scholarly journals Shipboard Wave Measurements in the Southern Ocean

2017 ◽  
Vol 34 (9) ◽  
pp. 2113-2126 ◽  
Author(s):  
Björn Lund ◽  
Christopher J. Zappa ◽  
Hans C. Graber ◽  
Alejandro Cifuentes-Lorenzen
Keyword(s):  
Southern Ocean ◽  
Wave Frequency ◽  
Laser Altimeter ◽  
Frequency Spectra ◽  
Retrieval Method ◽  
Wave Measurements ◽  
X Band ◽  
Full Study ◽  
Shipboard Wave Measurements ◽  
Accurate Wave

AbstractSurface wave measurements from ships pose difficulties because of motion contamination. Cifuentes-Lorenzen et al. analyzed laser altimeter and marine X-band radar (MR) wave measurements from the Southern Ocean Gas Exchange Experiment (SOGasEx). They found that wave measurements from both sensors deteriorate precipitously at ship speeds 3 m s−1. This study demonstrates that MR can yield accurate wave frequency–direction spectra independent of ship motion. It is based on the same shipborne SOGasEx wave data but uses the MR wave retrieval method proposed by Lund et al. and a novel empirical transfer function (ETF). The ETF eliminates biases in the MR wave spectra by redistributing energy from low to high frequencies. The resulting MR wave frequency–direction spectra are shown to agree well with laser altimeter wave frequency spectra from times when the ship was near stationary and with WAVEWATCH III (WW3) model wave parameters over the full study period.

scholarly journals A Multisensor Comparison of Ocean Wave Frequency Spectra from a Research Vessel during the Southern Ocean Gas Exchange Experiment

2013 ◽  
Vol 30 (12) ◽  
pp. 2907-2925 ◽  
Author(s):  
Alejandro Cifuentes-Lorenzen ◽  
James B. Edson ◽  
Christopher J. Zappa ◽  
Ludovic Bariteau
Keyword(s):  
High Frequency ◽  
Doppler Radar ◽  
Inertial Sensors ◽  
Wave Spectrum ◽  
Ocean Wave ◽  
Modulation Transfer ◽  
Laser Altimeter ◽  
Frequency Spectra ◽  
Wave Statistics ◽  
Wave Measurements

Abstract Obtaining accurate measurements of wave statistics from research vessels remains a challenge due to the platform motion. One principal correction is the removal of ship heave and Doppler effects from point measurements. Here, open-ocean wave measurements were collected using a laser altimeter, a Doppler radar microwave sensor, a radar-based system, and inertial measurement units. Multiple instruments were deployed to capture the low- and high-frequency sea surface displacements. Doppler and motion correction algorithms were applied to obtain a full 1D (0.035–1.3 ± 0.2 Hz) wave spectrum. The radar-based system combined with the laser altimeter provided the optimal low- and high-frequency combination, producing a frequency spectrum in the range from 0.035 to 1.2 Hz for cruising speeds ≤3 m s−1 with a spectral rolloff of f−4 Hz and noise floor of −20/−30 dB. While on station, the significant wave height estimates were comparable within 10%–15% among instrumentation. Discrepancies in the total energy and in the spectral shape between instruments arise when the ship is in motion. These differences can be quantified using the spectral behavior of the measurements, accounting for aliasing and Doppler corrections. The inertial sensors provided information on the amplitude of the ship’s modulation transfer function, which was estimated to be ~1.3 ± 0.2 while on station and increased while underway [2.1 at ship-over-ground (SOG) speed; 4.3 m s−1]. The correction scheme presented here is adequate for measurements collected at cruising speeds of 3 m s−1 or less. At speeds greater than 5 m s−1, the motion and Doppler corrections are not sufficient to correct the observed spectral degradation.

scholarly journals Quantifying wave measurement differences in historical and present wave buoy systems

2021 ◽  
Author(s):  
Robert Edward Jensen ◽  
Val Swail ◽  
Richard Harry Bouchard
Keyword(s):  
Complex Nature ◽  
Frequency Spectra ◽  
Measurement Systems ◽  
Wave Measurements ◽  
Directional Sensors ◽  
Wave Measurement ◽  
Western Us ◽  
Directional Wave ◽  
Wind Sea ◽  
Wave Properties

