Yeli Yuan

Theoretical expression for an ocean internal soliton synthetic aperture radar image and determination of the soliton characteristic half width

This paper deals with the development of techniques for satellite synthetic aperture radar (SAR) ocean image interpretation. We derived a theoretical model of a radar image for a Korteweg-de Vries type ocean internal soliton and validated the model using ocean internal wave signals taken from ERS-1 SAR and RADARSAT SAR images. The results indicate that the model perfectly simulates ocean internal soliton signatures with double-sign variations of radar backscatter. On the basis of the model, we developed the curve fitting method and the peak-to-peak method for determining the internal soliton characteristic half widths, which then were used to calculate the internal soliton amplitudes. The test results indicate that ocean internal soliton amplitudes derived by the two methods agree with in situ data acquired on the Portuguese Continental Shelf and in the South China Sea with reasonable accuracy. The role that wind fields play in ocean radar remote sensing was also analyzed. Finally, the modulation ratio of ocean internal waves on radar images was quantitatively estimated.

The local properties of ocean surface waves by the phase-time method

Traditionally, investigation of statistical properties of ocean waves has been limited largely to global quantities related to elevation and amplitude such as the power spectral and various probability density functions. Although these properties give valuable information about the wave field, the results cannot be related directly to any portion of the time data from which it was derived. We present a new approach using phase information to view and study the properties of frequency modulation, wave group structures, and wave breaking. We apply the method here to ocean wave time series data and identify a new type of wave group (containing the large “rogue” waves), but the method also has the capability of broad applications in the analysis of time series data in general.

Statistical Characteristics of Breaking Waves

The modification of the shape of the wave spectrum in the high-frequency range and the amount of energy loss, due to wave breaking are examined. The original waves are assumed to be Gaussian, stationary, and of finite bandwidth. Breaking is assumed to occur when the vertical acceleration at any point on the surface reaches g/2. Based on the wave breaking model, an approximate but accurate spectrum of breaking waves and an exact expression of the amount of energy loss due to wave breaking are derived. It is shown that the spectrum which corresponds to minimum rate of energy loss has an upper limit proportional to in the high-frequency range.

Evidence of the coexistence of upstream and downstream solitary wavetrains in the real atmosphere

From a true colour image of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard the Orbview-2 satellite, we observed two packets of orderly wave clouds on two sides of Hainan Island in the South China Sea. A packet of 23 wave clouds stretches southward from the island. A second packet of more than 20 wave clouds stretches north-eastward off the north-east coast of the island. The concave orientation of the wave cloud lines implies that both packets are propagating away from the island. A chart of geopotential height and velocity at 850 mbar shows a south-westerly air flow over the island; hence the two wave cloud packets propagate upstream and downstream, simultaneously. Thus, we have found new evidence of the coexistence of both upstream and downstream solitary wavetrains generated in the real atmosphere by land topographic disturbances. Comparison with theoretical results supports this conclusion.