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Sudhir Kumar Chaturvedi,Chan Su Yang,Jung Hwan Song,Kazuo Ouchi,P. Shanmugam 大韓遠隔探査學會 2011 大韓遠隔探査學會誌 Vol.27 No.3
The purpose of this study is to estimate the spherical wave parameters that appears in synthetic aperture radar (SAR) image acquired over the coast of Chukk, Micronesia. The retrieval of ocean wave parameters consists of two main stages: the first is to determine the dominant wavelengths by Fast Fourier Transform (FFT) over 16 sub-image areas and the second is to estimate wave slopes and heights using dispersion relationship under various water wave conditions. It is assumed that the spherical waves are linear and progressive. These type of waves have the range and azimuth components traveling in radial directions. The azimuth travelling waves are more affected by the velocity bunching mechanism and it is difficult to estimate the wave parameters for these affected areas in SAR imagery. In order to compensate these effects, the velocity bunching ratio (VBR) based on modulation transfer function (MTF) was compared with the intensity ratio for neighbor area in the radial direction in order to assign the spherical wave properties for azimuthally travelling waves. Dispersion relation provides the good estimates for the wave heights for all the selected sub-image areas in the range of 1m to 2m. VBR based on MTF was found to be 0.78 at wave height of 1.36m, while the intensity-based VBR was 0.69 which corresponds to the height of 1.75m. It can be said that the velocity bunching accounts for azimuthally travelling spherical waves and the difference results from the sea-bottom effects.
Ship Recognition by Integration of SAR and AIS
Chaturvedi, Sudhir Kumar,Yang, Chan-Su,Ouchi, Kazuo,Shanmugam, Palanisamy Cambridge University Press 2012 The Journal of navigation Vol.65 No.2
<P>A novel design of an integrated system using Synthetic Aperture Radar (SAR) image and Automatic Identification System (AIS) data is proposed in this paper for the purpose of identifying ships at sea. TerraSAR-X® (SpotLight mode) images and AIS data collected over Incheon Port (Korea) and Tokyo Bay (Japan) were used on different dates. Four main steps for integration of SAR and AIS based ships can be identified, namely: ‘Time Matching’ to retrieve the respective Dead Reckoning (DR) position of the ships at SAR image acquisition times; ‘Position Matching’ based on a nearest neighbourhood re-sampling method with compensation of position shift; ‘Size Matching’ and ‘Speed Matching’. Under each of the matching criteria, the measurement error in each of the matching criteria was found to be less than 20% and the SAR extracted ship's hull boundaries were presented on a screen to display the system results. The results of this study will contribute to the design a Near-Real-Time (NRT) operational system for ship detection, identification, and classification by SARs in different data acquisition modes over various geographical locations at different acquisition times. This novel integrated system design will provide a most important preliminary step towards integration based on ships' hull monitoring in order to recognize ‘friend’ and ‘foe’ ship targets over a huge oceanic region and would be useful for coast guards as an early warning system.</P>
Chaturvedi, Sudhir Kumar,Yang, Chan-Su,Song, Jung-Hwan,Ouchi, Kazuo,Shanmugam, P. The Korean Society of Remote Sensing 2011 大韓遠隔探査學會誌 Vol.27 No.3
The purpose of this study is to estimate the spherical wave parameters that appears in synthetic aperture radar (SAR) image acquired over the coast of Chukk, Micronesia. The retrieval of ocean wave parameters consists of two main stages: the first is to determine the dominant wavelengths by Fast Fourier Transform (FFT) over 16 sub-image areas and the second is to estimate wave slopes and heights using dispersion relationship under various water wave conditions. It is assumed that the spherical waves are linear and progressive. These type of waves have the range and azimuth components traveling in radial directions. The azimuth travelling waves are more affected by the velocity bunching mechanism and it is difficult to estimate the wave parameters for these affected areas in SAR imagery. In order to compensate these effects, the velocity bunching ratio (VBR) based on modulation transfer function (MTF) was compared with the intensity ratio for neighbor area in the radial direction in order to assign the spherical wave properties for azimuthally travelling waves. Dispersion relation provides the good estimates for the wave heights for all the selected sub-image areas in the range of 1m to 2m. VBR based on MTF was found to be 0.78 at wave height of 1.36m, while the intensity-based VBR was 0.69 which corresponds to the height of 1.75m. It can be said that the velocity bunching accounts for azimuthally travelling spherical waves and the difference results from the sea-bottom effects.
DESIGN OF INTEGRATED SYSTEM FOR SHIP IDENTIFICATION
Chan-Su Yang,Sudhir Kumar Chaturvedi,Jung-Hwan Song,P. Shanmugam 해양환경안전학회 2011 해양환경안전학회 학술발표대회 논문집 Vol.2011 No.06
This paper describes the concept to design ship detection and identification systemwith combined use of Automatic Identification System (AIS) reports over Synthetic Aperture Radar (SAR) data. TerraSAR-X data (HH-polarization) in spotlight mode acquired on May 2, 2010 is used in this work with AIS-reports taken as ground truth. Till so far, only ship detection algorithms like CFAR (Constant False Alarm Rate), Alpha-stable distribution etc. were presented in most of the literatures for ship detection but also there are some limitation for ship detection performance like metrological conditions, image properties, speckle noise occurrence etc. Here, we present integration concept of both data by means of time matching of AIS-reports with image acquisition in order to estimate ship’s dead-reckoning (DR) location from AIS-report and are projected over an image along with the ship’s hull design for suitability and accurate reliability results. Nearest distance search method are applied to designate the SAR-derived ship targets within certain region of interest around DR. At last, DR based ship’s hull pattern is shifted over SAR-derived ship targets to conclude matched performance result in a well suitable manner.