To see the other types of publications on this topic, follow the link: Oceanographic radars.
Dissertations / Theses on the topic 'Oceanographic radars'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 45 dissertations / theses for your research on the topic 'Oceanographic radars.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Domps, Baptiste. "Identification et détection de phénomènes transitoires contenus dans des mesures radar à faible rapport signal à bruit : Applications conjointes aux problématiques océanographique et atmosphérique." Electronic Thesis or Diss., Toulon, 2021. http://www.theses.fr/2021TOUL0001.
Full textAbstract:
L'observation de la dynamique de l'atmosphère et de la surface de l'océan peut être réalisée par télédétection radar. L'approche habituelle consiste, dans les deux cas, à calculer numériquement le spectre Doppler des échos temporels reçus à l'aide d'une transformée de Fourier discrète. Bien que satisfaisante pour la plupart des applications, cette méthode ne convient pas pour l'observation de phénomènes transitoires, plus courts que le temps d'intégration nécessaire à l'observation radar. Nous utilisons une technique alternative, basée sur une représentation autorégressive des séries temporelles radar et associée à la méthode dite à entropie maximale. Cette approche est appliquée à la mesure de courants de surface par radar côtier dans la bande des hautes fréquences, puis à celle de vent dans la basse atmosphère par radar en bande L. Dans les deux situations, nous montrons à l'aide de simulations numériques, de comparaisons avec d'autres instruments et d'études de cas que l'approche proposée conduit à des estimations fiables des grandeurs géophysiques (courants marins et vitesses de vent) pour des temps d'intégration brefs, là où la méthode conventionnelle échoueObservations of atmospheric and ocean surface dynamics can be performed via radar remote sensing. The usual approach consists, in both cases, in numerically calculating the Doppler spectrum of the received temporal echoes using a discrete Fourier transform. Although satisfactory for most applications, this method is not suitable for observations of transient phenomena due to being shorter than the integration time required for radar observations. We use an alternative technique based on an autoregressive representation of the radar time series combined with the maximum entropy method. This approach is applied to coastal radar measurements of surface currents in the high frequency band as well as to L-band radar measurements of wind in the lower atmosphere. For both cases, through numerical simulations and case studies, we compare our approach with others that use different instruments. We show that for short integration times, where conventional methods fail, our proposed approach leads to reliable estimates of geophysical quantities (ocean currents and wind speeds)
2
McGregor, J. A. "HF radar oceanography." Thesis, University of Canterbury. Physics, 1985. http://hdl.handle.net/10092/7578.
Full textAbstract:
The development of a 26MHz pulsed Doppler radar system for remote sensing of ocean surface conditions is described. This radar obtains Doppler spectra of echoes from ocean waves within the range 10-40 km from the shore. From these Doppler spectra it is possible to estimate oceanographic parameters such as sea state, wind speed, wind direction, radial components of current velocities and properties of swell.
The work concentrates on the radar design principles and includes a detailed study of the effect of ground wave propagation conditions on the performance of radar systems of this type. Results obtained with the radar are discussed from the points of view of both the performance of the system and the oceanographic information contained in the Doppler spectra.
3
Middleditch, Andrew. "Spectral analysis in high frequency radar oceanography." Thesis, University of Sheffield, 2006. http://etheses.whiterose.ac.uk/3590/.
Full textAbstract:
High Frequency radar systems provide a unique opportunity to measure evolving littoral oceanic dynamics at high temporal and spatial resolution. Backscattered electromagnetic signals from ocean waves are modulated by Bragg resonant scattering. A perturbation analysis yields an expression for the spectral content of radar signals which can be exploited to provide estimates of oceanographic parameters: the radial component of surface current can be extracted from the frequency locations of the first order peaks; the ocean wave directional spectrum is related to the second order continuum via a non-linear integral equation. The periodogram, based on a Fourier decomposition of radax data, is the standard method used to derive frequency spectra. Limitations in this approach, caused by inhomogeneities in the underlying ocean field, are investigated. An instantaneous frequency technique is proposed in this thesis which mitigates the spectral distortion by demodulating the backscattered radax signals -a filtering procedure is developed which measures the temporally varying Bragg components. Alternative spectral techniques are analysed in order to validate the filter: an autoregressive paxa, metric modelling approach and an eigendecomposition method. The filter is evaluated, using radar and in situ data, which establishes its potential for ocean remote sensing. Significant improvements in the quantity and accuracy of wave measurements are demonstrated. Properties and constraints of the filter are derived using simulated data. Finally, the generic structure of the extracted instantaneous frequency signals is investigated and related to oceanographic processes.
4
Gommenginger, Christine Pascale. "On the applicability of a conventional microwave marine radar system to quantitative measurements of the ocean surface roughness and oceanographic applications." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241939.
Full text
5
Castaneda, Julian Jose. "Modelling and measuring (by H.F. radar) dispersion in the coastal zone." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241137.
Full text
6
Schilperoort, Daniel E. "The effect of the Agulhas Current on synthetic aperture radar derived wind fields." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/22952.
Full textAbstract:
In this study, 5 years (987 swaths) of high resolution wind speeds, derived from Advanced Synthetic Aperture Radar data collected over the Agulhas Current region, are studied to investigate the effect of warm, high intensity currents on the ocean's surface roughness and resulting derived wind fields. The wind data are derived using the CMOD5.n GMF with CFS reanalysis wind data as direction input. The CFS direction data are validated using ASCAT derived wind observations Globcurrent ocean current velocity data is used to investigate the difference between the satellite derived wind speeds compared to surface velocities of the current and the true wind speed. The, so called, current-relative effect is investigated for different wind direction regimes, namely: upcurrent, downcurrent, crosscurrent west and crosscurrent east. Our analyses are conducted for 6 locations of interest, evenly spaced along the Northern Agulhas Current. MODIS, SEVIRI and OSTIA SST data are used as proxy for locating the core of the Agulhas and it's temperature fronts, as well as to investigate wind speed modifications as a result of ocean-atmosphere energy transfer. It is found that higher resolution SAR derived winds have a greater ability to represent higher intensity and smaller scale wind features in comparison to winds derived from Scatterometers. A combination of the current relative effect and SST-atmospheric heating for upcurrent wind directions results in a sharp increase in mean wind speeds over the inshore boundary of the current of between 5m/s and 7m/s (50−60%). Individual events can reach as high as 15m/s (100%) over 10′s of kilometres. For downcurrent winds, the expected current relative effect is overridden by increased wind speeds of up to 5m/s (40%) across the entire current due to the influence of SSTs. The mean effect of SSTs on wind speeds has a stronger effect than the current relative effect on wind speed changes over the current. The wind speed differences are best represented under moderate wind speeds, between 5−15m/s. This investigation will contribute to future satellite wind speed derivations to identifying new wind speed and surface roughness altering effects. It will also serve to increase understanding of high resolution wind features and sharp changes over ocean features.
7
Ocampo, Torres Francisco Javier. "The effects of wind wave directionality on the radar imaging of ocean swell." Thesis, University of Southampton, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280827.
Full text
8
Marom, Moshe. "Interferometric SAR imaging of ocean surface currents and wavefields." Thesis, Monterey, Calif. : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA239312.
Full textAbstract:
Dissertation (Ph.D. in Physical Oceanography)--Naval Postgraduate School, June 1990.Dissertation supervisor: Thornton, E.B. "June 1990." Description based on title screen as viewed on 19 October 2009. DTIC Identifiers: INSAR (INTERFEROMETRIC SAR). Author(s) subject terms: Interferometric SAR, scene coherence time, 2D wavenumber spectra, surface currents. Includes bibliographical references (p. 192-198). Also available in print.
9
Greenwood, Andrew D. "Azimuth modulation of the radar backscatter at near-normal incidence /." Diss., CLICK HERE for online access, 1995. http://contentdm.lib.byu.edu/ETD/image/etd5.pdf.
Full text
10
Smith, Justin Dewitt. "Studies to improve estimation of the electromagnetic bias in radar altimetry /." Diss., CLICK HERE for online access, 1999. http://contentdm.lib.byu.edu/ETD/image/etd17.pdf.
Full text
11
Fox, Alan David. "The use of high-frequency radar to study surface currents associated with a shelf sea frontal system." Thesis, Bangor University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316344.
Full text
12
Violante-Carvalho, Nelson. "The use of ERS-1 synthetic aperture radar for measurement and modeling of the directional wave spectrum." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288191.
Full text
13
Densham, Martin P. J. "Bathymetric mapping with QuickBird data." Thesis, Monterey, California. Naval Postgraduate School, 2005. http://hdl.handle.net/10945/2121.
Full textAbstract:
Two algorithms are used to determine bathymetry in the littoral region using QuickBird multispectral satellite observations. The algorithms determine water-leaving radiance and convert this to water depth values. The first algorithm uses a ratio of two wavebands and the second uses the sum of several wavebands. Relative bathymetric errors are determined for the clear water of Looe Key (USA) and the turbid water of Plymouth Sound (UK). Bathymetric measurements from LIDAR and chart data are compared to derived depths to assess their accuracies. An amended version of the ratio method is proposed for use in turbid water to improve accuracy. The results show that the standard ratio and turbidity algorithms have a relative error of 11.7% and 16.5% respectively in clear water. In turbid water the average error of the turbidity algorithm is 11.6% and the amended ratio algorithm average error is 13%.Royal Navy
14
Crevier, Louis-Philippe. "Dependence of the transport in channel models of the ACC on the Rossby radius of deformation." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21532.
