A design concept has been developed for a holographic instrument to measure scattering and beam transmission properties of ocean waters. The holographic concept not only uniquely supports the measurement technique but allows for a possible compact expendable design. This holographic design measures the medium modulation transfer function (MTF) at specific spatial frequencies and uses these data to approximate the complete MTF with a spline blending technique. A sinusoidal bar pattern is imaged by diffraction optics as a two dimensional pattern through the water medium and tank faces onto a linear detector array and recorded as contrast loss. A Fourier-Bessel transform technique was used to retrieve the small angle scattering function in the angular region from 0.005 degree(s) to 0.5 degree(s). Monte Carlo simulations of the instrument with sample path lengths of 25 and 100 cm and Tongue of the Ocean water types are used to demonstrate performance. The instrument design hologram was constructed for an initial set of laboratory particle seeding experiments. Results were found to be consistent with those generated from model simulations using Mie calculated scattering functions for sample particle size distributions.

A unique underwater optical instrument is described that measures the volume scattering function (VSF) in the retro (180 degree(s)) direction, i.e., (beta) ((pi) ). The instrument, referred to as Beta Pi, was designed and built at SRI International and was recently deployed in Monterey Bay. Spectral measurements of direct backscatter are achieved by imaging the backward scattered light from a laser beam with a charged-coupled device (CCD) camera. A large beam splitter, approximately 23 cm in diameter, is used to obtain the necessary monostatic geometry for imaging light scattered from the beam in the retro direction. With a 200 mm focal length, f/2 lens, measurements of volume scattering over the angular range from exactly 180 degree(s) to about 179 degree(s) are achieved. The angular resolution of the CCD/lens system is 0.0057 degree(s). The resolution of the scattering measurements, however, is determined by the divergence half-angle of the beam, which is about 0.02 degree(s). A fiber optic cable transmits the laser flux from the surface to a collimator in the underwater housing, so that almost any laser with a fiber optic coupler can be used as the source. An in-water calibration scheme is described and it is shown that the accuracy of the measured VSF at 180 degree(s) is only slightly less than the accuracy of the measured spectral beam attenuation coefficient. A measurement of the VSF from 179 degree(s) to 180 degree(s), made in shallow waters in Monterey Bay using a Nd:YAG (532 nm) laser, is shown.

The spectral variations of the efficiency factors for absorption, total scattering and backscattering have been computed via Mie theory using a three-layered sphere model, with the size distribution function and the spectral values of the refractive index of each layer as input parameters. When compared with the results of a model for homogeneous spherical cells (with an equivalent bulk refractive index), these theoretical predictions allow the modifications of the efficiency factors due to heterogeneities within algal cells to be assessed. Such a comparison has been performed for a coccolithophorid suspension (Emiliania huxleyi), for which the spectral values of the refractive index have been derived from the experimental absorption and scattering coefficients. While the internal structures induce insignificant modifications in absorption and only weak modifications in total scattering, they appear to be able to increase the backscattering efficiency by a factor as high as 50, depending mainly on the calcite shell thickness. The internal structures also induce spectral changes in backscattering.

Bubbles in water or ice are examples of scatterers where the refractive index of the scatterer is less than the surrounding media. For most situations of interest, the size of the bubble is much greater than a wavelength so that many prominent features of the scattering may be identified by the application of ray methods. Such features include: caustics (associated with backward and forward glory scattering and their unfoldings for spheroidal bubbles), critical angle scattering (which may be observed in sunlit bubble clouds in sea water), and Brewster angle scattering (where the reflection of parallel polarized light is quenched). The scattering amplitude near singular features such as caustics and critical angle scattering require physical-optics corrections or, in the case of the critical angle, a detailed asymptotic analysis. Various ones of these features and polarization properties have been observed with laser illumination of freely rising spherical or spheroidal bubbles in water. Modulation of the extinction cross section and modulation of the critical angle scattering were used to study the dynamics of bubbles in laboratory experiments.

Numerical results are presented to show the interactive electromagnetic scattering from two air bubbles in water. The results are derived using the translational addition theorem originally employed by W. Trinks to solve the two sphere scattering problem, as well as a recursive definition of the translational addition theorem coefficients developed by J. H. Bruning and Y. T. Lo who also summarize simplifications to the theorem developed by later researchers. The computer program calculates the forward scattering extinction coefficients and the elements of the Mueller transformation matrix. Besides extinction calculations, side scattering resonance predictions are made. The interactive resonance phenomena for the two spherical scatterers show an approach to modeling the transition between single scatterer to bulk scatterer behavior.

Laboratory measurements of light scattering on the axenic cultures of unicellular alga Chlorella vulgaris monoculture confirm the thesis of multi-level light scattering by the cell i.e., both by outer cell membrane and the internal structure of the cell, as well as by its molecular structures. In the measurements, the technique of dynamic light scattering and analysis by the regulation method was used, indicate that the light scattering phenomenon is affected by particles of sizes corresponding either to overall dimensions of the cell or to the dimensions of its internal structures. A correlation was found between the suggested sizes and the stage of physiological evolution of the culture. The measurements of 10 functions constituting the elements of the scattering matrix for an alive Chlorella vulgaris culture and cultures with internal cell structures modified by chemical and mechanical agents evidence that the internal structures of cells play an important role in the interaction of phytoplankton and light.

