Determining scale and sea state from water video

Abstract

In most image processing and computer vision applications, real-world scale can only be determined when calibration information is available. Dynamic scenes further complicate most situations. However, some types of dynamic scenes provide useful information that can be used to recover real-world scale. In this paper, we focus on ocean scenes and propose a method for finding sizes in real-world units and the sea state from an uncalibrated camera. Fourier transforms in the space and time dimensions yield spatial and temporal frequency spectra. For water waves, the dispersion relation defines a square relationship between the wavelength and period of a wave. Our method applies this dispersion relation to recover the real-world scale of an ocean sequence. The sea state--including the peak wavelength and period, the wind speed that generated the waves, and the wave heights--is also determined from the frequency spectrum of the sequence combined with stochastic oceanography models. The process is demonstrated on synthetic and real sequences, validating the results with known scene geometry. This has wide applications in port monitoring and coastal surveillance.

Motion Estimation for Dynamic Texture Videos Based on Locally and Globally Varying Models

“…A semitransparent constraint model was proposed assuming long-term smooth motion [49]. Using an experimental room, an IBC based on a cross-correlation method was estimated using an optic reflection model [15], [21], [40]. State-of-the-art optical flow models [38], [39], [48] use hyperparameter estimation based on stochastic models such as Ito's formula [38] and Bayesian inference [39], [48].…”

“…Therefore, we will introduce a novel velocity constraint based on a wave phenomenon model from wave theory [25]. In [25], it is stated that there is a relationship between wave number and angular frequency [20], [21]. This relationship explains the effect that when the wave number increases/decreases, the angular frequency increases/decreases.…”

Synthesizing waves from animated height fields

“…This allows us to use data from a relatively small window in time and detect temporal changes in dispersion under the assumption that angular frequency is a function of the wave vector and time. Spencer et al [2006] determine the scale of waves and sea state from video. In particular the scale is found by assuming a deep water dispersion relation and measuring the difference between propagation speeds for different wavelengths.…”

Motion estimation method based on physical properties of waves

“…Thus, flow waves with various orientations were ignored. Holland [14] and Spencer et al [15] analyzed many basic wave properties, such as the wave frequency and wavelength from a wave video of a seashore/the ocean in sunlight. In their methods, a dispersion relationship, which we also use, played a central role in deriving wave-related physical parameters.…”

“…A wave generation equation from ocean engineering [19] is used to model an image brightness change intergrated with the [10]'s basic model. To constrain the estimated velocity, a velocity-frequency relation equation [14,15,19] and a statistical property of the wave phenomenon [18,19] are applied. Optical flow and wave related parameters are obtained by a two-step optimization algorithm using two consecutive images.…”