David K. Costello

Aggregation of diatom bloom in a mesocosm: Bulk and individual particle optical measurements

Optical measurements were acquired during a controlled, diatom-dominated, phytoplankton bloom and aggregation event engineered in a 1200 liter laboratory mesocosm. Observations included beam attenuation (c) at 660 nm and particle absorption spectra for phytoplankton and detritus. Despite intense bloom conditions in the mesocosm (chlorophyll a concentrations exceeding 165 mg/l and c exceeding 9 m-1), most optical parameters covaried linearly with biochemical parameters. There were significant positive correlations for dry mass versus the particle attenuation coefficient (cp) at 660 nm, particulate organic carbon versus the computed particle scattering coefficient (bp) at 660 nm, and chlorophyll a versus the measured particulate absorption coefficient (ap) at 660 nm, and chlorophyll a versus the measured absorption coefficient for phytoplankton (a.) at 673 run. Multiple-component model simulations of optical and biochemical measurements accurately predicted particulate organic carbon (POC), particulate organic nitrogen (PON), and chlorophyll a concentrations using cp and ap measurements. Similar equations for cp and ap estimates using the biochemical measurements are also presented. New commercially available instruments to measure c(λ) and a(λ) should make remote PON, POC, and Chl a estimates practical upon measurements of site-specific relationships similar to those presented here.

Ocean-science mission needs: real-time AUV data for command, control, and model inputs [West Florida Shelf]

Predictive models for tides, hydrodynamics, and bio-optical properties affecting the visibility and buoyancy of coastal waters are needed to evaluate the safety of personnel and equipment engaged in maritime operations under potentially hazardous conditions. Predicted currents can be markedly different for two-layer systems affected by terrestrial runoff than for well-mixed conditions because the layering decouples the surface and bottom Ekman layers and rectifies the current response to oscillatory upwelling- and downwelling-favorable winds. Standard ocean models (e.g. Princeton Ocean Model) require initial and boundary data on the physical and optical properties of the multilayered water column to provide accurate simulations of heat budgets and circulation. Two observational systems are designed to measure vertically structured conditions on the West Florida Shelf (WFS): a tethered buoy network and an autonomous underwater vehicle (AUV). The AUV is described with a focus on the observational systems that challenge or limit the communications command and control network for various types of measurement programs. These include vertical oscillatory missions on shelf transects to observe the optical and hydrographic properties of the water column, and bottom-following missions for measuring the bottom albedo. Models of light propagation, absorption, and conversion to heat as well as determination of the buoyancy terms for physical models require these measurements.

Development of the marine-aggregated-particle profiling and enumerating rover

The in situ imaging of marine particles shares many of the signal-to-noise difficulties of underwater imaging in general. Natural and traditional artificial illumination, for example, allow light scattered from particles outside the imaging volume, reducing the image contrast. Sizing and classification of small-particle images (magnification approaching 1 or more) have additional difficulties associated with a limited depth-of-field and the resulting noise from illuminated but unfocused targets in the field of view. Moreover, target sizing and classification are uncertain without individual target range information. The new marine particle imaging instrument to be discussed employs diode laser illumination (675 nm) with line-generator optics to produce a thin light sheet at the system focal plane. This light sheet and narrow-band, optical filters are utilized to minimize noise associated with diffuse ambient illumination since significant red ambient illumination is lost below 5 m depth. It also removes the uncertainty involved in the determination of the three-dimensional position and size of a target in a two-dimensional image. An additional problem inherent in marine particle research is that the size of the particles of interest ranges over several orders of magnitude (micrometers to centimeters diameter). The instrument addresses this problem of scale with coincident video imaging systems of high and low spatial resolution. Shape-generated feature vectors and particle optical attributes are extracted from digitized particle images and utilized in an automatic particle classification scheme. The strategy is multidimensional and incorporates a pattern recognition algorithm rooted in the theory of moment invariants.

Scattering phase function of very large particles in the ocean

Scattering properties of large particles are mostly unknown, either in theory or measurement, primarily due to the significant variations of large particle characteristics in the natural environment and the inability to sample non- invasively. The Marine-Aggregated, Profiling and Enumerating Rover, measures scattering angles in the vicinity of 50, 90 and 130 degrees caused by very large particles ranging from 280 micrometers and up. Measurements were made during SIGMA cruise, April 13-21, 1994 in East Sound, Washington, using structured light sheet formed by 4 diode lasers of 660nm wavelength. The results fit the analytic phase function used by Beardsley and Zaneveld, and indicate a significant elevation of back-scattering efficiency throughout the water column for all downcasts during our multi-day experiments. Some of this increase in efficiency can be explained by multiple scattering, using Monte Carlo simulation, assuming independent scattering. Measured in-situ particle size distributions, in conjunction with Mie theory, demonstrate that large particles are significant scatterers in the ocean and contribute up to 20 percent of total scattering. These measurements support previous theories that large, marine- snow types of particles enhance back scattering efficiency and, when present, contribute significantly to remote sensing signals.