AbstractAn intra-measurement evaluation was undertaken, deploying a NOMAD buoy equipped with three National Data Buoy Center and two Environment and Climate Change Canada-AXYS sensor/payload packages off Monterey, California; a Datawell Directional Waverider buoy was deployed within 19 km of the NOMAD site. The six independent wave measurement systems reported hourly estimates of the frequency spectra, and when applicable, the four Fourier directional components. The integral wave parameters showed general agreement among the five sensors compared to the neighboring Datawell Directional Waverider, with the Inclinometer and the Watchman performing similarly to the more sophisticated 3DMG, HIPPY, and Triaxys sensor packages. As the Hm0 increased, all but the Inclinometer were biased low; however, even the Watchman reported reasonable wave measurements up to about 6–7 m, after which the Hm0 becomes negatively biased up to about a meter, comparable to previous studies. The parabolic fit peak spectral wave period, Tpp, results showed a large scatter, resulting from the complex nature of multiple swell wave systems compounded by local wind-sea development, exacerbated by a variable that can be considered as temporally unstable. The three directional sensors demonstrated that NOMAD buoys are capable of measuring directional wave properties along the western US coast, with biases of about 6 to 9 deg, and rms errors of approximately 30 deg. Frequency spectral evaluations found similarities in the shape, but a significant under estimation in the high frequency range. The results from slope analyses also revealed a positive bias in the rear face of the spectra, and a lack of invariance in frequency as suggested by theory.

scholarly journals Spectral shapes and parameters from three different wave sensors

2021 ◽  
Author(s):  
Anne Karin Magnusson ◽  
Robert Jensen ◽  
Val Swail
Keyword(s):  
Frequency Spectra ◽  
Measurement Systems ◽  
Wave Measurements ◽  
Climate Monitoring ◽  
Production Platform ◽  
Wave Sensors ◽  
Central North Sea ◽  
Wave Forecasting ◽  
Wave Properties

AbstractThe quality of wave measurements is of primary importance for the validation of wave forecasting models, satellite wave calibration and validation, wave physics, offshore operations and design and climate monitoring. Validation of global wave forecasts revealed significant regional differences, which were linked to the different wave buoy systems used by different countries. To fully understand the differences between the wave measurement systems, it is necessary to go beyond investigations of the integral wave parameters height, period and direction, into the frequency spectra and the four directional Fourier parameters that are used to estimate the directional distribution. We here analyse wave data measured from three different sensors (non-directional Datawell Waverider buoy, WaveRadar Rex, Optech laser) operating at the Ekofisk oil production platform located in the central North Sea over a period of several months, with significant wave height ranging from 1 to 10 m. In general, all three sensors provide similar measurements of the integral wave properties and frequency spectra, although there are some significant differences which could impact design and operations, forecast verification and climate monitoring. For example, the radar underestimates energy in frequency bands higher than 8 s by 3–5%, swell (12.5–16 s) by 5–13%, while the laser has 1–2% more energy than the Waverider in the most energetic bands. Lee effects of structures are also estimated. Lower energy at the frequency tail with the radar has an effect on wave periods (they are higher); wave steepness is seen to be reduced by 10% in the wind seas. Goda peakedness and the unidirectional Benjamin-Feir index are also examined for the three sensors.

On the Average Shape of the Largest Waves in Finite Water Depths

2020 ◽  
Vol 50 (4) ◽  
pp. 1023-1043
Author(s):  
Ioannis Karmpadakis ◽  
Chris Swan
Keyword(s):  
Single Point ◽  
Random Wave ◽  
Wave Interactions ◽  
Frequency Spectra ◽  
Wave Measurements ◽  
Key Characteristics ◽  
Average Shape ◽  
Time Histories ◽  
Two Populations ◽  
Water Depths

AbstractThis paper investigates the average shape of the largest waves arising in finite water depths. Specifically, the largest waves recorded in time histories of the water surface elevation at a single point have been examined. These are compared to commonly applied theories in engineering and oceanographic practice. To achieve this both field observations and a new set of laboratory measurements are considered. The latter concern long random simulations of directionally spread sea states generated using realistic Joint North Sea Wave Project (JONSWAP) frequency spectra. It is shown that approximations related to the linear theory of quasi-determinism (QD) cannot describe some key characteristics of the largest waves. While second-order corrections to the QD predictions provide an improvement, key effects arising in very steep or shallow water sea states are not captured. While studies involving idealized wave groups have demonstrated significant changes arising as a result of higher-order nonlinear wave–wave interactions, these have not been observed in random sea states. The present paper addresses this discrepancy by decomposing random wave measurements into separate populations of breaking and nonbreaking waves. The characteristics of average wave shapes in the two populations are examined and their key differences discussed. These explain the mismatch between findings in earlier random and deterministic wave studies.