Full textAbstract:
It has been suggested that the transport of the Antarctic Circumpolar Current is set, essentially, by the southward Sverdrup flux at latitudes just north of Drake Passage. Although this idea is consistent with observations, it has been critized in that Sverdrup dynamics fail at Drake Passage latitudes. Here, we think of the total transport as being comprised of two components: one associated with the basin-like dynamics to the north of Drake Passage and the other associated with the dynamics of the Drake Passage latitude band itself. The Drake Passage latitudes are often simulated using channel models with bottom topography. For a two-layer channel, large topography effectively blocks geostrophic contours at depth and allows zonally-reconnecting contours in the upper layer. This concentrates the through-channel transport in the model's upper layer. Furthermore, it is argued that the statistical steady state for wind-driven channel flow (that is not too viscous) should be baroclinically unstable. Assuming marginal instability then leads to an estimate of the through-channel transport.A two-layer primitive-equation channel model with bottom topography and wind forcing is used to test this relationship. Model integrations are made to obtain statistical steady states for a range of parameters. The Rossby radius and the wind strength are varied as the theory predicts that transport should go like the square of the former and be relatively insensitive to the latter. Integrations to test the robustness of these results to model resolution are also conducted.
15
Toh, Kwang Yong Daniel. "Evaluation of surface current mapping performance by SeaSonde High Frequency radar through simulations." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Dec%5FToh.pdf.
Full text
16
Martinez-Diaz-de-Leon, Asdrubal. "The use of the ERS-2 synthetic aperture radar to study the wind driven ocean circulation in the Gulf of Tehuantepec, Mexico, during Norte events." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246236.
Full text
17
Enriquez, Andres E. "An investigation of surface current patterns related to upwelling in Monterey Bay, using high frequency radar." Thesis, Monterey, California. Naval Postgraduate School, 2004. http://hdl.handle.net/10945/1595.
Full textAbstract:
Approved for public release; distribution is unlimitedHigh Frequency (HF) radar backscatter instruments are under development and testing in the marine science and defense science communities for their abilities to remotely sense surface parameters in the coastal ocean over large areas. In the Navy context, the systems provide real-time mapping of ocean surface currents and waves critical to characterization and forecasting of the battlespace environment. In this study, HF radar, aircraft and satellite information were used to investigate and describe surface current in Monterey Bay, California, for a period of ten months, from June 01st, 2003 to March 31st, 2004. A network of five CODAR-type HF radar instruments measured hourly surface currents over the bay. The measurements were averaged over one-hour intervals and total surface velocities were mapped on a grid in the Monterey Bay. From the M1 Buoy located in the middle of the bay, an uninterrupted time series of wind intensity and direction was obtained for the whole period. Major upwelling events were observed during the period of June 14 to June 27, July 4 to July 19, August 8 to August 18 and other upwelling events were observed until late October. These periods of upwelling favorable winds are common during summer with durations of 10 to 20 days. Often they are interrupted by periods of relaxation state of just a few days as the winds veer to the northwest or northeast. Cyclonic circulation cells are developed on shore during upwelling conditions and an anticyclonic circulation in the middle of the bay is observed when the wind shifts to the southwest producing a strong flow out of the bay close to the coastline off Point Piǫs. Downwelling conditions are much common less than upwelling, with occurrences during winter and early fall storms with events lasting between two to five days. When the wind blows to the northeast with an intensity of 4 m/s or more for more than 12 hours, a well developed anticyclonic gyre forms in the middle of the bay. This is associated with a strong current, 35 to 40 cm/s, which flushes out in the southern part of the bay close to the coast off Point Piǫs. This flow reverses when the winds veer to the southwest and enter into the Bay with less intensity.
First Lieutenant, Chilean Navy
18
Enriquez, Andres. "An investigation of surface current patterns related to upwelling in Monterey Bay, using high frequency radar /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FEnriquez.pdf.
Full text
19
Warrick, Abbie Lynn 1967. "Application of wavelet and radon-based techniques to the internal wake problem in synthetic aperture radar images." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/282191.
Full textAbstract:
One problem of interest to the oceanic engineering community is the detection and enhancement of internal wakes in open water synthetic aperture radar (SAR) images. Internal wakes, which occur when a ship travels in a stratified medium, have a "V" shape extending from the ship, and a chirp-like feature across each arm. The Radon transform has been applied to the detection and the enhancement problems in internal wake images to account for the linear features while the wavelet transform has been applied to the enhancement problem in internal wake images to account for the chirp-like features. Although the Radon transform accentuates linear features, there have been several difficulties applying this transform to the wake detection and enhancement problem because the transform is not localized. In a recent article by Copeland et. al., a localized Radon transform (LRT) was developed and was shown to reduce the speckle noise. In this dissertation, another derivation of the LRT is obtained which shows that this transform is equivalent to the Radon transform with a rectangular window function. Several properties not considered in the article are derived using the new formulation. Another transform which has been applied to internal wake images is the wavelet transform. In a recent paper by Teti et. al., the wavelet transform was applied to slices through internal wakes in SAR images. Although the wavelet transform reduced the speckle noise in SAR wake images, it required extracting a line from the image. In this dissertation, a wavelet localized Radon transform is developed which performs the wavelet transform on all lines in an image without explicitly extracting slices of the image. The fundamental theory for this transform is developed and several examples are considered. This transform is then expanded to include features which occur over a region with a significant length. The fundamental theory for this new transform, a localized Radon transform with a wavelet filter, is developed and several examples are provided. These new transforms are then incorporated into optimal and sub-optimal detection schemes for images with linear features, including ship wakes, which are contaminated by additive Gaussian noise.
20
O'loughlin, Benjamin. "Evaluation of Search and Rescue Planning Tools on the West Florida Shelf." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6557.
Full textAbstract:
The Coast Guard conducts over 20,000 search and rescue cases a year with approximately 5% of them occurring within the coastal waters of the West Florida Shelf (WFS). Each search effort is planned using the Coast Guard’s Search and Rescue Optimal Planning System (SAROPS) which uses model inputs to create composite probability distributions based on the results of Monte Carlo projections of thousands of particle trajectories. However, SAROPS is limited by the quality of model inputs and their associated errors. This study utilizes observations from three surface drifter deployments on the WFS to evaluate the effectiveness of available surface current models, including one model not currently in use by the Coast Guard. Additionally, the performance of high-frequency (HF) Radar observations is evaluated against the models. The HF Radar root-mean-square errors (RMSE) were found to be on the order of 10 cm/s, and a model created with objectively mapped HF Radar data was found to out-perform all available models. Additionally, a comparison of model skills (using a normalized Lagrangian separation method) showed the West Florida Coastal Ocean Model (WFCOM) to have better skill on both the inner and outer shelf regions of the WFS when compared to other models.
21
Magnusson, Jan. "Snow Interception Measurements using Impulse Radar." Thesis, Uppsala University, Department of Earth Sciences, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-88848.
Full textAbstract:
Interception av snö eller regn på trädkronor är en viktig del av det hydrologiska kretsloppet. Upp till en tredjedel av all snö som faller över skogsområden når aldrig marken på grund av stora avdunstningsförluster av interceptionsförrådet, vilket minskar vårflöden i älvar. Goda prognoser av dessa flöden är viktiga för vattenkraftsindustrin. För att kunna förbättra modeller, i vilka interceptions-avdunstningsprocessen ingår, krävs lämpliga mätmetoder för interceptionförrådet av snö. Syftet med detta arbete var att undersöka om impulsradarutrustning kan användas för att mäta interceptionsförrådet av snö på barrträd. Metoden bygger på att mäta hastigheten och utsläckningen hos en elektromagnetisk impulsvåg, vilken skickas från en sändarantenn genom ett avsnitt skog till en mottagarantenn. Både utsläckningen och hastigheten påverkas av snö och vatten på trädens kronor, och kan med så kallade blandningsformler relateras till mängd vatten. Blandningsformler beskriver de elektromagnetiska egenskaperna hos heterogena material. Laboratorietester visade att interception av flytande vatten på små trädkronor gav upphov till förändringar av impulsvågens hastighet och utsläckning mätbara med radarutrustningen. Uppskattningar av mängden intercepterat vatten från radarmätningarna gav en överskattning jämfört med oberoende referensmätningar, däremot stämde relativa variationer väl överens mellan mätningarna. Tydliga samband mellan impulsvågens utsläckning och mängden intercepterat vatten kunde inte bestämmas från experimenten. Utsläckningsresultaten var svårtolkade och lämpliga blandningsformler hittades inte i litteraturen. Metoden testades även en vecka i fält i norra Sverige. Trots att installationen inte var den bästa visade resultaten ändå god överensstämmelse mellan uppskattade förändringar av interceptionsförrådet från radarmätningarna, och observerade väderförändringar samt oberoende referensmätningar med en trädvågsanordning. Resultaten tyder på att metoden kan ge goda uppskattningar av interceptionsförrådet, då en väl fungerande installation av utrustningen används och efter att vidare kalibreringsförsök genomförts.
Interception of rain or snow in forest canopies is an important component of the hydrological cycle. Up to one third of the total winter precipitation never reaches the ground in forest areas due to evaporation losses of intercepted snow, which reduces spring-time water flow in rivers. Accurate spring flow predictions are important for the hydro-power industry. Appropriate measurement methods of intercepted snow are needed in order to improve models involving the interception evaporation process. The aim of this study was to explore the possibilities of an impulse radar system to measure the snow interception storage on coniferous trees. The method is based on measurements of the velocity and attenuation of an electromagnetic impulse wave, generated in a transmitting antenna and sent through a forest section and detected by a receiving antenna. The attenuation and velocity is affected by ice and water in the canopy air space, and can be related to amounts of water using so-called mixing formulas that describe the average electromagnetic properties of heterogeneous materials. Controlled laboratory measurements on small canopies showed that interception of liquid water was well above the detectable limits of the radar system, with respect to both attenuation and velocity changes. Estimations of the mass of intercepted water based on velocity changes overestimated the reference measurements, but relative variations were well captured. No clear relation could be found between amount of water on canopies and impulse wave attenuation from the experiments. The attenuation results were difficult to interpret, and appropriate mixing formulas were not found in the literature. The method was further tested for one week under field conditions in northern Sweden. In spite of a non-optimal equipment installation results of estimated changes of the interception storage showed a good agreement with observed weather variations and reference measurements using a tree weighing device. The method can have good conditions to give correct estimations of the snow interception storage, using appropriate installation and further calibration measurements.
