Search results for " optics"
showing 10 items of 5880 documents
The high overtone and combination levels of SF6 revisited at Doppler-limited resolution: A global effective rovibrational model for highly excited vi…
2017
Abstract Sulfur hexafluoride is an important prototypal molecule for modeling highly excited vibrational energy flow and multi quanta absorption processes in hexafluoride molecules of technological importance. It is also a strong greenhouse gas of anthropogenic origin. This heavy species, however, features many hot bands at room temperature (at which only 30% of the molecules lie in the ground vibrational state), especially those originating from the lowest, v 6 =1 vibrational state. Using a cryogenic long path cell with variable optical path length and temperatures regulated between 120 and 163 K, coupled to Synchrotron Radiation and a high resolution interferometer, Doppler-limited spectr…
Evaluation of the S-NPP VIIRS land surface temperature product using ground data acquired by an autonomous system at a rice paddy
2018
Abstract The S-NPP VIIRS Land Surface Temperature (LST) product attained the stage V1 of validation maturity (provisional validated) at the end of 2014. This paper evaluates the current VIIRS V1 LST product versus concurrent ground data acquired at a rice paddy site from December 2014 to August 2016. The experimental site has three different seasonal and homogeneous land covers through the year, which makes the site interesting for validation activities. An autonomous and multiangular system was used to record continuous ground data at the site. The data acquired at zenith angles similar to the VIIRS viewing angles were used for the validation to avoid possible differences between satellite…
Remote sensing algorithms for estimation of fractional vegetation cover using pure vegetation index values: A review
2020
Abstract Green fractional vegetation cover ( f c ) is an important phenotypic factor in the fields of agriculture, forestry, and ecology. Spatially explicit monitoring of f c via relative vegetation abundance (RA) algorithms, especially those based on scaled maximum/minimum vegetation index (VI) values, has been widely investigated in remote sensing research. Although many studies have explored the effectiveness of RA algorithms over the past 30 years, a literature review summarizing the corresponding theoretical background, issues, current state-of-the-art techniques, challenges, and prospects has not yet been published. The overall objective of the present study was to accomplish a compre…
Atmospheric and Instrumental Effects on the Fluorescence Remote Sensing Retrieval
2018
Accurately disentangling the tiny Solar–Induced Chlorophyll Fluorescence (SIF) from canopy reflected solar irradiance by using passive remote sensing techniques is always challenging. Regardless the scale at which SIF is measured, i.e., proximal sensing, airborne or satellite level; instrumental and atmospheric effects must be accounted for and compensated as part of the SIF retrieval strategy. Regarding the instrumental effects, the use of very high spectral resolution spectrometers makes mandatory an accurate characterization of the Instrument Spectral Response Function (ISRF); and – in the case of imager spectrometers – an accurate characterization of the full instrument response in the …
Line parameters and shapes of high clusters: R-branch of the nu3 band of CH4 in He mixtures
2002
International audience; The IR absorption spectra of CH4 in pure gas and in mixture with helium were studied in the region of nu3 band at higher J line clusters R(17)-R(22). The frequencies and intensities of rotation-vibration lines were estimated from the experimental spectra at Doppler shape conditions. The line frequencies and intensities were calculated and used for the attribution of overlapped lines in clusters. The calculated line intensities are close to the experimental values. The calculated frequency structure of the higher J manifolds are somewhat wider than the observed one. The shapes of helium-broadened line clusters were compared with those calculated accounting for line mi…
How much is enough? : The convergence of finite sample scattering properties to those of infinite media
2021
We study the scattering properties of a cloud of particles. The particles are spherical, close to the incident wavelength in size, have a high albedo, and are randomly packed to 20% volume density. We show, using both numerically exact methods for solving the Maxwell equations and radiative-transfer-approximation methods, that the scattering properties of the cloud converge after about ten million particles in the system. After that, the backward-scattered properties of the system should estimate the properties of a macroscopic, practically infinite system. (C) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.o…
Vibration Monitoring of the Mechanical Harvesting of Citrus to Improve Fruit Detachment Efficiency
2019
The introduction of a mechanical harvesting process for oranges can contribute to enhancing farm profitability and reducing labour dependency. The objective of this work is to determine the spread of the vibration in citrus tree canopies to establish recommendations to reach high values of fruit detachment efficiency and eliminate the need for subsequent hand-harvesting processes. Field tests were carried out with a lateral tractor-drawn canopy shaker on four commercial plots of sweet oranges. Canopy vibration during the harvesting process was measured with a set of triaxial accelerometer sensors with a datalogger placed on 90 bearing branches. Monitoring of the vibration process, fruit pro…
Automatic measurement of wood fiber orientation and knot detection using an optical system based on heating conduction.
2015
In this paper, a new approach to computing the deviation of wood grain is proposed. To do this, the thermal conduction properties of timber are used (higher conduction in the fiber direction). Exciting the surface of the wood with a laser and capturing the thermal conduction using a thermal camera, an ellipse can be observed. Using a method similar to the tracheid effect, it is possible to extract information from this ellipse, such as the slope of grain and the presence of knots. With this method it is therefore possible to extend the mechanical model (assessing the mechanical properties of timber) to take certain singularities into account. Using this approach, the slope of grain can be e…
Spectroscopic analysis of hot-water- and dilute-acid-extracted hardwood and softwood chips
2017
Hot-water and dilute sulfuric acid pretreatments were performed prior to chemical pulping for silver/white birch (Betula pendula/B. pubescens) and Scots pine (Pinus sylvestris) chips to determine if varying pretreatment conditions on the original wood material were detectable via attenuated total reflectance (ATR) infrared spectroscopy. Pretreatment conditions varied with respect to temperature (130 °C and 150 °C) and treatment time (from 30 min to 120 min). The effects of the pretreatments on the composition of wood chips were determined by ATR infrared spectroscopy. The spectral data were compared to those determined by common wood chemistry analyses to evaluate the suitability of ATR spe…
Electrochemical polymerization of ambipolar carbonyl-functionalized indenofluorene with memristive properties
2019
Abstract Carbonyl-functionalized indenofluorene was electropolymerized with a high faradaic efficiency of 85% and the solid state properties of the resulting polymeric thin films were investigated. They displayed modular optical properties depending on their oxidation state. The approach used for inorganic semiconductors was applied to polyindeonofluorene derivative. Mott-Schottky analysis evidenced a switching from p-type to n-type electrical conduction, suggesting an ambipolar behaviour of the polymer. As an application, flexible organic memristors were fabricated and resistive switching properties were observed.