Swell and Wind Wave Inversion Using a Single Very High Frequency (VHF) Radar

AbstractA hybrid, empirical radar wave inversion technique that treats swell and wind waves separately is presented and evaluated using a single 48-MHz radar unit and in situ wave measurements. This hybrid approach greatly reduces errors in radar wave inversion during swell seas. Our analysis suggests that, prior to the inversion, the second-order spectrum should be normalized using Barrick’s weighting function because this process removes harmonic and corner reflection peaks from the inversion and improves the results. In addition, the resulting calibration constants for the wind wave component are not wave-frequency dependent and are similar in magnitude to those found in previous studies using different operating-frequency radars. This result suggests radar frequency independence, although additional experimental verification is required. The swell component of the model presented here ignores the effect of swell’s propagation direction on the radar signal. Although this approach has several limitations and may only be useful near the coast (where swell propagates close to perpendicular to the coastline), the resulting wave inversion is accurate even when swell is propagating close to perpendicular to the radar beam direction. RMS differences relative to in situ wave height measurements range from 0.16 to 0.25 m as the radar beam angle increases from 22° to 56°.

Download Full-text

Evaluation and Validation of HF Radar Swell and Wind wave Inversion Method

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-20-0186.1 ◽

2021 ◽

Author(s):

Zaid R. Al-Attabi ◽

George Voulgaris ◽

Daniel C. Conley

Keyword(s):

Wind Wave ◽

Wave Spectrum ◽

Empirical Method ◽

Hf Radar ◽

Inversion Method ◽

Bulk Wave ◽

Single Beam ◽

In Situ Data ◽

Wave Inversion

AbstractAn examination of the applicability and accuracy of the empirical wave inversion method in the presence of swell waves is presented. The ability of the method to invert Doppler spectra to wave directional spectra and bulk wave parameters is investigated using one-month data from a 12 MHz WERA High Frequency (HF) radar system and in-situ data from a wave buoy. Three different swell inversion models are evaluated: LPM (Lipa et al. 1981), WFG (Wang et al. 2016) and EMP, an empirical approach introduced in this study. The swell inversions were carried out using two different scenarios: (1) a single beam from a single radar site and two beams from a single radar site, and (2) two beams from two sites (a single beam per site) intersecting each other at the buoy location. The LPM method utilized using two beams from two different sites was found to provide the best estimations of swell parameters (swell height RMS error 0.24m) and showed a good correlation with the partitioned swell in-situ values. For the wind wave inversion, the empirical method presented here is used with an empirical coefficient of 0.3 which seems to be suitable for universal application for all radar operating frequencies. The inverted swell parameters are used to create a swell spectrum which is combined with the inverted wind wave spectrum to create a full directional wave spectrum. The wave inversion method presented in this study although empirical does not require calibration with in situ data and can be applied to any beam forming system and operating frequency.

Download Full-text

STORM ICE OIL WIND WAVE WATCH SYSTEM (SIOWS): WEB GIS APPLICATION FOR MONITORING THE ARCTIC

Proceedings of International Conference "Managinag risks to coastal regions and communities in a changinag world" (EMECS'11 - SeaCoasts XXVI) ◽

10.31519/conferencearticle_5b1b93852689d4.28131112 ◽

2017 ◽

Author(s):

Alexander Myasoedov ◽

Sergey Azarov ◽

Ekaterina Balashova ◽

...

Keyword(s):

Satellite Data ◽

Wind Wave ◽

Arctic Region ◽

Web Gis ◽

The Arctic ◽

Flexible Tool ◽

In Situ Data ◽

Current State ◽

Watch System

Working with satellite data, has long been an issue for users which has often prevented from a wider use of these data because of Volume, Access, Format and Data Combination. The purpose of the Storm Ice Oil Wind Wave Watch System (SIOWS) developed at Satellite Oceanography Laboratory (SOLab) is to solve the main issues encountered with satellite data and to provide users with a fast and flexible tool to select and extract data within massive archives that match exactly its needs or interest improving the efficiency of the monitoring system of geophysical conditions in the Arctic. SIOWS - is a Web GIS, designed to display various satellite, model and in situ data, it uses developed at SOLab storing, processing and visualization technologies for operational and archived data. It allows synergistic analysis of both historical data and monitoring of the current state and dynamics of the "ocean-atmosphere-cryosphere" system in the Arctic region, as well as Arctic system forecasting based on thermodynamic models with satellite data assimilation.

Download Full-text

Future Changes in Wave Conditions at the German Baltic Sea Coast Based on a Hybrid Approach Using an Ensemble of Regional Climate Change Projections

Water ◽

10.3390/w13020167 ◽

2021 ◽

Vol 13 (2) ◽

pp. 167

Author(s):

Norman Dreier ◽

Edgar Nehlsen ◽

Peter Fröhle ◽

Diana Rechid ◽

Laurens M. Bouwer ◽

...

