Comment: On the different approaches of Rayleigh optical depth determination

Srivastava et al. (2009) presented Rayleigh scattering cross-sections and optical depths for Earth’s atmosphere that are approximately 3% smaller than previously accepted. Their analysis was based on quantum-mechanical theory for anisotropic scattering in the Cabannes line published in papers that seem to have introduced some confusion about determining the anisotropy and King factors. This comment clarifies these factors and shows that including the frequency-shifted rotational Raman lines gives the traditional King factor and the correct Rayleigh scattering for the optical depth.     

The optical parameters of the atmosphere of Venus

This work is devoted to the derivation of the optical properties of the Venus atmosphere from “Venera-10” optical measurements. Within the framework of a two-layer model of Venus atmosphere it is found that in the spectral interval 0.52 – 0.85 μm the optical thickness of the upper cloud layer is ≈ 50 and the optical parameters of the lower layer are similar to the Rayleigh ones. Comparison is made between the measurements of radiation field within the atmosphere and the results of strict calculations. A preliminary conclusion is suggested that there are considerable numbers of aerosol particles with a radius ? 0.03 μm in the lower layer. The results of the upper boundary of the cloud layer is estimated to be ≈ 70 km.     

Density structure of the Sgr B2 molecular cloud probed by low-J lines of CS.

We have observed the CS (2-1) and (3-2), and 13CS (2-1) transitions toward the Galactic Center molecular cloud Sgr B2 which consists of several clumps with different chemical properties. We have newly identified a cloud at 30 km s-1 from a CS (2-1) optical depth map. This cloud lies 1.5' South from the Sgr B2 (M) position and has a diameter of approximately 2.5 pc and a total column density of 7 x 10(23) cm-2 assuming optically thin emission of the 13CS (2-1) line. Towards the 2'N Cloud no evidence for a density enhancement is found, which suggests that the strong emission from HNCO and HCO+2 is due to chemical effects. The main isotopic CS lines show broad wing components similar to previous studies, but we find rotational temperatures Trot(CS) < 10 K at this region.     

瑞利激光雷达反演中层大气温度算法

瑞利激光雷达是探测中层大气温度的重要设备,具有高时空分辨率且不存在探测盲区的优点.为充分利用激光雷达探测到的原始数据,改进了传统的Chanin-Haunchecorne方法,采用由均匀搜索生成温度初值的方式反演大气温度.位于北京延庆（40.3°N,116.2°E）的瑞利激光雷达具有589nm和532nm两个通道,将589nm通道用于计算,532nm通道作为参考.在150~250K区间等间隔选取多个温度初值,利用589nm通道反演60~70km高度范围内的大气温度廓线和大气密度廓线,利用参考密度廓线选取准确的温度初值,反演得到准确的大气温度廓线.将589nm通道和532nm通道反演的温度廓线相比较,发现二者具有较高的一致性.改进后的方法有效利用了信噪比较差的光信号,使589nm通道的温度探测上限从60km提高到70km.      

Shape and motion estimate of LEO debris using light curves

We have derived a tri-axial ellipsoidal model of an LEO object, a Cosmos 2082 rocket body, including its rotational axis direction, rotation period, precession, and a compositional parameter, using only light curve data from an optical telescope. The brightness of the object was monitored for two days and least-squares fitting was used to determine these values. The derived axial ratios are 100:18:18, the coordinates of the rotational axis direction on the celestial sphere are R.A. = 305.8° and Dec. = 2.6°, and its observed average rotation period is 41 s. When precession is considered, its amplitude and precession period are 30.5° and 29.4 min. These results show that optical light curve data are sufficient to determine the shapes and the motions of LEO objects.     

青岛上空中层大气密度和温度的激光雷达探测

介绍了中国电波传播研究所瑞利散射激光雷达系统的结构和性能, 阐述了激光雷达探测中层大气密度和温度的工作原理, 给出了青岛地区中层大气密度和温度的初步探测结果. 通过与卫星、探空气球和大气模式数据的结果对比, 验证了激光雷达探测大气温度的可靠性. 基于2008-2009两年的观测, 获得了青岛地区上空中层大气温度的季节变化和平均分布. 激光雷达观测结果表明, 青岛地区平流层温度比CIRA86模式结果高, 且二者偏差呈夏秋季小、冬春季大的特点, 中间层温度则正好相反.      

