Estimation of sediment settling velocity in estuarine and coastal waters using optical remote sensing data

A robust method has been developed for estimating sediment settling velocity (w_s) from high resolution optical remote sensing data in estuarine, coastal and harbor waters. This method estimates settling velocity as a function of the drag coefficient (C_d), Reynolds number (Re), grain size (D₅₀), specific gravity (Δ_SG) and grain shape (in terms of the Corey Shape Factor – CSF). These parameters were derived from the particulate inherent optical properties such as backscattering (b_bp), beam attenuation (c_p), suspended sediment concentration and turbidity using Landsat 8 OLI and HICO data. Preliminary results for the Gulf of Cambay in the eastern Arabian Sea and Yangtze river estuary in the East China Sea, showed that satellite-retrieved settling velocities (m?s^?1) varied from very low values in clear oceanic waters, intermediate values in coastal waters, to very high values in river plumes and sediment-laden coastal waters. The remote sensing retrievals of sediment properties and their settling velocities were generally consistent with the field and laboratory results, which indicate that the proposed methodology will have important implications in various coastal engineering, environmental and management studies.     

Space debris observations with the Slovak AGO70 telescope: Astrometry and light curves

The Faculty of Mathematics, Physics and Informatics of Comenius University in Bratislava, Slovakia (FMPI) operates its own 0.7-m Newtonian telescope (AGO70) dedicated to the space surveillance tracking and research, with an emphasis on space debris. The observation planning focuses on objects on geosynchronous (GEO), eccentric (GTO and Molniya) and global navigation satellite system (GNSS) orbits. To verify the system’s capabilities, we conducted an observation campaign in 2017, 2018 and 2019 focused on astrometric and photometric measurements. In last two years we have built up a light curve catalogue of space debris which is now freely available for the scientific community. We report periodic signals extracted from more than 285 light curves of 226 individual objects. We constructed phase diagrams for 153 light curves for which we obtained apparent amplitudes.     

BN/SiBCN light-leakage-proof coatings of silica optical fiber for long term sensors at high temperatures

SiBCN and BN/SiBCN light-leakage-proof coatings were prepared on silica optical fibers for sensing applications at high temperatures. Scanning electron microscopy was used to characterize the surface morphology and microstructure of the coated fiber. Mechanical and optical properties of the coated fiber were characterized by Raman, optical and tensile tests. Compared with the original fiber, the tensile strength of SiBCN and BN/SiBCN coated fiber show an increase of about 60% and 90% at room temperature, respectively. In addition, the tensile strength of BN/SiBCN coated silica optical fiber was increased by about 42% at 700 °C. It has been found that the improvement of the strength of BN/SiBCN coated silica optical fiber is related to the healing of defects and residual compressive stress in fibers. From the light transmittance performance of the coated fiber, it was found that BN/SiBCN double coating could be an ideal total reflection solution to protect silica optical fiber from light leakage during high temperature sensing operation.     

基于单叶双曲面的标准Stewart并联结构六维力传感器各向同性优化设计

基于Stewart并联结构六维力/力矩传感器在空间六维力的准确检测上具有广泛前景,设计低耦合、高精度、易于标定和使用的六维力/力矩传感器是其结构设计的关键问题.传统Stewart并联结构几何参数描述为6个相互耦合的变量,不利于实现设计参数与设计指标的解耦,而且非正交条件下的各向同性使得六维力/力矩传感器仍存在耦合,为此...     

Navigation sensors and systems in GNSS degraded and denied environments

Position, velocity, and timing(PVT) signals from the Global Positioning System(GPS)are used throughout the world but the availability and reliability of these signals in all environments has become a subject of concern for both civilian and military applications. This presentation summarizes recent advances in navigation sensor technology, including GPS, inertial, and other navigation aids that address these concerns. Also addressed are developments in sensor integration technology with several examples described, including the Bluefin-21 system mechanization.     

航天器用薄膜温度传感器的研制及性能研究

飞行器以高超声速飞行时瞬间温升可达1 600℃以上,为了保证飞行器的可靠和运行安全,准确实时测量热防护系统表面温度显得尤为重要。针对高温环境实时测温的技术难题,结合磁控溅射技术和陶瓷烧结技术,提出了一种引线和传感器基底一体化的微小型高温薄膜温度传感器结构。采用高温检定炉对传感器陶瓷基底的高温绝缘性进行了测试,并使用多种微观形貌表征方法对传感器主要结构材料进行筛选,得到薄膜温度传感器制备所需的最佳材料组合。进行了薄膜温度传感器静态标定和综合性能高温考核试验,结果表明,所研制传感器灵敏度、重复性的变化与标准热电偶基本保持一致,在实际环境温度低于1 500℃时,传感器测量误差不超过4‰,可在1 200℃高温环境中连续准确测温6 h以上,且测温上限高达1 800℃,验证了该传感器在高温环境中进行测温的可行性和实用性,为航天器表面温度测量和热防护系统优化提供科学依据。     

A Celestial Analytic Positioning Method by Stellar Horizon Atmospheric Refraction

This article, in allusion to the limitation of conventional stellar horizon atmospheric refraction based on orbital dynamics model and nonlinear Kalman filter in practical applications, proposes a new celestial analytic positioning method by stellar horizon atmospheric refraction for high-altitude flight vehicles, such as spacecraft, airplanes and ballistic missiles. First, by setting up the geometric connexion among the flight vehicle, the Earth and the altitude of starlight refraction, an expression for the relationship of starlight refraction angle and atmospheric density is deduced. Second, there are produced a novel measurement model of starlight refraction in a continuous range of altitudes (CRA) from 20 km to 50 km on the basis of the standard atmospheric data in stratosphere, and an empirical formula of stellar horizon atmospheric refraction in the same altitudes against the tangent altitude. Third, there is introduced a celestial analytic positioning algorithm, which uses the least square differential correction instead of nonlinear Kalman filter. The information about positions of a flight vehicle can be obtained directly by solving a set of nonlinear measurement equations. The stellar positioning algorithm adopts the characteristics of stellar horizon atmospheric refraction thereby removing needs for orbit dynamics models and priori knowledge of flight vehicles. The simulation results evidence the validity of the proposed stellar positioning algorithm.     

Coherent matter wave inertial sensors for precision measurements in space

We analyze the advantages of using ultra-cold coherent sources of atoms for matter-wave interferometry in space. We present a proof-of-principle experiment that is based on an analysis of the results previously published in Richard et al. (2003) from which we extract the ratio h/m for ⁸⁷Rb. This measurement shows that a limitation in accuracy arises due to atomic interactions within the Bose–Einstein condensate. Finally we discuss the promising role of coherent-matter-wave sensors, in particular inertial sensors, in future fundamental physics missions in space.     

高精度低速回转台自动化检定方法与实现

介绍了一个由工业控制机和智能测量仪器组成的自动化检定系统，采用定角测时法，利用高精度光学棱体和激光测角技术，实现了对高精度低速回转台的自动化检定。阐述了自动化检定系统的组成、转速检定原理、软件设计和数据处理方法，并给出了实际应用的结果。