Algorithms for path radiance and attenuation to provide color-corrections for underwater imagery, characterize optical properties and determine bottom albedo

There is growing interest in the development and utilization of optical instrumentation to measure water properties of coastal waters for ground-truthing satellite data. Current methods for determining above-water remote-sensing reflectance assume vertical homogeneity in the water column. In cases where in-water vertical structure and bottom reflectance confound standard algorithms, new methods must be developed to incorporate inhomogeneities. This paper addresses the available avenues for characterizing optical properties, color-correcting underwater imagery and determining bottom albedo values. The method begins by deriving backscatter from remote-sensing reflectance data collected near the red end of the visible spectrum near the surface where bottom reflectance is negligible and path radiance is maximal. Measured upwelling radiance is divided by measured downwelling irradiance yielding underwater remote sensing reflectance values. The backscattering coefficient is then modeled for each wavelength and the path radiance calculated and removed using measured attenuation coefficients. The above values are used to reduce the algorithm to an equation for bottom albedo by removing the bias associated with path radiance and the filter effects associated with the water path to and from the bottom. The calculated bottom reflectance is needed to interpret and correct above-water remote-sensing reflectance and satellite imagery. The results are illustrated using comparisons of color-corrected and non-color-corrected in-situ imagery of specific corals and their immediate surroundings. Imagery of a coral scene at various altitudes is also presented to illustrate spectral changes due to changes in thickness of the water column between the camera and the bottom.

New Instrumentation and Platforms for Subsurface Optical Measurements

The underwater light field is affected by the geometry of the incident radiance, the sea-surface state, the inherent optical properties of the water-column constituents, the distribution of these constituents, and, in shallow areas, the bottom albedo. New instrumentation and platforms designed to assist in the quantification of the above are described. The new instrumentation includes the Marine Aggregated Particle Profiling and Enumerating Rover (MAPPER), the next-generation MAPPER II system, and the Bottom Classification and Albedo Package (BCAP). the new platforms include a custom manufactured remotely operated vehicle (ROV) designed to deploy the MAPPER II module, the BCAP module, and a vertical-profiling instrument suite, and an autonomous underwater vehicle (AUV) designed for optical measurements in coastal waters. These include the deployment of the BCAP module on long- range, bottom-mapping missions.

Some effects of the sensitivity threshold and spatial resolution of a particle imaging system on the shape of the measured particle size distribution

Particle volume spectra are often inferred from optically measured particle areal size distributions after the areal size distributions have been transformed into equivalent spherical diameter (ESD) distributions. Resolution and sensitivity differences between imaging systems result in different shapes for the measured particle size distribution. Additionally, the sensitivity threshold of the imaging system is not only fundamental to the determination of the particle edge but also determines the optical density level below which material will not be imaged. All this affects the measured size of a particle. This contribution utilizes laboratory data and unique, synchronous, ocean field data collected by three coincident imaging systems to evaluate these effects in the study of large marine particles. An algorithm rooted in the theory of moment invariants is presented which avoids the distortions to the particle size distributions when the size of non-spherical and/or porous particles are presented as ESD.

Optical inspection of ports and harbors: laser-line sensor model applications in 2 and 3 dimensions

There are 361 ports of interest to the US Coast Guard regarding homeland security issues. Speed and accuracy of inspections there for “foreign objects” is critical to maintaining the flow of commerce through these ports. A fusion of acoustic and optical imaging technologies has been implemented to rapidly locate anomalies acoustically and inspect them optically. Results of field tests are presented. Effective deployment of AUV- or ROV-mounted optical sensors to inspect ship hulls and port facilities will depend on accurate, real-time prediction of the sub-surface optical environment and upon accurate sensor models parameterized for the time and place of inspection. For bi-static laser-line scanner sensors such as the Real-time Ocean Bottom Optical Topographer (ROBOT), ambient light decreases the range to the inspection object (e.g. hull) for which laser-line contrast is adequate for ranging and imaging in 3-D. Reduced range implies narrower swaths and longer inspection times. A 2-D and 3-D hybrid marine optical model (HyMOM) of the environment beneath ships or adjacent to sea walls and pilings has been developed, applied and validated in eutrophic and mesotrophic settings, and a Monte Carlo sensor model of ROBOT has been developed. Both are discussed and combined to evaluate sensor performance in different environments. To provide the inherent optical properties needed to run such models, data from the Autonomous Marine Optical System (AMOS) were collected and transmitted back to the laboratory. Examples of AMOS results and model outputs are presented.

Multispectral imagery, hyperspectral radiometry, and unmanned underwater vehicles: tools for the assessment of natural resources in coastal waters

In many coastal oceans of the world, the flora and fauna are under stress. In some areas, seagrasses, coral reefs, fish stocks, and marine mammals are disappearing at a rate great enough to capture the attention of, and in some cases, provoke action by local, national, and international governing bodies. The governmental concern and consequent action is most generally rooted in the economic consequences of the collapse of coastal ecosystems. In the United States, for example, some experts believe that the rapid decline of coral reef communities within coastal waters is irreversible. If correct, the economic impact on the local fisheries and tourism industries would be significant. Most scientists and government policy makers agree that remedial action is in order. The ability to make effective management decisions is hampered, however, by the convolution of the potential causes of the decline and by the lack of historical or even contemporary data quantifying the standing stock of the natural resource of concern. Without resource assessment, neither policy decisions intended to respond to ecological crises nor those intended to provide long-term management of coastal resources can be prudently made. This contribution presents a methodology designed to assess the standing stock of immobile coastal resources (eg. seagrasses and corals) at high spatial resolution utilizing a suite of optical instrumentation operating from unmanned underwater vehicles (UUVs) which exploits the multi-spectral albedo and fluorescence signatures of the flora and fauna.

Nanosurfaces for nanosensing

Nanoscale electric field confinement and enhancement is a well known phenomenon for small particles and flat interfaces. Senspex is using E-Beam lithography to develop nanosensors for the detection of biological and chemical hazards. The sensors that are being developed are a square array of metallic cubes; each cube has dimensions of approximately 100nm x 100nm x 30nm and a pitch of 125nm in the x- and y-directions. Senspexs numerical simulations show that the intense electric field in the minute volume between the cubes will lead to a high probability of detection for small concentrations of analyte in real world situations.