Comparisons are made between a refined model using coupled-dipole theory and the first Born approximation for light scattering from helices. The use of the first Born approximation to model polarized light scattering from a thin wire helix is further developed in order to include all sixteen Mueller scattering matrix elements. (The Mueller matrix fully describes how a structure alters the polarization state of light upon scattering). Comparisons of predicted Mueller matrices between the two theories show that, in some cases, good agreement is obtained. The predicted Mueller matrix for an ensemble of randomly oriented helices using the first Born approximation is calculated. The models based on the first Born approximation and on coupled-dipole theory were also compared to data taken from octopus sperm. We conclude that the first Born approximation may be useful for predicting some elements such as S₁₄ (the matrix element that describes the depolarization of incident circularly polarized light), but for other elements the coupled-dipole theory is better suited.

Heterotrophic bacteria may play a significant role in the scattering of light in the ocean. The scattering properties of these microbes are very sensitive to cell size, which is difficult to measure in the submicron size range by common electronic and microscopic techniques. Assessment of bacterial contribution to light scattering is further complicated by the fact that the size of the cells may change under differing conditions of growth. We examined the size of bacterial cells that were either fast-growing or starving by application of the dynamic light scattering (DLS) method. Laboratory cultures of mixed populations of bacteria from oceanic waters off Southern California were measured. In the DLS method, the autocorrelation function of the time-dependent intensity of light scattered by small suspended particles is a measure of Brownian motion which, via the diffusion coefficient, provides information about the particle size distribution. The scattered intensity weighted sizes of formalin-preserved bacteria obtained from DLS were generally consistent with average cell sizes determined by epifluorescence microscopy. This consistency was supported by simulation of the intensity weighted size distribution by means of Mie scattering calculations for microscopically determined size distribution. In addition, the microscopic analysis showed that while the equivalent spherical diameter of fast-growing bacteria was on average 0.85 micrometers , the diameter of starved cells was 40 to 50% less. The starved cells were thus quite similar in size to bacteria found in the nutrient-poor open ocean environments. The cultures of starved bacteria contained small numbers of yeast cells (2 - 4 micrometers in size), and the sensitivity of the DLS analysis to such relatively large scatterers was evident. Our study indicates that the dynamic light scattering, a fast and noninvasive technique, offers new perspectives to study bacteria and other oceanic microparticles.

We describe the use of the optical trapping technique to the study of micron-sized particles and cell samples, from which scattering, particle size, and optical parametric data can be derived. Its application to the study of phytoplanktonic cells and other biogenic particles is also presented. In comparison to conventional flow cytometric or volume scattering measurement systems, an optical trap utilizes the radiation forces, derived from a highly focused laser beam, to confine the particle under study to an optical potential well. The optical trap, therefore, functions simultaneously as both a non-contact micromanipulator and microforce transducer. In addition, forward angle light scattering measurements can be made while the cell sample is held by the focused laser beam. Forward light scattering measurements and calculations for optically trapped spherical test particles and mammalian cells, under low power (< 10 mW), are presented for the cases when the laser beam spot size (omega) _o is approximately r, (lambda) /2n < (omega) _o < r, and (omega) _o approximately (lambda) /2n, respectively, where r is the cell radius and n is the refractive index of the surrounding water medium. Scattering data over the range from approximately 0 degree(s) to 45 degree(s) is shown to be a sensitive function of beam radius, particle size, and relative refractive index. The optical trapping technique should prove to be a powerful tool in the study of the optical properties of marine cells and organisms, and their dependence on external optical stimuli.

Knowledge of the marine particle volume concentration is critical to many oceanographic research efforts. A description of particle volume concentration is most often estimated by assuming particle volumes based on a particle size distribution. This requires the enumeration (ideally, in situ) of a statistically significant number of particles across the size spectrum. This becomes increasingly difficult as one approaches the large-particle end of the size distribution because of the low concentrations of large particles found in most waters. However, even though number concentrations are generally low, the volume flux of large particles and their effect on the underwater light field may be significant. The Marine Aggregated Particle Profiling and Enumerating Rover (MAPPER) is an instrument under development to help address the difficulties associated with the enumeration and analysis of large marine particles. MAPPER will utilize visible diode lasers (670 nm) to produce a structured-light sheet (SLS) coincident with the image planes of video imaging systems of various resolutions. This contribution focuses on the development of the diode laser SLS, on the sheet/system characterization required to make possible the retrieval of quantitative, individual-particle information, and on the unique information offered by imaging in an SLS as opposed to other structured-light volumes. The deviation of the implemented sheet from the `ideal' sheet is presented as are the first field data acquired by deploying the SLS module on a remotely operated vehicle testbed.

Knowledge of the spatial and temporal variability of the optical properties of a particular water mass has important applications in biological and physical oceanography. As a step towards acquiring the capability to measure the variation in inherent water properties in three dimensions, an underwater optical imaging technique based on the volumetric reconstruction of serially acquired image planes was used to experimentally determine the spatial microstructure of phytoplankton distributions. Volume fluorescence, (beta) (phi) (90 degree(s), 450 nm, 685 nm), and scattering, (beta) (90 degree(s), 450 nm), images were acquired and processed for three-dimensional distribution analysis. In support of the experimental imaging equipment design and to verify applicability of the technique over a wide range of oceanic parameters, computer modeling of this serial sectioning technique was accomplished. Image plane intensity calculations implemented in the model accounted for wavelength specific differential variations in attenuation over the light propagation paths. Modeling and experimental results indicate that the underwater optical serial sectioning technique is practical for in-situ determination of cubic meter volume fluorescence and scattering functions of phytoplankton distributions with chlorophyll (alpha) concentrations as low as 0.1 mg Chl (alpha) /m³.

