Ozone column density determination from direct irradiance measurements in the ultraviolet performed by a four-channel precision filter radiometer

Ultraviolet light was measured at four channels (305, 311, 318, and 332 nm) with a precision filter radiometer (UV-PFR) at Arosa, Switzerland (46.78 degrees , 9.68 degrees , 1850 m above sea level), within the instrument trial phase of a cooperative venture of the Swiss Meteorological Institute (MeteoSwiss) and the Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center. We retrieved ozone-column density data from these direct relative irradiance measurements by adapting the Dobson standard method for all possible single-difference wavelength pairs and one double-difference pair (305/311 and 305/318) under conditions of cloud-free sky and of thin clouds (cloud optical depth <2.5 at 500 nm). All UV-PFR retrievals exhibited excellent agreement with those of collocated Dobson and Brewer spectrophotometers for data obtained during two months in 1999. Combining the results of the error analysis and the findings of the validation, we propose to retrieve ozone-column density by using the 305/311 single difference pair and the double-difference pair. Furthermore, combining both retrievals by building the ratio of ozone-column density yields information that is relevant to data quality control. Estimates of the 305/311 pair agree with measurements by the Dobson and Brewer instruments within 1% for both the mean and the standard deviation of the differences. For the double pair these values are in a range up to 1.6%. However, this pair is less sensitive to model errors. The retrieval performance is also consistent with satellite-based data from the Earth Probe Total Ozone Mapping Spectrometer (EP-TOMS) and the Global Ozone Monitoring Experiment instrument (GOME).     

Short-wave infrared transfer radiometer for the calibration of the moderate-resolution imaging spectrometer and the advanced spaceborne thermal emission and reflection radiometer

A short-wave infrared (700-2500-nm) radiometer has been designed and built to calibrate and cross calibrate spherical-integrating sources used in the calibration of satellite sensors residing on NASA's Earth Observing System platforms. We describe the design, predicted and measured performance, and calibration of the transfer radiometer.     

On the determination of the thermal diffusion factor from column measurements

A new method for experimental determination of the thermal diffusion factor _T for binary gas mixtures with a thermal diffusion column (TDC) is developed, based on A. M. Rozen's equation of TDC. The experimental results for _T are obtained in a reduced form in this approximation. An experimental reference point, determined in the same TDC with a standard gas mixture, is used for the transformation of the results for _T in absolute units. The proposed method is applicable for arbitrary gas mixtures, irrespective of the mass difference of the components.     

Determining the irradiance signal from an asymmetric source with directional detectors: application to calibrations of radiometers with diffusers

The energy transfer integral between radiating rectangular and detecting circular parallel plates having nonideal angular characteristics is solved for modeling the distance dependence of the irradiance signal. The equation derived for the irradiance signal, which is called the modified inverse-square law, depends on the position, shape, size, and angular characteristics of the light source and the detector. We apply the new model equation to the calibration of a spectroradiometer to determine accurately the distance offsets, which fix the positions of the effective receiving apertures of diffusers used in the entrance optics of spectroradiometers. Earlier measurement results, e.g., for solar UV irradiance, may include uncorrected effects and can be corrected reliably as diffuser offsets and other correction factors are determined with the modified inverse-square law. Simplifications of the modified inverse-square law for analyzing the distance offsets and the correction factors are studied. Simplified equations for the diffuser offset analysis may be used without losing the accuracy when the cosine response of the diffuser is reasonably good. However, for diffusers whose angular responsivities deviate much from the cosinusoidal angular responsivity, large approximation errors in the diffuser offset values may appear if the angular effects are not properly taken into account.     

