Spectral Slope Parameter Research Articles

The effect of surface irradiance on the absorption spectrum of chromophoric dissolved organic matter in the global ocean

The cycling pathways of chromophoric dissolved organic matter (CDOM) within marine systems must be constrained to better assess the impact of CDOM on surface ocean photochemistry and remote sensing of ocean color. Photobleaching, the loss of absorption by CDOM due to light exposure, is the primary sink for marine CDOM. Herein the susceptibility of CDOM to photobleaching by sea surface-level solar radiation was examined in 15 samples collected from wide-ranging open ocean regimes. Samples from the Pacific, Atlantic, Indian and Southern Oceans were irradiated over several days with full-spectrum light under a solar simulator at in situ temperature in order to measure photobleaching rate and derive an empirical matrix, εsurf (m−1μEin−1), which quantifies the effect of surface irradiance on the spectral absorption of CDOM. Irradiation responses among the ocean samples were similar within the ultraviolet (UV) region of the spectrum spanning 300–360nm, generally exhibiting a decrease in the CDOM absorption coefficient (m−1) and concomitant increase in the CDOM spectral slope parameter, S (nm−1). However, an unexpected irradiation-induced increase in CDOM absorption between approximately 360 and 500nm was observed for samples from high-nutrient low-chlorophyll (HNLC) environments. This finding was linked to the presence of dissolved nitrate and may explain discrepancies in action spectra for dimethylsulfide (DMS) photobleaching observed between the Equatorial Pacific and Subtropical North Atlantic Oceans. The nitrate-to-phosphate ratio explained 27–70% of observed variability in εsurf at observation wavelengths of 330–440nm, while the initial spectral slope of the samples explained up to 52% of variability in εsurf at observation wavelengths of 310–330nm. These results suggest that the biogeochemical and solar exposure history of the water column, each of which influence the chemical character and thus the spectral quality of CDOM and its photoreactivity, are the main factors regulating the susceptibility of CDOM to photodegradation in the surface ocean. The εsurf parameter reported herein may be applied to remote sensing retrievals of CDOM to estimate photobleaching at the surface on regional to global scales.

Horizontal and vertical distributions of colored dissolved organic matter during the Southern Ocean Gas Exchange Experiment

[1] Field and remote sensing measurements of colored dissolved organic matter (CDOM) were acquired in the Southern Ocean during the 2008 Gas Exchange experiment. Values of CDOM absorption coefficient at 440 nm (ag440) ranged from ∼0.02 to ∼0.06 m−1. In general, CDOM was higher in the region sampled during this study than in other regions of the Southern Ocean. CDOM showed an inverse correlation with salinity, and the spectral slope parameter S varied directly with salinity. These relationships, water circulation patterns, and characteristics of South Georgia Island suggested that runoff was a source of CDOM in the study site. Analysis of seasonal variability of ag440 using ocean color imagery of areas away from the effect of South Georgia Island showed seasonal fluctuations between ∼0.02 to ∼0.03 m−1. CDOM production models showed that in situ production could also account for seasonal changes in CDOM.

Controls on dissolved organic carbon composition and export from rice-dominated systems

Rice field outflow can contain high con- centrations of dissolved organic carbon (DOC), which plays a crucial role in drinking water quality and aquatic ecosystem processes. This study examined the relationship between potential determining factors (i.e. rice area, outflow, drainwater reuse, soil proper- ties, and time, measured as the day in the growing season) and the concentration and composition of DOC exported from 11 rice-dominated subwatersheds. Samples were collected from subwatershed inflow and outflow every 1-2 weeks from May through Septem- ber 2008 and analyzed for DOC concentration, trihalomethane formation potential (THMFP), and also specific ultraviolet absorbance (SUVA254) and the spectral slope parameter (S), which are indicators of DOC composition. Concentrations of DOC across all subwatersheds and sampling dates ranged from 1.56 to 14.43 mg L -1 (mean = 4.32 mg L -1 ). Linear mixed effects (LME) analysis indicated that DOC concentra- tion decreased over time, and that THMFP, and DOC and THM flux, decreased over time, but increased with outflow. LME analysis of the SUVA254 and S param- eters indicated that the fraction of aromatic DOC moieties increased with time, outflow, and reuse. Additionally, apparent peaks in DOC concentrations, THMFP, and SUVA254 coincided with the onsets of flooding and draining. Lastly, subwatersheds with outflow less than approximately 4,700 m 3 ha -1 behaved as sinks of DOC. Our findings suggest that water management factors such as outflow, reuse, and discrete irrigation events, all of which vary over the course of the growing season, were the dominant determinants of DOC concentration and composition.

