 2017. Seasonal and interannual variability of the eastern tropical Pacific fresh pool, J. Geophys. Res. Oceans, doi: 10.1002/2016JC012130.

Alory, G., C. Maes, T. Delcroix, N. Reul, and S. Illig, 2012. Seasonal dynamics of sea surface salinity off Panama: the far eastern Pacific fresh pool. J. Geophys. Res., 117, C04028, doi:10.1029/2011JC007802.

3- The extra-equatorial anomalies

The unprecedented spatial and temporal coverage of the SMOS mission reveals poleward pathways of equatorial SSS anomalies as shown for the 2011 La Niña (Hasson et al. 2014) and for the 2014-2015 El Niño events (Hasson et al. 2017 submitted). Anomalies created at the equator by the displacement of the western Pacific fresh-pool and off the equator are exported poleward by the Ekman drift in a complex system of tropical currents.

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Caption: 2010-2017 latitude-time plot of SMOS SSS anomalies produced by the CEC-LOCEAN averaged between 150º and 170ºW. The NINO3.4 index is displayed on top, centered on the equator, blue during La Niña and red during El Niño https://www.esrl.noaa.gov/psd/gcos_wgsp/Timeseries/Data/nino34.long.anom.data. (SMOS CATDS CPDC L3Q products)

To know more about associated work:

A. Hasson, M. Puy, J. Boutin and E. Guilyardi; Northward Propagation across the Tropical North Pacific Ocean Revealed by Surface Salinity: How El Niño Anomalies Reach Hawaii?, submitted to JGR-Oceans

A. Hasson, T. Delcroix, J. Boutin, R. Dussin, and J. Ballabrera-Poy (2014); Analyzing the 2010–2011 La Niña signature in the tropical Pacific sea surface salinity using in situ data, SMOS observations, and a numerical simulation, Journal of Geophysical Research: Oceans, 119(6), 3855-3867, doi:10.1002/2013JC009388.

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.

Soon 8 candles for SMOS!! (2/8)

Category : Non classé, Satellite

After the first image it was obvious that SMOS was running smoothly but still more works had to be done. The Commissioning phase started. We were tasked to make the first products, validate them and select the final mode of operations. For instance two options were possible, dual or full polarisation. If full pol was attractive, it also meant a degradation of sensitivity. Luckily after many tests (SMOS was operated alternatively full and dual pol, one week each for enough time to be able to reach a decision) it was found that thanks to the instrument excellent performances ful pol was perfectly acceptable and was thus selected. But all was not nice. Over oceans reaching the hundredth of a K was challenging , stability was yet to … stabilize etc. For the former  J. Tenerelli suggested to use a diagnostic tool the so called OTT (Ocean Target Transformation) which was soon to become « the tool » over ocean surfaces. for the latter the instrument did stabilize in May. This is why we generally recommend to only use data from June 2010 for delicate studies. But all this was expected and did not come as a surprise. the surprises were really bad news…

First the local oscillators of one arm, once disturbed, did seem unable to relock and needed a complete reboot… not good. This was swiftly cured by using switch to the redundant (nominal actually) segment. Again business as usual. What was not was teh discovery of RFI (radio frequency interferences) in our protected band!!

We expected some perturbations and our algorithms all had a RFI detection scheme … what we did not expect is such a large quantities of sources !

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Situation (RFI probability) in December 2009 – July 2010 (P Richaume)

This obviously needed some sort of an action! we started identifying, locating, reporting these bad guys. Some were out of band emissions, but too strong to be legal, some downright « outlaws ». emitting in band. The work was/is done by Colleagues at ESAC and at CESBIO while the  reporting is done through the ANFR and managed / coordinated by ESA with some success as in many areas the situation is significantly improved (North America, Greenland, western Europe, …). the « cleanest country is probably Australia while the darkest is Japan which changed in 2011 from rather OK to completely obscured by RFI. Japan is no more on the L band Map!

These findings enabled Aquarius to be prepared while SMAP could design a very sophisticated receiver able to reduce the impact of RFI on data.

But we have to be very careful many frequency greedy groups are also lurking in the background on top of those mentioned above… which could jeopardize the wealth of results L band radiometry ids offering us (more about this in the next posts) and which can be illustrated by the first ever Soil moisture – Ocean Salinity map ever produced from space .. thanks to SMOS

Image1Soil Moisture and Ocean salinity over the globe (August 2010) (F Cabot).

Note that since 2010 many progresses were made and we have much improved results by now… stay tuned!

Soon 8 candles for SMOS!! (1/8)

Category : Non classé

As a consequence, and following an idea suggested by Nemesio, we will endeavour to post every day for the next 8 days a small story on SMOS…

Today let us reminisce a little…

smos ready for launchSMOS & Proba 2 Launch campaign with Rockot launcher

SMOS (and Proba) under the shroud and then on the Launch pad

At the end of October 2009, the  satellite (SMOS on a PROTEUS platform), with its friend Proba, was packaged on a Rockot launcher and launched smoothly, accurately and efficiently on its orbit on November 2 2009. All the deployment (solar panels, arms loaded with antennas) went also a clockwork to enable the reception and processing of the first image ever taken from space at L band with an interferometer on November 17th.

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Crucial moment: Arms are being deployed

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The First Soil moisture Map

Yes! this is indeed the first ever soil moisture image made from a space borne interferometer. Obviously it is not perfect but it simply showed that it worked!! the next challenge was to retrieve Sea surface Salinity… and improve the soil moisture retrievals  stay tuned

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