Dissertations / Theses on the topic 'Ocean optic'

In an effort to investigate the role of turbulence in near-forward scattering, laboratory measurements of scattering on turbulent flow were carried out in a Rayleigh-Bénard convective tank. Particle Image Velocimetry and profiling thermistor temperature measurements are used to characterize the turbulent flow through determination of the large scale flow features, turbulent kinetic energy dissipation rates, and thermal dissipation rates. Polarized diffractometer measurements allow for determination of the turbulence-induced depolarization rate, which is comparable to that observed with polarimetric lidar. Measurements were made over a range of turbulent strengths, with Rayleigh number between 10^8 and 3*10^9, and with turbulent parameters corresponding to those characteristic of the oceanic mixed layer. Results show that the turbulence-induced depolarization rate is indirectly proportional to the strength of the turbulent flow, suggesting that light beam depolarization from turbulent flow may contain useful information regarding the smallest length scales of turbulent flow.

For decades, traditional remote sensing retrieval methods that rely solely on the spectral intensity of the water-leaving light have provided indicators of aquatic ecosystem health. With the increasing demand for new water quality indicators and improved accuracy of existing ones, the limits of traditional remote sensing approaches are becoming apparent. Use of the additional information intrinsic to the polarization state of light is therefore receiving more attention. One of the major challenges inherent in any above-surface determination of the water-leaving radiance, scalar or vector, is the removal of extraneous light which has not interacted with the water body and is therefore not useful for remote sensing of the water itself. Due in-part to the lack of a proven alternative, existing polarimeter installations have thus far assumed that such light was reflected by a flat sea surface, which can lead to large inaccuracies in the water-leaving polarization signal. This dissertation rigorously determines the full Mueller matrices for both surface-reflected skylight and upwardly transmitted light by a wind-driven ocean surface. A Monte Carlo code models the surface in 3D and performs polarized ray-tracing, while a vector radiative transfer (VRT) simulation generates polarized light distributions from which the initial Stokes vector for each ray is inferred. Matrices are computed for the observable range of surface wind speeds, viewing and solar geometries, and atmospheric aerosol loads. Radiometer field-of-view effects are also assessed. Validation of the results is achieved using comprehensive VRT simulations of the atmosphere-ocean system based on several oceanographic research cruises and specially designed polarimeters developed by the City College of New York: one submerged beneath the surface and one mounted on a research vessel. When available, additional comparisons are made at 9 km altitude with the NASA Research Scanning Polarimeter (RSP). Excellent agreement is achieved between all instrumentation, demonstrating the accuracy of the modeling approach and validating the computed Mueller matrices. Further, the results are used to demonstrate the feasibility for polarimetric retrieval of the total attenuation coefficient for Case II waters, a feat which is not possible using scalar remote sensing methods.

Thesis (S.M.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 1998.
Includes bibliographic references (p. 77-83).
This thesis presents an investigation of the influence of surface waves on momentum exchange. A quantitative comparison of direct covariance friction velocity measurements to bulk aerodynamic and inertial dissipation estimates indicates that both indirect methods systematically underestimate the momentum flux into developing seas. To account for wave-induced processes and yield improved flux estimates, modifications to the traditional flux parameterizations are explored. Modification to the bulk aerodynamic method involves incorporating sea state dependence into the roughness length calculation. For the inertial dissipation method, a new parameterization for the dimensionless dissipation rate is proposed. The modifications lead to improved momentum flux estimates for both methods.
by Michiko J. Martin.
S.M.

