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Groundwater H.,WET Labs Inc. | Twardowski M.S.,WET Labs Inc. | Dierssen H.M.,University of Connecticut | Sciandra A.,Laboratoire Doceanographie Of Villefranche | Freeman S.A.,WET Labs Inc.
Journal of Atmospheric and Oceanic Technology | Year: 2012

Knowledge of particle size distributions (PSDs) in seawater is important for understanding several facets of marine science, such as the behavior of light scattering in seawater, phytoplankton dynamics, and biogeochemical cycling. Here, a method has been developed to quantify the size distribution of particle suspensions and characterize their chemical composition utilizing a scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) and applying image analysis techniques, including automatic thresholding. The method was validated by verifying the PSD and chemical composition of the Arizona Test Dust (ATD), which has a well-documented size distribution and chemical composition. Size distributions of ATD particles containing specific elements important in the marine environment, such as silicon, iron, calcium, aluminum, and potassium, were quantified. PSDs determined with the technique in field samples from coastal Long Island Sound and the remote South Pacific were compared with other sizing methods, including electroresistivity and laser diffractometry. Most accurate results for PSD determinations occurred when the particle mass loading on the filter was between 0.04 and 0.1mg cm22. With this in mind, immediate feedback in the field can be provided to prepare appropriate filtration sample volumes due to a linear relationship between the beam attenuation coefficient at 650nm (c650) and the total suspended matter (TSM). Overall, the method presents two defining advantages in 1) minimizing user bias, because the majority of the analysis is automated, and 2) providing an elemental distribution in the context of a particle size distribution. © 2012 American Meteorological Society.

Chekalyuk A.,Lamont Doherty Earth Observatory | Barnard A.,WET Labs Inc. | Quigg A.,Texas A&M University at Galveston | Quigg A.,Texas A&M University | And 2 more authors.
Optics Express | Year: 2014

The new Aquatic Laser Fluorescence Analyzer (ALFA) provides spectral and temporal measurements of laser-stimulated emission (LSE) for assessment of phytoplankton pigments, community structure, photochemical efficiency (PY), and chromophoric dissolved organic matter (CDOM). The instrument was deployed in the Northern Gulf of Mexico to evaluate the ALFA analytical capabilities across the estuarine-marine gradient. The robust relationships between the pigment fluorescence and independent pigment measurements were used to validate the ALFA analytical algorithms and calibrate the instrument. The maximal PY magnitudes, PYm = PY(1-1.35·10-4PAR)-1, were estimated using the underway measurements of PY and photosynthetically active radiation (PAR). The chlorophyll (Chl) spatial patterns were calculated using the ratio of Chl fluorescence to PY to eliminate the effect of non-photochemical quenching on the underway Chl assessments. These measurements have provided rich information about spatial distributions of Chl, PYm, CDOM, and phytoplankton community structure, and demonstrated the utility of the ALFA instrument for oceanographic studies and bio-environmental surveys. The data suggest that the fluorescence measurements with 514 nm excitation can provide informative data for characterization of the CDOM-rich fresh, estuarine, and coastal aquatic environments. ©2014 Optical Society of America.

Czerski H.,University of Southampton | Twardowski M.,WET Labs Inc. | Zhang X.,University of North Dakota | Vagle S.,Canadian Department of Fisheries and Oceans
Journal of Geophysical Research: Oceans | Year: 2011

Many studies have investigated bubble size distributions in the ocean, but the measured size range does not normally extend to bubbles with a radius below 20 m. Bubbles smaller than this are thought to have a significant effect on the optical properties of the ocean, potentially affecting remotely sensed measurements of ocean color and the optical detection of particulates and dissolved matter. Such optical data are becoming the major source of oceanic information about algal blooms, primary productivity, sediment loading and the spread of pollutants. The challenges associated with measuring these bubbles are difficulty of calibrating sensors with independent bubble size measurements and lack of knowledge about the organic coating on the bubbles. This paper describes simultaneous oceanic measurements of these small bubbles using independent optical and acoustical techniques. These measurements agree well, and an investigation of the bubble coating parameters was made. Both the optical and acoustical properties of bubbles are affected by this organic coating, and a comparison of these measurements narrows down the choice of possible coating parameters. Our results suggest that the bubbles measured in this study were likely to have a coating with a thickness of 10 nm and a refractive index of 1.18, and that the coating thickness is the more important parameter for optical inversions. The research described here is the first attempt to constrain these parameters in the ocean using two independent techniques and suggests that further studies of this type could result in significant insight into oceanic bubble coatings. Copyright 2011 by the American Geophysical Union.

