基于主成分分析的多能谱CT图像分析方法研究

基于光子计数探测器的能谱CT,可以同时采集多个能谱通道的投影数据,并获得相应能量范围内物质的吸收特征,可以有效应用于物质识别与材料分解。主成分分析是一种很好的多元数据分析技术,可以用于处理多能谱CT数据。本文分别在投影域和图像域对能谱CT数据进行主成分分析,并对分析结果做出系统比较。为了减少噪声的影响,提高能谱CT图像的彩色表征性能,提出双域滤波与像素值平方相结合的方法,用于含噪声的主成分图像去噪,然后将所选取的主成分图像映射到RGB颜色通道。实验结果表明,无论是在投影域还是图像域进行主成分分析,都可以获取清晰的CT图像,识别出物质的不同成分。相较于在图像域的主成分分析方法,在投影域进行主成分分析能够保留物质的更多细节,获取更清晰的彩色CT图像。      

Ozone depletion in the plume of a solid-fueled rocket

The local effects of the emission of a solid-fueled rocket on the stratospheric ozone concentration have been investigated by photochemical model calculations. A one-dimensional horizontal model has been applied which calculates the trace gas composition at a single atmospheric altitude spatially resolved around the exhaust plume. Different cases were tested for the emissions of the Space Shuttle concerning the composition of the exhaust and the effects of heterogeneous reactions on atmospheric background aerosol.The strongest depletion of ozone is achieved when a high amount of the emitted chlorine is Cl₂. If it is purely HCl, the effect is smallest, though in this case the heterogeneous reactions show their largest influence. From the results it may be estimated whether ozone depletion caused by rocket launches can be detected by satellite instruments. It appears that the chance of coincidental detection of such an event is rather small.     

Spectral Aerosol Transmittance in the Ultraviolet and Visible Spectra in Athens,Greece

This work investigates the spectral atmospheric transmittance due to aerosols in the urban environment of Athens during a period of one year. The spectral transmittance due to aerosols is derived using measurements of spectral direct-beam solar irradiance in the 310–575 nm spectral band. This derivation is accomplished by using a radiative transfer model for estimating the partial spectral atmospheric transmittance functions due to Rayleigh scattering, and absorption by ozone, nitrogen dioxide and water vapor. The seasonal and diurnal variation of the aerosol transmittance is investigated and the results are discussed with a view to air pollution sources, meteorological factors and topographic characteristics of the Athens basin.     

Hardness variation rate of precipitating electrons during <Emphasis Type="Italic">Pi</Emphasis>3 auroral pulsations

Photometric measurements of pulsating auroras have been carried out in the Pi3 range of geomagnetic pulsations with periods of 2–10 min with the use of auroral all-sky camera films obtained at the Lovozero Observatory. The new all-sky camera developed at the Polar Geophysical Institute uses the CCD matrix. This makes it possible to obtain simultaneous images in red, green, and blue spectral ranges and thus to investigate temporal luminosity variations in these spectral regions. The hardness of penetrating auroral electrons with a time resolution of a few seconds is qualitatively estimated. It is found that the energy of the electrons that cause auroras in the Pi3 pulsation range is not constant over the pulsation period. It is maximal at the lowest luminosity and minimal at its peaks. Luminosity pulsations are compared with geomagnetic pulsations, and it is established that large differences between luminosity variations in different parts of the sky explain the incomplete correspondence between the records of auroral and geomagnetic pulsations.     

Modeling of aircraft exhaust emissions and infrared spectra for remote measurement of nitrogen oxides

Infrared (IR) molecular spectroscopy is proposed to perform remote measurements of NO_x concentrations in the exhaust plume and wake of aircraft. The computer model NIRATAM is applied to simulate the physical and chemical properties of the exhaust plume and to generate low resolution IR spectra and synthetical thermal images of the aircraft in its natural surroundings. High-resolution IR spectra of the plume, including atmospheric absorption and emission, are simulated using the molecular line-by-line radiation model FASCODE2. Simulated IR spectra of a Boeing 747–400 at cruising altitude for different axial and radial positions in the jet region of the exhaust plume are presented. A number of spectral lines of NO can be identified that can be discriminated from lines of other exhaust gases and the natural atmospheric background in the region around 5.2 µm. These lines can be used to determine NO concentration profiles in the plume. The possibility of measuring nitrogen dioxide NO₂ is also discussed briefly, although measurements turn out to be substantially less likely than those of NO. This feasibility study compiles fundamental data for the optical and radiometric design of an airborne Fourier transform spectrometer and the preparation of in-flight measurements for monitoring of aircraft pollutants.     

