tau: A 1D radiative transfer code for transmission spectroscopy of extrasolar planet atmospheres

The tau code is a 1D$1D$ line-by-line radiative transfer code, which is generally applicable for modelling transmission spectra of close-in extrasolar planets. The inputs are the assumed pressure–temperature profile of the planetary atmosphere, the continuum absorption coefficients and the absorption cross-sections for the trace molecular absorbers present in the model, as well as the fundamental system parameters taken from the published literature. The program then calculates the optical path through the planetary atmosphere of the radiation from the host star, and quantifies the absorption due to the modelled composition in a transmission spectrum of transit depth as a function of wavelength. The code is written in C++, parallelised using OpenMP, and is available for public download and use from http://www.ucl.ac.uk/exoplanets/.     

Uncertainties in radiative transfer computations: consequences on the MERIS products over land

The main objectives of MERIS (MEdium Resolution Imaging Spectrometer) consist of atmospheric processes related to the water vapour column and aerosol optical properties designed for meteorological applications, and the land surface properties as well as the bio‐optical oceanography. In this context, operational MERIS level‐2 processing uses auxiliary data generated by two radiative transfer tools. These two codes simulate upwelling radiances within a coupled ‘atmosphere–land’ system, using different approaches based on the matrix‐operator method (FUB, Freie Universität Berlin), the discrete ordinate method and the successive orders technique (ULCO, Université du Littoral Côte d'Opale). Intervalidation of these two radiative transfer tools was performed in order to implement them in the MERIS level‐2 processing. For cases without gaseous absorption, the scattering processes both by the molecules and the aerosols were retrieved within a few tenths of a percentage point. Nevertheless, some substantial discrepancies occur if the polarization is not accounted for, mainly in the Rayleigh scattering computations. Errors on the aerosol optical thickness reach up to 25% in some geometries as observed in the MERIS images. The parametrization of gaseous absorption (H₂O and O₂) defined for each of these two codes leads to a good agreement for the MERIS bands with residual absorption. In the strong absorption bands (761.75 nm and 900 nm), the FUB computations well match the results derived from a line‐by‐line (LBL) code with a very high spectral resolution. Note that the oxygen absorption at 761.75 nm is very sensitive to the characteristics of the sensor spectral response and requires accurate calculations with the LBL code. Consequently, the ULCO code has been implemented in the MERIS level‐2 processing to include polarization in the scattering processes and to correct for slightly gaseous absorption, the FUB code to derive the water vapour abundance, and the LBL code to determine the barometric pressure. Impacts of the differences in the look‐up table generation on the level‐2 products (aerosol model, surface reflectance and barometric pressure) are also analysed and illustrated.     

Impact Analysis of a Dual-Crawler-Driven Robot

This paper presents the impact analysis of a new dual-crawler-driven robot. This dual-crawler-driven robot is realized by connecting rigidly two crawler modules. In this newly proposed crawler module, a planetary gear reducer is deployed as the power transmission device to give two different outputs with just one actuator. Compared with the crawler driven by two actuators, our crawler module driven by one actuator could show good impact absorption when the robot collides with an obstacle due to the fact that there exists an output redundancy in each module. To determine what the advantage of our mechanism to the impact absorption is, impact analysis of the robot is conducted from the external components of the robot to its internal transmission parts while the robot encounters a collision with obstacles. The results of impact effect to the actuators in our mechanism are correspondingly derived in comparison with that in the conventional mechanism where each output is provided by one actuator. Numerical results are used to demonstrate the advantage of our mechanism on impact absorption.     

多线程遥感影像实时渐进传输

目的 针对异构网络环境下,不同终端用户对遥感影像质量的不同需求而导致的影像数据量过大、传输及显示延迟过长等问题,提出一种在线压缩—实时传输—实时解压缩的遥感影像渐进传输模型。方法 模型采用多线程流水线同步处理的加速算法,将基于质量渐进压缩的SPIHT算法与多线程流水线技术相结合,在VC++环境下,将遥感影像在线压缩成码流,在压缩的同时,启动多线程采用Socket信道对压缩码流实时发送,客户端收到码流后,利用多线程实时解压缩并显示。通过采用多线程技术,使得压缩、传输和解压缩同步进行,从而减少了整体处理时间。结果 实验结果表明,提出的实时压缩渐进传输模型,在不影响影像质量的前提下,算法处理速度提高近2倍。每个渐进分层影像与原影像的相似度比多分辨率渐进压缩分层影像与原影像的相似度平均增加20%。结论 该模型有效地解决了遥感影像渐进传输过程中压缩、传输和解压缩的不同步问题,从而提高了渐进传输效率。与多分辨率渐进传输比较,此渐进传输模型具有更好的视觉效果。     

