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Pierre Prandi - One of the best experts on this subject based on the ideXlab platform.
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Arctic Sea Level During the Satellite Altimetry Era
Surveys in Geophysics, 2017Co-Authors: A. Carret, O. B. Andersen, Michael Ablain, Jon-arild Johannessen, Ana Blázquez, Pierre Prandi, Anny CazenaveAbstract:Results of the sea-level budget in the high latitudes (up to 80°N) and the Arctic Ocean during the satellite Altimetry era. We investigate the closure of the sea-level budget since 2002 using two Altimetry sea-level datasets based on the Envisat waveform retracking: temperature and salinity data from the ORAP5 reanalysis, and Gravity Recovery And Climate Experiment (GRACE) space gravimetry data to estimate the steric and mass components. Regional sea-level trends seen in the Altimetry map, in particular over the Beaufort Gyre and along the eastern coast of Greenland, are of halosteric origin. However, in terms of regional average over the region ranging from 66°N to 80°N, the steric component contributes little to the observed sea-level trend, suggesting a dominant mass contribution in the Arctic region. This is confirmed by GRACE-based ocean mass time series that agree well with the Altimetry-based sea-level time series. Direct estimate of the mass component is not possible prior to GRACE. Thus, we estimated the mass contribution from the difference between the Altimetry-based sea level and the steric component. We also investigate the coastal sea level with tide gauge records. Twenty coupled climate models from the CMIP5 project are also used. The models lead us to the same conclusions concerning the halosteric origin of the trend patterns.
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Monitoring Sea Level in the Coastal Zone with Satellite Altimetry and Tide Gauges
Surveys in Geophysics, 2017Co-Authors: Paolo Cipollini, Francisco M. Calafat, Svetlana Jevrejeva, Angelique Melet, Pierre PrandiAbstract:We examine the issue of sustained measurements of sea level in the coastal zone, first by summarizing the long-term observations from tide gauges, then showing how those are now complemented by improved satellite Altimetry products in the coastal ocean. We present some of the progresses in coastal Altimetry, both from dedicated reprocessing of the radar waveforms and from the development of improved corrections for the atmospheric effects. This trend towards better altimetric data at the coast comes also from technological innovations such as Ka-band Altimetry and SAR Altimetry, and we discuss the advantages deriving from the AltiKa Ka-band altimeter and the SIRAL altimeter on CryoSat-2 that can be operated in SAR mode. A case study along the UK coast demonstrates the good agreement between coastal Altimetry and tide gauge observations, with root mean square differences as low as 4 cm at many stations, allowing the characterization of the annual cycle of sea level along the UK coasts. Finally, we examine the evolution of the sea level trend from the open to the coastal ocean along the western coast of Africa, comparing standard and coastally improved products. Different products give different sea level trend profiles, so the recommendation is that additional efforts are needed to study sea level trends in the coastal zone from past and present satellite altimeters. Further improvements are expected from more refined processing and screening of data, but in particular from the constant improvements in the geophysical corrections.
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Sea level variability in the Arctic Ocean observed by satellite Altimetry
Ocean Science Discussions, 2012Co-Authors: Pierre Prandi, Michael Ablain, Anny Cazenave, Nicolas PicotAbstract:Abstract. We investigate sea level variability in the Arctic Ocean from observations. Variability estimates are derived both at the basin scale and on smaller local spatial scales. The periods of the signals studied vary from high frequency (intra-annual) to long term trends. We also investigate the mechanisms responsible for the observed variability. Different data types are used, the main one being a recent reprocessing of satellite Altimetry data in the Arctic Ocean. Satellite Altimetry data is compared to tide gauges measurements, steric sea level derived from temperature and salinity fields and GRACE ocean mass estimates. We establish a consistent regional sea level budget over the GRACE availability era (2003–2009) showing that the sea level drop observed by Altimetry over this period is driven by ocean mass loss rather than steric effects. The comparison of Altimetry and tide gauges time series show that the two techniques are in good agreement regarding sea level trends. Coastal areas of high variability in the Altimetry record are also consistent with tide gauges records. An EOF analysis of September mean Altimetry fields allows identifying two regions of wind driven variability in the Arctic Ocean: the Beaufort Gyre region and the coastal European and Russian Arctic. Such patterns are related to atmospheric regimes through the Arctic Oscillation and Dipole Anomaly.
