1,721,120 research outputs found
Retrieval of sea water optically active parameters from hyperspectral data by means of generalized radial basis function neural networks
No full textThe authors present a new methodology for estimating the concentration of sea water optically active constituents from remotely sensed hyperspectral data, based on generalized radial basis function neural networks (GRBF-NNs). This family of NNs is particularly suited to approximate relationships like those between hyperspectral reflectance data and the concentrations of optically active constituents of the water body, which are highly nonlinear, especially in case II waters. Three main water constituents are taken into account: phytoplankton, nonchlorophyllous particles, and yellow substance. Each parameter is estimated by means of a specific multi-input single-output GRBF-NN. The authors adopt a recently proposed network learning strategy based on the combined use of the regression tree procedure and forward selection. The effectiveness of this approach, which is completely general and can be easily applied to any hyperspectral sensor, is proved using data simulated with an ocean color model over the channels of the medium resolution imaging spectrometer (MERIS), the new generation ESA sensor to be launched in 2001. The authors define the estimation algorithms over waters of cases I, II, and I+II and compare their performance with that of classical band-ratio, single-band, and multilinear algorithms. Generally, the GRBF-NN algorithms outperform the classical ones, except for the multilinear over case I waters. A particular improvement Is over case II waters, where the mean square error (MSE) can be reduced by one or two orders of magnitude over the error of multilinear and band-ratio algorithms, respectivel
Do multiple peaks in the Radon Transform of westward propagating sea surface height anomalies correspond to higher order Rossby wave Baroclinic modes?
Full text linkThis study examines the presence of multiple peaks from 2 dimensional Fourier and Radon Transform analysis for the entire South Pacific basin from 10 years of sea level anomalies determined from ERS (European Remote Sensing satellite) and T/P altimeter observations and attempts to determine whether their speeds resemble those of higher order baroclinic Rossby wave modes
Observed variability of the South Pacific westward sea level anomaly signal in the presence of bottom topography
No full textThis study investigates the behavior of westward propagating sea level anomalies across the South Pacific Ocean, with a focus on the long Rossby wave signal determined from filtered TOPEX/Poseidon and ERS satellite altimeter data. An evaluation of the energy variability of the signal using a two-dimensional Radon Transform analysis suggests that Rossby waves interact with both ridges and seamounts at various locations across the basin. Anomalously slow Rossby wave phase speeds are found over steep, isolated bathymetric features in the tropical South Pacific and over the plateau around New Zealand. Interaction with ridges increases the energetic variability, range of dominant propagation speeds, and meridional deviations in the Rossby wave signal
Surface distribution of chlorophyll, particles and gelbstoff in the Atlantic jet of the Alboran Sea: from submesoscale to subinertial scales of variability
No full textThe surface distribution of light attenuation due to particles (c) as well as chlorophyll-a and gelbstoff fluorescence (Fch and Fcd, respectively) were recorded during an OMEGA (EU funded, MAST III project) cruise in the northwestern Alborán Sea through a high spatial (zonally separated by 10 km and virtually meridionally continuous) and temporal (about 3 days between each of the three repeated surveys made in the zone) resolution sampling design. The distributions obtained for these variables were tightly linked to the physical forcing at the different scales that the sampling design was able to resolve. Low values dominate the quasi permanent anticyclonic gyre occupying the western Alborán Sea, whereas the frontal zone directly affected by the entrance of the Atlantic jet depicts much higher records for c, Fch and Fcd.High geostrophic Froude numbers in the jet, and the subsequent increase in turbulence diffusion of nutrients towards the surface, cannot alone justify this spatial distribution. Instead, high phytoplankton concentration at the jet could also result from the entrainment and advection of water from the upwelling zone at the Spanish coast. However, T–S characteristics suggest that this is neither the most important process for the biological enrichment of the jet, so that other mechanisms such as vertical ageostrophic velocities at the edge of the gyre must also be considered. Due to the time needed for phytoplankton growth, the intense horizontal velocities associated to the jet can decouple the sectors where deep nutrient-rich waters reach the surface from sectors where high values of the recorded variables are observed. The decoupling hinders a differentiation of this fertilization mechanism from other possible alternatives as mixing at the sills in the Strait of Gibraltar.In the third survey, the spatial structure of surface warm waters in the gyre and cold waters in the front became less apparent. ADCP data show a southward migration of the jet in a fluctuation probably related to transient states in the Atlantic jet and western Alborán gyre system. The qualitative response of c, Fch and Fcd to these scales of variability was very similar and close to the changes observed in temperature. However, the values of Fcd varied in a much narrower range than c or Fch (a factor of 2 and 10, respectively), which indicates a distinct control for the abundance of Gelbstoff. This control dumps the range of variability in the western Alborán and its origin is discussed in the context of photobleaching or bacterial degradation of these substances
The influence of bottom topography on long Rossby wave propagation in the South Pacific Ocean
Full text linkThe present study investigates the long wavelength, baroclinic Rossby wave signal from 10 years of sea level anomalies in the South Pacific Ocean determined from ERS (European Remote Sensing satellite) and T/P altimeter observations, and attempts at correlating the results with bathymetry
Regional bio-optical algorithms for the Alboran Sea from a reflectance model and in situ data
No full textA method for tracking individual planetary waves in remotely sensed data
No full textWe describe a methodology for tracking individual planetary waves in longitude-time plots of satellite data, based on fitting an elementary wave shape model to subsets of the data by maximum likelihood, then reconstructing the trajectory and evolution of every single wave (where for ‘single wave’ we mean an individual positive or negative westward propagating anomaly) by joining the elementary waves according to their similarity. We then illustrate the potential of the methodology with an example at 34°N in the Atlantic Ocean, and its adaptability to different cases with a second example on eastward-propagating Kelvin waves in the equatorial Pacific. Although the examples given use sea surface height anomaly data, the technique lends itself to be applied to any space-time plot of any dataset displaying propagation, and in particular to sea surface temperature data
Il compostaggio
No full textFondamenti del processo di compostaggio, analisi dei parametri influenzanti il processo, controllo ed ottimizzazione delle reazioni biologiche, confronto dei metodi di compostaggio e delle tecnologie di attuazione
- …
