Science Service System

Summary of Proposal COA0061

TitleCoastal zone mapping and monitoring using SAR
Investigator Yang, Chan Su - Korea ocean Research and Development Insitute, Korea Ocean Satellite Center
Team Members
Research Scientist Shanmugam, Palanisamy - Korea Ocean Research and Development Institute, Ocean Satellite Research Group
SummaryThe main objectives of this research are to (1) characterize the complex network of tidal flats/coastal wetlands along the Korean western coastal areas using image fusion/classification techniques applied to SAR and optical data sets (2) Estimate the aquaculture facilities around the Korean western coastal areas and identify potential areas for acquaculture farming using feature extraction techniques applied to SAR data (3) Develop algorithms to retrieve and monitor the hyghly dynamic suspended sediments along the Korean western and southern coastal areas using SAR data and in-situ bio-optical data. In addition to this, we plan to use SAR and combined SAR+optical data for delineating potential areas of red tides that occur along the southern coastal areas (4) Validate the results of above methods using concurrent in-situ data that will be collected during the satellite overpass. The main data requirements for achieving the above results include TSAR data, other satellite multispectral data, groudtruth data and bio-optical data. The outcome of this integrated research is (1) Tidal channel morphology and classification maps (2) Wetland/vegetation classification maps (3) Aquaculture forming area map (4) Suspended sediment maps for Korean west coastal areas (5) Red tide maps. The total number of TSAR producres required for this research project will be about 25-30 nos.
Detailed reportRemote sensing has become an important tool for mapping and monitoring coastal environmental features and various scales of changes caused by natural and anthropogenic factors and processes. However, mapping and monitoring of these features are limited with the optical remote sensing data that are eventually affected by frequent cloud cover over the coastal areas; therefore researchers have looked for other methods based on radar remote sensing. In this regard Synthetic Aperture Radar (SAR) data have proven useful in detection and monitoring of coastal area. The German mission, TerraSAR-X, designed to provide high quality data, will make significant contribution to the enhanced understanding of hydrology, geology, land environment, renewable resources and oceanography. The current proposal aims to investigate potential utility of TerraSAR data in Korean coastal waters. For coastal area mapping and monitoring, shorter X-band SAR data will be advantageous over longer C- and L-bands SAR data for detecting and monitoring small scale features of coastal/marine ecosystem. The main objectives of this research are to (1) characterize the complex network of coastal wetlands along the Korean western coastal areas using image fusion/classification techniques applied to SAR and optical data sets (2) Estimate the aquaculture facilities around the Korean western coastal areas and identify potential areas for aquaculture farming using feature extraction techniques applied to SAR data (3) Improve the prediction model of oil slicks movement under the strong tidal current condition using SAR data, wind and current information. This report is organized based on published papers which are described here as following studies: Study I: Analysis of bar morphology using multi-temporal and multi-sensor satellite images: Example from the Han Estuary, Korea This study describes a new powerful technique of studying bar morphology using multi-sensor and multi-temporal satellite images with examples from the inaccessible field sites of the Han Estuary in Korea. The technique utilizes the ability of multi-spectral optical sensors for classifying the types of land cover, and the ability of SAR for acquiring radar imagery during day and night, irrespective of cloud cover. Combining the data acquired by both types of sensors at different times, the bar morphology of the Han Estuary is analyzed in this study. The Han Estuary is situated on the North Limit Line (NNL) dividing North and South Korea, and considered to have retained its rich ecological value. However, because of the limited access to the estuary, little information is available on the morphology of the Han Estuary, and the technique based on satellite remote sensing described in this paper is the most suitable and only approach to obtain information on such inaccessible areas. In the study, the bar morphology of the Han Estuary from the years 2000 to 2009 is investigated using multi-temporal spaceborne optical sensors including those on board of SPOT-5, LANDSAT-7, QuickBird, KOMPSAT-2, and OrbView-3, and also C-band SAR on board of RADARSAT-1 and ENVISAT with limited field survey data. In this study 16 sets of optical data and 12 sets of SAR data were used to examine the spatial and temporal variations of bar morphology and the effects of tide and precipitation. The results show that there was some variation in shape and size of bars depending on the location. The tidal effect is large on the bars closer to the open Yellow Sea, and the effect of precipitation was observed on the bars located in the mouths of rivers. Based on the changes of the bar–water boundary, a topographical map was produced, showing the relative height of bars. Using the technique of satellite remote sensing, this paper has shown, for the first time, the long-term bar morphological characteristics of the restricted Han Estuary on the NLL, and the authors anticipate that the results together with the relative height map of bars will constitute the basis of future morphological and ecological studies in this important estuary. Study II: Extraction of Underwater Laver Cultivation Nets by SAR Polarimetric Entropy This study 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. The cultivation nets were placed in very shallow water below the sea surface, so that the surface is almost specular at L-band under low-to-moderate wind speeds. TerraSAR-X amplitude images were also analyzed, showing similar image contrast at VV polarization to those of PALSAR images. At HH polarization, however, TerraSAR-X has higher ability of detecting the cultivation nets than PALSAR, mainly because of larger difference in RCS at X-band between the sea surfaces with and without the cultivation nets. This difference in amplitude is too small for PALSAR L-band images, particularly at HH polarization, to accurately detect the net areas. In order to improve the detection accuracy by PALSAR, we used entropy analysis, resulting in clear difference between the dominant surface scattering of low entropy from open sea surface and the random process (system noise) of high entropy over the underwater net areas. Finally, CFAR was applied to entropy images to estimate the net area, and comparison with the true net size showed good agreement. Study III: Analysis of the Contribution of Wind Drift Factor to Oil Slick Movement under Strong Tidal Condition: Hebei Spirit Oil Spill Case. The purpose of this study is to investigate the effects of the wind drift factor under strong tidal conditions in the western coastal area of Korea on the movement of oil slicks caused by the Hebei Spirit oil spill accident in 2007. The movement of oil slicks was computed using a simple simulation model based on the empirical formula as a function of surface current, wind speed, and the wind drift factor. For the simulation, the Environmental Fluid Dynamics Code (EFDC) model and AWS were used to generate tidal and wind fields respectively. Simulation results were then compared with 5 sets of spaceborne optical and synthetic aperture radar (SAR) data. The fixed wind drift factor may cause uncertainty for prediction results of oil slick movement using the empirical formula. In this study, the effect of the wind drift factor was investigated for the case of the 2007 Hebei Spirit accident under strong tidal condition by comparing the results of numerical simulation with 5 sets of satellite image data. It was found that the best matching rates were obtained with different wind drift factors, and that the optimum drift factor is, to first order, linearly proportional to the wind speed. Based on the regression relation, a modified empirical equation was proposed, and using this equation the movement of oil slicks was re-calculated by numerical simulation. Comparison of the results with the satellite data showed high matching rate of over 60%, in particular, the new model improved the matching accuracy by 9% under strong wind speed and high tidal condition in comparison with the conventional model. For more stringent validation, further study is required with more data and other location which has difference conditions, such as bottom topography, dominant surface current, etc., since the present model was derived from the limited data as a preliminary result. From the present study, it was found that highest matching rate between the simulation results and satellite imagery was obtained with different values of the wind drift factor, and to first order, this factor was linearly proportional to the wind speed. Based on the results, a new modified empirical formula was proposed for forecasting the movement of oil slicks on the coastal area. According to the brief description of the studies stated beforehand, it can be mentioned as a concluding remark that the TerraSAR-X data has proved its potentiality in several fields of remote sensing.

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