Informing ocean color inversion products by seeding with ancillary observations.

Ocean reflectance inversion algorithms provide many products used in ecological and biogeochemical models. While a number of different inversion approaches exist, they all use only spectral remote-sensing reflectances (Rrs(λ)) as input to derive inherent optical properties (IOPs) in optically deep oceanic waters. However, information content in Rrs(λ) is limited, so spectral inversion algorithms may benefit from additional inputs. Here, we test the simplest possible case of ingesting optical data ('seeding') within an inversion scheme (the Generalized Inherent Optical Property algorithm framework default configuration (GIOP-DC)) with both simulated and satellite datasets of an independently known or estimated IOP, the particulate backscattering coefficient at 532 nm (bbp(532)). We find that the seeded-inversion absorption products are substantially different and more accurate than those generated by the standard implementation. On global scales, seasonal patterns in seeded-inversion absorption products vary by more than 50% compared to absorption from the GIOP-DC. This study proposes one framework in which to consider the next generation of ocean color inversion schemes by highlighting the possibility of adding information collected with an independent sensor.

Plankton Imagery Data Inform Satellite-Based Estimates of Diatom Carbon.

Estimating the biomass of phytoplankton communities via remote sensing is a key requirement for understanding global ocean ecosystems. Of particular interest is the carbon associated with diatoms given their unequivocal ecological and biogeochemical roles. Satellite-based algorithms often rely on accessory pigment proxies to define diatom biomass, despite a lack of validation against independent diatom biomass measurements. We used imaging-in-flow cytometry to quantify diatom carbon in the western North Atlantic, and compared results to those obtained from accessory pigment-based approximations. Based on this analysis, we offer a new empirical formula to estimate diatom carbon concentrations from chlorophyll a. Additionally, we developed a neural network model in which we integrated chlorophyll a and environmental information to estimate diatom carbon distributions in the western North Atlantic. The potential for improving satellite-based diatom carbon estimates by integrating environmental information into a model, compared to models that are based solely on chlorophyll a, is discussed.

Seasonal bias in global ocean color observations.

In this study, we identify a seasonal bias in the ocean color satellite-derived remote sensing reflectances (Rrs(λ);sr-1) at the ocean color validation site, Marine Optical BuoY. The seasonal bias in Rrs(λ) is present to varying degrees in all ocean color satellites examined, including the Visible Infrared Imaging Radiometer Suite, Sea-Viewing Wide Field-of-View Sensor, and Moderate Resolution Imaging Spectrometer. The relative bias in Rrs has spectral dependence. Products derived from Rrs(λ) are affected by the bias to varying degrees, with particulate backscattering varying up to 50% over a year, chlorophyll varying up to 25% over a year, and absorption from phytoplankton or dissolved material varying by up to 15%. The propagation of Rrs(λ) bias into derived products is broadly confirmed on regional and global scales using Argo floats and data from the cloud-aerosol lidar with orthogonal polarization instrument aboard the cloud-aerosol lidar and infrared pathfinder satellite. The artifactual seasonality in ocean color is prominent in areas of low biomass (i.e., subtropical gyres) and is not easily discerned in areas of high biomass. While we have eliminated several candidates that could cause the biases in Rrs(λ), there are still outstanding questions regarding potential contributions from atmospheric corrections. Specifically, we provide evidence that the aquatic bidirectional reflectance distribution function may in part cause the observed seasonal bias, but this does not preclude an additional effect of the aerosol estimation. Our investigation highlights the contributions that atmospheric correction schemes can make in introducing biases in Rrs(λ), and we recommend more simulations to discern these influence Rrs(λ) biases. Community efforts are needed to find the root cause of the seasonal bias because all past, present, and future data are, or will be, affected until a solution is implemented.

Particulate Backscattering in the Global Ocean: A Comparison of Independent Assessments.