The crucial parameters required for the design of underwater optical systems are optical absorption and scattering as a function of location, depth, and wavelength in the ocean. DREV has developed, built, and deployed an underwater probe (NEARSCAT), whose sole purpose is to gather information about the underwater light field in the waters of interest to Canada. The instrument is unique in that it can scan all wavebands in the visible spectrum from 400 nm to 700 nm. It can also continuously sample up to 6 arbitrarily chosen wavelength bands simultaneously with a resolution of 10 nm. The instrument can separate the absorption and scattering components of seawater. This instrument was deployed at 16 locations along the East Coast of Canada, ranging from the north of Baffin Island to Cabot Strait. It was also deployed at 21 stations on the West Coast of Canada. The water column was sampled to a maximum depth of 300 m. The data was found to be extremely consistent and of high quality. We found that the waters were much less absorbing than was previously believed. A strong scattering layer was found to exist near the surface, and extending to a depth of 40 meters. This layer does not strongly absorb. The lack of absorption, the strong layering of scattering, and the predominance of narrow-angle forward scattering has important consequences for optical underwater systems as it implies that signal recovery techniques will be effective in the underwater environment and allow much better performance than was previously thought to be possible.

Preliminary results are reported for estimating the spatial profile of bioluminescence in seawater from in situ measurements of the downward and upward irradiance and scalar irradiance. The explicit estimation method is based on the two stream approximation to radiative transfer and enables an estimation of the bioluminescence with two fitted parameters that require a previous estimation of the angular shape of the volume scattering function. The implicit estimation method is an iterative approach that utilizes the conjugate gradient method. Both methods enable one to estimate the bioluminescence when the absorption coefficient is not known. A comparison of numerical results from the two methods is given.

Water Raman scattering is influenced by the optical factors external to the clear marine hydrosol or bounding it (the air/water interface). At shorter wavelengths (< 490 nm) detectable water Raman scattering is confined to the near surface layers, where an increase in solar zenith angle increases the water Raman emission. Among the effects of water Raman scattering is an increase in the irradiance ratio (reflectance) of the surface layers. Skylight tends to lessen the production of water Raman scattering by a few percent at shorter wavelengths. At longer wavelengths (> 500 nm) the surface effects disappear as hydrosol absorption becomes the dominant factor. However, at depth large solar zenith angles cause `shoaling' of Raman production, i.e., water Raman scattering effects occur closer to the surface layers than is the case for smaller zenith angles. The water leaving irradiance, significantly affected by Raman emission in clear ocean waters, changes little or not at all with solar zenith angle.

Interest in making use of the existence of Fraunhofer lines to reduce solar background noise for the Satellite Laser Communications (SLC) program prompted the requirement for making underwater in situ characterizations of five Fraunhofer lines in the blue-green spectrum. Recent papers which discuss and attempt to explain frequent occurrences of high measured values for underwater irradiance raised concerns about the persistence of Fraunhofer lines. The effect of an increased light field could significantly reduce (potentially eliminate) the absorption depth of Fraunhofer lines and reduce their solar rejection benefits to optical communications. These characterizations were made from a surface ship off of the coast of Hawaii in August 1989. Fraunhofer lines at 420, 440, 486, 518, and 532 nm were characterized at the surface and at four discrete depths to a maximum of 90 m. These are the first known characterizations of Fraunhofer lines underwater. A high resolution scan from 450 to 550 nm was also made at a depth of 73 m. The results from this experiment showed no differences between the surface and underwater scans, suggesting the effects of inter- wavelength scattering is less than originally proposed.

It is demonstrated that Fraunhofer lines in the solar spectrum will be filled in by inelastic scattering in the ocean. The relative depth of a Fraunhofer line, (eta) , defined as the ratio of the irradiance at the center of the Fraunhofer line to the background continuum, can then be used to measure the amount of inelastic scattering in the light field, i.e., by measuring (eta) , the relative contributions of elastic and inelastic processes to the light field can be deduced. An oceanographic instrument was developed to measure in-situ inelastic scattering in the ocean. It utilizes a 1 m monochrometer, a CCD camera, two irradiance collectors with fiber optic light guide. Results of preliminary field measurements are presented and discussed.

The measurement of light absorption by photosynthetic microalgae is of concern to algal physiologists and plankton ecologists. Interest in this topic by algal physiologists originated with the measurement of quantum efficiency. Recently, plankton ecologists have also felt the need for accurate measurements of phytoplankton quantum efficiency within the submarine light field. In addition, the need for absorption measurements is pivotal to the development of algorithms for global remote sensing. The pioneering research in algal light absorption was done by physiologists such as Shibata and Duysens continued by Latimer and Butler. Their techniques were applied to natural phytoplankton populations by Kiefer and Yentsch. In the course of these developments we may have overlooked the essential problems of absorption measurements. The papers of Shibata and Duysens make the point that spectral definition concerns the ratio of absorption to scattering. The instrumental constraints associated with the measurement technique changes that ratio. It is unclear how much scattering is associated with the phytoplankton as opposed to the optical configuration. Perhaps our present methods are not realistic for optically characterizing natural waters. In this paper we compare spectral absorption measured in a configuration where absorption markedly dominates scattering to situations where scattering is a major component of attenuation. We have placed these extremes in the context of optical closure of light attenuation in natural waters.

