A Marine Radar Wind Sensor

A new method for retrieving the wind vector from radar-image sequences is presented. This method, called WiRAR, uses a marine X-band radar to analyze the backscatter of the ocean surface in space and time with respect to surface winds. Wind direction is found using wind-induced streaks, which are very well aligned with the mean surface wind direction and have a typical spacing above 50 m. Wind speeds are derived using a neural network by parameterizing the relationship between the wind vector and the normalized radar cross section (NRCS). To improve performance, it is also considered how the NRCS depends on sea state and atmospheric parameters such as air–sea temperature and humidity. Since the signal-to-noise ratio in the radar sequences is directly related to the significant wave height, this ratio is used to obtain sea state parameters. All radar datasets were acquired in the German Bight of the North Sea from the research platform FINO-I, which provides environmental data such as wind measurements at different heights, sea state, air–sea temperatures, humidity, and other meteorological and oceanographic parameters. The radar-image sequences were recorded by a marine X-band radar installed aboard FINO-I, which operates at grazing incidence and horizontal polarization in transmit and receive. For validation WiRAR is applied to the radar data and compared to the in situ wind measurements from FINO-I. The comparison of wind directions resulted in a correlation coefficient of 0.99 with a standard deviation of 12.8°, and that of wind speeds resulted in a correlation coefficient of 0.99 with a standard deviation of 0.41 m s^−1. In contrast to traditional offshore wind sensors, the retrieval of the wind vector from the NRCS of the ocean surface makes the system independent of the sensors’ motion and installation height as well as the effects due to platform-induced turbulence

Developing a remote sensing system based on X-band radar technology for coastal morphodynamics study

New data processing techniques are proposed for the assessment of scopes and limitations from radar-derived sea state parameters, coastline evolution and water depth estimates. Most of the raised research is focused on Colombian Caribbean coast and the Western Mediterranean Sea. First, a novel procedure to mitigate shadowing in radar images is proposed. The method compensates distortions introduced by the radar acquisition process and the power decay of the radar signal along range applying image enhancement techniques through a couple of pre-processing steps based on filtering and interpolation. Results reveal that the proposed methodology reproduces with high accuracy the sea state parameters in nearshore areas. The improvement resulting from the proposed method is assessed in a coral reef barrier, introducing a completely novel use for X-Band radar in coastal environments. So far, wave energy dissipation on a coral reef barrier has been studied by a few in-situ sensors placed in a straight line, perpendicular to the coastline, but never been described using marine radars. In this context, marine radar images are used to describe prominent features of coral reefs, including the delineation of reef morphological structure, wave energy dissipation and wave transformation processes in the lagoon of San Andres Island barrier-reef system. Results show that reef attenuates incident waves by approximately 75% due to both frictional and wave breaking dissipation, with an equivalent bottom roughness of 0.20 m and a wave friction factor of 0.18. These parameters are comparable with estimates reported in other shallow coral reef lagoons as well as at meadow canopies, obtained using in-situ measurements of wave parameters.DoctoradoDoctor en Ingeniería Eléctrica y Electrónic

