Oceanographic Applications of ALOS PALSAR Imagery to the Coast of Korea Peninsula
Duk-jin Kim(1), Jinho Kang(1), Hoonyol Lee(2) and Younsoo Kim(1)
(1) Korea Aerospace Research Institute, 45 Eoeun-Dong, Yuseong-Gu, Daejeon, 305-333, Korea
(2) Kangwon National University, 192-1, Hyoja 2Dong, Chuncheon, Kangwon-do 200-701, Korea
Synthetic Aperture Radar (SAR) is one of the most cost-effective and powerful all-weather tools to observe the ocean surface without much restriction compare to optical sensors. The SAR system has ability to observe ocean surface through the sensor’s high spatial resolutions and large spatial coverage extents, which makes the sensor a suitable monitoring tool to asses such oceanic variables including surface winds, waves, currents and coastal environment. In this study, two research themes have been carried out to evaluate potential use of SAR data for an oceanographic application in the coast of Korean Peninsula by utilizing ALOS PALSAR as well as now-operating SAR satellite (ERS-2 SAR, ENVISAT ASAR, RADARSAT-1, TerraSAR-X).
The first research theme is to study ocean surface currents through SAR image with Doppler effect. SAR has ability to measure the Doppler shift information of object in motion and the shift is proportional to the object’s line-of-sight velocity. The Doppler centroid estimated from raw SAR signal differs from a predicted value based on the predicted motion of the satellite and Earth rotation. This difference can be converted to a surface Doppler velocity. Utilizing the methodology, ocean surface current in Yellow Sea was collected with ALOS PALSAR for analyses, and the estimated results were compared with in-situ measurements obtained from HF Radar.
The second research theme is to study a recent oil spill occurred on coast of South Korea with SAR imageries. On December 7, 2007, maritime oil spill has occurred on the coast of the Yellow Sea in South Korea. About 10,500 tons of crude oil was spilled into the Sea. After the spill occurred, several SAR images including TerraSAR-X, ENVISAT ASAR, and ALOS PALSAR have acquired imageries over the area from December 9 to December 20. This study investigates the dark patches shown in the multi-frequency SAR images and the influence of environmental conditions. The results of damping ratio measured at each radar frequency are modeled and analyzed. Several automatic techniques for oil spill detection from SAR images are also applied.