Spectral and temporal characteristics of aerosol optical depth over a wet tropical location in North East India

A network of multi wavelength solar radiometer (MWR) stations has been in operation since the 1980s in India for measurement of aerosol optical depth (AOD). This network was augmented recently with the addition of a large number of stations located across the length and breath of India covering a variety of climate regimes. The spectral and temporal variations of aerosol optical depths observed over Dibrugarh located in the North East of India (27.3°N, 94.5°E) are investigated by analyzing the data obtained from a MWR during October 2001–September 2003 using the Langley technique. AOD varies with time of the day, month of the year and season. From January to April and October to December, aerosol optical depth decreases with wavelength whereas during May–September aerosol optical depth has been found to be nearly independent of wavelengths. AOD is higher during pre-monsoon season (March–May) and lower in the monsoon (June–September) season at about all wavelengths. The temporal variation of AOD over Dibrugarh have also been compared with those reported from selected locations in India.     

Direct radiative forcing from black carbon aerosols over urban environment

There is growing evidence that the earth’s climate is changing and will likely continue to change in the future. It is still debated whether these changes are due to natural variability of the climate system or a result of increases in the concentration of greenhouse gases in the atmosphere. Black carbon (BC) has become the subject of interest for a variety of reasons. BC aerosol may cause environmental as well as harmful health effects in densely inhabited regions. BC is a strong absorber of radiation in the visible and near-infrared part of the spectrum, where most of the solar energy is distributed. Black carbon is emitted into the atmosphere as a byproduct of all combustion processes, viz., vegetation burning, industrial effluents and motor vehicle exhausts, etc. In this paper, we present results from our measurements on black carbon aerosols, total aerosol mass concentration and aerosol optical depth over an urban environment namely Hyderabad during January to May, 2003. Diurnal variations of BC indicate high BC concentrations during 6:00–9:00 and 19:00–23:00 h. Weekday variations of BC concentrations increase gradually from Monday to Wednesday and gradually decrease from Thursday to Sunday. Analysis of traffic density along with meteorological parameters suggests that the primary determinant for BC concentration levels and patterns is traffic density. Seasonal variations of BC suggest that the BC concentrations are high during dry season compared to rainy season due to the scavenging by air. The fraction of BC to total mass concentration has been observed to be 7% during January to May. BC showed positive correlation with total mass concentration and aerosol optical depth at 500 nm. Radiative transfer calculations suggests that during January to May, diurnal averaged aerosol forcing at the surface is −33 Wm² and at the top of the atmosphere (TOA) above 100 km it is observed to be +9 Wm⁻². The results have been discussed in detail in the paper.     

A statistical study of C IV regions in 20 Oe-stars

In this paper, using the Gauss-Rotation model (GR model), we analyse the UV C IV resonance lines in the spectra of 20 Oe-stars of different spectral subtypes, in order to detect the structure of C IV region. We study the presence and behavior of absorption clouds and analyse their characteristics. From this analysis we can calculate the values of a group of physical parameters, such as the apparent rotational and radial velocities, the random velocities of the thermal motions of the ions, the Full Width at Half Maximum (FWHM), the optical depth, as well as the absorbed energy and the column density of the independent regions of matter, which produce the main and the satellite clouds of the studied spectral lines. Finally, we present the relations between these physical parameters and the spectral subtypes of the studied stars and we give our results about the structure of the C IV region in their atmosphere.     

Validation of space-born Moderate Resolution Imaging Spectroradiometer remote sensors aerosol products using application of ground-based Multi-wavelength Radiometer

The measurements of aerosol optical properties were carried out during April 2006 to March 2011 over Mohal (31.9°N, 77.12°E) in the northwestern Indian Himalaya, using the application of ground-based Multi-wavelength Radiometer (MWR) and space-born Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensors. The average (±standard deviation) values of aerosol optical depth (AOD) at 500 nm, Ångström exponent and turbidity coefficient during the entire measurement period were 0.25 ± 0.09, 1.15 ± 0.42 and 0.12 ± 0.06 respectively. About 86% AOD values retrieved from MODIS remote sensor were found within an uncertainty limit (Δτ_pλ = ±0.05 ± 0.15τ_pλ). In general, the MWR derived AOD values were higher than that of MODIS retrieval with absolute difference ∼0.02. During the entire period of measurement space-born MODIS remote sensor and ground-based MWR observation showed good correspondence with significant correlation coefficient ∼0.78 and root mean square difference ∼0.06. For daily observations the relative difference between these two estimates stood less than 9%. However, satellite-based and ground-based observation showed good correspondence, but further efforts still needed to eliminate systematic errors in the existing MODIS algorithm.     

