Lead-vapor filters for high-spectral-resolution temperature lidar

The analysis of Rayleigh-scattered laser radiation with atomic-vapor filters used for temperature measurements is investigated. The choices for the filter material and the optimum parameter configuration for daytime measurements are presented. In laboratory experiments the backscattered radiation from synthetic air stimulated by a cw dye laser at 283 nm was analyzed with two lead-vapor cells in one oven. The effects of different parameters on the accuracy of the measurement are determined from both theory and experiment, and actual air-temperature measurements are presented. Calculations for a real lidar show not only the performance, but also the limitations, of such a measurement system.     

Validation of atmospheric sounders by correlative measurements

A linear mathematical model for the statistical estimate of the bias and noise of satellite sounders and a case study are presented. The model provides the tool for proper comparison of actual performance of the remote sensing system while in orbit to correlative data sets. The model accounts for: (i) noncoincidence in time and space of satellite and validating systems sampling; (ii) different characteristics of the validated and validating systems, e.g., different vertical resolutions and noise levels. In the case study the model is applied to validation of temperature profile retrievals using radiosondes for the reference.     

Ultraviolet high-spectral-resolution Doppler lidar for measuring wind field and aerosol optical properties

An ultraviolet incoherent Doppler lidar that incorporates the high-spectral-resolution (HSR) technique has been developed for measuring the wind field and aerosol optical properties in the troposphere. An injection seeded and tripled Nd:YAG laser at an ultraviolet wavelength of 355 nm was used in the lidar system. The HRS technique can resolve the aerosol Mie backscatter and the molecular Rayleigh backscatter to derive the signal components. By detecting the Mie backscatter, a great increase in the Doppler filter sensitivity was realized compared to the conventional incoherent Doppler lidars that detected the Rayleigh backscatter. The wind velocity distribution in a two-dimensional cross section was measured. By using the HSR technique, multifunction and absolute value measurements were realized for aerosol extinction, and volume backscatter coefficients; the laser beam transmittance, the lidar ratio, and the backscatter ratio are derived from these measurements.     

Extinction-to-backscatter ratio of Asian dust observed with high-spectral-resolution lidar and Raman lidar

Extinction-to-backscatter ratio or lidar ratio is a key parameter in the issue of backscatter-lidar inversions. The lidar ratio of Asian dust was observed with a high-spectral-resolution lidar and a combined Raman elastic-backscatter lidar during the springs of 1998 and 1999. The measured values range from 42 to55 sr in most cases, with a mean of 51 sr. These values are significantly larger than those predicted by the Mie computations that incorporate measured Asian dust size distributions and a range of refractive index with a typical value of 1.55-0.005i. The enhancement of lidar ratio is mostly due to the nonsphericity of dust particles, as indicated by the T-matrix calculations for spheroid particles and a number of other theoretical studies. In addition, possible contamination of urban aerosols may also contribute somewhat in optically thin cases. Mie theory, although it can well describe spherical particle scattering, will not be sufficient to represent the scattering characteristics of irregular particles such as Asian dust, especially in directions larger than approximately 90 degrees when the size parameter is large.     

Vertical profiles of aerosol volume from high-spectral-resolution infrared transmission measurements. I. Methodology

The wavelength-dependent aerosol extinction in the 800-1250-cm(-1) region has been derived from ATMOS (atmospheric trace molecule spectroscopy) high-spectral-resolution IR transmission measurements. Using models of aerosol and cloud extinction, we have performed weighted nonlinear least-squares fitting to determine the aerosol-volume columns and vertical profiles of stratospheric sulfate aerosol and cirrus cloud volume. Modeled extinction by use of cold-temperature aerosol optical constants for a 70-80% sulfuric-acid-water solution shows good agreement with the measurements, and the derived aerosol volumes for a 1992 occultation are consistent with data from other experiments after the eruption of Mt. Pinatubo. The retrieved sulfuric acid aerosol-volume profiles are insensitive to the aerosol-size distribution and somewhat sensitive to the set of optical constants used. Data from the nonspherical cirrus extinction model agree well with a 1994 mid-latitude measurement indicating the presence of cirrus clouds at the tropopause.     

