GNSS观测数据的质量直接关系到GNSS的测量精度和可靠性。文章在周跳探测、相位平滑伪距等研究的基础上,从多路径效应、电离层延迟、电离层延迟变化率等方面对GNSS观测数据质量检核进行了研究,并编写了一款新的GNSS观测数据质量检核软件G-QC,实现了质量检核报告的可视化。该软件能兼容RINEX第2版及第3版。通过与TEQC(translation,editing and quality checking,TEQC)软件包的质量检核结果进行比对,验证了算法的正确性。利用所编制的软件G-QC实现了对GPS/BD双模接收机静态和动态观测数据的质量检核。
Employing multiple pulsars and using an appropriate algorithm to establish ensemble pulsar timescale can reduce the influences of various noises on the long-term stability of pulsar timescale,compared to a single pulsar.However,due to the low timing precision and significant red noises of some pulsars,their participation in the construction of ensemble pulsar timescale is often limited.Inspired by the principle of solving non-stationary sequence modeling using co-integration theory,we put forward an algorithm based on co-integration theory to establish an ensemble pulsar timescale.It is found that this algorithm can effectively suppress some noise sources if a co-integration relationship between different pulsar data exists.Different from the classical weighted average algorithm,the co-integration method provides the chance for a pulsar with significant red noises to be included in the establishment of an ensemble pulsar timescale.Based on data from the North American Nanohertz Observatory for Gravitational Waves(NANOGrav),we found that the co-integration algorithm can successfully reduce several timing noises and improve the long-term stability of the ensemble pulsar timescale.
Relic gravitational waves （RGWs）, a background originating during inflation, would leave imprints on pulsar timing residuals. This makes RGWs an important source for detection of RGWs using the method of pulsar timing. In this paper, we discuss the effects of RGWs on single pulsar timing, and quantitatively analyze the timing residuals caused by RGWs with different model parameters. In principle, if the RGWs are strong enough today, they can be detected by timing a single millisecond pulsar with high precision after the intrinsic red noises in pulsar timing residuals are understood, even though simultaneously observing multiple millisecond pulsars is a more powerful technique for extracting gravitational wave signals. We correct the normalization of RGWs using observations of the cosmic microwave background （CMB）, which leads to the amplitudes of RGWs being reduced by two orders of magnitude or so compared to our previous works. We obtained new constraints on RGWs using recent observations from the Parkes Pulsar Timing Array, employing the tensor-to-scalar ratio r = 0.2 due to the tensor-type polarization observations of CMB by BICEP2 as a reference value, even though its reliability has been brought into question. Moreover, the constraints on RGWs from CMB and Big Bang nucleosynthesis will also be discussed for comparison.