22
Murphy, Richard M. "Analysis of high-resolution COAMPS with observed METOC data to demonstrate atmospheric impact on EM propagation." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Sep%5FMurphy.pdf.
Full textAbstract:
Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, September 2005.Thesis Advisor(s): Kenneth L. Davidson. Includes bibliographical references. Also available online.
23
Dumas, Dylan. "Nouvelles techniques de traitement du signal en radio-océanographie." Electronic Thesis or Diss., Toulon, 2022. http://www.theses.fr/2022TOUL0008.
Full textAbstract:
La mesure des courants marins de surface par radar HF soulève plusieurs problématiques au niveau de la calibration des radars, de la résolution spatiale et des signaux parasites. Le traitement conventionnel fonctionnant par balayage azimutal appelé formation de voie a une résolution angulaire limitée pour la plupart des radars à réseau de phase et les méthodes de traitement à haute résolution pour la recherche des directions d'arrivées produisent généralement des cartes lacunaires. Dans cette thèse nous proposons : a) une technique de traitement à haute résolution angulaire permettant d'obtenir des cartes pleines et peu bruitées ; b) une méthode de calibration automatique des antennes ; c) des méthodes de suppression des artefacts liés aux interférences radio et aux échos parasites. Ces méthodes, initialement prévues pour les radars à réseau de phase, ont été adaptées aux radars compacts CODAR dont la principale difficulté est la calibration en raison de la nature des antennes. Les mesures de courant obtenues avec ces nouvelles techniques ont été validées par des campagnes in situ avec des erreurs dans la fourchette basse de la littérature scientifiqueThe measurement of sea surface currents by HF radar raises several issues in terms of radar calibration, spatial resolution and parasite signals. Conventional azimuth scanning processing called beam forming has limited angular resolution for most phased array radar and high angular resolution processing methods called direction finding generally produce lacunary maps. In this thesis we propose : a) a high angular resolution processing technique based on direction finding algorithm allowing to obtain full and low-noise maps ; b) an automatic antenna calibration method ; c) other methods to removing artifacts related to radio frequency interference and clutter echoes. These methods, initially planned for phased array radars, have been adapted to compact radars called CODAR where the main difficulty is the calibration due to the nature of the antennas. The measurements obtained with these new techniques have been validated with in situ campaigns with errors in the low range of the scientific literature
24
Schreiber, Floriane. "Estimation des conditions océanographiques par inversion de données issues d'un radar imageur non calibré." Electronic Thesis or Diss., Toulon, 2020. http://www.theses.fr/2020TOUL0016.
Full textAbstract:
De nombreux modèles empiriques de distribution statistique du fouillis de mer existent mais ne sont pas directement paramétrable par l’état de mer, et ainsi il n’est pas possible d’y pratiquer une méthode d’inversion. Pour modéliser la distribution statistique de l’intensité, nous utilisons un modèle deux-échelles (TSM) paramétré directement par l’état de mer via la mss (mean square slope). Ce modèle permet de retrouver de manière cohérente la NRCS mais ne parvient pas à décrire de manière la distribution du fouillis de mer simultanément dans les deux canaux de polarisations directs dû à une surestimation du rapport de polarisation (RP) de Bragg.Pour corriger ce problème, nous avons développé une formulation originale du RP qui inclue un unique paramètre effectuant une transition dynamique entre le régime de Bragg et de Kirchhoff. Cette formulation intégrée au modèle TSM permet de corriger le RP et d’obtenir une modélisation cohérente de la statistique du fouillis de mer, simultanément dans les deux polarisations. A l’aide d’une méthode d’inversion, le modèle permet d'estimer l’état de mer d’un radar imageur. La pertinence de ce modèle est établie dans différentes configurations, mais aussi pour des données présentant des incertitudes de calibrationMany empirical models describing sea clutter statistical distribution exist but they do not directly depend on the sea sate. They are not suitable to perform inversion. To model the statistical distribution of the backscattered intensity, we use a two-scale model (TSM) which is linked to the sea state via the mss (mean square slope). This model allows to retrieve the NRCS but does not perfectly describes the sea clutter distribution simultaneously in the two direct polarization channels. This is due to an overestimation of the Bragg polarization ratio (PR)
25
Maingot, Christopher. "Observation of Natural and Artificial Features on the Sea Surface from Synthetic Aperture Radar Satellite Imagery with In-situ Measurements." NSUWorks, 2011. http://nsuworks.nova.edu/occ_stuetd/201.
Full textAbstract:
Synthetic aperture radar imaging is an effective tool for imaging the sea surface because of its response to changes in sea surface roughness. This allows for the remote sensing of features on the sea surface, which modulate se surface roughness. In this work, 18 synthetic aperture radar images were collected from the TerraSAR-X and RADARSAT-2 satellites in the Port Everglades, Florida area. In-situ measurements were collected in conjunction with the satellite images in order to provide more information on the features visible in the imagery, and aid in identification of the origin of the features. Information on ships in the area of the satellite image footprints was collected using an automatic information system. Weather conditions were recorded by a meteorological station and a National Oceanic and Atmospheric Administration weather radar station. Waves and currents in the observational area were recorded with acoustic Doppler current profilers and wave gauges. Sonar systems and conductivity, depth, and salinity profilers were used to identify stratification in the water column. Surfactant release experiments were also conducted to explore the affects of surface active materials. Results of the experiment show the manifestation of atmospheric effects, oceanic fronts and eddies, wind shadowing, natural and artificial slicks, and ships and ship wakes on the synthetic aperture radar imagery. Atmospheric conditions were found to play a significant role in the visibility of features on the sea surface, and sometimes masked the appearance of features on the ocean surface. Overall the most reliable feature capable of being imaged on the sea surface by the synthetic aperture radar satellites was the signatures of ships and their wakes.
26
Gunadharma, Gautama Budhi. "Oil-spill monitoring in Indonesia." Thesis, Ecole nationale supérieure Mines-Télécom Atlantique Bretagne Pays de la Loire, 2017. http://www.theses.fr/2017IMTA0036/document.
Full textAbstract:
L'Indonésie, l’une de plus grands archipels, a été menacé avec la pollution provenant de la marée noire. Le gouvernement d’Indonésie en coopération avec le gouvernement Français a développé un système d'observation de l'océan par satellite afin de supporter de développement durable. Ce système est intégré dans les systèmes d'océanographie opérationnelle dans le cadre du projet de développement des infrastructures de l'océanographie spatiale (INDESO). Le contexte de cette thèse est dans le cadre du projet INDESO notamment dans applications d’INDESO pour suivre des déversements de pétrole dans les mers d’Indonésie. Dans ce contexte,cette thèse propose de nouvelles méthodologies et analyses. Cette thèse comportait deux contributions principales. La première contribution est sur la récupération des paramètres de dérive des déversements d'hydrocarbures à partir d'une analyse conjointe des observations SAR (Synthetic Aperture Radar) et des résultats d'un modèle de transport de déversement de pétrole. Dans cette première partie, nous estimons les paramètres de dérive de pétrole. On a exploité un modèle de transport de déversement de pétrole lagrangien,de sorte que la dérive simulée de déversement d'hydrocarbures modèles puisse correspondre à l'observation de satellite. Pour confirmer l'origine du déversement de pétrole détecté à une date donnée par une observation de SAR, nous avons effectué des simulations avec différentes dates de début de fuite, duré de fuite et différentes valeurs de pondération deux facteurs dominants i.e. vent et courant. Nous avons développé une nouvelle méthode pour l'assimilation de ces paramètres de fuite de pétrole à comparer avec d'une détection dérivée d'un déversement d'hydrocarbures. Nous avons appliqué la méthodologie proposée sur le plus grand accident en Indonésie, l'accident de Montara. La deuxième contribution est l'évaluation globale du risque de déversement d'hydrocarbures en Indonésie. Nous sommes concentrés sur la zone de gestion des pêches de l'Indonésie. Dans cette analyse, nous avons proposé une méthodologie qui considère le déversement de pétrole, qui a des sources différentes et leurs impacts à l'environnement, mais aussi sur les perspectives sociales et économiques. Pour l'évaluation de la vulnérabilité des zones marines protégées, nous avons également exploité le modèle de 2D lagrangien. L'accent mis sur les zones de gestion des pêches (FMA) afin de fournir une analyse synoptique sur l'ensemble du territoire maritime d’Indonésie. Chaque FMA présente les caractéristiques spécifiques des paramètres environnementaux etsocio-économiques. Nous avons évalué le risque de déversement d'hydrocarbures dans chaque zone de gestion sur la base de tous ces facteurs. Le résultat de cette étude peut être utilisé dans la planification d'une action pour réduire les impacts négatifs du déversement d'hydrocarburesIndonesia as the biggest archipelago has a major threat coming from oil spill. Due to the increasing concerns of environment protection for sustainable development, the government of Indonesia in cooperation with government of France developed an ocean observation system with one of its pilot applications is oil spills monitoring. This system is integrated in the operational oceanography systems within the project of Infrastructure Development of Space Oceanography (INDESO). The context of this thesis is in the frame of INDESO project particularly in the monitoring of oil spill in the Indonesian seas. Within the context above, this thesis propose new methodologies and analyses. This thesis involved two main contributions. The first contribution addressed the retrieval of oil spill drift parameters from a joint analysis of SAR observations of an oil spill and of outputs of a Lagrangian oil spill transport model. In this first part, we estimate oil spill drift parameters. The proposed framework exploited a Lagrangian oil spill transport model such that the simulated oil spill drift could match a SAR-based observation of an oil spill. In the considered 2D Lagrangian model there were two dominant factors, i.e. wind and surface current. To confirm the origin of the oil spill detected on a given date through a SAR observation, we performed simulations with various leakage starting dates, leakage durations, and different values of wind and current weighing coefficients. We developed a novel framework for the assimilation of these oil leakage parameters from a SAR-derived detection of an oil spill. We applied the proposed methodology on the most famous oil spill accident in Indonesia, the Montara case. The second contribution was the global assessment of oil spill risk inIndonesia. We focused on the 11 Indonesia Fisheries Management Area to support the sustainability development of marine and fisheries. In this analysis we proposed methodology that considered the oil spillfrom different source and their impacts not only to the environment, but also from social and economic perspectives. For the assessment of vulnerability of Marine Protected Areas to oil spill pollution, we also exploited the oil spill trajectory model. The focus was given to Fisheries Management Areas as a means to provide synoptic analysis over theentire Indonesian maritime territory. Using different information from many institutional reports, we collected and analyzed the potential source of oil spill in each FMA. Each FMA has specific characteristics in terms environmental and socioeconomic features. We assessed the oil spill risk in each FMA based on all these factors. The result of this study can be used in the mitigation planning to reduce the negative impacts of oil spill
27
Vella, Katie E. "Microbial Effects on the Production and Transformation of Surfactants Within the Microlayer and Subsurface Waters in Application to Remote Sensing Techniques." NSUWorks, 2012. http://nsuworks.nova.edu/occ_stuetd/34.
