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Träfflista för sökning "WFRF:(Heuzé Céline) "

Sökning: WFRF:(Heuzé Céline)

  • Resultat 1-10 av 23
  • [1]23Nästa
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1.
  • Heuzé, Céline, 1988, et al. (författare)
  • Near-Real Time Detection of the Re-Opening of the Weddell Polynya, Antarctica, from Spaceborne Infrared Imagery
  • 2018
  • Ingår i: IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium. - 2153-6996. - 9781538671504
  • Konferensbidrag (refereegranskat)abstract
    • A hole in the Antarctic sea ice cover, the Weddell Polynya, unexpectedly re-opened in winter 2017 for the first time since 1976. Models suggest that the polynya opened because warm oceanic water moved up to the surface, melting the ice from below. Here three temperature thresholds applied to near-hourly spaceborne infrared imagery (AVHRR) successfully detect the appearance of a warm spot up to five days before the polynya opened in June and September 2017. Traditional sea ice concentration and thickness criteria could only detect the polynya once it was open. An automatised warning system, using near-real time passive monitoring of warm spots, would allow researchers to reroute vessels or autonomous sensors in order to finally study the polynya as a whole when it opens again, from its preconditioning to its impacts on the climate system.
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2.
  • Stiller-Reeve, Mathew, et al. (författare)
  • Improving together: better science writing through peer learning
  • 2016
  • Ingår i: Hydrology and Earth System Sciences. - 1027-5606 .- 1607-7938. ; 20, s. 2965-2973
  • Tidskriftsartikel (refereegranskat)abstract
    • Science, in our case the climate and geosciences, is increasingly interdisciplinary. Scientists must therefore com- municate across disciplinary boundaries. For this communi- cation to be successful, scientists must write clearly and con- cisely, yet the historically poor standard of scientific writing does not seem to be improving. Scientific writing must im- prove, and the key to long-term improvement lies with the early-career scientist (ECS). Many interventions exist for an ECS to improve their writing, like style guides and courses. However, momentum is often difficult to maintain after these interventions are completed. Continuity is key to improving writing. This paper introduces the ClimateSnack project, which aims to motivate ECSs to develop and continue to improve their writing and communication skills. The project adopts a peer-learning framework where ECSs voluntarily form writ- ing groups at different institutes around the world. The group members learn, discuss, and improve their writing skills to- gether. Several ClimateSnack writing groups have formed. This paper examines why some of the groups have flourished and others have dissolved. We identify the challenges involved in making a writing group successful and effective, notably the leadership of self-organized groups, and both individual and institutional time management. Within some of the groups, peer learning clearly offers a powerful tool to improve writ- ing as well as bringing other benefits, including improved general communication skills and increased confidence.
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3.
  • Ahlberg, Erik, et al. (författare)
  • "Vi klimatforskare stödjer Greta och skolungdomarna"
  • Ingår i: Dagens nyheter (DN debatt). - 1101-2447.
  • Tidskriftsartikel (populärvet., debatt m.m.)abstract
    • DN DEBATT 15/3. Sedan industrialiseringens början har vi använt omkring fyra femtedelar av den mängd fossilt kol som får förbrännas för att vi ska klara Parisavtalet. Vi har bara en femtedel kvar och det är bråttom att kraftigt reducera utsläppen. Det har Greta Thunberg och de strejkande ungdomarna förstått. Därför stödjer vi deras krav, skriver 270 klimatforskare.
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4.
  • Aldenhoff, Wiebke, 1985, et al. (författare)
  • Comparison of ice/water classification in Fram Strait from C- A nd L-band SAR imagery
  • 2018
  • Ingår i: Radar remote sensing of sea ice in the Polar regions. ; 59:76pt2, s. 112-123
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper an algorithm for ice/water classification of C- A nd L-band dual polarization synthetic aperture radar data is presented. A comparison of the two different frequencies is made in order to investigate the potential to improve classification results with multi-frequency data. The algorithm is based on backscatter intensities in co- A nd cross-polarization and autocorrelation as a texture feature. The mapping between image features and ice/water classification is made with a neural network. Accurate ice/water maps for both frequencies are produced by the algorithm and the results of two frequencies generally agree very well. Differences are found in the marginal ice zone, where the time difference between acquisitions causes motion of the ice pack. C-band reliably reproduces the outline of the ice edge, while L-band has its strengths for thin ice/calm water areas within the icepack. The classification shows good agreement with ice/water maps derived from met.no ice-charts and radiometer data from AMSR-2. Variations are found in the marginal ice zone where the generalization of the ice charts and lower accuracy of ice concentration from radiometer data introduce deviations. Usage of high-resolution dual frequency data could be beneficial for improving ice cover information for navigation and modelling.
