An algorithm for a near real-time data processing of GPS common-view observations

Near real-time transfer of GPS common-view data is no longer a problem, but near real-time data processing of the data still calls for study, because it is not yet achieved by the usual smoothing and filtering techniques. Based on the characteristics of the GPS common-view data, a Kalman filtering algorithm is designed for estimating the time difference between two sites, while greatly reducing the observational noise. The algorithm is applied to the time difference between the National Time Service Center (NTSC) of China and the Communications Research Laboratory (CRL) of Japan (Over 2000 km apart), and to that between the CRL and the Korean Research Institute of Standards and Sciences (KRIS) (over 1000 km apart). The root mean square errors of the results obtained by the Kalman filter relative to those obtained from the Circular T of BIPM are less than 2.9 ns and 2.6 ns, in the two cases. Further, it is pointed out that, when multi-site data within a common-view network are available we can further improve the accuracy of the time comparisons by indirect observation adjustment. This statement was justified by application to the data from all three stations, i.e. NTSC, CRL, and KRIS.     

单频GPS周跳检测与估计算法

提出一种单频GSP载波相位中的野值，周跳俭测与模糊度估计算法，采用三阶多项式的卡尔曼滤波检测野值与周跳，而用一种最佳小波估计模糊度，该算法适用于采样间隔为1秒的载波相位测量，用1995．6．22Topex星载GPS数据计算的结果表明，它有限高的效率，可以准确估计信号中断几秒内的模糊度。     

相位求差法与相位率法探测与修复周跳的比较

目前对GPS载波相位观测值周跳的探测与修复有多种方法,但是各种方法都不很完善。介绍常用的周跳探测与修复方法,并利用相位求差法和相位率法进行周跳探测与修复试验。结果表明2种方法均能准确地锁定发生小周跳的历元,而且能高效地修复观测值;然而,相位求差法需要双频观测数据,而相位率法仅需要单频观测数据。     

TurboEdit方法中周跳检测算法的改进

介绍GIPSY(GNSS-inferred positioning system)中周跳检测与修复的TurboEdit算法,在此基础上对TurboEdit方法的周跳检测条件进行分析,在用宽巷组合检测周跳的过程中采用滑动平均的方法替代宽巷模糊度中对每一历元之前的所有数据整体求平均的方法,同时在用电离层残差组合检测周跳中采用相邻历元的载波相位电离层残差组合求差的方法,从而避免引入观测噪声较大的伪距电离层残差组合。实验表明:改进后的TurboEdit法对于发生在观测数据质量不好时段的周跳、Turboedit法的检测盲点以及频繁周跳的检测能力都有所提高。     

The reduction and analysis of GPS common view data

The atomic time scale (such as TAI) obtained from atomic clocks of time laboratories distributed in various locations requires that the means of time comparison should have the same degree of stability as the atomic clocks in use. GPS CV is currently the most widely adopted means of time comparison in the world, and its data reduction and error analysis are indispensable means for improving the accuracy and precision of the technique. The data reduction and analysis of the GPS CV data of CRL-CSAO are taken as an example to illustrate various problems to be solved and the accuracy achieved.     

On the singular points of the Abelian integral transformation in the GPS/LEO occultation technique

In the inversion terrestrial atmosphere technique the inversion of theAbelian integral is one of the most often used methods for deriving the refractive index profile of the terrestrial atmosphere from GPS/LLEO radio occultation data. There exists the problem of singular point in the Abelian integral. Different methods for solving this problem are discussed and a method of finding an analytic solution of the Abelian integral after a variable transformation is proposed. The accuracies of the various methods are compared by means of simulation calculations.     

An orbit determination algorithm by means of the satellite-borne GPS data and Kalman filter

Using the Kalman filter algorithm, we have processed on-board GPS data of Shenzhou 4. The research focuses on three problems, namely, the selection criteria for the model error variance matrix of the Kalman filter, the effects of GPS signal interruption or runs of outliers on the recursive filtering, and the method to monitor the filter running status (normal or divergent). The aim is to evaluate the reliability of long-time stationary running of this algorithm used for on-board autonomous orbit determination     

Prediction of solar cycle 24 and beyond

In the previous study (Hiremath, Astron. Astrophys. 452:591, 2006a), the solar cycle is modeled as a forced and damped harmonic oscillator and from all the 22 cycles (1755–1996), long-term amplitudes, frequencies, phases and decay factor are obtained. Using these physical parameters of the previous 22 solar cycles and by an autoregressive model, we predict the amplitude and period of the present cycle 23 and future fifteen solar cycles. The period of present solar cycle 23 is estimated to be 11.73 years and it is expected that onset of next sunspot activity cycle 24 might starts during the period 2008.57±0.17 (i.e., around May–September 2008). The predicted period and amplitude of the present cycle 23 are almost similar to the period and amplitude of the observed cycle. With these encouraging results, we also predict the profiles of future 15 solar cycles. Important predictions are: (i) the period and amplitude of the cycle 24 are 9.34 years and 110 (±11), (ii) the period and amplitude of the cycle 25 are 12.49 years and 110 (±11), (iii) during the cycles 26 (2030–2042 AD), 27 (2042–2054 AD), 34 (2118–2127 AD), 37 (2152–2163 AD) and 38 (2163–2176 AD), the sun might experience a very high sunspot activity, (iv) the sun might also experience a very low (around 60) sunspot activity during cycle 31 (2089–2100 AD) and, (v) length of the solar cycles vary from 8.65 years for the cycle 33 to maximum of 13.07 years for the cycle 35.     

Helioseismic solar cycle changes and splitting coefficients

Using the GONG data for a period over four years, we have studied the variation of frequencies and splitting coefficients with solar cycle. Frequencies and even-order coefficients are found to change significantly with rising phase of the solar cycle. We also find temporal variations in the rotation rate near the solar surface.     