Simultaneous determination of the thermal conductivity and diffusivity of metals using an electronic heater

A nonstationary method allowing simultaneous determination of the thermal conductivity and diffusivity of metals using an electronic heater is described.Notation q_e heat flux density - t temperature - x distance to thermocouple - heating time - t₀ temperature at time zero - thermal conductivity of material examined - a thermal diffusivity of material - c coefficient describing the energy losses - X₁, x₂, x₃ distance to first, second, and third thermocouples, respectively - ₁, ₂, ₃ times during which specimen is heated to temperature t at points X₁, x₂, X₃, respectively     

热带测雨卫星搭载的仪器及其探测结果

针对降水遥感和探测,简要介绍了卫星红外遥感方法和被动微波遥感方法,着重讨论了热带测雨卫星及其搭载仪器。随后介绍了热带测雨卫星多仪器探测结果的应用,并以夏季热对流降水为例,分析了其降水结构、云顶高度和雨顶高度及其与地表降水之间的关系,同时也阐述了如何利用热带测雨卫星和测雨雷达长时间资料,来分析亚洲地区降水的气候分布。最后对卫星主动微波探测降水的发展做了简要展望。     

Fabrication of an interdigitated array electrode on ZnSe and its application to electrooptical measurements using FT-IR spectroscopy

An interdigitated array electrode (IDA) is fabricated on an IR-transparent substrate for use in electrooptical measurements using Fourier transform infrared (FT-IR) spectroscopy. The fabrication of the IDA and its unique sampling geometry for transmission spectroscopy is detailed. The gold IDA was patterned on the ZnSe substrate using a photolithographically defined liftoff process. An IR flow cell was modified to enable the substrate containing the IDA to be used for electrooptical measurements in transmission. The utility of the electrooptical cell is demonstrated by application to two model systems. In the first, changes in the conductivity and spectral features of a receptor membrane (Nafion) upon dehydration are measured. In the second, the measurement of the electric-field-induced orientation of a liquid-crystalline film of 4-n-pentyl-4'-cyanobiphenyl was conducted in a new experimental geometry, with IR transmission normal to the direction of the applied electric field. Difference spectroscopy facilitated the observation of the change in orientation of the liquid crystal with applied potential. These systems demonstrate the general utility of the fabrication scheme described here. It also illustrates its facile adaptation to infrared difference spectroscopy as a means of studying complex phenomena in electrochemical and electrooptical systems.     

Optimization of thermal processes using an Eulerian formulation and application in laser surface hardening

A systematic design approach has been developed for thermal processes combining the finite element method, design sensitivity analysis and optimization. Conductive heat transfer is solved in an Eulerian formulation, where the heat flux is fixed in space and the material flows through a control volume. For constant velocity and heat flux distribution, the Eulerian formulation reduces to a steady-state problem, whereas the Lagrangian formulation remains transient. The reduction to a steady-state problem drastically improves the computational efficiency. Streamline Upwinding Petrov–Galerkin stabilization is employed to suppress the spurious oscillations. Design sensitivities of the temperature field are computed using both the direct differentiation and the adjoint methods. The systematic approach is applied in optimizing the laser surfacing process, where a moving laser beam heats the surface of a plate, and hardening is achieved by rapid cooling due to the heat transfer below the surface. The optimization objective is to maximize the rate of surface hardening. Constraints are introduced on the computed temperature and temperature rate fields to ensure that phase transformations are activated and that melting does not occur. Copyright © 2000 John Wiley & Sons, Ltd.     

Single- and dual-fiber fluorescence probes: application to oil-film measurements in an internal combustion engine

Single- and dual-fiber fluorescence probes have been utilized to study oil-film behavior in a firing Diesel engine. A detailed analysis of the response characteristics of these probes was performed, and universal response curves have been generated through identification of the appropriate nondimensional parameters. For single-fiber probes a single curve was obtained, and for dual-fiber probes families of curves were identified based on three geometric dimensionless parameters. The complementary response characteristics of the single- and dual-fiber probes allows determination of the oil distribution within the piston-liner gap. The dual-fiber probe is not sensitive at small distances. Thus its signal originates solely from the piston surface, whereas the single-fiber probe is most sensitive at small distances and hence to the wall oil film. The engine data from the dual-fiber probe confirmed the presence of an oil film on the piston and provided a means of quantifying the transport of this oil within the engine.     