Particle backscatter and extinction profiling with the spaceborne high-spectral-resolution Doppler lidar ALADIN: methodology and simulations

The European Space Agency will launch the Atmospheric Laser Doppler Instrument (ALADIN) for global wind profile observations in the near future. The potential of ALADIN to measure the optical properties of aerosol and cirrus, as well, is investigated based on simulations. A comprehensive data analysis scheme is developed that includes (a) the correction of Doppler-shifted particle backscatter interference in the molecular backscatter channels (cross-talk effect), (b) a procedure that allows us to check the quality of the cross-talk correction, and (c) the procedures for the independent retrieval of profiles of the volume extinction and backscatter coefficients of particles considering the height-dependent ALADIN signal resolution. The error analysis shows that the particle backscatter and extinction coefficients, and the corresponding extinction-to-backscatter ratio (lidar ratio), can be obtained with an overall (systematic+statistical) error of 10%-15%, 15%-30%, and 20%-35%, respectively, in tropospheric aerosol and dust layers with extinction values from 50 to 200 Mm(-1); 700-shot averaging (50 km horizontal resolution) is required. Vertical signal resolution is 500 m in the lower troposphere and 1000 m in the free troposphere. In cirrus characterized by extinction coefficients of 200 Mm(-1) and an optical depth of >0.2, backscatter coefficients, optical depth, and column lidar ratios can be obtained with 25%-35% relative uncertainty and a horizontal resolution of 10 km (140 shots). In the stratosphere, only the backscatter coefficient of aerosol layers and polar stratospheric clouds can be retrieved with an acceptable uncertainty of 15%-30%. Vertical resolution is 2000 m.     

An option generation and selection methodology for process equipment selection

The option generation and selection (OGS) methodology forms part of a general approach for the design of agile chemical plants based on business, product and process knowledge, with support from information models. This paper describes an equipment OGS tool that encompasses the principles of combinatorial process and plant design. The main components of the methodology are: an equipment option generation model described as a set of objects, and the net relationships between them, and an equipment option selection model which consists of procedures for equipment selection. The two models are supported by databases containing information specific to each equipment type, the concept on which the equipment is based, and relationships with other equipment types. Robust, systematic and complete forms of these models can be used as the basis of an expert system for process equipment design, with equipment selected using these tools satisfying the requirements of both specific processes and families of processes (that contain common features, similar functional groups or similar raw material requirements for process operations). Application of the methodology also allows the evaluation of options for reconfiguring existing plant.     

Wavelength selection for true-color holography

We discuss wavelength selection for true-color holography by investigating the sampling nature of the holographic process. During holographic recording the chosen wavelengths point sample the surfacereflectance functions of the objects in a scene. To understand the effect of this sampling on color perception, we study the tristimulus values of points in the reconstructed hologram. The sampling results in the holographic process being mathematically equivalent to integral approximations for the tristimulus integrals. By selecting efficient approximations, we infer wavelengths to use in color holography. Our analysis not only suggests wavelengths for the usual three-color holography but also suggests the use of four or more wavelengths to improve color reproduction in holography.     

Asymptotic criteria for model selection

Summary A general frame is given in which model selection criteria can be derived. At first conditions are stated under which the asymptotic distribution of minimum discrepancy estimators can be given. The results are used to derive an approximation to the expected discrepancy. Estimators of this expectation, i.e. model selection criteria, are proposed.

