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Underwater temperature and salinity microstructure can lead to localized changes in the index of refraction and can be a limiting factor in oceanic environments. This optical turbulence can affect electro-optical (EG) signal transmissions that impact various applications, from diver visibility to active and passive remote sensing. To quantify the scope of the impacts from turbulent (lows on EG signal transmission, and to examine and mitigate turbulence effects, we perform experiments in a controlled turbulence environment allowing the variation of turbulence intensity. This controlled turbulence setup is implemented at the Naval Research Laboratory Stennis Space Center (NRLSSC). Convective turbulence is generated in a classical Rayleigh-Benard tank and the turbulent flow is quantified using a state-of-the-art suite of sensors that includes high-resolution Acoustic Doppler Velocimeter profilers and fast thermistor probes. The measurements are complemented by very high-resolution non-hydrostatic numerical simulations. These computational fluid dynamics simulations allow for a more complete characterization of the convective How in the laboratory tank than would be provided by measurements alone. Optical image degradation in the tank is assessed in relation to turbulence intensity The unique approach of integrating optical techniques, turbulence measurements and numerical simulations helps advance our understanding of how to mitigate the effects of turbulence impacts on underwater optical signal transmission, as well as of the use of optical techniques to probe oceanic processes.

The Bahamas Optical Turbulence Experiment (BOTEX) was conducted in the summer of 2011 to investigate the impact of turbulence on underwater optical imaging. Underwater optical properties can be affected by turbulence in the water, due to localized changes in the index of refraction. We discuss measurements of current velocity and temperature, made with a Nortek Vector Acoustic Doppler Velocimeter (ADV) and PME Conductivity- Temperature (CT) probe, as well as observations made with a Rockland Oceanographic Vertical Microstructure Profiler (VMP). The instruments were deployed in close proximity in the field and in the context of measurements of optical target clarity. Turbulent kinetic energy dissipation (TKED) and temperature dissipation (TD) rates are calculated from the ADV/CT measurements and compared to TKED and TD estimated from the data collected with the VMP. The results show reasonable agreement between the two methods; differences are attributed to turbulence patchiness and intermittence, as well as sampling challenges. The study also highlights the importance of collecting concurrent data on temperature, current velocity, and current shear to assess the turbulence impact on underwater optical properties.

It is a well-known fact that the major degradation source on electro-optical imaging underwater is from scattering by particles of various origins and sizes. Recent research indicates that, under certain conditions, the apparent degradation could also be caused by the variations of index of refraction associated with temperature and salinity microstructures in the ocean and lakes. The combined impact has been modeled previously through the simple underwater imaging model. The current study presents the first attempts in quantifying the level of image degradation due to optical turbulence in natural waters in terms of modulation transfer functions using measured turbulence dissipation rates. Image data collected from natural environments during the Skaneateles Optical Turbulence Exercise are presented. Accurate assessments of the turbulence conditions are critical to the model validation and were measured by two instruments to ensure consistency and accuracy. Optical properties of the water column in the field were also measured in coordination with temperature, conductivity, and depth. The results show that optical turbulence degrades the image quality as predicted and on a level comparable to that caused by the particle scattering just above the thermocline. Other contributing elements involving model closure, including temporal and spatial measurement scale differences among sensors and mitigation efforts, are discussed., The original document contains color images.

Acoustical and optical signal transmission underwater is of vital interest for both civilian and military applications. The range and signal to noise during the transmission, as a function of system and water optical properties, in terms of absorption and scattering, determines the effectiveness of deployed electro-optical (EO) technology. The impacts from turbulence have been demonstrated to affect system performance comparable to those from particles by recent studies. This paper examines the impacts from underwater turbulence on both acoustic scattering and EO imaging degradation, and establishes a framework that can be used to correlate these. It is hypothesized here that underwater turbulence would influence the acoustic scattering cross section and the optical turbulence intensity coefficient in a similar manner. Data from a recent field campaign, Skaneateles Optical Turbulence Exercise (SOTEX, July, 2010) is used to examine the above relationship. Results presented here show strong correlation between the acoustic scattering cross-sections and the intensity coefficient related to the modulation transfer function of an EO imaging system. This significant finding will pave ways to utilize long range acoustical returns to predict EO system performance., Published in Optics Express, v21 n4 25 p4368-4375, 25 Feb 2013.

During October 9 22, 2010, NRL conducted a field experiment in Monterey Bay, California. Personnel from the NRL Ocean Sciences (Code 7330) and Coastal and Ocean Sensing (Code 7230) Branches, and the Monterey Bay Aquarium Research Institute (MBARI) were aboard the UNOLS Research Vessel Pt. Sur. During the same time period, additional Code 7230 personnel performed a series of flights over the Bay aboard an airplane equipped with hyperspectral remote sensing instruments. This document contains a description of the NRL activities, sampling instrumentation, methods, and data processing. Plots of the monthly timeseries data are followed by plots from each day of October 2010 (organized by hydrocast number) and brief notes on the environment from cruise and flight logs. This is not a complete set of all data products collected or derived and is intended only to provide an overview and serve as a basis for further investigation. The plots presented in the document are not necessarily final versions; additional quality control and/or processing steps may be found necessary., The original document contains color images.

