Blar i forfatter "Johnsen, Harald"

Viser treff 1-6 av 6

    • Comparing SAR based short time-lag cross-correlation and Doppler derived sea ice drift velocities 

      Kræmer, Thomas; Johnsen, Harald; Brekke, Camilla; Engen, Geir (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-23)
      This paper shows initial results from estimating Doppler radial surface velocities (RVLs) over Arctic sea ice using the Sentinel-1A (S1A) satellite. Our study presents the first quantitative comparison between ice drift derived from the Doppler shifts and drift derived using time-series methods over comparable time scales. We compare the Doppler-derived ice velocities with global positioning system ...

    • Emulating sentinel-1 Doppler radial ice drift measurements using envisat ASAR data 

      Kræmer, Thomas; Johnsen, Harald; Brekke, Camilla (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-05)
      Using data from the Envisat Advanced Synthetic Aperture Radar (ASAR) instrument, this paper demonstrates how the high-precision radial surface velocity product, which will become available with the European Space Agency's Sentinel-1 satellite, can complement the analysis of sea ice motion. High-resolution Doppler frequency measurements are used to estimate the subsecond line-of-sight motion of ...

    • High-resolution polar low winds obtained from unsupervised sar wind retrieval 

      Tollinger, Mathias; Graversen, Rune; Johnsen, Harald (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-11-18)
      High-resolution sea surface observations by spaceborne synthetic aperture radar (SAR) instruments are sorely neglected resources for meteorological applications in polar regions. Such radar observations provide information about wind speed and direction based on wind-induced roughness of the sea surface. The increasing coverage of SAR observations in polar regions calls for the development of ...

    • Improving Doppler frequency estimation from Envisat data 

      Kræmer, Thomas; Johnsen, Harald; Brekke, Camilla (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-11-06)
      This paper shows that Envisat ASAR data are degraded by a small periodic variation in gain between internal calibration cycles of the antenna, which introduces a significant bias when we try to estimate line-of-sight surface velocities from the estimated Doppler frequency shifts. We investigate the impact of the gain problems on the derived surface velocity product and propose a simple correction ...

    • Improving Doppler frequency estimation from Envisat data 

      Kræmer, Thomas; Johnsen, Harald; Brekke, Camilla (Conference object; Konferansebidrag, 2014)

    • SKIM, a Candidate Satellite Mission Exploring Global Ocean Currents and Waves 

      Ardhuin, Fabrice; Brandt, Peter; Gaultier, Lucile; Donlon, Craig James; Battaglia, Alessandro; Boy, Francois; Casal, Tania; Chapron, Bertrand; Collard, Fabrice; Cravatte, Sophie; Delouis, Jean-Marc; De Witte, Erik; Dibarboure, Gerald; Engen, Geir; Johnsen, Harald; Lique, Camille; López-Dekker, Paco; Maes, Christophe; Martin, Adrien; Marie, Louis; Menemenlis, Dimitris; Nouguier, Frederic; Peureux, Charles; Rampal, Pierre; Ressler, Gerhard; Rio, Marie-Helene; Rommen, Bjorn; Shutler, Jamie D.; Suess, Martin; Tsamados, Michel; Ubelmann, Clement; van Sebille, Erik; van den Oever, Martin; Stammer, Detlef (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-04-30)
      The Sea surface KInematics Multiscale monitoring (SKIM) satellite mission is designed to explore ocean surface current and waves. This includes tropical currents, notably the poorly known patterns of divergence and their impact on the ocean heat budget, and monitoring of the emerging Arctic up to 82.5°N. SKIM will also make unprecedented direct measurements of strong currents, from boundary currents ...