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

Detection and characterization of deep water wave breaking using moderate incidence angle microwave backscatter from the sea surface

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1990The importance of wave breaking in both microwave remote sensing and air-sea interaction has led to this investigation of the utility of a Ku-Band CW Doppler scatterometer to detect and characterize wave breaking in the open ocean. Field and laboratory measurements by previous authors of microwave backscatter from sharp-crested and breaking waves have shown that these events can exhibit characteristic signatures in moderate incidence angle measurements of the radar cross-section (RCS) and Doppler spectrum. Specifically, breaking events have been associated with polarization independent sea spikes in the RCS accompanied by increased mean frequency and bandwidth of the Doppler spectrum. Simultaneous microwave, video, and environmental measurements were made during the SAXON experiment off Chesapeake Bay in the fall of 1988. The scatterometer was pointed upwind with an incidence angle of 45 degrees and an illumination area small compared to the wavelength of the dominant surface waves. An autocovariance estimation technique was used to produced time series of the RCS, mean Doppler frequency, and Doppler spectral bandwidth in real-time. The joint statistics of the microwave quantities indicative of breaking are used to investigate detection schemes for breaking events identified from the video recordings. The most successful scheme is based on thresholds in both the RCS and the Doppler bandwidth determined from joint distributions for breaking and non-breaking waves. Microwave events consisting of a sea spike in the RCS accompanied by a large bandwidth are associated with the steep forward face of waves in the early stages of breaking. The location of the illumination area with respect to the phase of the breaking wave, the stage of breaking development, and the orientation of an individual crest with respect to the antenna look-direction all influence the detect ability of a breaking event occurring in the vicinity of the radar spot. Since sea spikes tend to occur on the forward face of waves in the process of breaking, the whitecap associated with a given sea spike may occur after the crest of the wave responsible for the sea spike has passed the center of the illumination area. Approximately 70% of the waves which produce whitecaps within a distance of 5m of the bore sight location are successfully identified by a threshold-based detection scheme utilizing both RCS and bandwidth information. The sea spike statistics are investigated as functions of wave field parameters and friction velocity u*. For VV and HH polarization, the frequency of sea spike occurrence and the sea spike contribution to the mean RCS show an approximately cubic dependence on u*, which is consistent with theoretical modelling and various measures of whitecap coverage. The data also suggest that the average RCS of an individual sea spike is not dependent on u*. At high friction velocities (u*≈40-50cms-l), the contribution of sea spikes to the mean RCS is in the range of 5-10% for VV and 10-20% for HH. The wind speed dependence of the percentage of crests producing sea spikes is comparable to that of the fraction of breaking crests reported by previous authors. The percentage of wave crests producing sea spikes is found to vary approximately as (Re*)1.5, where Re* is a Reynolds number based on u* and the dominant surface wavelength. This result agrees with measurements of the degree of wave breaking by. previous authors and is shown to be consistent with a cubic dependence on u *. Models for the probability of wave breaking as a function of moments of the wave height spectrum are compared to our results. The Doppler frequency and bandwidth measurements are also used to inquire into the kinematics of the breaking process.This work was funded by grants from the MIT Sloan Basic Research Fund, the National Science Foundation (Physical Oceanography), and the Office of Naval Research (Physical Oceanography). Additional funding was provided by the National Aeronautics and Space Administration through the Graduate Student Researchers' Fellowship Program

Electromagnetic Scattering and Statistic Analysis of Clutter from Oil Contaminated Sea Surface

In order to investigate the electromagnetic (EM) scattering characteristics of the three dimensional sea surface contaminated by oil, a rigorous numerical method multilevel fast multipole algorithm (MLFMA) is developed to preciously calculate the electromagnetic backscatter from the two-layered oil contaminated sea surface. Illumination window and resistive window are combined together to depress the edge current induced by artificial truncation of the sea surface. By using this combination, the numerical method can get a high efficiency at a less computation cost. The differences between backscatters from clean sea and oil contaminated sea are investigated with respect to various incident angles and sea states. Also, the distribution of the sea clutter is examined for the oil-spilled cases in this paper

HF Radar Measurements of Surface Waves in the Gulf of Naples (Southeastern Tyrrhenian Sea): Comparison With Hindcast Results at Different Scales

HF radar systems wave measurements are evaluated against numerical simulations in the Gulf of Naples (Southeastern Tyrrhenian Sea). Wave measurements are obtained from three CODAR SeaSonde HF radars installed along the coast of the Gulf of Naples. The numerical models employed are WavewatchIII, implemented on a regional scale with a resolution of about 10 km in longitude and latitude in the whole Mediterranean Sea, and SWAN, implemented with a 200 m resolution in the area of interest. Numerical simulations are also validated against experimental data acquired by a buoy installed offshore the Gulf of Naples. The agreement between HF radar measurements and model hindcasts is evaluated through the estimate of statistical error indices for the main wave characteristics (significant wave height, mean period, and mean direction). The consistency between wave parameters retrieved by HF radars and hindcasted by the models opens the way to future integration of the two systems as well as to the utilization of HF radar wave parameters that could be envisaged for data assimilation in wave models