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Zusammenfassung Ein allgemeiner Rahmen wird gegeben, in dem man Kriterien zur Modellauswahl herleiten kann. Zuerst werden Bedingungen angeführt, unter denen man die asymptotische Verteilung von Minimum-Diskrepanz-Schätzern angeben kann. Mit den Resultaten wird dann eine Annäherung an die erwartete Gesamtdiskrepanz berechnet. Schätzer dieser Erwartung, also Kriterien zur Modellauswahl, werden vorgeschlagen.

     

Model selection for modified gravity

In this article, we review model selection predictions for modified gravity scenarios as an explanation for the observed acceleration of the expansion history of the Universe. We present analytical procedures for calculating expected Bayesian evidence values in two cases: (i) that modified gravity is a simple parametrized extension of general relativity (GR; two nested models), such that a Bayes' factor can be calculated, and (ii) that we have a class of non-nested models where a rank-ordering of evidence values is required. We show that, in the case of a minimal modified gravity parametrization, we can expect large area photometric and spectroscopic surveys, using three-dimensional cosmic shear and baryonic acoustic oscillations, to 'decisively' distinguish modified gravity models over GR (or vice versa), with odds of ?1:100. It is apparent that the potential discovery space for modified gravity models is large, even in a simple extension to gravity models, where Newton's constant G is allowed to vary as a function of time and length scale. On the time and length scales where dark energy dominates, it is only through large-scale cosmological experiments that we can hope to understand the nature of gravity.     

Genetic algorithm attributes for component selection

This paper uses a genetic algorithm for component selection given a user-defined system layout, a database of components, and a defined set of design specifications. A genetic algorithm is a search method based on the principles of natural selection. An introduction to genetic algorithms is presented, and genetic algorithm attributes that are useful for component selection are explored. A comparison of these attributes is performed using two industrial design problems. A set of genetic algorithm attributes including integer coding, uniform crossover, anti-incest mating, variable mating and mutation rates, retention of population members from generation to generation, and an attention shifted penalty function are suggested for a more efficient search in component selection problems.     

Weibull model selection for reliability modelling

A large number of models have been derived from the two-parameter Weibull distribution and are referred to as Weibull models. They exhibit a wide range of shapes for the density and hazard functions, which makes them suitable for modelling complex failure data sets. The WPP and IWPP plot allows one to determine in a systematic manner if one or more of these models are suitable for modelling a given data set. This paper deals with this topic.     

Diversity selection for phase-diverse phase retrieval

Wavefront-sensing performance is assessed for focus-diverse phase retrieval as the aberration spatial frequency and the diversity defocus are varied. The analysis includes analytical predictions for optimal diversity values corresponding to the recovery of a dominant spatial-frequency component in the pupil. The calculation is shown to be consistent with the Cramér-Rao lower bound by considering a sensitivity analysis of the point-spread function to the spatial frequency being estimated. A maximum value of diversity defocus is also calculated, beyond which wavefront-sensing performance decreases as diversity defocus is increased. The results are shown to be consistent with the Talbot imaging phenomena, explaining multiple periodic regions of maximum and minimum contrast as a function of aberration spatial frequency and defocus. Wavefront-sensing performance for an iterative-transform phase-retrieval algorithm is also considered as diversity defocus and aberration spatial frequency are varied.     

Strongly consistent model selection for densities

Let f be an unknown multivariate density belonging to a set of densities \(\mathcal{F}_{k^{*}}\) of finite associated Vapnik–Chervonenkis dimension, where the complexity k ^* is unknown, and ? _k ?? _k+1 for all k. Given an i.i.d. sample of size n drawn from f, this article presents a density estimate \(\hat{f}_{K_{n}}\) yielding almost sure convergence of the estimated complexity K _n to the true but unknown k ^* and with the property \(\mathbf{E}\{\int|\hat{f}_{K_{n}}-f|\}=\mbox{O}(1/\sqrt{n}\,)\). The methodology is inspired by the combinatorial tools developed in Devroye and Lugosi (Combinatorial methods in density estimation. Springer, New York, 2001) and it includes a wide range of density models, such as mixture models and exponential families.