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Registros recuperados: 35
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A Multivariate Regression Approach to Adjust AATSR Sea Surface Temperature to In Situ Measurements ArchiMer
Tandeo, Pierre; Autret, Emmanuelle; Piolle, Jean-francois; Tournadre, Jean; Ailliot, Pierre.
The Advanced Along-Track Scanning Radiometer (AATSR) onboard Envisat is designed to provide very accurate measurements of sea surface temperature (SST). Using colocated in situ drifting buoys, a dynamical matchup database (MDB) is used to assess the AATSR-derived SST products more precisely. SST biases are then computed. Currently, Medspiration AATSR SST biases are discrete values and can introduce artificial discontinuities in AATSR level-2 SST fields. The new AATSR SST biases presented in this letter are continuous. They are computed, for nighttime and best proximity confidence data, by linear regression with different MDB covariables (wind speed, latitude, aerosol optical depth, etc.). As found, the difference between dual-view and nadir-only SST...
Tipo: Text Palavras-chave: Validation; Sea surface temperature (SST); Remote sensing; Advanced Along Track Scanning Radiometer (AATSR).
Ano: 2009 URL: http://archimer.ifremer.fr/doc/2009/publication-6135.pdf
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A satellite altimeter model for ocean slick detection - art. no. C04004 ArchiMer
Tournadre, Jean; Chapron, Bertrand; Reul, Nicolas; Vandemark, D.
[1] About 5% of Ku-band altimeter ocean data are degraded by the occurrence of high radar return cross sections (sigma(0)), usually called sigma(0) blooms. During blooms, which occur during no or low wind conditions, the mean altimeter waveform can significantly depart from the expected shape. In about 60% of the cases the waveforms are distorted to such an extent that either the range tracker loses lock or the off-nadir angle estimate becomes unrealistic. The analysis of high data rate altimeter waveforms during bloom events reveals the presence of V-shaped patterns similar to the ones observed during rain events. These patterns trace small-scale (i.e., smaller than the altimeter footprint) changes in surface backscatter. Such variations of surface...
Tipo: Text Palavras-chave: Slick; Sigma blooms; Altimeter waveforms.
Ano: 2006 URL: http://archimer.ifremer.fr/doc/2006/publication-1353.pdf
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Altimeter dual-frequency observations of surface winds, waves, and rain rate in tropical cyclone Isabel - art. no. C01004, ArchiMer
Quilfen, Yves; Tournadre, Jean; Chapron, Bertrand.
[1] Extreme weather events such as tropical cyclones are difficult to observe with conventional means. Satellite-based observations provide essential measurements of key parameters governing tropical cyclones. They are critical for short-term forecasting. Radiometers onboard the Defense Meteorological Satellite Program satellite series, WindSat and Tropical Rainfall Measuring Mission satellites, scatterometers onboard the ERS, ADEOS, and QuikScat satellites offer unprecedented synoptic observations of surface wind and atmospheric liquid water content, revealing the storm structures with good accuracy. However, satellite estimates do not provide direct measurements of geophysical parameters and can suffer from limitations linked to the sensors...
Tipo: Text Palavras-chave: Mesearement limitations; Dual frequency altimeter; High resolution measurement; Tropical cyclone.
Ano: 2006 URL: http://archimer.ifremer.fr/doc/2006/publication-1033.pdf
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An inverse estimate of the dynamic topography of the ocean ArchiMer
Legrand, P; Schrama, Ejo; Tournadre, Jean.
The mean dynamic topography of the surface of the ocean is estimated using a finite difference inverse model of the ocean circulation constrained by a prior TOPEX/Poseidon-EGM96 estimate and an ocean density climatology. The EGM96 geoid uncertainties are represented by their full covariance matrix. The model finds a solution that yields a new 1°-resolution dynamic topography estimate with a 5 cm precision. The existence of this solution suggests that the uncertainties in EGM96, despite being much smaller than in previous geopotential models, are nonetheless realistic. The geodetic information constrains the inverse estimate of the ocean circulation, particularly at high latitudes.