The establishment of a continuous declination system with photoelectric astrolabe Mark I—An international cooperation between Lintong and Irkutsk

We propose a cooperative observational project of using the photo-electric astrolabe Mark I of Shaanxi Observatory in Irkutsk. As the instrument will be equipped with a Z = 45° angle prism, it will have no blind zone when used at latitude (φ = 52°. Important contribution can be expected to the establishing of fundamental reference system and the maintenance of the Hipparcos Catalogue system.     

A method of astronomical autonomous orbit and attitude determinations for satellites

A method of realtime autonomous orbit determination for earth satellites using the extended Kalman filtering is proposed. The observed quantities are: the satellite-sun direction vector measured by a sun sensor, the satellite-earth and satellite-moon direction vectors measured by an ultraviolet sensor, and the geocentric distance measured by a radar altimeter. At the same time the satellite attitude to the earth is also determined. Results of our simulation of the autonomous orbit determination show that the precision of the orbit determinations is better than 200 m. The effects of the sampling period, orbital inclination, orbital eccentricity and orbital altitude on the precision of orbit determination are analyzed and compared, and certain principles helpful for improving the precision of orbit determination are suggested.     

An elementary model for the dust cycle in galaxies

We give an elementary model for the evolution of dust in galaxies, based on abundance arguments. The model takes account of grain core production in both supernovae and giant stars, and includes mantle growth in the interstellar medium. Destruction of grain cores does not appear to be a dominant effect. We show that a self-consistent picture can be made in which the interstellar dust mass is an approximately constant fraction of the heavy element mass in the interstellar medium. This result is demonstrated to be essentially independent of outflow or inflow of interstellar material.     

Measurement and analysis of rotation in close binaries. I. Observations and results

A set of close binaries have been observed using the same instrumental configuration at Kitt Peak National Observatory, USA. The rotation velocities for 99 components in 75 binaries, derived by two methods, are given here, including 55 components for the first time. These high-accuracy velocities provide a reliable observational basis for investigating synchronism in binaries and the various synchronizing mechanisms.     

J 2000.0 positions and proper motions of 257 stars in the central part of the Praesepe astrometric standard region

We given the J2000.0 position and proper motions of 257 stars in the central 1.5° × 1.5° area of the Praesepe astrometric standard region with accuracies of 0.005˜0.10 arcsec for the position in each direction and 0.0002˜0.006 arcsec/yr for the proper motions in each direction.     

GPS定时噪声分析与控制

分析了选择可用性干扰的噪声特性,得到了选择可用干扰的数学模型。建立起时刻差方程的状态空间的描述,利用离散的状态方程,用卡尔曼滤波的方法减小ＳＡ干扰对校频,定时精度的影响。     

Climate and carbon cycle changes under the overshoot scenario

The “overshoot scenario” is an emissions scenario in which CO₂ concentration in the atmosphere temporarily exceeds some pre-defined, “dangerous” threshold (before being reduced to non-dangerous levels). Support for this idea comes from its potential to achieve a balance between the burdens of current and future generations in dealing with global warming. Before it can be considered a viable policy, the overshoot scenario needs to be examined in terms of its impacts on the global climate and the environment. In, particular, it must be determined if climate change cause by the overshoot scenario is reversible or not, since crossing that “dangerous” CO₂ threshold could result in climate change from which we might not be able to recover. In this study, we quantify the change in several climatic and environmental variables under the overshoot scenario using a global climate model of intermediate complexity. Compared to earlier studies on the overshoot scenario, we have an explicit carbon cycle model that allows us to represent carbon-climate feedbacks and force the climate model more realistically with CO₂ emissions rates rather than with prescribed atmospheric pCO₂. Our standard CO₂ emissions rate is calculated on the basis of historical atmospheric pCO₂ data and the WRE S650 non-overshoot stabilization profile. It starts from the preindustrial year 1760, peaks in the year 2056, and ends in the year 2300. A variety of overshoot scenarios were constructed by increasing the amplitude of the control emissions peak but decreasing the peak duration so that the cumulative emissions remain essentially constant. Sensitivity simulations of various overshoot scenarios in our model show that many aspects of the global climate are largely reversible by year 2300. The significance of the reversibility, which takes roughly 200 years in our experiments, depends on the time horizon with which it is viewed or the number of future generations for whom equity is sought. At times when the overshoot scenario has emissions rates higher then the control scenario, the transient changes in atmospheric and oceanic temperatures and surface ocean pH can be significant, even for moderate overshoot scenarios that remain within IPCC SRES emissions scenarios. The large transient changes and the centennial timescale of climate reversibility suggest that the overshoot might not be the best mitigation approach, even if it technically follows the optimal economic path.     

An algorithm for solving the pulsar equation

We present an algorithm of finding numerical solutions of pulsar equation. The problem of finding the solutions was reduced to finding expansion coefficients of the source term of the equation in a base of orthogonal functions defined on the unit interval by minimizing a multi-variable mismatch function defined on the light cylinder. We applied the algorithm to Scharlemann and Wagoner boundary conditions by which a smooth solution is reconstructed that by construction passes successfully the Gruzinov’s test of the source function exponent.      

An Approach of Tropospheric Correction for VLBI Phase-Referencing using GPS Data

The dominant source of error in VLBI phase-referencing is the troposphere at observing frequencies above 5 GHz. We compare the tropospheric zenith delays derived from VLBI and GPS data at VLBA stations collocated with GPS antennas. The systematic biases and standard deviations both are at the level of sub-centimeter. Based on this agreement, we suggest a new method of tropospheric correction in phase-referencing using combined VLBI and GPS data.