Total Atmospheric Transmittance in the UV and VIS Spectra in Athens,Greece

This work investigates the seasonal and diurnal variation of total spectral transmittance of solar radiation. Such a study dealing with ultraviolet and visible wavelengths (310–575 nm) is carried out in Athens for the first time. The spectral values presented are averages over a number of records in a period of 42 days and have been calculated using ground-based spectral measurements of direct-beam irradiance. The data were recorded on selected days throughout a year by a simple pyrheliometer capable of performing spectral measurements. All data were recorded under clear-sky conditions in the city center of Athens and the total spectral atmospheric transmittance was estimated in the direction of local zenith to become independent of any optical mass effects. The comparison between seasons reveals that the atmospheric transmittance is higher in the cold period of the year than in the warm, simply because the photochemical pollution in the summer is more severe. Various features of seasonal and diurnal variation are also discussed with respect to emission sources, topographic peculiarities and wind regime.     

A kind of information on short-term and imminent earthquake precursors—research on atmospheric electric field anomalies before earthquakes

The long-time practice of observational research on earthquake prediction has shown that the information on short-term and imminent earthquake precursors can hardly be detected, but it is very important for practical and effective earthquake prediction. The result of analysis and study in this paper has shown that the anomaly of quasi-static atmospheric electric field may be a kind of reliable information on short-term and imminent earthquake precursors. On such a basis, the 20 years’ continuous and reliable data of atmospheric electric field observed at the Baijiatuan seismic station are used to study the correlation between the anomalies in seismic activity and relative quiet periods bear on the occurrence of near earthquakes within 200 km range around Beijing after the Tangshan earthquake. The observational results recently reported before hand in written form and earthquakes that actually occurred in near field in corresponding time periods are compared and analyzed. The efficacy of these written prediction opinions about near earthquakes in the recent 10 years is tested. From the test results, the brilliant prospect that the anomaly of quasi-static atmospheric electric field may really become a reliable mark for making short-term and imminent earthquake predictions is discussed. Besides, as a preliminary step, some judgment indexes for predicting earthquakes by use of the observational data of atmospheric electric field before earthquakes are put forward. In the last part, it is pointed out that it would be possible to obtain more believable judgment indexes for determining the three elements of near earthquakes before greater earthquakes (M _S≥5) only if a relatively reasonable station network (2–4 stations every 10 000 km²) is deployed and further investigation is made. Contribution No. 97A0040, Institute of Geophysics, State Seismological Bureau, China. This subject is sponsored by Program No. 95-04-05-01-04, State Seismological Bureau, China.     

The diffuse-to-global and diffuse-to-direct-beam spectral irradiance ratios as turbidity indexes in an urban environment

Continuous measurements of solar spectral radiation using the Multi-filter Rotating Shadow Band Radiometer (MFRSR) are performed at the Actinometric Station of the National Observatory of Athens (ASNOA). The present study utilizes three clear-sky days of continuous observations, from local sunrise to local sunset, in order to investigate the daily variation of the radiation components (diffuse, global and direct-beam) as well as their ratios (diffuse-to-global, DGR, and diffuse-to-direct-beam, DDR) under different atmospheric conditions. Both ratios have received great scientific interest, especially for investigating solar irradiance modifications under various atmospheric conditions, aerosol load and optical properties. Apart from this, the present study shows that the DDR can constitute a measure of atmospheric turbidity when it is determined at longer wavelengths, while the DGR cannot. The effect of the solar zenith angle (SZA) on both ratios is significant at the shorter wavelengths with varying sensitivities depending on the aerosol field and sun elevation. The present study confirms the results obtained by previous solar irradiance measurements in Athens and also those computed via radiative transfer codes and sheds light on the scientific knowledge of the use of spectral DDR as an atmospheric turbidity index.     