Planetary exploration by robotic aerovehicles

Planetary aerobots are a new type of telerobotic science platform that can fly and navigate in a dynamic 3-dimensional atmospheric environment, thus enabling the global in situ exploration of planetary atmospheres and surfaces. Aerobots are enabled by a new concept in planetary balloon altitude control, developed at JPL, which employs reversible-fluid changes to permit repeated excursions in altitude. The essential physics and thermodynamics ofreversible-fluid altitude control have been demonstrated in a series of altitude-control experiments conducted in the Earth's atmosphere, which are described. Aerobot altitude-control technology will be important in the exploration of seven planets and satellites in our solar system. Three of these objects—Venus, Mars, and the Saturnian satellite Titan—have accessible solid surfaces and atmospheres dominated by the dense gases nitrogen or carbon dioxide. They will be explored with aerobots using helium or hydrogen as their primary means of buoyancy. The other four planets—Jupiter, Saturn, Uranus, and Neptune—have deep atmospheres that are predominantly hydrogen. It may be possible to explore these atmospheres with aerobots inflated with atmospheric gas that is then radiatively heated from the hotter gaseous depths below. To fulfill their potential, aerobots to explore the planets will need autonomous state estimators to guide their observations and provide information to the altitude-control systems. The techniques of acquiring these data remotely are outlined. Aerobots will also use on board altitude control and navigation systems to execute complex flight paths including descent to the surface and exploiting differential wind velocities to access different latitude belts. Approaches to control of these systems are examined. The application of aerobots to Venus exploration is explored in some detail: The most ambitious mission described, the Venus Flyer Robot (VFR), would have the capability to make repeated short excursions to the high-temperature surface environment of Venus to acquire data and then return to the Earth-like upper atmosphere to communicate and recool its electronic systems. Finally a Planetary Aerobot Testbed is discussed which will conduct Earth atmospheric flights to validate autonomous-state-estimator techniques and flight-path-control techniques needed for future planetary missions.     

基于FPGA的H.264码流实时传输系统设计

在研究华为海思Hi3516A进行视频编码压缩的过程中,针对其压缩码流仅支持本地保存和网络流媒体应用的局限性,提出了一种基于FPGA和以太网接口的H.264码流实时传输方案;Hi3516A视频编码端采用RAW _SOCKET原始套接字协议构建UDP帧,通过网口传输H.264压缩码流到FPGA平台;FPGA使用一片2 Gbit的DDR3作为数据缓存介质,保证网口速率的匹配和一次传输的H.264 Nalu包的完整性;利用USB2.0接口回传码流到PC进行功能测试;从模拟传输本地文件和实际传输视频两方面对系统功能进行测试;模拟传输本地文件测试中,PC端网口发送55,844,864字节本地文件到本系统,USB上位机接收的系统返回数据大小与发送数据大小相同,证明数据传输完整;实际传输视频测试中,MilkPlayer软件播放USB上位机保存的码流文件,画面流畅,无卡顿及明显丢帧,使用FFmpeg软件解码码流文件,测试表明,数据压缩比均值达143:1,与系统设定值相比,存在4％左右的误差,USB上位机12h和24 h保存接收码流测试中,数据量分别达到22.3 GB和43.5 GB,码流文件播放效果良好;因此,此系统能实现H.264码流的实时传输,满足设计要求,具有很好的实用价值.     

Study of aerosols and molecular extinction effects in ultraviolet DIAL remote sensing in the lower atmosphere

