GNSS-R/IR监测地表冻融状态对延迟多普勒波形和多路径数据影响分析

将GNSS-R/IR技术的应用领域拓展到地表冻融状态的监测中,本文利用冻融土混合介质介电常数模型计算土壤介电常数,采用双站全极化相干反射率模型和随机粗糙面散射模型,分别计算了经冻融土反射的GPS相干反射量的镜像反射率,以及GPS非相干反射分量的漫散射特性。模拟分析了冻融转换时,GPS多路径信息(GNSS-IR)以及包含漫散射信号的延迟多普勒图(GNSS-R)的变化特征。理论研究表明冻融转换过程中,地表介电常数的变化导致GPS多路径信息和延迟多普勒图的明显变化。本文从散射机理上揭示了利用GNSS-R和GNSS-IR遥感进行地表冻融特性监测的理论依据。     

Laser-based validation of GLONASS orbits by short-arc technique

 The International GLONASS Experiment (IGEX-98) was carried out between 19 October 1998 and 19 April 1999. Among several objectives was the precise orbit determination of GPS and GLONASS satellites and its validation by laser ranging observations. Local laser-based orbit corrections (radial, tangential and normal components in a rotating orbital local reference frame) are computed using a geometrical short-arc technique. The order of magnitude of these corrections is at the level of few decimeters, depending on the considered components. The orbit corrections are analyzed as a function of several parameters (date, orbital plane, geographical area). The mean corrections are at the level of several centimeters. However, when averaging over the entire campaign and for all the satellites, no mean radial, tangential and normal orbit corrections are found. The origin of the observed corrections is considered (errors due to the geocentric gravitational constant, the non-gravitational forces, the thermal equilibrium of on-board equipment, the reference systems, the location and the signature of the retroreflector array, and the precision of the satellite laser ranges). Some features are also due to errors in the radio-tracking GLONASS orbits. Further investigations will be needed to better understand the origin of various biases. Received: 17 February 2000 / Accepted: 31 January 2001     

陀螺经纬仪跟踪式观测逆转点数据的平差模型

针对跟踪式定向观测中的逆转点数据 ,采用Schuler Wolf模型替代传统的等权处理 ,并对该模型进行了改造 ,包括初始信号作为参数求解、关联系数 ρ进行迭代估计等 ;用多项式衰减替代理想情况下的指数衰减 ,作为平差处理的函数模型。实测数据解算结果表明 ,由此组成的逆转点平差模型具有解算精度高、残差为白噪声信号、参数求解比较稳定等优点。     

全球定位系统(GPS)技术的最新进展 第四讲 精密单点定位(下)

2 数据处理 2.1 数据预处理 数据预处理的目的主要是为了解决下列问题:周跳的探测及修复;粗差观测值的剔除;整周模糊度的确定;用相位平滑伪距以获得较精确的伪距观测值.数据预处理工作的好坏将直接关系到精密单点定位的质量.     

附有限制条件的间接平差秩亏时解法初探

在附有限制条件的间接平差的应用中,若所列观测方程中实际用到的未知参数的个数少于所选参数的总数u时,就会出现法方程系数阵秩亏的问题。为了解决此问题,在理论公式推导的基础上,给出了一种新的解决方法,并结合算例进行了验证。     

ISIS IR: The first infrared fibre-fed spectrograph

ISIS IR is the first attempt to use fibre optics for near infrared spectroscopy (1.8m). It is a field spectrograph (2D spectroscopy), and can work at various resolving powers (up to 25000). It can be transported anywhere, and soon it will be used at CFHT with one NICMOS 3-based camera.Département d'Astrophysique Extragalactique et de Cosmologie     

Bayesian foreground analysis with CMB data

The quality of CMB observations has improved dramatically in the last few years, and will continue to do so in the coming decade. Over a wide range of angular scales, the uncertainty due to instrumental noise is now small compared to the cosmic variance. One may claim with some justification that we have entered the era of precision CMB cosmology. However, some caution is still warranted: The errors due to residual foreground contamination in the CMB power spectrum and cosmological parameters remain largely unquantified, and the effect of these errors on important cosmological parameters such as the optical depth τ and spectral index n_s is not obvious. A major goal for current CMB analysis efforts must therefore be to develop methods that allow us to propagate such uncertainties from the raw data through to the final products. Here we review a recently proposed method that may be a first step towards that goal.     

Clusters and groups of galaxies in the 2dF galaxy redshift survey: A new catalogue

We create a new catalogue of groups and clusters, applying the friends‐of‐friends method to the 2dF GRS final release. We investigate various selection effects due to the use of a magnitude limited sample. For this purpose we follow the changes in group sizes and mean galaxy number densities within groups when shifting nearby observed groups to larger distances. We study the distribution of sizes of dark matter haloes in N ‐body simulations and compare properties of these haloes and the 2dF groups. We show that at large distances from the observer luminous and intrinsically greater groups dominate, but in these groups only very bright members are seen, which form compact cores of the groups. These two effects almost cancel each other, so that the mean sizes and densities of groups do not change considerably with distance. Our final sample contains 10750 groups in the Northern part, and 14465 groups in the Southern part of the 2dF survey with membership N _gal ≥ 2. We estimate the total luminosities of our groups, correcting for group members fainter than the observational limit of the survey. The cluster catalogue is available at our web‐site ( http://www.aai.ee/∼maret/2dfgr.html ). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)