Improvement of dark object method in atmospheric correction of hyperspectral remotely sensed data

The existing methods in atmospheric correction of hyperspectral data usually focus on removing the effects of water vapor and other absorptive gases, while this paper mainly studies the method of re- moving the influence of the aerosol and the water vapor simultaneously. Because the hyperspectral data has a larger number of bands, the conventional dark object method cannot be applied to the at- mospheric correction of the hyperspectral data which can be improved, as described in this paper, by adequately making use of spectral characteristics of the hyperspectral data with an iterative correction during the whole process. The effects of the aerosol and water vapor are eliminated at the same time finally. The improved dark object method is used to do the atomospheric correction of the Hyperion data in Yanzhou, Shandong Province as an example. And the result indicates that it can correct the atmospheric influence of the hyperspectral data quickly and remarkably.     

基于边线的遥感影像道路震害快速提取方法研究

重大地震灾害发生以后, 快速准确地提取灾区的道路震害信息对于应急救援工作具有重要意义。 由于地震造成的破坏非常复杂, 没有固定的光谱特征变化模式, 而且影像中存在大量同物异谱和同谱异物现象。 因此, 传统基于光谱特征的遥感影像道路震害提取方法, 不仅提取精度较低, 而且通用性不强, 需要根据不同影像调整参数。 道路边线是一种稳定的道路几何特征, 其特征变化能够准确地表现道路的状态变化。 基于此, 本文研究了一种基于道路边线的震害信息快速提取方法。 该方法利用震后遥感影像提取完好道路边线, 与震前道路线分布数据进行变化检测, 从而实现震害路段的提取。 最后, 利用汶川震区的遥感影像进行实例验证, 与人工解译的结果进行比较。 结果表明, 该方法能够快速准确地提取道路震害信息。     

Modelling the diurnal evolution of the resonance spectral structure of the atmospheric noise background in the Pc 1 frequency range

We calculate the frequency spectrum of the electromagnetic background noise in frequency range 0.1–5 Hz based on the model attributing its formation to the ionospheric resonant filtration of the radiation from distant lightning discharges (Belyaev, P.P., Polyakov, S.V., Rapoport, V.O., Trakhtengerts, V.Y., 1989. Theory of formation of the resonance spectral structure of atmospheric electromagnetic noise background in the range of short-period geomagnetic pulsations, Izvestiya vuzov-Radiofizika 32(7) 802–810). Characteristics of the spectral resonance structure (SRS) formed due to the ionospheric Alfvén resonator are obtained and their dependence on ionospheric parameters is considered; the SRS variation during a day is discussed. The calculations are compared with the ULF ground based observations at Sodankylä and Nizhny Novgorod; consistency of theory and experiment is demonstrated. Opportunities to use such data to determine some of ionosphere parameters are discussed.     

Gravimetric survey terrain correction using linear analytical approximation

Various methods for computing the terrain correction in a high‐precision gravity survey are currently available. The present paper suggests a new method that uses linear analytical terrain approximations. In this method, digital terrain models for the near‐station topographic masses are obtained by vectorizing scan images of large‐scaled topographic maps, and the terrain correction computation is carried out using a Fourier series approximation of discrete height values. Distant topography data are represented with the help of digital GTOPO30 and Shuttle Radar Topography Mission cartographic information. We formulate linear analytical approximations of terrain corrections for the whole region using harmonic functions as the basis of our computational algorithm. Stochastic modelling allows effective assessment of the accuracy of terrain correction computation. The Perm Krai case study has shown that our method makes full use of all the terrain data available from topographic maps and digital terrain models and delivers a digital terrain correction computed to a priori precision. Our computer methodology can be successfully applied for the terrain correction computation in different survey areas.     

