Abstract
It is generally accepted that synthetic aperture radar (sar) images can be quite useful for a better understanding of hydrodynamic processes in the ocean, because they provide valuable information on the location and spatial scales of oceanic features such as fronts, internal waves, and eddies. However, the retrieval of actual surface current fields from the shape and modulation depth of radar signatures is a much more challenging problem, since the imaging mechanism is a complex and nonlinear two-step mechanism which cannot be inverted easily. In this article we review the state-of-the-art in modeling radar signatures of current features, and we present the concept of an iterative scheme for inverting radar images into current fields, which will be implemented within the framework of the European project marsais. We estimate the accuracy and spatial resolution of the proposed remote sensing system on the basis of findings from recent case studies and some dedicated simulations. According to the results of our analyses, it should be possible to retrieve spatial surface current variations and current gradients from a typical spaceborne C band sar image with an accuracy on the order of 20% and a spatial resolution on the order of 50 m.
Résumé
Il est généralement admis que les images de radars à synthèse d’ouverture (rso) peuvent être très utiles pour la compréhension des processus hydrodynamiques dans l’océan, car elles fournissent des informations de valeur sur la position et l’importance des caractéristiques de surface océaniques, tels les fronts, les ondes internes ou les tourbillons. Cependant, la récupération des champs de courants de surface à partir de la forme et de la modulation des signatures radars est un problème bien plus délicat, car le mécanisme d’imagerie se fait en deux étapes complexes et non-linéaires qui ne peuvent être inversées facilement. Dans cet article nous présentons l’état de l’art de la modélisation de la signature radar des caractéristiques de courant et nous présentons le concept d’un schéma itératif pour l’inversion des images radars en champs de courants. Ce schéma sera implanté dans le cadre du projet européen marsais. Nous estimons la précision et la résolution spatiale du système de télédétection proposé sur la base des découvertes provenant de cas d’études récents et de quelques simulations qui leur étaient dédiées. D’après les résultats de nos analyses, il devrait être possible de retrouver les variations spatiales des courants de surface et les gradients de courant à partir d’images RSO bande C typiques avec une précision de l’ordre de 20 % et une résolution spatiale d’environ 50 m.
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Romeiser, R., Ufermann, S. & Alpers, W. Remote sensing of oceanic current features by synthetic aperture radar — achievements and perspectives. Ann. Télécommun. 56, 661–671 (2001). https://doi.org/10.1007/BF02995560
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DOI: https://doi.org/10.1007/BF02995560
Key words
- Remote sensing
- Land observation satellite
- Océanographic survey
- Synthetic aperture radar
- Sea current
- Radar signature
- Back scattering
- Modelling
- Inverse problem