Optimized spectral microwindows for data analysis of the Michelson Interferometer for Passive Atmospheric Sounding on the Environmental Satellite

For data analysis of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) atmospheric limb emission spectroscopic experiment on Environmental Satellite microwindows, i.e., small spectral regions for data analysis, have been defined and optimized. A novel optimization scheme has been developed for this purpose that adjusts microwindow boundaries such that the total retrieval error with respect to measurement noise, parameter uncertainties, and systematic errors is minimized. Dedicated databases that contain optimized microwindows for retrieval of vertical profiles of pressure and temperature, H(2)O, O(3), HNO(3), CH(4), N(2)O, and NO(2) have been generated. Furthermore, a tool for optimal selection of subsets of predefined microwindows for specific retrieval situations has been provided. This tool can be used further for estimating total retrieval errors for a selected microwindow subset. It has been shown by use of this tool that an altitude-dependent definition of microwindows is superior to an altitude-independent definition. For computational efficiency a dedicated microwindow-related list of spectral lines has been defined that contains only those spectral lines that are of relevance for MIPAS limb sounding observations.     

Selection of optimized microwindows for atmospheric spectroscopy

In atmospheric Fourier transform spectroscopy so-called microwindows are usually analyzed for retrieval of trace constituents rather than the spectrum as a whole. These microwindows, which are sets of consecutive spectral grid points, contain one or more prominent transitions of the target species, whereas it is desirable for the signal of interfering species to be minimum. An objective, quantitative method is presented to optimize the microwindow boundaries with respect to random errors, signal of interfering species, other parameter and systematic errors and to select optimum microwindows with respect to their associated retrieval errors. Case studies for N(2)O microwindows are performed for a spaceborne limb emission experiment to assess the dependence of the optimum microwindow width on the retrieval concept.     

Optimized forward model and retrieval scheme for MIPAS near-real-time data processing

An optimized code to perform the near-real-time retrieval of profiles of pressure, temperature, and volume mixing ratio (VMR) of five key species (O(3), H(2)O, HNO(3), CH(4), and N(2)O) from infrared limb spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) experiment on board the European Space Agency (ESA) Environmental Satellite ENVISAT-1 was developed as part of a ESA-supported study. The implementation uses the global fit approach on selected narrow spectral intervals (microwindows) to retrieve each profile in sequence. The trade-off between run time and accuracy of the retrieval was optimized from both the physical and the mathematical points of view, with optimizations in the program structure, in the radiative transfer model, and in the computation of the retrieval Jacobian. The attained performances of the retrieval code are noise error on temperature <2 K at all the altitudes covered by the typical MIPAS scan (8-53 km with 3-km resolution), noise error on tangent pressure <3%, and noise error on VMR of the target species <5% at most of the altitudes covered by the standard MIPAS scan, with a total run time of less than 1 min on a modern workstation.     

Apodization effects in the retrieval of volume mixing ratio profiles

In remote sensing applications, spectra measured by Fourier-transform spectrometers are routinely apodized. A rigorous analysis approach would explicitly account for correlations induced in the covariance matrix by apodization, but these correlations are often ignored to simplify and speed up the processing. Using spectra measured by the Atmospheric Trace Molecule Spectroscopy missions, we investigated the effect of apodization on the retrieval of volume mixing ratio profiles for the case in which these correlations are ignored. Minor discrepancies occur between results for apodized and unapodized spectra, particularly when lines with a low signal-to-noise ratio are fitted. A set of microwindows is reported for O3 in the range of 1550-3350 cm(-1).     

Bandpass-resampling effects for the retrieval of surface emissivity

The retrieval of surface emissivity in the 8-14-microm region from remotely sensed thermal imagery requires channel-averaged values of atmospheric transmittance, path radiance, and downwelling sky flux. Band-pass resampling introduces inherent retrieval errors that depend on atmospheric conditions, spectral region, bandwidth, flight altitude, and surface temperature. This simulation study is performed for clear sky conditions and moderate atmospheric water vapor contents. It shows that relative emissivity retrieval errors can reach as much as 3% for broadband sensors (1-2-microm bandwidth) and 0.8% for narrowband instruments (0.15 microm), even for constant surface emissivity. For spectrally varying surface emissivities the relative retrieval error increases for the broadband instrument by approximately 2% in channels with strong emissivity changes of 0.05-0.1. The corresponding retrieval errors for narrowband sensors increase by approximately 3-4%. The channels in the atmospheric window regions with lower transmittance, i.e., 8-8.5 and 12.5-14 microm, are most sensitive to retrieval errors.     

