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2D ocean waves spectra from space: a challenge for validation and synergetic use ArchiMer
Mouche, Alexis; He, W.; Husson, R.; Guitton, Gilles; Chapron, Bertrand; Li, Huimin.
Sentinel-1 A now routinely acquires data over the ocean since 2014. Data are processed by ESA through the Payload Data Ground Segment up to Level-2 for Copernicus users. Level-2 products consist of geo-located geophysical parameters related to wind, waves and ocean current. In particular, Sentinel-1A wave measurements provide 2D ocean swell spectra (2D wave energy distribution as a function of wavelength and direction) as well as integrated parameters such as significant wave height, dominant wavelength and direction for each partition. In 2016, Sentinel-1 B will be launched by ESA and GF-3 by CNSA. Then in 2018, CFOSAT (China France Oceanography Satellite project), a joint mission from the Chinese and French Space Agencies, will be launched. They will...
Tipo: Text Palavras-chave: Ocean remote sensing; Synthetics aperture radar; Ocean wave-spectrometer; 2D ocean wave spectrum; Level-4.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00364/47469/47488.pdf
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A C-Band Geophysical Model Function for Determining Coastal Wind Speed Using Synthetic Aperture Radar ArchiMer
Lu, Yiru; Zhang, Biao; Perrie, William; Mouche, Alexis; Li, Xiaofeng; Wang, He.
A new geophysical model function (GMF), called C_SARMOD2, has been developed to relate high-resolution C-band normalized radar cross section (NRCS), acquired in VV polarization over the ocean, to the 10-m height wind speed. A total of 3078 RADARSAT-2 and Sentinel-1A VV-polarized synthetic aperture radar (SAR) images, acquired under different wind speed conditions, were collocated with in situ buoy measurements. The paired dataset was used to derive transfer functions and coefficients of C_SARMOD2, and then to validate the wind speed retrievals. The comparison between SAR-retrieved wind speeds and buoy measurements show almost no bias and a root mean square error of 1.84 m/s. Two representative quad-and dual-polarization SAR images, acquired from coastal...
Tipo: Text Palavras-chave: Coastal wind speed; Geophysical model function (GMF); Synthetic aperture radar (SAR).
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00452/56390/60555.pdf
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A labelled ocean SAR imagery dataset of ten geophysical phenomena from Sentinel‐1 wave mode ArchiMer
Wang, Chen; Mouche, Alexis; Tandeo, Pierre; Stopa, Justin; Longépé, Nicolas; Erhard, Guillaume; Foster, Ralph C.; Vandemark, Douglas; Chapron, Bertrand.
The Sentinel‐1 mission is part of the European Copernicus program aiming at providing observations for Land, Marine and Atmosphere Monitoring, Emergency Management, Security and Climate Change. It is a constellation of two (Sentinel‐1 A and B) Synthetic Aperture Radar (SAR) satellites. The SAR wave mode (WV) routinely collects high‐resolution SAR images of the ocean surface during day and night and through clouds. In this study, a subset of more than 37,000 SAR images is labelled corresponding to ten geophysical phenomena, including both oceanic and meteorologic features. These images cover the entire open ocean and are manually selected from Sentinel‐1A WV acquisitions in 2016. For each image, only one prevalent geophysical phenomenon with its prescribed...
Tipo: Text Palavras-chave: Manual labelling; Ocean surface phenomena; Sentinel-1 wave mode; Synthetic aperture radar.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00512/62406/66659.pdf
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A new generation of Tropical Cyclone Size measurements from space ArchiMer
Reul, Nicolas; Chapron, Bertrand; Zabolotskikh, E.; Donlon, C.; Mouche, Alexis; Tenerelli, Joseph; Collard, F.; Piolle, Jean-francois; Fore, A.; Yueh, S.; Cotton, J.; Francis, P.; Quilfen, Yves; Kudryavtsev, V..
