Iterative regularization methods for atmospheric remote sensing

In this paper we present different inversion algorithms for nonlinear ill-posed problems arising in atmosphere remote sensing. The proposed methods are Landweber's method (LwM), the iteratively regularized Gauss-Newton method, and the conventional and regularizing Levenberg-Marquardt method. In addition, some accelerated LwMs and a technique for smoothing the Levenberg-Marquardt solution are proposed. The numerical performance of the methods is studied by means of simulations. Results are presented for an inverse problem in atmospheric remote sensing, i.e., temperature sounding with an airborne uplooking high-resolution far-infrared spectrometer.     

An efficient inversion algorithm for atmospheric remote sensing with application to UV limb observations

In this paper we present a retrieval algorithm for atmospheric remote sensing. The algorithm combines Tikhonov regularization and the iteratively regularized Gauss-Newton method and is devoted to the solution of multi-parameter inverse problems with simple bounds on the variables. The basic features of the algorithm: the solution of the bound-constrained minimization problem, the selection of the optimal regularization parameter, the derivation of the global regularization matrix and the characterization of the solution (error analysis) are discussed in detailed. The inversion algorithm is applied to ozone retrieval from SCIAMACHY limb scatter measurements in the ultraviolet spectral range.     

定量化红外遥感应用的高精度水浴黑体

辐射定标是红外遥感信息定量化的关键技术之一。根据定量化红外遥感应用的需求,研制了高精度水浴黑体辐射源,并应用均匀镜-漫反射模型法对其发射率进行了计算。提出了基于绝对低温辐射计的常温黑体定标方法。性能测试结果表明,该黑体辐射源可用于遥感探测器中的红外辐射定标。     

Detection of elevated tropospheric hydrogen peroxide (H2O2) mixing ratios in atmospheric chemistry experiment (ACE) subtropical infrared solar occultation spectra

We report measurements of hydrogen peroxide (H₂O₂) profiles from infrared solar occultation spectra recorded at 0.02 cm⁻¹ resolution by the atmospheric chemistry experiment (ACE) during 2004 and 2005. Mixing ratios as high as 1.7 ppbv (1 ppbv=1×10⁻⁹ per unit volume) were measured in the subtropical troposphere. Back trajectories, fire count statistics, and simultaneous measurements of other species from the same occultation provide evidence that the elevated H₂O₂ mixing ratios originated from a young biomass-burning plume. The ACE time series show only a few cases with elevated H₂O₂ mixing ratios likely because of the short lifetime of H₂O₂ and the limited sampling during biomass-burning time periods.     

直射太阳光红外吸收光谱技术遥测大气中二氧化碳柱浓度

大气中二氧化碳浓度持续增高导致环境和气候变化等问题成为人们关注的焦点. 为了实时遥测二氧化碳气体柱浓度, 研究了一种地基低分辨遥测系统和实时光谱数据反演分析方法. 利用该系统在合肥地区进行了连续观测, 从太阳吸收光谱中实时获取了整层大气透过率. 采用逐线积分非线性最小二乘光谱反演算法, 从整层大气透过率中反演了二氧化碳柱浓度和氧气柱浓度, 并以氧气柱浓度为内标函数获得了二氧化碳干空气柱体积混合比, 精密度优于3%. 将2012年9月25日12时到15时本系统测量的二氧化碳干空气柱体积混合比均值与此时段过境本站点区域的日本温室气体卫星观测结果进行了比较, 两者偏差小于1%.可见, 该系统和方法具有很高的精密度和准确度, 是一种有效的温室气体观测手段. 关键词： 红外吸收光谱技术 遥测 二氧化碳 柱浓度     

Analytic evaluation of the weighting functions for remote sensing of blackbody planetary atmospheres: a general linearization approach

An analytic approach is proposed for the evaluation of weighting functions for remote sensing of a blackbody planetary atmosphere based on straightforward, general linearization. In the present paper, this approach is applied to the case of remote sensing with the nadir (down-looking) geometry. Expressions for weighting functions for various atmospheric parameters are derived. It is demonstrated that in a realistic case of temperature-dependent atmospheric absorption, an additional term appears in the expression for the temperature weighting function which contains the temperature derivative of the atmospheric absorption coefficient. The approach is applied to the case of a semi-infinite atmosphere and then, to the atmosphere of a finite optical depth with the underlying surface. In this, latter case, the expressions are also obtained for partial derivatives of observed radiances with respect to surface parameters: surface pressure, temperature and emissivity.     

Atmospheric weighting functions and surface partial derivatives for remote sensing of scattering planetary atmospheres in thermal spectral region: general adjoint approach

An approach to formulation of inversion algorithms for remote sensing in the thermal spectral region in the case of a scattering planetary atmosphere, based on the adjoint equation of radiative transfer (Ustinov (JQSRT 68 (2001) 195; JQSRT 73 (2002) 29); referred to as Papers 1 and 2, respectively, in the main text), is applied to the general case of retrievals of atmospheric and surface parameters for the scattering atmosphere with nadir viewing geometry. Analytic expressions for corresponding weighting functions for atmospheric parameters and partial derivatives for surface parameters are derived. The case of pure atmospheric absorption with a scattering underlying surface is considered and convergence to results obtained for the non-scattering atmospheres (Ustinov (JQSRT 74 (2002) 683), referred to as Paper 3 in the main text) is demonstrated.     