Methods for determining regularization for atmospheric retrieval problems

The atmosphere of Earth has already been investigated by several spaceborne instruments, and several further instruments will be launched, e.g., NASA's Earth Observing System Aura platform and the European Space Agency's Environmental Satellite. To stabilize the results in atmospheric retrievals, constraints are used in the iteration process. Therefore hard constraints (discretization of the retrieval grid) and soft constraints (regularization operators) are included in the retrieval. Tikhonov regularization is often used as a soft constraint. In this study, different types of Tikhonov operator were compared, and several new methods were developed to determine the optimal strength of the constraint operationally. The resulting regularization parameters were applied successfully to an ozone retrieval from simulated nadir sounding spectra like those expected to be measured by the Tropospheric Emission Spectrometer, which is part of the Aura platform. Retrievals were characterized by means of estimated error, averaging kernel, vertical resolution, and degrees of freedom.     

Ground-based differential absorption lidar for water-vapor and temperature profiling: methodology

A comprehensive formulation of the differential absorption lidar (DIAL) methodology is presented that explicitly includes details of the spectral distributions of both the transmitted and the backscattered light. The method is important for high-accuracy water-vapor retrievals and in particular for temperature measurements. Probability estimates of the error that is due to Doppler-broadened Rayleigh scattering based on an extended experimental data set are presented, as is an analytical treatment of errors that are due to averaging in the nonlinear retrieval scheme. System performance requirements are derived that show that water-vapor retrievals with an accuracy of better than 5% and temperature retrievals with an accuracy of better than 1 K in the entire troposphere are feasible if the error that results from Rayleigh-Doppler correction can be avoided. A modification of the DIAL technique, high-spectral-resolution DIAL avoids errors that are due to Doppler-broadened Rayleigh backscatter and permits simultaneous water-vapor and wind measurements with the same system.     

An improved lead compensation technique for three-wire resistancetemperature detectors

An improved lead resistance compensation technique for use with three-wire resistance temperature detectors is presented. The present practice of using the three-wire concept in an unbalanced bridge to provide signal to direct reading instruments produces nearly 1% error for a lead resistance as low as 1 Ω. In contrast, the new method limits the error to below 0.1% with much higher lead wire resistances     

显微放大率测量方法的不确定度分析

确定现行光学仪器目视显微放大率测量方法的准确度限,可通过建立目视显微放大率测量方法的误差链,找出误差源,根据误差源属性进行A类或B类不确定度分析,从而得出目视显微放大率测量方法合成的扩展不确定度可以达到U90=0.4%.现行光学仪器目视显微放大率测量方法,可以满足1.2%允差要求的检验;按2次检测合并要求,可以满足1.7%允差要求的检验.     

Remote sensing of ocean color and aerosol properties: resolving the issue of aerosol absorption

Current atmospheric correction and aerosol retrieval algorithms for ocean color sensors use measurements of the top-of-the-atmosphere reflectance in the near infrared, where the contribution from the ocean is known for case 1 waters, to assess the aerosol optical properties. Such measurements are incapable of distinguishing between weakly and strongly absorbing aerosols, and the atmospheric correction and aerosol retrieval algorithms fail if the incorrect absorption properties of the aerosol are assumed. We present an algorithm that appears promising for the retrieval of in-water biophysical properties and aerosol optical properties in atmospheres containing both weakly and strongly absorbing aerosols. By using the entire spectrum available to most ocean color instruments (412-865 nm), we simultaneously recover the ocean's bio-optical properties and a set of aerosol models that best describes the aerosol optical properties. The algorithm is applied to simulated situations that are likely to occur off the U.S. East Coast in summer when the aerosols could be of the locally generated weakly absorbing Maritime type or of the pollution-generated strongly absorbing urban-type transported over the ocean by the winds. The simulations show that the algorithm behaves well in an atmosphere with either weakly or strongly absorbing aerosol. The algorithm successfully identifies absorbing aerosols and provides close values for the aerosol optical thickness. It also provides excellent retrievals of the ocean bio-optical properties. The algorithm uses a bio-optical model of case 1 waters and a set of aerosol models for its operation. The relevant parameters of both the ocean and atmosphere are systematically varied to find the best (in a rms sense) fit to the measured top-of-the-atmosphere spectral reflectance. Examples are provided that show the algorithm's performance in the presence of errors, e.g., error in the contribution from whitecaps and error in radiometric calibration.     