Light passing through the atmosphere is scattered and absorbed by the molecules and particles in the atmosphere. This can adversely restrict and limit not only the signal-to-noise ratio (SNR) but also the accuracy and sensitivity of measurements, especially in long-path remote sensing. Usually, in differential absorption lidar (DIAL) techniques, errors are increased mainly because of the different extinction and backscattering properties of the atmosphere at the DIAL probe wavelengths. In this work we have investigated the effects of background aerosol and molecular extinction in DIAL remote sensing in the lower atmosphere for several visibilities at ultraviolet (UV) wavelengths by taking into account the dependence of refraction on the air temperature and pressure. For simplicity, we neglected the spatial inhomogeneity of aerosols in the lower atmosphere. Because of the weak attenuation produced by oxygen and other gaseous atmospheric constituents in this region compared with that from ozone, only ozone is considered as significant among the expected errors. Values for the total attenuation (km^?1) at wavelengths 200–400 nm are tabulated for several values of visibility. The acquired results show that the absorption and scattering by the molecules and aerosols vary with wavelength and visibility. The aerosol attenuation in the UV region varies smoothly and thereby errors caused by aerosol scattering can be neglected in remote sensing by UV-DIAL. In addition, aerosols play a very important role in lidar remote sensing in the lower atmosphere by scattering and absorption of radiation, which is considered as a significant factor. At high altitudes, the aerosol concentration is lower than at the ground; the molecular scattering is important, especially for wavelengths greater than 310 nm, where ozone attenuation is not important. The obtained results are important for accurate UV-DIAL measurements of concentration as well as when real-world signals are not available, for example when designing lidar and simulating or when access to real-world signals is not possible.     

基于CEEMD与CPSO-ELM的行星齿轮传动箱故障研究

鉴于现有行星齿轮传动箱应用在多种复杂环境,且在外界扰动较大时,齿轮磨损故障信号具有非平稳等特点,很难准确分离和识别出故障信号及故障类型,为解决问题,提出了一种基于互补集合经验模态分解(CEEMD)、混沌粒子群核极限学习机(CPSO-ELM)的行星齿轮传动箱故障信号处理及识别算法.为了验证CPSO-ELM算法对行星齿轮传...     

Effects of the atmosphere on the detection of surface changes from Landsat multispectral scanner data

The atmospheric effects on radiometric data recorded in the Landsat multispectral scanner system (MSS) bands are compiled for cases of representative and ideal atmospheric conditions. The effects are expressed as a difference between the Earth's surface spectral reflectivity, a₀, and the surface-atmosphere system spectral reflectivity, a_s, derived from the satellite data,

a_s?a₀ = ?a₀[l+(l/μ₀)](B+W) + 2a² ₀B + g(μ₀)B/2μ₀

where μ₀ is the cosine of the solar zenith angle, B and W are the backscattering and absorption optical thickness respectively, and the function g( μ₀) is the anisotropy of backscattering to the zenith from the direct beam. This formula is accurate only for an atmosphere of low optical thickness. Also, the equation applies only to large areas having a uniform reflectivity, because adjacency effects due to reflection from the terrain surrounding the object pixel and subsequent scattering by the atmosphere are not considered.

It is concluded that in the quantitative monitoring of surface changes from satellites, scattering effects predominate in some applications (for example, bathy-metric mapping of coastal waters), whereas absorption effects predominate in other applications (for example, monitoring desert fringe areas). Different measurements are more appropriate for assessing the scattering effects than for assessing the absorption effects.

These effects on the monitoring of surface changes by the use of Landsat MSS data are discussed in terms of departures of the actual atmosphere at the time of a satellite passage from a ‘minima’ atmosphere having no aerosols and characterized by gaseous absorption corresponding to minimal water vapour amounts.     

Spectral optimization for constituent retrieval in Case 2 waters I: Implementation and performance

We describe in detail the implementation of the spectral optimization algorithm (SOA) for Case 2 waters for processing of ocean color data. This algorithm uses aerosol models and a bio-optical reflectance model to provide the top-of atmosphere (TOA) reflectance. The parameters of both models are then determined by fitting the modeled TOA reflectance to that observed from space, using non-linear optimization. The algorithm will be incorporated into the SeaDAS software package as an optional processing switch of the Multi-Sensor Level-1 to Level-2 code. To provide potential users with an understanding of the accuracy and limitations of the algorithm, we generated a synthetic data set and tested the performance of the SOA with both correct and incorrect bio-optical model parameters. Application of the SOA to actual SeaWiFS data in the Lower Chesapeake Bay (for which surface measurements were available) showed that 20% errors in the bio-optical model parameters still enabled retrieval of chlorophyll a and the total absorption coefficient of dissolved plus particulate detrital material at 443 nm with an error of less than 30% and 20%, respectively. In a companion paper we present a validation study of the application of the algorithm in the Chesapeake Bay.     

