Estimate of significant wave height from non-coherent marine radar images by multilayer perceptrons
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RESEARCH
Open Access
Estimate of significant wave height from noncoherent marine radar images by multilayer perceptrons Raúl Vicen-Bueno*, Cristina Lido-Muela and José Carlos Nieto-Borge
Abstract One of the most relevant parameters to characterize the severity of ocean waves is the significant wave height (Hs). The estimate of Hs from remotely sensed data acquired by non-coherent X-band marine radars is a problem not completely solved nowadays. A method commonly used in the literature (standard method) uses the square root of the signal-to-noise ratio (SNR) to linearly estimate Hs. This method has been widely used during the last decade, but it presents some limitations, especially when swell-dominated sea states are present. To overcome these limitations, a new non-linear method incorporating additional sea state information is proposed in this article. This method is based on artificial neural networks (ANNs), specifically on multilayer perceptrons (MLPs). The information incorporated in the proposed MLP-based method is given by the wave monitoring system (WaMoS II) and concerns not only to the square root of the SNR, as in the standard method, but also to the peak wave length and mean wave period. Results for two different platforms (Ekofisk and FINO 1) placed in different locations of the North Sea are presented to analyze whether the proposed method works regardless of the sea states observed in each location or not. The obtained results empirically demonstrate how the proposed non-linear solution outperforms the standard method regardless of the environmental conditions (platform), maintaining real-time properties. Keywords: significant wave height, marine radar, multilayer perceptrons, neural networks, sea surface, ocean waves
1. Introduction Ocean waves are oscillations of the free sea surface caused by the wind. Under severe meteorological conditions, ocean waves can be dangerous for human marine activities, such as navigation, on- and off-shore management, etc. One of the most important parameters to define the severity of a given ocean wave field is the so-called significant wave height, Hs, which is usually defined as the average of the one-third largest wave heights of the ocean wave field of study. Hs is usually estimated using in-situ sensors, such as buoys, recording time series of wave elevation information. A complementary technique to analyze ocean waves is to use remote sensing imaging methods, such as coherent radars [1-3], or conventional X-band marine radars [4-6], which are non-coherent radars commonly installed in moving vessels, as well as in * Correspondence: [email protected] Department of Signal Theory and Communications, Superior Polytechnic School, University of Alcalá, Alcalá de Henares, 28805, Madrid, Spain
on- and off-shore platforms, or marine traffic control towers. These non-coherent radars image the sea surface at grazing incidence with horizontal polarization. Radar images are caused by the interaction of the electromagnetic fields transmitted by the radar antenna with th
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