Full textAbstract:
The sea surface microlayer is a millimeter-scale interfacial layer between the atmosphere and the ocean. A number of studies have suggested that there is a unique ecosystem for marine bacteria in the sea surface microlayer, but little information exists on the microbial community composition of this ecosystem due to sampling complexities. In this work, we present an improved method to sample and compare the bacterial diversity of the sea surface microlayer with that of subsurface water at the same site. Bacterial samples were collected from the sea surface microlayer with a sampling method, which minimized sample contamination from the research platform and the subsurface water. Sampling was conducted using a polycarbonate membrane filter to obtain the bacterial community structure at open water and coastal water sites in the Straits of Florida. The microlayer sampling was planned to coincide with synthetic aperture radar satellite overpasses (COSMO SkyMed), which capture a range of fine-scale features on the sea surface. The presence of surfactants affect the synthetic aperture radar imaging process because surfactants in the sea surface microlayer suppress short gravity-capillary ocean surface waves, thereby decreasing the backscatter and allowing the radar to detect surfactant-covered areas. Although sources of surfactants vary, certain marine bacteria are known to produce and transform surfactants, which suggest that these surfactant-related marine bacteria have an important biological influence on fine-scale synthetic aperture radar satellite imagery. Therefore, the comparison between synthetic aperture radar satellite images and in situ field samples may be used for interpreting and studying fine-scale features on the sea surface. The surfactant-associated bacterial composition of the sampling sites was determined using high-throughput, 454 pyrosequencing methods. A total of 61,663 sequences were analyzed and the results indicated the presence of surfactant-associated bacteria such as Moraxellaceae, Halomonadaceae, Enterobacteriaceae, Bacillaceae, and Nocardiaceae. By establishing these bacterial groups that influence the presence of surfactants, remote sensing techniques which involve monitoring the microlayer are expected to be enhanced and may provide additional information on the state of the upper ocean ecosystem.
28
Howe, Kathryn. "DNA Analysis of Surfactant-Associated Bacteria in a Natural Sea Slick in the Gulf of Mexico Observed by TerraSAR-X." NSUWorks, 2017. http://nsuworks.nova.edu/occ_stuetd/451.
Full textAbstract:
Under low wind speed conditions, surfactants accumulate at the air-sea interface, dampen short-gravity capillary (Bragg) waves, and form natural sea slicks that are detectable visually and in synthetic aperture radar (SAR) imagery. Marine organisms, such as phytoplankton, zooplankton, seaweed, and bacteria, produce and degrade surfactants during various life processes. This study coordinates in situ sampling with TerraSAR-X satellite overpasses in order to help guide microbiological analysis of the sea surface microlayer (SML) and associated subsurface water (SSW). Samples were collected in the Gulf of Mexico during a research cruise (LASER) in February 2016 to determine abundance of surfactant associated bacteria in the sea surface microlayer and subsurface water column. By using real time polymerase chain reaction (quantitative PCR, or qPCR) to target Bacillus spp. associated with surfactant production, results indicate that more surfactant-associated bacteria reside in the subsurface water in low wind speed conditions. Sequencing results suggest that Bacillus and Pseudomonas are more abundant in the SSW in low wind speed conditions. These results indicate that these bacteria reside in the SSW, presumably producing surfactants that move to the surface via physical processes, accumulate on and enrich the sea surface microlayer.
29
Hamilton, Bryan. "DNA Analysis of Surfactant Associated Bacteria in the Sea Surface Microlayer in Application to Satellite Remote Sensing Techniques: Case Studies in the Straits of Florida and the Gulf of Mexico." NSUWorks, 2015. http://nsuworks.nova.edu/occ_stuetd/39.
Full textAbstract:
Several genera of bacteria residing in the sea surface microlayer and in the near-surface layer of the ocean have been found to be involved in the production and decay of surfactants. Under low wind speed conditions, surfactants can suppress short gravity capillary waves at the sea surface and form natural sea slicks. These features can be observed with both airborne and satellite-based synthetic aperture radar (SAR). Using a new microlayer sampling method, a series of experiments have been conducted in the Straits of Florida and the Gulf of Mexico in 2013 to establish a connection between the presence of surfactant-associated bacteria in the upper layer of the ocean and sea slicks. In a number of cases, sampling coincided with TerraSAR-X and RADARSAT-2 satellite overpasses to obtain SAR images of each study site. Samples collected from slick and non slick conditions have been analyzed using real time PCR techniques to determine Bacillus relative abundance in each area sampled. Previous work has shown that the sea surface microlayer plays a role in air-sea gas exchange, sea surface temperature, climate-active aerosol production, biochemical cycling, as well as the dampening of ocean capillary waves. Determining the effect of surfactant-associated bacteria on the state of the sea surface may help provide a more complete global picture of biophysical processes at the air-sea interface and uptake of greenhouse gases by the ocean.
30
Bennich, David, William Bredberg, Jimmy Olsson, Stenberg Louis Rulewski, Malin Smith, and Johnny Söderqvist. "En jämförelse mellan fjärranalystekniker och vågbojar för mätning av oceanografiska parametrar i svenska vatten." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-323069.
Full textAbstract:
För övervakning av svenska vatten krävs noggranna mätningar av oceanografiska parametrar såsom våghöjd, vågriktning, ytvattentemperatur och ytströmmar. Mätdata för parametrarna samlas in av Sveriges Meteorologiska och Hydrologiska Institut (SMHI) och används till prognoser, sjöfart samt forskning. I denna studie undersöktes möjligheten att ersätta eller komplettera vågbojarna av modellen Directional Waverider MkIII som SMHI använder idag, med ny kommersiellt tillgänglig fjärranalysteknik. Projektet begränsades till att studera två högfrekvens-radartekniker och en X-bandradar. Studien är platsspecifik och utreder kvalitetsmässiga, ekonomiska och miljömässiga för- och nackdelar med de utvalda radarteknikerna i relation till vågbojarna. En litteraturstudie och modellering av data över parametrar som påverkar radarteknikernas räckvidd och datatillgänglighet genomfördes. Ur modelleringen drogs slutsatsen att det är möjligt att erhålla likvärdig datatillgänglighet med vågradar som med vågboj. Vidare modellering ledde till slutsatsen att radarteknikerna begränsas till ungefär hälften av sin optimala räckvidd i Östersjön på grund av den låga salthalten, och därför är Sveriges västkust bättre lämpad för placering av radarteknik. Undersökning av isbildning i havsvatten, som kan begränsa radarteknikernas räckvidd, ledde till slutsatsen att Sveriges västkust också är att föredra utifrån detta perspektiv. Med anledning av radarteknikers möjlighet att utföra mätningar över större områden, finner studien att det finns goda grunder för att motivera en ersättning eller komplettering av vågbojarna med modern radarteknik. Vidare talar radarteknikernas goda anpassningsförmåga, lägre inverkan på miljön och enklare underhållskrav jämfört med vågbojarna till dess fördel. Att övergå till radarteknik medför däremot högre installations- och driftkostnader i jämförelse med vågbojar.
31
Elfström, Daniel, and Max Stefansson. "How design storms with normally distributed intensities customized from precipitation radar data in Sweden affect the modeled hydraulic response to extreme rainfalls." Thesis, Uppsala universitet, Luft-, vatten- och landskapslära, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-437729.
