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Author

Sherwin Ladner

Other affiliations: Stennis Space Center
Bio: Sherwin Ladner is an academic researcher from United States Naval Research Laboratory. The author has contributed to research in topics: Ocean color & Physical oceanography. The author has an hindex of 10, co-authored 50 publications receiving 419 citations. Previous affiliations of Sherwin Ladner include Stennis Space Center.


Papers
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Journal ArticleDOI
TL;DR: The results of a study of optical scattering and backscattering of particulates for three coastal sites that represent a wide range of optical properties that are found in U.S. near-shore waters can be well approximated by a power-law function of wavelength.
Abstract: We present the results of a study of optical scattering and backscattering of particulates for three coastal sites that represent a wide range of optical properties that are found in U.S. near-shore waters. The 6000 scattering and backscattering spectra collected for this study can be well approximated by a power-law function of wavelength. The power-law exponent for particulate scattering changes dramatically from site to site (and within each site) compared with particulate backscattering where all the spectra, except possibly the very clearest waters, cluster around a single wavelength power-law exponent of -0.94. The particulate backscattering-to-scattering ratio (the backscattering ratio) displays a wide range in wavelength dependence. This result is not consistent with scattering models that describe the bulk composition of water as a uniform mix of homogeneous spherical particles with a Junge-like power-law distribution over all particle sizes. Simultaneous particulate organic matter (POM) and particulate inorganic matter (PIM) measurements are available for some of our optical measurements, and site-averaged POM and PIM mass-specific cross sections for scattering and backscattering can be derived. Cross sections for organic and inorganic material differ at each site, and the relative contribution of organic and inorganic material to scattering and backscattering depends differently at each site on the relative amount of material that is present.

126 citations

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TL;DR: In this paper, satellite-derived bio-optical properties (chlorophyll a or absorption due to phytoplankton) were used to improve the model predictions in a coastal ocean on time scales of 1-5 days.
Abstract: [1] Data assimilation experiments with the coupled physical, bio-optical model of Monterey Bay are presented. The objective of this study is to investigate whether the assimilation of satellite-derived bio-optical properties can improve the model predictions (phytoplankton population, chlorophyll) in a coastal ocean on time scales of 1–5 days. The Monterey Bay model consists of a physical model based on the Navy Coastal Ocean Model and a biochemical model which includes three nutrients, two phytoplankton groups (diatoms and small phytoplankton), two groups of zooplankton grazers, and two detrital pools. The Navy Coupled Ocean Data Assimilation system is used for the assimilation of physical observations. For the assimilation of bio-optical observations, we used reduced-order Kalman filter with a stationary forecast error covariance. The forecast error covariance is specified in the subspace of the multivariate (bio-optical, physical) empirical orthogonal functions estimated from a monthlong model run. With the assimilation of satellite-derived bio-optical properties (chlorophyll a or absorption due to phytoplankton), the model was able to reproduce intensity and tendencies in subsurface chlorophyll distributions observed at water sample locations in the Monterey Bay, CA. Data assimilation also improved agreement between the observed and model-predicted ratios between diatoms and small phytoplankton populations. Model runs with or without assimilation of satellite-derived bio-optical observations show underestimated values of nitrate as compared to the water sample observations. We found that an instantaneous update of nitrate based on statistical relations between temperature and nitrate corrected the model underestimation of the nitrate fields during the multivariate update.

37 citations

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TL;DR: The regional and monthly intensity of photosynthetically available radiation (PAR) (350-700 nm) just below the sea surface (EdPAR−) for the Arabian Sea is determined from solar irradiance models and 7 years of satellite data (1979-1985) as discussed by the authors.
Abstract: The regional and monthly intensity of photosynthetically available radiation (PAR) (350–700 nm) just below the sea surface (EdPAR−) for the Arabian Sea is determined from solar irradiance models and 7 years of satellite data (1979–1985). Model results of high spatial resolution (18 km) PAR distribution computed from actual monthly measurements (aerosols, cloud cover, and ozone) displayed small-scale patchiness that is not observed in PAR climatology models. Two elevated PAR periods are observed each year, as opposed to a single elevated period per year observed in the North Atlantic during the summer. When the biannual cycle for each of the 7 years is compared with the 7-year average, interannual changes in intensity and time are observed. Additionally, the PAR cycle is found to vary regionally within the Arabian Sea. The bimodal PAR distribution shows elevated peaks in May and October and minima in December (corresponding to the winter equinox) and July. The second minima occurs at the onset of the southwest monsoon, apparently in response to increased cloud cover and aerosols associated with the monsoon. This summer minima varied latitudinally. It originates in the southern regions (0°–10° latitude) in April and migrates north as the influence of the southwest monsoon moves northward, reaching the northern Oman coast (20° latitude) in August. Additionally, the summer minima is less pronounced as the southwest monsoon moves northward. Maximum PAR intensity is observed in early spring (preceding the minima), originating in the southern Arabian Sea and extending northward into the central Arabian Sea. The timing of the northward movement of this spring maximum is slightly different each year. The net yearly PAR intensity for each of the 7 years appears to remain approximately the same, despite the interannual variability in the cycle and regional variability. The timing and location of PAR cycles are important since they must be coupled with nutrient availability to understand biological cycles. We determined that for the Arabian Sea, PAR cycles determined by climatology may be inadequate to define the submarine light field and that high-resolution PAR cycles are needed to resolve realistic bio-optical and nutrient cycles.