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A New Estimation of Mean Sea Level in the Arctic Ocean from Satellite Altimetry
Marine Geodesy, 2012Co-Authors: Pierre Prandi, Michael Ablain, Anny Cazenave, Nicolas PicotAbstract:Sea level monitoring in the Arctic Ocean can provide useful information in the context of a rapid change of several parts of the Arctic climate system. Satellite Altimetry systems are affected by various problems at high latitudes. As a consequence, no precise and reliable mean sea level record is available yet from Altimetry products. After identifying some of the issues that affect satellite Altimetry in the Arctic Ocean region, we describe the tailored processing that has been applied to along-track mono-mission Altimetry data. We generate a new dataset of weekly gridded sea level anomaly fields over the Arctic region for the period spanning from 1993 to 2009 based on multisatellite Altimetry missions. We demonstrate the improvements achieved by this new dataset, among which a better data coverage. The grids are used to describe some features of mean sea level variability in the Arctic Ocean both at basin-wide and local scales. The regional trend estimated for the Arctic Ocean mean sea level over all latitudes from 66 degrees N to 82 degrees N is 3.6 mm/yr with an uncertainty of 1.3 mm/yr (90% confidence) and without any glacial isostatic adjustment (GIA) correction applied. The record displays large inter-annual variability, but no strong correlation with climate indices was found. Spatial patterns in sea level trends and variability over the Arctic region are also investigated.
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is coastal mean sea level rising faster than the global mean a comparison between tide gauges and satellite Altimetry over 1993 2007
Geophysical Research Letters, 2009Co-Authors: Pierre Prandi, Anny Cazenave, M. BeckerAbstract:[1] Based on a careful selection of tide gauges records from the Global Sea Level Observing System network, we investigate whether coastal mean sea level is rising faster than the global mean derived from satellite Altimetry over the January 1993–December 2007 time span. Over this 15-year time span, mean coastal rate of sea level rise is found to be +3.3 ± 0.5 mm/yr, in good agreement with the Altimetry-derived rate of +3.4 ± 0.1 mm/yr. Tests indicate that the trends are statistically significant, hence coastal sea level does not rise faster than the global mean. Although trends agree well, tide gauges-based mean sea level exhibits much larger interannual variability than Altimetry-based global mean. Interannual variability in coastal sea level appears related to the regional variability in sea level rates reported by satellite Altimetry. When global mean sea level is considered (as allowed by satellite Altimetry coverage), interannual variability is largely smoothed out.
Anny Cazenave - One of the best experts on this subject based on the ideXlab platform.
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Arctic Sea Level During the Satellite Altimetry Era
Surveys in Geophysics, 2017Co-Authors: A. Carret, O. B. Andersen, Michael Ablain, Jon-arild Johannessen, Ana Blázquez, Pierre Prandi, Anny CazenaveAbstract:Results of the sea-level budget in the high latitudes (up to 80°N) and the Arctic Ocean during the satellite Altimetry era. We investigate the closure of the sea-level budget since 2002 using two Altimetry sea-level datasets based on the Envisat waveform retracking: temperature and salinity data from the ORAP5 reanalysis, and Gravity Recovery And Climate Experiment (GRACE) space gravimetry data to estimate the steric and mass components. Regional sea-level trends seen in the Altimetry map, in particular over the Beaufort Gyre and along the eastern coast of Greenland, are of halosteric origin. However, in terms of regional average over the region ranging from 66°N to 80°N, the steric component contributes little to the observed sea-level trend, suggesting a dominant mass contribution in the Arctic region. This is confirmed by GRACE-based ocean mass time series that agree well with the Altimetry-based sea-level time series. Direct estimate of the mass component is not possible prior to GRACE. Thus, we estimated the mass contribution from the difference between the Altimetry-based sea level and the steric component. We also investigate the coastal sea level with tide gauge records. Twenty coupled climate models from the CMIP5 project are also used. The models lead us to the same conclusions concerning the halosteric origin of the trend patterns.
