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151.
Onur Erturk Orhan Arikan Feza Arikan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
Electron density distribution is the major determining parameter of the ionosphere. Computerized Ionospheric Tomography (CIT) is a method to reconstruct ionospheric electron density image by computing Total Electron Content (TEC) values from the recorded Global Positioning Satellite System (GPS) signals. Due to the multi-scale variability of the ionosphere and inherent biases and errors in the computation of TEC, CIT constitutes an underdetermined ill-posed inverse problem. In this study, a novel Singular Value Decomposition (SVD) based CIT reconstruction technique is proposed for the imaging of electron density in both space (latitude, longitude, altitude) and time. The underlying model is obtained from International Reference Ionosphere (IRI) and the necessary measurements are obtained from earth based and satellite based GPS recordings. Based on the IRI-2007 model, a basis is formed by SVD for the required location and the time of interest. Selecting the first few basis vectors corresponding to the most significant singular values, the 3-D CIT is formulated as a weighted least squares estimation problem of the basis coefficients. By providing significant regularization to the tomographic inversion problem with limited projections, the proposed technique provides robust and reliable 3-D reconstructions of ionospheric electron density. 相似文献
152.
首先对GPS信号产生原理进行了分析,然后给出了一种基带数字信号源的产生方法,即用码发生器产生伪随机码,先和导航数据进行调制,再调制上用DDS产生的载波信号,最终形成一颗或多颗GPS卫星信号.该方法用FPGA实现,不仅可以模拟GPS卫星信号的特性,而且考虑到调试接收机的动态捕获性能,信号源中还模拟了信号在运动状态下的情况.该方法为接收机基带信号处理部分的调试节省了大量的时间,针对基带部分提供信号源,减少了调试中其他因素(例如射频部分)的错误而带来的干扰. 相似文献
153.
154.
海南地区电离层不规则体纬向漂移速度的观测和研究 总被引:3,自引:2,他引:1
根据中国海南富克(19.3°N,109.1°E)三点GPS观测系统2007年3月至11月的观测数据,利用互相关方法分析了三站闪烁信号的时间延迟,得出了不规则体纬向漂移的基本特征.在中国海南地区,闪烁主要发生在春秋季节,夜间不规则体的纬向漂移速度以东向为主,大小在50~150 m/s之间;平均东向漂移速度随时间呈下降趋势.另外,在闪烁刚发生时,不规则体纬向速度起伏较大,这可能与不规则体的随机起伏以及等离子体泡产生时垂直速度较大有关.中国海南地区不规则体纬向漂移速度的这些基本特征与低纬其他地区的测量结果较为一致. 相似文献
155.
通过“往返试飞”消除风速影响从而由 GPS测得的地速求得真空速,运用近似理想气体理论,建立Ma数真值与真空速、大气总温的关系,解算出 Ma数真值,得到“GPS速度法”;或者考虑真实大气与标准大气的差异,在水平航线上引入气压高度常值偏差及航路气压修正系数,建立 GPS几何高度与气压高度的关系,结合“速度法”求得的任一 Ma数点的校准量,解算出气压高度真值,得到“GPS高度法”。通过对某型飞机的飞行试验,验证了这些方法的可靠性与实用性。 相似文献
156.
全球卫星导航系统的近期进展 总被引:6,自引:0,他引:6
20世纪末,卫星导航发展势态出现了GLONASS星座维持困难,GPS推行现代化计划和欧洲Galileo计划出台三大新闻。有望于2010年左右Galileo星座和GPS星形成互补和卫为余度。最近,美国国会削减GPS预算,在GPS民用进展上投下阴影,GPS单一导航手段暂难实行,有利于欧洲争取时间,积极筹措Galileo系统。 相似文献
157.
158.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(5):1402-1413
The present paper reports coordinated ionospheric irregularity measurements at optical as well as GPS wavelengths. Optical measurements were obtained from Tiny Ionospheric Photometer (TIP) sensors installed onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. GPS radio signals were obtained from a dual frequency GPS receiver operational at Calcutta (22.58°N, 88.38°E geographic; geomagnetic dip: 32.96°; 13.00°N, 161.63°E geomagnetic) under the SCIntillation Network Decision Aid (SCINDA) program. Calcutta is located near the northern crest of Equatorial Ionization Anomaly (EIA) in the Indian longitude sector. The observations were conducted during the unusually low and prolonged solar minima period of 2008–2010. During this period, four cases of post-sunset GPS scintillation were observed from Calcutta. Among those cases, simultaneous fluctuations in GPS Carrier-to-Noise ratios (C/No) and measured radiances from TIP over a common ionospheric volume were observed only on February 2, 2008 and September 25, 2008. Fluctuations observed in measured radiances (maximum 0.95 Rayleigh) from TIP due to ionospheric irregularities were found to correspond well with C/N0 fluctuations on the GPS links observed from Calcutta, such effects being noted even during late evening hours of 21:00–22:00 LT from locations around 40° magnetic dip. These measurements indicate the existence of electron density irregularities of scale sizes varying over several decades from 135.6 nm to 300–400 m well beyond the northern crest of the EIA in the Indian longitude sector during late evening hours even in the unusually low solar activity conditions. 相似文献
159.