In situ absorption data collected with a reflective-tube absorption meter are presented. Various procedures for correcting the data for scattering error and for extracting chlorophyll absorption from the raw signal are explored. Based on our knowledge of the distribution of particle types and on measured backscattering, the scattering correction as a function of total scattering is found to vary significantly with depth. However, absorption in the near infrared is shown to be highly correlated with backscattering. We thus postulate that this signal is mainly due to the scattering error and possibly to absorption by dissolved substances and particles of a detrital nature. Thus, the infrared signal seems to provide a good correction for the measured a(676) to obtain chloropigment absorption. Indeed, a(676) - a(750) (corrected for water absorption and 750 temperature dependence) was found to correlate strongly with fluorescence. However, a(750) was found to be highly temperature dependent, so a(712) was chosen for this purpose in future measurements. An examination of optical microstructure in East Sound, Orcas Island, Washington showed numerous peaks with vertical dimensions of the order of tens of centimeters. These peaks may contain the majority of the biomass in the system. The relative magnitude of the a(676) - a(712) and the a(712) signals varied greatly from one peak to another and systematically with depth, presumably reflecting the nature and physiological states of the populations in the various peaks.

Bacteria, when packed in high cellular concentrations, are able to affect the spectral absorption efficiency of detrital matter. Fluorescence analysis indicated that bacteria can be recognized by their emission properties, when settled on natural organic particulates, such as cellulose or chitin. Similar properties were observed on natural detrital particulates, where their spectral absorption and fluorescence emission appear to be determined by their concentration of residual photosynthetic pigments and bacterial content.

The spectral fluorescence efficiency function ((eta) ((lambda) _x,(lambda) _m) equals quanta fluoresced per nm interval of (lambda) _m per quanta absorbed at (lambda) _x, (lambda) _x equals excitation wavelength, (lambda) _m equals emission wavelength) has been determined for several different fulvic and humic acid samples, and the 3-dimensional surfaces have been described mathematically. These data are used along with a published two-flow irradiance model to calculate the effect of solar-stimulated fluorescence due to colored dissolved organic matter (CDOM; also gelbstoff) on irradiance reflectance just below the sea surface along a transect taken on the West Florida Shelf. In addition, a strategy is suggested for using (eta) ((lambda) _x,(lambda) _m) and mass-specific absorption coefficient measurements of CDOM to determine CDOM concentrations from remotely sensed fluorescence measurements.

A technique that allows for the preservation of spectral fluorescence properties of phytoplankton cells is presented. Laboratory cultures and field samples were concentrated and embedded within gelatin to preserve the spectral fluorescence properties of phytoplankton cells. Fluorescence excitation spectra (Ex: 400 - 650 nm, Em: 683 nm) obtained from samples prepared according to this method were compared to the spectra obtained from traditional cell suspensions, and by microphotometry. The spectra produced by samples prepared following this method remain spectrally intact if stored at -70 degree(s)C, and allowed to return to room temperature prior to measurement.

Examples of the diel variability in chlorophyll are presented from data from moored in situ fluorometers and from profiles of beam attenuation coefficient plotted against fluorescence. The data are discussed in terms of the three primary processes thought to influence the diel variability: (1) fluorescence yield per unit chlorophyll a. (2) chlorophyll changes per cell (or, biomass), and (3) changes in phytoplankton biomass. A provisional model is presented which incorporates these three processes, and its shortcomings are discussed. Finally, the problem of incorporating diel variability in plankton models is considered. For the model given, it is found that there is no consistent set of parameters which describe the observed diel chlorophyll variability for pre-bloom and bloom conditions in the Northeast Atlantic (spring 1989).

Numerous empirical data from nine large Polish-Russian research expeditions and other smaller expeditions to various regions of the World Ocean during 1978 - 1991 were used to compile this first approximate model of statistical relationships, chiefly between the concentration of chlorophyll a and the solar irradiance just below the sea surface on the one hand, and the vertical distribution of chlorophyll a, phytoplankton absorption spectra, downward irradiance attenuation spectra, the quantum yield of photosynthesis, as well as other mean diurnal characteristics of primary production in waters of different trophicity on the other. These model relationships served to work out an algorithm for computing the vertical distributions of light energy and primary production characteristics in particular types of sea water from data on chlorophyll a concentration and irradiance at the sea surface. Verification of these model formulas with the aid of empirical data from a variety of sources has shown that they provide good results -- the mean statistical errors with respect to in situ measurements range from ca 10% to 80%, depending on the characteristic in question. In order to improve the accuracy of this algorithm, a much larger number of statistical data is needed, and closer attention must be paid to the effect of nutrients and other environmental factors on the characteristics being assessed. This algorithm could be especially useful in the remote sensing of primary production in the ocean.