Remote sensing is a powerful tool for studying the marine environment; however, many images are contaminated by sun glint, the specular reflection of light from the water surface. Improved radiative transfer modelling could lead to better methods for estimating and correcting sunglint. This thesis explores the effect of using detailed numerical models of the sea surface when investigating the transfer of light through the atmosphere-ocean system. New numerical realisations that model both the shape and slope of the sea surface have been created; these contrast with existing radiative transfer models, where the air-water interface has slope but not elevation. Surface realisations including features on a scale from 3 mm to 200 m were created by a Fourier synthesis method, using up to date spectra of the wind-blown sea surface. The surfaces had mean square slopes and elevation variances in line with those of observed seas, for wind speeds up to 15 m/s. Ray-tracing using the new surfaces gave estimates of reflected radiance that were similar to those made using slope statistics methods, but significantly different in 41% of cases tested. The mean difference in the reflected radiance at these points was 19%, median 7%. Elevation-based surfaces give increased sideways scattering and reduced forward scattering of light incident on the sea surface. The elevation-based models have been applied to estimate pixel-pixel variation in ocean colour imagery and to simulate scenes viewed by three types of sensor. The simulations correctly estimated the size and position of the glint zone. Simulations of two ocean colour images gave a lower peak reflectance than the original values, but higher reflectance at the edge of the glint zone. The use of the simulation to test glint correction methods has been demonstrated, as have global Monte Carlo techniques for investigating sensitivity and uncertainty in sun glint correction. This work has shown that elevation-based sea surface models can be created and tested using readily-available computer hardware. The new model can be used to simulate glint in a variety of situations, giving a tool for testing glint correction methods. It could also be used for glint correction directly, by predicting the level of sun glint in a given set of conditions.

Amplification of low-light-level optical images is important for extending the range of lidar systems that image and detect objects in the atmosphere and underwater. The use of range-gating to produce images of particular range bins is also important in minimizing the image degradation due to light that is scattered backward from aerosols, smoke, or water along the imaging path. For practical lidar systems that must be operated within sight of unprotected observers, eye safety is of the utmost importance. This dissertation describes a new type of eye-safe, range-gated lidar sensing element based on Solid-state Raman Image Amplification (SSRIA) in a solid-state optical crystal. SSRIA can amplify low-level images in the eye-safe infrared at 1.556 μm with gains up to 106 with the addition of only quantum-limited noise. The high gains from SSRIA can compensate for low quantum efficiency detectors and can reduce the need for detector cooling. The range-gate of SSRIA is controlled by the pulsewidth of the pump laser and can be as short as 30-100 cm, using pump pulses of 2-6.7 nsec FWHM. A rate equation theoretical model is derived to help in the design of short pulsed Raman lasers. A theoretical model for the quantum noise properties of SSRIA is presented. SSRIA results in higher SNR images throughout a broad range of incident light levels, in contrast to the increasing noise factor with reduced gain in image intensified CCD's. A theoretical framework for the optical resolution of SSRIA is presented and it is shown that SSRIA can produce higher resolution than ICCD's. SSRIA is also superior in rejecting unwanted sunlight background, further increasing image SNR. Lastly, SSRIA can be combined with optical pre-filtering to perform optical image processing functions such as high-pass filtering and automatic target detection/recognition. The application of this technology to underwater imaging, called Marine Raman Image Amplification (MARIA) is also discussed. MARIA operates at a wavelength of 563 nm, which passes most efficiently through coastal ocean waters. The imaging resolution of MARIA in the marine environment can be superior to images produced by laser line scan or standard range-gated imaging systems.

