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J. Font, J. Boutin,
N. Reul,
P. Spurgeon,
J. Ballabrera,
A. Chuprin,
C. Gabarró,
J. Gourrion,
S. Guimbard,
C. Hénocq, [......],
M. Portabella,
R. Sabia,
M. Talone,
J. Tenerelli,
A. Turiel,
J.L. Vergely,
P. Waldteufel,
X. Yin,
S. Zine,
S. Delwart
Proceedings of the SMOS Science Workshop, CNES-ESA, Arles, France, Arles, France; 09/2011
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J. Font, J. Boutin,
N. Reul,
P. Spurgeon,
S. Delwart,
J. Ballabrera,
A. Chuprin,
C. Gabarró,
J. Gourrion,
C. Hé- nocq, [......],
F. Petitcolin,
M. Portabella,
R. Sabia,
M. Talone,
J. Tenerelli,
A. Turiel,
J.-L. Vergely,
P. Waldteufel,
X. Yin,
S. Zine
Mercator Ocean Quarterly Newsletter. 01/2011; 42:3-11.
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G. Reverdin,
L. Marié,
P. Lazure,
F. d'Ovidio, J. Boutin,
P. Testor,
N. Martin,
A. Lourenco,
F. Gaillard,
A. Lavin, [......],
J. Mader,
A. Rubio,
P. Blouch,
J. Rolland,
Y. Bozec,
G. Charria,
F. Batifoulier,
F. Dumas,
S. Louazel,
J. Chan
Journal of Marine Systems 01/2011; · 2.13 Impact Factor
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ABSTRACT: In the present paper, different methods are proposed for the detection and mitigation of the undesirable effects of radio frequency interference (RFI) in microwave radiometry. The first of these makes use of kurtosis to detect the presence of non-Gaussian signals, whereas the second imposes a threshold on the standard deviation of brightness temperatures, in order to distinguish natural emission variations from RFI. Finally, the third approach is based on the use of a threshold applied to the third and fourth Stokes parameters. All of these methods have been applied and tested, with a CAROLS radiometer operating in the L-band, on data acquired during airborne campaigns made in spring 2009 over the South West of France. The performance of each, or of two combined approaches is analyzed with our database. We thus show that the kurtosis method is well adapted to pulsed RFI, whereas the method based on the second moment is well adapted to continuous-wave RFI.
Microwave Radiometry and Remote Sensing of the Environment (MicroRad), 2010 11th Specialist Meeting on; 04/2010
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M. Zribi,
M. Parde,
D. Hauser,
P. Fanise, J. Boutin,
C. Albergel,
J.C. Calvet,
M. Crapeau,
M. Dechambre,
Y. Kerr,
E.L. Baeza,
A. Mialon,
G. Reverdin,
A. Ruis,
K. Saleh,
J.P. Wigneron
[show abstract]
[hide abstract]
ABSTRACT: The CAROLS, L band radiometer, is built and designed as a copy of EMIRAD II radiometer of DTU team. It is a Correlation radiometer with direct sampling and fully polarimetric (i.e 4 Stockes). It will be used in conjunction with other airborne instruments (in particular the C-Band scatterometer (STORM) and IEEEC GPS system, Infrared CIMEL radiometer and one visible camera), in coordination with in situ field campaigns for SMOS CAL/VAL. The instruments are implemented on board the French research airplane ATR42. A scientific campaign with thirteen flights is realized over south-western France, Valencia site and Bay of Biscay (Atlantic Ocean) in spring 2009. In order to qualify the radiometer data, different types of aircraft movements were realized: circle flights, wing and nose wags. Simultaneously to flights, different ground measurements were made over continental surfaces and ocean. Results show a good quality of data. For continental surfaces, important Radio-Frequency Interferences (RFI) were observed over a large part of the studied region.