Passive remote sensing of aerosols from space now and in the future

Aerosols modify scattered solar radiation leaving the atmosphere and this fact will be exploited to determine the aerosol optical depth. The interaction processes between solar radiation and aerosol particles are outlined. A quasi-linear relationship (‘conversion curves’) between the radiance at the satellite, L_sat, and the aerosol optical depth, a_Dλ, is found from both numerical and empirical studies. Because L_sat is not only controlled by a_Dλ, but also by a series of other atmospheric parameters (perturbing quantities), the concept of ‘favourable viewing conditions’ is presented, where the effects of the perturbing quantities are minimal. The paper ends with some lines of thought on a concept for a turbidity satellite.     

空间目标在天基光学探测中的特性分析与仿真

分析了空间目标的分布及几何特性,研究了空间目标光学特性与天基探测系统、太阳以及目标自身参数的关系,提出了空间目标光学特性仿真的思路,建立的天基空间目标光学特性分析系统可以计算并绘制相对距离、太阳相位角及目标星等变化曲线.由于很难获取准确的空间目标实际光度数据,文中提出了对仿真结果的验证方法.通过对仿真结果的分析,得出了天基空间目标光学探测的特点,为天基光学探测和识别的研究提供了参考.      

Retrieval of aerosol optical characteristics from polarization measurements of reflected solar radiation above the oceans

The reflected near infrared solar radiation observed from space above the oceans is due mainly to the atmosphere scattering, as the ocean surface is nearly black. The molecular Rayleigh contribution is also minimized at infrared wavelengths and it can be evaluated. It is shown that the degree of polarization is much more sensitive to the aerosol properties than the radiance. Measurements of polarization at two wavelengths and with an angular scanning are simulated and an inversion algorithm is proposed. It aims at finding an “equivalent aerosol model,” which reproduces the optical thickness and the asymmetry factor of the actual aerosol at all wavelengths in the solar spectrum.     

飞行时间成像系统的数字仿真技术

飞行时间传感器的仿真主要用于评估基于光相位信息的深度数据的处理算法,现有的方法包括基于对场景三维模型生成的特定噪声模式的仿真模型和基于光信号传播的物理过程仿真模型两大类,为飞行时间成像系统建立了特定的仿真平台.但现有的工作并未考虑环境光干扰对测量数据间的非线性耦合关系,而这种关系是附着/着陆敏感器的重要设计要素之一.本文针对小行星附着任务的需求,研究并建立了包含环境光矢量的飞行时间成像仿真环境,验证了包括环境光模型的飞行时间成像仿真方法,对于飞行时间成像技术在光照条件下的成像性能的评估具有重要意义和应用前景.     

High vertical resolution water vapour profiles in the upper troposphere and lower stratosphere retrieved from MAESTRO solar occultation spectra

An algorithm has been developed that retrieves water vapour profiles in the upper troposphere and lower stratosphere from optical depth spectra obtained by the Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (MAESTRO) instrument onboard the SCISAT satellite as part of the Atmospheric Chemistry Experiment (ACE) mission. The retrieval relies on ro-vibrational absorption of solar radiation by water vapour in the 926–970 nm range. During the iterative inversion process, the optical depth spectra are simulated at the spectral resolution and sampling frequency of MAESTRO using the correlated-k approximation. The Chahine inversion updates the water vapour volume mixing ratio (VMR), adjusting all retrieval layers simultaneously, to match the observed differential optical depth due to absorption by water vapour and ozone at each tangent height. This approach accounts for significant line saturation effects. Profiles are typically obtained from ∼22 km down to the cloud tops or to 5 km, with relative precision as small as 3% in the troposphere. In the lower stratosphere, the precision on water vapour VMR is ∼1.3 μmol/mol in an individual retrieval layer (∼1 km thick). The spectral capability of MAESTRO allows for the clear separation of extinction due to water vapour and aerosol, and for the fitting quality to be quantified and used to determine an altitude-dependent convergence criterion for the retrieval. In the middle troposphere, interhemispheric differences in water vapour VMR are driven by oceanic evaporation whereas in the upper troposphere, deep convection dominates and a strong seasonal cycle is observed at high latitudes.     

