Developing a Remote Sensing System Based on X-Band Radar Technology for Coastal Morphodynamics Study

Doctorate Programme in Electrical and Electronics Engineering, Department of Electrical and Electronics Engineering, Universidad del Norte.This PhD thesis is a step further in the understanding of novel applications for X-Band radarsto study morphodynamics and wave hydrodynamics in coastal areas. New data processingtechniques are proposed for the assessment of scopes and limitations from radar-derived seastate parameters, coastline evolution and water depth estimates. Most of the raised research isfocused on Colombian Caribbean coast and the Western Mediterranean Sea.First, a novel procedure to mitigate shadowing in radar images is proposed. The methodcompensates distortions introduced by the radar acquisition process and the power decay ofthe radar signal along range applying image enhancement techniques through a couple ofpre-processing steps based on filtering and interpolation. Results reveal that the proposedmethodology reproduces with high accuracy the sea state parameters in nearshore areas. The bestperformance is achieved when the significant wave height (Hs) is at least 0.5 m and preferablyhigher and the peak period isTp≥4 s.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, waveenergy dissipation on a coral reef barrier has been studied by a few in-situ sensors placed in astraight line, perpendicular to the coastline, but never been described using marine radars. Inthis context, this dissertation use marine radar images to describe prominent features of coralreefs, including the delineation of reef morphological structure, wave energy dissipation andwave 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 frictionaland wave breaking dissipation, with an equivalent bottom roughness of 0.20 m and a wavefriction factor of 0.18. These parameters are comparable with estimates reported in other shallowcoral reef lagoons as well as at meadow canopies, obtained using in-situ measurements of waveparameters. Besides, the mean height of the reef elements is also estimated in the entire radarcoverage area. Results are both in the same order of magnitude of measured data reported byprevious studies and in good agreement with the geometric parameters proposed by in-canopyflow models for branched species, such asStylophoraandPocillopora, which are also common inthe coral carpets of San Andres Island.Finally, the assessment of morphological mapping facilities of X-Band radars is performedby comparing radar-derived bathymetry and shoreline estimates with in-situ data and thepreviously reported video performance at the study sites. Results reveal a promising combineduse of X-Band radars and stereo-video systems as complementing monitoring tools in coastalareas. Therefore, radars and optical video systems should be considered as complementingmorphological mapping tools, instead of excluding, in order to provide higher-resolution andmore accurate bathymetric estimates and shoreline measurements in a broad area.Finalmente, debo agradecer al Instituto Colombiano para el Desarrollo de la Ciencia y laTecnología, COLCIENCIAS, por haber financiado gran parte de mis estudios doctorales otorgán-dome una beca a partir de la convocatoria 757 de 2016. De igual forma agradezco a la Universidad del Norte por complementar esta financiación mediante la concesión de la beca institucional COLCIENCIAS-Uninorte desde el año 2015. Además, agradezco al Consejo Superior de Investigaciones Científicas (CSIC) por otorgar la beca i-COOP+2016 para la cooperación internacional (COOPA20156) que soportó financieramente mi estancia de dieciséis meses en el Instituto Mediterráneo de Estudios Avanzados (IMEDEA, Esporles, España)