A data set of sea surface stereo images to resolve space-time wave fields

Abstract

Stereo imaging of the sea surface elevation provides unique field data to investigate the geometry and dynamics of oceanic waves. Typically, this technique allows retrieving the 4-D ocean topography (3-D space + time) at high frequency (up to 15–20 Hz) over a sea surface region of area ~104 m2. Stereo data fill the existing wide gap between sea surface elevation time-measurements, like the local observation provided by wave-buoys, and large-scale ocean observations by satellites. The analysis of stereo images provides a direct measurement of the wavefield without the need of any linear-wave theory assumption, so it is particularly interesting to investigate the nonlinearities of the surface, wave-current interaction, rogue waves, wave breaking, air-sea interaction, and potentially other processes not explored yet. In this context, this open dataset aims to provide, for the first time, valuable stereo measurements collected in different seas and wave conditions to invite the ocean-wave scientific community to continue exploring these data and to contribute to a better understanding of the nature of the sea surface dynamics.

A Low-Cost Stereo Video System for Measuring Directional Wind Waves

“…Particular mismatches can occur on the edge of the matched area. To deal with those potential errors, it is recommended to consider only those points lying in the central part of the matched area [34]. For the data provided here, most of the image pixels were matched (1.4 million, as seen in Figure 3-red dots).…”

“…Our main goal is to present a simple and effective way to synchronize video records from smartphones or any video device with audio built-in using a stereo system to estimate the surface elevation. The technique per se has been extensively tested under a variety of sea state conditions [14,28,29,33,34,36]. Here, to demonstrate that the proposed synchronization technique is robust, some comparisons with in situ wave measurements as ground truth are discussed.…”

“…More recently, Bergamasco et al [29] proposed WASS (Waves Acquisition Stereo System), the first open-source stereo processing pipeline for sea waves 3-D reconstruction. Its availability, combined with the low cost of the required setup, contributed to the flourishing of numerous works including [31][32][33][34]. Compared to conventional instruments, a stereo video system is considered a low-cost observation method, requiring a pair of synchronized video cameras connected to a computer.…”

Deep neural networks for active wave breaking classification

“…From the original images, randomly selected subsets of size 256 × 256 pixels centered on the fitted ellipses were extracted and manually labelled as either active wave breaking (label 1, or positive) or otherwise (label 0, or negative). The present training dataset was generated using raw video imagery data from Guimarães et al 36 and consisted of 19,000 training and 1300 testing images (see Table 1). The training dataset is further split into 80% training and 20% validation data 37 .…”

“…Note that up to the clustering step, all calculations were done in pixel domain and "time" was obtained from sequential frame numbers. To convert between pixel and metric coordinates, the grids constructed using the stereo-video dataset available from Guimarães et al 36 were used in the present study. If stereo video data are not available, such conversions could be done knowing the camera position in real-world (that is, metric) coordinates, which is usually done using surveyed ground control points 53,54 .…”