Phytoplankton serve as the bottom of the marine food web and therefore play an essential role in marine ecosystems. On the other hand, coastal phytoplankton communities can adversely affect the marine ecosystem and humans. A variety of techniques have been developed to measure and study phytoplankton, including in situ methods (e.g., flow cytometry) and laboratory methods (e.g., microscopic taxonomy). These provide accurate measurements of phytoplankton taxa and concentrations, yet they are limited in space and time, and synoptic information is difficult to obtain with these techniques. Optical remote sensing may provide complementary information for its synoptic nature, as demonstrated by satellite estimates of major phytoplankton taxa in major ocean basins. It has remained a challenge, however, for coastal and estuarine waters due to their optical complexity. One pioneering work relied on hyperspectral absorption spectra of phytoplankton pigments (Millie et al., 1995), from which Gymnodinium breve (i.e., Karenia brevis) blooms on the West Florida shelf could be detected and quantified in situ. However, whether a similar approach can be developed for estuarine waters where toxic blooms are often found is still unknown. Thus, the objective of this study is to test and develop an approach to classify major phytoplankton taxa found in two estuaries in Florida, U.S.A., based on optical analysis of the phytoplankton absorption spectra. In this study, over 250 surface water samples were collected on numerous cruise surveys from two Florida estuaries (Tampa Bay, ∼1000 km2 on the west coast; and the Indian River Lagoon, ∼900 km2 on the east coast). The samples were filtered and then processed using standard NASA protocols to determine 1) their spectral absorption coefficients due to phytoplankton pigments, aph (λ) (m-1), and 2) their chlorophyll a concentrations (mg m-3). aph (λ) was further normalized by Chl a, resulting in chlorophyll-specific absorption coefficient, a aph∗ (λ) (m2 mg-1). For each sample, phytoplankton cell counts were enumerated by the Florida Wildlife Conservation Commission (FWC) Fish and Wildlife Research Institute (FWRI) through microscopic taxonomy. The a aph∗ (λ) data were then categorized based on the dominant phytoplankton taxa, and were separated as either bloom or non-bloom using a 100,000 cell∕L threshold of the dominant taxa. Three techniques were tested for classifying phytoplankton taxa using absorption spectra; a first derivative summation, a relative height analysis, and an integration analysis. The integration technique proved to be the most successful of the three. This technique performed an integration of a aph∗ (572-600nm) against a linear baseline, and yielded an 81% success rate (13 of 16 samples) and 9% false positive rate (13 of 144 samples) in separating blooms of the dinoflagellate Pyrodinium bahamense from other bloom and non-bloom taxa found in the Tampa Bay estuary. The same integration technique, but with the wavelength range shifted to 471 nm - 490 nm, was also applied to the samples collected in the Indian River Lagoon estuary from summer 2011 to study the green flagellate of the class Pedinophyceae.. The results showed an 80% success rate (8 of 10 samples) and a 0.5% false positive rate (1 of 156 samples) in separating the Pedinophyceae bloom taxa from other bloom and non-bloom taxa found in both the Indian River Lagoon and Tampa Bay. The number of bloom samples was relatively low (16 from Tampa Bay and 10 from IRL). Thus, the results from this study are preliminary and will require more sampling in order to further develop this technique to a practical method for field use. However, the results obtained from this study are comparable to those from other techniques for classification of phytoplankton taxa, for example, BreveBuster, SIPPER, FlowCAM, and satellite ocean color remote sensing of the open ocean. Yet this technique extends to optically complex estuarine waters, and therefore may represent a step towards the ultimate goal of applying satellite remote sensing in characterizing phytoplankton taxa in estuaries. Once confirmed with more samples from the same two estuaries as well as from other estuaries, an immediate next step may be the implementation of in situoptical instruments on either buoys (e.g., MARVIN in Tampa Bay) or flow-through systems to provide continuous characterization of major phytoplankton taxa in the two estuaries.