Phase Retrieval Using Conjugate Gradient Minimization

Abstract

A new algorithm for phase retrieval from the Fourier modulus is presented. The technique differs from the iterative transform algorithm in both the choice of error metric and the use of a conjugate gradient minimization research. Results are presented for noisy simulated data and also for measured photon-limited data.     

测量仪器分类论

本文是对测量仪器“器”和“具”之分的发展，提出把测量仪器分为提供量值和测量量值两类。提供量值的仪器复现或输出一定的对应标称值信号；测量量值的仪器则是把输入信号指示出来。作者试图对不同专业的仪器从本质上进行分类，并由此得出测量仪器校准的4种方法，同时提出以偏差表征提供量值仪器，以示值误差表征提供量值仪器。     

OSIS: remote sensing code for estimating aerosol optical properties in urban areas from very high spatial resolution images

The achievement of new satellite or airborne remote sensing instruments enables the more precise study of cities with metric spatial resolutions. For studies such as the radiative characterization of urban features, knowledge of the atmosphere and particularly of aerosols is required to perform first an atmospheric compensation of the remote sensing images. However, to our knowledge, no efficient aerosol characterization technique adapted both to urban areas and to very high spatial resolution images has yet been developed. The goal of this paper is so to present a new code to characterize aerosol optical properties, OSIS, adapted to urban remote sensing images of metric spatial resolution acquired in the visible and near-IR spectral domains. First, a new aerosol characterization method based on the observation of shadow/sun transitions is presented, offering the advantage to avoid the assessment of target reflectances. Its principle and the modeling of the signal used to solve the retrieval equation are then detailed. Finally, a sensitivity study of OSIS from synthetic images simulated by the radiative transfer code AMARTIS v2 is also presented. This study has shown an intrinsic precision of this tool of Δτ(a)=0.1.τ(a) ± (0.02 + 0.4.τ(a)) for retrieval of aerosol optical thicknesses. This study shows that OSIS is a powerful tool for aerosol characterization that has a precision similar to satellite products for the aerosol optical thicknesses retrieval and that can be applied to every very high spatial resolution instrument, multispectral or hyperspectral, airborne or satellite.     

Optical remote sensing of marine constituents in coastal waters: a feasibility study

Optical remote sensing of ocean color is a well-established technique for inferring ocean properties. However, most retrieval algorithms are based on the assumption that the radiance received by satellite instruments is affected only by the phytoplankton pigment concentration and correlated substances. This assumption works well for open ocean water but becomes questionable for coastal waters. To reduce uncertainties associated with this assumption, we developed a new algorithm for the retrieval of marine constituents in a coastal environment. We assumed that ocean color can be adequately described by a three-component model made up of chlorophyll a, suspended matter, and yellow substance. The simultaneous retrieval of these three marine constituents and of the atmospheric aerosol content was accomplished through an inverse-modeling scheme in which the difference between simulated radiances exiting the atmosphere and radiances measured with a satellite sensor was minimized. Simulated radiances were generated with a comprehensive radiative transfer model that is applicable to the coupled atmosphere-ocean system. The method of simulated annealing was used to minimize the difference between measured and simulated radiances. To evaluate the retrieval algorithm, we used simulated (instead of measured) satellite-received radiances that were generated for specified concentrations of aerosols and marine constituents, and we tested the ability of the algorithm to retrieve assumed concentrations. Our results require experimental validation but show that the retrieval of marine constituents in coastal waters is possible.     

Classification of measuring devices by their accuracy

Conclusions It is proposed to divide the general criterion for the accuracy of measures and measuring instruments expressed by a conventional sign or number into two notations, those of accuracy categories and accuracy classes. Categories of accuracy should be assigned to such groups of measuring devices (sets of measures of various nominal values) for which it is impossible to establish a single-valued characteristic expressed in relative units or measurement units. Categories of accuracy represent a nominal characteristic and its content can only be determined by evaluating the relation between a scale of a certain grade of accuracy and the numerical parameters which determine the accuracy of measurement by means of a given device without introducing corrections. Classes of accuracy characterize devices for which a given error characterizes completely and in a single-valued manner their metrological properties.For a more complete metrological characterization of measures and measuring instruments, it is advisable to indicate on the measures or measuring instruments, or in their certificates, in addition to their nominal categories and classes also their ranges, scale factors, or scale values.It is possible to use a double classification system, i.e., to assign to a single measure or measuring instrument both its category and class of accuracy. It has already been pointed out that the category characterizes the degree to which a measure of measuring instrument approaches its maximum attainable accuracy with the existing technique for measuring the given physical value. The class of accuracy indicates the tolerated and actually attainable limiting measurement error.     