Full textAbstract:
Intense but short-term cloudbursts may cause severe flooding in urban areas. Such short-term cloudbursts mostly are of convective character, where the rain intensity may vary considerably within relatively small areas. Using uniform design rains where maximum intensity is assumed over the whole catchment is common practice in Sweden, though. This risks overestimating the hydraulic responses, and hence lead to overdimensioning of stormwater systems. The objective of this study was to determine how the hydraulic response to cloudbursts is affected by the spatial variation of the rain in relation to the catchment size, aiming to enable improved cloudburst mapping in Sweden. Initially, the spatial variation of heavy rains in Sweden was investigated by studying radar data provided by SMHI. The distribution of rainfall accumulated over two hours from heavy raincells was investigated, based on the assumption that the intensity of convective raincells can be approximated as spatially Gaussian distributed. Based on the results, three Gaussian test rains, whose spatial variation was deemed a representative selection of the radar study, were created. In order to investigate how the hydraulic peak responses differed between the Gaussian test rains and uniform reference rains, both test and reference rains were modeled in MIKE21 Flow model. The modelling was performed on an idealised urban model fitted to Swedish urban conditions, consisting of four nested square catchments of different sizes. The investigated hydraulic peak responses were maximum outflow, proportion flooded area and average maximum water depth. In comparison with spatially varied Gaussian rains centered at the outlets, the uniform design rain with maximum rain volume overestimated the peak hydraulic response with 1-8%, independent of catchment size. Uniform design rains scaled with an area reduction factor (ARF), which is averaging the rainfall of the Gaussian rain over the catchment, instead underestimated the peak response, in comparison with the Gaussian rains. The underestimation of ARF-rains increased heavily with catchment size, from less than 5 % for a catchment area of 4 km2 to 13 - 69 % for a catchment area of 36 km2. The conclusion can be drawn that catchment size ceases to affect the hydraulic peak response when the time it takes for the whole catchment to contribute to the peak response exceeds the time it takes for the peak to be reached. How much the rain varies over the area which is able to contribute to the peak response during the rain event, can be assumed to decide how much a design rain without ARF overestimates the peak responses. If the catchment exceeds this size, an ARF-scaled rain will underestimate the peak responses. This underestimation is amplified with larger catchments. The strong pointiness of the CDS-hyetograph used in the study risks underestimating the differences in hydraulic peak responses between the test rains and a uniform rain without ARF, while the difference between test rains and uniform rains with ARF risks being overestimated.Intensiva men kortvariga skyfall kan orsaka omfattande översvämningsproblematik i urbana områden. Trots att sådana kortvariga skyfall oftast är av konvektiv karaktär, där regnintensiteten kan variera avsevärt inom relativt små områden, används idag uniforma designregn där maxintensitet antas över hela avrinningsområdet. Detta riskerar att leda till en överskattning av hydrauliska responser, och följaktligen överdimensionering av dagvattensystem. Denna studie syftar till att utreda hur den hydrauliska responsen av skyfall påverkas av regnets spatiala variation, i relation till avrinningsområdets storlek. Ytterst handlar det om att möjliggöra förbättrad skyfallskartering i Sverige. Initialt undersöktes den spatiala variationen hos kraftiga regn i Sverige, genom en studie av radardata tillhandahållen av SMHI. Utbredningen av regnmängd ackumulerad över två timmar från kraftiga regnceller undersöktes utifrån antagandet att intensiteten hos konvektiva regnceller kan approximeras som spatialt gaussfördelad. Baserat på resultatet skapades tre gaussfördelade testregn vars spatiala variation ansågs utgöra ett representativt urval från radarstudien. För att undersöka hur de hydrauliska responserna skiljer sig åt mellan de gaussfördelade testregnen och uniforma referensregn, modellerades såväl test- som referensregn i MIKE 21 Flow model. Modelleringen utfördes på en idealiserad stadsmodell anpassad efter svenska urbana förhållanden, bestående av fyra nästlade kvadratiska avrinningsområden av olika storlekar. De hydrauliska responser som undersöktes var maximalt utflöde, maximal andel översvämmad yta samt medelvärdesbildat maximalvattendjup, alltså toppresponser. Jämfört med spatialt varierade gaussregn centrerade kring utloppen överskattade ett uniformt designregn med testregnens maximala volym de hydrauliska toppresponserna med 1-8 %, oberoende av avrinningsområdets storlek. Uniforma designregn skalade med area reduction factor (ARF), vilken medelvärdesbildar gaussregnets nederbörd över avrinningsområdet, underskattade istället toppresponsen jämfört med gaussregnen. ARF-regnets underskattning ökade kraftigt med avrinningsområdets storlek, från mindre än 5 % för ett avrinningsområde på 4 km2, till 13 - 69 % för ett avrinningsområde på 36 km2. Slutsatsen kan dras att avrinningsområdets storlek upphör att påverka den hydrauliska toppresponsen, då tiden det tar för hela avrinningsområdet att samverka till toppresponsen överstiger tiden till denna respons. Hur mycket regnet varierar över det område som under regnhändelsen hinner samverka till toppresponsen, kan antas avgöra hur mycket ett designregn utan ARF överskattar toppresponserna. Överstiger avrinningsområdet denna storlek kommer ett ARF-regn att underskatta toppresponserna, och underskattningen förstärks med ökande avrinningsområdesstorlek. Den kraftiga temporala toppigheten hos den CDS-hyetograf som användes i studien riskerar att underskatta skillnaderna i hydraulisk topprespons mellan testregnen och ett uniformt regn utan ARF, medan skillnaden mellan testregn och uniforma regn med ARF istället riskerar att överskattas.
32
Parks, Georgia. "Microbial Analysis of Surfactant-Associated Bacteria in the Sea Surface Microlayer and Remote Sensing of Associated Slicks." Thesis, NSUWorks, 2019. https://nsuworks.nova.edu/occ_stuetd/515.
Full textAbstract:
The sea-surface microlayer (SML) is the boundary layer at the air-sea interface where many biogeochemical processes occur. Many organisms (e.g., bacteria) produce surface active agents (surfactants) for life processes, which accumulate in the SML and dampen short gravity-capillary waves, resulting in sea surface slicks. Synthetic aperture radar (SAR) is capable of remotely sensing these features on the sea surface by measuring reflected backscatter from the ocean surface in microwaves. This study coordinates SAR overpasses with in situ SML and subsurface (SSW) microbial sample collection to guide subsequent analysis after 16s rRNA sequencing on the Illumina MiSeq. In April 2017, 138 SML and SSW samples were collected near a targeted oil-seep where the Taylor Platform was knocked down in the Gulf of Mexico, both in and out of visually-observed oil slicks. In July and August 2018, 220 SML and SSW samples were collected near the Looe Key coral reef and a coastal seagrass area. Analysis of microbial abundance and diversity between the two experiments shows that within oil slicks, surfactant- and oil-associated bacteria prefer to reside within the SSW rather than in the SML. In natural slicks in the coastal seagrass area, these bacteria are more abundant in the SML. Outside of these slicks, surfactant-associated bacteria are more abundant within the SML than the SSW. This suggests that the presence of oil reduces the habitability of the SML, whereas natural slicks created by foam and other surfactants creates a more habitable environment in the SML. With lower wind speed, abundance of these bacteria are greater, as increased wind speed results in a harsher environment. The diurnal cycle had an effect on the relative abundance of surfactant-associated bacteria in the SML and SSW. Our results demonstrate the usefulness of synthetic aperture radar to remotely sense sea surface slicks in coordination with in situ surfactant-associated bacteria data collection of the sea surface slicks.
33
Duarte, Vagner da Silva. "Feições oceanográficas observadas no noroeste do Mar de Weddell e no Estreito de Bransfield (Antártica), a partir de relações entre o retroespalhamento SAR e medições de espessura do gelo marinho." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/94762.