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5.
  • Aldenhoff, Wiebke, et al. (författare)
  • Comparison of ice/water classification in Fram Strait from C- and L-band SAR imagery
  • 2018
  • Ingår i: Annals of Glaciology. - 0260-3055. ; 59:76pt2, s. 112-123
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper an algorithm for ice/water classification of C- and L-band dual polarization synthetic aperture radar data is presented. A comparison of the two different frequencies is made in order to investigate the potential to improve classification results with multi-frequency data. The algorithm is based on backscatter intensities in co- and cross-polarization and autocorrelation as a texture feature. The mapping between image features and ice/water classification is made with a neural network. Accurate ice/water maps for both frequencies are produced by the algorithm and the results of two frequencies generally agree very well. Differences are found in the marginal ice zone, where the time difference between acquisitions causes motion of the ice pack. C-band reliably reproduces the outline of the ice edge, while L-band has its strengths for thin ice/calm water areas within the icepack. The classification shows good agreement with ice/water maps derived from met.no ice-charts and radiometer data from AMSR-2. Variations are found in the marginal ice zone where the generalization of the ice charts and lower accuracy of ice concentration from radiometer data introduce deviations. Usage of high-resolution dual frequency data could be beneficial for improving ice cover information for navigation and modelling.
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6.
  • Aldenhoff, Wiebke, et al. (författare)
  • Comparison of Sentinel-1 SAR And Sentinel-3 Altimetry Data For Ice Type Discrimination
  • 2019
  • Ingår i: Geoscience and Remote Sensing Symposium (IGARSS), 2019 IEEE International. ; , s. 4238-4240
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper near co-incidental Sentinel-1 C-band SAR imagery and Sentinel-3 SRAL Ku-band altimeter data are compared for their capabilities of sea ice type discrimination. Knowledge of sea ice type is important for climate research and safety in Arctic offshore operations.First-year ice is characterised by a low SAR backscatter intensity in both HH and HV polarisation compared to multi-year ice, while the altimeter waveform parameters show high pulse peakiness and peak power compared to multi-year ice. Thus SAR imagery and altimetry can principally discriminate different ice types. The complexity of the backscattered radar signal however impedes a clear separation of the two types for all cases. Cross comparison of the two sensors offers an opportunity of high resolution validation data, which is often lacking for sea ice studies.
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7.
  • Aldenhoff, Wiebke, 1985, et al. (författare)
  • Comparison of Sentinel-1 Sar and Sentinel-3 Altimetry Data for Sea Ice Type Discrimination
  • 2019
  • Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). - 9781538691540 ; , s. 4238-4240
  • Konferensbidrag (refereegranskat)abstract
    • In this paper near co-incidental Sentinel-1 C-band SAR imagery and Sentinel-3 SRAL Ku-band altimeter data are compared for their capabilities of sea ice type discrimination. Knowledge of sea ice type is important for climate research and safety in Arctic offshore operations.First-year ice is characterised by a low SAR backscatter intensity in both HH and HV polarisation compared to multi-year ice, while the altimeter waveform parameters show high pulse peakiness and peak power compared to multi-year ice.Thus SAR imagery and altimetry can principally discriminate different ice types. The complexity of the backscattered radar signal however impedes a clear separation of the two types for all cases. Cross comparison of the two sensors offers an opportunity of high resolution validation data, which is often lacking for sea ice studies.
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8.
