Remote Sensing of Ocean Internal Waves

Dear Colleagues,

This Special Issue involves using satellites and other instruments to detect and study the internal waves that occur within the ocean. The existence of internal waves (IWs) in the depth of marine waters is caused by stable stratification, which corresponds to water density increases in the direction of the gravity force. Internal waves play an important role in processes of horizontal and vertical exchange and mixing of waters, and in the formation of the thermohaline circulation of water objects as well. Motions caused by IWs have a great influence on dynamic processes in the World Ocean and on its surface. The amplitude of IWs can reach one hundred meters in the ocean and the length of waves can reach many kilometers, but variations of the water surface are usually insignificant at that. Nevertheless, IWs can manifest on the ocean surface under certain conditions, modulating short wind gravity‒capillary waves by their orbital currents.

IWs are known to strongly affect processes in the ocean. Motions induced by IWs transpierce the whole body of ocean water and also play an important role in processes at its surface. They can propagate over several hundred kilometers and transport both mass and momentum. IW propagation is accompanied by a considerable velocity shear that can lead to turbulence and mixing. That is why IWs, and mechanisms of their generation, development, propagation, and decay, are always a research focus.

One of the primary methods for the remote sensing of ocean internal waves is using satellite synthetic aperture radars (SARs). The surface manifestation of internal waves (SMIWs) usually look like alternating parallel bands of enhanced and attenuated surface roughness. The resulting surface roughness variations are translated into contrast variations in the radar data. SMIWs are made visible in the SAR data due to: (i) associated with IW orbital currents that modulate, in one way or another, the short surface wave spectra; and (ii) surface films that cause changes in the surface tension.

Ocean Color Data, obtained via high-resolution sensors, can also be used for studying ocean internal waves, especially from those obtained in sun glint areas. Satellite observations of SMIWs enable determining their spatial parameters and regions of regular occurrence, as well as analyzing possible generation mechanisms and evolution. Combined analysis of satellite radar and VIS/NIR data open the possibilities to (1) consider smaller scales since data with resolutions of units of meters are now available; (2) compare radar and optical data obtained almost simultaneously in the same region and at same high resolution; and (3) investigate IW development and propagation in time due to smaller intervals between the observations.

Another method for the remote sensing of ocean internal waves is using acoustic instruments. Acoustic instruments, such as sonar systems and ADCP, can be used to measure the velocity and direction of the waves as they move through the water. This information can be used to create detailed maps of the internal wave field.

In addition to remote sensing, other techniques can also be used for studying ocean internal waves. For example, oceanographic buoys equipped with sensors can be used to measure the temperature, salinity, and velocity of the water at different depths. These measurements can provide valuable information about the structure and dynamics of the internal wave field.

Of interest are all the articles on internal waves in the ocean and on the shelf, where remote sensing methods are used, as well as contact methods of measurements in natural measurements. In addition, data from laboratory experiments and numerical simulations are welcome.

Dr. Andrey N. Serebryany
Prof. Dr. Olga Lavrova
Guest Editors

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• remote sensing
• sensor
• ocean internal waves
• internal solitons
• satellite
• radar
• Ocean Colour Data
• acoustic
• ADCP
• ocean circulation
• mixing
• ocean energy transfer