26 citations

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TL;DR: In this article, a new approach for spectral sharpening is developed by utilizing the spatial covariance of the spectral bands for sharpening the M bands (412, 443, 486, 551, 671) with the I-1 band (645,nm; 375-m resolution).

18 citations

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TL;DR: In this paper, a high-resolution coupled atmosphere-ocean-wave model with comprehensive physics is used to model the weather, ocean circulation, and wave field in the Bay of Bengal.
Abstract: Large freshwater fluxes into the Bay of Bengal by rainfall and river discharges result in strong salinity fronts in the bay. In this study, a high-resolution coupled atmosphere-ocean-wave model with comprehensive physics is used to model the weather, ocean circulation, and wave field in the Bay of Bengal. Our objective is to explore the submesoscale activity that occurs in a realistic coupled model that resolves mesoscales and allows part of the submesoscale field. Horizontal resolution in the atmosphere varies from 2 to 6 km and is 13 km for surface waves, while the ocean model is submesoscale permitting with resolutions as high as 1.5 km and a vertical resolution of 0.5 m in the upper 10 m. In this paper, three different cases of oceanic submesoscale features are discussed. In the first case, heavy rainfall and intense downdrafts produced by atmospheric convection are found to force submesoscale currents, temperature, and salinity anomalies in the oceanic mixed layer and impact the mesoscale flow. In a second case, strong solitary-like waves are generated by semidiurnal tides in the Andaman Sea and interact with mesoscale flows and fronts and affect submesoscale features generated along fronts. A third source of submesoscale variability is found further north in the Bay of Bengal where river outflows help maintain strong salinity gradients throughout the year. For that case, a comparison with satellite observations of sea surface height anomalies, sea surface temperature, and chlorophyll shows that the model captures the observed mesoscale eddy features of the flow field, but in addition, submesoscale upwelling and downwelling patterns associated with ageostrophic secondary circulations along density fronts are also captured by the model.

15 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, a TSM algorithm is developed for turbid waters, suitable for any ocean colour sensor including MERIS, MODIS and SeaWiFS. But it does not consider the effect of bidirectional effects.

498 citations

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TL;DR: In this paper, a semi-empirical single-band turbidity retrieval algorithm using the near infrared (NIR) band at 859 nm in highly turbid waters is assessed.

290 citations

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TL;DR: In this paper, the authors present an overview of the dynamical response to seasonal monsoonal forcing and the characteristics of the physical environment that fundamentally drive regional biogeochemical variability.

210 citations

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TL;DR: In this paper, the bloom variability patterns of phytoplankton in the Indian Ocean were examined using a wide field-of-view sensor (WiFS) and an ocean general circulation model (OGCM).
Abstract: A climatology of Sea-viewing Wide Field-of-View Sensor (SeaWiFS) chlorophyll data over the Indian Ocean is used to examine the bloom variability patterns, identifying spatio-temporal contrasts in bloom appearance and intensity and relating them to the variability of the physical environment. The near-surface ocean dynamics is assessed using an ocean general circulation model (OGCM). It is found that over a large part of the basin, the seasonal cycle of phytoplankton is characterized by two consecutive blooms, one during the summer monsoon, and the other during the winter monsoon. Each bloom is described by means of two parameters, the timing of the bloom onset and the cumulated increase in chlorophyll during the bloom. This yields a regional image of the influence of the two monsoons on phytoplankton, with distinct regions emerging in summer and in winter. By comparing the bloom patterns with dynamical features derived from the OGCM (horizontal and vertical velocities and mixed-layer depth), it is shown that the regional structure of the blooms is intimately linked with the horizontal and vertical circulations forced by the monsoons. Moreover, this comparison permits the assessment of some of the physical mechanisms that drive the bloom patterns, and points out the regions where these mechanisms need to be further investigated. A new outcome of this study is that in many distinct areas, time shifts of 1-2 months are witnessed in the timing of the bloom onsets in adjoining regions. These time shifts are rationalized in terms of horizontal advection and Rossby wave propagation.

208 citations

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TL;DR: In this article, the authors analyzed the relationship between the concentration of suspended particles represented by dry mass and optical properties, including particle beam attenuation, side scattering, and backscattering, obtained from an intensive sampling program in coastal and offshore waters around Europe and French Guyana.
Abstract: This study analyzes relationships between concentration of suspended particles represented by dry mass, [SPM], or area, [AC], and optical properties including particulate beam attenuation (cp), side scattering (bs), and backscattering (bbp), obtained from an intensive sampling program in coastal and offshore waters around Europe and French Guyana. First-order optical properties are driven by particle concentration with best predictions of [SPM] by bbp and bs, and of [AC] by cp. Second-order variability is investigated with respect to particle size, apparent density (dry weight-to-wet-volume ratio), and composition. Overall, the mass-specific particulate backscattering coefficient, b m (5bbp:[SPM]), is relatively well constrained, with variability of a factor of 3–4. This coefficient is well correlated with particle composition, with inorganic particles having values about three times greater (b m5 0.012 m2 g21) than organic particles (b m5 0.005 m 2 g21). The mass-specific particulate attenuation coefficient, c m (5cp:[SPM]), on the other hand, varies over one order of magnitude and is strongly driven (77% of the variability explained) by particle apparent density. In this data set particle size does not affect c m and affects b m only weakly in clear (case 1) waters, despite size variations over one order of magnitude. A significant fraction (40–60% )o f the variability inb m remains unexplained. Possible causes are the limitation of the measured size distributions to the 2–302-mm range and effects of particle shape and internal structure that affect bbp more than cp and were not accounted for.

174 citations