Full textAbstract:
A quase inacessibilidade de grandes partes do Oceano Austral torna o conhecimento da espessura do gelo marinho limitado. Esta informação é essencial para a determinação do balanço de massa deste componente da criosfera. Na transição do inverno para a primavera de 2006, uma equipe de pesquisadores, coletou uma série de perfis de espessura de gelo marinho no norte e noroeste do mar de Weddell. Eles estavam a bordo do navio de pesquisa alemão Polarstern do Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung (AWI) e utilizaram um sistema composto por um sensor eletromagnético, altímetro laser e um Sistema de Posicionamento Global Diferencial (DGPS) aerotransportado por helicóptero. Simultaneamente, a Agência Espacial Europeia (ESA), adquiriu imagens ENVISAT ASAR WSM da área de pesquisa. O objetivo principal desta tese é determinar a relação existente entre o retroespalhamento medido pelo Radar de Abertura Sintética e a espessura do gelo marinho obtida pelo HEM (Helicopter-borne ElectroMagnetic system) usando os dados citados acima. Utilizamos os programas de computador NEST®, MATLAB®, EXCEL®, ArcGIS®/ArcMAP®, para processar, analisar e selecionar as imagens, para determinar a relação entre o retroespalhamento e as medidas, quase-tempo-coincidentes, de espessura do gelo. Projetamos as trajetórias dos voos sobre as imagens obtidas nas mesmas datas e extraímos os pixels referentes aos locais onde foram medidas as espessuras de gelo marinho. Apropriamos os valores de espessura do gelo para a área de cada pixel sobre o qual se referiam. Uma análise estatística determinou que o parâmetro que melhor representa a espessura do gelo dentro da área do pixel é a média. A regressão linear é a melhor forma de ajuste das relações entre o valor de retroespalhamento do pixel e a espessura do gelo marinho contido na área deste pixel. O coeficiente de correlação linear de Pearson, resultante de análise paramétrica, indica uma forte correlação (0,75) entre retroespalhamento e espessura do gelo marinho. Porém, a análise não paramétrica de Spearman resultou em um coeficiente de correlação baixo (0,06) o que pode indicar que os dados analisados são compostos por duas populações distintas (e.g., gelo de primeiro ano e plurianual). Contudo, a análise não paramétrica de Kolmogorov-Smirnov aventa a possibilidade de que não tenhamos amostrado toda população. Esta seria a razão de não haver valores de espessuras relativas ao intervalo entre -9.21dB e -1.35dB, o que poderia induzir ao baixo valor do coeficiente de correlação na análise de Spearman. Aplicamos a equação linear: y=0,6345x+12,015 às imagens e pudemos separá-las em doze classes: uma para água e onze para gelo marinho, estas com intervalos de um metro. Isto possibilitou a observação de importantes feições oceanográficas como: canais de águas abertas; cristas de compressão, decaimento do gelo marinho, deslocamento de icebergs (como indicadores de correntes, marés e ventos), liberação de gelo por geleiras de maré, desprendimento de iceberg da plataforma de gelo Larsen C, esteiras de ondas e vórtices oceânicos. Com base no exposto, podemos afirmar que, estatisticamente, nossos resultados são robustos e significantes, com nível de confiança entre 95% e 99%. A equação que propomos é um primeiro passo para inferir-se a espessura do gelo marinho a partir de coeficientes de retroespalhamento SAR.The almost inaccessibility of large parts of the Southern Ocean makes the knowledge on the sea-ice thickness limited. This information is essential for determining the mass balance of this cryosphere component. During the transition from winter to spring 2006, a researcher team performed several sea-ice thickness profiles in the north and northwest of the Weddell Sea. They were aboard the German research vessel Polarstern from the Alfred-Wegener-Institute, Helmholtz-Zentrum für Polar- und Meeresforschung (AWI) and utilizing for those measurements a Helicopter-borne Electromagnetic system (HEM). The HEM is composed of an electromagnetic sensor, laser altimeter, and a Differential Global Positioning System (DGPS). Simultaneously, the European Space Agency (ESA) ENVISAT ASAR WSM acquired images from the research area. The main objective of this thesis is to determine the relationship between the Synthetic Aperture Radar backscattering and the HEM’s sea-ice thickness measurements using data listed above. We used the computer programs: NEST®, MATLAB®, EXCEL®, ArcGIS® / ArcMap®, to process, analyze and select images, in order to determine the relationship between the backscattering and the quasi-time-coincident ice thickness measurements. We projected the flights trajectories on the images obtained on the same dates, extracting the pixels pertaining to the places where the sea-ice thicknesses were determined. We ascribed ice thickness values for each area covered by the pixel. A statistical analysis determined that the best ice thickness parameter within a pixel area is its mean. Linear regression is the best way to adjust the relationship between the pixel backscatter value and the sea-ice thickness contained within the pixel area. The Pearson linear correlation coefficient, resulting from parametric analysis, indicates a strong correlation (0.75) between backscatter and sea-ice thickness. However, the nonparametric Spearman analysis resulted in a low correlation coefficient (0.06), which may indicate that the analyzed data consist of two distinct populations (e.g., first-year and multi-year ice). However, the Kolmogorov-Smirnov nonparametric analysis brought up the possibility that we just have not sampled the entire population. This could explain the no existence of sea-ice thicknesses values on the interval from -9.21dB to -1.35dB, which could lead to the low correlation coefficient in the Spearman analysis. We applied the linear equation: =,+, to the images, separating them into twelve classes: one for water and eleven to sea-ice, the latter in one-meter thickness intervals. The results enabled the observation of important oceanographic features such as open water channels, pressure ridges, sea-ice decay, icebergs motion (as indicators of currents, tides and winds), glaciers discharge, iceberg calving from Larsen C ice shelf, wakes and oceanic eddies. Based on the foregoing, we can say that, statistically, our results are robust and significantly, with a confidence level from 95% to 99%. The proposed equation is a first step to inferring sea-ice thickness from SAR backscatter coefficients.
34
Kreiselmeier, Janis. "Development of a Flood Model Based on Globally-Available Satellite Data for the Papaloapan River, Mexico." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-256399.
Full textAbstract:
Flood inundation modelling is highly dependent on an accurate representation of floodplain topography. These remotely sensed accurate data are often not available or expensive, especially in developing countries. As an alternative, freely available Digital Elevation Models (DEMs), such as the near-global Shuttle Radar Topography Mission (SRTM) data, have come into the focus of flood modellers. To what extent these low-resolution data can be exploited for hydraulic modelling is still an open research question. This benchmarking study investigated the potentials and limitations of the SRTM data set for flood inundation modelling on the example of the Papaloapan River, Mexico. Furthermore the effects of vegetation signal removal from the SRTM DEM as in Baugh et al. (2010) were tested. A reference model based on a light detection and ranging (LiDAR) DEM was set up with the model code LISFLOOD-FP and run for two flood events. Test models based on SRTM DEMs were run and output flood extents compared to the reference model by applying a measure of fit. This measure of fit, which was based on binary wet/dry maps of both model outputs, gave information on how well the test models simulated the flood inundation extents compared to the reference model by giving a percentage of the model performance from theoretically 0 to 100 %. SRTM-based models could not reproduce the promising results of previous studies. Flood extents were mostly underestimated and commonly flooded areas were almost exclusively made up out of the main channel surface. One of the reasons for this likely was the much steeper slope of the SRTM DEM as opposed to the LiDAR DEM where water probably was conducted much faster though the main channel. Too high bank cells as well as generally more pronounced elevation differences of the SRTM DEM throughout the whole floodplain were another problem of the SRTM DEM preventing accurate flood inundation simulations. Vegetation signal removal was successful to a certain degree improving the fit by about 10 %. However, a realistic shape of flood extent could not be simulated due to too big pixel sizes of the used canopy height data set. Also, the conditioned models overestimated flooded areas with increasing vegetation signal removal, rendering some of the models useless for comparison, as water leaving the model domain could not be accounted for in the measure of fit. This study showed the limitations of SRTM data for flood inundation modeling where an accurate approximation of the river slope as well as accurately captured bank cells and floodplain topography are crucial for the simulated outcome. Vegetation signal removal has been shown to be potentially useful but should rather be applied on more densely covered catchments.Översvämningar skapar stora problem världen över och fler och fler människor lever i områden som är utsatta för risk för att svämmas över. Dessutom förväntas översvämningar förekomma mer frekvent i många delar av världen i framtiden på grund av klimatförändringar. Skada orsakad av översvämningar kan överstiga flera miljarder US$. Men översvämningar orsakar också andra problem, förutom ekonomiska förluster. De senaste 10 åren har mer än 60 000 människor dött på grund av översvämningar. Ytterligare 900 000 000 människor har drabbats på något sätt. Därför är det viktigt att man vet vilka områden som är utsatta för hög risk. Ett av de verktyg för att avgöra översvämningsrisker är hydrauliska datormodeller som försöker förutse hur en bestämd översvämning breder ut sig. Modellerna är baserade på fysiska principer och topografisk information. Helst vill man ha topografisk information med hög kvalitet och upplösning. Ofta har man data från fjärranalyser, insamlade från flygplan. Ett exempel på det är LiDAR-data som är baserad på laser. Dock är det ofta dyrt eller inte tillgängligt med LiDAR i avlägsna områden och utvecklingsländer, där man behöver sådan data som mest. Därför har forskare försökt att använda globalt tillgängliga topografiska data av låg kvalitet för hydrauliska modeller. En sådan datauppsättning är det så kallade SRTM-datat från amerikanska NASA. SRTM samlas in med hjälp av radarstrålar från satelliter. I flera studier har man fått goda resultat inom översvämningsmodellering med SRTM. Dock måste man testa det vidare för fler avrinningsområden. I den här studien har man försökt att använda SRTM i en hydraulisk modell för den mexikanska floden Papaloapan. För att se hur bra (eller dålig) SRTM-modellen är för att simulera hur en översvämning sprids har man jämfört den med en modell baserad på högkvalitativ LiDAR-data. Båda modellerna simulerade samma översvämningar. Topografiska information från SRTM-data är oftast inkorrekt där det finns väldigt tät och hög vegetation, eftersom radarsignalen då inte räcker till marken och den uppskattade höjden är därför för hög i sådana områden. Av denna anledning ville man därför i denna studie även testa hur resultatet av SRTM-modellen skulle förbättras om man tog bort viss vegetation. Dessvärre var den utformade SRTM-modellen inte så bra för det här fallstudieområdet och SRTM-modellen förutspådde mycket mindre översvämningar än den förmodade mer korrekta LiDAR-modellen. Då vegetation avlägsnandes kunde man förbättra SRTM-modellen till viss mån, men det var fortfarande inte tillräckligt för det här området. Denna studie visar att det är viktigt att fortsätta undersöka hur passande och användbart SRTM är, eftersom det har visat sig att SRTM inte är lämpligt för att förutspå översvämningar i alla delar av världen.
35
Arnold-Bos, Andreas. "La surveillance maritime en imagerie radar bistatique : théorie, simulation, contribution à la détection automatique du sillage des navires." Phd thesis, Université de Bretagne occidentale - Brest, 2010. http://tel.archives-ouvertes.fr/tel-00763477.
Full textAbstract:
Nous étudions la faisabilité de la détection du sillage de navires en imagerie radar, éventuellement bistatique, afin d'obtenir des paramètres tels que le cap et la vitesse du navire. Dans un premier temps, on décrit la chaîne d'acquisition radar bistatique ainsi que l'environnement maritime, en particulier les modèles de diffusion des ondes électromagnétiques sur des surfaces océaniques et la manière d'obtenir une carte des hauteurs des vagues de sillage de Kelvin d'un navire. On décrit ensuite un simulateur de signaux radars bruts en configuration bistatique, en validant les résultats obtenus avec des données radar monostatiques disponibles dans la littérature. La seconde partie de la thèse est dédiée à l'étude de la détectabilité du sillage de navires. On traite tout d'abord du cas de la détection du sillage d'eau morte, en réalisant un test comparatif de quatre chaînes de référence représentatives. On traite ensuite la détectabilité du sillage de Kelvin dans des images radar de haute résolution, en commençant par discuter le choix d'une configuration radar optimisant la visibilité du sillage, puis en présentant un algorithme de détection et de traitement basé sur la théorie du filtrage adapté stochastique. Cet algorithme fonctionne également sur des données d'imagerie spatiale optiques haute résolution.
36
Kurata, Naoko. "Sea Surface Microlayer Microbial Observation System." NSUWorks, 2012. http://nsuworks.nova.edu/occ_stuetd/188.