富营养化水体环境中COD浓度遥感监测系统设计

对富营养化水体环境中COD浓度进行遥感监测,可以预防富营养化水体环境中COD浓度增加,提高水体水质,增加水循环次数,减少水体中有机物的污染。当前富营养化水体环境中COD浓度遥感监测系统设计方法,以Modis遥感影像数据为原理,依据富营养化水体环境中COD浓度的特征提取结果,对富营养化水体环境中COD浓度进行遥感监测,没有具体对遥感监测系统进行详细地设计,无法获取富营养化水体环境中COD浓度高精度的遥感监测信息,存在遥感监测结果偏差大的问题。提出了一种基于Zigbee的富营养化水体环境中COD浓度遥感监测系统设计方法。该方法先对Zigbee的富营养化水体环境中COD浓度遥感监测系统进行硬件设计,采用IMF对富营养化水体环境中COD浓度进行特征提取,以特征提取结果为基础,依据COD浓度指数时间序列实现富营养化水体环境中COD浓度遥感监测,最后利用Retinex法对COD浓度遥感监测的图像进行处理,完成对富营养化水体环境中COD浓度的遥感监测。仿真实验结果证明,所提系统设计方法可以精确地对富营养化水体环境中COD浓度进行安全快速的遥感监测。     

Computation of the analysis error covariance in variational data assimilation problems with nonlinear dynamics

The problem of variational data assimilation for a nonlinear evolution model is formulated as an optimal control problem to find the initial condition function. The data contain errors (observation and background errors), hence there will be errors in the optimal solution. For mildly nonlinear dynamics, the covariance matrix of the optimal solution error can often be approximated by the inverse Hessian of the cost functional. Here we focus on highly nonlinear dynamics, in which case this approximation may not be valid. The equation relating the optimal solution error and the errors of the input data is used to construct an approximation of the optimal solution error covariance. Two new methods for computing this covariance are presented: the fully nonlinear ensemble method with sampling error compensation and the ‘effective inverse Hessian’ method. The second method relies on the efficient computation of the inverse Hessian by the quasi-Newton BFGS method with preconditioning. Numerical examples are presented for the model governed by Burgers equation with a nonlinear viscous term.     

Long-term evolution in the tropospheric concentration of chlorofluorocarbon 12 (CCl2F2) derived from high-spectral resolution infrared solar absorption spectra: retrieval and comparison with in situ surface measurements

The average tropospheric volume mixing ratios of chlorofluorocarbon 12 (CCl₂F₂) have been retrieved from high-spectral resolution ground-based infrared solar-absorption spectra recorded from March 1982 to October 2003 with the McMath Fourier transform spectrometer at the US National Solar Observatory facility on Kitt Peak in southern Arizona (31.9°N, 111.6°W, 2.09 km altitude). The retrievals are based on fits to the unresolved ν₈ band Q-branches near using the SFIT2 retrieval algorithm. The annual increase rate was equal to (16.88±1.37) parts per trillion (10^-12) by volume at the beginning of the time series, March 1982, or (4.77±0.04)%, 1 sigma, declining progressively to (2.49±1.24) parts per trillion, by volume at the end, October 2003, or (0.46±0.24)%, 1 sigma. Average tropospheric mixing ratios from the solar spectra have been compared with average surface flask and in situ sampling measurements from the Climate Monitoring and Diagnostics Laboratory (CMDL) station at Niwot Ridge, CO, (USA) (40.0°N, 105.5°W, 3013 m altitude). The average ratio and standard deviation of the monthly means of the retrieved tropospheric mixing ratios relative to the CMDL surface mixing ratios is (1.01±0.03) for the overlapping time period. Both datasets demonstrate the progressive impact of the Montreal protocol and its strengthening amendments on the trend of CCl₂F₂, though a tropospheric decrease has yet to be observed.     

Reliability in reconstruction of the axisymmetric refractive index profiles from transverse interferograms. Accurate versus approximate methods: A comparative study

A mathematical formalism related to the approximate as well as the accurate interferometric data reduction schemes is briefly outlined and subsequently applied in the reconstruction of the assumed (Luneburg) axisymmetric refractive index distribution. The presented comparative analysis confirms the generally held opinion that the approximate methods (“straight-line” and Kokubun-Iga approaches) may provide quite reasonable results in the examination of refractively inhomogeneous disturbances characterized by weak gradient and moderate index variation. On the other hand, the accurate scheme for transverse interferometric data interpretation and reduction, based on the close-form correlation between the fringe shift and the deflection function, [1] remains the only method for reliable reconstruction of strongly refracting index profiles, independently of magnitude of refraction and ambiguity of the fringes. This fact is of considerable importance for transverse interferometry of fibers (preform rods) and/or GRIN-rod lenses characterized by high numerical apertures.     

