127 research outputs found
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 IngenierĂa ElĂ©ctrica y ElectrĂłnic
Ocean wind and wave parameter estimation from ship-borne x-band marine radar data
Ocean wind and wave parameters are important for the study of oceanography, on- and
off-shore activities, and the safety of ship navigation. Conventionally, such parameters
have been measured by in-situ sensors such as anemometers and buoys. During the
last three decades, sea surface observation using X-band marine radar has drawn wide
attention since marine radars can image both temporal and spatial variations of the sea
surface. In this thesis, novel algorithms for wind and wave parameter retrieval from
X-band marine radar data are developed and tested using radar, anemometer, and buoy
data collected in a sea trial off the east coast of Canada in the North Atlantic Ocean.
Rain affects radar backscatter and leads to less reliable wind parameters measurements.
In this thesis, algorithms are developed to enable reliable wind parameters
measurements under rain conditions. Firstly, wind directions are extracted from raincontaminated
radar data using either a 1D or 2D ensemble empirical mode decomposition
(EEMD) technique and are seen to compare favourably with an anemometer reference.
Secondly, an algorithm based on EEMD and amplitude modulation (AM) analysis to
retrieve wind direction and speed from both rain-free and rain-contaminated X-band
marine radar images is developed and is shown to be an improvement over an earlier 1D
spectral analysis-based method.
For wave parameter measurements, an empirical modulation transfer function (MTF)
is required for traditional spectral analysis-based techniques. Moreover, the widely used
signal-to-noise ratio (SNR)-based method for significant wave height (HS) estimation
may not always work well for a ship-borne X-band radar, and it requires external sensors
for calibration. In this thesis, two methods are first presented for HS estimation from
X-band marine radar data. One is an EEMD-based method, which enables satisfactory
HS measurements obtained from a ship-borne radar. The other is a modified shadowingbased
method, which enables HS measurements without the inclusion of external sensors.
Furthermore, neither method requires the MTF. Finally, an algorithm based on the Radon transform is proposed to estimate wave direction and periods from X-band marine radar
images with satisfactory results
Advances in Sonar Technology
The demand to explore the largest and also one of the richest parts of our planet, the advances in signal processing promoted by an exponential growth in computation power and a thorough study of sound propagation in the underwater realm, have lead to remarkable advances in sonar technology in the last years.The work on hand is a sum of knowledge of several authors who contributed in various aspects of sonar technology. This book intends to give a broad overview of the advances in sonar technology of the last years that resulted from the research effort of the authors in both sonar systems and their applications. It is intended for scientist and engineers from a variety of backgrounds and even those that never had contact with sonar technology before will find an easy introduction with the topics and principles exposed here
Comparison of sea-ice freeboard distributions from aircraft data and cryosat-2
The only remote sensing technique capable of obtain- ing sea-ice thickness on basin-scale are satellite altime- ter missions, such as the 2010 launched CryoSat-2. It is equipped with a Ku-Band radar altimeter, which mea- sures the height of the ice surface above the sea level. This method requires highly accurate range measure- ments. During the CryoSat Validation Experiment (Cry- oVEx) 2011 in the Lincoln Sea, Cryosat-2 underpasses were accomplished with two aircraft, which carried an airborne laser-scanner, a radar altimeter and an electro- magnetic induction device for direct sea-ice thickness re- trieval. Both aircraft flew in close formation at the same time of a CryoSat-2 overpass. This is a study about the comparison of the sea-ice freeboard and thickness dis- tribution of airborne validation and CryoSat-2 measure- ments within the multi-year sea-ice region of the Lincoln Sea in spring, with respect to the penetration of the Ku- Band signal into the snow
Assessment and validation of bathymetric inversion techniques using synthetic waves
Bathymetric inversion using video images is a new and promising technique in order to monitor beach morphology. In this TFG, a Boussinesq model called FunWave and a linear wave propagation routine will be used to create synthetic wave propagation over different bathymetries. Two bathymetric inversion methodologies will be subsequently applied to retrieve the bathymetry, comparing their results and analysing their sensitivity to different aspects, in order to understand and improve their performance
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