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ABSTRACT: Ship detection is an important application of global monitoring of environment and security. In order to overcome the limitations by other systems, surveillance with satellite synthetic aperture radar (SAR) is used because of its possibility to provide ship detection at high resolution over wide swaths and in all weather conditions. A new X-band radar onboard the TerraSAR-X (TS-X) satellite gives access to spatial resolution as fine as 1 m. In this paper, first results on the combined use of TS-X ship detection, automatic identification system (AIS), and satellite AIS (SatAIS) is presented. The AIS system is an effective terrestrial method for tracking vessels in real time typically up to 40 km off the coast. SatAIS, as a space-based system, allows almost global coverage for monitoring of ships since not all ships operate their AIS and smaller ships are not equipped with AIS. The system is considered to be of cooperative nature. In this paper, the quality of TS-X images with respect to ship detection is evaluated, and a first assessment of its performance for ship detection is given. The velocity of a moving ship is estimated using complex TS-X data. As test cases, images were acquired over the North Sea, Baltic Sea, Atlantic Ocean, and Pacific Ocean in Stripmap mode with a resolution of 3 m at a coverage of 30 km 100 km. Simultaneous information on ship positions was available from TS-X and terrestrial as well as SatAIS. First results on the simultaneous superposition of SatAIS and high-resolution radar images are presented.
IEEE Transactions on Geoscience and Remote Sensing 04/2011; · 2.89 Impact Factor
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ABSTRACT: We investigate small-scale features using SAR imagery, including sharp frontal interfaces, slicks of artificial and natural origin, and wakes of surface ships. Collection of the ground truth data helps in the understanding of the physical mechanisms behind the patterns visible in the image.
Geoscience and Remote Sensing Symposium (IGARSS), 2010 IEEE International; 08/2010
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ABSTRACT: Due to the relatively small amount of in situ data available for the open oceans, remote sensing techniques take an important role in the retrieval of geophysical information, particularly during extreme events. The work presented here aims at the improvement of prediction of cyclone intensity using synthetic aperture radar (SAR) images. A new method to measure the hurricane intensity using SAR images, in combination with a parametric Holland-type model of wind speed, is presented. The algorithm is based on a least square minimization of the difference between the parametric model results and the SAR measurement. The radius of the maximum wind speed, required as input for the minimization procedure, is estimated from the SAR image using wavelet analysis. Information on wind direction is extracted from the SAR image through analysis of image features caused by boundary layer rolls. The root-mean-square error of the suggested method has been validated to be equal to 3.9 m/s. The study is based on a data set of wide-swath SAR images of about 400 km ?? 400 km coverage, acquired by the European Envisat satellite, over tropical cyclones. As a case study, hurricane Katrina is investigated in detail. A total of five tropical cyclone images will be used to validate the results of the new algorithm.
IEEE Transactions on Geoscience and Remote Sensing 05/2010; · 2.89 Impact Factor
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ABSTRACT: A pilot experiment was conducted in the period from April to June 2008 in the Straits of Florida near Port Everglades, Florida, in order to study the dynamics of far wakes of ships. In this experiment, a small boat with downward-looking sonar made ??snakelike?? sections through wakes of ships of opportunity during the TerraSAR-X overpasses. The ship and its parameters (length, speed, course, etc.) were identified utilizing an automated identification system. The sonar responded to the clouds of microbubbles generated in the ship wake by the propulsion system and ship-hull turbulence. The ship wakes were traced in the sonar signal typically from 10 to 30 min after the ship's passage. A preliminary analysis of the measurements suggests that the visibility of the centerline ship wake in synthetic aperture radar (SAR) images is correlated with the presence of microbubbles in the wake. This supports the hypothesis that natural surfactants scavenged and brought to the surface by rising bubbles play an important role in the wake visibility in SAR. The influence of the wind-wave field on the ship wake, as well as the effect of screening of the wind-wave field by the ship's hull, adds another level of complexity to wake patterns observed in SAR images.