Tipo: Text
Ano: 2003 URL: https://archimer.ifremer.fr/doc/2003/publication-361.pdf
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Antarctic icebergs: A significant natural ocean sound source in the Southern Hemisphere ArchiMer
Matsumoto, Haru; Bohnenstiehl, Delwayne R.; Tournadre, Jean; Dziak, Robert P.; Haxel, Joseph H.; Lau, T. -k. A.; Fowler, Matt; Salo, Sigrid A..
In late 2007, two massive icebergs, C19a and B15a, drifted into open water and slowly disintegrated in the southernmost Pacific Ocean. Archived acoustic records show that the high-intensity underwater sounds accompanying this breakup increased ocean noise levels at mid-to-equatorial latitudes over a period of ∼1.5 years. More typically, seasonal variations in ocean noise, which are characterized by austral summer-highs and winter-lows, appear to be modulated by the annual cycle of Antarctic iceberg drift and subsequent disintegration. This seasonal pattern is observed in all three Oceans of the Southern Hemisphere. The life cycle of Antarctic icebergs affects not only marine ecosystem but also the sound environment in far-reaching areas and must be...
Tipo: Text Palavras-chave: Antarctica; Iceberg; Ocean noise; Seasonality; Trend.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00205/31613/30035.pdf
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Antarctic icebergs distributions 1992-2014 ArchiMer
Tournadre, Jean; Bouhier, Nicolas; Girard-ardhuin, Fanny; Remy, F..
Basal melting of floating ice shelves and iceberg calving constitute the two almost equal paths of freshwater flux between the Antarctic ice cap and the Southern Ocean. The largest icebergs (>100 km2) transport most of the ice volume but their basal melting is small compared to their breaking into smaller icebergs that constitute thus the major vector of freshwater. The archives of nine altimeters have been processed to create a database of small icebergs (<8 km2) within open water containing the positions, sizes, and volumes spanning the 1992–2014 period. The intercalibrated monthly ice volumes from the different altimeters have been merged in a homogeneous 23 year climatology. The iceberg size distribution, covering the 0.1–10,000 km2 range,...
Tipo: Text Palavras-chave: Iceberg; Altimetry; Southern Ocean.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00307/41863/41114.pdf
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Antarctic icebergs distributions, 2002-2010 ArchiMer
Tournadre, Jean; Ardhuin, Fanny; Legresy, Benoit.
Interest for icebergs and their possible impact on southern ocean circulation and biology has increased during the recent years. While large tabular icebergs are routinely tracked and monitored using scatterometer data, the distribution of smaller icebergs (less than some km) is still largely unknown as they are difficult to detect operationally using conventional satellite data. In a recent study, Tournadre et al. (2008) showed that small icebergs can be detected, at least in open water, using high resolution (20 Hz) altimeter waveforms. In the present paper, we present an improvement of their method that allows, assuming a constant iceberg freeboard elevation and constant ice backscatter coefficient, to estimate the top-down iceberg surface area and...
Tipo: Text
Ano: 2012 URL: http://archimer.ifremer.fr/doc/00083/19444/17050.pdf
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Antarctic icebergs melt over the Southern Ocean : climatology and impact on sea ice ArchiMer
Merino, Nacho; Le Sommer, Julien; Durand, Gael; Jourdain, Nicolas C.; Madec, Gurvan; Mathiot, Pierre; Tournadre, Jean.
Recent increase in Antarctic freshwater release to the Southern Ocean is suggested to contribute to change in water masses and sea ice. However, climate models differ in their representation of the freshwater sources. Recent improvements in altimetry-based detection of small icebergs and in estimates of the mass loss of Antarctica may help better constrain the values of Antarctic freshwater releases. We propose a model-based seasonal climatology of iceberg melt over the Southern Ocean using state-of-the-art observed glaciological estimates of the Antarctic mass loss. An improved version of a Lagrangian iceberg model is coupled with a global, eddy-permitting ocean/sea ice model and compared to small icebergs observations. Iceberg melt increases sea ice...