Planetary rovers�� wheel�Csoil interaction mechanics: new challenges and applications for wheeled mobile robots

With the increasing challenges facing planetary exploration missions and the resultant increase in the performance requirements for planetary rovers, terramechanics (wheel–soil interaction mechanics) is playing an important role in the development of these rovers. As an extension of the conventional terramechanics theory for terrestrial vehicles, the terramechanics theory for planetary rovers, which is becoming a new research hotspot, is unique and puts forward many new challenging problems. This paper first discusses the significance of the study of wheel–soil interaction mechanics of planetary rovers and summarizes the differences between planetary rovers and terrestrial vehicles and the problems arising thereof. The application of terramechanics to the development of planetary rovers can be divided into two phases (the R&D phase and exploration phase for rovers) corresponding to the high-fidelity and simplified terramechanics models. This paper also describes the current research status by providing an introduction to classical terramechanics and the experimental, theoretical, and numerical researches on terramechanics for planetary rovers. The application status of the terramechanics for planetary rovers is analyzed from the aspects of rover design, performance evaluation, planetary soil parameter identification, dynamics simulation, mobility control, and path planning. Finally, the key issues for future research are discussed. The current planetary rovers are actually advanced wheeled mobile robots (WMRs), developed employing cutting-edge technologies from different fields. The terramechanics for planetary rovers is expected to present new challenges and applications for WMRs, making it possible to develop WMRs using the concepts of mechanics and dynamics.     

基于二维码的数据传输系统设计

基于二维码的数据传输系统面向涉密场景,旨在实现涉密信息系统之间的自动数据传输。文中设计了涉密信息系统之间的数据通信流程,即发送端将传输数据按二维码帧容量切分为多帧,按序合成并显示二维码图像序列,接收端使用摄像头等设备采集二维码图像信息,合成传输数据,并按预定规则对接收情况进行反馈,完成收发两端之间的数据通信。与现有采用人工交互或安全铰链设备的方案相比,基于二维码的数据传输系统解决了自动化程度低、传输效率低、设备昂贵等问题,实现了网络隔离条件下自动高效的数据传输,适用于涉密信息系统中具有较高时效性要求的信息交互。     

Hydrogen Sulfide Molecules Lidar Sensing in the Atmosphere

The optimum operation modes of the Raman lidar and the differential absorption and scattering lidar for the hydrogen sulfide molecules sensing in the atmosphere at the low permissible concentration level have been studied and the error estimation of the hydrogen sulfide molecules concentration measurement in the atmosphere by the Raman lidar and the differential absorption and scattering lidar has been executed. The computer simulation of the two types of such a lidar equations has been fulfilled for this purpose. The measurement relative accuracy for the range of the studied molecules concentration of 10¹¹–10¹⁴ cm^–3 at the 3.83 μ laser radiation wavelength and the ranging distances from 10 do1000 m lies in the range of 20–26% for the differential absorption and scattering lidar.     

Technical Note: Equivalence of modified Gaussian model (MGM) in wavenumber and Gaussian in wavelength for deconvolution of hyperspectral reflectance spectra

A modified Gaussian model (MGM) is used to separate overlapping absorption features into their fundamental bands in mineral reflectance spectra; it is widely used in the planetary remote sensing community. To facilitate its use for earth‐observation studies where it has not been widely adopted, we show that the MGM analysis in wavenumber is numerically equivalent to Gaussian analysis in wavelength, improving access to software that is capable of the analysis. The two approaches were tested on a synthetic spectrum and a measured mineral spectrum. Results for the two methods are as close to identical as computationally possible, confirming their equivalency.     

A parallel multiphase flow code for the 3D simulation of explosive volcanic eruptions

A new parallel code for the simulation of the transient, 3D dispersal of volcanic particles in the atmosphere is presented. The model equations, describing the multiphase flow dynamics of gas and solid pyroclasts ejected from the volcanic vent during explosive eruptions, are solved by a finite-volume discretization scheme and a pressure-based iterative non-linear solver suited to compressible multiphase flows. The solution of the multiphase equation set is computationally so demanding that the simulation of the transient 3D dynamics of eruptive columns would not be cost-effective on a single workstation. The new code has been parallelized by adopting an ad hoc domain partitioning scheme that enforces the load balancing in the presence of a large number of topographic blocking-cells. An optimized communication layer has been built over the Message-Passing Interface. It is shown that the present code has a remarkable efficiency on several high-performance platforms and makes it possible, for the first time, to simulate fully 3D eruptive scenarios on realistic volcano topography.     