IEEE Transactions on Geoscience and Remote Sensing 03/2010; · 2.89 Impact Factor
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ABSTRACT: The detectability of ships on synthetic aperture radar (SAR) images is validated by coastal (live) AIS and space AIS. The monitoring area chosen for surveillance is mainly the German coast and the Panama Canal. The detectability in respect to environmental parameters like wind field, sea state, currents and changing coastlines due to tidal effects is investigated. In the South Atlantic tracking of the German research vessel Polarstern has been performed. Issues of piracy in particular in respect to ships hijacked at the Somali coast are discussed. Possibilities and limitations of a near real time service are evaluated. As images from the SAR sensor do not only contain information on intensity, but as well on the phase of the returned signal, ship speed can be derived from Doppler effects. The ship wakes contain additional information on ship speed and type of ship. Some examples using the ESA satellites ERS and ENVISAT, that provide large coverage (up to 400 km) at moderate resolution (30 meters) are given together with high resolution images from TerraSAR-X.
OCEANS 2009 - EUROPE; 06/2009
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ABSTRACT: TerraSAR-X (TSX) is a high resolution right looking radar satellite, launched on June 15, 2007. TSX carries a high frequency X-band SAR sensor that can be operated in different modes (coverage and resolution) and has quad polarization and dual receive antenna mode used for along track interferometry (ATI) experimental acquisitions.
Radar Conference, 2009 IEEE; 06/2009
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ABSTRACT: TerraSAR-X is a new German X-band radar satellite launched on June 15, 2007. In this mission operational spaceborne synthetic aperture radar (SAR) system with very high spatial resolution is set up producing remote sensing products for commercial and scientific use. TerraSAR-X is a scientific and technological continuation of the successful Space Shuttle missions SIR-C/X and SRTM. Due to its polarimetric and interferometric capabilities as well as the high spatial resolution of up to 1m, the TerraSAR-X sensor is a very interesting tool for oceanography. The presentation will give an overview of several applications, which are of both scientific and commercial interest, like e.g. current and ocean wave measurements, monitoring of morph dynamical processes or high resolution wind field retrieval. The potential as well as limitations of the instrument will be summarized and compared with existing sensors. Necessary steps to translate existing C-band SAR inversion algorithms for wind and wave measurements to X-band will be discussed. A strategy will be outlined to achieve this by a combination of theoretical investigations and the use of existing experimental data acquired by both airborne and ground based X-band radar. First results on the adaption of existing C-band wind retrieval algorithms will be presented. This will in particular include comparisons with in situ measurements taken at the FINO I platform in the North Sea. Wind and ocean wave parameter retrievals will be presented, e.g., based on TerraSAR-X scenes taken over the English Channel.
Synthetic Aperture Radar (EUSAR), 2008 7th European Conference on; 07/2008
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ABSTRACT: In this paper, we show how satellite images taken by space-borne radar sensors can be used to determine mesoscale high-resolution wind fields in synergy with cloud parameters from optical data and, thus, help in the task of maintenance and planning offshore wind farms. The aim of this paper is to use synthetic aperture radar (SAR) and medium resolution imaging spectrometer (MERIS) onboard the environmental satellite (ENVISAT) in synergy to analyze severe weather systems, in particular, to describe the spatial evolution of the atmospheric boundary layer processes involved in cold air outbreaks. We investigated the fine-scale structure of a severe weather case on November 1, 2006 over the North Sea using satellite data. The satellite data are compared with numerical model results of the German Weather Service ldquoLokal Modellrdquo (LM) and the high-resolution limited area model (HIRLAM). LM and HIRLAM show differences in mesoscale turbulent behavior and coastal shadowing. Maximum wind speeds of up to 25 m/s are measured by SAR and are confirmed by the models. Significant differences are observed in the location of the maxima. High-resolution ENVISAT ASAR measurements provide very detailed information on small-scale atmospheric features, which seem to not be captured well by the analyzed numerical models, in particular, in coastal areas. Meteosat second generation (MSG) is used to determine the movement of cloud patterns. Cloud patterns seen in the optical data and radar cross-section modulation give a consistent dynamical picture of the atmospheric processes. The relevance for offshore wind farming is discussed.