Tipo: Text Palavras-chave: Icebergs; Southern Ocean; Sea ice; Freshwater fluxes.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00335/44579/44294.pdf
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Anthropogenic pressure on the open ocean: The growth of ship traffic revealed by altimeter data analysis ArchiMer
Tournadre, Jean.
Marine ecosystems are under increasing anthropogenic pressures from marine and terrestrial activities. Ship traffic, the major cause of change in the open ocean, and its temporal evolution are still largely unknown because of lack of data. Altimeter data provide a new powerful tool to detect and monitor the ship traffic through a method of analysis of echo waveform. The archive of seven altimeter missions has been processed to create a two decade database of ship locations. The estimated annual density maps compare well with the ones obtained from Automatic Identification System. The ship traffic analysis shows a global fourfold growth between 1992 and 2012, the largest increase being observed in the Indian Ocean and the Chinese seas reflecting the world...
Tipo: Text Palavras-chave: Altimetry; Ship traffic; Pollution; Anthropogenic pressure.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00229/34039/32432.pdf
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Cloud and rain effects on ALTIKA/SARAL Ka band radar altimeter. Part I: modeling and mean annual data availability ArchiMer
Tournadre, Jean; Lambin, J; Steunou, N.
The AltiKa project developed by the French Centre National d'Etudes Spatiales is based on a wide-band Ka-band altimeter (35.75 GHz). The technical characteristic of the instrument will offer higher performance both in terms of spatial and vertical resolution that will lead to improved observation of ice, coastal areas, inland waters and wave height. An Indian Space Research Organization satellite, Saral will embark the AltiKa altimeter. The launch is scheduled at the end of 2010. The major drawback of Ka band use is the attenuation of the radar signal by atmospheric liquid water. Clouds and rain effects will thus be a strong constraining factor, because the altimeter link budget imposes an attenuation of less than 3 dB. The impact of rain and clouds on...
Tipo: Text Palavras-chave: Geophysical parameters estimates; Rain and cloud impact; Ka band altimeter.
Ano: 2009 URL: http://archimer.ifremer.fr/doc/2008/publication-4720.pdf
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Cloud and rain effects on ALTIKA/SARAL Ka band radar altimeter. Part II: Definition of a rain/cloud flag ArchiMer
Tournadre, Jean; Lambin, J; Steunou, N.
The main instrument of the French-Indian Altika/ SARAL mission scheduled for launch in 2010, is the Kaband Altika altimeter. The high attenuation due to atmospheric water (liquid or vapor) at this frequency band is the major drawback of the use of Ka-band. In part I of this paper, the impact of rain/clouds on Ka-band data and on the accuracy of the estimates of the geophysical parameters have been analyzed and quantified using an analytical model of waveform. Waveform distortion and errors on the geophysical parameters can be significant especially for small dense clouds and rain cells. It is thus necessary to flag the data potentially affected by rain and clouds. The use of a single channel for Altika prevents the use of the classical dual-frequency rain...
Tipo: Text Palavras-chave: Rain/cloud flag; Rain and cloud impact; Ka band altimeter.
Ano: 2009 URL: http://archimer.ifremer.fr/doc/2008/publication-4721.pdf
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Demonstration of ocean surface salinity microwave measurements from space using AMSR-E data over the Amazon plume ArchiMer
Reul, Nicolas; Saux Picart, Stephane; Chapron, Bertrand; Vandemark, D.; Tournadre, Jean; Salisbury, J..
Microwave Sea Surface Salinity (SSS) measurements can be performed by isolating the emissivity response to salinity changes from numerous geophysical effects, including surface temperature and wind waves. At L-band frequencies (1 to 2 GHz), the sensitivity to SSS is sufficient but it falls off quickly as frequency is increased. Nevertheless, methods using higher microwave frequencies with much lower SSS sensitivity than at L band, can already be tested. In particular, combining 6 and 10 GHz data in vertical polarization efficiently minimizes sea surface roughness and thermal impacts. Using AMSR-E data, the retrieved bi-monthly maps of SSS at 0.5 degrees resolution over the region of the Amazon plume show relative accuracy in-line with the future L-band...