How well do we know the particulate backscattering coefficient (bbp) in the global ocean? Satellite lidar bbp has never been validated globally and few studies have compared lidar bbp to bbp derived from reflectances (via ocean color) or in situ observations. Here, we validate lidar bbp with autonomous biogeochemical Argo floats using a decorrelation analysis to identify relevant spatiotemporal matchup scales inspired by geographical variability in the Rossby radius of deformation. We compare lidar, float, and ocean color bbp at the same locations and times to assess performance. Lidar bbp outperforms ocean color, with a median percent error of 18% compared to 24% in the best case and a relative bias of -11% compared to -21%, respectively. Phytoplankton carbon calculated from ocean color and lidar exhibits basin-scale differences that can reach ±50%.

Evaluating satellite estimates of particulate backscatter in the global open ocean using autonomous profiling floats.

Satellite retrievals of particulate backscattering (bbp) are widely used in studies of ocean ecology and biogeochemistry, but have been historically difficult to validate due to the paucity of available ship-based comparative field measurements. Here we present a comparison of satellite and in situ bbp using observations from autonomous floats (n = 2,486 total matchups across three satellites), which provide bbp at 700 nm. With these data, we quantify how well the three inversion products currently distributed by NASA ocean color retrieve bbp. We find that the median ratio of satellite derived bbp to float bbp ranges from 0.77 to 1.60 and Spearman's rank correlations vary from r = 0.06 to r = 0.79, depending on which algorithm and sensor is used. Model skill degrades with increased spatial variability in remote sensing reflectance, which suggests that more rigorous matchup criteria and factors contributing to sensor noisiness may be useful to address in future work, and/or that we have built in biases in the current widely distributed inversion algorithms.

Southern Ocean Biogeochemical Float Deployment Strategy, With Example From the Greenwich Meridian Line (GO-SHIP A12).

Biogeochemical Argo floats, profiling to 2,000-m depth, are being deployed throughout the Southern Ocean by the Southern Ocean Carbon and Climate Observations and Modeling program (SOCCOM). The goal is 200 floats by 2020, to provide the first full set of annual cycles of carbon, oxygen, nitrate, and optical properties across multiple oceanographic regimes. Building from no prior coverage to a sparse array, deployments are based on prior knowledge of water mass properties, mean frontal locations, mean circulation and eddy variability, winds, air-sea heat/freshwater/carbon exchange, prior Argo trajectories, and float simulations in the Southern Ocean State Estimate and Hybrid Coordinate Ocean Model (HYCOM). Twelve floats deployed from the 2014-2015 Polarstern cruise from South Africa to Antarctica are used as a test case to evaluate the deployment strategy adopted for SOCCOM's 20 deployment cruises and 126 floats to date. After several years, these floats continue to represent the deployment zones targeted in advance: (1) Weddell Gyre sea ice zone, observing the Antarctic Slope Front, and a decadally-rare polynya over Maud Rise; (2) Antarctic Circumpolar Current (ACC) including the topographically steered Southern Zone chimney where upwelling carbon/nutrient-rich deep waters produce surprisingly large carbon dioxide outgassing; (3) Subantarctic and Subtropical zones between the ACC and Africa; and (4) Cape Basin. Argo floats and eddy-resolving HYCOM simulations were the best predictors of individual SOCCOM float pathways, with uncertainty after 2 years of order 1,000 km in the sea ice zone and more than double that in and north of the ACC.

Surgeon use of medical jargon with parents in the outpatient setting.

OBJECTIVE: Unexplained medical terminology impedes clinician/parent communication. We describe jargon use in a pediatric surgical setting. METHODS: We evaluated encounters between parents of children with sleep-disordered breathing (SDB; n = 64) and otolaryngologists (n = 8). Participants completed questionnaires evaluating demographics, clinical features, and parental role in decision-making via a 4-point categorical item. Two coders reviewed consultations for occurrence of clinician and parent utterance of medical jargon. Descriptive statistics established a profile of jargon use, and logistic regression evaluated associations between communication factors with jargon use. RESULTS: Unexplained medical jargon was common (mean total utterances per visit = 28.9,SD = 19.5,Range = 5-100), including SDB-specific jargon (M = 8.3,SD = 8.8), other medical terminology (M = 13.9,SD = 12) and contextual terms (M = 3.8,SD = 4). Parents used jargon a mean of 4.3 times (SD = 4.6). Clinicians used more jargon in consults where they perceived parents as having greater involvement in decision-making (OR = 3.4,p < 0.05) and when parents used more jargon (OR = 1.2,p < 0.05). CONCLUSIONS: Jargon use in pediatric surgical consultations is common and could serve as a barrier to informed or shared parent decision-making. This study provides a foundation for further research into patterns of jargon use across surgical populations. PRACTICE IMPLICATIONS: Results will be integrated into communication training to enhance clinician communication, foster self-awareness in language use, and create strategies to evaluate parental understanding.