Near-infrared thermal lens spectrometer based on an erbium-doped fiber amplifier and an acousto-optic tunable filter, and its application in the determination of nucleotides

A novel spectrometer that is based on the use of the thermal lens effect for sensitive measurements of absorption in the near-IR region has been developed. In this instrument the near-IR excitation light (from 1515 to 1590 nm) was provided by an erbium-doped fiber amplifier (EDFA). An acousto-optic tunable filter (AOTF) was used to spectrally disperse the light from the EDFA. The AOTF was used in a new configuration in which, instead of the diffracted light, the transmitted light was used. The heat generated as a consequence of the absorption of the near-IR excitation beam by the sample was monitored by a He-Ne laser. The sensitivity of this spectrometer was found to be at least two to three times higher than that of conventional transmission measurements. Its application in the sensitive determination of nucleotides (adenosine, cytidine, guanosine, and thymidine) is described.     

A new method for the evaluation of thermal conductivity and thermal diffusivity from transient hot strip measurements

The standard straight-line fit to data of a transient hot strip (THS) experiment to determine the thermal conductivity and thermal diffusivitya suffers from two major drawbacks: First, due to the statistical nature of the estimation procedure, there is no relation between the uncertainty of the measured value on one hand and the transport properties obtained on the other. Second, in order to account for he heat capacity of the strip and outer boundary conditions, two intervals of the plot must he rejected before analyzing it. So far, these intervals are selected arbitrarily. We now treat the THS working equation as a function of the four parameters concerned. a.U ₀ (initial voltage), andt ₀ (time delay). Chi-square fittings. following the Levenberg-Marquardt algorithm. are performed separately for several overlapping time intervals of the entire plot to find and a with minimal standard deviation. In the course of subsequent iterations an individual weighting factor is applied to each point to account for systematic errors. This procedure yields the "best" values of anda along with their individual errors. comprising the systematic and the statistical errors. Experimental results on Pyrex glass 7740 were taken to verify the new procedure.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder. Colorado, U.S.A.     

Retrieval of atmospheric ozone profiles from an infrared quantum cascade laser heterodyne radiometer: results and analysis

Following the recent development of a ground-based prototype quantum cascade laser heterodyne radiometer operating in the midinfrared, atmospheric ozone profile retrievals from a solar occultation measurement campaign performed at the Rutherford Appleton Laboratory on 21 September 2006 are presented. Retrieval is based on the optimal estimation method. High resolution (0.0073 cm(-1)) atmospheric spectra recorded by the laser heterodyne radiometer and covering a microwindow (1033.8-1034.5 cm(-1)) optimized for atmospheric ozone measurements were used as measurement vectors. As part of the evaluation of this novel instrument, a comprehensive analysis of the retrievals is presented, demonstrating the high potential of quantum cascade laser heterodyne radiometry for atmospheric sounding. Vertical resolutions of 2 km near the ground and about 3 km in the stratosphere were obtained. The information content of the retrieval was found to be up to 48 bits, which is much higher than any other passive ground-based instrument. Frequency mismatches of several absorption peaks between the forward model and experimental spectra have been observed and significantly contribute to the retrieval noise error in the upper-troposphere lower-stratosphere region. Retrieved ozone vertical profiles were compared to ozonesonde data recorded at similar latitudes. The agreement is generally excellent except for the 20 to 25 km peak in ozone concentration, where ozonesonde data were found to be 20% lower than the amount retrieved from the laser heterodyne radiometer spectra. Quantum cascade laser based heterodyne radiometry in the midinfrared has been demonstrated to provide high spectral resolution and unprecedented vertical resolution for a passive sounder in a highly compact and mechanically simple package.     

Retrieval of atmospheric optical parameters from airborne flux measurements: application to the atmospheric correction of imagery

Methodologies that employ auxilliary flux data collected by upward- and downward-looking optical sensors to improve atmospheric corrections of airborne multispectral images are presented and evaluated. Such flux data often are collected in current airborne sensors to produce bidirectional reflectance factor (BRF) images and estimates of hemispherical-hemispherical reflectance. The fact that these images must then be corrected for atmospheric interference raises the question as to whether the auxilliary flux information can be employed to estimate some of the input parameters required by atmospheric correction models. Radiative transfer simulations are employed to demonstrate that the utilization of the downwelling and upwelling fluxes as a means of inferring intrinsic atmospheric optical information can be used to better characterize the local atmosphere and accordingly to improve the atmospheric corrections applied to the apparent BRF images.     

