Eingang zum Volltext in OPUS
Hinweis zum Urheberrecht
Dissertation zugänglich unter
Extreme Wind and Wave Conditions in Tropical Cyclones Observed from Synthetic Aperture Radar Images
Extreme Wind- und Wellenbedingungen bei tropischen Wirbelstuermen von Synthetic Aperture Radar Satelliten aus beobachtet
Dokument 1.pdf (5.665 KB)
Freie Schlagwörter (Deutsch):
Fernerkundung , Synthetic Aperture Radar , tropischen Wirbelstuermen
Freie Schlagwörter (Englisch):
Remote Sensing , Synthetic Aperture Radar , Tropical Cyclones
38.03 , 38.90
Graßl, Hartmut (Prof. Dr.)
Tag der mündlichen Prüfung:
Kurzfassung auf Englisch:
Tropical cyclone is a generic term which comprises hurricanes in the Atlantic Ocean and Northeast Pacific Ocean, typhoons in the Northwest Pacific Ocean, and cyclones in the Indian Ocean and Southwest Pacific ocean.
Tropical cyclones account for a significant fraction of damage, injury and loss of life. Current models are still not able to provide robust quantitative forecasts on track and intensity changes, mainly due to the lack of reliable measurements of the initial state conditions. There are still a lot of aspects in the physics of tropical cyclones, which are not well understood. Of particular importance are processes taking place at the air sea interface, which is a key component in the heat flux driving the cyclone. Due to the relatively small amount of in situ data available within cyclones remote sensing techniques play an important role in the retrieval of geophysical information. Because of their all weather capability and wide swath coverage space borne active microwave sensors like the Synthetic Aperture Radar are of particular interest in this context
Several studies have demonstrated that SAR images of the ocean surface contain information on sea state and wind field. Different techniques can be used to retrieve the propagation direction of ocean waves, the surface wind speed and direction to identify and analyze mesoscale surface features.
The study presented hereafter focuses on the use of Synthetic Aperture Radar (SAR) data for the retrieval of the tropical cyclones characteristic parameters. It is part of the EXTROP project (Investigation of Tropical and Extratropical Cyclones using Satellite data), which concentrates also on the study of the evolution of tropical cyclones and on their transition to extratropical cyclones that can affect Europe. Six PhD candidates have been funded by the EXTROP project; two focusing on numerical modeling of cyclones, two investigating the cyclones’ characterization using passive remote sensing. The two last PhD topics considered the use of active remote sensing (radar, altimeters) for wind field retrieval; the present work is dedicated to the development of techniques for tropical cyclone analysis using SAR (Synthetic Aperture Radar) data.
The first part of the thesis consists of an overview of the state of the art in the field of tropical cyclone characterization. An extensive bibliographic study has been performed in order to reassess the basic principles of the SAR imaging of sea surfaces and to highlight the advantages and drawbacks of the methodologies and techniques applied for tropical cyclone analysis.
The second part of the thesis is then dedicated to the presentation of the algorithms developed in the framework of the PhD for the retrieval of tropical cyclone intensity, based on the use of SAR image intensity and of numerical model.
A new technique to derive the maximum wind speed and the hurricane strength from SAR images is then proposed. The problem of saturation in tropical cyclone wind regime is overcome basing the technique on the combined use of SAR measurements for areas of wind speed of 20 m/s or less and a parametric model for tropical cyclone wind speed. The radius of maximum wind speed required as input for the model is measured from the SAR image using a technique based on wavelet transform. Wind directions have been computed from the SAR image using spectral analysis to detect the area containing feature associated with the wind flow and an interpolation technique. The procedure has been applied to five images of tropical cyclones showing agreement with in situ measurements. Maximum wind speed up to70 m/s can be determined with an RMS error of 3.9 m/s.