Methotrexate or expectant management in women with an ectopic pregnancy or pregnancy of unknown location and low serum hCG concentrations? A randomized comparison.

STUDY QUESTION: What is the treatment success rate of systemic methotrexate (MTX) compared with expectant management in women with an ectopic pregnancy or a pregnancy of unknown location (PUL) with low and plateauing serum hCG concentrations? SUMMARY ANSWER: In women with an ectopic pregnancy or a PUL and low and plateauing serum hCG concentrations, expectant management is an alternative to medical treatment with single-dose systemic MTX. WHAT IS KNOWN AND WHAT THIS PAPER ADDS: MTX is often used in asymptomatic women with an ectopic pregnancy or a PUL with low and plateauing serum hCG concentrations. These pregnancies may be self-limiting and watchful waiting is suggested as an alternative, but evidence from RCTs is lacking. The results of this RCT show that expectant management is an alternative to treatment with systemic MTX in a single-dose regimen in these women. STUDY DESIGN, SIZE, DURATION: A multicentre RCT women were assigned to systemic MTX (single dose) treatment or expectant management, using a web-based randomization program, block randomization with stratification for hospital and serum hCG concentration (<1000 versus 1000-2000 IU/l). The primary outcome measure was an uneventful decline of serum hCG to an undetectable level (<2 IU/l) by the initial intervention strategy. Secondary outcome measures included additional treatment, side effects and serum hCG clearance time. PARTICIPANTS, SETTING, METHODS: From April 2007 to January 2012, we performed a multicentre study in The Netherlands. All haemodynamically stable women >18 years old with both an ectopic pregnancy visible on transvaginal sonography and a plateauing serum hCG concentration <1500 IU/l or with a PUL and a plateauing serum hCG concentration <2000 IU/l were eligible for the trial. MAIN RESULTS: We included 73 women of whom 41 were allocated to single-dose MTX and 32 to expectant management. There was no difference in primary treatment success rate of single-dose MTX versus expectant management, 31/41 (76%) and 19/32 (59%), respectively [relative risk (RR) 1.3 95% confidence interval (CI) 0.9-1.8]. In nine women (22%), additional MTX injections were needed, compared with nine women (28%) in whom systemic MTX was administered after initial expectant management (RR 0.8; 95% CI 0.4-1.7). One woman (2%) from the MTX group underwent surgery compared with four women (13%) in the expectant management group (RR 0.2; 95% CI 0.02-1.7), all after experiencing abdominal pain within the first week of follow-up. In the MTX group, nine women reported side effects versus none in the expectant management group. No serious adverse events were reported. Single-dose systemic MTX does not have a larger treatment effect compared with expectant management in women with an ectopic pregnancy or a PUL and low and plateauing serum hCG concentrations. WIDER IMPLICATIONS OF THE FINDINGS: Sixty percent of women after expectant management had an uneventful clinical course with steadily declining serum hCG levels without any intervention, which means that MTX, a potentially harmful drug, can be withheld in these women. BIAS, LIMITATION AND GENERALISABILITY: A limitation of this RCT is that it was an open (not placebo controlled) trial. Nevertheless, introduction of bias was probably limited by the strict criteria to be fulfilled for treatment with MTX. STUDY FUNDING: This trial is supported by a grant of the Netherlands Organization for Health Research and Development (ZonMw Clinical fellow grant 90700154). TRIAL REGISTRATION: ISRCTN 48210491.

