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Spaceborne microwave sensors, such as microwave scatterometers, radar altimeters, and microwave radiometers, can observe the sea surface day and night and are not affected by clouds. Except for the synthetic aperture radar, their spatial resolution is in the order of 10 km. While visible and infrared radiometers provide high-resolution images of chlorophyll a concentration and sea surface temperature, microwave sensors focus on global observations of physical parameters of the sea surface. To achieve accurate observation, it is indispensable to develop algorithms that are based on the physical processes at the air-sea boundary, evaluate observation accuracy, comprehend the error characteristics, and provide feedback for algorithm improvement. In this paper, I would like to summarize my research on ocean observations using three different types of microwave sensors and their applications as well as describe future prospects. [ABSTRACT FROM AUTHOR]

The Synthetic Aperture Radar (SAR) around the western entrance of the Tsugaru Strait has yielded well-defined images of an internal-wave packet accompanied by two or three surface-streaks (surface convergence within the same water mass), which is active during the stratified season, and whose wavelength is in the order of several hundred meters. Most of the waves in the packet were observed near the topographically shallow parts of the sill. Temporal changes were repeatedly observed in the internal waves confined to the sill using a high-frequency echosounder profiler within one-day in the summer 2017. The acoustic images suggest that a wave packet of extraordinary amplitude (> 150 m) has developed transiently around the downstream side of the sill at the ascending passage flow. This wave packet consists of two or three successive streak bands, with very disturbed sea surface conditions overlying wave troughs, i.e., strong downwelling areas. The dynamics of such waves developing over the sill is studied through a fully nonlinear nonhydrostatic numerical model. The vertical fluid stratification and temporal change of the barotropic passage flow were adjusted to approximate our observation conditions. The results suggest that the wave packet is effectively amplified near the downstream side of the sill, where the Froude number becomes a critical point, because upstream propagating waves on the sill slope stagnate and overlap efficiently. In this dynamical process, however, even if the wave grows to large amplitude, it does not form a well-organized solitary wave, but is rather scattered due to the strong dispersion of waves. [ABSTRACT FROM AUTHOR]

The Synthetic Aperture Radar (SAR) around the western entrance of the Tsugaru Strait has yielded well-defined images of an internal-wave packet accompanied by two or three surface-streaks (surface convergence within the same water mass), which is active during the stratified season, and whose wavelength is in the order of several hundred meters. Most of the waves in the packet were observed near the topographically shallow parts of the sill. Temporal changes were repeatedly observed in the internal waves confined to the sill using a high-frequency echosounder profiler within one-day in the summer 2017. The acoustic images suggest that a wave packet of extraordinary amplitude (> 150 m) has developed transiently around the downstream side of the sill at the ascending passage flow. This wave packet consists of two or three successive streak bands, with very disturbed sea surface conditions overlying wave troughs, i.e., strong downwelling areas. The dynamics of such waves developing over the sill is studied through a fully nonlinear nonhydrostatic numerical model. The vertical fluid stratification and temporal change of the barotropic passage flow were adjusted to approximate our observation conditions. The results suggest that the wave packet is effectively amplified near the downstream side of the sill, where the Froude number becomes a critical point, because upstream propagating waves on the sill slope stagnate and overlap efficiently. In this dynamical process, however, even if the wave grows to large amplitude, it does not form a well-organized solitary wave, but is rather scattered due to the strong dispersion of waves. [ABSTRACT FROM AUTHOR]