The JHU/APL Optical Profiler System (OPS), consisting of a MER1048 spectral radiometer, a beam transmissometer, a backscatterometer, and temperature and conductivity sensors, has been deployed across the Gulf of Alaska, in the Sargasso Sea, in the Bahamas, and in the Caribbean Sea near St. Croix. The data provide profiles of the diffuse attenuation coefficient, K_d, the irradiance reflectance coefficient, R_E, the radiance reflectance coefficient, R_L, the beam attenuation coefficient, c, light scattered nearly directly backward, (beta) (170 degree(s)), near 488 nm, temperature and BV frequency. The data exhibit salient changes in the optical profiles among the locations, and the relationship between stratification and optical properties also varies significantly. The optical parameters are clearly related to one another, and these data are used to evaluate the accuracy of various empirical relationships, such as those of Gordon-Morel and Morel, in explaining these correlations. We also examine new relationships based solely on these data.

As part of an effort to permit a computation of the diffuse attenuation coefficient, k, as a function of depth, given a satellite derived surface k value at 490 nm, a method which involves the spectral eigenanalysis of specific datasets was formulated. The method consists of breaking the k_d and k_u spectral datasets for a specific ocean region/season into single wavelength data matrices for each station. Then, an eigenanalysis is performed on each of these individual data matrices. Using the resulting eigenvectors and scalar multiples for each data matrix, the original k profiles may be reconstructed. Moreover, by parameterizing the scalar multiples of the eigenvectors for each station in terms of the satellite surface k values, an associated k profile may be computed for a given surface k value.

The light attenuation coefficient c()) is a key parameter which gives information about basic optical properties of marine environment. However, quick and frequent measurement of full light attenuation spectra is not always possible. Usually good correlation between the light attenuation coefficients of different parts of spectra makes possible to derive a full attenuation spectra based on its two or three values, typically in blue, green and red range. The current presentation will describe one of such a method based on analysis of covariance matrix of the data set. The matrix consists of [c(,2), c(,)] elements, and is build upon a sufficient amount of field measurements in certain area. As it is known, set of characteristic values of that matrix makes possible to estimate in optimal way any realization of analyzed random function. Any value of c() may be expressed as a sum of its mean value and linear combination of certain coefficients and characteristic vectors of covariance matrix. The method was tested on light attenuation data sets taken on the Baltic Sea. The estimated error of derived spectra was less than 15 %. The conditions and range of application is discussed.

The primary purpose of fiber optic penetrators is to provide a safe and reliable optical path through a hermetic barrier. The penetrators must resist pressure, humidity, corrosion, and maintain optical and mechanical integrity. Many optical fiber penetrators are manufactured from a combination of epoxies and application of a physical pressure seal onto the fiber. While providing a short term solution, epoxy lacks long term hermetic protection. Physical force applied to the fiber from a pressure seal may affect the refractive index of the optical cladding in soft and hard clad silica fibers. This presentation describes methods to provide a positive hermetic seal to a variety of optical fibers. These penetrators do not use lenses, prisms, or other conventional optical relay systems. Penetrators are intrinsically radiation hard and offer the convenience of providing a standard connector interface on one or both sides of the device. Examples of aquatic and high vacuum penetrators are presented. Application for this technology spans fiber geometry from single mode to large core step index fibers. Uses include communications and high energy transmission. This technology also is applicable to fiber based sensors.

The in situ absorption meter, based on the reflective tube absorption meter principle in which both scattered and directly transmitted light are measured by a single receiver, was originally proposed as a alternative means to measuring in situ concentrations of chlorophyll a and phaeophytin. By measuring differential absorption between two wavelengths, 676 nm and 712 nm, a scattering correction mechanism was provided which provides accurate absorption measurements in natural waters. As the instrument design evolved six wavelengths were eventually installed to measure absorption throughout the visible and near IR spectrum. An operational overview of the instrument describes the primary optical and electrical components of the instrument and provides a basic understanding of how the absorption measurement is performed. After initial field tests, laboratory tests were performed to quantify the instrument's operational characteristics. Precision, linearity, and performance in the presence of a scattering medium were tested to determine the instrument's utility in performing in situ quantitative analysis of chlorophyll. The instrument demonstrated precision approaching 0.02 (mu) g/1 at a 7 Hz acquisition rate, excellent linearity over a 40 (mu) g/1 range, and less than two percent error in measurement accuracy under scatterer to absorber concentration ratios in excess of 1000:1.

As the theoretical understanding of bio-optical relationships increases, new tools for measuring ocean optical properties will be needed, particularly using a spectral resolution approaching 1 nm. Continuing improvements in grating technology for spectrometers coupled with the development of high quality CCD detectors has afforded the opportunity to experiment with a number of innovative instrument designs. However, optical sensors for use in oceanographic instruments must be designed to operate over a wide dynamic range, both spectrally over the region of interest, and radiometrically over a wide range of signal level as flux is lost with increasing depth. This is especially true for work in the ultraviolet, where signal levels are very low compared to the visible region of the spectrum and where attenuation of the flux by water is high. In this paper, the use of optical fibers, imaging spectrographs, and CCD photodetectors in the construction of a multi-channel marine spectroradiometer is presented. Stress induced changes in transmission can result in large artifacts when uncompensated optical fibers are used as part of the light path. Special emphasis is placed on the impact of stray-light characterization on the use of the spectrograph. The design and specification of the fiber optic cable, disperser, and CCD camera are presented, as well as implications to ocean optics of the special considerations that must be taken into account when spectrographs are deployed in the sea.