Monitoring the brain metabolites of children with acute encephalopathy caused by the H1N1 virus responsible for the 2009 influenza pandemic: a quantitative in vivo H MR spectroscopy study

Background and Purpose

Influenza viral infection, which results in central nervous system dysfunction, is a major cause of acute encephalopathy (AE). The purpose of this study was to investigate the changes in the concentrations of brain metabolites in children with AE using single-voxel magnetic resonance spectroscopy (MRS) and to provide diagnostic information about the relationship between the symptoms of AE and metabolite concentrations.

Materials and Methods

The subjects were 10 children (mean age: 6.2 years; range: 1–13) with AE caused by the novel influenza A virus responsible for the 2009 influenza pandemic. The serial MRS data (TE/TR=30/5000 ms, 3 T) acquired from the basal ganglia (BG) and centrum semiovale (CS) of each patient were categorized into three periods: (1) initial neurological symptom presentation and the start of treatment (n= 10), (2) short-term follow-up (n= 9) and (3) long-term follow-up (n= 3). As controls, the magnetic resonance (MR) spectra of eight age-matched children were also investigated.

Results

In both regions, the concentrations of the major metabolites (N-acetylaspartate, creatine, choline, myo-inositol, glutamate/glutamine complex and glutamate) only showed minor fluctuations between the three periods. On the other hand, higher levels of taurine (Tau) were observed in the BG during the second period (P=.005), and increased levels of glucose were observed in the CS during the first (P=.005) and second (P=.036) periods.

Conclusions

Serial monitoring of brain metabolite changes was carried out with a clinical MR system. The concentrations of major metabolites only displayed very minor fluctuations in response to mild H1N1-related AE. However, a higher Tau concentration was found to be associated with neurological symptoms. Further studies are required to improve our understanding of the detailed activity of Tau in AE.     

Structural and energetic properties of alkylfluoride–BF3 complexes in the gas phase and condensed‐phase media: computations and matrix infrared spectroscopy

We have undertaken an experimental and computational study of the structural properties of a few alkylfluoride–BF₃ complexes (RF′–BF₃), which are proposed intermediates in a certain class of Friedel–Crafts reactions. Using density functional theory and second‐order Møller–Plesset calculations, we have obtained gas‐phase structures, frequencies, and B–F′ bond potentials for CH₃F–BF₃, (CH₃)₂CHF–BF₃, and (CH₃)₃CF–BF₃. All the complexes are weakly‐bonded in the gas phase, with B–F′ distances (X3LYP/aug‐cc‐pVTZ) of about 2.4 Å and binding energies (MP2/aug‐cc‐pVTZ) ranging from 5.4 and 6.7 kcal/mol. Accordingly, gas‐phase bond potentials are relatively shallow and flat for these complexes. However, even though the inner walls of the potentials are rather soft (the energies rise by only about 5 to 10 kcal/mol between 2.4 and 1.6 Å), we observe no global or local minima at short B–F′ distances. For the (CH₃)₂CHF–BF₃ and (CH₃)₃CF–BF₃ potentials in dielectric media, we do observe a distinct flattening along the inner wall, which results in shelf‐like region near 1.7 Å, but this feature is not a true local minimum. We have also obtained low‐temperature infrared spectra of the (CH₃)₂CHF–BF₃ complex in solid neon, and the frequencies agree quite favorably with those obtained via computations, which validates the computational assessment of the gas‐phase complexes. Copyright © 2011 John Wiley & Sons, Ltd.     

On the accuracy of classical, semiclassical and quantum methods in collision line broadening calculations: Comparative analysis for C2H2-Ar, He systems

Accuracies of classical, semiclassical and quantum methods are comprehensively examined in calculations of impact line widths of C₂H₂ molecules perturbed by Ar and He. The field of comparative study covers both infrared absorption and Raman scattering lines of acetylene having rotational quantum number J=0-30 at temperatures 173 and 296 K. Calculations have been made by fully classical method and by three basic least approximate semiclassical methods, namely, Neilsen-Gordon (NG) method, peaking approximation (PA) and Smith-Giraud-Cooper (SGC) method. Most accurate ab initio potential energy surfaces (PES) of Yang et al. (1996) [21] and Mozsynski et al. (1995) [22] have been applied to model C₂H₂-Ar and C₂H₂-He interactions. The comparison has been made also with available experimental data and with the results of rigorous fully quantum-mechanical calculations within close coupling and coupled states approaches in identical conditions. Semiclassical methods are proved to be not so much accurate as it is generally believed since all they gave in the cases considered seriously underestimated results. The fundamental issue of the adequacy of simplified trajectories in collision broadening calculations is finally reasonably solved. In cases of C₂H₂-Ar and C₂H₂-He systems the use of the “exact” isotropic trajectories (i.e. driven only by the isotropic part of PES) is the main reason of failing of NG, PA and SGC methods. Thus the neglecting of back-influence of the RT exchange on the classical path is a principal defect of semiclassical methods. Finally, the application of simplified trajectories is recognized as inadequate and risky in broadening calculations for molecules having relatively small rotational constants when accurate ab initio PES are applied.