Optical signal transmission underwater is of vital interests to both civilian and military applications. The range and signal to noise during the transmission, as a function of system and water optical properties determines the effectiveness of EO technology. These applications include diver visibility, search and rescue, mine detection and identification, and optical communications. The impact of optical turbulence on underwater imaging has been postulated and observed by many researchers. However, no qualitative studies have been done until recently, in terms of both the environmental conditions, and impacts on image quality as a function of range and spatial frequencies Image data collected from field measurements during SOTEX (Skaneateles Optical Turbulence Exercise, July 22-31. 2010) using the Image Measurement Assembly for Subsurface Turbulence (IMAST) are presented Optical properties of the water column in the field were measured using WETLab's ac-9 and Laser In Situ Scattering and Transmissometer (LISST, Sequoia Scientific), in coordination with physical properties including CTD (Seabird), dissipation rate of kinetic energy and heat, using both the Vector velocimeter and CT combo (Nortek and PME). and shear probe based Vertical Microstructure Profiler (VMP. Rockland). The strong stratification structure in the water column provides great opportunity to observe various dissipation strengths throughout the water column, which corresponds directly with image quality as shown. Initial results demonstrate general agreement between data collected and model prediction, while discrepancies between measurements and model suggest higher spatial and temporal observations are needed in the future.

Enhancing visibility through scattering media is important in many fields for gaining information from the scattering medium. In the ocean, in particular, enhancement of imaging and visibility is important for divers, navigation, robotics, and target and mine detection and classification. Light scattering from particulates and turbulence in the ocean strongly affect underwater visibility. The magnitude of this degrading effect depends upon the underwater environment, and can rapidly degrade the quality of underwater imaging under certain conditions. To facilitate study of the impact of turbulence upon underwater imaging and to check against our previously developed model, quantified observation of the image degradation concurrent with characterization of the turbulent flow is necessary, spanning a variety of turbulent strengths. Therefore, we present field measurements of turbulence microstructure from the July 2010 Skaneateles Optical Turbulence Exercise (SOTEX), during which images of a target were collected over a 5 m path length at various depths in the water column, concurrent with profiles of the turbulent strength, optical properties, temperature, and conductivity. Turbulence was characterized by the turbulent kinetic energy dissipation (TKED) and thermal dissipation (TD) rates, which were obtained using both a Rockland Scientific Vertical Microstructure Profiler (VMP) and a Nortek Vector velocimeter in combination with a PME Conductivity and Temperature (CT) sensor. While the two instrumental setups demonstrate reasonable agreement, some irregularities highlight the spatial and temporal variability of the turbulence field. Supplementary measurements with the Vector/CT in a controlled laboratory convective tank will shed additional light on the quantitative relationship between image degradation and turbulence strength., Published in the Proceedings of SPIE, v8030 p80300A-1 to 80300A-11, Ocean Sensing and Monitoring III, 2011.

We focus on the validation of a simplified approach to bathymetry retrieval from hyperspectral imagery (HSI) in the very shallow water limit (less than 1-2 m), where many existing bathymetric LIDAR sensors perform poorly. In this depth regime, near infrared (NIR) reflectance depends primarily on water depth (water absorption) and bottom type, with suspended constituents playing a secondary role. Our processing framework exploits two optimal regions where a simple model depending on bottom type and water depth can be applied in the very shallow limit. These two optimal spectral regions are at a local maximum in the near infra-red reflectance near 810 nm, corresponding to a local minimum in absorption, and a maximum in the first derivative of the reflectance near 720 nm. These two regions correspond to peaks in spectral correlation with bathymetry at these depths., Published in Marine Geodesy, v33 p53-75, 2010. Prepared in cooperation with NOAA NGS, Silver Spring, MD; Marine Information Resources Corp, Ellicott City, MD; and others.

Hyperion is a hyperspectral sensor on board NASA's EO-1 satellite with a spatial resolution of approximately 30 m and a swath width of about 7km. It was originally designed for land applications, but its unique spectral configuration and high spatial resolution make it attractive for studying complex coastal ecosystems, which require such a sensor for accurate retrieval of environmental properties. In this paper, Hyperion data over an area of the Florida Keys is used to develop and test algorithms for atmospheric correction and for retrieval of subsurface properties. Remote-sensing reflectance derived from Hyperion data is compared with those from in situ measurements. Furthermore, water's absorption coefficients and bathymetry derived from Hyperion imagery are compared with sample measurements and LIDAR survey, respectively. For a depth range of approx. 1-25 m, the Hyperion bathymetry match LIDAR data very well; while the absorption coefficients differ by approx. 16.5% on average. More importantly, in this top-to-bottom processing of Hyperion imagery, there is no use of any a priori or ground truth information. The results demonstrate the usefulness of such spaceborne hyperspectral data and the techniques developed for effective and repetitive observation of complex coastal regions., Published in Applied Remote Sensing, v1 p011502-1 through 011502-16, 26 Dec 2007. Prepared in cooperation with NOAA/NESDIS/NCDDC, Stennis Space Center, MS, and with NAVOCEANO, Stennis Space Center, MS. Prepared in collaboration with Planning Systems, Inc., Stennis Space Center, MS; and Oregon State University, Corvallis, OR. The original document contains color images. All DTIC reproductions will be in black and white.