Optical sensors for use in oceanographic instruments must be designed to operate over a wide dynamic range, both spectrally from the UV through the visible region, and radiometrically as flux is lost with increasing depth. The output from a discrete sensor results from the convolution of the sensor's spectral response with the spectral distribution of irradiance, which changes radically with depth. Thus, a number of factors must be optimized in the instrument design. This is particularly true in the ultraviolet, where spectral leakage from longer wavelengths may significantly influence the output of a sensor at depth. This paper presents a theoretical basis for the evaluation of discrete sensor performance, with special emphasis on sensors for use in the ultraviolet region of the spectrum. The analysis includes a detailed description of the calibration and spectral response function for two channels of a new UV radiometer, the PUV-500, and compares this description with data taken in clear ocean waters in the equatorial Pacific. Finally, a theoretical analysis of two channels of the instrument, 308 and 340 nm, is used to evaluate the potential for measuring total column ozone with this design.

The recent development of moorable underwater spectral radiometers provides the possibility of long-term observations of bio-optical properties of the ocean at a sampling frequency of a few seconds to minutes. However, interpretation of the observed attenuation coefficients in terms of variations in the inherent optical properties (IOPs) or the biological properties is not straightforward for several reasons. First, even in a homogeneous ocean the attenuation coefficient K_d will be a function of depth, illumination at the surface, and the surface roughness, as well as the IOPs of the ocean. Next, a moored instrument cannot measure K_d as a function of depth but instead measures the mean K_d between discrete depths. Finally, K_d will depend on the (unknown) vertical structure of the optical properties of the water column. The dependence of the mean K_d on these factors is studied with Monte Carlo simulations of radiative transfer in the ocean-atmosphere system. Preliminary results from this study are presented.

Measurements of ship shadow were made from a manned submersible, equipped with a downwelling PAR irradiance sensor. These measurements were made as transects under the surface ship during clear sky conditions and three separate profiles (on the shady side, under the ship, and on the sunny side) during overcast conditions. Results from the clear sky measurements agree with previous numerical simulations, indicating only small errors due to ship shadow. During overcast conditions, the profiles indicate the shadow effects are detectable to considerable depth, but not at a distance of one optical depth from the ship rail on the sunny side. These measurements also demonstrate the effectiveness of manned submersibles for optical oceanographic studies.

A new electro-optic radiance distribution camera system is described. This system is based upon cooled CCD array cameras and includes a multi-channel irradiance meter, tilt and roll sensors, flux-gate compass and several auxiliary channels. The system is controlled with an internal '386Sx computer and includes a 450 MByte hard drive for image storage. Data archiving is performed through a SCSI interface to an external 1.4 GByte DAT tape drive which is attached when the instrument is on deck. Some preliminary calibration data on the system is also included.

A Monte Carlo model has been used to determine a set of point spread functions and modulation transfer functions for underwater imaging in different environments. The results have been used to examine the validity of a linear approximation theory. The conclusions are that the linear approximation theory works to some extent, however, a slight modification can be used in order to obtain good quantitative agreement. In particular, an empirical effective beam attenuation function is used for each different environment in order to insure the accuracy of the linear treatment.

Research is currently underway to investigate the physical mechanisms which cause loss of coherence in scattered light. It has been shown that, for Brownian motion of particles in a scattering medium, the coherence of incident light decreases rapidly with path length and diffusion coefficient. Experiments confirm that laser light scattered by a water column loses coherence as a function of path length and water turbidity. An experiment has been performed which measures coherence length versus temperature, optical path length, and water quality. The results are reported here. Based on these results and research into the causes of spectral broadening, experiments are proposed to measure each type of broadening mechanism with a much higher degree of accuracy.

Temporal pulse stretching is a consequence of the multiple scatter by ocean water of a laser pulse. Although the physical process behind pulse stretching is intuitively clear, there is no widely held quantitative definition of it. Here temporal pulse stretching is defined in terms of temporal moments of the radiance at a fixed position and orientation with respect to the initial pulse axis. This definition has been chosen because it is directly measurable from the waveform output of a radiometer. The first temporal moment is a measure of the apparent delay of the pulse, and the variance from the second moment describes the increasing width. Using a WKB approach, an expression is obtained for the first two temporal moments for waveforms measured at positions along the initial pulse axis. Quantitative predictions of the temporal delay and width are made for a pulse which is initially a collimated point. To within an error of no more than 12%, the delay and width are proportional. Stretching effects on waveforms are shown graphically in plots at various distances from the source.

High data rate underwater laser communications are highly constrained by laser propagation characteristics in the marine environment. We conducted communications experiments in freshwater and coastal seawater using an amplitude-modulated (i.e., pulsed) green laser beam detected by a remote optical receiver. We measured functional relationships between propagation distance, data rate, and error rate. Laser communications are degraded by absorption and scattering due to water, dissolved substances, suspended particulates, and marine biologics. Spatial beam spreading reduces the amount of optical signal that is collected by the detector. Pulse stretching temporally smears adjacent laser pulses, limiting maximum attainable data rate. Determining the capabilities of such a system requires characterization of the underwater communications channel. Relatively, little data is available regarding the relationship between optical water properties and the temporal behavior of laser pulses with pulsewidths in the nanosecond regime. We have conducted a series of experiments to measure both spatial and temporal properties of the propagating laser pulses. These through-water measurements have been made in the laboratory, in large fresh water tanks, in natural ponds, and in coastal seawater. We discuss spatial and temporal propagation characteristics of the underwater environment, and their relationships to the predicted performance supported by the communications channel.