Combined microwave brightness temperature measurements from recent L- and dual C-band satellite radiometers provide new estimates of surface wind speed structure in Tropical Cyclones which enhances temporal sampling capability for gale (34-knots), damaging (50-knots) and destructive (64-knots) wind radii. Wind radii estimates in Tropical Cyclones (TC) are crucial to help determine the TC wind structure for the production of effective warnings and to constrain initial conditions for a number of applications. In that context, we report on the capabilities of a new generation of satellite microwave radiometers operating at L-band frequency (~1.4 GHz) and dual C-band (~6.9 and 7.3 GHz). These radiometers provide wide swath (> 1000 km) coverage at a spatial...
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Ano: 2017 URL: http://archimer.ifremer.fr/doc/00376/48758/49151.pdf
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A new ocean SAR cross-spectral parameter: definition and directional property using the global Sentinel-1 measurements ArchiMer
Li, Huimin; Chapron, Bertrand; Mouche, Alexis; Stopa, Justin.
Space‐borne synthetic aperture radar (SAR) measurements have already been proven to be invaluable in detecting and quantifying properties of ocean swell systems. With the improved spatial resolution, Sentinel‐1 wave mode measurements can further be extended towards shorter scale waves, i.e. within the surface wave equilibrium range. In this study, a new parameter is derived from filtering SAR image cross‐spectra around range‐traveling intermediate wind waves (wavelengths 15‐20 m). This parameter captures both the radar cross section variability and its time evolution. Given the dependence of intermediate waves on local wind field, this parameter is statistically documented to confirm its sensitivity to both wind speed and wind direction. Comparable to...
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Ano: 2019 URL: https://archimer.ifremer.fr/doc/00482/59394/62160.pdf
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A simplified asymptotic theory for ocean surface electromagnetic wave scattering ArchiMer
Mouche, Alexis; Chapron, Bertrand; Reul, Nicolas.
The normalized radar cross-section ( NRCS) expression of the Local Curvature Approximation (LCA-1) is derived to first order. The polarization sensitivity of this model is compared to the Kirchhoff Approximation ( KA), Two-Scale Model (TSM), Small Slope Approximation (SSA-1) and Small Perturbation Method (SPM-1) to first order in the backscattering configuration. Analytical comparisons and numerical simulations show that LCA-1 and TSM could be rewritten with the same formulation and that their polarization sensitivities are comparable. Comparisons with experimental data acquired in C- and Ku-band reveal that the polarization sensitivities of these models are not adequate. However, the NRCS azimuth modulation predicted by LCA-1 is found to be dependent on...
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Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/publication-3001.pdf
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A study of the slope probability density function of the ocean waves from radar observations ArchiMer
Hauser, D.; Caudal, G.; Guimbard, Sebastien; Mouche, Alexis.
Radar observations of the sea surface at C-Band and small incidence angles are used to investigate some properties of the surface slope probability density function (pdf). The method is based on the analysis of the variation of the radar cross-section with incidence angle, assuming a backscattering process following the Geometrical Optics theory. First, we assess the limit of this model in our experimental configuration by using simulations of radar cross-sections with a more accurate backscattering model, namely the Physical Optics model. We show that roughness properties with scales larger than 12 cm can be analyzed in our configuration (C-Band, incidence 7 to 16 degrees). The radar data are then analyzed in terms of filtered mean square slope under the...
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Ano: 2008 URL: http://archimer.ifremer.fr/doc/00000/11028/33570.pdf
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Analysis of Dual-Frequency Ocean Backscatter Measurements at Ku- and Ka-Bands Using Near-Nadir Incidence GPM Radar Data ArchiMer
Nouguier, Frederic; Mouche, Alexis; Rascle, Nicolas; Chapron, Bertrand; Vandemark, Douglas.
Global colocalized ocean surface measurements using the Global Precipitation Measurement near-nadir dual-frequency Ku- and Ka-band microwave measurements are analyzed and compared. Focusing on the Ka and Ku cross-sections fall-off with incidence angles, the contemporaneous measurements enable to more precisely document differing ocean scattering characteristics for both microwave frequencies. Sensitivity with wind speed and significant wave height is further reported using global comparisons with numerical estimates. As demonstrated, the bifrequency capability can provide direct means to efficiently separate short-scale wave contributions, between mean squared slope and curvature characteristics, and to further gain valuable insights concerning near-nadir...