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Effect of the processing methodology on satellite Altimetry-based global mean sea level rise over the Jason-1 operating period
Journal of Geodesy, 2014Co-Authors: Olivier Henry, Michael Ablain, Benoit Meyssignac, Steve Nerem, Dallas Masters, Anny Cazenave, Gilles GarricAbstract:Determining how the global mean sea level (GMSL) evolves with time is of primary importance to understand one of the main consequences of global warming and its potential impact on populations living near coasts or in low-lying islands. Five groups are routinely providing satellite Altimetry-based estimates of the GMSL over the Altimetry era (since late 1992). Because each group developed its own approach to compute the GMSL time series, this leads to some differences in the GMSL interannual variability and linear trend. While over the whole high-precision Altimetry time span (1993–2012), good agreement is noticed for the computed GMSL linear trend (of $$3.1\pm 0.4$$ 3.1 ± 0.4 mm/year), on shorter time spans (e.g., $${
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Sea level variability in the Arctic Ocean observed by satellite Altimetry
Ocean Science Discussions, 2012Co-Authors: Pierre Prandi, Michael Ablain, Anny Cazenave, Nicolas PicotAbstract:Abstract. We investigate sea level variability in the Arctic Ocean from observations. Variability estimates are derived both at the basin scale and on smaller local spatial scales. The periods of the signals studied vary from high frequency (intra-annual) to long term trends. We also investigate the mechanisms responsible for the observed variability. Different data types are used, the main one being a recent reprocessing of satellite Altimetry data in the Arctic Ocean. Satellite Altimetry data is compared to tide gauges measurements, steric sea level derived from temperature and salinity fields and GRACE ocean mass estimates. We establish a consistent regional sea level budget over the GRACE availability era (2003–2009) showing that the sea level drop observed by Altimetry over this period is driven by ocean mass loss rather than steric effects. The comparison of Altimetry and tide gauges time series show that the two techniques are in good agreement regarding sea level trends. Coastal areas of high variability in the Altimetry record are also consistent with tide gauges records. An EOF analysis of September mean Altimetry fields allows identifying two regions of wind driven variability in the Arctic Ocean: the Beaufort Gyre region and the coastal European and Russian Arctic. Such patterns are related to atmospheric regimes through the Arctic Oscillation and Dipole Anomaly.
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A New Estimation of Mean Sea Level in the Arctic Ocean from Satellite Altimetry
Marine Geodesy, 2012Co-Authors: Pierre Prandi, Michael Ablain, Anny Cazenave, Nicolas PicotAbstract:Sea level monitoring in the Arctic Ocean can provide useful information in the context of a rapid change of several parts of the Arctic climate system. Satellite Altimetry systems are affected by various problems at high latitudes. As a consequence, no precise and reliable mean sea level record is available yet from Altimetry products. After identifying some of the issues that affect satellite Altimetry in the Arctic Ocean region, we describe the tailored processing that has been applied to along-track mono-mission Altimetry data. We generate a new dataset of weekly gridded sea level anomaly fields over the Arctic region for the period spanning from 1993 to 2009 based on multisatellite Altimetry missions. We demonstrate the improvements achieved by this new dataset, among which a better data coverage. The grids are used to describe some features of mean sea level variability in the Arctic Ocean both at basin-wide and local scales. The regional trend estimated for the Arctic Ocean mean sea level over all latitudes from 66 degrees N to 82 degrees N is 3.6 mm/yr with an uncertainty of 1.3 mm/yr (90% confidence) and without any glacial isostatic adjustment (GIA) correction applied. The record displays large inter-annual variability, but no strong correlation with climate indices was found. Spatial patterns in sea level trends and variability over the Arctic region are also investigated.
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is coastal mean sea level rising faster than the global mean a comparison between tide gauges and satellite Altimetry over 1993 2007
Geophysical Research Letters, 2009Co-Authors: Pierre Prandi, Anny Cazenave, M. BeckerAbstract:[1] Based on a careful selection of tide gauges records from the Global Sea Level Observing System network, we investigate whether coastal mean sea level is rising faster than the global mean derived from satellite Altimetry over the January 1993–December 2007 time span. Over this 15-year time span, mean coastal rate of sea level rise is found to be +3.3 ± 0.5 mm/yr, in good agreement with the Altimetry-derived rate of +3.4 ± 0.1 mm/yr. Tests indicate that the trends are statistically significant, hence coastal sea level does not rise faster than the global mean. Although trends agree well, tide gauges-based mean sea level exhibits much larger interannual variability than Altimetry-based global mean. Interannual variability in coastal sea level appears related to the regional variability in sea level rates reported by satellite Altimetry. When global mean sea level is considered (as allowed by satellite Altimetry coverage), interannual variability is largely smoothed out.