The modulation transfer function (MTF) of sea water is a very important parameter for ocean optics, lidar, laser beam transmission and image transmission in the sea. V.A.Del Grosso1,2 , L.E.Metens and published measured.results of MTF in the sea in 1975,1977,and 1978.In general, the measurement MTF method is measuring laser beam transmission by means of setting up a blue—green laser transmitter and reciving system in the sea. This kind of method is very difficult to measure MTF in various different depths and sea area, because the moved of transmitter and recieving system from a sea arae to another sea area is not convenient and realiation. In this paper, we suggest to get MTF in the sea from natural radiance field by means of the relation between MTF and natural radiance field, we give the relation between MTF and natural radiance field by information transmission theory in section 2, the point spread function(PSF) and spatial angular frequricy spectrum in the sea in section 3, the inherent optical properties derived from MTF in section 4.

Limits of the polarization technique in discriminating backscattered noise for a monostatic underwater viewing system are discussed. The approach presented is based on an analytical solution of the vector equation for radiative transfer in the small angle approximation. The influence of the water optical properties, the receiver range gate, and the field of view on the background reduction are investigated. Estimates are made of the enhancement of the target's apparent contrast and of the detection range that can be achieved for typical environmental conditions.

A careful analysis of the scattering and absorption data base of the waters off the coasts of Canada has persuaded us that a laser assisted camera system will have a significantly improved viewing performance over conventional systems. With this purpose in mind, we designed and built the laser underwater camera image enhancer system (LUCIE). The system uses a 2 kHz diode-pumped frequency-doubled Nd:YAG laser as an illumination source. The light is collected by a 10 cm diameter zoom lens. The detector is a gated image intensifier with a 7 ns gate and a gain which is continuously variable from 500 to 1,000,000. The gate delay is adjusted to the focal distance of the lens system. This ensures that only the scattering occurring near the target is seen by the camera system. In the strongly scattering waters typical of harbor approaches this system has a range of from 4 to 6 times that of a conventional camera with floodlights. The system has been tested in a water tank facility at DREV and has been mounted on the HYSUB 5000 remotely operated vehicle (ROV) for sea trials. The images from the system are sent to the surface via a high performance analog link with a bandwidth of 8 MHz. The images are processed to remove the effect of marine snow. This processing and the high repetition rate of the laser, which ensures a lack of speckle, both contribute significantly to the clarity of the images. The NEARSCAT transmissometer- nephelometer system is operated simultaneously with the LUCIE system and this allows us to have the fundamental data necessary for evaluating the performance of the imaging system and validating transmission, scattering, and imaging models.

The design and construction of a synchronous-scanning underwater imaging system capable of rapid two-dimensional scanning is described. The imager employs a 7 W all-lines argon ion laser in conjunction with a galvanometrically driven raster scanner and an image-dissector tube receiver. The imager is capable of directly generating real-time RS-170 video imagery. The results of in-water test of the imaging system demonstrate operating ranges of up to 4 attenuation lengths (AL) when running at real-time frame rates, ranges of 5.1 - 5.5 AL when operating with an 8-frame running average, and ranges of 6.3 AL when using a 128-frame running average. Future frame averaging requirements are expected to be relaxed, due to improvements in the detector preamplifier. The system performance was compared with that of several floodlight/silicon intensified target (SIT) television camera configurations, which produced a maximum imaging range of about 2.6 AL. Also, an imaging configuration that used the raster-scanned beam of the laser as an illumination source for the SIT camera was tested. That system had an ultimate range of about 4 AL.

In applying an ocean lidar equation, a reflectance and a refractivity of a random surface of the water is the most difficult parameter for an actual ocean lidar observation. A flight test of an airborne ocean lidar and a surface test of a shipboard ocean lidar showed variations of intensity of light scattered from a depth of the water. We built a multiparameteric shipboard ocean lidar to examine a hypothesis that variations of light scattered or fluorescence from the depth could be given as a function of light reflected at the surface of the water. As a result, we have confirmed that light scattered or fluorescence from the depth was independently given from variations of light reflected at the surface of the water on the current lidar system.

The paper contains a comparative analysis and discussion of resultant recommendations for the optimization of an airborne lidar's parameters, with application to modern lidar systems as employed in various countries for the ocean and continental shelf research. As criteria for the systems comparison in different remote sensing conditions (aircraft altitude, depth, day/night, zenithal sun angle, sea-water attenuation coefficient, receiver optical system's field of view (FOV), laser wavelength, etc.,) Sakitt's D-index of discriminability is used. We demonstrate the optical signal, as determined by the following process: reflecting from boundary -- backscattering in the atmosphere -- secondary reflecting from boundary, to be the cause for limiting the distance of underwater measurements. Some estimates for the bottom depth values to be achieved by a `super-lidar' are presented.