Tipo: Text
Ano: 2009 URL: http://archimer.ifremer.fr/doc/2009/publication-6620.pdf
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Detection of iceberg using Delay Doppler and interferometric Cryosat-2 altimeter data ArchiMer
Tournadre, Jean; Bouhier, Nicolas; Boy, F.; Dinardo, S..
The Cryosat-2 Synthetic Aperture Interferometric Radar Altimeter (SIRAL) altimeter is the first altimeter that can operate in three different modes over the ocean: the classical pulse limited LRM, the Delay Doppler or SAR and the SAR Interferometric modes. It offers a unique opportunity to test, validate and compare the capabilities of the three modes for the detection and analysis of small icebergs (<3 km in length) already demonstrated for classical altimeters. Over most of the sea-ice free ocean, SIRAL operates in LRM mode and the classical iceberg detection algorithm can be applied without modification. It can also be applied to the Reduced SAR or pseudo-LRM data computed from SAR and SARin data. In SAR mode, iceberg signatures are bright spots in...
Tipo: Text Palavras-chave: Small iceberg detection using Cryosat-2 three modes of operation; Estimation of iceberg's area; Estimation of iceberg's free-board from; Interferometric altimeter data.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00439/55089/56586.pdf
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Determination of rain cell characteristics from the analysis of TOPEX altimeter echo waveforms ArchiMer
Tournadre, Jean.
Radar meteorologists have estimated, over a number of years, rainfall rate with ground-based radars. Since the 1970s, use of weather radar as an active technique to measure rainfall from space has been proposed, and a number of radar concepts, including modified radar altimeter design, were proposed. However, no attempt has yet been made to determine rain cell characteristics from available altimeter data. This paper presents a method to estimate rainfall rate and rain cell diameter from TOPEX/Poseidon dual frequency radar altimeter waveforms. The rain-affected waveforms are first selected using a criterion based on a departure from a normal Ku-C-band backscatter coefficient relationship and on a threshold of liquid water content estimated by the TOPEX...
Tipo: Text
Ano: 1998 URL: http://archimer.ifremer.fr/doc/00448/55941/57483.pdf
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Global oceanic precipitation: A joint view by TOPEX and the TOPEX microwave radiometer ArchiMer
Chen, Ge; Chapron, Bertrand; Tournadre, Jean; Katsaros, Kristina; Vandemark, Douglas.
The TOPEX/POSEIDON mission offers the first opportunity to observe rain cells over the ocean by a dual-frequency radar altimeter (TOPEX) and simultaneously observe their natural radiative properties by a three-frequency radiometer (TOPEX microwave radiometer (TMR)). This work is a feasibility study aimed at understanding the capability and potential of the active/passive TOPEX/TMR system for oceanic rainfall detection. On the basis of past experiences in rain flagging, a joint TOPEX/TMR rain probability index is proposed. This index integrates several advantages of the two sensors and provides a more reliable rain estimate than the radiometer alone. One year's TOPEX/TMR TMR data are used to test the performance of the index. The resulting rain frequency...
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Ano: 1997 URL: http://archimer.ifremer.fr/doc/00336/44719/44883.pdf
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Iceberg detection in open water by altimeter waveform analysis ArchiMer
Tournadre, Jean; Whitmer, K; Ardhuin, Fanny.
Small icebergs (edge lengths <1 km) are difficult to detect and track. In a recently published study, it was demonstrated that small targets (ships, islets,...) emerging from the sea can be detected by the analysis of high-rate altimeter waveforms. The analysis of Jason altimeter data revealed that small icebergs also have a detectable signature in the thermal noise part of the altimeter waveforms for open water. These signatures are very similar to that of transponders and are almost deterministic. An automated method based on the detection of parabolic shapes in the thermal part of the waveforms by analysis of the convolution product with a filter has been developed and applied to 1 year of Jason high-rate waveform data. In addition, the minimum...
Tipo: Text Palavras-chave: Antarctica; Iceberg; Altimeter waveform.