Particulate optical scattering coefficients along an Atlantic Meridional Transect.

The particulate optical backscattering coefficient (bbp) is a fundamental optical property that allows monitoring of marine suspended particles both in situ and from space. Backscattering measurements in the open ocean are still scarce, however, especially in oligotrophic regions. Consequently, uncertainties remain in bbp parameterizations as well as in satellite estimates of bbp. In an effort to reduce these uncertainties, we present and analyze a dataset collected in surface waters during the 19th Atlantic Meridional Transect. Results show that the relationship between particulate beam-attenuation coefficient (cp) and chlorophyll-a concentration was consistent with published bio-optical models. In contrast, the particulate backscattering per unit of chlorophyll-a and per unit of cp were higher than in previous studies employing the same sampling methodology. These anomalies could be due to a bias smaller than the current uncertainties in bbp. If that was the case, then the AMT19 dataset would confirm that bbp:cp is remarkably constant over the surface open ocean. A second-order decoupling between bbp and cp was, however, evident in the spectral slopes of these coefficients, as well as during diel cycles. Overall, these results emphasize the current difficulties in obtaining accurate bbp measurements in the oligotrophic ocean and suggest that, to first order, bbp and cp are coupled in the surface open ocean, but they are also affected by other geographical and temporal variations.

Plankton and particle size and packaging: from determining optical properties to driving the biological pump.

Understanding pelagic ecology and quantifying energy fluxes through the trophic web and from the surface to the deep ocean requires the ability to detect and identify all organisms and particles in situ and in a synoptic manner. An idealized sensor should observe both the very small living or dead particles such as picoplankton and detritus, respectively, and the large particles such as aggregates and meso- to macroplankton. Such an instrument would reveal an astonishing amount and diversity of living and nonliving particles present in a parcel of water. Unfortunately such sensors do not exist. However, complex interactions constrain the space, temporal, and size distributions of these objects in such ways that general rules can be inferred from the measurement of their optical properties. Recent technological developments allow for the in situ measurement of the optical properties and size distributions of particles and plankton in a way such that synoptic surveys are possible. This review deals with particle and plankton size distributions (PSDs) as well as how particles' geometry and nature affect their optical properties. Finally, we propose the integration of the PSD into size-structured mathematical models of biogeochemical fluxes.

Gonadotropins and female sex steroid hormones in cyst fluid and serum from patients with ovarian tumors.

The objective of the present study was to determine the concentrations of LH, FSH, 17beta-estradiol and progesterone in ovarian cyst fluid and serum from patients with benign and malignant ovarian tumors and to assess the correlation of the gonadotropin and female sex steroid hormone concentrations with menopausal and tumor status. Ovarian cyst fluid and blood samples were prospectively collected from 103 patients with ovarian tumors. Seventy-four of the patients had benign ovarian tumors while 29 patients had malignant ovarian tumors. Malignant ovarian tumors showed significantly higher LH and FSH cyst fluid concentrations compared to concentrations from patients with benign tumors. Within the malignant subset, LH and FSH concentrations correlated with increasing FIGO stage and grade. Furthermore, LH and FSH cyst fluid concentrations showed strong correlations (r > 0.62) with serum concentrations in case of malignant tumors, especially in postmenopausal women, but not in case of benign tumors. The highest gonadotropin concentrations were observed in cyst fluid from malignant ovarian tumors. The most probable explanation for this is an increased vascular permeability within the cysts. Supportive evidence for such an increased vascular permeability is our previous finding of significantly higher VEGF concentrations in cyst fluid from malignant ovarian tumors. The possibility of ectopic production of LH and FSH by malignant ovarian tissue cannot completely be ruled out.

Spectral variability of the particulate backscattering ratio.