Modeling overall voice quality with a small set of acoustic parameters.

Despite the great need for valid measures of voice quality, we are still unable to adequately quantify what a person sounds like. Drawing on recent theoretical and experimental work, we propose assessment of overall quality as a whole, rather than using individual rating scales. This paper describes experiments evaluating a psychoacoustic model that includes vocal tract formant frequencies and bandwidths, four source spectral slope parameters (H1–H2, the slope of the harmonic spectrum from 2–4 kHz and from 450–452 kHz, and the overall spectral slope from H2 to the highest harmonic), the noise-to-harmonics ratio, F0, and slow variability in F0 and amplitude (tremor). To assess the adequacy of this model, we will copy-synthesize 30 pathological voices while manipulating only these parameters. To the extent that listeners judge that the natural and synthetic tokens match exactly, the psychoacoustic model will be considered valid. Discussion will include analysis of mismatches to determine what parameters should be added to or subtracted from the model and its application for use in evaluation of disordered voice quality and modes of phonation. [Work supported by NIH.]

Exudation and decomposition of chromophoric dissolved organic matter (CDOM) from some temperate macroalgae

The quantity of chromophoric or coloured dissolved organic matter (CDOM) released by eleven species of intertidal and sub-tidal macroalgae commonly found on UK shores was investigated. The subsequent breakdown of CDOM was also measured by exposing collected CDOM samples to light and dark conditions for over two weeks. CDOM absorption properties were compared at a fixed wavelength of 440 nm and across two integrated wave - bands; UV-A (400–315 nm) and UV-B (315–280 nm). Absorption spectra of macroalgal CDOM samples were typically characterized by peaks and shoulders in the UV bands, features which were species specific. The spectral slope, derived using the log-linear method, proved to be very specific to the species and to the effect of light. Slope measurements ranged from 0.010 to 0.027 nm −1, in the range of normal seawater values. Significantly more CDOM was produced by algae which were illuminated, providing evidence for a light driven exudation mechanism. Averaged across all species, exudation in the dark accounted for 63.7% of that in the light in the UV-B band. Interspecific differences in exudation rate encompassed an order of magnitude, with the highest absorption measurements attributable to brown algae. However, some brown algae produced considerably less CDOM (e.g. Pelvetia canaliculata), which were more comparable to the green and red species. Over an exposure time of 16 days, significant photochemical degradation of CDOM was observed using a natural summer sunlight regime, showing that natural solar radiation could be an important removal mechanism for newly produced algal CDOM. Though the most obvious effect was a decrease in absorption, photo-bleaching also caused a significant increase in the spectral slope parameter of 0.004 nm −1.

Discriminatory classification of natural and anthropogenic waters in two U.K. estuaries

