Alexis Mouche | Ifremer - Academia.edu (original) (raw)

Papers by Alexis Mouche

Journal of Geophysical Research: Oceans, 2015

Journal of Geophysical Research: Oceans, 2016

Springer Earth System Sciences, 2016

Journal of Applied Meteorology and Climatology, 2015

2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 2015

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Due to the underdetermined nature of the inverse problem for SAR wind, ancillary information is r... more Due to the underdetermined nature of the inverse problem for SAR wind, ancillary information is routinely used. Up to now one of the more mature approaches is certainly to use radar cross section in combination with wind information from a numerical model into a Bayesian scheme.

Sentinel-1 (S-1) is the first of the five missions that European Spatial Agency is developing for... more Sentinel-1 (S-1) is the first of the five missions that European Spatial Agency is developing for the Copernicus initiative. S-1 constellation comprises two polar orbiting satellites. They will operate day and night performing C-band synthetic aperture radar imaging to acquire imagery regardless of the weather. The launch date for the First Sentinel-1 (Sentinel-1 A) is the 4th of April 2014. Sentinel-1 B will follow in 2016. S-1 will work in a pre-programmed operation mode to avoid conflicts and to produce a consistent long term data archive built for applications based on long time series. S-1 ensures the continuity of global swell spectra measurements from space already available since 1991 with ERS-1, ERS-2 and ENVISAT/ASAR thanks to the so called Wave Mode. This acquisition mode is dedicated to swell measurements in open ocean. The ESA Ocean Swell product already available at CERSAT for the past missions will be routinely produced and freely available to the scientific community...

International Journal of Remote Sensing, 2015

This paper represents a consensus on the state-of-the-art in wind retrieval using synthetic apert... more This paper represents a consensus on the state-of-the-art in wind retrieval using synthetic aperture radar (SAR), after the SEASAR 2012 workshop "Advances in SAR Oceanography" hosted by the European Space Agency (ESA) and the Norwegian Space Centre in Tromsø, Norway 18–22 June 2012. We document the recent advances of the methodologies, which are capitalizing on the improved capabilities of the modern generation of SAR sensors providing Doppler grid and multi-polarizations. The many applications of SAR wind retrieval have also benefitted from on the improved availability of wide swath modes (~500 km) with excellent coverage, giving much better overview of regional and mesoscale wind features. The accuracy of offshore wind retrieval is robust and generally in the order of 1.5 m/s in speed and 20° in direction, whereas the new methodologies steadily improve the performance for the more challenging conditions near cyclones and complex coastal topography.

Geophysical Research Letters, 2015

Swell evolution from the open ocean into sea ice is poorly understood, in particular the amplitud... more Swell evolution from the open ocean into sea ice is poorly understood, in particular the amplitude attenuation expected from scattering and dissipation. New synthetic aperture radar (SAR) data from Sentinel-1 wave mode reveal intriguing patterns of bright oscillating lines shaped like instant noodles. We investigate cases in which the oscillations are in the azimuth direction, around a straight line in the range direction. This observation is interpreted as the distortion by the SAR processing of crests from a first swell, due to the presence of a second swell. Since deviations from a straight line should be proportional to the orbital velocity towards the satellite, swell height can be estimated, from 1.5 to 5 m in the present case. The evolution of this 13 s period swell across the ice pack is consistent with an exponential attenuation on a length scale of 200 km.

2012 IEEE International Geoscience and Remote Sensing Symposium, 2012

ABSTRACT So far, sea surface scattering polarization sensitivity is still difficult to fully unde... more ABSTRACT So far, sea surface scattering polarization sensitivity is still difficult to fully understand. To gain understanding, full polarization C-band data spectral analysis is considered and the de-polarization (HV) and polarization ratio (PR) are jointly analysed with in-situ wind and wave observations.

Atmospheric phenomena often leave fingerprints on the sea surface, which are detectable by synthe... more Atmospheric phenomena often leave fingerprints on the sea surface, which are detectable by synthetic aperture radar (SAR). Here we present some representative examples of SAR images acquired by the Advanced

Remote Sensing of Environment, 2015

The offshore wind climatology in the Northern European seas is analysed from ten years of Envisat... more The offshore wind climatology in the Northern European seas is analysed from ten years of Envisat synthetic aperture radar (SAR) images using a total of 9256 scenes, ten years of QuikSCAT and two years of ASCAT gridded ocean surface vector wind products and high-quality wind observations from four meteorological masts in the North Sea. The traditional method for assessment of the wind resource for wind energy application is through analysis of wind speed and wind direction observed during one or more years at a meteorological mast equipped with well-calibrated anemometers at several levels. The cost of such measurements is very high and therefore they are only sparsely available. An alternative method is the application of satellite remote sensing. Comparison of wind resource statistics from satellite products is presented and discussed including the uncertainty on the wind resource. The diurnal wind variability is found to be negligible at some location but up to 0.5 m s −1 at two sites. Synergetic use of observations from multiple satellites in different orbits provides wind observations at six times in the diurnal cycle and increases the number of observations. At Horns Rev M2, FINO1 and Greater Gabbard satellite and in situ collocated samples show differences in mean wind speed of −2%, −1% and 3%, respectively. At Egmond aan Zee the difference is 10%. It is most likely due to scatterometer data sampled further offshore than at the meteorological mast. Comparing energy density with all samples at Horns Rev M2 shows overestimation 7-19% and at FINO1 underestimation 2-5% but no clear conclusion can be drawn as the comparison data are not collocated. At eight new offshore wind farm areas in Denmark, the variability in mean energy density observed by SAR ranges from 347 W m −2 in Sejerøbugten to 514 W m −2 at Horns Rev 3. The spatial variability in the near-shore areas is much higher than at areas located further offshore.

OCEANS 2007 - Europe, 2007

In coastal oceanography, currents are difficult to measure with a good temporal and spatial resol... more In coastal oceanography, currents are difficult to measure with a good temporal and spatial resolution. Nevertheless, precise knowledge of these currents is crucial for certain applications such as pollution monitoring. Up until now, very few instruments have been able to provide current measurements. Although techniques based on HF radar and satellite-based Synthetic Aperture Radar(SAR) are promising, comparisons between these two approaches must be carefully formulated since the approaches differ in terms of scattering geometry, radiation frequency, and antenna footprint. In this document, we present a brief review of these two approaches as well as a comparison between them using data acquired over the Iroise Sea in France. Since the dominant source of currents in this area is tidal in nature, we also compare the results to the currents predicted by the tidal model MARS2D. The results are encouraging: the SAR-derived currents (specifically, the component of the current in the radial direction along the SAR beam) are qualitatively similar to the equivalent projected radial components deduced from HF measurements and MARS2D output. It must be noted, however, that the HF radar results may be compromised by the presence of island, and the SAR results may be compromised owing to the sensitivity to wind waves.

ABSTRACT Several algorithms have been proposed to retrieve near-surface wind fields from C-band s... more ABSTRACT Several algorithms have been proposed to retrieve near-surface wind fields from C-band synthetic aperture radar (SAR) images acquired over the ocean. They mainly differ in the way how to retrieve wind direction. Conventionally, the wind direction is taken from an atmospheric model or extracted from linear features visible on SAR images. Recently a new wind retrieval algorithm has been proposed by Mouche et al. (2012), which includes also the Doppler shift induced by motions of the sea surface. We have tested this algorithm on complex wind fields encountered over the Black Sea. It is shown that the new algorithm yields better near-surface wind fields than conventional wind retrieval algorithms.