M. Becker - One of the best experts on this subject based on the ideXlab platform.
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is coastal mean sea level rising faster than the global mean a comparison between tide gauges and satellite Altimetry over 1993 2007
Geophysical Research Letters, 2009Co-Authors: Pierre Prandi, Anny Cazenave, M. BeckerAbstract:[1] Based on a careful selection of tide gauges records from the Global Sea Level Observing System network, we investigate whether coastal mean sea level is rising faster than the global mean derived from satellite Altimetry over the January 1993–December 2007 time span. Over this 15-year time span, mean coastal rate of sea level rise is found to be +3.3 ± 0.5 mm/yr, in good agreement with the Altimetry-derived rate of +3.4 ± 0.1 mm/yr. Tests indicate that the trends are statistically significant, hence coastal sea level does not rise faster than the global mean. Although trends agree well, tide gauges-based mean sea level exhibits much larger interannual variability than Altimetry-based global mean. Interannual variability in coastal sea level appears related to the regional variability in sea level rates reported by satellite Altimetry. When global mean sea level is considered (as allowed by satellite Altimetry coverage), interannual variability is largely smoothed out.
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Is coastal mean sea level rising faster than the global mean? A comparison between tide gauges and satellite Altimetry over 1993-2007
Geophysical Research Letters, 2009Co-Authors: Pierre Prandi, Anny Cazenave, M. BeckerAbstract:Based on a careful selection of tide gauges records from the Global Sea Level Observing System network, we investigate whether coastal mean sea level is rising faster than the global mean derived from satellite Altimetry over the January 1993-December 2007 time span. Over this 15-year time span, mean coastal rate of sea level rise is found to be + 3.3 +/- 0.5 mm/yr, in good agreement with the Altimetry-derived rate of + 3.4 +/- 0.1 mm/yr. Tests indicate that the trends are statistically significant, hence coastal sea level does not rise faster than the global mean. Although trends agree well, tide gauges-based mean sea level exhibits much larger interannual variability than Altimetry-based global mean. Interannual variability in coastal sea level appears related to the regional variability in sea level rates reported by satellite Altimetry. When global mean sea level is considered (as allowed by satellite Altimetry coverage), interannual variability is largely smoothed out. Citation: Prandi, P., A. Cazenave, and M. Becker (2009), Is coastal mean sea level rising faster than the global mean? A comparison between tide gauges and satellite Altimetry over 1993-2007, Geophys. Res. Lett., 36, L05602, doi:10.1029/2008GL036564.
C. K. Shum - One of the best experts on this subject based on the ideXlab platform.
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Satellite radar Altimetry for monitoring small rivers and lakes in Indonesia
Hydrology and Earth System Sciences, 2015Co-Authors: Yohanes Budi Sulistioadi, C. K. Shum, Kuo-hsin Tseng, H. Hidayat, Muhammad Sumaryono, A. Suhardiman, Fajar Setiawan, Sunarso SunarsoAbstract:Remote sensing and satellite geodetic observations are capable of hydrologic monitoring of freshwater resources. Although satellite radar Altimetry has been used in monitoring water level or discharge, its use is often limited to monitoring large rivers (>1 km) with longer interval periods (>1 week) because of its low temporal and spatial resolutions (i.e., satellite revisit period). Several studies have reported successful retrieval of water levels for small rivers as narrow as 40 m. However, processing current satellite Altimetry signals for such small water bodies to retrieve water levels accurately remains challenging. Physically, the radar signal returned by water bodies smaller than the satellite footprint is most likely contaminated by non-water surfaces, which may degrade the measurement quality. In order to address this scientific challenge, we carefully selected the waveform shapes corresponding to the range measurement resulting from standard retrackers for the European Space Agency's (ESA's) Envisat (Environmental Satellite) radar Altimetry. We applied this approach to small (40–200 m in width) and medium-sized (200–800 m in width) rivers and small lakes (extent 2 ) in the humid tropics of Southeast Asia, specifically in Indonesia. This is the first study that explored the ability of satellite Altimetry to monitor small water bodies in Indonesia. The major challenges in this study include the size of the water bodies that are much smaller than the nominal extent of the Envisat satellite footprint (e.g., ~250 m compared to ~1.7 km, respectively) and slightly smaller than the along-track distance (i.e., ~370 m). We addressed this challenge by optimally using geospatial information and optical remote sensing data to define the water bodies accurately, thus minimizing the probability of non-water contamination in the Altimetry measurement. Considering that satellite Altimetry processing may vary with different geographical regions, meteorological conditions, or hydrologic dynamic, we further evaluated the performance of all four Envisat standard retracking procedures. We found that satellite Altimetry provided a good alternative or the only means in some regions of measuring the water level of medium-sized rivers and small lakes with high accuracy (root mean square error (RMSE) of 0.21–0.69 m and a correlation coefficient of 0.94–0.97). In contrast to previous studies, we found that the commonly used Ice-1 retracking algorithm was not necessarily the best retracker among the four standard waveform retracking algorithms for Envisat radar Altimetry observing inland water bodies. As a recommendation, we propose to include the identification and selection of standard waveform shapes to complete the use of standard waveform retracking algorithms for Envisat radar Altimetry data over small and medium-sized rivers and small lakes.