Keyword(s):

21St Century ◽

Wind Wave ◽

Regional Climate ◽

Hybrid Approach ◽

Wave Modelling ◽

Long Term Changes ◽

Mean Wave Period ◽

Wave Conditions ◽

Sea Coast

In this study, the projected future long-term changes of the local wave conditions at the German Baltic Sea coast over the course of the 21st century are analyzed and assessed with special focus on model agreement, statistical significance and ranges/spread of the results. An ensemble of new regional climate model (RCM) simulations with the RCM REMO for three RCP forcing scenarios was used as input data. The outstanding feature of the simulations is that the data are available with a high horizontal resolution and at hourly timesteps which is a high temporal resolution and beneficial for the wind–wave modelling. A new data interface between RCM output data and wind–wave modelling has been developed. Suitable spatial aggregation methods of the RCM wind data have been tested and used to generate input for the calculation of waves at quasi deep-water conditions and at a mean water level with a hybrid approach that enables the fast compilation of future long-term time series of significant wave height, mean wave period and direction for an ensemble of RCM data. Changes of the average wind and wave conditions have been found, with a majority of the changes occurring for the RCP8.5 forcing scenario and at the end of the 21st century. At westerly wind-exposed locations mainly increasing values of the wind speed, significant wave height and mean wave period have been noted. In contrast, at easterly wind-exposed locations, decreasing values are predominant. Regarding the changes of the mean wind and wave directions, westerly directions becoming more frequent. Additional research is needed regarding the long-term changes of extreme wave events, e.g., the choice of a best-fit extreme value distribution function and the spatial aggregation method of the wind data.

Download Full-text

Wave Breaking Dissipation in a Young Wind Sea

Journal of Physical Oceanography ◽

10.1175/jpo-d-12-0237.1 ◽

2014 ◽

Vol 44 (1) ◽

pp. 104-127 ◽

Cited By ~ 31

Author(s):

Michael Schwendeman ◽

Jim Thomson ◽

Johannes R. Gemmrich

Keyword(s):

Wind Waves ◽

Phase Speed ◽

Field Studies ◽

Turbulent Energy ◽

Strength Parameter ◽

Video Recordings ◽

Sonar System ◽

Wind Sea ◽

Equilibrium Range

Abstract Coupled in situ and remote sensing measurements of young, strongly forced wind waves are applied to assess the role of breaking in an evolving wave field. In situ measurements of turbulent energy dissipation from wave-following Surface Wave Instrument Float with Tracking (SWIFT) drifters and a tethered acoustic Doppler sonar system are consistent with wave evolution and wind input (as estimated using the radiative transfer equation). The Phillips breaking crest distribution Λ(c) is calculated using stabilized shipboard video recordings and the Fourier-based method of Thomson and Jessup, with minor modifications. The resulting Λ(c) are unimodal distributions centered around half of the phase speed of the dominant waves, consistent with several recent studies. Breaking rates from Λ(c) increase with slope, similar to in situ dissipation. However, comparison of the breaking rate estimates from the shipboard video recordings with the SWIFT video recordings show that the breaking rate is likely underestimated in the shipboard video when wave conditions are calmer and breaking crests are small. The breaking strength parameter b is calculated by comparison of the fifth moment of Λ(c) with the measured dissipation rates. Neglecting recordings with inconsistent breaking rates, the resulting b data do not display any clear trends and are in the range of other reported values. The Λ(c) distributions are compared with the Phillips equilibrium range prediction and previous laboratory and field studies, leading to the identification of several inconsistencies.

Download Full-text

High sampling rate thermistor string observations at the slope of Great Meteor Seamount

Ocean Science ◽

10.5194/os-1-17-2005 ◽

2005 ◽

Vol 1 (1) ◽

pp. 17-28 ◽

Cited By ~ 16

Author(s):

H. van Haren ◽

R. Groenewegen ◽

M. Laan ◽

B. Koster

Keyword(s):

High Frequency ◽

North Atlantic Ocean ◽

Sampling Rate ◽

Very High Frequency ◽

High Sampling ◽

High Sampling Rate ◽

In Situ Calibration ◽

Great Meteor Seamount ◽

Very High

Abstract. A high sampling rate (1 Hz) thermistor string has been built to accommodate the scientific need to accurately monitor high-frequency and vigorous internal wave and overturning processes in the ocean. The thermistors and their custom designed electronics can register temperature at an estimated precision of about 0.001° C with a response time faster than 0.25 s down to depths of 6000 m. With a quick in situ calibration using SBE 911 CTD an absolute accuracy of 0.005° C is obtained. The present string holds 128 sensors at 0.5 m intervals, which are all read-out within 0.5 s. When sampling at 1 Hz, the batteries and the memory capacity of the recorder allow for deployments of up to 2 weeks. In this paper, the instrument is described in some detail. Its performance is illustrated with examples from the first moored observations, which show Kelvin-Helmholtz overturning and very high-frequency (Doppler-shifted) internal waves besides occasionally large turbulent bores moving up the sloping side of Great Meteor Seamount, Canary Basin, North-Atlantic Ocean.