Tipo: Text Palavras-chave: Microwave; Radar cross section; Scattering; Spaceborne radar.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00352/46334/47128.pdf
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Application of a new algorithm using Doppler information to retrieve complex wind fields over the Black Sea from ENVISAT SAR images ArchiMer
Alpers, Werner; Mouche, Alexis; Horstmann, Jochen; Ivanov, Andrei Yu.; Barabanov, Vladyslav S..
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 they retrieve the wind direction. Conventionally, the wind direction is taken from atmospheric models or is extracted from the linear features sometimes visible in SAR images. Recently, a new wind retrieval algorithm has been proposed, which also includes the Doppler shift induced by motions of the sea surface. In this article, we apply three wind retrieval algorithms, including the one using Doppler information, to three complex wind events encountered over the Black Sea and compare the SAR-derived wind fields with model wind fields calculated using the high-resolution weather...
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Ano: 2015 URL: http://archimer.ifremer.fr/doc/00253/36390/35443.pdf
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Calibration of the Normalized Radar Cross Section for Sentinel-1 Wave Mode ArchiMer
Li, Huimin; Mouche, Alexis; Stopa, Justin E.; Chapron, Bertrand.
Sentinel-1 (S-1) is a two-satellite constellation for continuity of operational synthetic aperture radar (SAR) observations. Wave mode (WV) is the default mode over open ocean for S-1 to monitor global ocean waves and wind field. Therefore, proper radiometric calibration is essential to accurately infer these geophysical quantities. Based on the global data set acquired by S-1A WV, assessment of normalized radar cross section (NRCS) is carried out through comparison with CMOD5.N predictions over open ocean. The calibration accuracy quantified by NRCS residuals between SAR measurements and CMOD5.N demonstrates distinct features for two incidence angles (23.8° and 36.8°). Particularly, NRCS at 23.8° is overall consistent with CMOD5.N, while NRCS at 36.8°...
Tipo: Text Palavras-chave: CMOD5.N; Radiometric calibration; Sentinel-1A (S-1A); Wave mode (WV).
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00457/56882/59006.pdf
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CFOSAT: A new Chinese-French satellite for joint observations of ocean wind vector and directional spectra of ocean waves ArchiMer
Hauser, D.; Tison, C.; Amiot, T.; Delaye, L.; Mouche, Alexis; Guitton, Gilles; Aouf, L.; Castillan, P..
CFOSAT (the China France Oceanography Satellite) is a joint mission from the Chinese and French Space Agencies, devoted to the observation ocean surface wind and waves so as to improve wind and wave forecast for marine meteorology, ocean dynamics modeling and prediction, climate variability knowledge, fundamental knowledge of surface processes. Currently under Phase D (manufacturing phase), the launch is now planned for mid-2018 the later. The CFOSAT will carry two payloads, both Ku-Band radar: the wave scatterometer (SWIM) and the wind scatterometer (SCAT). Both instruments are based on new concepts with respect to existing satellite-borne wind and wave sensors. Indeed, one of the originalities of CFOSAT is that it will provide simultaneously and in the...
Tipo: Text Palavras-chave: Satellite; Radar; Surface ocean waves; Surface ocean wind; Scatterometer; CFOSAT.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00363/47468/47487.pdf
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Comparing satellite SAR and wind farm wake models ArchiMer
Hasager, C. B.; Vincent, P.; Husson, Romain; Mouche, Alexis; Badger, M.; Pena, A.; Volker, P.; Badger, J.; Di Bella, A.; Palomares, A.; Cantero, E.; Correia, P. M. F..
