Wave measurement methods from moving vessels using GNSS Reflectometry

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K19848
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 63:Environmental analyses and evaluation and related fields
• Research Institution: Kyushu University
• Principal Investigator: Ichikawa Kaoru 九州大学, 応用力学研究所, 准教授 (40263959)
• Project Period (FY): 2021-07-09 – 2024-03-31
• Keywords: GNSS / 海面反射 / 干渉計 / 波浪計 / 有義波高 / 波浪周期 / フェリー観測

Outline of Final Research Achievements

Estimation of wave fields is essential for marine transports and developments. Although the accuracy of estimation has improved by the progress of numerical models, wave observations are still insufficient especially in coastal areas. This study, therefore, established a low-cost method to observe wave fields from moving ships.
The GNSS signals reflected at the sea surface travel a longer path than the direct signals, so the mixed signal intensity fluctuates depending on the phase difference of two signals. Every time when the excess path length changes by the wavelength of GNSS signals, approximately 0.2 m, due to the sea surface height changes by waves, periodic interference fringes appear in the received signal intensity. By measuring the periodicity and number of these fringes, the wave period and significant wave height (SWH) can be estimated. By applying to actual observation data on a ferry, both estimations of the wave period and SWH were confirmed practically accurate.

Free Research Field

海洋物理学

Academic Significance and Societal Importance of the Research Achievements

海運や海洋資源開発には波浪予測が不可欠だが，複雑な地形や海流の影響を受けて変化しやすい沿岸域の波浪予測の精度を上げるには，細かな波浪観測が不可欠である。国土交通省港湾局のナウファスなど，沿岸域の波浪観測網の維持管理は予算と手間のかかる事業であり，安価なシステムの開発が望まれている。
一方，今回の測定装置は，安価で小型・省電力のGNSS受信装置で構成されており，小型のアンテナを船体舷側に設置するだけで完了できる。つまり，低予算で多数の船に取付けて波浪観測網を充実させることができる。観測網が実現すれば，海運・海洋資源開発の観点から社会的な意義は大きい。