Chan-Su Yang

An analysis of the radar backscatter fromoil-covered sea surfaces usingmomentmethod andMonte-Carlo simulation: preliminary results

An analysis of the radar backscattering from the ocean surface covered by oil spill is presented using a microwave scattering model and Monte-Carlo simulation. In the analysis, a one-dimensional rough sea surface is numerically generated with an ocean waveheight spectrum for a given wind velocity. A two-layered medium is then generated by adding a thin oil layer on the simulated rough sea surface. The electric fields backscattered from the sea surface with two-layered medium are computed with the method of moments (MoM), and the backscattering coefficients are statistically obtained with N independent samples for each oil-spilled surface using the Monte-Carlo technique for various conditions of surface roughness, oil-layer thickness, frequency, polarization and incidence angle. The numerical simulation results are compared with theoretical models for clean sea surfaces and SAR images of an oil-spilled sea surface caused by the Hebei (Hebei province, China) Spirit oil tanker in 2007. Further, conditions for better oil spill extraction are sought by the numerical simulation on the effects of wind speed and oil-layer thickness at different incidence angles on the backscattering coefficients.

Detection of Ocean Wave Parameters Using Synthetic Aperture Radar (SAR) Data

This study describes the estimation of spherical wave parameters that appears in Synthetic Aperture Radar (SAR) images acquired over the coast of Chukk, Micronesia. The main causes for the interaction of SAR signals with ocean waves can be retrieved through the Bragg scattering mechanism. Dominant wavelengths were retrieved by means of Fast Fourier Transform (FFT) analysis in terms of peak frequency responses. Sea surface slopes were then obtained from the dispersion relation with consideration of different water wave conditions for each subset area, and wave heights were estimated with the use of dominant wavelengths and sea surface slopes. The work presented in this paper may be useful to retrieve the various wave parameters over different regions. The method used is a novel technique to correlate the relationship between SAR image parameters and dispersion relation.

Extraction of Underwater Laver Cultivation Nets by SAR Polarimetric Entropy

This letter describes a technique of extracting and estimating the underwater laver cultivation nets by using the entropy analysis of polarimetric synthetic aperture radar (PolSAR) data. The cultivation nets are placed at 10-20 cm below the sea surface, so that the Bragg waves responsible for L-band radar backscatter do not fully develop in this area of effectively shallow water. Consequently, the surface becomes smooth, and the backscatter radar cross section (RCS) becomes small in comparison with that from deep water without cultivation nets. If RCS from the cultivation area is at the system noise level, the image can be considered as arising from a random process, and the polarimetric entropy should be higher than the open sea area where the radar backscatter is dominated by the single-bounce surface scattering process. We will show that, using the data acquired by Phased Array L-band SAR onboard the Advanced Land Observing Satellite over the Tokyo Bay, Japan, the polarimetric entropy is an effective means of extracting underwater cultivation areas in comparison with the amplitude images. The area of the laver cultivation is then estimated by applying a constant false alarm rate to the entropy images to yield good agreement with the ground-truth data.

Estimation of internal wave velocity in the shallow South China Sea using single and multiple satellite images

This paper presents results on the estimation of the phase velocity of internal waves (IWs) in the shallow waters of the South China Sea in terms of the water depth using satellite data. To calculate the phase velocity, two methods are considered. The first is based on the different positions of IW images acquired by Environmental Satellite-advanced synthetic aperture radar (ASAR) and Terra–Moderate Resolution Imaging Spectroradiometer (MODIS) in a very short time interval, and the second method uses the images of several packets of IWs associated with semidiurnal tidal period in either a single ASAR or MODIS image. The former is termed as the multitemporal images (MTI) method, and the latter is referred to as the tidal period images (TPI) method. The results show that the wave velocities estimated by the MTI method have strong correlation with those derived from a depth-dependent IW propagation theory, while those by the TPI method have moderate correlation. Both the methods can be used to estimate the IW phase velocity but with reduced accuracy by the TPI method. The main reason of this reduced accuracy is the long tidal period during which the characteristics of IWs change as they propagate over long distance in the water of variable currents and/or bottom topography.