Full textAbstract:
Chapter 2
The sea surface microlayer is a biogenic thin layer, comprising less than one millimeter of the ocean surface. This surface layer has gained much attention due to its dampening effect on ocean capillary ripples. The chemistry of the air-sea interface has been studied for decades; however, the structure and function of the marine bacterial community within the sea surface microlayer are still understudied. Although various sea surface microlayer sampling techniques were developed over the past decades, aseptic bacterial sampling in the open ocean is a rather challenging task. In this study, a new approach is presented. It is designed for bacterial sampling of the sea surface microlayer, which intends to reduce sampling contamination from the vessel, subsurface water and the investigators. A 47mm polycarbonate membrane was utilized at each sampling site. In addition, the metagenomic approach using the new generation 454 high-throughput DNA sequencing system was employed to compensate for the small sample size. Two sample sets were collected in summer 2010 and fall 2011 from the sea surface microlayer and underlying water (20 cm deep). A contamination assessment was carried out to determine that contamination might have been caused during the use of the sampling techniques. A total of 14,120 bacterial 16S rRNA gene sequences with an average length of 437.8 bp were obtained. A total of 1,254 Operational Taxonomic Units (OTUs) were constructed and 268 genera were identified. The results indicated that the bacterial compositions of the sea surface microlayer samples were distinct from those of the underlying water samples. This experiment demonstrated that the new generation sequencing platform and microbial metagenomics analysis software together served as powerful tools to gain a deeper understanding of microbial communities within the sea surface microlayer. Furthermore, it is suggested that the newly employed sampling methods could be used to obtain a snapshot of bacterial community structure as well as environmental conditions.
Chapter 3
Synthetic aperture radar (SAR) remote sensing captures various fine-scale features on the ocean surface such as coastal discharge, oil pollution, vessel traffic, algal blooms and sea slicks. Although numerous factors potentially affect the SAR imaging process, the influence of biogenic and anthropogenic surfactants has been suggested as one of the primary parameters, especially under relatively low wind conditions. Surfactants have a tendency to dampen the short gravity-capillary ocean waves causing the sea surface to smoothen, thus allowing the radar to detect areas of surfactants. Surfactants are found in sea slicks, which are the accumulation of organic material shaped as elongated bands on the ocean’s surface. Sea slicks are often observable with the naked eye due to their glassy appearance and can also be seen on SAR images as dark scars. While the sources of surfactants can vary, some are known to be associated with marine bacteria. Countless numbers of marine bacteria are present in the oceanic environment, and their biogeochemical contributions cannot be overlooked. Not only do marine bacteria produce surfactants, but they also play an important role in the transformation of surfactants. In this study, we profiled the surfactant-associated bacteria composition within the biogenic thin layer of the ocean surface more commonly referred as the sea surface microlayer (SML). Bacterial samples were collected from the SML for comparative analysis from both within and outside of sea slick areas as well as the respective underlying subsurface water. The bacterial microlayer sampling coincided with SAR satellite, RADARSAT-2, overpasses to demonstrate the simultaneous in-situ measurements during a satellite image capture. The SML sampling method was designed to enable aseptic bacterial sampling. A 47 mm polycarbonate membrane was utilized at each sampling site to obtain a snapshot of the bacterial community structure at a specific space and time. Also, a new generation high-throughput sequencing method was employed to compensate for the small sample size acquired. A total of 27,006 nucleotide sequences (16S rRNA genes) with an average 437.8 bp in length were analyzed. The results revealed the presence of industrially important surfactant-producing marine bacteria, Acinetobacter, Bacillus, Corynebacterium and surfactant-degrading marine bacteria, Escherichia. In addition, Pseudomonas was detected which can be either a producer, decomposer or both. Recognizing that there is still a large number of marine bacterial species that have not been taxonomically classified nor recognized as surfactant-associated species, the effects on SAR imaging due to a high number of surfactant-associated marine bacteria is expected. This study has provided the basis for the biological importance for fine-scale synthetic aperture satellite imaging. Moreover, this new approach is expected to have applications in monitoring biological and chemical properties of the sea surface across the globe.
37
Crossett, Daniel James. "Coral Propagation: A Growth and Survival Comparison among Six Scleractinian Boulder Corals Employing In Situ and Ex Situ Nursery Techniques." NSUWorks, 2013. http://nsuworks.nova.edu/occ_stuetd/180.
Full textAbstract:
Knowledge of effective reef restoration techniques are necessary in this age of worldwide coral reef decline. Coral transplantation is a restoration technique employed after natural (i.e. hurricanes) and anthropogenic (i.e. vessel groundings) physical disturbance events. The study was conducted to compare the efficacy of propagating small colony fragments in laboratory and field conditions in terms of survival and growth. Fragment growth and survival were assessed for six scleractinian boulder corals common to Florida and Caribbean reefs: Montastraea annularis, M. cavernosa, Diploria clivosa, Siderastrea siderea, S. radians and Dichocoenia stokesii. Broken coral colonies were salvaged from vessel grounding sites and marine debris, fragmented into pucks and secured to travertine tiles. One hundred and fifty-three coral colony fragments were cultivated in an ex situ laboratory nursery and 133 coral colony fragments were cultivated in an in situ field nursery and monitored for 13 months. Survival of all colonies was 94%, with 98% survival in the laboratory treatment and 89% survival in the field treatment. Complete colony mortality was documented in three S. radians colonies, all in the laboratory treatment. All colony loss in the field treatment was due to colony pucks being detached from the tiles. Overall mean percent change in colony tissue area from initial to final monitoring events was calculated to determine growth. Across species, growth was greater in the laboratory treatment (76 ± 4 % SEM) in comparison to the field treatment (27 ± 5 % SEM). Positive growth was observed in D. clivosa, D. stokesii, M. annularis, M. cavernosa and S. siderea in the laboratory treatment. In the field treatment, D. clivosa, M. annularis and M. cavernosa were the only species that exhibited positive growth. Negative growth was observed in both the laboratory and field treatments for S. radians. In conclusion, colonies propagated in the ex situ nursery (laboratory treatment) had higher growth and survival than colonies propagated in the in situ nursery (field treatment). A critical acclimation period accomplished through the use of stable laboratory conditions will produce healthier, more secure coral colonies that may be used to repopulate disturbed reef sites.
38
Martin, Adrien. "Analyse des mesures radiométriques en bande-L au-dessus de l'océan : Campagnes CAROLS." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00850877.
Full textAbstract:
Un regain d'intérêt pour la télédétection de la salinité de surface de l'océan (SSS) par radiométrie en bande-L (21cm) est apparu dans les années 1990 et a conduit au lancement des missions spatiales SMOS (nov. 2009) et Aquarius (juin 2011). Cependant, en raison du faible rapport signal sur bruit, l'inversion de la SSS à partir des mesures radiométriques en bande-L est très difficile. Ce travail porte sur l'étude de la signature radiométrique en bande-L des propriétés de la surface de l'océan (en particulier SSS et rugosité) à partir des mesures du radiomètre aéroporté en bande-L CAROLS, acquises dans le golfe de Gascogne en 2009 et 2010. Une première étude a montré que la SSS déduite des mesures du radiomètre CAROLS était précise à mieux que 0.3 pss dans une zone de forte variabilité spatio-temporelle avec une meilleure précision que les modèles océanographiques côtiers. La seconde étude qui combine les mesures passives (CAROLS) et active (diffusiomètre en bande-C STORM) a mis en évidence l'amélioration des nouveaux modèles de rugosité par rapport aux modèles pré-lancement satellitaires. Par ailleurs, l'étude a montré l'importance de la prise en compte des moyennes et grandes échelles de rugosité (> 20 cm) pour l'interprétation des mesures radiomé- triques loin du nadir.
39
Zelenke, Brian Christopher. "An empirical statistical model relating winds and ocean surface currents : implications for short-term current forecasts." Thesis, Connect to the title online, 2005. http://hdl.handle.net/1957/2166.
Full text
40
Farquharson, Gordon. "Microwave radar observations of nearshore ocean dynamics." 2005. https://scholarworks.umass.edu/dissertations/AAI3163667.
Full textAbstract:
The relationship between microwave imaging radar measurements of the nearshore ocean region and nearshore dynamics is studied. Normalized radar cross section and Doppler velocity are estimated from radar measurements of nearshore waves at near-grazing angles. Radar scattering is classified using joint histograms of radar cross section and Doppler velocities. Scattering in these distributions is investigated through comparisons with theoretical wave predictions, video particle image velocimetry (PIV), and in situ acoustic Doppler velocimeter (ADV) measurements. This analysis shows that shoaling and breaking waves measured through radar grating lobes significantly affect Doppler velocities near the edges of the images and also scattering from the back faces of waves. Doppler velocities from breaking waves are found to agree well with wave phase velocity predictions in the surf zone (the rms difference is 0.14 m/s), and large radar cross section features are correlated with breaking waves and the motion of surf-zone bores in video imagery. Differences in inter-bore velocities are expected, since the measurements are not collocated. However; Doppler inter-bore velocities are found to correlate well with fluid velocities (the correlation coefficient is 0.65), but are offset by around 0.8 m/s. This offset may be due to a combination of the Bragg wave phase velocities, radar sensitivity to short wavelength waves in the nearshore which is limited by the spatial resolution of the radar, and inherent biasing of Doppler velocities towards velocities of large NRCS scattering. In low-wind conditions, radar measurements of the nearshore show patches of increased backscatter. Animation of sequences of the images shows movement of these patches. A feature-tracking algorithm based on PIV is presented to quantify the velocities of the observed features. The nature of the patches is also investigated through comparison with video images. It is concluded that the patches of backscatter are due to low-grazing angle scattering from streaks of foam, however contributions from mechanically-generated surface roughness are not ruled out. Comparisons between surface velocities derived from the feature-tracking algorithm and subsurface velocities measured by in situ current meters show best agreement for sensors beyond the surf zone. It is concluded that the estimated velocity fields are related to nearshore flows such as wave-induced cell circulations and longshore currents.