An understanding of the physical properties of sea ice and their variability is critical both to interpret observations of the optical properties and to develop models of radiative transfer. Sea ice has an intricate structure consisting of platelets of fresh ice with inclusions of brine and air. The total volume and the distribution of these inclusions strongly affect the optical properties. The physical properties of the ice are highly dependent on the growth conditions and the seasonal evolution of the ice. Consequently, the state and structure of the ice exhibit large spatial and temporal variability. For example, the crystal texture can be granular or columnar, while crystal sizes can vary from millimeters to a few centimeters. Observed brine volumes can vary from 0% in the surface layer of multi-year ice to as much as 50% in the skeletal layer at the bottom of a growing ice sheet. Densities show a similar variability ranging from 0.60 to 0.92 g/cm³. Because of this variability there is a need to use the large body of ice property observations to develop ice properties models, either of an empirical or physical nature.

We have investigated the possibility of using optical instruments to detect the presence of frazil ice in Arctic leads. Frazil ice was successfully detected with a transmissometer but could not be seen with scattering sensors. Field measurements were made in Arctic leads north of Alaska during the spring of 1992 as a part of the lead experiment (LEADEX). On two occasions, the temperature, salinity, and transmission signals show the presence of frazil. Because a transmissometer cannot distinguish ice from other types of particles, we present a concept for a dual wavelength absorption meter that would be able to distinguish between frazil ice and biological particles.

Time series studies of the spectral irradiance fields beneath multiyear pack ice were conducted in the Eastern Arctic Basin at 82 - 83 degree(s)N as part of the Coordinated Eastern Arctic Research Experiment (CEAREX). Particulate matter was collected from the multiyear pack ice as well as first year ice in a refrozen lead. The vertical distribution within the ice and the spectral absorption properties of the particulates were determined in order to estimate their contribution to the optical properties of the sea ice. Among the particulates contained in sea ice detritus was common throughout all portions of the pack ice and was the major light absorbing particulate matter in the ice at the time of the observation. Algal cells and mineral- like particulates also were present, yet they contributed to the light-absorbing properties to a lesser extent than the detritus. During early spring, particulate matter contributed little to the bulk attenuation coefficients of the multiyear ice, however, it was estimated to have a more substantial contribution to the attenuation coefficients of first year ice in a refrozen lead. Results of a single stream multilayer radiative transfer model that simulates concentrations of biogenic particulate matter observed in Arctic sea ice indicates that particulate matter within sea ice plays a substantial role in radiative energy transfer and has the potential to seasonally alter spectral irradiance regimes within the ice covered Arctic Ocean.

A knowledge of the reflection of light from a sea ice cover is important for both the interpretation of remote sensing imagery at visible and near-infrared wavelengths and for climatological studies involving the energy balance of the polar regions. Spectral measurements of albedo, bidirectional reflectance function (BDRF), and polarized reflectance were made for sea ice conditions found during the onset of melt in the Canadian Arctic. The wavelength region studied was from the ultraviolet to the near infrared (370 - 1000 nm). Results for five surface types are presented: (1) dry snow, (2) dry snow with a glazed surface, (3) bare ice, (4) blue ice, and (5) a melt pond. Results indicate that spectral albedos decrease at all wavelengths as the melt season progresses and the surface conditions evolve from (1) through (5), and that the decrease is most pronounced at longer wavelengths. Reflectance data suggest that (1) at most angles reflectance has the same spectral shape as albedo, (2) at 30 degree(s) elevation reflectance is for the most part azimuthally isotropic and (3) at 60 degree(s) elevation a significant specular component was evident at 0 degree(s) azimuth, especially for the bare ice case.

In this paper, we describe an experiment to measure the point spread function (PSF) of Arctic ice that was conducted by personnel of the Naval Ocean Systems Center in 1985. SRI International designed and developed the instrumentation. In April, data were collected on refrozen leads in pack ice concentrated near the Beaufort Gyre. The location was about 200 miles from the North Pole at approximately 86 degrees north and 88 degrees west. PSF measurements were made with a Hasselblad camera and a pulsed Lambertian (cosine) source gated to the camera. Recently, SRI digitized the film data with a charge-coupled device (CCD) camera and performed a digital analysis of the images. Results from two sites of new and first- year ice, 0.66 m and 2.1 m thick, respectively, are presented. Because of the strong multiple scattering by sea ice, and the limited area of the ice surface that could be imaged by the camera, the data obtained only partially characterize the PSF of the ice. The paper concludes with suggestions for improving future sea ice PSF measurements.

Light scattering at near forward angles has received considerable attention in the past. However, measurements below a scattering angle of 0.1 degree(s) have not previously been made for particle suspensions due to the presence of the unscattered incident light beam. In this paper, we review a new technique for measuring light scattering near, as well as precisely at, a scattering angle of zero degrees. The existence of coherent scattering effects at zero degrees is considered and both theoretical predictions and experimental data are presented.

A short review of the present-day state of the problems in retrieving the microphysical properties of oceanic particles from light scattering properties. It is found that the best procedure for determining particle size distributions uses the small angle method in determining the large particles and a fitting method to determine medium and small particles. Comparing the size distribution determined found using the optical method to the geological method finds similar numbers of large particles, but the optical method finds many more small particles than the geological.