Microwave Radiometry and Remote Sensing of the Environment (MicroRad), 2010 11th Specialist Meeting on; 04/2010
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J. Font, J. Boutin,
N. Reul,
P. Spurgeon,
J. Ballabrera,
A. Chuprin,
C. Gabarró,
J. Gourrion,
C. Hénocq,
S. Lavender, [......],
A. Turiel,
J.L. Vergely,
P. Waldteufel,
X. Yin,
S. Zine,
Delwart,
S. Sabia,
A.L. Aretxabaleta,
A. Camps,
A. Monerris
Proceedings of the ESA Living Planet Symposium; 01/2010
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Mehrez Zribi,
Mickael Parde,
Daniele Hauser,
Pascal Fanise, J. Boutin,
C. Albergel,
J.-C. Calvet,
M. Crapeau,
Monique Dechambre,
Y. Kerr,
E.L. Baeza,
A. Mialon,
G. Reverdin,
A. Ruis,
K. Saleh,
J.-P. Wigneron
[show abstract]
[hide abstract]
ABSTRACT: The CAROLS, L band radiometer, is built and designed as a copy of EMIRAD II radiometer of DTU team. It is a Correlation radiometer with direct sampling and fully polarimetric (i.e 4 Stockes). It will be used in conjunction with other airborne instruments (in particular the C-Band scatterometer (STORM) and IEEEC GPS system, Infrared CIMEL radiometer and one visible camera), in coordination with in situ field campaigns for SMOS CAL/VAL. The instruments are implemented on board the French research airplane ATR42. A scientific campaign with thirteen flights is realized over south-western France, Valencia site and Bay of Biscay (Atlantic Ocean) in spring 2009. In order to qualify the radiometer data, different types of aircraft movements were realized: circle flights, wing and nose wags. Simultaneously to flights, different ground measurements were made over continental surfaces and ocean. Results show a good quality of data. For continental surfaces, important Radio-Frequency Interferences (RFI) were observed over a large part of the studied region
Microwave Radiometry and Remote Sensing of the Environment (MicroRad); 01/2010
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M. Zribi,
D. Hauser,
M. Parde,
P. Fanise,
P. Leroy,
M. Dechambre, J. Boutin,
G. Reverdin,
J.C. Calvet,
A. Weill,
J.P. Wigneron,
N. Skou,
S.S. Sobjaerg,
A. Ruis,
E. Cadareche
[show abstract]
[hide abstract]
ABSTRACT: The CAROLS, L band radiometer, is built and designed as a copy of EMIRAD II radiometer of DTU team. It is a Correlation radiometer with direct sampling and fully polarimetric (i.e 4 Stockes). It will be used in conjunction with other airborne instruments (in particular the C-Band scatterometer (STORM) and IEEC GPS system, Infrared CIMEL radiometer, one visible camera), in coordination with in situ field campaigns for SMOS CAL/VAL. The instruments are implemented on board the French research airplane ATR42. A validation campaign with four flights was made over south west of France, Hourtin Lake and Bay of Biscay (Atlantic Ocean) in September 2007. In order to qualify the radiometer data, different types of aircraft movements were realized: circle flights, wing and nose wags. Simultaneously to flights, different ground measurements were made over continental surfaces and ocean. First results show a good quality of data over ocean surfaces. For continental surfaces, important Radio-Frequency Interferences (RFI) were observed over a large part of the studied region.
Microwave Radiometry and Remote Sensing of the Environment, 2008. MICRORAD 2008; 04/2008
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S. Zine, J. Boutin,
J. Font,
N. Reul,
P. Waldteufel,
C. Gabarro,
J. Tenerelli,
F. Petitcolin,
J.-L. Vergely,
M. Talone,
S. Delwart
[show abstract]
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ABSTRACT: The L-band interferometric radiometer onboard the Soil Moisture and Ocean Salinity mission will measure polarized brightness temperatures (Tb). The measurements are affected by strong radiometric noise. However, during a satellite overpass, numerous measurements are acquired at various incidence angles at the same location on the Earth's surface. The sea surface salinity (SSS) retrieval algorithm implemented in the Level 2 Salinity Prototype Processor (L2SPP) is based on an iterative inversion method that minimizes the differences between Tb measured at different incidence angles and Tb simulated by a full forward model. The iterative method is initialized with a first-guess surface salinity that is iteratively modified until an optimal fit between the forward model and the measurements is obtained. The forward model takes into account atmospheric emission and absorption, ionospheric effects (Faraday rotation), scattering of celestial radiation by the rough ocean surface, and rough sea surface emission as approximated by one of three models. Potential degradation of the retrieval results is indicated through a flagging strategy. We present results of tests of the L2SPP involving horizontally uniform scenes with no disturbing factors (such as sun glint or land proximity) other than wind-induced surface roughness. Regardless of the roughness model used, the error on the retrieved SSS depends on the location within the swath and ranges from 0.5 psu at the center of the swath to 1.7 psu at the edge, at 35 psu and 15degC. Dual-polarization (DP) mode provides a better correction for wind-speed (WS) biases than pseudofirst Stokes mode (ST1). For a WS bias of -1 mmiddots<sup>-1</sup>, the corresponding SSS bias at the center of the swath is equal to -0.3 psu in DP mode and to -0.5 psu in ST1 mode. The inversion methodology implicitly assumes that WS errors follow a Gaussian distribution, even though these errors should follow more closely a Rayleigh distribution. For this -