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Detection of Envisat RA2/ICE-1 retracked radar Altimetry bias over the Amazon basin rivers using GPS
Advances in Space Research, 2013Co-Authors: S. Calmant, C. K. Shum, J. S. Da Silva, D. M. Moreira, F. Seyler, J. F. Cretaux, G. GabaldaAbstract:Altimetry is now routinely used to monitor stage variations over rivers, including in the Amazon basin. It is desirable for hydrologic studies to be able to combine Altimetry from different satellite missions with other hydrogeodesy datasets such as leveled gauges and watershed topography. One requirement is to accurately determine Altimetry bias, which could be different for river studies from the Altimetry calibrated for deep ocean or lake applications. In this study, we estimate the bias in the Envisat ranges derived from the ICE-1 waveform retracking, which are nowadays widely used in hydrologic applications. As a reference, we use an extensive dataset of altitudes of gauge zeros measured by GPS collocated at the gauges. The thirty-nine gauges are spread along the major tributaries of the Amazon basin. The methodology consists in jointly modeling the vertical bias and spatial and temporal slope variations between Altimetry series located upstream and downstream of each gauge. The resulting bias of the Envisat ICE-1 retracked Altimetry over rivers is 1.044 +/- 0.212 m, revealing a significant departure from other Envisat calibrations or from the Jason-2 ICE-1 calibration. (C) 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.
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polyaxial figures of the moon from the lunar reconnaissance orbiter laser Altimetry and multi mission synthesis of the lunar shape
Journal of Geodetic Science, 2012Co-Authors: H. Bâki Iz, C. K. ShumAbstract:Last decade witnessed a plethora of missions to the Moon by China (Chang’E-1 and Chang-E-2), Japan (SELenological and ENgineering Explorer, SELENE), India (Chandrayaan-1) andUSA (Lunar ReconnaissanceOrbiter), all carried out laser Altimetrymeasurements. This study is a follow up to a series of earlier investigations that produced a number of new models to represent the gross geometric shape of the Moon using Uni ed Lunar Control 2005, Chang’E-1, and SELENE laser Altimetry data using the Lunar Reconnaissance Orbiter laser Altimetrymeasurements. The symmetric and asymmetric polyaxial geometricmodels derived fromLunar ReconnaissanceOrbiter laser Altimetry data, namely, three, four and six-axial lunar gure parameters, are compared and contrasted with the corresponding model parameters estimated from the Chang’E-1 and SELENE laser Altimetry. All solutions produced geometric shape, orientation parameters, and the parameters of the geometric center of lunar gurewith respect to the center ofmass of theMoon showing remarkable agreementwith each other within 100 m. A combined solution by the fusion of uniformly sampled laser Altimetry data from all three missions produced the best estimates for the lunar shape, orientation, and lunar center of gure parameters, and their realistic error estimates.