Radar studies of turbulence and lidar studies of the nickel layer in the Arctic mesosphere

Thesis (M.S.) University of Alaska Fairbanks, 2016This thesis presents studies of the Arctic middle atmosphere using Incoherent Scatter Radar (ISR) and resonance lidar at Poker Flat Research Range (PFRR), Chatanika, Alaska. The Poker Flat Incoherent Scatter Radar (PFISR) provides measurements of mesospheric turbulence and the resonance lidar provides measurements of mesospheric nickel layer. We develop retrieval and analysis techniques to determine the characteristics of the turbulence and the nickel layer. We present measurements of mesospheric turbulence with PFISR on 23 April 2008 and 18 February 2013. We characterize mesospheric turbulence in terms of the energy dissipation rate as a function of altitude and time on these days. We present an extensive analysis of the radar measurements to show that the use of high quality PFISR data and an accurate characterization of the geophysical conditions are essential to achieve accurate turbulent measurements. We find that the retrieved values of the energy dissipation rate vary significantly based on how the data is selected. We present measurements of mesospheric nickel layer with resonance lidar on the night of 27-28 November 2012 and 20-21 December 2012. We characterize the mesospheric nickel layer in terms of the nickel concentration as a function of altitude on these days. We find that our nickel concentrations are significantly higher than expected from studies of meteors. We present an extensive analysis of the lidar measurements to show that these measurements of unexpectedly high values of the nickel concentrations are accurate and not biased by the lidar measurements.Chapter 1: Introduction -- 1.1 The middle atmosphere -- 1.2 Wave breaking and turbulence -- 1.3 Radar detection of turbulence -- 1.4 Mesospheric metal layers -- 1.5 Scope of this study -- Chapter 2: Theory of ISR turbulence measurements -- 2.1 Turbulence -- 2.2 Radar measurement technique -- 2.3 The Poker Flat Incoherent Scatter Radar -- Chapter 3: ISR measurements of turbulence -- 3.1 Fitting method and spectral model -- 3.2 PFISR measurements on 23 April 2008 -- 3.3 PFISR measurements on 18 February 2013 -- 3.4 Conclusion -- Chapter 4: Lidar measurement of mesospheric nickel layer -- 4.1 Lidar experiment and observations -- 4.2 Identification of nickel signal -- 4.3 Determination of nickel concentration -- 4.4 Discussion and conclusions -- Chapter 5: Summary and future work -- 5.1 PFISR measurement of turbulence in the mesosphere -- 5.2 Lidar measurements of nickel in the mesosphere -- Reference

Occurrence and Energy Dissipation of Breaking Surface Waves in the Nearshore Studied with Coherent Marine Radar

Wave breaking influences air-sea interactions, wave induced forces on coastal structures, sediment transport and associated coastline changes. A good understanding of the process and a proper incorporation of wave breaking into earth system models is crucial for a solid assessment of the impacts of climate change and human influences on coastal dynamics. However, many aspects are still poorly understood which can be attributed to the fact that wave breaking is difficult to observe and study because it occurs randomly and involves multiple spatial and temporal scales. Within this doctoral work, a nearshore field experiment was planned and conducted on the island of Sylt in the North Sea to investigate the dynamics of wave breaking. The study combines in-situ observations, numerical simulations and remote sensing using shore-based coherent marine radar. The field measurements are used to investigate the coherent microwave backscatter from shoaling and breaking waves. Three major developments result from the study. The first one is a forward model to compute the backscatter intensity and Doppler velocity from known wave kinematics. The second development is a new classification algorithm to identify dominant breakers, whitecaps and radar imaging artifacts within the radar raw data. The algorithm is used to infer the fraction of breaking waves over a sub- and an inter-tidal sandbar as well as whitecap statistics and results are compared to different parameterizations available in literature. The third development is a new method to deduce the energy of the surface roller from the Doppler velocity measured by the radar. The roller energy is related to the dissipation of roller energy by the stress acting at the surface under the roller. From the spatial gradient of roller energy, the transformation of the significant wave height is computed along the entire cross-shore transect. Comparisons to in-situ measurements of the significant wave height from two bottom mounted pressure gauges and a wave rider buoy show a total root-mean-square-error of 0.20 m and a bias of −0.02 m. It is the first time that measurements of the spatio-temporal variation of the bulk wave energy dissipation together with the fraction of breaking waves are achieved in storm conditions over such a large distance of more than one kilometer. The largest dissipation rates (> 300 W/m² ) take place on a short distance of less than one wave length (≈ 50 m) at the inter-tidal sandbar. However, during storm conditions 50 % of the incoming wave energy flux is already dissipated at the sub-tidal sandbar. The simultaneous measurements of the occurrence frequency and the energy dissipation facilitate an assessment of the bulk dissipation of individual breaking waves. For the spilling-type breakers in this area, the observed dissipation rate is about 30 % smaller than the dissipation rate according to the generally used bore analogy. This must be considered within nearshore wave models if accurate predictions of the breaking probability are required