Evaluation on the Capability of Revealing Ocean Swells from Sentinel-1A Wave Spectra Measurements

2020 ◽  
Vol 37 (7) ◽  
pp. 1289-1304
Author(s):  
Xuan Wang ◽  
Romain Husson ◽  
Haoyu Jiang ◽  
Ge Chen ◽  
Guoping Gao
Keyword(s):  
Wave Energy ◽  
Wave Spectrum ◽  
Wave Mode ◽  
Wave Frequency ◽  
Wave Parameter ◽  
Wave System ◽  
Wave Spectra ◽  
Wave Measurements ◽  
The Difference ◽  
Level 2

AbstractWave measurements retrieved by Sentinel-1A level-2 ocean (OCN) products are sensitive to swells other than wind seas, and are considered to provide a finer resolution of ocean swells. To assess the capability of swell retrieval globally, OCN products are validated against WAVEWATCH III (WW3) wave spectra for two available incidence angles [“wave mode” (WV); WV1: 23°; WV2: 36°], focused on the integral wave parameters and most energetic wave system of Sentinel-1A. The wave parameter difference between Sentinel-1A and WW3 along antenna look angles for WV1 demonstrates the obvious impact of the nonlinearity influence in the azimuth direction, resulting in an unrealistically high wave height at the low wave frequency, and the spurious split of wave systems in the range direction, due to the vanishing of velocity bunching modulation. WV2 is less pronounced in these two aspects, but tends to shift wave energy to a higher wave frequency in the range direction. The inside discrepancy of wave energy has two noticeable features: the difference in peak wavelengths in the wave spectrum is positively clustered in the azimuth direction and negatively clustered in the range direction; some of the most energetic partitions derived from Sentinel-1A are difficult to assign to any wave systems in WW3. This phenomenon could be related to wind-wave coupling as the azimuth cutoff/WW3 peak wavelength is confined to a ratio below 0.5 for the negative difference between Sentinel-1A and WW3 peak wavelengths and the spectral distance of most energetic wave system in Sentinel-1A highly resembles “swell pools.”

scholarly journals Ocean Wind and Wave Measurements Using X-Band Marine Radar: A Comprehensive Review

2017 ◽  
Vol 9 (12) ◽  
pp. 1261 ◽  
Author(s):  
Weimin Huang ◽  
Xinlong Liu ◽  
Eric Gill
Keyword(s):  
Comprehensive Review ◽  
Wave Measurements ◽  
X Band ◽  
Marine Radar ◽  
Ocean Wind

An Integrated Wave Monitoring Network for the Hellenic Seas

2008 ◽  
Author(s):  
Takvor Soukissian ◽  
Ioannis Morfis ◽  
Alexakis Stylianos
Keyword(s):  
Monitoring Network ◽  
Wave Model ◽  
Offshore Structures ◽  
Marine Research ◽  
Wave Measurements ◽  
Radar Network ◽  
X Band ◽  
Wave Radar ◽  
Measuring Techniques ◽  
Radar Wave

In this paper, an integrated wave monitoring network for the Hellenic Seas is presented and its components are described. The network is comprised from wave buoys and nautical X-band radars covering most of the important areas of the Hellenic seas as regards complicated wave propagation patterns. The buoy wave monitoring network is part of the POSEIDON system for the monitoring, information and forecasting of the state of the Hellenic Seas. The X-band wave radar network is under development within the context of the OKEANOS project in co-operation with the Hellenic Navy Hydrographic Service. The measuring techniques and principles of both types of devices (buoys and X-band radars) are also described. The wave measurements from the network are mainly used for improving the operational wave forecasts provided by the Hellenic Centre for Marine Research (HCMR), for individual planning purposes and in the design and construction of coastal and offshore structures. Two experimental coastal sites have been selected for comparing the radar wave data with data from directional wave buoys and the WAM wave model.

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