Bio-optical inversion scheme based on the radiative transfer equation.

An inversion algorithm based on a forward optical model based on a radiative transfer equation is developed in terms of IOPs with explicit inclusion of the volume scattering function (VSF). Key results from the analysis are: 1) the inversion retrievals perform to comparable levels as the operational configuration of the NASA's Generalized Inherent Optical Property (GIOP) framework; 2) closure error between RT r and measured r have no significant effect on predicting the accuracy of the derived IOPs; and 3) $\tilde {b}_{bp}$ is important to ZTT, but not explicitly included in other types of comparable semi-analytic algorithms.

Dynamics of microcystins and saxitoxin in the Indian River Lagoon, Florida.

Harmful algal blooms that can produce toxins are common in the Indian River Lagoon (IRL), which covers ~250 km of Florida's east coast. The current study assessed the dynamics of microcystins and saxitoxin in six segments of the IRL: Banana River Lagoon (BRL), Mosquito Lagoon (ML), Northern IRL (NIRL), Central IRL (CIRL), Southern IRL (SIRL), and the St. Lucie Estuary (SLE).

An overview of approaches and challenges for retrieving marine inherent optical properties from ocean color remote sensing.

Ocean color measured from satellites provides daily global, synoptic views of spectral waterleaving reflectances that can be used to generate estimates of marine inherent optical properties (IOPs). These reflectances, namely the ratio of spectral upwelled radiances to spectral downwelled irradiances, describe the light exiting a water mass that defines its color. IOPs are the spectral absorption and scattering characteristics of ocean water and its dissolved and particulate constituents.

Measurement uncertainties in PSICAM and reflective tube absorption meters.

The nature and magnitude of measurement uncertainties (precision and accuracy) associated with two approaches for measuring absorption by turbid waters (b(532 nm) ranging from 0.20 m to 22.89 m) are investigated here: (a) point source integrating cavity absorption meters (PSICAM), and (b) reflective tube absorption meters (AC-9 and AC-s - both WET Labs Inc.

Evaluation of a flow cytometry method to determine size and real refractive index distributions in natural marine particle populations.

A flow cytometric (FC) method was developed to retrieve particle size distributions (PSDs) and real refractive index (n) information in natural waters. Geometry and signal response of the sensors within the flow cytometer (CytoSense, CytoBuoy b.v.

Evidence for ubiquitous preferential particle orientation in representative oceanic shear flows.

In situ measurements were undertaken to characterize particle fields in undisturbed oceanic environments. Simultaneous, co-located depth profiles of particle fields and flow characteristics were recorded using a submersible holographic imaging system and an acoustic Doppler velocimeter, under different flow conditions and varying particle concentration loads, typical of those found in coastal oceans and lakes. Nearly one million particles with major axis lengths ranging from ∼14 μm to 11.

Assessing uncertainties in scattering correction algorithms for reflective tube absorption measurements made with a WET Labs ac-9.

In situ absorption measurements collected with a WET Labs ac-9 employing a reflective tube approach were scatter corrected using several possible methods and compared to reference measurements made by a PSICAM to assess performance. Overall, two correction methods performed best for the stations sampled: one using an empirical relationship between the ac-9 and PSICAM to derive the scattering error (ε) in the near-infrared (NIR), and one where ε was independently derived from concurrent measurements of the volume scattering function (VSF). Application of the VSF-based method may be more universally applicable, although difficult to routinely apply because of the lack of commercially available VSF instrumentation.

Vertically- resolved phytoplankton carbon and net primary production from a high spectral resolution lidar.

Passive ocean observing sensors are unable to detect subsurface structure in ocean properties, resulting in errors in water column integrated phytoplankton biomass and net primary production (NPP) estimates. Active lidar (light detection and ranging) sensors make quantitative measurements of depth-resolved backscatter (bbp) and diffuse light attenuation (Kd) coefficients in the ocean and can provide critical measurements for biogeochemical models. Sub-surface phytoplankton biomass, light, chlorophyll, and NPP fields were characterized using both in situ measurements and coincident airborne high spectral resolution lidar (HSRL-1) measurements collected as part of the SABOR (Ship-Aircraft Bio-Optical Research) field campaign.

Assessing the link between chlorophyll concentration and absorption line height at 676 nm over a broad range of water types.

The relationship between absorption at 676 nm normalized to chlorophyll-a, i.e., specific absorption aph*(676), and various optical and environmental properties is examined in extensive data sets from Case I and Case II waters found globally to assess drivers of variability such as pigment packaging.

Polarimetric imaging and retrieval of target polarization characteristics in underwater environment.

Polarized light fields contain more information than simple irradiance and such capabilities provide an advanced tool for underwater imaging. The concept of the beam spread function (BSF) for analysis of scalar underwater imaging was extended to a polarized BSF which considers polarization. The following studies of the polarized BSF in an underwater environment through Monte Carlo simulations and experiments led to a simplified underwater polarimetric imaging model.

Open-ocean fish reveal an omnidirectional solution to camouflage in polarized environments.

