JEOS:RP - Journal of the European Optical Society Rapid publications
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Above-water reflectance for the evaluation of adjacency effects in Earth observation data: initial results and methods comparison for near-coastal waters in the Western Channel, UK
Get PDFUn-supervised hyperspectral remote-sensing reflectance data (<15 km from the shore) were collected from a moving research vessel. Twodifferent processing methods were compared. The results were similar to concurrent Aqua-MODIS and Suomi-NPP-VIIRS satellite data
Influence of oil-in-water emulsions on fluorescence properties as observed by excitation-emission spectra
Get PDFOil poses a major threat to marine ecosystems. This work describes a set of studies focused on introducing an efficient method for the identification of oil in the form of oil emulsions through fluorescence spectra analyses. Hence the concept of classification of oil pollution in seawater based on fluorescence spectroscopy using a high sensitive fluorimeter [1] suitable for laboratory and in situ measurements is introduced. We consider that this approach, in the future, will make it possible to collect specific fluorescence information allowing us to build a base of the oil standards. Here we examined excitation-emission fluorescence spectra (EEMs) of water containing oil-in-water emulsion prepared artificially under laboratory conditions. Water polluted with oil-in-water emulsion was studied with the objective to estimate differences in three-dimensional fluorescence spectra. Studies included various types of oils and oil concentrations. Essential differences in fluorescence spectra for various oils are indicated
Semi-Huber quadratic function and comparative study of some MRFs for Bayesian image restoration
Get PDFThe present work introduces an alternative method to deal with digital image restoration into a Bayesian framework, particularly, the use of a new half-quadratic function is proposed which performance is satisfactory compared with respect to some other functions in existing literature. The bayesian methodology is based on the prior knowledge of some information that allows an efficient modelling of the image acquisition process. The edge preservation of objects into the image while smoothing noise is necessary in an adequate model. Thus, we use a convexity criteria given by a semi-Huber function to obtain adequate weighting of the cost functions (half-quadratic) to be minimized. The principal objective when using Bayesian methods based on the Markov Random Fields (MRF) in the context of image processing is to eliminate those effects caused by the excessive smoothness on the reconstruction process of image which are rich in contours or edges. A comparison between the new introduced scheme and other three existing schemes, for the cases of noise filtering and image deblurring, is presented. This collection of implemented methods is inspired of course on the use of MRFs such as the semi-Huber, the generalized Gaussian, the Welch, and Tukey potential functions with granularity control. The obtained results showed a satisfactory performance and the effectiveness of the proposed estimator with respect to other three estimators
Mid-Spatial Frequency Error (PSD-2) of optics induced during CCOS and full-aperture polishing
Get PDFMid-Spatial Frequency (MSF) Wavefront Error of optics divided into the PSD-1 and PSD-2 ranges plays an important role in the performance of high power laser systems. The present work focuses on the PSD-2 range in terms of short ripples which haven’t been well studied in the literature. Characteristics and origins of these short ripples were detailed, whereafter small tool computer controlled polishing (CCP) and conventional full aperture polishing experiments were conducted on fused silica. It is revealed that PSD2 error is independent of the main process parameters including lap rotating rate and polishing pressure in continuous polishing and tool path pitch and crossfeed velocity in small tool CCP processes. Whereas the type of polishing lap has a decisive effect on PSD2 error of the optics. The pitch lap shows superiority in restraint of short ripples over polyurethane pad. By introducing diamond conditioner for dressing polyurethane pad, the PSD2 error has been greatly decreased
Signal of single scattering albedo in water leaving polarization
Get PDFThe purpose of this article is to examine whether the change in single scattering albedo in the surface layer of the sea will cause significantchanges in the polarization of light emerging from the sea. The results of a polarization resolving Monte Carlo radiative transfer calculationsare presented. Bubble clouds of different bubble concentrations are used to achieve a wide range of single scattering albedo variability. Thevariability of the polarization signal is largest in the direction looking towards the sun which is unfortunate due to sun reflection. Howeverthe variability is also significant at direction perpendicular to solar azimuth angle which should it make possible to use this signal in remotesensing. The polarization degree of water leaving radiation, together with reflectance can be used to determine the backscattering ratio ofthe observed sea water
Short-time Fourier transform laser Doppler holography
Get PDFWe report a demonstration of laser Doppler holography at a sustained acquisition rate of 250 Hz on a 1 Megapixel complementary metal-oxide-semiconductor (CMOS) sensor array and image display at 10 Hz frame rate. The holograms are optically acquired in off-axis configuration, with a frequency-shifted reference beam. Wide-field imaging of optical fluctuations in a 250 Hz frequency band is achieved by turning time-domain samplings to the dual domain via short-time temporal Fourier transformation. The measurement band can be positioned freely within the low radio-frequency (RF) spectrum by tuning the frequency of the reference beam in real-time. Video-rate image rendering is achieved by streamline image processing with commodity computer graphics hardware. This experimental scheme is validated by a non-contact vibrometry experiment
Design of subwavelength optical fibre for low-loss Terahertz transmission
Get PDFA low-loss Terahertz (THz) transmission optical fibre with a subwavelength core is reported in this article. The main fibre is composed of a subwavelength solid polymer core and a tube. The tube is used to prevent the extending of THz wave to the external environment. Two solid ends are introduced to suspend the subwavelength core in the air. The solid fibre ends are found have low splicing losses with the main fibre. The proposed fibre provides a simple technique for the transmission of THz wave in a short distance
Monte Carlo code for the study of the dynamic light field at the wavy atmosphere-ocean interface
Get PDFA radiative transfer model has been developed to study the solar radiation budget at the wave-deflected air-sea interface. The model is used to characterize fluctuations of the underwater light field, i.e. down- and upwelling irradiance, irradiance reflectance, and upwelling radiance just below the surface, subject to changing sun zenith angles and percentages of diffuse sky radiation to the total insolation. The focusing of sunlight is most effective under clear skies; the variability of downwelling irradiance is significantly smaller under overcast conditions. In general, maximum and deep-reaching fluctuations arise at high sun positions, but the behaviour is much more differentiated and exceptions are discussed. Furthermore, wave shadowing effects have been studied; these become increasingly important for low sun elevations. There are indications that the light transmission into water up to now is overestimated for solar zenith angles near the horizon
An alternative approach to the tomographic reconstruction of smooth refractive index distributions
Get PDFContinuous, mathematically smooth Phase Objects with radial symmetry are reconstructed from cross sections of their refractive index distribution by a novel method, consisting of a linear combination of Gaussian basis functions, whose technical details are discussed. As an application example, this approach is used to get a fast and accurate estimation of the temperature distribution of an actual soldering tip
Synthetic adjacent pulse repetition interval length method to solve integer ambiguity problem: theoretical analysis
Get PDFThis paper describes a novel approach for realizing femtosecond optical frequency comb (FOFC)-based length measurement. This approach is based on the analogy between the phase unwrapping problem and the integer ambiguity problem. Because the conventional synthetic wavelength method can solve the former, we investigated the possibility of using a synthetic adjacent pulse repetition interval length method to solve the latter. The results of theoretical analyses and numerical investigations show the feasibility of the proposed method. Our results should contribute toward the further development of FOFC-based length measurement methods