Ano: 2008 URL: http://archimer.ifremer.fr/doc/2008/publication-4530.pdf
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Impact of rain cell on scatterometer data: 1. Theory and modeling - art. no. 3225 ArchiMer
Tournadre, Jean; Quilfen, Yves.
[1] The two scatterometers currently in operation, the Ku-band NASA Seawinds on the QuikScat satellite and the C-band AMI-Wind on the ERS-2 satellite, are designed to infer the ocean wind vectors from sea surface radar backscatter measurements. They provide excellent coverage of the ocean, and their wind products are of great value for ocean and meteorological communities. However, the presence of rain within scatterometer cells can significantly modify the sea surface backscatter coefficient and hence alter the wind vector retrieval. These perturbations can hamper the analysis of wind fields within atmospheric low-pressure systems or tropical cyclones. Rain perturbations result from volume scattering and attenuation by raindrops in the atmosphere as well...
Tipo: Text Palavras-chave: Model of interaction; Ocean surface winds; Rain; Scatterometer.
Ano: 2003 URL: http://archimer.ifremer.fr/doc/2003/publication-513.pdf
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Impact of rain cell on scatterometer data: 2. Correction of Seawinds measured backscatter and wind and rain flagging ArchiMer
Tournadre, Jean; Quilfen, Yves.
In October and early November 1999, the GOGP99 experiment collected hydrological, currentmeter, tide recorder, thermistor and drifting buoy data near the Strait of Hormuz. Data analysis provides the water mass structure in the Strait: Persian Gulf Water (PGW) core is banked against the Omani coast, while Indian Ocean Surface Water (IOSW) lies near the Iranian coast. These water masses are most often covered by a homogeneous surface layer. Thermohaline characteristics of the PGW core decrease substantially downstream, from the Persian/Arabian Gulf to the Gulf of Oman. PGW and IOSW thermohaline characteristics and distribution also exhibit notable changes at periods shorter than a month as shown by repeated hydrological sections. The tidal signal measured...
Tipo: Text Palavras-chave: Wind retrieval; Rain; Scatterometer.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/2005/publication-388.pdf
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Impacts of oil spills on altimeter waveforms and radar backscatter cross-section ArchiMer
Cheng, Yongcun; Tournadre, Jean; Li, Xiaofeng; Xu, Qing; Chapron, Bertrand.
Ocean surface films can damp short capillary-gravity waves, reduce the surface mean square slope, and induce “sigma0 blooms” in satellite altimeter data. No study has ascertained the effect of such film on altimeter measurements due to lack of film data. The availability of Environmental Response Management Application (ERMA) oil cover, daily oil spill extent and thickness data acquired during the Deepwater Horizon (DWH) oil spill accident provides a unique opportunity to evaluate the impact of surface film on altimeter data. In this study, the Jason-1/2 passes nearest to the DWH platform are analyzed to understand the waveform distortion caused by the spill as well as the variation of σ0 as a function of oil thickness, wind speed and radar band. Jason-1/2...
Tipo: Text Palavras-chave: Oil spill; Altimeter; Sigma0 bloom; Waveform.
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00381/49203/49635.pdf
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Interactions between the Agulhas Current and the eastern margin of the Agulhas Bank ArchiMer
Krug, Marjolaine; Tournadre, Jean; Dufois, F..
Interactions between the Agulhas Current and the ecologically important region of the Agulhas Bank are studied through the analysis of high resolution along-track altimetry, merged mapped altimetry and in situ measurements of current speed and direction undertaken from a moored Accoustic Doppler Current Profiler (ADCP). Comparisons between current observations collected from the ADCP and the satellite altimeters are made to evaluate the validity of the analysis conducted on the altimetry. Both altimetry and in situ observations show that Natal Pulses are a major driver of variability along the eastern margin of the Agulhas Bank. On average, it is estimated that the circulation along the eastern margin of the Agulhas Bank is influenced by Natal Pulses for...
Tipo: Text Palavras-chave: Agulhas Current; Agulhas Bank; Natal pulse; Satellite oceanography; Altimetry.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00186/29676/28457.pdf
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