The aim of the paper is to present offshore wind farm wake observed from satellite Synthetic Aperture Radar (SAR) wind fields from RADARSAT-1/-2 and Envisat and to compare these wakes qualitatively to wind farm wake model results. From some satellite SAR wind maps very long wakes are observed. These extend several tens of kilometres downwind e.g. 70 km. Other SAR wind maps show near-field fine scale details of wake behind rows of turbines. The satellite SAR wind farm wake cases are modelled by different wind farm wake models including the PARK microscale model, the Weather Research and Forecasting (WRF) model in high resolution and WRF with coupled microscale parametrization.
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Ano: 2015 URL: http://archimer.ifremer.fr/doc/00275/38671/37155.pdf
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Direct ocean surface velocity measurements from space: Improved quantitative interpretation of Envisat ASAR observations ArchiMer
Johannessen, J; Chapron, Bertrand; Collard, F; Kudryavtsev, V; Mouche, Alexis; Akimov, D; Dagestad, K.
Previous analysis of Advanced Synthetic Aperture Radar (ASAR) signals collected by ESA's Envisat has demonstrated a very valuable source of high-resolution information, namely, the line-of-sight velocity of the moving ocean surface. This velocity is estimated from a Doppler frequency shift, consistently extracted within the ASAR scenes. The Doppler shift results from the combined action of near surface wind on shorter waves, longer wave motion, wave breaking and surface current. Both kinematic and dynamic properties of the moving ocean surface roughness can therefore be derived from the ASAR observations. The observations are compared to simulations using a radar imaging model extended to include a Doppler shift module. The results are promising....
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Ano: 2008 URL: http://archimer.ifremer.fr/doc/2008/publication-5168.pdf
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DopSCAT: A mission concept for simultaneous measurements of marine winds and surface currents ArchiMer
Fois, Franco; Hoogeboom, Peter; Le Chevalier, Francois; Stoffelen, Ad; Mouche, Alexis.
A radar scatterometer operates by transmitting a pulse of microwave energy toward the ocean's surface and measuring the normalized (per-unit-surface) radar backscatter coefficient (σ°). The primary application of scatterometry is the measurement of near-surface ocean winds. By combining σ° measurements from different azimuth angles, the 10 m vector wind can be determined through a Geophysical Model Function (GMF), which relates wind and backscatter. This paper proposes a mission concept for the measurement of both oceanic winds and surface currents, which makes full use of earlier C-band radar remote sensing experience. For the determination of ocean currents, in particular, the novel idea of using two chirps of opposite slope is introduced. The...
Tipo: Text Palavras-chave: Ocean surface currents; Ocean Doppler signature; Doppler scatterometry.
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00312/42306/41638.pdf
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Earth-viewing L-band radiometer sensing of sea surface scattered celestial sky radiation - Part I: General characteristics ArchiMer
Tenerelli, Joseph; Reul, Nicolas; Mouche, Alexis; Chapron, Bertrand.
The "galactic glitter" phenomenon at L-band, i.e., the scattering of celestial sky radiation by the rough ocean surface, is examined here as a potential source of error for sea surface salinity (SSS) remote sensing. We begin by considering the transformations that must be applied to downwelling celestial noise in order to compute the eventual impact on the antenna temperature. Then, outside the context of any particular measurement system, we use approximate scattering models along with a model for the equilibrium wind wave spectrum to examine how the scattered signal at the surface might depend on the geophysical conditions and scattering geometry. It is found that, when the specular point lies far away from the galactic plane, where the incident...
Tipo: Text Palavras-chave: Scattering; Remote sensing; Radiometry.
Ano: 2008 URL: http://archimer.ifremer.fr/doc/2008/publication-3922.pdf
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Estimates of ocean wave heights and attenuation in sea ice using the SAR wave mode on Sentinel-1A ArchiMer
Ardhuin, Fabrice; Collard, Fabrice; Chapron, Bertrand; Ardhuin, Fanny; Guitton, Gilles; Mouche, Alexis; Stopa, Justin.
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-1A 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 toward the satellite, swell height can be estimated, from 1.5 to 5 m in the present case. The evolution of this...