RV减速器运动精度影响因素的分析研究

RV减速器作为新型的摆线针轮行星传动装置,具有传动比大、体积小、传动效率高、传动稳定的优点,近年来发展较为迅速,是一些高精密传动场景的最佳选择。作为RV减速器最重要的性能指标—传动精度,是减速器行业领域不断精进的目标。在本文中,通过分析RV减速器的结构以及传动机理,对其运动精度的影响因素进行了分析,并结合机械零部件的生产加工工艺,对其零部件的工艺做了相关的调整,以期达到经济的生产成本,又可得到较为理想的运动精度。     

基于部分信息的SLT-LT联合码防窃听方案设计

近年来, 信息的安全传输备受人们关注, 现有的物理层安全技术从信息论的角度出发, 将物理层安全编码与传输信道的动态物理特性进行结合, 实现信息的保密传输。作为一种纠删码, LT(Luby transform)码由于其编码随机性、码率不固定等特性,使得窃听者不能直接从泄露的编码符号中得到有用信息, 只要合法用户在窃听者之前接收到足够数量的编码符号, 便可实现信息的安全传输。而作为一种转移 LT(Shifted LT, SLT)码, SLT 码能高效恢复信息的同时具有更小的译码开销。因此, 我们将 SLT码应用于 Wyner 降阶窃听信道模型进行研究, 提出一种基于部分信息转移的 SLT-LT 联合码防窃听方案, 信源利用接收者已知的部分信息对度分布进行调整, 并对信源符号进行 SLT-LT 码级联编码。由于窃听信道是合法信道的降阶信道, 因此外在的窃听者截获到的消息符号是合法接收者的降阶版本, 在相同时间内, 合法接收者能够收到更多消息符号, 随着编解码过程的不断进行, 合法接收者的优势不断累积, 能够优先完成解码, 而度分布的调整以及级联编码方案使得编码符号的平均度进一步增大,窃听者难以完成解码, 进一步降低了窃听者译出率; 之后, 对所提方案的编解码性能以及安全性进行理论分析, 并通过实验仿真进行验证, 仿真结果表明, 与其他防窃听 LT 方案相比, 本文所提方案仅增加少量的译码开销但具有更好的安全性能。     

Lidar remote sensing of the mixed layer height over a tropical urban Indian station

Mixed layer is an important parameter which controls meteorological conditions in the lower atmosphere. Transport and diffusion of pollutants in the lower atmosphere is highly dependant on the structure of the planetary boundary layer, one important feature of which is the height of the well-mixed layer. In the present study, continuous wave, bistatic argon ion lidar-derived scattered signal strength from different heights in the lower troposphere over Pune (18? 32′ N, 73? 51′ E, 559 m above mean sea level), India during the period April 2007–January 2008 has been recorded remotely and by employing simple statistical tools, the mixed layer height (MLH) and transition layer thickness (TLT) have been estimated. The results show that sufficient mixing of atmospheric constituents such as aerosols exists in the boundary layer in the post-sunset hours during the summer season, enabling estimation of MLH and TLT. On the other hand, during winter months as mixing ceases/weakens by late evening hours, the mixed layer depth is either low or not easily discernible. In view of the importance of mixed layer depth information for various atmospheric applications, the remote sensing tool used and the simple methodology followed here seem promising.     

行星减速机的反向间隙的测量方法研究

介绍了行星减速机反向间隙的定义,分析了行星减速机的内部传动结构及反向间隙产生的缘由,以及行星减速机反向间隙对其的整体精度的影响.对塞规测量和咬铅条法这两种常见的测量反向间隙的方法进行比较.最终根据现场实际状况以及摆杆偏摆的理论模型,给出了一种比较简易快速的行星减速机反向间隙的测量方法,给出了判断反向间隙是否超标的依据.     

MR码编码与译码算法研究及仿真实验

传真图像的信息量非常大,对其进行数据压缩,不仅可以节省存储空间,而且可以有效地降低传输时间。针对MR码,设计了一种编码和译码算法,并利用MATLAB软件进行实现;采用该算法对传真图像进行数据压缩,并比较MH编码和MR编码的压缩比,仿真实验表明,该算法可以满足传真图像对压缩比和压缩速度的要求,并证明了该算法的可行性。