reason, the use of wind components, which typically exhibit Gaussian error distributions, may be preferred in the retrieval. However, the use of noisy wind components creates WS and SSS biases at low WSs (0.1 psu at 3 mmiddots<sup>-1</sup>). At a sea surface temperature (SST) of 15degC, the retrieved SSS is weakly sensitive to the SST biases, with the SSS bias always lower than 0.3 psu for SST biases ranging from -0.5degC to -2degC. In DP mode, biases in the vertical total electron content (TEC) of the atmosphere result in SSS biases smaller than 0.2 psu. The pseudofirst Stokes mode is insensitive to TEC. Failure to fully account for sea surface roughness scattering effects in the computation of sky radiation contribution leads to a maximum SSS bias of 0.2 psu in the selected configuration, i.e., a descending orbit over the Northern Pacific in February. To achieve SSS biases that are smaller than 0.2 psu, special care must be taken to correct for biases at low WS and to ensure that the bias on the mean WS (averaged over 200 km times 200 km and ten days) remains smaller than 0.5 mmiddots<sup>-1</sup>.
IEEE Transactions on Geoscience and Remote Sensing 04/2008; · 2.89 Impact Factor
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ABSTRACT: The Soil Moisture and Ocean Salinity (SMOS) mission (launch scheduled for 2008) aims at obtaining global maps of soil moisture and sea surface salinity (SSS). It uses an L-band (1.4 GHz) microwave interferometric radiometer to obtain brightness temperatures (Tb) at the Earth surface at horizontal and vertical polarizations. They will be used to retrieve both geophysical variables, following specifically designed algorithms that will be applied when the satellite field-of-view is covering land or ocean surfaces respectively. The retrieval of salinity is a complex process that requires the knowledge of environmental information and an accurate processing of the radiometer measurements, because of the narrow range of ocean Tb and the strong impact on the measures of geophysical parameters (such as sea state). Here we present the baseline approach chosen to retrieve sea surface salinity from SMOS data, as developed and implemented by the joint team of scientists and engineers responsible for the SMOS Salinity Level 2 Prototype Processor. We present academic tests conducted over homogeneous scenes with the prototype. In these configurations, external perturbation sources (sky radiation, sun glint, ...) are not taken into account. Roughness is the main sea surface signal disturbing SSS retrieval.
Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International; 08/2007
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ABSTRACT: In preparation for SMOS Cal/Val phase, we simulate SMOS retrieved data (first cm) from in situ data (a few meters depth). We study vertical gradients of salinity in the Tropical Atlantic Ocean with three types of data: TSG and XCTD measurements from boats (POLARSTERN and ARAMIS project) and from ARGO floats. Between 0 and 10degnorth, nearly 5% of vertical gradients between 5 and 10 m are larger than 0.1 psu. They appeared in a zone characterized by warm SST and low wind and are linked to rain events or river discharges. The mean value of all the data stays less than 0.02 psu. However their distribution is skewed towards positives values, implying a non Gaussian repartition of differences between SMOS and in situ data.
Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International; 08/2007
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ABSTRACT: This paper aims at studying the quality of the sea surface salinity (SSS) retrieved from soil moisture and ocean salinity (SMOS) data in coastal areas. These areas are characterized by strong and variable SSS gradients [several practical salinity units (psu)] on relatively small scales: the extent of river plumes is highly variable, typically at kilometric and daily scales. Monitoring this variability from SMOS measurements is particularly challenging because of their resolution (typically 30-100 km) and because of the contamination by the nearby land. A set of academic tests was conducted with a linear coastline and constant geophysical parameters, and more realistic tests were conducted over the Bay of Biscay. The bias of the retrieved SSS has been analyzed, as well as the root mean square (rms) of the bias, and the retrieved SSS compared to a numerical hydrodynamic model in the semirealistic case. The academic study showed that the Blackman apodization window provides the best compromise in terms of magnitude and fluctuations of the bias of the retrieved SSS. Whatever the type of vegetation cover, a strong negative bias, greater than 1 psu, was found when nearer than 36 km from the coast. Between 44 and 80 km, the type of vegetation cover has an impact of less than a factor 2 on the bias, and no influence further than 80 km from the coast. The semirealistic study conducted in the Bay of Biscay showed a bias over ten days lower than 0.2 psu for distances greater than 47 km, due to an averaging over various geometries (coastline orientation, swath orientation, etc.). The bias showed a weak dependence on the location of the grid point within the swath. Despite the noise on the retrieved SSS, contrasts due to the plume of the Loire River and the Gironde estuary remained detectable on ten-day averaged maps with an rms of 0.57 psu. Finally, imposing thresholds on the major axis of the measurements brought little improvement to the bias, whereas it increased the rms and-
could lead to strong swath restriction: a 49-km threshold on the major axis resulted in an effective swath of 800-900 km instead of 1200 km.