Tipo: Text Palavras-chave: Ocean waves; SAR; Sea ice.
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00256/36718/35332.pdf
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Extrapolating Satellite Winds to Turbine Operating Heights ArchiMer
Badger, Merete; Pena, Alfredo; Hahmann, Andrea N.; Mouche, Alexis; Hasager, Charlotte B..
Ocean wind retrievals from satellite sensors are typically performed for the standard level of 10 m. This restricts their full exploitation for wind energy planning, which requires wind information at much higher levels where wind turbines operate. A new method is presented for the vertical extrapolation of satellite-based wind maps. Winds near the sea surface are obtained from satellite data and used together with an adaptation of the Monin–Obukhov similarity theory to estimate the wind speed at higher levels. The thermal stratification of the atmosphere is taken into account through a long-term stability correction that is based on numerical weather prediction (NWP) model outputs. The effect of the long-term stability correction on the wind profile is...
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Ano: 2016 URL: http://archimer.ifremer.fr/doc/00334/44477/44158.pdf
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GF-3 SAR Ocean Wind Retrieval: The First View and Preliminary Assessment ArchiMer
Wang, He; Yang, Jingsong; Mouche, Alexis; Shao, Weizeng; Zhu, Jianhua; Ren, Lin; Xie, Chunhua.
Gaofen-3 (GF-3) is the first Chinese civil C-band synthetic aperture radar (SAR) launched on 10 August 2016 by the China Academy of Space Technology (CAST), which operates in 12 imaging modes with a fine spatial resolution up to 1 m. As one of the primary users, the State Oceanic Administration (SOA) operationally processes GF-3 SAR Level-1 products into ocean surface wind vector and plans to officially release the near real-time SAR wind products in the near future. In this paper, the methodology of wind retrieval at C-band SAR is introduced and the first results of GF-3 SAR-derived winds are presented. In particular, the case of the coastal katabatic wind off the west coast of the U.S. captured by GF-3 is discussed. The preliminary accuracy assessment of...
Tipo: Text Palavras-chave: GF-3; Synthetic aperture radar (SAR); Ocean surface wind; Validation.
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00396/50731/51435.pdf
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Global C-Band Envisat, RADARSAT-2 and Sentinel-1 SAR measurements in copolarization and cross-polarization ArchiMer
Mouche, Alexis; Chapron, Bertrand.
Using colocated ASCAT and ECMWF winds, a careful global analysis of ENVISAT and Sentinel-1 synthetic aperture radar (SAR) measurements helps to refine, at medium resolution (tens of kilometers) and especially for HH configuration, a C-band geophysical model function (GMF, i.e., C-SARMOD) to analyze wind sensitivity for different incidence and azimuth angles. Results unify major findings from previous global and case studies for polarization ratio (PR, VV/HH), polarization difference (PD, VV-HH), and cross-polarization (CP). At lower level than standard two-scale predictions, PR increases with increasing incidence angle and decreases with increasing wind speed. PR further exhibits a strong azimuthal modulation, with maximum values in downwind...
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Ano: 2015 URL: http://archimer.ifremer.fr/doc/00289/40022/38605.pdf
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Importance of the sea surface curvature to interpret the normalized radar cross section - art. no. C10002 ArchiMer
Mouche, Alexis; Chapron, Bertrand; Reul, Nicolas; Hauser, D; Quilfen, Yves.
[1] Asymptotic models ( small perturbation and small slope approximation at first-order, Kirchhoff approximation or two-scale model) used to predict the normalized radar cross section of the sea surface generally fail to reproduce in detail backscatter radar measurements. In particular, the predicted polarization ratio versus incidence and azimuth angles is not in agreement with experimental data. This denotes the inability of these standard models to fully take into account the roughness properties with respect to the sensor's configuration of measurement ( frequency, incidence, and polarization). On the basis of particular assumptions, to decompose the scattered electromagnetic field between zones covered with freely propagating waves and others where...
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Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/publication-3577.pdf
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