LainePoiss—a lightweight and ice-resistant wave buoy

Wave buoys are a popular choice for measuring sea surface waves, and there is also an increasing interest for wave information from ice-covered water bodies. Such measurements require cost-effective, easily deployable, and robust devices. We have developed LainePoiss (LP)---an ice-resistant and lightweight wave buoy. It calculates the surface elevation by double integrating the data from the inertial sensors of the micro-electromechanical system (MEMS), and transmits wave parameters and spectra in real-time over cellular or satellite networks. LP was validated through: 1) sensor tests, 2) wave tank experiments, 3) a field validation against a Directional Waverider, 4) an inter-comparison of several buoys in the field, and 5) field measurements in the Baltic Sea marginal ice zone. These extensive field and laboratory tests confirmed that LP performed well (e.g., the bias of significant wave height in the field was 0.01 m, correlation 0.99 and scatter index of 8 %). LP was also deployed with an Unmanned Aerial Vehicle and we present our experience of such operations. One issue that requires further development is the presence of low-frequency artefacts caused by the dynamic noise of the gyroscope. For now, a correction method is presented to deal with the noise.

Spatially Distributed Sea Wave Measurements

In recent years, there has been growing interest in remote and proximal observation of sea surface waves [...]

The wave spectrum in archipelagos

Sea surface waves are important for marine safety and coastal constructions, but mapping the wave properties at complex shorelines, such as coastal archipelagos, is challenging. The wave spectrum, E(f), contains a majority of the information about the wave field, and its properties have been studied for decades. Nevertheless, any systematic research into the wave spectrum in archipelagos has not been made. In this paper we present wave buoy measurements from 14 locations in the Finnish archipelago. The shape of the wave spectrum showed a systematic transition from a single peaked spectrum, to a spectrum with a wide frequency range having almost constant energy. The exact shape also depended on the wind direction, since the fetch, island, and bottom conditions are not isotropic. The deviation from the traditional spectral form is strong enough to have a measurable effect on the definitions of the significant wave height. The relation between the two definitions in the middle of the archipelago was H1/3 = 0.881 Hs, but the ratio varied with the spectral width (Hs was defined using the variance). At this same location the average value of the single highest wave, Hmax/Hs, was only 1.58. A wider archipelago spectrum was also associated with lower confidence limits for the significant wave height compared to the open sea (6 % vs. 9 %). The challenges regarding the instability of the peak frequency and the difficulties in finding a good characteristic frequency for an archipelago spectrum is discussed. The mean frequency, weighted with E(f)4, is proposed as a compromise between stability, and bias with respect to the peak frequency.