Genetic algorithm for informative basis function selection from the wavelet packet decomposition with application to corrosion identification using acoustic emission

Chemical process installations are exposed to aggressive chemicals and conditions leading to corrosion. The damage from corrosion can lead to an unexpected plant shutdown and to the exposure of people and the environment to chemicals. Due to changes within and on the surface of materials subjected to corrosion, energy is released in the form of acoustic waves. This acoustic activity can be captured and used for corrosion monitoring in chemical process installations. Wavelet packet coefficients extracted from the acoustic activity have been considered to determine whether corrosion occurs, and to identify the type of corrosion process, at least for the most important corrosion processes in the chemical process industry. Feature subset selection is then applied to these wavelet coefficients to achieve a much higher accuracy in the identification of different corrosion processes than when no feature subset selection is applied to the acoustic waves. However, due to the statistical dependencies that potentially exist between the wavelet coefficients, the latter should not be selected independently from each other. Local discriminant basis selection algorithms do not take the statistical dependencies between wavelet coefficients into account. In this paper, we have used several mutual information-based approaches that take these dependencies into account and compared them to the wavelet-specific local discriminant basis selection algorithm. Furthermore, a hybrid filter-wrapper genetic algorithm, which uses a relevance-redundancy approach as a local search procedure, was designed. The highest classification accuracies are obtained with the hybrid filter-wrapper genetic algorithm, for all classifiers used in this paper. Furthermore, the proposed algorithm easily outperformed one of the most commonly used classifiers in chemometrics: partial least squares discriminant analysis (PLS-DA). A naïve Bayes classifier that uses the features selected by the hybrid filter-wrapper genetic algorithm was able to identify the absence of corrosion, uniform corrosion, pitting and stress corrosion cracking, with an accuracy of up to 87.20%.     

Precision of determination of the coordinates of an underwater cable from the results of measurements of its magnetic field

The precision of the coordinates of an underwater cable that are determined from the measurements of the strength of the magnetic field created by the cable is estimated. The maximum total or minimum difference signal of the horizontal component of the field with the use of two sensors as well as the minimum vertical component of the magnetic field with the use of a single sensor are recorded.     

Doses to the scanned individual and to the operator from an X-ray body scanner system

The X-ray body scanner (BS) is going to find common use as a body-checking equipment at the entrance borders of countries, to find illicit drugs or forbidden items which have been hidden inside the body cavities, or attached to the body parts of the passengers. Considering the tissue weighting factors of the sensitive organs, the total effective dose due to the scanning by the system was estimated to be 3.8 μSv per scan. The ambient dose equivalent rates within the distance range of 300-40 cm from the X-ray generator were measured to be 4.5 up to 50 μSv h(-1). It is concluded that, in general, BS systems could be a safe device for the operators and people who are being scanned. But using such systems should be justified for everybody and special care should be taken for children and pregnant ladies.     

Refractive sounding by use of satellite solar occultation measurements including an assessment of its usefulness to the stratospheric aerosol and gas experiment program

Vertical profiles of atmospheric density and temperature obtained with the technique of solar refractive sounding can potentially be used to improve satellite solar occultation trace species retrievals by reducing the uncertainties associated with Rayleigh scattering and the temperature dependence of absorption bands. The required refraction measurements and the algorithm utilized to recover density and temperature are described. Simulations are performed to estimate the measurement accuracy that is necessary to retrieve useful meteorological soundings at stratospheric altitudes. The method is applied to data measured by the Stratospheric Aerosol and Gas Experiment (SAGE) II. Unfortunately, because of poor vertical sampling and measurement uncertainties, the meteorological profiles derived from the SAGE II data are not consistently accurate enough to improve the SAGE II estimates for the concentrations of trace species. However, the qualitatively decent results provide optimism for future development and implementation of visible refractive sounding as a tool to help improve the accuracy of trace species retrievals within solar or stellar occultation experiments, including the SAGE III program.     

Density and thermal expansion coefficient of liquid helium-4 from measurements of the dielectric constant

Measurements have been made of the dielectric constant of liquid helium from 1.15 K to 4.9 K. The density and thermal expansion coefficient have been derived from these measurements using the Clausius-Mossotti equation. Comparison is made to modern measurements. Formulae are presented representing the absolute density and thermal expansion coefficient from 0 K to 4.9 K. Difficulties and uncertainties in these results are discussed.