Wavelet-Discrete Cosine Transform Synergy for Ship Motion-Based Sea State Estimation in Autonomous Ships

Developing a robust autonomous sea state estimation (SSE) model stands as a pivotal challenge in advancing autonomous ships. Presently, deep learning (DL) methodologies have showcased remarkable efficacy in SSE tasks. Nonetheless, the dynamic nature of ship motion introduces temporal variations alongside frequency domain characteristics like periodic swinging, posing challenges for existing DL approaches. Most prevailing DL techniques, predominantly leveraging Convolutional Neural Networks or Long Short-Term Memory Networks, often fail to effectively harness frequency domain information post feature extraction. To tackle these limitations head-on, this paper introduces a pioneering SSE model. Specifically, in order to solve the frequency-domain feature extraction problem, we design a wavelet transform-based frequency domain encoder to extract relevant frequency-domain features from ship motion data by discriminating the contribution of different frequencies in the signal. Subsequently, in order to better integrate the extracted ship motion features, we designed a Feature Perception module based on discrete cosine transform. This module adeptly merges the extracted feature insights while prioritizing crucial frequency domain features. Following rigorous experimentation, our methodology exhibits superior performance compared to existing baseline techniques in SSE, a capability of profound significance for autonomous ships. Moreover, across diverse public multivariate time series classification datasets, our model outperforms current state-of-the-art approaches, underscoring its scalability across distinct domains.