基于MODTRAN模型对高分五号卫星断层逸出气体探测能力的辐射模拟

地下流体监测数据和地表断层调查都显示构造活动强烈期和大地震前后活动断裂带会伴有大量气体逸出。 中国即将发射的高分五号(GF-5)卫星搭载的大气环境红外甚高光谱分辨率探测仪及全谱段光谱成像仪两个传感器, 主要以大气气体的探测为应用目标。 本文基于两个传感器的参数设置, 使用大气辐射传输模型, 对断层逸出气体中的水汽、 CH₄和CO₂三种气体在大气中的含量变化对卫星传感器的辐射影响进行了仿真模拟, 分析了两个传感器对水汽、 CH₄和CO₂气体异常的探测能力。 结果表明, GF-5卫星两个红外传感器特定的光谱通道对大气水汽、 CH₄和CO₂气体异常变化均有不同程度的敏感性, 可以期待发展具有较高精度的相关气体遥感反演模型, 用于地震的监测及预测。     

Interannual variations in the areas of thermokarst lakes in Central Yakutia

At present, close attention is given to studies of thermokarst lakes from the standpoint of cryolite zone response to global climate warming. However, other factors, which have an effect on the variation in areas of lakes, in particular, the atmospheric precipitation, receive little attention, while the atmospheric precipitation is one of the main sources of water recharge for many water objects. In this connection, interannual variations in the areas of lakes as a function of precipitation were analyzed on the territory of Central Yakutia. The studies were based on the analysis of space images taken at different time. As the result, it was shown that precipitation has a considerable effect on variations in the areas of thermokarst lakes; there is a direct relationship between variations in lake areas and precipitation; only some single high-water or low-water years have no effect on these variations. Variations in areas of lakes during summer were also analyzed with a view to use the results in choosing the images for studies of interannual variations. It has been revealed that the areas of thermokarst lakes decrease from June to August; this means that the images obtained within a short period at the end of the summer period should be used.     

近岸Ⅱ类水体表层悬浮泥沙浓度遥感模式研究进展

因为具有明显的时间与空间分辨率优势,遥感数据成为近岸Ⅱ类水体悬浮泥沙浓度(SSC)信息提取研究的重要数据源之一.悬浮泥沙遥感信息提取的现状可归纳为:(1)建立近岸Ⅱ类水体SSC遥感模式的方法有三种类型,分别是基于地面光谱与SSC测量的反射率反演方法、基于图像信息法和基于大气辐射传输理论模型法;(2)基于地面测量的反射率反演方法属于理论与经验相结合的方法,也是目前用于SSC定量化遥感模式研究的常用方法.其数学表达形式包括线性关系式、对数关系式、负指数关系式、Gordon模式和综合模式等;(3)到目前为止已有的Ⅱ类水体SSC遥感模式适用性方面还不理想,远未达到与试验室分析相匹配的精度.文章认为:加强地面水文光谱实验研究,建立多光谱SSC定量模式,以高分辨率和高光谱遥感融合数据为基础的SSC定量遥感是今后该方向发展趋势.     

Atmospheric effects on repeat-pass InSAR measurements over Shanghai region

It is well known that interferometric synthetic aperture radar (InSAR) measurements are affected by the atmosphere especially the troposphere. We use Shanghai as an example to analyze the properties of the effects based on a number of SAR interferograms over the region. First, Radon transform is used to examine the isotropic property of the effects. The results show that the effects in all the interferograms are anisotropic although they exhibit different patterns. Two different methods, the Jarque-Bera and the Hinich tests, are then applied to test the Gaussianity of atmospheric effects. Both of the tests reveal that the atmospheric effects are non-Gaussian. Finally, spectral analysis of the atmospheric effects is carried out and the results show that the power spectra of the atmospheric signatures in all the interferograms studied follow approximately the power law distribution. The scaling exponents estimated show that the atmospheric signatures in all the interferograms are non-stationary but with stationary increments. It is estimated based on the estimated scaling exponents that external data with spatial resolutions as high as about 0.3 km, are required to determine and correct for over 90% of the atmospheric effects in the SAR interferograms.     

