Sun glitter imaging of submarine sand waves on the Taiwan Banks: Determination of the relaxation rate of short waves

Abstract

[1] Above sand waves on the seafloor, surface short waves, which are responsible for the radiance distribution in remote sensing imagery, are modulated gradually by the submarine topography. The relaxation rate m r characterizes the rate at which the short waves reach their saturation range after being disturbed. It is a key parameter in the weak hydrodynamic interaction theory and is also a most important parameter in the imaging mechanism used for mapping submarine bottom topography. In this study, a robust expression containing intensity and phase (advection effect) modulations of the perturbed action spectrum of short waves was deduced, by using the first-order weak hydrodynamic interaction theory. On the basis of the phase modulation, a method was developed to determine the relaxation rate in the Sun glitter imaging mechanism. The relaxation rates were estimated using in situ data measured on a cruise over the sand waves of the Taiwan Banks, a sea area between the East China Sea and the South China Sea, on 28-29 August 2006. Results showed that, under a wind speed of 5.0 m s −1 , the relaxation rate of short waves was about 0.055 s −1 in response to current variations and about 0.025 s −1 equivalently in response to sea bottom topographic variations. The former value could be applied to interpret the amplitude of submarine topography by using satellite imagery, while the latter one (equivalent relaxation rate m′ r ) could help to more accurately calibrate the spatial position of the retrieved sea bottom topography.

Himawari-8 Geostationary Satellite Observation of the Internal Solitary Waves in the South China Sea

“…All AHI images have been calibrated and georeferenced. Three factors limit the detection or continuous tracking of ISWs in the ocean: (1) the sea surface signatures of ISWs are overlaid with clouds so it is difficult to extract the ISW wave crests; (2) the displacements of ISW wave crests is too small to differentiate in ten minutes; (3) the relative angle between the sun and the satellite is not meet the imaging mechanism of ISWs under the condition of sun glint (Bai et al, 2014a;Cox and Munk, 1954;Gagliardini, 2011;Jackson and Alpers, 2010;Shao et al, 2011;Zhang and Wang, 2010). To ensure accuracy, we abandon some degraded images mainly due to the above three factors, and resulted in 19 images observing the ISW 'b' in the north of Dongsha atoll.…”

Bathymetric mapping of submarine sand waves using multiangle sun glitter imagery: a case of the Taiwan Banks with ASTER stereo imagery

“…According to Shao et al, 31 μ is approximately 0.055 s −1 for the Taiwan Banks. EðkÞ denotes the spectral energy density of waves, and ∂U∕∂x denotes the current velocity gradient.…”

Whitecap features induced by submarine sand waves in stereo optical imagery

“…Therefore, limited solar radiance reaches the seafloor, making it particularly difficult to identify seafloor bathymetry. However, the submarine sand waves are always visible using sun glitter images [Shao et al, 2011]. In the last few decades, numerous studies have surveyed sand wave characteristics in the Taiwan Banks [e.g., Boggs, 1974;Liu, 1996;Du et al, 2008;Shao et al, 2014;Zhang et al, 2014;Bao et al, 2014].…”