Sea state from monoscopic ocean video in real environments

Video of the ocean surface is used as a means for estimating useful information about the scene. A methodology is first introduced for approximating the pixel to metre scale from high-scale videos of the ocean, such as from an aeroplane. Radar images are used for testing. The temporal and spatial domains are associated through the phase modulation of waves, and a process is introduced that selects the waves with the highest energy to be used for estimating the pixel scale. The spatial information is then used with the calculated pixel scale for approximating the sea state. Due to the difficulty of obtaining high-scale videos, a methodology is then introduced that uses the temporal variation from video, and specifically time series of pixel intensities. It aims to isolate and utilise the temporal variation of the wave field from all other video elements, such as environmental brightness fluctuations. The methodology utilises the Kalman filter and the least squares approximate solution for providing an uncalibrated video amplitude spectrum. A method is proposed for scaling this spectrum to metres with the use of an empirical model of the ocean. The significant wave height is estimated from the calibrated video amplitude spectrum. Videos of the ocean in real environments from a shipborne camera and a tower are used for testing. In both sets of data, in situ buoy information is used solely for validation. The next technique aims to approximate the sea state from the same kind of data, namely videos of the ocean in real environments, without calibrating a video amplitude spectrum. The proposed methodology tracks the principal component of the movement of water in the video, which is speculated to be associated with the dominant frequency of the ocean. To accomplish this, the singular spectrum analysis algorithm and the extended Kalman filter are used. Then, the shape of an empirical spectrum is utilised in order to translate the dominant frequency output into a significant wave height estimation. The problem of not using ocean theory associated with a particular empirical energy spectrum for calibration is examined in the next methodology. A secondary oscillatory component from the singular spectrum analysis algorithm is identified with the incorporation of the extended Kalman filter. Ocean theory involving the equilibrium range of oceans is used for calibration. The shipborne videos are used for testing the behaviour of the techniques for approximately the same sea state of 3.1m to 3.4m of significant wave height. The tower videos are used for testing the techniques for a variety of sea states ranging between 0.5m and 3.6m of significant wave height. From all methodologies, the maximum observed values of root mean square error 0.37m and of mean absolute percentage error 18% suggest that the work is promising at estimating these states

A Variational Stereo Method for the Three-Dimensional Reconstruction of Ocean Waves

We develop a novel remote sensing technique for the observation of waves on the ocean surface. Our method infers the 3-D waveform and radiance of oceanic sea states via a variational stereo imagery formulation. In this setting, the shape and radiance of the wave surface are given by minimizers of a composite energy functional that combines a photometric matching term along with regularization terms involving the smoothness of the unknowns. The desired ocean surface shape and radiance are the solution of a system of coupled partial differential equations derived from the optimality conditions of the energy functional. The proposed method is naturally extended to study the spatiotemporal dynamics of ocean waves and applied to three sets of stereo video data. Statistical and spectral analysis are carried out. Our results provide evidence that the observed omnidirectional wavenumber spectrum S(k) decays as k-2.5 is in agreement with Zakharov's theory (1999). Furthermore, the 3-D spectrum of the reconstructed wave surface is exploited to estimate wave dispersion and currents

Use of synthetic aperture radar in estimation of wave climate for coastal engineering design

Thesis (Ph.D.) University of Alaska Fairbanks, 1995Development of Alaska's maritime resources requires design of efficient, reliable, safe facilities by coastal engineers who have a thorough knowledge of site specific wave climate: wave height, length, period, direction, and storm duration. Unfortunately, lack of wave information and validated hindcast models along the Alaskan coast often results in costly overdesigned facilities or underdesigned coastal structures which have a high risk of performance failure. To expand the nearshore wave climate availability, use of spaceborne synthetic aperture radar (SAR) data to estimate wave parameters was evaluated. SAR data were examined in raw and filtered forms, and the extracted wave climate compared to field measured data at three sites. Based on this comparison, the applications and limitations of SAR estimated parameters were established and incorporation of the information into current design practice was addressed. SAR based spectra were dominated by low frequency spectral peaks, likely due to random noise associated with SAR images, as these peaks were not present in the field measured spectra. Due to discrepancies between SAR and measured spectra, wave height, and storm duration could not be determined. Although error ranged from 12.5% to over 100% for SAR estimated wave lengths, the fact that wave lengths, although inaccurate, could be determined from SAR is promising. SAR based wave direction compared favorably to theoretical propagation directions which affirms the potential of wave parameter extraction from SAR data. However, directional field data were not available for comparison. Due to the current errors associated with SAR based wave estimations, SAR estimated wave climate cannot be incorporated into coastal design practice at this time. Research results suggest SAR data still hold great potential for estimating wave parameters. Examination of SAR based wave climate in an extensively monitored, open ocean setting would be beneficial, and the influence of environmental factors on SAR imaging of waves warrants additional investigation. Furthermore, development of a tandem SAR platform with temporal resolution on the order of seconds would be useful for wave period estimation and interferometric wave height determination. After this background research has been accomplished, another evaluation of SAR based nearshore wave climate would be worthwhile