IEEE Transactions on Geoscience and Remote Sensing 08/2007; · 2.89 Impact Factor
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ABSTRACT: The European Space Agency SMOS (Soil Moisture and Ocean Salinity) mission aims at obtaining global maps of soil moisture and sea surface salinity from space for large scale and climatic studies. It uses an L-band (1400-1427 MHz) microwave interferometric radiometer by aperture synthesis (MIRAS) to measure brightness temperature at the Earth surface at horizontal and vertical polarizations (Th and Tv). These two parameters will be used together to retrieve the geophysical variables. The retrieval of salinity is a complex process that requires the knowledge of other environmental information and an accurate processing of the radiometer measurements, due to the narrow range of ocean brightness temperatures and the strong impact in the measured values of different geophysical parameters (as sea state) other than salinity. Here we present the baseline approach chosen by ESA to retrieve sea surface salinity from MIRAS data, as it has been developed and implemented by the joint team of scientists and engineers responsible for the SMOS ocean salinity level 2 prototype processor.
Geoscience and Remote Sensing Symposium, 2006. IGARSS 2006. IEEE International Conference on; 09/2006
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ABSTRACT: We determine the distribution of oceanic CO2 partial pressure (pCO(2)) with respect to remotely sensed parameters (sea surface temperature (SST) and chlorophyll (Chl)) in order to gain an understanding of the small-scale (10-100 km) pCO(2) variability and to estimate the net air-sea CO2 flux in the region (125 degrees E-205 degrees E; 45 degrees S-60 degrees S), which represents 22% of the Southern Ocean area between 45 degrees S and 60 degrees S. We split the study area into several biogeochemical provinces. In chlorophyll-poor regions, pCO(2) is negatively correlated with SST, indicating that pCO(2) is mostly controlled by mixing processes. For Chl > 0.37 mg m(-3), pCO(2) is negatively correlated with Chl, indicating that pCO(2) variability is mostly controlled by carbon fixation by biological activity. We deduce fields of pCO(2) and of air-sea CO2 fluxes from satellite parameters using pCO(2)-SST, pCO(2)-chlorophyll relationships and air-sea gas exchange coefficient, K, from satellite wind speed. We estimate an oceanic CO2 sink from December 1997 to December 1998 of -0.08 GtC yr(-1) with an error of 0.03 GtC yr(-1). This sink is approximately 38% smaller than that computed from the Takahashi et al. (2002) climatological distribution of Delta pCO(2) for the 1995 year but with the same K (-0.13 GtC yr(-1)). When we correct ocean pCO(2) for the interannual variability between 1995 and 1998, the difference is even larger, and we cannot reconcile both estimates in February-March and from June to November. This strengthens the need of new in situ measurements for validating extrapolation methods and for improving knowledge of interannual pCO(2) variability.
Journal of Geophysical Research-Oceans. 01/2005; 110(C9).
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ABSTRACT: The results from two field experiments in the Mediterranean Sea are used to study the wind speed dependence of brightness temperature at L-band. During the EuroSTARRS airborne experiment, an L-band radiometer made measurements across a large wind speed gradient, enabling us to study this dependence at high wind speed. We compare our results with a two-scale emissivity model using several representations of the sea state spectrum. While the results are encouraging, unfortunately the accuracy of the measurements does not permit us to distinguish between the so-called twice Durden and Vesecky spectrum and the Elfouhaily spectrum above 7 m·s<sup>-1</sup>. The effect of foam is certainly small. During the WISE 2001 field experiment carried on an oil rig, we studied this dependence at low wind speed, finding an abrupt decrease of the wind speed effect on the brightness temperature below 3 m·s<sup>-1</sup>.