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laurentia crustal motion observed using topex poseidon radar Altimetry over land
Journal of Geodynamics, 2008Co-Authors: C. K. Shum, Yuchan Yi, Alexander BraunAbstract:Abstract A new method to estimate the vertical crustal motion from satellite Altimetry over land was developed. The method was tested around Hudson Bay, where the observed vertical motion is largely caused by the incomplete glacial isostatic adjustment (GIA) as a result of the Laurentide ice sheet deglaciation since the last glacial maximum (LGM). Decadal (1992–2003) TOPEX/POSEIDON radar Altimetry data over land surfaces were used. The results presented here are improved compared to a previous study (Lee, H., Shum, C.K., Kuo, C.Y., Yi, Y., Braun, A., 2008. Application of TOPEX Altimetry for solid Earth deformation studies. Terr. Atmos. Ocean. Sci. 19, 37–46. doi:10.3319/TAO.2008.19.1-2.37(SA).) which estimated vertical motion only over relatively flat land surfaces (standard deviation of the height variation β = 0.4) whereas the combination of land Altimetry solution with other measurements match best with the models RF3S20 ( β = 0.0) or RF3S20 ( β = 0.2) in terms of mean and standard deviation of the differences. It is anticipated that this innovative technique could potentially be used to provide additional constraints for GIA model improvement, and be applied to other geodynamics studies.
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THE ACCURACY AND APPLICATIONS OF SATELLITE Altimetry
Geophysical Journal International, 1995Co-Authors: C. K. Shum, John C Ries, Byron D TapleyAbstract:Summary The recently launched TOPEX/POSEIDON altimeter mission is achieving an unprecedented accuracy in the measurement of the absolute sea-level, demonstrating that satellite radar Altimetry has evolved into one of the fundamental instruments for providing synoptic observations of the global oceans with a temporal sampling of a few days to a month. This paper assesses the current estimated accuracy of measurements using the available satellite radar altimeter systems in observing the absolute sea-level. The accuracy of sea-level measurements depends on the ability to compute accurate orbits of the altimetric satellites, the fidelity of the terrestrial reference system (TRF), and the knowledge of instrument biases of the altimeter instruments. In this paper, some applications of satellite Altimetry to contemporary problems in marine geodesy, oceanography, an global change studies are discussed. Major advances for many of these problems are feasible with the abundance of satellite Altimetry missions within this decade. The launch of ERS-1 and TOPEX/POSEIDON has initiated a decade of high-accuracy measurements of the absolute sea-level from satellite Altimetry which holds potential for enhancing our knowledge of dynamics of the global ocean, and its influence on global climate changes.
Nicolas Picot - One of the best experts on this subject based on the ideXlab platform.
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Satellite Altimetry Measurements of Sea Level in the Coastal Zone
Surveys in Geophysics, 2019Co-Authors: Stefano Vignudelli, Leelueng Fu, Jacques Benveniste, Florence Birol, Nicolas Picot, Matthias Raynal, Hélène RoinardAbstract:Satellite radar Altimetry provides a unique sea level data set that extends over more than 25 years back in time and that has an almost global coverage. However, when approaching the coasts, the extraction of correct sea level estimates is challenging due to corrupted waveforms and to errors in most of the corrections and in some auxiliary information used in the data processing. The development of methods dedicated to the improvement of altimeter data in the coastal zone dates back to the 1990s, but the major progress happened during the last decade thanks to progress in radar technology [e.g., synthetic aperture radar (SAR) mode and Ka-band frequency], improved waveform retracking algorithms, the availability of new/improved corrections (e.g., wet troposphere and tidal models) and processing workflows oriented to the coastal zone. Today, a set of techniques exists for the processing of coastal Altimetry data, generally called “coastal Altimetry.” They have been used to generate coastal Altimetry products. Altimetry is now recognized as part of the integrated observing system devoted to coastal sea level monitoring. In this article, we review the recent technical advances in processing and the new technological capabilities of satellite radar Altimetry in the coastal zone. We also illustrate the fast-growing use of coastal Altimetry data sets in coastal sea level research and applications, as high-frequency (tides and storm surge) and long-term sea level change studies.