The ability to distinguish water inputs from both natural and anthropogenic sources was investigated in the complex environment of an urban estuary (Tyne) and a relatively pristine estuary (Tweed). We used a data set from a total of 11 estuarine transects, comprising measurements of bulk dissolved organic matter (dissolved organic carbon and nitrogen), dissolved nitrogen (total dissolved nitrogen, ammonium, nitrate+nitrite and dissolved organic nitrogen), optical absorbance measurements (a350, S290-350) and fluorescence excitation emission matrix measurements (fluorophores A, H, B and T intensity and A and H emission wavelength maxima). In order to investigate trends within the numerous parameters measured, multivariate statistics were employed. Principal components analyses showed 63.4% of the variability in the total data set can be explained by two sets of components and 74.9% of the variability by the spectrophotometric measurements alone. In both analyses the first component correlated to the mixing of terrestrial and marine waters and the second component was correlated to sources of pollution such as domestic sewage. Within the data set, river flow and terrestrially derived DOM were significantly correlated, and situations with high river input showed an increase in terrestrial signature in the estuary. Discriminant analyses were also carried out and indicated that 59.8% (total data set) and 53.3% (solely spectrophotometric data) of the samples can be correctly classified into their respective groups (water categories) assigned on the basis of salinity and sampling location. Overall the results clearly show the potential of spectrophotometric techniques to discriminate distinct water categories with different DOM characteristics. In particular, measurement of the fluorophore H emission maxima, the spectral slope parameter, S290-350, and fluorophores T and B intensity enabled discrimination of DOM from riverine, estuarine, marine, and sewage affected water categories. The results presented here indicate the ability of spectrophotometric data alone to distinguish between marine, anthropogenic and terrestrial DOM and distinguish terrestrial DOM from different catchments (Tyne vs. Tweed). With current advances in the in-situ deployment of absorbance and fluorescence spectroscopy it is anticipated that multivariate statistics will gain importance as a cost effective, powerful and diagnostic approach to assessing the distributions of water types and their associated DOM characteristics and fluxes at the land-ocean interface.

Spatial and seasonal distribution of chromophoric dissolved organic matter and dissolved organic carbon in the Middle Atlantic Bight

Spatial and seasonal distributions of chromophoric dissolved organic matter (CDOM) absorption, fluorescence (excited at 355 nm; F n) and dissolved organic carbon (DOC) concentration in coastal waters of the Middle Atlantic Bight (MAB) were acquired. A linear relationship was observed between CDOM absorption at 355 nm [ a CDOM(355)] and F n on the shelf of the MAB ( a CDOM(355)≤1 m −1), but this relationship curved downward for higher a CDOM(355) and F n values in the Chesapeake Bay (CB) and the Delaware Bay (DB) source waters ( a CDOM(355)≥1 m −1), suggesting the presence of different end members with higher F n/ a CDOM(355) ratios, the occurrence of a photochemical/biological processing of the CDOM as it moves down the estuaries or the involvement of both of these processes. Strong evidence was acquired for the photobleaching of CDOM in the surface waters of the MAB during summertime stratification, as indicated by the highly nonlinear dependence of a CDOM(355) and F n on salinity in surface waters, the concomitant increase of the CDOM spectral slope parameter ( S) and the much lower ratio of a CDOM to DOC ( a CDOM/DOC) observed in surface waters. The a CDOM/DOC ratio decreased by over an order of magnitude with increasing salinity, owing primarily to two reasons: (1) the substantial photobleaching of CDOM in the surface waters of the shelf and (2) the very different content of CDOM and DOC in the freshwater and oceanic end members. These results indicate that CDOM represents only a small portion of the DOC pool in offshore waters and that the sources and sinks of CDOM and DOC are uncoupled despite the often-observed correlation between CDOM and DOC in the coastal environment.

Cluster Correlation in Mixed Models

We evaluate the dependence of the cluster correlation length, rc, on the mean intercluster separation, Dc, for three models with critical matter density, vanishing vacuum energy (Λ = 0), and COBE normalization: a tilted cold dark matter (tCDM) model (n = 0.8) and two blue mixed models with two light massive neutrinos, yielding Ωh = 0.26 and 0.14 (MDM1 and MDM2, respectively). All models approach the observational value of σ8 (and hence the observed cluster abundance) and are consistent with the observed abundance of damped Lyα systems. Mixed models have a motivation in recent results of neutrino physics; they also agree with the observed value of the ratio σ8/σ25, yielding the spectral slope parameter Γ, and nicely fit Las Campanas Redshift Survey (LCRS) reconstructed spectra. We use parallel AP3M simulations, performed in a wide box (of side 360 h-1 Mpc) and with high mass and distance resolution, enabling us to build artificial samples of clusters, whose total number and mass range allow us to cover the same Dc interval inspected through Automatic Plate Measuring Facility (APM) and Abell cluster clustering data. We find that the tCDM model performs substantially better than n = 1 critical density CDM models. Our main finding, however, is that mixed models provide a surprisingly good fit to cluster clustering data.