  • Aldenhoff, W., et al. (författare)
  • First-Year and Multiyear Sea Ice Incidence Angle Normalization of Dual-Polarized Sentinel-1 SAR Images in the Beaufort Sea
  • 2020
  • Ingår i: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. - 1939-1404. ; 13, s. 1540-1550
  • Tidskriftsartikel (refereegranskat)abstract
    • Automatic and visual sea ice classification of SAR imagery is impeded by the incidence angle dependence of backscatter intensities. Knowledge of the angular dependence of different ice types is therefore necessary to account for this effect. While consistent estimates exist for HH polarization for different ice types, they are lacking HV polarization data, especially for multiyear sea ice. Here we investigate the incidence angle dependence of smooth and rough/deformed first-year and multiyear ice of different ages for wintertime dual-polarization Sentinel-1 C-band SAR imagery in the Beaufort Sea. Assuming a linear relationship, this dependence is determined using the difference in incidence angle and backscatter intensities from ascending and descending images of the same area. At cross-polarization rough/deformed first-year sea ice shows the strongest angular dependence with -text{0.11} dB/1{circ } followed by multiyear sea ice with -text{0.07} dB/text{1}{circ }, and old multiyear ice (older than three years) with -text{0.04} dB/text{1}{circ }. The noise floor is found to have a strong impact on smooth first-year ice and estimated slopes are therefore not fully reliable. At co-polarization, we obtained slope values of -0.24, -0.20, -text{0.15}, and -text{0.10} dB/text{1}{circ } for smooth first-year, rough/deformed first-year, multiyear, and old multiyear sea ice, respectively. Furthermore, we show that imperfect noise correction of the first subswath influences the obtained slopes for multiyear sea ice. We demonstrate that incidence angle normalization should not only be applied to co-polarization but should also be considered for cross-polarization images to minimize intra ice type variation in backscatter intensity throughout the entire image swath. © 2008-2012 IEEE.
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9.
  • Aldenhoff, Wiebke, et al. (författare)
  • Sensitivity of radar altimeter waveform to changes in sea ice type at resolution of Synthetic Aperture Radar
  • 2019
  • Ingår i: Remote Sensing. - 2072-4292. ; 11:22
  • Tidskriftsartikel (refereegranskat)abstract
    • Radar altimetry in the context of sea ice has mostly been exploited to retrieve basin-scale information about sea ice thickness. In this paper, we investigate the sensitivity of altimetric waveforms to small-scale changes (a few hundred meters to about 10 km) of the sea ice surface. Near-coincidental synthetic aperture radar (SAR) imagery and CryoSat-2 altimetric data in the Beaufort Sea are used to identify and study the spatial evolution of altimeter waveforms over these features. Open water and thin ice features are easily identified because of their high peak power waveforms. Thicker ice features such as ridges and multiyear ice floes of a few hundred meters cause a response in the waveform. However, these changes are not reflected in freeboard estimates. Retrieval of robust freeboard estimates requires homogeneous floes in the order of 10 km along-track and a few kilometers to both sides across-track. We conclude that the combination of SAR imagery and altimeter data could improve the local sea ice picture by extending spatially scarce freeboard estimates to regions of similar SAR signature.
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10.
  • Aldenhoff, Wiebke, 1985, et al. (författare)
  • Sensitivity of radar altimeterwaveform to changes in sea ice type at resolution of synthetic aperture radar
  • 2019
  • Ingår i: Radar remote sensing of sea ice in the Polar regions. ; 11:22
  • Tidskriftsartikel (refereegranskat)abstract
    • Radar altimetry in the context of sea ice has mostly been exploited to retrieve basin-scale information about sea ice thickness. In this paper, we investigate the sensitivity of altimetric waveforms to small-scale changes (a few hundred meters to about 10 km) of the sea ice surface. Near-coincidental synthetic aperture radar (SAR) imagery and CryoSat-2 altimetric data in the Beaufort Sea are used to identify and study the spatial evolution of altimeter waveforms over these features. Open water and thin ice features are easily identified because of their high peak power waveforms. Thicker ice features such as ridges and multiyear ice floes of a few hundred meters cause a response in the waveform. However, these changes are not reflected in freeboard estimates. Retrieval of robust freeboard estimates requires homogeneous floes in the order of 10 km along-track and a few kilometers to both sides across-track. We conclude that the combination of SAR imagery and altimeter data could improve the local sea ice picture by extending spatially scarce freeboard estimates to regions of similar SAR signature.
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