Classification of Passing Vessels Around the Ieodo Ocean Research Station Using Automatic Identification System (AIS): November 21-30, 2013

본 연구에서는 2013년 11월 21일부터 30일까지 9일간 이어도 종합해양과학기지에 선박자동식별장치(AIS)를 설치하여 관할해역과 한·중 잠정조치수역의 항행 선박 및 어업활동을 모니터링하기 위해 선박정보를 수집하였다. 수집된 AIS 원시자료는 자체적으로 개발된 프로그램을 이용해 선박의 고유정보(해상이동업무식별번호, IMO 번호, 호출 부호, 선명 등)와 위치정보(위치, 속력, 침로 등)를 추출하고, 국적과 선종 정보만을 이용해 선박을 분류하였다. 선박의 국적정보는 해상식별부호(MID)로 파악되는데, 소형선박에서 많이 탑재하고 있고 기능이 보다 간소화된 소출력의 Class B AIS는 국제해사기구(IMO)의 탑재 요건을 따르고 있지 않아 국적을 알 수 없는 선박이 다수 존재함을 확인하였다. 국적정보를 가지고 있는 선박 중에서는 중국선박과 한국선박이 많았으며, 선종정보를 가지고 있는 선박 중에서는 화물선, 어선 순으로 많았다. 또한 국적을 알 수 없는 선박의 특성을 파악하기 위해 이어도해양과학기지 주변의 항행빈도수가 높은 중국선박과 한국선박의 항적과 비교하였으며, 이를 통해 국적미상 선박이 중국선박의 항행경로와 높은 유사성을 보이는 것을 확인하였다. 따라서 이 해역에서 중국어선은 선단의 형태로 자주 출몰하는 것으로 판단된다.

Algorithm Implementation for Detection and Tracking of Ships Using FMCW Radar

Abstract − This study focuses on a ship detection and tracking method using Frequency Modulated ContinuousWave (FMCW) radar used for horizontal surveillance. In general, FMCW radar can play an important role inmaritime surveillance, because it has many advantages such as low warm-up time, low power consumption, andits all weather performance. In this paper, we introduce an effective method for data and signal processing ofship’s detecting and tracking using the X-band radar. Ships information was extracted using an image-basedprocessing method such as the land masking and morphological filtering with a threshold for a cycle datamerged from raw data (spoke data). After that, ships was tracked using search-window that is ship’s expectedrectangle area in the next frame considering expected maximum speed (19 kts) and interval time (5 sec). Byusing this method, the tracking results for most of the moving object tracking was successful and those resultswere compared with AIS (Automatic Identification System) for ships position. Therefore, it can be said that thepractical application of this detection and tracking method using FMCW radar improve the maritime safety aswell as expand the surveillance coverage cost-effectively. Algorithm improvements are required for an enhance-ment of small ship detection and tracking technique in the future.Keywords: FMCW radar (FMCW 레이더), Ship detection(선박 탐지), Ship tracking(선박 추적), AIS(선박자동식별장치 )

Comparison with L-, C-, and X-band real SAR images and simulation SAR images of spilled oil on sea surface

In recent years, the oil spill detection over sea surface and similar oil material filtration are attracting much attention from the ecological point of view, and synthetic aperture radar (SAR) is considered as an effective way of monitoring such phenomenon due to the day-and-night and all weather observation capability. In this paper, results of the oil slick detection experiment by multi-frequency space borne SARs are reported. On December 7, 2007, an oil tanker was wrecked in the Yellow Sea off the Korean west coast, spilling over 12, 000 tons of crude oil, and causing considerable damage on the coastal environment. In order to analyze the impact of the oil spill, we acquired 4 sets of multi-frequency spaceborne SAR images, including TerraSAR-X X-band data, ENVISAT ASAR and RADARSAT-1 C-band data, and ALOS-PALSAR L-band data. We also computed, as a preliminary study, the backscatter radar cross section (RCS) based on the physical optics model at three microwave frequencies for different wave damping ratios by oil slick. In this paper, we describe the present status of the study on oil slick detection, and suggest the possible future direction to be taken.