41
Bathgate, Jonathan Stacy. "Extensions to the COSRAD HF ocean surface radar : extraction of swell wave parameters." Thesis, 2005. https://researchonline.jcu.edu.au/1287/1/01front.pdf.
Full textAbstract:
Routine extraction of ocean surface information from HF radar spectra has, to this point,
been predominantly limited to surface currents and wind parameters which rely on the
analysis of the first-order spectral lines. Recently, wind wave parameters are also being
supplied in a routine manner. Their calculation involves the ratio of first and second-order
spectral energies to produce significant wave heights and direction. Parameter extraction
from portions of the long ocean wave spectrum has proven difficult. The derivation of the
second-order cross-section by Barrick (1972b) led to solutions for the extraction of swell
wave information (Lipa and Barrick, 1980). However, this still did not lead to a reliable
supply of long wave information. Only recently has there been some success with full
directional spectrum analysis under certain conditions, (Wyatt, 1999). The solutions
provided by Lipa and Barrick (1980) are evaluated in this thesis on data collected by the
coastal ocean surface radar (COSRAD). The results proved unsatisfactory due to the high
sensitivity required by the solutions.
To develop an original method of extraction for swell wave information, two sets of data
were acquired using a pair of COSRAD systems overlooking Tweed Heads and Bass Strait
in 2001. At Bass Strait the radar was configured to cover a sweep (approximately 60
degrees) every 60 minutes with spatial resolution of the order of 3km. Spectral preprocessing
procedures included frequency and power level normalization prior to
incoherent averaging. We average 8 adjacent pixels over a 2-hour period to improve the
signal to noise ratio and aid in the identification and manipulation of the second-order swell
peaks that lie about the strong first-order Bragg lines in the spectrum.
A new method for the extraction of swell wave parameters from HF radar spectra is
presented along with results and comparisons to a directional wave buoy which lies in the
coverage zone. The method of extraction of the parameters, period, direction and height,
relies on a frequency modulation approach that describes the hydrodynamic interaction of the swell waves with the resonant, shorter, Bragg waves. The analysis process minimises
the electromagnetic second-order interaction and a simulation model was used to validate
the approach. This simplified method provides a fast means of examining swell conditions
over large areas of the ocean surface. The automated algorithm returned results that
compared favourably with the wave buoy at both deployment locations. The best results
were achieved during periods of swell activity that exceeded 0.3 m in height, below this
value the second-order sidebands became noisy and unreliable. During these periods the
swell height was measured to within ±0.1 m of the wave buoy. The swell direction was
measured to accuracies of ±10 degrees and the swell period to ±1 second. The results
support the use of the COSRAD HF ocean surface radar for mapping swell in the nearshore
zone and shows potential for the routine extraction of parameters in near real-time.
A routine for the extraction of wind direction was also developed and tested on data
collected during the deployment at Tweed Heads. A comparison of pairs methodology for
the resolution of the inherent ambiguity in wind direction about the radar beam is
presented. The determination of an appropriate spreading parameter is demonstrated, as
carried out previously by Heron and Prytz (2002), to refine the directional results in
comparison with wind wave data from the wave buoy.
42
Bathgate, Jonathan Stacy. "Extensions to the COSRAD HF ocean surface radar : extraction of swell wave parameters." 2005. http://eprints.jcu.edu.au/1287/1/01front.pdf.
Full textAbstract:
Routine extraction of ocean surface information from HF radar spectra has, to this point, been predominantly limited to surface currents and wind parameters which rely on the analysis of the first-order spectral lines. Recently, wind wave parameters are also being supplied in a routine manner. Their calculation involves the ratio of first and second-order spectral energies to produce significant wave heights and direction. Parameter extraction from portions of the long ocean wave spectrum has proven difficult. The derivation of the second-order cross-section by Barrick (1972b) led to solutions for the extraction of swell wave information (Lipa and Barrick, 1980). However, this still did not lead to a reliable supply of long wave information. Only recently has there been some success with full directional spectrum analysis under certain conditions, (Wyatt, 1999). The solutions provided by Lipa and Barrick (1980) are evaluated in this thesis on data collected by the coastal ocean surface radar (COSRAD). The results proved unsatisfactory due to the high sensitivity required by the solutions. To develop an original method of extraction for swell wave information, two sets of data were acquired using a pair of COSRAD systems overlooking Tweed Heads and Bass Strait in 2001. At Bass Strait the radar was configured to cover a sweep (approximately 60 degrees) every 60 minutes with spatial resolution of the order of 3km. Spectral preprocessing procedures included frequency and power level normalization prior to incoherent averaging. We average 8 adjacent pixels over a 2-hour period to improve the signal to noise ratio and aid in the identification and manipulation of the second-order swell peaks that lie about the strong first-order Bragg lines in the spectrum. A new method for the extraction of swell wave parameters from HF radar spectra is presented along with results and comparisons to a directional wave buoy which lies in the coverage zone. The method of extraction of the parameters, period, direction and height, relies on a frequency modulation approach that describes the hydrodynamic interaction of the swell waves with the resonant, shorter, Bragg waves. The analysis process minimises the electromagnetic second-order interaction and a simulation model was used to validate the approach. This simplified method provides a fast means of examining swell conditions over large areas of the ocean surface. The automated algorithm returned results that compared favourably with the wave buoy at both deployment locations. The best results were achieved during periods of swell activity that exceeded 0.3 m in height, below this value the second-order sidebands became noisy and unreliable. During these periods the swell height was measured to within ±0.1 m of the wave buoy. The swell direction was measured to accuracies of ±10 degrees and the swell period to ±1 second. The results support the use of the COSRAD HF ocean surface radar for mapping swell in the nearshore zone and shows potential for the routine extraction of parameters in near real-time. A routine for the extraction of wind direction was also developed and tested on data collected during the deployment at Tweed Heads. A comparison of pairs methodology for the resolution of the inherent ambiguity in wind direction about the radar beam is presented. The determination of an appropriate spreading parameter is demonstrated, as carried out previously by Heron and Prytz (2002), to refine the directional results in comparison with wind wave data from the wave buoy.
43
Popstefanija, Ivan P. "Remote sensing of ocean currents using a multifrequency microwave radar." 1991. https://scholarworks.umass.edu/dissertations/AAI9132897.
Full textAbstract:
A remote sensing system for measuring ocean surface currents is presented in this thesis. Included are a review of the Stepped Frequency Delta K (SFDK) radar system hardware, a description of the system performance, experimental results of ocean current measurements, and comparisons of the measurements with a conventional current probe and a wind driven current model. Important features of this radar system are (1) its capability to perform real time processing of the collected data and (2) its frequency agility, which provides significant improvement of the system's signal-to-clutter ratio. The real time processing capabilities were essential to the collection and monitoring of the ocean currents for long periods of time that is necessary to understand and interpret the results. The SFDK radar participated in two month long experiments. During the first experiment at N. Truro, MA, the SFDK radar demonstrated its ability to make precise phase velocity measurements over long periods of time. During the second experiment on the Chesapeake Light Tower, the radar was able to sense both tidal and wind driven current components. Comparison of radar data and in situ measurements during the CLT experiment shows that the instrument possesses a unique capability to measure near surface currents--not possible with in situ probes.
44
Perkovic, Dragana. "Radar remote sensing of currents and waves in the nearshore zone." 2008. https://scholarworks.umass.edu/dissertations/AAI3322189.
Full textAbstract:
The relationship between microwave radar and optical video imaging of the nearshore region is studied. The remotely sensed data were used to estimate the longshore currents and the surf zone width. Doppler radar relies on small scale surface roughness that scatters the incident electromagnetic radiation so that velocities are obtained from the Doppler shift of the backscattered radiation. Video relies on texture and contrast of scattered sunlight from the sea surface, and velocity estimates are determined using Particle Imaging Velocimetry (PIV). This study compares video PIV-derived and Doppler radar surface velocities over a 1 km alongshore by 0.5 km cross-shore area in the surf zone of a natural beach. The two surface velocity estimates are strongly correlated (R2 ≥ 0:79) over much of the surf zone. Estimates differ at the outer edge of the surf where strong breaking is prevalent, with radar estimated velocities as much as 50% below the video estimates. Both systems observe a strong eddy-like mean flow pattern over 200 m section of coastline with the mean alongshore current changing direction at about the mid surf zone. The radar and PIV velocities at particular locations in the surf zone track each other well over a 6 hour period, showing strong modulations in the mean alongshore flow occurring on 10-20 minute time intervals. The offshore region in the absence of sufficiently strong wind is sometimes barely visible, while the surf zone always appears very bright in radar backscatter images due to persistent surface roughness produced by breaking waves. The backscatter and coherence radar images were used in conjunction with edge detection filters to estimate the surf zone width from radar data. The surf zone width from video data is calculated using the time-stacking techniques. The comparison of surf zone width over 6 hours showed the rms difference of 8.8 m close to the radar location while the radar had the tendency to overestimate the distance for most of the run. The correlation of two measurements was high at 0.89. At locations farther than 600 m away from the radar the surf zone width rms differences were higher, up to 24 m, while correlation remained high. The differences are attributed to the estimate of the shoreline in radar images due to different scattering properties of wet and dry sand. The good spatial and temporal agreement between the two remote measurement techniques which rely on very different mechanisms, suggests that both are reasonably approximating the nearshore processes.
45
Comeau, William Joseph. "Design specifications of an incoherent pulsed doppler sonar instrument for monitoring hydrothermal vent characteristics." 1990. http://catalog.hathitrust.org/api/volumes/oclc/21062340.html.
Full text