Churnside J.H.,National Oceanic and Atmospheric Administration | Sullivan J.M.,WET Labs Inc. | Sullivan J.M.,University of Rhode Island | Twardowski M.S.,WET Labs Inc.
Optics Express | Year: 2014

Bio-optical models are used to develop a model of the lidar extinction-to-backscatter ratio applicable to oceanographic lidar. The model is based on chlorophyll concentration, and is expected to be valid for Case 1 waters. The limiting cases of narrow- and wide-beam lidars are presented and compared with estimates based on in situ optical measurements. Lidar measurements are also compared with the model using in situ or satellite estimates of chlorophyll concentration. A modified lidar ratio is defined, in which the properties of pure sea water are removed. This modified ratio is shown to be nearly constant for wide-beam lidar operating in lowchlorophyll waters, so accurate inversion to derive extinction and backscattering is possible under these conditions. This ratio can also be used for lidar calibration. © 2014 Optical Society of America.

Nencioli F.,University of California at Santa Barbara | Chang G.,Sea Engineering Inc. | Twardowski M.,WET Labs Inc. | Dickey T.D.,University of California at Santa Barbara
Biogeosciences | Year: 2010

Optical properties were collected along a transect across cyclonic eddy Opal in the lee of Hawaii during the E-Flux III field experiment (10-27 March 2005). The eddy was characterized by an intense doming of isopycnal surfaces, and by an enhanced Deep Chlorophyll Maximum Layer (DCML) within its core. The phytoplankton bloom was diatom dominated, evidencing an eddy-induced shift in ecological community. Four distinct regions were identified throughout the water column at Opal's core: a surface mixed layer dominated by small phytoplankton; a layer dominated by "senescent" diatoms between the bottom of the upper mixed layer and the DCML; the DCML; and a deep layer characterized by decreasing phytoplankton activity. We focused on two parameters, the ratio of chlorophyll concentration to particulate beam attenuation coefficient, [chl]/ c, and the backscattering ratio (the particle backscattering to particle scattering ratio), b̃bp, and tested their sensitivity to the changes in particle composition observed through the water column at the eddy center. Our results show that [chl]/ c is not a good indicator. Despite the shift in ecological community, the ratio remains controlled primarily by the variation in chlorophyll concentration per cell with depth (photoadaptation), so that its values increase throughout the DCML. Steeper increase of [chl]/ c below the DCML suggest that remineralization might be another important controlling factor. On the other hand, b̃bp clearly indicates a shift from a small phytoplankton to a diatom dominated community. Below an upper layer characterized by constant values, the b̃bp showed a rapid decrease to a broad minimum within the DCML. The higher values below the DCML are consistent with enhanced remineralization below the eddy-induced bloom. Both the "senescent" and the "healthy" diatom layers are characterized by similar optical properties, indicating some possible limitations in using optical measurements to fully characterize the composition of suspended material in the water column. The inverse relationship between b̃bp and [chl]/ c, reported by others for Case II waters, is observed neither for the background conditions, nor in the presence of the eddy-induced diatom bloom. Between the two parameters, only the backscattering ratio showed the potential to be a successful indicator for changes in particle composition in Case I waters. © Author(s) 2010.