Nearshore bathymetry in the Canadian Arctic is poorly surveyed, but is vital knowledge for coastal communities that rely on marine transportation for resources and development. Nautical charts currently available are often outdated and surveying by traditional methods is both time consuming and expensive. Satellite-derived bathymetry (SDB) offers a significantly cheaper and faster option to provide information on nearshore bathymetry. The two most common approaches to SDB are empirical and physics-based. The empirical approach is simple and typically does well when calibrated with high-quality in-situ data, whereas the physics-based approach is more difficult to implement and requires precise atmospheric correction. This project tests the practical use of five methods within the empirical and physics-based approaches to SDB, using Landsat 8 and Sentinel-2 satellite imagery, at seven sites across Nunavut. Methods tested include: the Ratio-Transform, Multiband, and Random Forest Regression methods (empirical) and radiative transfer modeling (physics-based) using two atmospheric correction models: ACOLITE and Deep Water Correction. All methods typically use geolocated water depth data for validation, as well as calibration for the empirical methods. Spectral reflectance for model inputs were collected in Cambridge Bay, NU. Water depth data were acquired from the Canadian Hydrographic Service. All processing was conducted within the framework of plugins developed for the open-source GIS software, QGIS. Results from the empirical methods were typically poor due to poor calibration data, though Random Forest Regression performed well when good calibration data were available. Due to poor quality validation data, error for the physics-based results cannot be adequately quantified in most places. Additionally, atmospheric correction remains a challenge for the physics-based methods. Overall, results indicate that where large, high-quality calibration datasets are available, Random Forest Regression performs best of all methods tested, with little bias and low mean absolute error in water less than 10 m deep. As such datasets are rare in the Arctic, the physics-based method is often the only option for SDB and is an excellent qualitative tool for informing communities of shallow bathymetry features and assessing navigation risk.

This PhD study focusses on the use of MEdium Resolution Imaging Spectrometer (MERIS) data for reliable and quantitative water-quality assessment of optically-complex waters (lake, brackish and coastal waters). The thesis is divided into two parts: A. intercalibration of reflectance measurements in different optically-complex water bodies (Paper I), and validation of various satellite processing algorithms for the coastal zone (Paper II). B. Applications: the use of MERIS data in integrated coastal zone management mostly using Himmerfjärden bay as an example. Himmerfjärden bay is one of the most frequently monitored coastal areas in the world and it is also the recipient of a large urban sewage treatment plant, where a number of full-scale nutrient management experiments have been conducted to evaluate the ecological changes due to changes in nutrient schemes in the sewage plant. Paper I describes the development and assessment of a new hyperspectral handheld radiometer for in situ sampling and validation of remote sensing reflectance.  The instrument is assessed in comparison with readily available radiometers that are commonly used in validation. Paper II has a focus on the validation of level 2 reflectance and water products derived from MERIS data. It highlights the importance of calibration and validation activities, and the current accuracy and limitations of satellite products in the coastal zone.  Bio-optical in situ data is highlighted as one of the key components for assessing the reliability of current and future satellite missions. Besides suspended particulate matter (SPM), the standard MERIS products have shown to be insufficient to assure data quality retrieval for Baltic Sea waters. Alternative processors and methods such as those assessed and developed in this thesis therefore will have to be put in place in order to secure the success of future operational missions, such as Sentinel-3. The two presented manuscripts in the applied part B of the thesis (paper III and IV), showed examples on the combined use of in situ measurements with optical remote sensing to support water quality monitoring programs by using turbidity and suspended particulate matter as coastal indicators (manuscript III). The article also provides  a new turbidity algorithm for the Baltic Sea and a robust and cost-efficient method for research and management.  A novel approach to improve the quality of the satellite-derived products in the coastal zone was demonstrated in manuscript IV. The analysis included, the correction for adjacency effects from land and an improved pixel quality screening.  The thesis provides the first detailed spatio-temporal description of the evolution of phytoplankton blooms in Himmerfjärden bay  using quality-assured MERIS data, thus forwarding our understanding of ecological processes in in Swedish coastal waters. It must be noted that monitoring from space is not a trivial matter in these optically-complex waters dominated by the absorption of coloured dissolved organic matter (CDOM). These types of coastal waters are especially challenging for quantitative assessment from space due to their low reflectance.  Papers III and IV thus also provide tools for a more versatile use in other coastal waters that are not as optically-complex as the highly absorbing Baltic Sea waters. The benefits of the increased spatial-temporal data coverage by optical remote sensing were presented, and also compared to in situ sampling methods (using chlorophyll-a as indicator).