The spectral dependency of the particulate backscattering ratio is relevant in the fields of ocean color inversion, light field modeling, and inferring particle properties from optical measurements. Aside from theoretical predictions for spherical, homogeneous particles, we have very limited knowledge of the actual in situ spectral variability of the particulate backscattering ratio. This work presents results from five research cruises that were conducted over a three-year period. Water column profiles of physical and optical properties were conducted across diverse aquatic environments that offered a wide range of particle populations. The main objective of this research was to examine the behavior of the spectral particulate backscattering ratio in situ, both in terms of its absolute magnitude and its variability across visible wavelengths, using over nine thousand 1-meter binned data points for each of five wavelengths of the spectral particulate backscattering ratio. Our analysis reveals no spectral dependence of the particulate backscattering ratio within our measurement certainty, and a geometric mean value of 0.013 for this dataset. This is lower than the commonly used value of 0.0183 from Petzold's integrated volume scattering data. Within the first optical depth of the water column, the mean particulate backscattering ratio was 0.010.

Pregnancy after radical trachelectomy: a real option?

INTRODUCTION: Radical trachelectomy is a surgical procedure for early-stage cervical carcinoma with preservation of the childbearing capacity. The current article presents a review of studies describing the results and complications of pregnancies after this procedure. METHODS: Sixteen studies were included (involving 355 radical trachelectomy procedures). Studies were reviewed for the number of patients included, the number attempting to conceive, the number who achieved pregnancy, the number of pregnancies achieved, the numbers of first and second trimester losses, and when delivery occurred in the third trimester. RESULTS: One hundred and fifty-three patients attempted to conceive during the follow-up period (range 1-144 months), this accounts for 43% of the patients that underwent radical trachelectomy. 70% of the patients attempting to conceive succeeded once or more than once. 161 pregnancies were described, finally resulting in 49% term deliveries. In about 15% of the patients who tried to conceive, cervical stenosis was found and resulted in menstrual disorders or fertility problems. Surgical dilatation resolved this problem in most cases but had to be repeated. Complications during pregnancy involved second trimester loss (13/161) and premature (< or =36 weeks AD) delivery (33/161). CONCLUSIONS: Pregnancy after radical trachelectomy is feasible. For various reasons, a number of patients (57%) did not try to get pregnant after the surgical procedure. The majority of the patients who tried to conceive after radical trachelectomy succeeded once or more than once (70%). Patients attempting to conceive need to be informed of the complications and risk factors, in particular, second trimester loss and premature delivery caused by premature rupture of membranes. Once pregnant, patients need to be carefully followed for cervical incompetence and other risk factors for premature rupture of membranes.

Clinical value of components of the plasminogen activation system in ovarian cyst fluid.

BACKGROUND: The aim of this study was to analyze the concentrations of different components of the plasminogen activation system in cyst fluid from malignant, borderline and benign ovarian tumors and to compare these results with clinicopathological characteristics (FIGO staging, histological grading, residual tumor, ascites, tumor recurrence and disease-free survival). MATERIALS AND METHODS: One hundred and seven cyst fluid samples were enrolled from 25 malignant, 12 borderline and 70 benign ovarian tumors. Determination of uPA, tPA, PAI-1, PAI-2, uPA:PAI-1 complex and tPA:PAI-1 complex was performed by specific double determinant ELISAs based on the concept described previously by Grebenschikov et al. With these ELISAs both complexes of the activators (uPA, tPA) with their inhibitor (PAI-1) can be measured as a separate component. RESULTS: Significant differences were found in median cyst fluid concentrations of uPA, PAI-1, uPA:PAI-1 and tPA:PAI-1 from malignant, borderline and benign ovarian tumors, with the highest levels in malignant ovarian tumors. Cystic endometriosis seems to be a special entity within the benign subclass. To achieve better discrimination between malignant and benign cases we introduced a new malignancy index: ([uPA:PAI-1]+[tPA:PAI-1])x [PAI-1]. The area under a Receiver Operating Characteristic (ROC) curve amounted to 0.80. Significantly higher concentrations were found in FIGO stages II-III-IV compared with stage I for uPA (p<0.05), tPA (p<0.05), uPA:PAI-1 (p<0.01) and tPA:PAI-1 (p<0.05). CONCLUSION: Concentrations of plasminogen activation system markers in cyst fluid from ovarian tumors are related to histological subtype. The most significant components are uPA, PAI-1 and the complexes uPA:PAI-1, tPA:PAI-1. The prognostic value of the components seems to be limited but might be important in detecting high-risk borderline or low stage patients.

