Sun-glint imagery of Landsat 8 for ocean surface waves

Abstract

Local changes in specular reflections of visible sunlight on the ocean surfaces can be captured effectively by satellite sensors operating in the visible range of the electromagnetic spectrum. This causes the sun-glint imagery to closely resemble the oceanic images obtained using Synthetic Aperture Radar (SAR) further allowing the identification of the various fine scale structures and patterns of the ocean. Moreover, at relevant spatial resolutions, cloud-free conditions as well as optimum relative positions of the sensor, sun and the wave front it is possible to image ocean waves, wave transformations and refraction patterns using Satellite Sun-glint imagery (SSGI). In the present study, Landsat OLI imagery captured along the coast of Brest, France is used to derive ocean wave characteristics such as wavelength, direction, amplitude and then mapped to better understand the process of wave transformation. The 2D fast Fourier transform technique has been used on Band 5 (NIR, 0.851 - 0.879μm) to derive the wavelength of swell waves in nearshore regions as well as to analyze the wavelength change. Furthermore, owing to the detector configuration of Landsat 8 OLI there is a small time lag between the channel acquisitions. This effectively helps to infer the space-time characteristics of the surface waves using the cross channel correlation between Band 5 and Band 6 subsequently enabling removal of the directional ambiguity associated with the wave spectra obtained from the analysis. The main purpose of this study is to demonstrate the importance of SSGI in deriving relevant coastal information which can be further utilized for bathymetry, surface current and wave motion determinations.