Wind-wave characterization in a wind-jet region: the Ebro delta case

This manuscript describes the wind-wave generation, development and fading in a complex area: a wind-jet region. The study region is the offshore Ebro Delta (NW Mediterranean Sea) where strong cross-shelf winds occur due to a topographic channelization. This leads to relatively short-fetch conditions, which interact with the swell component. The third-generation wave model SimulatingWAves Nearshore (SWAN) is implemented and fed by high-resolution wind fields. A combination of buoy and High Frequency (HF) radar data is used for model validation, resulting in a reasonable level of agreement. The numerical results characterize the wind-wave evolution during a wind jet. A bimodal spectrum is observed due to the interaction of swell and sea systems. The wave directional spreading exhibits lower values at the wind-jet axis. Finally, a reliability analysis of the wave data from an HF radar deployed at the region is carried out.Peer ReviewedPostprint (published version

Characteristics Of Convectively Induced Turbulence Determined From Tropical And Midlatitude Simulations

Out-of-cloud convectively induced turbulence (CIT) poses both a serious threat to aviation operations and a challenge to forecasting applications. This challenge is particularly large in the tropics, as CIT prediction and avoidance are limited due to sparse observations and lack of tropical turbulence research. This study uses high resolution numerical simulations to investigate out-of-cloud CIT properties including intensity, areal coverage, and location using popular turbulence diagnostics in both the tropics and midlatitudes. Convective types are varied in both regions to determine the influence of convective strength and stage (developing versus mature) on CIT characteristics. The Ellrod index, Richardson number, subgrid-scale eddy dissipation rate (EDR), and second-order structure functions are evaluated across various model resolutions and compared with observations of turbulence. Static stability and vertical wind shear are examined to characterize the environment and turbulence potential around simulated convection in the tropics and midlatitudes. This study found that model resolutions similar to operational forecasting systems underpredicted the probability of turbulence, while high resolutions had a probability of turbulence at aviation cruising altitudes that better agreed with observations. The biases in the probability of turbulence for various model resolutions were affected by storm type and synoptic features, and had more agreement for cases with strong dynamical forcing. Model resolution also influenced the locations that CIT was predicted. An investigation of variations in static stability and vertical wind shear in different locations around convective cores showed that these parameters subtly varied with model resolution and often did not correlate with the preferred direction of turbulence as would be expected from theory. A further study into convective stage found that developing convection poses the greatest threat to aviation as it is associated with the greatest turbulence intensity and probability of turbulence in both the tropics and midlatitudes. The environment near developing convection was altered more than near mature convection and likely increased turbulence production through shear-generation mechanisms and gravity wave propagation. This study motivates an increased effort to understand turbulence probability for convection globally in order to improve aviation thunderstorm avoidance guidelines

Short-term rainfall nowcasting: using rainfall radar imaging

As one of the most useful sources of quantitative precipitation measurement, rainfall radar analysis can be a very useful focus for research into developing methods for rainfall prediction. Because radar can estimate rainfall distribution over a wide range, it is thus very attractive for weather prediction over a large area. Short lead time rainfall prediction is often needed in meteorological and hydrological applications where accurate prediction of rainfall can help with flood relief, with agriculture and with event planning. A system of short-term rainfall prediction over Ireland using rainfall radar image processing is presented in this paper. As the only input, consecutive rainfall radar images are processed to predict the development of rainfall by means of morphological methods and movement extrapolation. The results of a series of experimental evaluations demonstrate the ability and efficiency of using our rainfall radar imaging in a nowcasting system