Characterisation and Simulation of the Multiscaling Properties of the Energy-Containing Scales of Horizontal Surface-Layer Winds

The multiscaling statistics of atmospheric surface-layer winds at low wavenumbers above farmland and in the lee of a mountain range were examined using a hot-wire and lightweight cup anemometer. It was found that the horizontal velocity spectra could be broken into high and low-wavenumber regimes according to the parameters given by this analysis. The low-wavenumber end of the spectrum possessed a spectral slope parameter that varied between values of 0.8 and 1.35 at the farmland site during the period of the experiment, and the high-wavenumber end – corresponding to the inertial range – possessed a spectral slope slightly greater than -5/3. The larger values for this parameter for the low-wavenumber end appeared to coincide with unstable conditions. In the lee of the mountain range, the low-wavenumber spectral slope parameter was larger still, at 1.45. The low-wavenumber signals over farmland were much less intermittent than inertial-range signals, but in the lee of the mountain range the intermittency increased. From this analysis, it was shown that the statistical properties of the recorded wind signal could be reproduced using a bounded random multiplicative cascade. The model was successfully used to simulate the wind velocity field directly, rather than simulating the energy dissipation field. Since the spectral slope parameter for low wavenumbers appeared to be a function of atmospheric stability, the method presented is a simple way of generating wind signals characteristic of a variety of atmospheric conditions.

Multitaper spectral estimation of power law processes

In many branches of science, particularly astronomy and geophysics, power spectra of the form f/sup -/spl beta//, where /spl beta/ is a positive power-law exponent, are common. This form of spectrum is characterized by a sharp increase in the spectral density as the frequency f decreases toward zero. A power spectrum analysis method that has proven very powerful wherever the spectrum of interest is detailed and/or varies rapidly with a large dynamic range is the multitaper method. With multitaper spectral estimation, a set of orthogonal tapers are applied to the time series, and the resulting direct spectral estimators ("eigenspectra") are averaged, thus, reducing the variance. One class of processes with spectra of the power-law type are fractionally differenced Gaussian processes that are stationary and can model certain types of long-range persistence. Spectral decay f/sup -/spl beta// can be modeled for 0</spl beta/<1. Estimation of the spectral slope parameter by regression on multitaper spectral ordinates is examined for this class of processes. It is shown that multitapering, or using sine or Slepian tapers, produces much better results than using the periodogram and is attractive compared with other competing methods. The technique is applied to a geophysical estimation problem.

F region meridional wind spectral behavior

Analyses of power spectral density slope and integrated power (energy) of upper thermospheric meridional wind for eight ionospheric stations in both hemispheres during a full year, have been performed. The observed spectral slope ranges between 1.2 and 3, depending on station location and epoch of the year, presenting levels and variability mostly related with geomagnetic latitude. However, the associated spectral energy seems to depend on geomagnetic latitude as well as on season at some latitudes, but in a different way from the spectral slope. Both parameters seem to be uncorrelated, suggesting that their evolution depends on different physical mechanisms. There is not significant correlation between the spectral slope and energy parameters with total meridional wind, indicating that they are associated with small‐scale phenomena rather than with total wind.

Intercalibration of 4He and 5Li nuclear thermometers for hot nuclei.

For hot nuclei with A\ensuremath{\simeq}120, a comparison is made between nuclear temperatures derived from spectral slope parameters for well-characterized equilibrated systems and those derived from state population ratios. When suitable account is taken of the deexcitation cascade, the two techniques lead to similar results, confirming the utility of the state ratio method. The general relationship between the measured quantities and the initial temperature for medium to heavy mass hot nuclei is discussed and a calibration of these is presented for measurements based on $^{4}\mathrm{He}$ and $^{5}\mathrm{Li}$ detection.