Research funders:

European Space Agency (ESA, contract no.21524/08/I-OL)

NordForsk funding: Nord AquaRemS Ref. no. 80106

NordForsk funding:  NordBaltRemS Ref.no. 42041

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Je présente les premières observations infrarouges des étoile FU Ori et AB Aur obtenues avec les interféromètres longue base IOTA(Umass, SAO) et PTI (JPL/NASA). Ces deux étoiles sont des prototypes des étoiles pré-séquence principale de faible masse (FU Ori) et de masse intermédiaire (AB Aur). Les deux sources sont résolues avec une résolution de l'ordre de l'unité astronomique. Divers scénarios sont envisagés. Les observations sont tout à fait compatibles avec la présence d'un disque d'accrétion autour de FU Ori. Afin d'améliorer les performances scientifiques et de diminuer la complexité des instruments interférométriques, je propose d'utiliser l'optique intégrée planaire pour la fonction de recombinaison. Je présente les résultats des caractérisations d'un recombinateur réalisé dans une technologie d'échanges d'ions sur substrat de verre. Cette "puce optique" comporte deux entrées et trois sorties : une voie interférométrique et deux voies de calibration photométrique. Elle est optimisée pour la bande H et assure le maintien de la polarisation. Les caractérisations montrent des pertes photoniques réduites, un contraste laser de ~ 90% et un contraste en bande large maximum de ~ 30%. Les origines de cette chute de contraste sont identifiées et des méthodes de caractérisation plus poussées sont proposées. Plusieurs perspectives de recombinaison multi-télescopes se dégagent à la suite de ce travail. Enfin, à la lumière de ces résultats, je présente le concept d'un instrument recombinateur portable baptisé IONIC, qui pourrait être le précurseur de l'instrumentation de deuxième génération des interféromètres monomodes au sol et dans l'espace. Ses principaux atouts sont la précision de mesures sur les visibilités, la compacité et la stabilité.

Les étoiles multiples sont nombreuses, tant parmi les objets jeunes de faible masse, les étoiles T Tauri, que parmi les astres de la Séquence Principale (SP). En ce qui concerne les étoiles jeunes de masse intermédiaire, les étoiles Ae/Be de Herbig (HAeBe), le statut de la binarité est peu connu. Nous avons réalisé une recherche systématique de binaires HAeBe en utilisant deux techniques: l'imagerie à haute résolution angulaire avec la méthode de l'Optique Adaptative d'une part, et la spectroscopie visible à haute résolution d'autre part. Ces techniques complémentaires nous ont permis d'identifier plus d'une vingtaine de nouvelles étoiles binaires; la fréquence de binarité déduite est d'au moins 50 %, voir supérieure à cause des biais observationnels discutés dans la thèse. Pour la première fois, les types spectraux des compagnons ont pu être déterminés dans une vingtaine de systèmes visuels. Les implications de nos observations pour la présence de disques de poussières et la détection d'émission X dans les étoiles HAeBe sont présentées. Les contraintes apportées pour les théories de formation des binaires sont discutées. Une partie importante de la thèse est consacrée à une étude approfondie de l'étoile triple TY CrA, l'unique système spectroscopique hiérarchisé parmi les étoiles Ae/Be de Herbig. Après une description complète des paramètres orbitaux et stellaires, la modélisation de la dynamique de cet objet particulier a été réalisée. Nos calculs théoriques montrent que la cohésion du système est assurée par effet de marée à l'oeuvre dans la binaire à éclipse centrale. L'environnement circumstellaire de TY CrA a également été étudié à partir d'observations spectroscopiques infrarouges avec le télescope spatial ISO et à partir d'images en Optique Adaptative dans le proche infrarouge.