Comptonization efficiencies of the variability classes of GRS 1915 + 105

The Galactic microquasar GRS 1915 + 105 exhibits at least seventeen types of variability classes. Intra and inter class transitions are reported to be observed within seconds to hours. Since the observation was not continuous, these classes appeared to be exhibited in a random order. Our goal is to predict a sequence of these classes. In this paper, we compute the ratio of the photon counts obtained from the power-law component and the blackbody component of each class and call this ratio as the ‘Comptonizing efficiency’ (CE) of that class. We sequence the classes in the ascending order of CE and find that this sequence matches with a few class transitions observed by RXTE satellite and IXAE instruments on board IRS-P3. A change in CE corresponds to a change in the optical depth of the Compton cloud. Our result implies that the optical depth of the Compton cloud gradually rises as the variability class becomes harder.     

薄壁试件脉冲热像法深度检测模型分析

脉冲热像法作为红外热像检测中具有定量分析能力的方法,其主要检测模型温差函数法在薄壁试件的缺陷深度检测时存在失效问题.为找出建模过程中的缺陷,以理想脉冲激励下一维有限形式的解析解替代原温差函数模型中的近似解,在温差曲线和温差导数曲线中,对模型中的核心参数峰值温差时间和峰值斜率时间的使用特性进行了比较分析.结果显示:峰值温差时间由参考点决定,而不由测试点决定,峰值温差时间不具备对缺陷深度的定量检测能力;峰值斜率时间的适用范围受到测试点与参考点实际深度之比的限制,根据给出的适用性判据公式求得该比值的上限在0.5附近,判据公式可作为使用峰值斜率时间的理论依据.     

Raman scattering as a probe of planetary atmospheres

The observable effects of Raman scattering on the spectra of the giant planets may provide new information on the composition and structure of these atmospheres. Satellite observations have already shown the influence of Raman scattering on the UV continuum albedo. A cross correlation technique is presented for detecting rotational and vibrational transitions of the Raman active gases in the atmosphere. This technique has been applied to ground-based visible spectra of Venus, Jupiter, Saturn and Uranus. Extension of this method into the UV would improve the detectability of the Raman lines because the ratio of Raman to Rayleigh cross section increases with decreasing wavelength. The technology currently exists to efficiently obtain high signal-to-noise ratio UV spectra through the use of silicon diode array detectors. Application of the cross-correlation technique to UV spectra obtained from space vehicles would give us a new important probe of the structure and composition of planetary atmospheres by enabling us to use the UV spectra of a planet to observe that would normally be an infrared molecular transition.     

Orbit determination by genetic algorithm and application to GEO observation

This paper demonstrates an initial orbit determination method that solves the problem by a genetic algorithm using two well-known solutions for the Lambert’s problem: universal variable method and Battin method. This paper also suggests an intuitive error evaluation method in terms of rotational angle and orbit shape by separating orbit elements into two groups. As reference orbit, mean orbit elements (original two-lines elements) and osculating orbit elements considering the J2 effect are adopted and compared. Our proposed orbit determination method has been tested with actual optical observations of a geosynchronous spacecraft. It should be noted that this demonstration of the orbit determination is limited to one test case. This observation was conducted during approximately 70 min on 2013/05/15 UT. Our method was compared with the orbit elements propagated by SGP4 using the TLE of the spacecraft. The result indicates that our proposed method had a slightly better performance on estimating orbit shape than Gauss’s methods and Escobal’s method by 120 km. In addition, the result of the rotational angle is closer to the osculating orbit elements than the mean orbit elements by 0.02°, which supports that the estimated orbit is valid.     

What gamma-ray deexcitation lines reveal about solar-flares

Gamma-ray emission from solar flares reveals information about the nature of the accelerated particles and about the physical conditions of the medium through which the accelerated particles are transported. In this paper, we present the gamma-ray line-production and loop transport models used in our calculations of high-energy emission. We discuss the calculated interaction time history, the depth distribution, the interacting-particle angular distribution, and fluence ratios of the narrow gamma-ray lines. We show the relationship between the γ-ray observables and the parameters of the transport and line-production models. For illustration, we use calculations of 4.44 MeV ¹²C nuclear deexcitation line-production. Applications of the calculations to flare observations by both SMM and RHESSI are also presented.