Post-radiotherapy contrast enhancement changes in fast dynamic MRI of cervical carcinoma.

This pilot study determines fast dynamic gadolinium enhanced MRI contrast enhancement parameters (onset of enhancement and time to peak enhancement) before and after radiotherapy in 10 cervical carcinoma patients. Before radiotherapy, onset of enhancement and time to peak enhancement were early, with a median of 4.5 and 5.2 seconds, respectively. High-grade tumors showed early enhancement, compared with low-grade. After radiotherapy, contrast enhancement patterns differed. In survivors, onset of enhancement after radiotherapy was later than before radiotherapy. In non-survivors, onset of enhancement after radiotherapy was still early. The median difference in onset of enhancement before and after radiotherapy in survivors and non-survivors was an increase of 3.2 and a decrease of 1.1 seconds, respectively. Early onset of enhancement after radiotherapy was a better predictor for survival than a high-signal intensity zone on post radiotherapy unenhanced T1/T2-weighted MRI. It is concluded that enhancement parameters from fast dynamic Gd-enhanced MR images can provide additional functional information with regard to tumor vascularization, and may have prognostic significance. It complements clinical examination and unenhanced MRI in determining the effectiveness of radiotherapy treatment in cervical carcinoma. Future studies will focus on the clinical utility and improvements of the estimation of contrast-enhanced parameters with this new technique.

Vascular endothelial growth factor in ovarian cyst fluid.

BACKGROUND: The purpose of the current study was to determine vascular endothelial growth factor (VEGF) concentrations in cyst fluid from malignant, borderline, and benign ovarian tumors, and to correlate these data with preoperative serum VEGF concentrations and clinicopathologic characteristics. METHODS: One hundred seven ovarian cysts were removed and punctured for cyst fluid collection. Histologic diagnosis revealed 25 malignant, 12 borderline, and 70 benign ovarian tumors. The VEGF concentrations of all the cyst fluid specimens as well as in 37 preoperatively collected serum samples were determined by making use of a sandwich type double determinant enzyme linked immunoadsorbent assay based on a combination of 4 polyclonal antibodies. RESULTS: Statistically significantly higher VEGF concentrations were found in cyst fluid from malignant (median, 21.5 microg/L) compared with borderline (median, 3.2 microg/L; P = 0.01) or benign tumors (median, 1.3 microg/L; P < 0.0001). Preoperative serum VEGF concentrations were significantly higher in patients with malignant (median, 0.63 microg/L; range, 0.016-17.7 microg/L) compared with nonmalignant tumors (median, 0.28 microg/L; range, 0.016-0.89 microg/L; P = 0.008). A significant correlation of preoperative serum VEGF was found with VEGF cyst fluid concentrations (r = 0.38; P = 0.02). Significantly higher VEGF cyst fluid concentrations were found in serous malignant (median, 31.9 microg/L) compared with mucinous malignant tumors (median, 4.7 microg/L; P = 0.004). Not significant, though higher median VEGF cyst fluid concentrations were found in advanced International Federation of Gynecology and Obstetrics (FIGO) Stage II, III, and IV, histologic Grade 2 and 3, patients with residual tumor greater than 2 cm, with malignant cells in ascites or peritoneal washings, or with recurrent disease, as compared with FIGO Stage I, histologic grade 1, patients with less than or equal to 2-cm residual tumor, without malignant cells in ascites/peritoneal washings, or without recurrent disease, respectively. CONCLUSIONS: It has become clear from the increased study sample that ovarian tumors of different histologic etiology vary in VEGF cyst fluid concentrations, with the highest VEGF cyst fluid concentrations in malignant tumors. The prognostic significance of VEGF cyst fluid concentrations in advanced FIGO stage seems to be of limited value but may be important in the selection of high risk FIGO Stage I and borderline types. Data from this study indicate a possible role for VEGF as a serum tumor marker.

