Search results for "SPECTRA"
showing 10 items of 3542 documents
A directional spectral mixture analysis method: application to multiangular airborne measurements
2006
This study aims at developing an operational approach-namely, directional spectral mixture analysis (DISMA)-for retrieving vegetation parameters like fractional vegetation cover (FVC) and leaf area index (LAI) from multispectral and multiangular data. The approach attempts to highlight the consistency of one-dimensional models and linear mixture approaches. DISMA combines spectral signatures of soil and vegetation components with an analytical approximation of the radiative transfer equation, giving rise to a fast invertible bidirectional reflectance distribution function (BRDF) model of discontinuous canopies. Both the forward model and its inversion using a simple technique based on looku…
Cloud detection for CHRIS/Proba hyperspectral images
2005
Accurate and automatic detection of clouds in satellite scenes is a key issue for a wide range of remote sensing applications. With no accurate cloud masking, undetected clouds are one of the most significant source of error in both sea and land cover biophysical parameter retrieval. Sensors with spectral channels beyond 1 um have demonstrated good capabilities to perform cloud masking. This spectral range can not be exploited by recently developed hyperspectral sensors that work in the spectral range between 400- 1000 nm. However, one can take advantage of their high number of channels and spectral resolution to increase the cloud detection accuracy, and to describe properly the detected c…
Delineation of Malignant Skin Tumors by Hyperspectral Imaging
2018
This chapter outlines a new non-invasive method for delineation of skin lesions such as lentigo maligna and lentigo maligna melanoma. The method is based on the analysis of hyperspectral (HS) images taken in vivo before surgical excision of the lesions. For this, characteristic features of the spectral signatures of diseased pixels and healthy pixels are extracted, which combine the intensities in a few selected wavebands with the coefficients of the wavelet frame transforms of the spectral curves. To reduce dimensionality and to reveal the internal structure of the datasets, the diffusion maps (DM) technique is applied. The averaged Nearest Neighbor and the Classification and Regression Tr…
Effetto della cultivar e del regime colturale sulla risposta spettrale della chioma in Vitis vinifera L.
2008
Lo studio consente di caratterizzare le risposte spettrali all’invaiatura di chioma ed acino di alcune cultivar a bacca nera della piattaforma ampelografica siciliana. La variabilità tra le risposte spettrali delle foglie all’interno della stessa chioma, nonché le variazioni spettrali anche al variare del regime irriguo consentono di effettuare un’analisi comparativa delle cultivar. In questo quadro, le firme spettrali integrano la descrizione ampelografica di chioma e bacche che caratterizza la Vitis Vinifera L.. Infine l’applicazione su un’area pilota di tecniche di classificazione di immagini remote basate sulle caratteristiche spettrali delle cultivar, consente di valutarne le performan…
The Tan 2Θ Theorem in fluid dynamics
2017
We show that the generalized Reynolds number (in fluid dynamics) introduced by Ladyzhenskaya is closely related to the rotation of the positive spectral subspace of the Stokes block-operator in the underlying Hilbert space. We also explicitly evaluate the bottom of the negative spectrum of the Stokes operator and prove a sharp inequality relating the distance from the bottom of its spectrum to the origin and the length of the first positive gap.
Commutators, C0-semigroups and resolvent estimates
2004
Abstract We study the existence and the continuity properties of the boundary values on the real axis of the resolvent of a self-adjoint operator H in the framework of the conjugate operator method initiated by Mourre. We allow the conjugate operator A to be the generator of a C 0 -semigroup (finer estimates require A to be maximal symmetric) and we consider situations where the first commutator [ H ,i A ] is not comparable to H . The applications include the spectral theory of zero mass quantum field models.
30 years of finite-gap integration theory
2007
The method of finite-gap integration was created to solve the periodic KdV initial problem. Its development during last 30 years, combining the spectral theory of differential and difference operators with periodic coefficients, the algebraic geometry of compact Riemann surfaces and their Jacobians, the Riemann theta functions and inverse problems, had a strong impact on the evolution of modern mathematics and theoretical physics. This article explains some of the principal historical points in the creation of this method during the period 1973–1976, and briefly comments on its evolution during the last 30 years.
The second Weyl coefficient for a first-order system
2020
For a scalar elliptic self-adjoint operator on a compact manifold without boundary we have two-term asymptotics for the number of eigenvalues between 0 and λ when λ → ∞, under an additional dynamical condition. (See [3, Theorem 3.5] for an early result in this direction.) In the case of an elliptic system of first order, the existence of two-term asymptotics was also established quite early and as in the scalar case Fourier integral operators have been the crucial tool. The complete computation of the coefficient of the second term was obtained only in the 2013 paper [2]. In the present paper we simplify that calculation. The main observation is that with the existence of two-term asymptoti…
Spectral Transmission of the Human Corneal Layers
2021
Este artículo se encuentra disponible en la siguiente URL: https://www.mdpi.com/2077-0383/10/19/4490 Este artículo de investigación pertenece a la sección "Ophthalmology". We have assessed the spectral transmittance of the different layers of the human cornea in the ultraviolet (UV), visible, and near-infrared (IR) spectral ranges. Seventy-four corneal sample donors were included in the study. Firstly, the corneal transmittance was measured using a spectrophotometer. Then, all samples were fixed for histopathological analysis, which allowed us to measure the thickness of each corneal layer. Finally, the absorption coefficients of the corneal layers were computed by a linear model reproducin…
Accurate spectroscopic constants of nitrogen determined from stimulated Raman spectra of the fundamental and first hot bands
1990
Nitrogen spectra of the Q-branch of the fundamental and the first hot bands were recorde with a high-resolution stimulated Raman spectrometer at atmospheric pressure and ca. 1300 K. The absolute frequencies of the Raman lines were measured with high accuracy, leading to a refinement of spectroscopic constants. A temperature estimation was also performed from the Raman intensities.