Difference between the spectra of acoustic gravity waves in daytime and nighttime hours due to nonequilibrium effects in the atmosphere

The singularities of the wave disturbance spectra of the nonequilibrium atmosphere in the range of acoustic gravity waves (AGWs) have been analyzed. Using the dispersion ratio for AGWs in the nonequilibrium atmosphere, it has been established that the spectra in the daytime and nighttime hours are different and this difference, caused by a nonequilibrium spectrum sensitivity to atmospheric temperature, can reach several percent in certain atmospheric regions. For the spectrum of the equilibrium model of the atmosphere, the difference between the daytime and nighttime spectra makes up several fractions of percent. As a result of the spectral treatment of variations in pressure and intensity of cosmic rays (CRs), it has been found out that the daytime AGW spectrum is higher-frequency than the nighttime spectrum. A comparison of the theoretical calculations of the AGW spectrum with observations has made it possible to distinguish the effect of nonequilibrium in the AGW spectral composition.     

On the water vapour absorption in the 8–13 μm spectral region for different atmospheric conditions

Experimental measurements of the absorption coefficient of atmospheric water vapour, at wavelengths between 8 and 13 m, are examined on the basis of atmospheric models describing the meteorological conditions of the observed atmospheres to obtain estimates of the foreign-broadening absorption coefficient for homogeneous paths. The results show that the variable contribution given by unresolved lines predominates on the continuum term due to wing effects of remote lines, even for rather high spectral resolutions.Associated with estimates of the self-broadening absorption coefficient, as proposed byRoberts et al. (1976), these data are applied to a wide set of atmospheric models, corresponding to various latitudes and seasons, indicating that the two components of the atmospheric absorption coefficient are closely related to the surface temperature. Because of the variable weights given by foreign- and self-broadening terms, the atmospheric absorption coefficient turns out to increase with the surface temperature with different rates at various wavelengths.     

星载SAR遥感图像反演海洋大气边界层高度

本研究将边界层相似理论与对流理论应用到具有海洋大气边界层(Marine Atmospheric Boundary Layer, MABL)对流特征的星载合成孔径雷达(Synthetic Aperture Radar, SAR)遥感图像,探讨了星载SAR遥感图像描述海气应力作用下水平扰动尺度变化的潜在可能性.针对具有三维对流涡旋Cell和二维水平滚轴涡旋Roll特征的星载SAR遥感图像,反演了中国海海域MABL高度,并与同步实验获取的MABL高度结果进行对比.结果表明,利用具有对流特征的星载SAR遥感图像反演MABL高度是可行的,展示了以高分辨率、大面积观测为特点的星载SAR遥感图像探测MABL的广阔前景.     

Doppler radar spectral width broadening due to beamwidth and wind shear

The spectral width observed by Doppler radars can be due to several effects including the atmospheric turbulence within the radar sample volume plus effects associated with the background flow and the radar geometry and configuration. This study re-examines simple models for the effects due to finite beam-width and vertical shear of the horizontal wind. Analytic solutions of 1- and 2-dimensional models are presented. Comparisons of the simple 2-dimensional model with numerical integrations of a 3-dimensional model with a symmetrical Gaussian beam show that the 2-dimensional model is usually adequate. The solution of the 2-dimensional model gives a formula that can be applied easily to large data sets. Analysis of the analytic solutions of the 2-dimensional model for off-vertical beams reveals a term that has not been included in mathematical formulas for spectral broadening in the past. This term arises from the simultaneous effects of the changing geometry due to curvature within a finite beamwidth and the vertical wind shear. The magnitude of this effect can be comparable to that of the well-known effects of beam-broadening and wind shear, and since it can have either algebraic sign, it can significantly reduce (or increase) the expected spectral broadening, although under typical conditions it is smaller than the beam-broadening effect. The predictions of this simple model are found to be consistent with observations from the VHP radar at White Sands Missile Range, NM.