Design of integrated ship monitoring system using SAR, RADAR, and AIS

When we talk about for the ship detection, identification and its classification, we need to go for the wide area of monitoring and it may be possible only through satellite based monitoring approach which monitors and covers coastal as well as the oceanic zone. Synthetic aperture radar (SAR) has been widely used to detect targets of interest with the advantage of the operating capability in all weather and luminance free condition (Margarit and Tabasco, 2011). In EU waters, EMSA(European Maritime Safety Agency) is operating the SafeSeaNet and CleanSeaNet systems which provide the current positions of all ships and oil spill monitoring information in and around EU waters in a single picture to Member States using AIS, LRIT and SAR images. In many countries, a similar system has been developed and the key of the matter is to integrate all available data. This abstract describes the preliminary design concept for an integration system of RADAR, AIS and SAR data for vessel traffic monitoring. SAR sensors are used to acquire image data over large coverage area either through the space borne or airborne platforms in UTC. AIS reports should be also obtained on the same date as of the SAR acquisition for the purpose to perform integration test. Land-based RADAR can provide ships positions detected and tracked in near real time. In general, SAR are used to acquire image data over large coverage area, AIS reports are obtained from ship based transmitter, and RADAR can monitor continuously ships for a limited area. In this study, we developed individual ship monitoring algorithms using RADAR(FMCW and Pulse X-band), AIS and SAR(RADARSAT-2 Full-pol Mode). We conducted field experiments two times for displaying the RADAR, AIS and SAR integration over the Pyeongtaek Port, South Korea.

On the eigenvalue analysis using HH-VV dual-polarization SAR data and its applications to monitoring of coastal oceans

In the conventional SAR (Synthetic Aperture Radar) polarimetry, fully polarimetric HH-HV-VH-VV quad polarization data are used. The advantage of using quad-polarization data is more information on the scattering objects than the single- and quad-polarization data; while the disadvantages are narrower swath and less frequent data takes. To fill the gap in-between, the present study examines the polarimetric analysis using HH-VV dual polarization. The model-based three- and four-component scattering power decomposition analyses are not possible with dual-polarization data, and thus, the study is focused on the eigenvalue decomposition analysis by comparing the entropy and mean alpha angle derived from dual-polarization data with those derived from quad polarization data, acquired by ALOS-PALSAR (Advanced Land Observing Satellite Phased Array L-band SAR) PLR (PoLaRimetric mode) and TerraSAR-X dual-polarization SpotLight mode over the Tokyo Bay, Japan. The preliminary results indicate that the values of dual-polarization entropy and alpha angle are almost the same as the quad-polarization values, indicating that dual-polarization data are as capable as quad-polarization data in the eigenvalue decomposition. The technique is then applied to estimating the underwater laver cultivation fields and ship detection.

Velocity estimation of moving targets on the sea surface by azimuth differentials of simulated-SAR image

Since the change in Doppler centroid according to moving targets brings alteration to the phase in azimuth differential signals, one can measure the velocity of the moving targets using this. In this study, we will investigate theoretically measuring velocity of an object from azimuth differential signals by using range compressed data which is the interim outcome of treatment from the simulated Synthetic Aperture Radar (SAR) Raw data of moving targets considering sea clutter. Also, it will provide evaluation for the elements that affect the estimation error of velocity from a single SAR sensor. In the concrete, by making RADARSAT-1 simulated image, the research includes comparisons for the means of velocity measurement classified by directions of movement as in the four following cases. 1. A case in which the object that becomes the target exists independently, 2. When there is a tidal current of 1 m/s, 3. When there exists moving targets of different velocity on the azimuth, 4. When the target is contiguous to the land where it has high back scatter factor. As a result, when the object, which becomes the target, independently exists on SAR image in the range of 128 pixels, the velocity of object could be measured with high accuracy. However, when there existed other moving targets in the range of 128 pixels or when the target was contiguous to the land of high back scatter factor, the velocity was in error by 10% at the maximum. This is because in the process of assuming the targets location, an error occurred due to the disturbed signals affected by the scatterers.