Retrieval of water vapor profiles with radio occultation measurements using an artificial neural network

A new method applying an artificial neural network （ANN） to retrieve water vapor profiles in the troposphere is presented. In this paper, a fully-connected, three-layer network based on the backpropagation algorithm is constructed. Month, latitude, altitude and bending angle are chosen as the input vectors and water vapor pressure as the output vector. There are 130 groups of occultation measurements from June to November 2002 in the dataset. Seventy pairs of bending angles and water vapor pressure profiles are used to train the ANN, and the sixty remaining pairs of profiles are applied to the validation of the retrieval. By comparing the retrieved profiles with the corresponding ones from the Information System and Data Center of the Challenging Mini-Satellite Payload for Geoscientific Research and Application （CHAMP-ISDC）, it can be concluded that the ANN is relatively convenient and accurate. Its results can be provided as the first guess for the iterative methods or the non-linear optimal estimation inverse method.     

Anomalous radar backscatter from Titan’s surface?

Since Cassini arrived at Saturn in 2004, its moon Titan has been thoroughly mapped by the RADAR instrument at 2-cm wavelength, in both active and passive modes. Some regions on Titan, including Xanadu and various bright hummocky bright terrains, contain surfaces that are among the most radar-bright encountered in the Solar System. This high brightness has been generally attributed to volume scattering processes in the inhomogeneous, low-loss medium expected for a cold, icy satellite surface. We can test this assumption now that the emissivity has been obtained from the concurrent radiometric measurements for nearly all the surface, with unprecedented accuracy (Janssen et al., and the Cassini RADAR Team [2009]. Icarus 200, 222-239). Kirchhoff’s law of thermal radiation relates the radar and radiometric properties in a way that has never been fully exploited. In this paper we examine here how this law may be applied in this case to better understand the nature of Titan’s radar-bright regions. We develop a quantitative model that, when compared to the observational data, allows us to conclude that either the reflective characteristics of the putative volume scattering subsurface must be highly constrained, or, more likely, organized structure on or in the surface is present that enhances the backscatter.     

New analysis of Lunar Prospector radio tracking data brings the nearside gravity field of the Moon with an unprecedented resolution

A new analysis of the Doppler tracking data from the Lunar Prospector mission in 1999 revealed a number of previously-unseen gravity anomalies at spatial scales as small as 27 km over the nearside. The tracking data at low altitudes (50 km or below) were better analyzed to resolve the nearside features without dampening from a power law constraint, by partitioning the gravity parameters concentrated on either the nearside or farside. The resulting model presents gravity anomalies correlated with topography with a correlation coefficient of 0.7 or higher from degree 50 to 150, the widest bandwidth yet. The gravity-topography admittance of ∼70 mGal/km is found from numerous craters of which diameters are 60 km or less. In addition, the new model produces orbits that fit to independent radio tracking data from the Lunar Reconnaissance Orbiter and Kaguya (SELENE) better than previous gravity models. This high-resolution model can be of immediate use to geophysical analysis of small craters. Our technique could be applied to an upcoming mission, the Gravity Recovery And Interior Laboratory and useful to extract short wavelength signals from the MESSENGER Doppler data.     

基于COSMIC掩星探测资料的云底高反演研究

本文基于相对湿度廓线进入云层时的突变实现云底高反演的思想,采用2008年11月至2009年1月的COSMIC掩星湿空气数据反演全球云底高度,并与探空资料反演结果进行对比分析,得出以下重要结论:(1)当温度－40 ℃相似文献   

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Correction on effect of Earth’s oblateness in inversion of GPS occultation data

By using observed CHAMP orbit ephemeredes and MSISE-90 dry air model and regarding the earth as a sphere and an ellipsoid respectively, phase delays are simulated and the simulated data are retrieved under different schemes. The comparison between the inverted temperature profiles and the model temperature profiles shows that by inverting observed data, we will get temperature results with large errors if the effect of Earth’s oblateness is omitted. The correction method is proved to be effective because the temperature errors decreased obviously with this method.     

应用WS/GPS技术的粪渣收运监控系统的开发

通过安装于粪渣收运车辆上的车载称重系统（WS）和全球卫星定位系统（GPS）,经由通用无线分组业务（GPRS）将粪渣收运车载重变化及其位置信息,实时传回监控中心的数据库中[1],并通过集成地理信息系统（GIS）的粪渣收运监控系统浏览、查询、管理粪渣收运情况。主要以车载重量变化信息作为收运监控参考的重要依据,并配合车辆定位...     

Surface circulation downstream of the Point Arena upwelling center

Measurements from recently installed 5 MHz high-frequency radar (CODAR) stations south of Point Arena, California, are used to describe surface current patterns during the upwelling season (June-August 2007). The systems provide hourly current maps on a 5-km grid, covering a region from approximately 10 to 150 km offshore (the continental shelf into the deep ocean). These HF-radar observations provide an unprecedented view of circulation in this “coastal transition zone”, between the wind-driven circulation over the shelf and the California Current circulation offshore. Circulation patterns include: (1) bifurcation of the coastal upwelling jet downstream of Point Arena into an along-shelf (down-coast) branch and an offshore branch, and (2) a large-scale anticyclonic meander that often develops into an eddy-like recirculation south of the bifurcation. The “recirculation” feature extends well offshore, with surface currents 50-100 km from the coast consistently opposing the wind stress. The spatial and temporal evolution of the surface current features during upwelling events affects surface transport from Point Arena to areas in the south, increasing the travel time of a substantial fraction of newly upwelled water from a few days to roughly two weeks. Thus, surface currents even far offshore influence coastal transport of nutrients, phytoplankton and larvae on ecologically relevant timescales, with resultant connectivity patterns very different than implied by a simple examination of the mean flow.     

基于DTU的加速度强振动记录终端的设计

设计基于DTU的强振记录终端,采用SOC系列C8051F015型单片机对MEMS加速度计的输出信号进行A/D转换,监测待测体所经受的强振加速度值,并通过DTU内嵌的GPRS无线网络通讯方式将数据发送到远程数据中心.该系统具有体积小,安装与操作方便,免维护等特性.     

Noise reduction methods in the analysis of near infrared lunar occultation light curves for high angular resolution measurements

A lunar occultation （LO） technique in the near-infrared （NIR） provides angular resolution down to milliarcseconds for an occulted source, even with ground- based 1 m class telescopes. LO observations are limited to brighter objects because they require a high signal-to-noise ratio （S/N ~40） for proper extraction of angular diameter values. Hence, methods to improve the S/N ratio by reducing noise using Fourier and wavelet transforms have been explored in this study. A sample of 54 NIR LO light curves observed with the IR camera at Mt Abu Observatory has been used. It is seen that both Fourier and wavelet methods have shown an improvement in S/N compared to the original data. However, the application of wavelet transforms causes a slight smoothing of the fringes and results in a higher value for angular diameter. Fourier transforms which reduce discrete noise frequencies do not distort the fringe. The Fourier transform method seems to be effective in improving the S/N, as well as improving the model fit, particularly in the fainter regime of our sample. These methods also provide a better model fit for brighter sources in some cases, though there may not be a significant imorovement in S/N.