IEEE Transactions on Geoscience and Remote Sensing 11/2004; · 2.89 Impact Factor
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A. Camps,
J. Font,
M. Vall-llossera,
C. Gabarro,
I. Corbella,
N. Duffo,
F. Torres,
S. Blanch,
A. Aguasca,
R. Villarino, [......],
V. Caselles,
A. Weill, J. Boutin,
S. Contardo,
R. Niclos,
R. Rivas,
S.C. Reising,
P. Wursteisen,
M. Berger,
M. Martin-Neira
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ABSTRACT: Soil Moisture and Ocean Salinity (SMOS) is an Earth Explorer Opportunity Mission from the European Space Agency with a launch date in 2007. Its goal is to produce global maps of soil moisture and ocean salinity variables for climatic studies using a new dual-polarization L-band (1400-1427 MHz) radiometer Microwave Imaging Radiometer by Aperture Synthesis (MIRAS). SMOS will have multiangular observation capability and can be optionally operated in full-polarimetric mode. At this frequency the sensitivity of the brightness temperature (T<sub>B</sub>) to the sea surface salinity (SSS) is low: 0.5 K/psu for a sea surface temperature (SST) of 20°C, decreasing to 0.25 K/psu for a SST of 0°C. Since other variables than SSS influence the T<sub>B</sub> signal (sea surface temperature, surface roughness and foam), the accuracy of the SSS measurement will degrade unless these effects are properly accounted for. The main objective of the ESA-sponsored Wind and Salinity Experiment (WISE) field experiments has been the improvement of our understanding of the sea state effects on T<sub>B</sub> at different incidence angles and polarizations. This understanding will help to develop and improve sea surface emissivity models to be used in the SMOS SSS retrieval algorithms. This paper summarizes the main results of the WISE field experiments on sea surface emissivity at L-band and its application to a performance study of multiangular sea surface salinity retrieval algorithms. The processing of the data reveals a sensitivity of T<sub>B</sub> to wind speed extrapolated at nadir of ∼0.23-0.25 K/(m/s), increasing at horizontal (H) polarization up to ∼0.5 K/(m/s), and decreasing at vertical (V) polarization down to ∼-0.2 K/(m/s) at 65° incidence angle. The sensitivity of T<sub>B</sub> to significant wave height extrapolated to nadir is ∼1 K/m, increasing at H-polarization up to ∼1.5 K/m, and decreasing at V-polarization down to -0.5 K/m at 65°. A modulation of the instantaneous brightness temperature T<sub>B</sub>(t) is found to be correlated with the measured sea surface slope spectra. Peaks in T<sub>B</sub>(t) are due to foam, which has allowed estimates of the foam brightness temperature and, taking into account the fractional foam coverage, - the foam impact on the sea surface brightness temperature. It is suspected that a small azimuthal modulation ∼0.2-0.3 K exists for low to moderate wind speeds. However, much larger values (4-5 K peak-to-peak) were registered during a strong storm, which could be due to increased foam. These sensitivities are satisfactorily compared to numerical models, and multiangular T<sub>B</sub> data have been successfully used to retrieve sea surface salinity.
IEEE Transactions on Geoscience and Remote Sensing 05/2004; · 2.89 Impact Factor
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ABSTRACT: In order to prepare the Soil Moisture and Ocean Salinity (SMOS) mission, we present 1) the sea surface salinity precision that could be achieved with the SMOS radiometer measurements and 2) the time and space scales over which averaged SMOS Tb should remain relatively constant in order to prepare after-launch monitoring of radiometer drifts. Leaving aside errors due to the instrument and the image reconstruction process, the SSS averaged over 200 × 200 km<sup>2</sup> areas and over 10 days retrieved from SMOS measurements should meet the GODAE requirements with a precision better than 0.1 psu in most oceanic regions, assuming random noise on W and SST of 2 m s<sup>-1</sup> and 1 °C, respectively. On another hand, this requirement will not be met if no a priori information on the wind speed is available. However, it is likely that SMOS Tb will suffer from temporal drifts and/or from regional biases linked to sun disturbances for instance. In these biases are going to be monitored using Tb averages, it will be necessary to take into account wind speed variability.
Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International; 08/2003
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02/2003; 525:117-124.
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02/2003; 525:133-136.
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02/2003; 525:51-59.