Microwave scattering from surf zone waves

Wave breaking in the surf zone is an important forcing mechanism on the generation of nearshore currents and in the driving of sediment transport. At the same time, wave breaking can have significant spatial and temporal variability that needs to be accounted for in the description of nearshore processes. Remote sensors are best suited to collect wave breaking measurements due to their large footprint and synoptic capabilities, but in order to extract quantitative wave parameters a proper understanding of the imaging mechanisms is essential. Microwave sensors have been shown to be able to measure wave parameters in deep water, but in the surf zone many of the assumptions the algorithms are based upon do not hold. Additionally, the dynamics of breaking waves are different and may affect in a yet determined way the signal. This dissertation first intends to address an observational gap regarding surf zone microwave measurements. A novel combination of synchronous, large coverage marine radar, calibrated pulsed Doppler radar and video observations from a field site enable the analysis of the evolution and characteristics of the wave signature. The combined data sets yield superior discrimination rates between breaking and non-breaking waves. Discrimination also allows the study of the microwave scattering by source, where active breaking is separated from remnant foam and steepening waves. Results show that the backscattered power from breaking waves, specifically from the wave roller, is a several dB larger than that of foam and steepening waves and independent of the environmental conditions and polarization state. While similar results have been obtained for deep water waves and variety of scattering models have been proposed, it is found that none of the models can describe all the data. Additionally, most of the models neglect the roller morphology. Therefore, in the last section a scattering model is introduced, in which the roller is treated as a volume where a collection of water droplets embedded in air can scatter incoherently. Multiple interactions of the scattered fields between particles and the boundaries are also accounted for. Though the model formulation is complex, it depends on a few physical parameters (diameter, volume fraction, medium permittivity) and no calibration constants. Comparison against data shows that the model does a reasonable job in predicting the observed scattering levels, polarization response and grazing angle dependencies, although is not capable to reproduce the maximum scattered levels observed and predicts polarization ratios always less than unity

Technique-Based Exploitation Of Low Grazing Angle SAR Imagery Of Ship Wakes

The pursuit of the understanding of the effect a ship has on water is a field of study that is several hundreds of years old, accelerated during the years of the industrial revolution where the efficiency of a ship’s engine and hull determined the utility of the burgeoning globally important sea lines of communication. The dawn of radar sensing and electronic computation have expanding this field of study still further where new ground is still being broken. This thesis looks to address a niche area of synthetic aperture radar imagery of ship wakes, specifically the imaging geometry utilising a low grazing angle, where significant non-linear effects are often dominant in the environment. The nuances of the synthetic aperture radar processing techniques compounded with the low grazing angle geometry to produce unusual artefacts within the imagery. It is the understanding of these artefacts that is central to this thesis. A sub-aperture synthetic aperture radar technique is applied to real data alongside coarse modelling of a ship and its wake before finally developing a full hydrodynamic model for a ship’s wake from first principles. The model is validated through comparison with previously developed work. The analysis shows that the resultant artefacts are a culmination of individual synthetic aperture radar anomalies and the reaction of the radar energy to the ambient sea surface and spike events

Studies of the Deepwater Horizon Oil Spill With the UAVSAR Radar

On 22- 23 June 2010, the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) L band radar imaged the Deepwater Horizon oil spill and the effects of oil that was transported within the Gulf of Mexico. We describe the campaign and discuss the unique contributions of the UAVSAR radar to the study of the detection, migration, and impact of oil from the spill. We present an overview of UAVSAR data analyses that support the original science goals of the campaign, namely, (1) algorithm development for oil slick detection and characterization, (2) mapping of oil intrusion into coastal wetlands and intercoastal waterways, and (3) ecosystem impact studies. Our study area focuses on oil-affected wetlands in Barataria Bay, Louisiana. The results indicate that fine resolution, low-noise, L band radar can detect surface oil-on-water with sufficient sensitivity to identify regions in a slick with different types of oil/emulsions and/or oil coverage; identify oil on waters in inland bays and differentiate mixed/weathered oil from fresh oil as it moves into the area; identify areas of potentially impacted wetlands and vegetation in the marshes; and support the crisis response through location of compromised booms and heavily oiled beaches