Damped reaction dynamics in 197Au + 208Pb collisions at 29 MeV/nucleon

Velocity and angular distributions of neutrons from the reaction 197Au + 208Pb at E A =29 MeV were measured in coincidence with charged reaction products. The neutron emission pattern is found to erolve smoothly with atomic number and energy of the coincident fragments, up to the highest degrees of energy dissipation observed. The velocity distribution of neutrons in coincidence with any type of fragment is essentially bimodal and can be understood in terms of sequential emission from fully accelerated primary projectile-like and target-like fragments. A relatively weak nonequilibrium neutron component is also observed. Neutron multiplicities and spectral slope parameters, as well as the deduced emitter velocities indicate consistently that, even for highly dissipative collisions associated with intermediate-mass fragments, the average damping of kinetic energy available in the entrance channel is incomplete.

Yellow substance in coastal and marine waters round the South Island, New Zealand

Abstract Yellow substance, the single largest component of dissolved organic matter in natural waters, is often the most important blue‐light‐absorbing constituent. The spectral absorption of yellow substance was measured by spectrophotometry in coastal (including fiord) and marine waters round toe South Island of New Zealand on Cruise 2027 (May 1989) of the RV Rapuhia; this examined a wide range of optical variables in relation to primary productivity and water mass characteristics. The spectral absorption by yellow substance fitted an exponential model, as is typical, and the spectral slope parameter varied only slightly (mean = 0.015 nm−1, standard deviation = 0.002 nm−1 ) for oceanic waters in the range 300–460 nm. The concentration of yellow substance, indicated by the absorption coefficient of filtrates at 440 nm (g440), varied more than two orders of magnitude, from 0.014 m−1 in the cold subantarctic water south‐east of the South Island, to 1.8 m−1 in humic‐stained surface water in Doubtful Sound. In marine waters, g440 was fairly tightly distributed around a mean of 0.06 m−1 ‐a value typical in sea waters. g440 did not correlate with phytoplankton pigment content of marine waters, probably because most of the yellow substance was old material, derived from terrestial production or long past marine production. Nor was g440 correlated with salinity. But there was a weak (probably incidental) correlation with temperature (r = +0.57), with higher values of yellow substance in the relatively warm waters along the South Island west coast than in the colder waters off the east coast. The concentration of yellow substance explained nearly half of the total variation in light (PAR) absorption at the stations visited.

Very-high-energy light charged-particle production near 0 degrees in heavy-ion collisions, 9

Very energetic light ions (primarily protons and alphas) with energies often approaching the full beam energy have been observed at or near {theta}=0{degree} in heavy-ion collisions, {ital Z}=8 to 28, {ital E}/{ital A}{dot =}9 to 40 MeV/nucleon from Ta and, in selected cases, Cu targets. Analysis of spectral shapes and angular distributions using a standard moving source model requires that the source velocity approaches the beam velocity as {theta}{r arrow}0{degree} and that the spectral slope parameters and apparent source temperatures be increased. Large values for the latter ({ital T}{sub {ital S}}{r arrow}16 MeV), which are typically twice as large as those deduced from complex fragment emission, are often required to fit the alpha particle spectra {theta}=0{degree}. Massive cluster transfer and other quasitransfer mechanisms may provide an alternative model for the generation of the {ital E}{r arrow}{ital E}{sub beam} alpha particles and other light fragments.

Temperatures, energies, and degree of thermal equilibration of fragments in damped nuclear reactions.

Experimental neutron multiplicities and spectral slope parameters are compared with evaporation calculations for the damped $^{165}$Ho${+\mathrm{}}^{56}$Fe reaction as a function of ${E}_{\mathrm{loss}}$ for different degrees of energy relaxation of the dinuclear system. These calculations indicate that the popular direct interpretation of the slope parameters in terms of the nuclear temperature of the emitter is poorly justified. Detailed comparisons for two different primary reaction fragment distributions show that the energy partition of the primary fragments is energy-loss dependent and, for small energy losses, far from thermal equilibrium. For ${E}_{\mathrm{loss}&lt;100}$ MeV, the ratio ${E}_{L}$(Fe-like)/${E}_{H}$(Ho-like)&gt;0.5 and for ${E}_{\mathrm{loss}=150}$ MeV, this ratio is given by ${A}_{L}$/${A}_{H}$.