Selection of a standardized signal level for information measurement systems

Conclusions The suggested technique for computing standardized signal levels provides a minimum number of elements in the system for given characteristics of the measuring transducers and information processing instruments, and a given additional error due to connecting simultaneously different numbers of instruments.Translated from Izmeritel'naya Tekhnika, No. 8, pp. 9–11, August, 1968.     

On the comparison of bilinear, cubic spline, and fuzzy interpolation techniques for robotic position measurements

This paper describes a novel technique for position error compensations of robots based on a fuzzy error interpolation method. A traditional robot calibration implements either model or modelless methods. The compensation of position error in a model-less method is to move the robot's end-effector to a target position in the robot workspace, and to find the target position error online based on the measured neighboring four-point errors around the target position. For this purpose, a stereo camera or other measurement device can be used to measure offline the position errors of the robot's end-effector at predefined grid points. By using the proposed fuzzy error interpolation technique, the accuracy of the position error compensation can be greatly improved, which is confirmed by the simulation results given in this paper. A comparison study among various interpolation methods, such as bilinear, cubic spline, and the fuzzy error interpolation technique is also made via simulation. The simulation results show that more accurate compensation results can be achieved using the fuzzy error interpolation technique compared with its bilinear and cubic spline counterparts.     

Analysis of the results of checking gauges and instruments

Conclusions Rational values of the permissible errors can be established only by analyzing the probable checking scrap. The latter is determined by technical and economic considerations which include: a) the permissibility of a certain small percentage of unsatisfactory instruments remaining in circulation, b) the permissibility of condemning a certain percentage of serviceable instruments, c) the cost of a checking method which reduces to the required small dimensions or eliminates scrap.No general relation between the permissible errors in the tested and reference measures or instruments is possible.A rational and reliable selection of permissible errors and methods of checking is only possible when sufficient data is available on the error distribution laws in the manufactured measures and instruments. The provision of such data should be one of the primary objects in testing standard instruments.Everything stated above refers to large scale testing of mass produced measures and measuring instruments when the aggregate of both the tested and reference measures and measuring instruments is sufficiently large. Above methods of calculations, however, are applicable to small groups of reference measures and instruments. In that case, however, it is necessary to use the discrete distribution of probable error densities which corresponds to the given number of instruments and their errors. Such a case could occur in evaluating checking results in any laboratory with a small number of reference measures or instruments. Such an evaluation is, of course, only possible if the errors of the available measures are determined with sufficient accuracy by more accurate methods than those normally used in checking these measures.     

Experimental investigation of the self- and N(2)-broadened continuum within the ν(2) band of water vapor

We present an experimental study of the self- and N(2)-broadened H(2) O continuum in microwindows within the ν(2) fundamental centered at ~1600 cm(-1). The continuum is derived from transmission spectra recorded at room temperature with a BOMEM Fourier transform spectrometer at a resolution of ~0.040 cm(-1). Although we find general agreement with previous studies, our results suggest that there is significant near-wing super-Lorentzian behavior that produces a highly wave-number-dependent structure in the continuum as it is currently defined.     

Carbon monoxide total column retrievals by use of the measurements of pollution in the troposphere airborne test radiometer

The Measurements of Pollution in the Troposphere (MOPITT) Airborne Test Radiometer (MATR) uses gas correlation filter radiometry from high-altitude aircraft to measure tropospheric carbon monoxide. This radiometer is used in support of the ongoing validation campaign for the MOPITT instrument aboard the Earth Observation System Terra satellite. A recent study of MATR CO retrievals that used data from the autumn of 2001 in the western United States is presented. Retrievals of the CO total column were performed and compared to in situ sampling with less than 10% retrieval error. Effects that influence retrieval, such as instrument sensitivity, retrieval sensitivity, and the bias between observations and the radiative transfer model, are discussed. Comparisons of MATR and MOPITT retrievals show promising consistency. A preliminary interpretation of MATR results is also presented.