Estimation of Internal Wave Properties by Along-Track Interferometric SAR

Abstract

Satellite remote sensing has been widely used to monitor the physical properties of ocean because of its wide and repeated coverage. Among many satellite sensors, synthetic aperture radar (SAR) is considered as one of the most effective sensors because of its all-weather and day-and-night data acquisition capability. The penetration depth of microwave into sea water is a few millimeters or less, and therefore SAR does not directly image underwater phenomena. However, internal waves (IWs) are often observed by SAR through the difference in sea surface roughness. In this study, we used TerraSAR-X along-track interferometry (ATI) data which contains IWs near Dongsha Island in the northeastern South China Sea, acquired on 22 April 2010. The purpose of this study is estimation of IW parameters such as amplitude and mixed layer depth. Sea current velocity induced by IWs was computed using an ATI technique to measure velocity of moving target from interferogram of complex images that is obtained by two separated antennas in along-track direction. The varying surface current induced by IWs is affected by water depth, water density, IW amplitude, and mixed layer depth. In this study, varying surface current was also computed using Korteweg-de Vries (KdV) equation that describes an ocean IW in a two-layer ocean with a hydrodynamic model. IW parameters were estimated by substituting surface current velocities by ATI into KdV eqsors because of its all-weather and day-and-night data acquisition capability. The penetration depth of microwave into sea water is a few millimeters or less, and therefore SAR does not directly image underwater phenomena. However, internal waves (IWs) are often observed by SAR through the difference in sea surface roughness. In this study, we used TerraSAR-X along-track interferometry (ATI) data which contains IWs near Dongsha Island in the northeastern South China Sea, acquired on 22 April 2010. The purpose of this study is estimation of IW parameters such as amplitude and mixed layer depth. Sea current velocity induced by IWs was computed using an ATI technique to measure velocity of moving target from interferogram of complex images that is obtained by two separated antennas in along-track direction. The varying surface current induced by IWs is affected by water depth, water density, IW amplitude, and mixed layer depth. In this study, varying surface current was also computed using Korteweg-de Vries (KdV) equation that describes an ocean IW in a two-layer ocean with a hydrodynamic model. IW parameters were estimated by substituting surface current velocities by ATI into KdV eq