The backscattering coefficient bb is one of the inherent optical properties of natural waters which means that it is independent of the ambient light field in the water. As such, it plays a central role in many problems of optical oceanography and is used in the characterization of natural waters. Essentially, any measurement that involves sending a beam of light into water must account for all inherent backscattering. Some of the applications that rely on the precise knowledge of the backscattering coefficient include studies of suspended particle distributions, optical bathymetry, and remote sensing. Many sources contribute to the backscattering, among them any suspended particles, air bubbles, and the water molecules themselves. Due to the importance of precise measurements and the ease with which water samples can be contaminated, an instrument to determine directly and quickly the backscattering coefficient in situ is highly desirable. We present such an instrument in both theory and experiment. We explain the theory behind our instrument and based on measurements made in the laboratory we demonstrate that our prototype shows the predicted behavior. We present data for increased extinction in the water, and show how measuring the extinction and taking it into account improves the quality of our measurements. We present calibration data obtained from three different particle sizes representing differently shaped volume scattering functions. Based on these measurements we demonstrate that our prototype has the necessary resolution to measure the backscattering coefficient bb over the whole range found in natural waters. We discuss potential improvements that should be made for a commercial version of the instrument.

One of the greatest challenges for Southern Ocean and Antarctic research is the development of robust methods for assessing the current and future impacts of climate change, and for evaluating regional differences in the rate and direction of that change. The Southern Ocean has been changing rapidly for at least the last 30 years, including measurable changes to phytoplankton communities. Climate projections suggest that they will continue to change. It is predicted that there will be continued southward movement of oceanographic fronts, in- creased warming and freshening (increased precipitation) of the surface ocean, shallowing of the mixed layer (increased stratification) and increased carbon dioxide enrichment and ab- sorption of the upper ocean. In order to capture and monitor the response of phytoplankton across the Southern Ocean, an economical observing system with high resolution in time and space is needed. This thesis examines the ability of ocean colour remote sensing to meet this challenge by accurately assessing and monitoring climate change impacts on phytoplankton. The ever-increasing number of in situ samples from the Southern Ocean, which can be used to calibrate and validate remote sensing algorithms, have the potential to make ocean colour radiometry a robust method for assessing climate change impacts on the Southern Ocean ecosystem. We investigated both calcite and chlorophyll products, two measurements that are key for assessing the impact of climate change on phytoplankton. Chlorophyll is used as a proxy for biomass and calcite is used to identify calcifying plankton, and to detect changes in calcification rates and carbon sequestration impacted by ocean acidification. We found that current satellite algorithms underestimate chlorophyll by as much as 50% and overestimate calcite by up to 400% in the Southern Ocean. Much of the in situ data used in this thesis were collected by ships transiting to and from the Antarctic on station re-supply missions that collected surface samples while the ship was sailing. This methodology naturally raised the question of how well does surface sampling capture the variability with depth in the euphotic zone. We determined that surface sampling of chlorophyll, either from ships or satellites, is an adequate representation of the ecologically important euphotic zone in the well-mixed regions of the Southern Ocean. This thesis concludes that customised ocean colour algorithms can be a robust method for assessing Southern Ocean phytoplankton and presents several methods and improved satellite products for doing so.

Tesis (Lic. en Física)--Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física, 2011.
El conocimiento del vector del viento en la superficie del mar a escala global es de vital importancia en estudios de cambio climático. En particular, es indispensable para la estimación de la salinidad del mar, principal objetivo de la misión SAC-D/Aquarius de la CONAE y la NASA. Para la obtención del vector de viento en la superficie del mar es necesario un Modelo de Transferencia Radiativa, para el rango de las microondas, que incluya una descripción en detalle de la dependencia de la radiación emitida por el mar con el módulo y la dirección del viento en su superficie. En este trabajo se implementó un modelo de emisión de radiación del mar semiempírico, basado en un modelo de superficie del mar de dos escalas. Se adaptó el modelo para dominio de trabajo del radiómetro montado en el satélite SAC-D, y se obtuvieron las estimaciones de temperaturas de brillo correspondientes.
Antecedentes históricos -- Fundamentos de la teledetección pasiva en las microondas -- La Teoría de la Transferencia Radiativa -- El viento y la emisión de radiación de la supercie del mar -- El espectro de ondas -- La espuma de mar -- Las olas capilares -- Cálculos para el MWR -- Los coecientes de scattering de Bragg.