Oceanic Internal Waves Observation Based On High-temporal Resolution Geostationary Orbit Optical Satellites

Oceanic internal waves are dynamic phenomenon widely distributed in the interior of various oceans around the world,which has an important impact on the marine ecological environment,maritime engineering construction,and marine military activities.Optical remote sensing is one of the main means of large-scale detection of oceanic internal waves which can obtain the distribution of spatial-temporal characteristics and dynamic morphological characteristics.During the propagation,affected by themselves and the external environment,the morphological characteristics of oceanic internal waves in optical remote sensing images are constantly changing,which requires uninterrupted continuous monitoring;at the same time,the phenomenon of brightness reversal occurs frequently,and the cause of this phenomenon is a scientific question worthy of study.In this paper,high temporal resolution geostationary orbit optical satellites data are used to study oceanic internal waves in Sulu Sea and Celebes Sea.Firstly,taking the internal wave in the Sulawesi Sea as an example,based on the calculation theory of sunglint and critical viewing angles,the common brightness reversal phenomena of oceanic internal waves are analyzed;secondly,the bright and dark patterns of oceanic internal waves in geostationary orbit optical satellites and polar-orbit optical satellites are compared;after fully understanding the bright and dark patterns of oceanic internal waves in optical images,the continuous tracking of oceanic internal waves in the Sulu Sea is realized based on high temporal resolution data,and the changes in their propagation direction and propagation speed during the propagation are analyzed.The main conclusions are as follows:(1)In the optical image,there is a brightness reversal phenomenon of the oceanic internal waves caused by the critical solar zenith angle in continuous moment images,and the critical relative azimuth angle is also existential that causes the brightness reversal phenomenon of the oceanic internal waves at different locations in a same image;and the specific values of the critical solar zenith angle and the critical relative azimuth angle are determined according to the actual imaging situation.(2)There is a boundary of sunglint in the geostationary optical satellite image,and the brightness reversal occurs when the oceanic internal waves cross this boundary,and the size of the boundary is variable,controlled by factors such as imaging time,imaging angle,and oceanic background wind speed.(3)Oceanic internal waves in geostationary orbit optical satellite images sunglint can exhibit a special pattern of bright-dark-bright.The bright and dark patterns of the same oceanic internal wave in the images acquired by different geostationary orbit optical satellites are consistent;the critical sensor viewing angle and the critical solar zenith angle will cause the bright and dark patterns of the same ocean internal wave in the geostationary orbit optical satellite and polar orbit optical satellite images to be reversed,but the essence is still that the relative position of the oceanic internal wave and the sunglint is changes.(4)Himawari-8 satellite and FY-4A satellite can track the changes of dynamical characteristics of oceanic internal waves.For example,oceanic internal waves are generated near the Sulu Islands and propagates northward into the Sulu Sea.The propagation direction is not unique when they are generated,and the propagation speeds are less than 0.8m/s;when the oceanic internal waves enter the Sulu Sea,their propagation directions are more than 300 °(north-west direction),and the propagation speeds are about 2m/s.During the propagation,the directions and speeds of oceanic internal waves are both affected by water depth.