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 04/2008; · 1.49 Impact Factor
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ABSTRACT: Space borne radar systems are capable of providing wind field information over the ocean. Radar instruments are of high value for operational applications because of their all weather and daylight capabilities. Synthetic aperture radar (SAR) instruments as flown on the European satellites ERS-2, ENVISAT or the Canadian platform RADARSAT are of particular interest for applications where high resolution two- dimensional information on the near surface wind field is needed. All these operate in C-band. The respective wind field algorithm CMOD was tuned to this wavelength. New research focussed on high speed cases to be able to measure wind speeds above 20 m/sec and on the W to HH polarisation ratio. For future missions like TerraSAR-X, to be launched in May 2007 new wind field algorithms tuned to X-band are needed. The TerraSAR-X instrument has a spatial resolution of up to 1 m and additional features like multi polarisation which make it a very interesting tool for oceanographic applications. In this paper a new X band wind field algorithm, XMOD1.0 is introduced. The algorithm is based on the detection of wind streaks in the SAR images and scatterometer measurements of [1]. Data from the SRTM mission flown on the shuttle in February 2000 and SIR C/X SAR in 1994 are used to test the algorithm. Results are validated against in situ data and model data from ECMWF. The potential of SAR measurements to support the optimal siting, the design, as well as the operation of offshore wind parks is shown. Applications for offshore wind farming of the TerraSAR-X mission will be discussed. The platform FINO 1 was chosen as a primary test site to calibrate and validate wind fields for X band satellite images. For the development, optimisation and validation of the retrieval algorithms comparisons with in situ data, e.g., acquired at the FINO platform will be carried out. The respective calibration and validations strategies will be summarized.
Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International; 08/2007
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ABSTRACT: Currently the European satellites ERS-2 and ENVISAT are flying on the same orbit with a time separation of 30 minutes. In this presentation pairs of the respective synthetic aperture radar data are analyzed with respect to different atmospheric and oceanic processes. The presented results were obtained in the framework of the ESA AO project COTAR. The tandem configuration exists since the launch of ENVISAT in 2002. In the presentation an overview will be given of the available image pairs acquired over the ocean on a global scale. Combinations of ERS-2 SAR data with both image mode and wide swath mode scenes provided by the ENVISAT ASAR are considered. The two SAR images enable the analysis of the change of radar cross section within half an hour. This temporal separation is very interesting for oceanographic applications because there are many processes like atmospheric fronts, convective cells, ocean tides, etc., which are detectable on this time scale. In the presentation tandem pairs acquired over the research platform FINO west of the island Borkum in the North Sea will be presented. The area is of high practical interest because of the planned Offshore Windpark Borkum West. The platform provides wind measurements at different heights and additional oceanic information to support the planning activities for this windpark. The dynamics of atmospheric structures is analysed. It is well known that the near surface wind field is a dominating factor for the normalized radar cross section of the sea surface. For this reason SAR scenes are well suited to study atmospheric effects with high spatial resolution. It is shown that the use of tandem pairs enables the study of processes like the propagation of an atmospheric fronts or the evolution of convective cells. Both effects are illustrated with different examples using additional information from in situ measurements. Furthermore existing techniques for the estimation of the wind field in 10 m height from SAR data ar-
e applied to both images. The evolution of the spatial structure of both wind speed and wind direction is analysed. The observations are related to some theoretical issues like, e.g., the Taylor hypothesis. Particular emphasize is put on the connection between the spatial and the temporal structure of the wind field. This topic is of high practical relevance, e.g., in the context of offshore windenergy exploitation. Additional applications like ship tracking, oil spill detection and the study of ocean wave field dynamics are briefly discussed as well.
Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International; 08/2007