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Conquering the coastal zone: a new frontier for satellite Altimetry
2012Co-Authors: Paolo Cipollini, Stefano Vignudelli, Nicolas Picot, Jérôme Benveniste, Laury Miller, Remko Scharroo, Ted Strub, Doug Vandemark, Simona Zoffoli, Ole Baltazar AndersenAbstract:Conquering the Coastal Zone: A New Frontier for Satellite Altimetry, keynote talk at the ESA/CNES "20 Years of Progress in Radar Altimetry" Symposium, Venice Lido, 24-29 September 2012
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Sea level variability in the Arctic Ocean observed by satellite Altimetry
Ocean Science Discussions, 2012Co-Authors: Pierre Prandi, Michael Ablain, Anny Cazenave, Nicolas PicotAbstract:Abstract. We investigate sea level variability in the Arctic Ocean from observations. Variability estimates are derived both at the basin scale and on smaller local spatial scales. The periods of the signals studied vary from high frequency (intra-annual) to long term trends. We also investigate the mechanisms responsible for the observed variability. Different data types are used, the main one being a recent reprocessing of satellite Altimetry data in the Arctic Ocean. Satellite Altimetry data is compared to tide gauges measurements, steric sea level derived from temperature and salinity fields and GRACE ocean mass estimates. We establish a consistent regional sea level budget over the GRACE availability era (2003–2009) showing that the sea level drop observed by Altimetry over this period is driven by ocean mass loss rather than steric effects. The comparison of Altimetry and tide gauges time series show that the two techniques are in good agreement regarding sea level trends. Coastal areas of high variability in the Altimetry record are also consistent with tide gauges records. An EOF analysis of September mean Altimetry fields allows identifying two regions of wind driven variability in the Arctic Ocean: the Beaufort Gyre region and the coastal European and Russian Arctic. Such patterns are related to atmospheric regimes through the Arctic Oscillation and Dipole Anomaly.
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A New Estimation of Mean Sea Level in the Arctic Ocean from Satellite Altimetry
Marine Geodesy, 2012Co-Authors: Pierre Prandi, Michael Ablain, Anny Cazenave, Nicolas PicotAbstract:Sea level monitoring in the Arctic Ocean can provide useful information in the context of a rapid change of several parts of the Arctic climate system. Satellite Altimetry systems are affected by various problems at high latitudes. As a consequence, no precise and reliable mean sea level record is available yet from Altimetry products. After identifying some of the issues that affect satellite Altimetry in the Arctic Ocean region, we describe the tailored processing that has been applied to along-track mono-mission Altimetry data. We generate a new dataset of weekly gridded sea level anomaly fields over the Arctic region for the period spanning from 1993 to 2009 based on multisatellite Altimetry missions. We demonstrate the improvements achieved by this new dataset, among which a better data coverage. The grids are used to describe some features of mean sea level variability in the Arctic Ocean both at basin-wide and local scales. The regional trend estimated for the Arctic Ocean mean sea level over all latitudes from 66 degrees N to 82 degrees N is 3.6 mm/yr with an uncertainty of 1.3 mm/yr (90% confidence) and without any glacial isostatic adjustment (GIA) correction applied. The record displays large inter-annual variability, but no strong correlation with climate indices was found. Spatial patterns in sea level trends and variability over the Arctic region are also investigated.
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IGARSS (3) - Basic Radar Altimetry Toolbox
IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008Co-Authors: Jérôme Benveniste, V. Rosmorduc, S. Niemeijer, Nicolas PicotAbstract:A NEW SET OF TOOLS FOR ALL Altimetry USERS The field of satellite radar Altimetry has matured to a point where it is now time to encourage a multimission approach and conceive an "all-altimeter" toolbox including a tutorial. Such an integrated approach and view is vital not only for assessing the current status of what offers altimeter products but also to show the system and consistency with the past. The Basic Radar Altimetry Toolbox (BRAT) is a collection of tools, tutorials and documents designed to facilitate the use of radar Altimetry data for Altimetry users, experienced as well as beginners, and particularly the users of the upcoming CryoSat mission. It is able to read most distributed radar Altimetry data, from ERS-1 & 2, TOPEX/Poseidon, Geosat Follow-on, JASON-1, Envisat, and the future Cryosat missions, to perform some processing, data editing and statistic and to visualise the results. A version 2 is being developed with additional visualisation features such as waveform viewing. Also, a release for the MacOS is planned. As part of the Toolbox, a Radar Altimetry Tutorial gives general information about Altimetry, the technique involved and its applications, as well as an overview of past, present and future missions, including information on how to access data and additional software and documentation. It also presents a series of data use cases, covering all uses of Altimetry over ocean, cryosphere and land, showing the basic methods for some of the most frequent manners of using Altimetry data.