MERIS imageries over coastal waters around the United States were ordered from ESA. These data either reveal enormous phytoplankton blooms (chlorophyll concentrations in the range of 100 - 1000 mg/m) or turbid river plume waters or optically shallow environments. We used in situ measurements to validate remote-sensing reflectance derived from MERIS. Further, we applied algorithms designed for optically deep or optically shallow waters, respectively, to derive water and/or bottom properties of the study area. The derived results were found consistent with in situ measurements or known values. Discussions were also provided regarding remaining issues related to MERIS data. These exercises and results demonstrate the great potentials and capabilities of using MERIS data to monitor water environments in coastal regions., The original document contains color images. All DTIC reproductions will be in black and white.

The Naval Research Laboratory Ocean Optics Section (Code 7333) at the Stennis Space Center, Mississippi (NRL/SSC), participated in the RASP-04 field experiment in Mamala Bay, Hawaii, from 10 August to 5 September 2004. Physical and optical measurements (temperature, salinity, depth, absorption, and attenuation coefficients) were collected at seven stations, on each of fourteen sampling days. Following stringent calibration and processing procedures, reduced data were compiled and provided to Naval Air Warfare Center (NAWC) personnel in near real time, to facilitate analyses, interpretation, and mission planning. Following the experiment, more extensive quality control and data processing were completed back at NRL/SSC, and final results and plots are presented here (all data and plots are provided on an accompanying CD), The extremely clear-water environment of Hawaii presented challenges, as absorption values were close to instrument detection limits. Nevertheless, the data were carefully quality-checked and a high-quality data set was collected., The original document contains color images.

There are two imagers on NASA's EO-1 satellite: Hyperion and Advanced Land Imager (ALI). Hyperion is a hyperspectral sensor with about 45 bands covering the spectral range of 430-900 nm, while ALI has only six (wide width) bands for the same range. Past studies have shown that data from both kinds of sensors can provide observations of important environmental properties, such as bathymetry and water turbidity. However, in the derivation of bathymetry using data from multi-band sensors (e.g., LANDSAT), usually bathymetry data at a few locations are required to be known first. Recently, a semi-analytical spectral optimization algorithm has been developed for remote-sensing of shallow-water environments. Using data from hyperspectral airborne and space-borne sensors, it has been demonstrated that bathymetry of optically shallow waters can be derived without a priori knowledge of depths at a few locations, and properties of water column and bottom can be retrieved simultaneously from remotely sensed data. In this study, the authors extend the optimization approach to ALI data with retrieved water and bottom properties compared with that from Hyperion data. From these results, they discuss the advantages/disadvantages of Hyperion and ALI sensors, and their potential applications for coastal observations., Presented at the International Conference on Remote Sensing for Marine and Coastal Environments (8th) held in Halifax, Nova Scotia (Canada), on 17-19 May 2005. The original document contains color images.

This study examines the problem of uniqueness in the relationship between the remote-sensing reflectance (Rrs) and the inherent optical properties (IOPs) of ocean water. The results show that diffuse reflectance of plane irradiance from ocean water is inherently ambiguous. Furthermore, in the 400 < lambda < 750 nanometer 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 (CDOM). The absorption coefficients have overlapping exponential responses that 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 one identify the regions of the Rrs spectrum where one 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, alpha(sub 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 alpha(sub ph)(lambda). (10 figures, 13 refs.)

River and estuarine outflow waters contain high loads of colored dissolved organic material (CDOM or gelbstoff), sediments, and biological matter with strong optical signatures. In regions with large, single point sources, interactions with ambient shelf waters are fairly simple. The buoyant outflow plumes tend to remain cohesive and become trapped against the contra solem coast. These plumes can extend for distances of more than 100 km along coast with characteristic widths of 5-15 km (internal Rossby radius of deformation) and thickness of a few 10's of meters. When winds turn to upwelling favorable, the plume waters are rapidly dispersed, mixing their optically important constituents across the shelf. Wind relaxation or a turn to downwelling favorable wind initiates a new along-coast plume. Such strong dynamic/optical interactions drive high variability in coastal optical character. The objective of this study is to examine this high dynamic variability in relationship to seasonal variations in forcing and constituent loading fields.