Influence of surface waves on measured and modeled irradiance profiles.

Classical radiative transfer programs are based on the plane-parallel assumption. We show that the Gershun equation is valid if the irradiance is averaged over a sufficiently large area. We show that the equation is invalid for horizontal areas of the order of tens of meters in which horizontal gradients of irradiance in the presence of waves are much larger than vertical gradients. We calculate the distribution of irradiance beneath modeled two-dimensional surface waves. We show that many of the features typically observed in irradiance profiles can be explained by use of such models. We derive a method for determination of the diffuse attenuation coefficient that is based on the upward integration of the irradiance field beneath waves, starting at a depth at which the irradiance profile is affected only weakly by waves.

Shape of the particulate beam attenuation spectrum and its inversion to obtain the shape of the particulate size distribution.

The link between the spectral shape of the beam attenuation spectrum and the shape of the particle size distribution (PSD) of oceanic particles is revisited to evaluate the extent to which one can be predicted from the other. Assuming a hyperbolic (power-law) PSD, N(D) ? D(-xi), past studies have found for an infinite distribution of nonabsorbing spheres with a constant index of refraction that the attenuation spectrum is hyperbolic and that the attenuation spectral slope gamma is related to the PSD slope xi by xi = gamma + 3. Here we add a correction to this model because of the finite size of the biggest particle in the population. This inversion model is given by xi = gamma + 3 - 0.5 exp(-6gamma). In most oceanic observations xi > 3, and the deviation between these two models is negligible. To test the robustness of this inversion, we perturbed its assumptions by allowing for populations of particles that are nonspherical, or absorbing, or with an index of refraction that changes with wavelength. We found the model to provide a good fit for the range of parameters most often encountered in the ocean. In addition, we found that the particulate attenuation spectrum, c(p)(lambda), is well described by a hyperbolic relation to the wavelength c(p) ? lambda(-gamma) throughout the range of the investigated parameters, even when the inversion model does not apply. This implies that knowledge of the particulate attenuation at two visible wavelengths could provide, to a high degree of accuracy, the particulate attenuation at other wavelengths in the visible spectrum.

Relationship of light scattering at an angle in the backward direction to the backscattering coefficient.

We revisit the problem of computing the backscattering coefficient based on the measurement of scattering at one angle in the back direction. Our approach uses theory and new observations of the volume scattering function (VSF) to evaluate the choice of angle used to estimate b(b). We add to previous studies by explicitly treating the molecular backscattering of water (b(bw)) and its contribution to the VSF shape and to b(b). We find that there are two reasons for the tight correlation between observed scattering near 120 degrees and the backscattering coefficient reported by Oishi [Appl. Opt. 29, 4658, (1990)], namely, that (1) the shape of the VSF of particles (normalized to the backscattering) does not vary much near that angle for particle assemblages of differing optical properties and size, and (2) the ratio of the VSF to the backscattering is not sensitive to the contribution by water near this angle. We provide a method to correct for the water contribution to backscattering when single-angle measurements are used in the back direction (for angles spanning from near 90 degrees to 160 degrees ) that should provide improved estimates of the backscattering coefficient.

The influence of coherent waves on the remotely sensed reflectance.

Oceanic waves have been found to contribute enhanced back-scattering in the direction of the illumination source in studies that assumed the ocean surface to be a random sum of waves. Here we investigate enhanced back-scattering by coherent capillary-gravity wave trains that co-exist near the crests of short gravity waves in the ocean. We find that the enhanced back-scattering effect is intensified relative to that of a random surface and that the effect is observed at larger angles. This effect may not only affect active sensors such as lidar, which have a viewing angle close to that of the source but possibly passive sensors as well. This effect is likely to result in biases when attempting closure between radiative transfer models that do not include realistic representation of the ocean surface and observed water leaving radiance.