Optical Properties Of Ocean Water Research Articles

Review Article on Microbiology

Microbiology is the study of microorganisms biological entities too small to be seen with the unaided eye. Most major advances in microbiology have occurred within the past 150 years, and several important subdisciplines of microbiology have developed during this time, including microbial ecology, molecular biology, immunology, industrial microbiology and biotech- nology. Microorganisms of various types exist in all three domains of life (the Bacteria, Archaea and Eukarya), and they are by far the most abundant life forms on Earth. Microscopic biological agents include bacteria, archaea, protists (protozoa and algae), fungi, parasitic worms (helminths) and viruses. Although a small percentage of microorganisms are harmful to certain plants and animals and may cause serious disease in humans, the vast majority of microorganisms provide beneficial services, such as assisting in water purification and the production of certain foods, and many are essential for the proper functioning of Earth's ecosystems. Molecular biology has revolutionized our understanding of the diversity, function, and community structure of marine microorganisms. Increasingly, tools and techniques derived from the biomedical diagnostics and research industries are used in parallel with sensors that characterize the physical, chemical, and optical properties of ocean waters.

Review on Microbiology and Molecular Biology

Microbiology is the study of microorgan- isms biological entities too small to be seen with the unaided eye. Most major advances in microbiology have occurred within the past 150 years, and several important subdisciplines of microbiology have developed during this time, including microbial ecology, molecular biology, immunology, industrial microbiology and biotech- nology. Microorganisms of various types exist in all three domains of life (the Bacteria, Archaea and Eukarya), and they are by far the most abundant life forms on Earth. Microscopic biological agents include bacteria, archaea, protists (protozoa and algae), fungi, parasitic worms (helminths) and viruses. Although a small percentage of microor- ganisms are harmful to certain plants and animals and may cause serious disease in humans, the vast majority of microorganisms provide beneficial services, such as assisting in water purification and the production of certain foods, and many are essential for the proper functioning of Earth's ecosystems. Molecular biology has revolutionized our understanding of the diversity, function, and community structure of marine microorganisms. Increasingly, tools and techniques derived from the biomedical diagnostics and research industries are used in parallel with sensors that characterize the physical, chemical, and optical properties of ocean waters.

Neural Network Reflectance Prediction Model for Both Open Ocean and Coastal Waters

Remote sensing of global ocean color is a valuable tool for understanding the ecology and biogeochemistry of the worlds oceans, and provides critical input to our knowledge of the global carbon cycle and the impacts of climate change. Ocean polarized reflectance contains information about the constituents of the upper ocean euphotic zone, such as colored dissolved organic matter (CDOM), sediments, phytoplankton, and pollutants. In order to retrieve the information on these constituents, remote sensing algorithms typically rely on radiative transfer models to interpret water color or remote-sensing reflectance; however, this can be resource-prohibitive for operational use due to the extensive CPU time involved in radiative transfer solutions. In this work, we report a fast model based on machine learning techniques, called Neural Network Reflectance Prediction Model (NNRPM), which can be used to predict ocean bidirectional polarized reflectance given inherent optical properties of ocean waters. This supervised model is trained using a large volume of data derived from radiative transfer simulations for coupled atmosphere and ocean systems using the successive order of scattering technique (SOS-CAOS). The performance of the model is validated against another large independent test dataset generated from SOS-CAOS. The model is able to predict both polarized and unpolarized reflectances with an absolute error (AE) less than 0.004 for 99% of test cases. We have also shown that the degree of linear polarization (DoLP) for unpolarized incident light can be predicted with an AE less than 0.002 for 99% of test cases. In general, the simulation time of SOS-CAOS depends on optical depth, and required accuracy. When comparing the average speeds of the NNRPM against the SOS-CAOS model for the same parameters, we see that the NNRPM is able to predict the Ocean BRDF 6000 times faster than SOS-CAOS. Both ultraviolet and visible wavelengths are included in the model to help differentiate between dissolved organic material and chlorophyll in the study of the open ocean and the coastal zone. The incorporation of this model into the retrieval algorithm will make the retrieval process more efficient, and thus applicable for operational use with global satellite observations.

Performance Evaluation of Short Range Underwater Optical Wireless Communications for Different Ocean Water Types

This paper has presented our interesting in wireless underwater communications for different ocean water types. Recent interest in ocean exploration has brought about a desire for developing wireless communication techniques in this challenging environment. Due to its high attenuation in water, a radio frequency (RF) carrier is not the optimum choice. Acoustic techniques have made tremendous progress in establishing wireless underwater links, but they are ultimately limited in bandwidth. In traditional communication systems, constructing a link budget is often relatively straight forward. In the case of underwater optical systems the variations in the optical properties of ocean water lead to interesting problems when considering the feasibility and reliability of underwater optical links. The main focus of this paper is to construct an underwater link budget which includes the effects of scattering and absorption of realistic ocean water. As well as we have developed the underwater optical wireless communication systems to have shorter ranges, that can provide higher bandwidth (up to several hundred Mbit/s) communications by the assistant of exciting high brightness blue LED sources, and laser diodes suggest that high speed optical links can be viable for short range application. The received signal power, signal to noise ratio, bit error rate, transmitted signal bandwidth, and transmission bit rates are the major interesting parameters for different ocean water mediums as a criteria of the best signal transmission characteristics of short wireless optical communications over wide range of the affecting parameters.