Despite appearing featureless to our eyes, the open ocean is a highly variable environment for polarization-sensitive viewers. Dynamic visual backgrounds coupled with predator encounters from all possible directions make this habitat one of the most challenging for camouflage. We tested open-ocean crypsis in nature by collecting more than 1500 videopolarimetry measurements from live fish from distinct habitats under a variety of viewing conditions.

Lidar extinction-to-backscatter ratio of the ocean.

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.

Benthic effects on the polarization of light in shallow waters.

Measurements of the upwelling polarized radiance in relatively shallow waters of varying depths and benthic conditions are compared to simulations, revealing the depolarizing nature of the seafloor. The simulations, executed with the software package RayXP, are solutions to the vector radiative transfer equation, which depends on the incident light field and three types of parameters: inherent optical properties, the scattering matrix, and the benthic reflectance. These were measured directly or calculated from measurements with additional assumptions.

Measurements and simulations of polarization states of underwater light in clear oceanic waters.

Polarization states of the underwater light field were measured by a hyperspectral and multiangular polarimeter and a video polarimeter under various atmospheric, surface, and water conditions, as well as solar and viewing geometries, in clear oceanic waters near Port Aransas, Texas. Some of the first comprehensive comparisons were made between the measured polarized light, including the degree and angle of linear polarization and linear Stokes parameters (Q and U), and those from Monte Carlo simulations that used concurrently measured water inherent optical properties and particle volume scattering functions as input. For selected wavelengths in the visible spectrum, measured and model-simulated polarization characteristics were found to be consistent in most cases.

Platform effects on optical variability and prediction of underwater visibility.

We present hydrographic and optical data collected concurrently from two different platforms, the R/P FLoating Instrument Platform and the R/V Kilo Moana, located about 2km apart in the Santa Barbara Channel in California. We show that optical variability between the two platforms was due primarily to platform effects, specifically the breakdown of stratification from mixing by the hull of R/P FLIP. Modeled underwater radiance distribution differed by as much as 50% between the two platforms during stratified conditions.

Angular shape of the oceanic particulate volume scattering function in the backward direction.

Analysis of several million particulate volume scattering functions (VSFs) from different field sites around the world's oceans and coastlines revealed that the shape of the VSF in the backward direction was remarkably consistent (5% or less variability at angles between 90 degrees and 170 degrees ). In agreement with theoretical models and past field measurements, the variability of the VSF shape (the VSF normalized to the backscattering coefficient) was found to be lowest between 110 degrees and 120 degrees . This study concludes that under most oceanic conditions, estimates of the particulate backscattering coefficient, using single angle scattering measurements near 110 degrees to 120 degrees and suitable conversion factors, are justified and should have a maximum uncertainty of less than a few percent once instrument noise is accounted for.

Scattering by solutions of major sea salts.

Increased scattering by seawater relative to that by pure water is primarily due to additional fluctuation of the refractive index contributed by sea salts. Salts with different ionic weight and sizes, while barely affecting the scattering that is due to density fluctuations, have a significant effect on the scattering that is due to concentration fluctuations. And this explains the major differences of their total scattering that would be observed.

Spectra of particulate backscattering in natural waters.

Hyperspectral profiles of downwelling irradiance and upwelling radiance in natural waters (oligotrophic and mesotrophic) are combined with inverse radiative transfer to obtain high resolution spectra of the absorption coefficient (a) and the backscattering coefficient (b(b)) of the water and its constituents. The absorption coefficient at the mesotrophic station clearly shows spectral absorption features attributable to several phytoplankton pigments (Chlorophyll a, b, c, and Carotenoids). The backscattering shows only weak spectral features and can be well represented by a power-law variation with wavelength (lambda): b(b) approximately lambda(-n), where n is a constant between 0.

Polarized light in coastal waters: hyperspectral and multiangular analysis.

Measurements of the underwater polarized light field were performed at different stations, atmospheric conditions and water compositions using a newly developed hyperspectral and multiangular polarimeter during a recent cruise in the coastal areas of New York Harbor - Sandy Hook, NJ region (USA). Results are presented for waters with chlorophyll concentrations 1.3-4.

Hyperspectral temperature and salt dependencies of absorption by water and heavy water in the 400-750 nm spectral range.

The temperature and salt dependencies of absorption by liquid water (H2O) and heavy water (D2O) were determined using a hyperspectral absorption and attenuation meter (WET Labs, AC-S). Sodium chloride (NaCl) was used as a proxy for seawater salts. There was no significant temperature (PsiT) or salt (PsiS) dependency of absorption at wavelengths <550 nm.

Use of optical scattering to discriminate particle types in coastal waters.

The particulate scattering characteristics of coastal waters were examined at nine locations around the United States, including near-shore sites in the Gulf of Mexico and the Atlantic and Pacific oceans. The scattering measurements were used in conjunction with inversion models to estimate particle size distributions and bulk refractive indices of the suspended particles. The relationships between various scattering properties and chlorophyll concentration were also investigated and compared with previous relationships described for case I waters.