Xuexi Liu Weiping Jiang Zhao Li Hua Chen Wen Zhao 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(11):3489-3504
Precise point positioning (PPP) usually takes about 30?min to obtain centimetre-level accuracy, which greatly limits its application. To address the drawbacks of convergence speed and positioning accuracy, we develop a PPP model with integrated GPS and BDS observations. Based on the method, stations with global coverage are selected to estimate the fractional cycle bias (FCB) of GPS and BDS. The short-term and long-term time series of wide-lane (WL) FCB, and the single day change of narrow-lane (NL) FCB are analysed. It is found that the range of GPS and BDS non-GEO (IGSO and MEO) WL FCB is stable at up to a 30-day-time frame. At times frame of up to 60?days, the stability is reduced a lot. Whether for short-term or long-term, the changes in the BDS GEO WL FCB are large. Moreover, BDS FCB sometimes undergoes a sudden jump. Besides, 17 and 10 stations were used respectively to investigate the convergence speed and positioning errors with six strategies: BDS ambiguity-float PPP (Bfloat), GPS ambiguity-float PPP (Gfloat), BDS/GPS ambiguity-float PPP (BGfloat), BDS ambiguity-fixed PPP (Bfix), GPS ambiguity-fixed (Gfix), and BDS/GPS ambiguity-fixed (BGfix). The average convergence speed of the ambiguity-fixed solution is greatly improved compared with the ambiguity-float solution. In terms of the average convergence time, the Bfloat is the longest and the BGfix is the shortest among these six strategies. Whether for ambiguity-float PPP or ambiguity-fixed PPP, the convergence reduction time in three directions for the combined system is the largest compared with the single BDS. The average RMS value of the Bfix in three directions (easting (E), northing (N), and up (U)) are 2.0?cm, 1.5?cm, and 5.9?cm respectively, while those of the Gfix are 0.8?cm, 0.5?cm, and 1.7?cm. Compared with single system, the BDS/GPS combined ambiguity-fixed system (BGfix) has the fastest convergence speed and the highest accuracy, with average RMS as 0.7?cm, 0.5?cm, and 1.9?cm for the E, N, U components, respectively. 相似文献
160.
Mir Reza Ghaffari Razin Amirreza Moradi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(5):1546-1558
In this paper, a new method of temporal extrapolation of the ionosphere total electron content (TEC) is proposed. Using 3-layer wavelet neural networks (WNNs) and particle swarm optimization (PSO) training algorithm, TEC time series are modeled. The TEC temporal variations for next times are extrapolated with the help of training model. To evaluate the proposed model, observations of Tehran GNSS station (35.69°N, 51.33°E) from 2007 to 2018 are used. The efficiency of the proposed model has been evaluated in both low and high solar activity periods. All observations of the 2015 and 2018 have been removed from the training step to test the proposed model. On the other hand, observations of these 2 years are not used in network training. According to the F10.7, the 2015 has high solar activity and the 2018 has quiet conditions. The results of the proposed model are compared with the global ionosphere maps (GIMs) as a traditional ionosphere model, international reference ionosphere 2016 (IRI2016), Kriging and artificial neural network (ANN) models. The root mean square error (RMSE), bias, dVTEC = |VTECGPS ? VTECModel| and correlation coefficient are used to assess the accuracy of the proposed method. Also, for more accurate evaluation, a single-frequency precise point positioning (PPP) approach is used. According to the results of 2015, the maximum values of the RMSE for the WNN, ANN, Kriging, GIM and IRI2016 models are 5.49, 6.02, 6.34, 6.19 and 13.60 TECU, respectively. Also, the maximum values of the RMSE at 2018 for the WNN, ANN, Kriging, GIM and IRI2016 models are 2.47, 2.49, 2.50, 4.36 and 6.01 TECU, respectively. Comparing the results of the bias and correlation coefficient shows the higher accuracy of the proposed model in quiet and severe solar activity periods. The PPP analysis with the WNN model also shows an improvement of 1 to 12 mm in coordinate components. The results of the analyzes of this paper show that the WNN is a reliable, accurate and fast model for predicting the behavior of the ionosphere in different solar conditions. 相似文献