Analytic algorithms for determining radiative transfer optical properties of ocean waters

A synthetic model for the scattering phase function is used to develop simple algebraic equations, valid for any water type, for evaluating the ratio of the backscattering to absorption coefficients of spatially uniform, very deep waters with data from upward and downward planar irradiances and the remotely sensed reflectance. The phase function is a variable combination of a forward-directed Dirac delta function plus isotropic scattering, which is an elementary model for strongly forward scattering such as that encountered in oceanic optics applications. The incident illumination at the surface is taken to be diffuse plus a collimated beam. The algorithms are compared with other analytic correlations that were previously derived from extensive numerical simulations, and they are also numerically tested with forward problem results computed with a modified FN method.

Uniqueness in remote sensing of the inherent optical properties of ocean water.

We examine the problem of uniqueness in the relationship between the remote-sensing reflectance (Rrs) and the inherent optical properties (IOPs) of ocean water. The results point to the fact that diffuse reflectance of plane irradiance from ocean water is inherently ambiguous. Furthermore, in the 400 < lambda < 750 nm region of the spectrum, Rrs(lambda) also suffers from ambiguity caused by the similarity in wavelength dependence of the coefficients of absorption by particulate matter and of absorption by colored dissolved organic matter. The absorption coefficients have overlapping exponential responses, which lead to the fact that more than one combination of IOPs can produce nearly the same Rrs spectrum. This ambiguity in absorption parameters demands that we identify the regions of the Rrs spectrum where we can isolate the effects that are due only to scattering by particulates and to absorption by pure water. The results indicate that the spectral shape of the absorption coefficient of phytoplankton, a(ph)(lambda), cannot be derived from a multiparameter fit to Rrs(lambda). However, the magnitude and the spectral dependence of the absorption coefficient can be estimated from the difference between the measured Rrs(lambda) and the best fit to Rrs(lambda) in terms of IOPs that exclude a(ph)(lambda).

Results of a Monte Carlo investigation of the diffuse attenuation coefficient

There has been a large effort to relate the apparent optical properties of ocean water to the inherent optical properties, which are the absorption coefficient a, the scattering coefficient b, and the scattering phase function rho(theta). The diffuse attenuation coefficient kdiff' has most often been considered an apparent optical property. However, kdiff' can be considered a quasi-inherent property kdiff' when defined as a steady-state light distribution attenuation coefficient. The Honey-Wilson research empirically relates kdiff' to a and b. The Honey-Wilson relation most likely applies to a limited range of water types because it does not include dependence on rho(theta). A series of Monte Carlo simulations were initiated to calculate kdiff' in an unstratified water column. The calculations, which reflected open ocean water types, used ranges of the single-scattering albedo omega(0) and the mean forward-scattering angle theta(m) for two analytic phase functions with different shapes. It was found that kdiff' is nearly independent of the shape of rho(theta) and can be easily parameterized in terms of a, b, and theta(m) for 0.11 <or= theta(m) <or= 0.48 rad and 0.5 <or= omega(0) <or= 0.95. kdiff' is an asymptotic quantity; that is, a steady-state distribution is reached only after many scattering lengths.

Optical properties of ocean waters in the vicinity of the Chatham Rise, South Pacific Ocean

Apparent optical properties of the water at 21 ocean stations in the South Pacific, east of New Zealand in the vicinity of the Chatham Rise, have been studied. Spectral irradiance attenuation and reflectance, and PAR irradiance attenuation, were measured in Sub-tropical and Sub-antarctic water masses, in the Sub-tropical Convergence zone between them, and in coastal waters. The waters studied are considered to be predominantly Jerlov optical types II and III. Anomalous features at wavelengths above 590 nm in the spectra of reflectance and of the vertical attenuation coefficient for upward irradiance were attributed predominantly to Raman emission with a contribution from chlorophyll fluorescence at longer wavelengths.

In situ methods for measuring the inherent optical properties of ocean waters

In situ attenuation (488 and 660 nm), absorption (488, 676, and 750 nm), backscattering (at 488 nm), and stimulated fluorescence were determined as functions of depth in oceanic and coastal waters off Oregon, using both commercial instruments and recently developed prototypes. The inability to perfectly constrain scattered light in these instruments necessitates correction to retrieve accurate optical coefficients. Because scattering is usually one order of magnitude higher than absorption, the correction is most critical for absorption coefficients. A correction procedure based on values obtained with the absorption meter in the infrared region (750 nm) was used to correct the measured spectral absorption coefficients. Realistic values of the backscattering coefficient were obtained from a prototype instrument, although accurate calibration could not be performed for this study.These measurements resulted in the first‐ever data set ofin situ profiles of attenuation, absorption, scattering, backscattering, and the backscattering ratio. The blue and red attenuation coefficients were tightly correlated, with a relationship varying from site to site. The red‐to‐blue absorption ratio varied both from site to site and vertically, indicating changes in the relative concentrations of chlorophyllous (phytoplankton) and nonchlorophyllous (biogenous or mineral) particles. The backscattering ratio also appeared to be very sensitive to vertical changes in particle composition. The in situ scattering coefficients were compared to those estimated with a Mie scattering model, using measured particle size distributions and particulate absorption coefficients as input parameters. By allowing the real part of the refractive index of particles to vary over the range of realistic values, convergence between measured and modeled values was obtained.