Chang G.,Sea Engineering Inc. | Twardowski M.S.,WET Labs Inc.
Journal of Geophysical Research: Oceans | Year: 2011

We computed the modulation transfer function (MTF), which is the magnitude of the Fourier transform of the point spread function, for two different water bodies using measurements of optical properties and analytical formulations. Knowledge of the MTF is important for the interpretation of images from underwater electro-optical systems. The data were collected from two field sites as part of the Office of Naval Research sponsored Radiance in a Dynamic Ocean program: (1) Scripps Institution of Oceanography (SIO) Pier, a shallow-water, eutrophic environment, and (2) the Santa Barbara Channel (SBC), a deeper, mesotrophic environment. Wavelet analysis was employed to investigate the sources of variability of the MTF and the periodicities at which they occur. Results suggest that the MTF was strongly related to wind conditions and advection events and the optical properties serving as proxies for particle concentration and composition in the SBC. Increased wind speeds and stresses resulted in upper water column mixing, decreased water clarity, and reductions in image transmission. Rip currents accompanied by high concentrations of reflective particles observed at SIO Pier resulted in increases in the MTF. Optically derived particle composition characteristics such as the bulk particle real index of refraction and particle size distribution are shown to be related to the variability of imaging performance at both field sites. © 2011 by the American Geophysical Union.

Bhandari P.,University of Miami | Voss K.J.,University of Miami | Logan L.,University of Miami | Twardowski M.,WET Labs Inc.
Journal of Geophysical Research: Oceans | Year: 2011

The spectral polarized radiance distribution provides the most complete description of the light field that can be measured. However, this is a very difficult parameter to measure, particularly near the surface, because of its large dynamic range, changes in the skylight illumination, and waves at the air-sea interface. To measure the Stokes vector of the downwelling light field, which contains the polarization information, requires the combination of four images acquired simultaneously. To achieve this, we used the downwelling polarized radiance distribution camera system (DPOL) during the Radiance in a Dynamic Ocean (RaDyO) program Santa Barbara Channel and Hawaiian experiments. DPOL consists of four fisheye lenses and a spectral filter changer that allow us to capture the downwelling hemisphere of the polarized radiance distribution at seven wavelengths. Our measurements show that very near the surface, for clear sky conditions, the dominant source of polarization is the refracted sky light. As one progresses in the water column the polarization due to light scattering by the water increases and polarization due to light scattering in the water becomes dominant. Copyright 2011 by the American Geophysical Union.

Roesler C.S.,Bowdoin College | Barnard A.H.,WET Labs Inc.
Methods in Oceanography | Year: 2013

The pigment absorption peak in the red waveband observed in phytoplankton and particulate absorption spectra is primarily associated with chlorophyll-a and exhibits much lower pigment packaging compared to the blue peak. The minor contributions to the signature by accessory pigments can be largely removed by computing the line height absorption at 676 nm above a linear background between approximately 650 nm and 715 nm. The line height determination is also effective in removing the contributions to total or particulate absorption by colored dissolved organic matter and non-algal particles, and is relatively independent of the effects of biofouling. The line height absorption is shown to be significantly related to the extracted chlorophyll concentration over a large range of natural optical regimes and diverse phytoplankton cultures. Unlike the in situ fluorometric method for estimating chlorophyll, the absorption line height is not sensitive to incident irradiance, in particular non-photochemical quenching. The combination of the two methods provides a combination of robust phytoplankton biomass estimates, pigment based taxonomic information and a means to estimate the photosynthetic parameter, E K, the irradiance at which photosynthesis transitions from light limitation to light saturation. © 2013 The Authors.

WET Labs Inc. | Date: 2011-10-04

Scientific and technical apparatus, namely, fluorometers; scattering meters, namely, single-channel backscattering meters, nine-wavelength backscattering meters, volume scattering function meters, threeangle volume scattering function meters, and turbidity meters; environmental characterization optics (ECO) meters; absorption and or attenuation meters; water quality meters; phosphate sensors; transmissometers; batteries and battery packs; and electronic communications systems comprised of computer hardware and software for the transmission of data between two points.

An apparatus, method, and apparatus for hematology analysis comprising using a holographic microscope, in one embodiment a transmission-type holographic microscope. In one aspect, laser light is provided and split into first and second sample beams, the first sample beam for imaging with a first magnification, the second sample beam for imaging with a second magnification. The first and second sample beams are passed through a sample volume requiring hematology analysis. The first and second sample beams are combined with a reference beam and captured for digital analysis. The present invention enables adequate blood cell type differentials with a single, easily implemented, cost-effective holographic technique.

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