Assessment of theoretical approaches to derivation of internal solitary wave parameters from multi-satellite images near the Dongsha Atoll of the South China Sea

This study assesses the accuracy and the applicability of the Korteweg-de Vries (KdV) and the nonlinear Schrodinger (NLS) equation solutions to derivation of dynamic parameters of internal solitary waves (ISWs) from satellite images. Visible band images taken by five satellite sensors with spatial resolutions from 5 m to 250 m near the Dongsha Atoll of the northern South China Sea (NSCS) are used as a baseline. From the baseline, the amplitudes of ISWs occurring from July 10 to 13, 2017 are estimated by the two approaches and compared with concurrent mooring observations for assessments. Using the ratio of the dimensionless dispersive parameter to the square of dimensionless nonlinear parameter as a criterion, the best appliable ranges of the two approaches are clearly separated. The statistics of total 18 cases indicate that in each 50% of cases, the KdV and the NLS approaches give more accurate estimates of ISW amplitudes. It is found that the relative errors of ISW amplitudes derived from two theoretical approaches are closely associated with the logarithmic bottom slopes. This may be attributed to the nonlinear growth of ISW amplitudes as propagating along a shoaling thermocline or topography. The test results using three consecutive satellite images to retrieve the ISW propagation speeds indicate that the use of multiple satellite images (>2) may improve the accuracy of retrieved phase speeds. Meanwhile, repeated multi-satellite images of ISWs can help to determine the types of ISWs if mooring data are available nearby.