Download Full-text

Artemis very high-frequency digital ultrasound-guided repositioning of a free cap after laser in situ keratomileusis

Journal of Cataract & Refractive Surgery ◽

10.1016/j.jcrs.2006.03.013 ◽

2006 ◽

Vol 32 (11) ◽

pp. 1877-1883 ◽

Cited By ~ 19

Author(s):

Dan Z. Reinstein ◽

Richard C. Rothman ◽

Darren G. Couch ◽

Timothy J. Archer

Keyword(s):

High Frequency ◽

Laser In Situ Keratomileusis ◽

Ultrasound Guided ◽

Very High Frequency ◽

Very High

Download Full-text

Loop-Type Wave-Generation Method for Generating Wind Waves under Long-Fetch Conditions

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-17-0043.1 ◽

2017 ◽

Vol 34 (10) ◽

pp. 2129-2139 ◽

Cited By ~ 6

Author(s):

Naohisa Takagaki ◽

Satoru Komori ◽

Mizuki Ishida ◽

Koji Iwano ◽

Ryoichi Kurose ◽

...

Keyword(s):

Wind Wave ◽

Wind Waves ◽

Peak Frequency ◽

Wave Generation ◽

New Wave ◽

Wave Tank ◽

Irregular Wave ◽

Wind Speeds ◽

Type Wave ◽

Wave Generator

AbstractIt is important to develop a wave-generation method for extending the fetch in laboratory experiments, because previous laboratory studies were limited to the fetch shorter than several dozen meters. A new wave-generation method is proposed for generating wind waves under long-fetch conditions in a wind-wave tank, using a programmable irregular-wave generator. This new method is named a loop-type wave-generation method (LTWGM), because the waves with wave characteristics close to the wind waves measured at the end of the tank are reproduced at the entrance of the tank by the programmable irregular-wave generator and the mechanical wave generation is repeated at the entrance in order to increase the fetch. Water-level fluctuation is measured at both normal and extremely high wind speeds using resistance-type wave gauges. The results show that, at both wind speeds, LTWGM can produce wind waves with long fetches exceeding the length of the wind-wave tank. It is observed that the spectrum of wind waves with a long fetch reproduced by a wave generator is consistent with that of pure wind-driven waves without a wave generator. The fetch laws between the significant wave height and the peak frequency are also confirmed for the wind waves under long-fetch conditions. This implies that the ideal wind waves under long-fetch conditions can be reproduced using LTWGM with the programmable irregular-wave generator.

Download Full-text

PROPAGATION OF WIND WAVES ON TIDES

Coastal Engineering Proceedings ◽

10.9753/icce.v21.36 ◽

1988 ◽

Vol 1 (21) ◽

pp. 36 ◽

Cited By ~ 1

Author(s):

Hendrick L. Tolman

Keyword(s):

Wave Propagation ◽

Wind Wave ◽

Numerical Models ◽

Wind Waves ◽

Absolute Frequency ◽

Shelf Seas ◽

Shelf Sea

Effects of instationary depths and currents in tides on shelf seas on wind wave propagation are investigated using two numerical models in two academical situations representing shelf sea conditions. It is shown that changes in absolute frequency, which are induced by the instationarity of depth and current, are significant in contrast to what is usually assumed. If these changes are neglected large and unpredictable errors may occur in calculated changes of wavenumber and amplitude.

Download Full-text

High-Range Resolution Spectral Analysis of Precipitation Through Range Imaging of the Chung-Li VHF Radar

10.5194/amt-2017-156 ◽

2017 ◽

Author(s):

Shih-Chiao Tsai ◽

Jenn-Shyong Chen ◽

Yen-Hsyang Chu ◽

Ching-Lun Su ◽

Jui-Hsiang Chen

Keyword(s):

Weighting Function ◽

Power Doppler ◽

Power Spectra ◽

Doppler Frequency ◽

Doppler Velocity ◽

Small Scale ◽

Range Imaging ◽

Very High Frequency ◽

Vhf Radar ◽

Range Resolution

Abstract. Multi-frequency range imaging (RIM) has been implemented in the Chung-Li very-high-frequency (VHF) radar, located on the campus of National Central University, Taiwan, since 2008. RIM processes the echo signals with a group of closely spaced transmitting frequencies through appropriate inversion methods to obtain high-resolution distribution of echo power in the range direction. This is beneficial to the investigation of the small scale structure embedded in dynamic atmosphere. Five transmitting frequencies were employed in the radar experiment for observation of the precipitating atmosphere during the period between 21 and 23 Aug, 2013. Using the Capon and Fourier methods, the radar echoes were synthesized to retrieve the temporal signals at a smaller range step than the original range resolution defined by the pulse width, and such retrieved temporal signals were then processed in the Doppler frequency domain to identify the atmosphere and precipitation echoes. An analysis called conditional averaging was further executed for echo power, Doppler velocity, and spectral width to verify the potential capabilities of the retrieval processing in resolving small-scale precipitation and atmosphere structures. Point-by-point correction of range delay combined with compensation of range weighting function effect has been performed during the retrieval of temporal signals to improve the continuity of power spectra at gate boundaries, making the small-scale structures in the power spectra more natural and reasonable. We examined stratiform and convective precipitations and demonstrated their different structured characteristics by means of the Capon-processed results.

Download Full-text