NAOC Open IR中国科学院国家天文台http://ir.bao.ac.cn:802021-10-23T18:39:25Z2021-10-23T18:39:25ZEstimation and Analysis of BDS-3 Differential Code Biases from MGEX ObservationsWang, QishengJin, ShuanggenYuan, LiangliangHu, YoujianChen, JieGuo, Jiabinhttp://ir.bao.ac.cn:80/handle/114a11/545702021-09-26T02:48:01Z2021-09-26T02:48:01ZTitle: Estimation and Analysis of BDS-3 Differential Code Biases from MGEX Observations
Authors: Wang, Qisheng; Jin, Shuanggen; Yuan, Liangliang; Hu, Youjian; Chen, Jie; Guo, Jiabin
Description: The third generation of China's BeiDou Navigation Satellite System (BDS-3) began to provide global services on 27 December, 2018. Differential code bias (DCB) is one of the errors in precise BDS positioning and ionospheric modeling, but the impacts on BDS-2 satellites and receiver DCB are unknown after joining BDS-3 observations. In this paper, the BDS-3 DCBs are estimated and analyzed using the Multi-Global Navigation Satellite System (GNSS) Experiment (MGEX) observations during the period of day of year (DOY) 002-031, 2019. The results indicate that the estimated BDS-3 DCBs have a good agreement with the products provided by the Chinese Academy of Sciences (CAS) and Deutsche Zentrum fur Luft- und Raumfahrt (DLR). The differences between our results and the other two products are within +/- 0.2 ns, with Standard Deviations (STDs) of mostly less than 0.2 ns. Furthermore, the effects on satellite and receiver DCB after adding BDS-3 observations are analyzed by BDS-2 + BDS-3 and BDS-2-only solutions. For BDS-2 satellite DCB, the values of effect are close to 0, and the effect on stability of DCB is very small. In terms of receiver DCB, the value of effect on each station is related to the receiver type, but their mean value is also close to 0, and the stability of receiver DCB is better when BDS-3 observations are added. Therefore, there is no evident systematic bias between BDS-2 and BDS-2 + BDS-3 DCB.2021-09-26T02:48:01ZPolish Ministry of Science and Higher Education SpUB granthttp://ir.bao.ac.cn:80/handle/114a11/545642021-09-26T02:47:59Z2021-09-26T02:47:59ZTitle: Polish Ministry of Science and Higher Education SpUB grant2021-09-26T02:47:59ZDetection statistics of the RadioAstron AGN surveyKovalev, Y. Y.Kardashev, N. S.Sokolovsky, K. V.Voitsik, P. A.An, T.Anderson, J. M.Andrianov, A. S.Avdeev, V. Yu.Bartel, N.Bignall, H. E.Burgin, M. S.Edwards, P. G.Ellingsen, S. P.Frey, S.Garcia-Miro, C.Gawronski, M. P.Ghigo, F. D.Ghosh, T.Giovannini, G.Girin, I. A.Giroletti, M.Gurvits, L. I.Jauncey, D. L.Horiuchi, S.Ivanov, D. V.Kharinov, M. A.Koay, J. Y.Kostenko, V. I.Kovalenko, A. V.Kovalev, Yu. A.Kravchenko, E. V.Kunert-Bajraszewska, M.Kutkin, A. M.Likhachev, S. F.Lisakov, M. M.Litovchenko, I. D.McCallum, J. N.Melis, A.Melnikov, A. E.Migoni, C.Nair, D. G.Pashchenko, I. N.Phillips, C. J.Polatidis, A.Pushkarev, A. B.Quick, J. F. H.Rakhimov, I. A.Reynolds, C.Rizzo, J. R.Rudnitskiy, A. G.Savolainen, T.Shakhvorostova, N. N.Shatskaya, M. V.Shen, Z. -Q.Shchurov, M. A.Vermeulen, R. C.de Vicente, P.Wolak, P.Zensus, J. A.Zuga, V. A.http://ir.bao.ac.cn:80/handle/114a11/545672021-09-26T02:47:59Z2021-09-26T02:47:59ZTitle: Detection statistics of the RadioAstron AGN survey
Authors: Kovalev, Y. Y.; Kardashev, N. S.; Sokolovsky, K. V.; Voitsik, P. A.; An, T.; Anderson, J. M.; Andrianov, A. S.; Avdeev, V. Yu.; Bartel, N.; Bignall, H. E.; Burgin, M. S.; Edwards, P. G.; Ellingsen, S. P.; Frey, S.; Garcia-Miro, C.; Gawronski, M. P.; Ghigo, F. D.; Ghosh, T.; Giovannini, G.; Girin, I. A.; Giroletti, M.; Gurvits, L. I.; Jauncey, D. L.; Horiuchi, S.; Ivanov, D. V.; Kharinov, M. A.; Koay, J. Y.; Kostenko, V. I.; Kovalenko, A. V.; Kovalev, Yu. A.; Kravchenko, E. V.; Kunert-Bajraszewska, M.; Kutkin, A. M.; Likhachev, S. F.; Lisakov, M. M.; Litovchenko, I. D.; McCallum, J. N.; Melis, A.; Melnikov, A. E.; Migoni, C.; Nair, D. G.; Pashchenko, I. N.; Phillips, C. J.; Polatidis, A.; Pushkarev, A. B.; Quick, J. F. H.; Rakhimov, I. A.; Reynolds, C.; Rizzo, J. R.; Rudnitskiy, A. G.; Savolainen, T.; Shakhvorostova, N. N.; Shatskaya, M. V.; Shen, Z. -Q.; Shchurov, M. A.; Vermeulen, R. C.; de Vicente, P.; Wolak, P.; Zensus, J. A.; Zuga, V. A.
Description: The largest Key Science Program of the RadioAstron space VLBI mission is a survey of active galactic nuclei (AGN). The main goal of the survey is to measure and study the brightness of AGN cores in order to better understand the physics of their emission while taking interstellar scattering into consideration. In this paper we present detection statistics for observations on ground-space baselines of a complete sample of radio-strong AGN at the wavelengths of 18, 6, and 1.3 cm. Two-thirds of them are indeed detected by RadioAstron and are found to contain extremely compact, tens to hundreds of mu as structures within their cores. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.2021-09-26T02:47:59ZNational Natural Science Foundation of China[61571309]http://ir.bao.ac.cn:80/handle/114a11/545602021-09-26T02:47:58Z2021-09-26T02:47:58ZTitle: National Natural Science Foundation of China[61571309]2021-09-26T02:47:58ZCalibration and Impact of BeiDou Satellite-Dependent Timing Group Delay BiasZhang, YizeWang, HuChen, JunpingWang, AhaoMeng, LingdongWang, Ershenhttp://ir.bao.ac.cn:80/handle/114a11/545632021-09-26T02:47:58Z2021-09-26T02:47:58ZTitle: Calibration and Impact of BeiDou Satellite-Dependent Timing Group Delay Bias
Authors: Zhang, Yize; Wang, Hu; Chen, Junping; Wang, Ahao; Meng, Lingdong; Wang, Ershen
Description: The accuracy of the timing group delay (TGD) transmitted in the broadcast ephemeris is an important factor that affects the service performance of a GNSS system. In this contribution, an apparent bias is found by comparing the orbit and clock difference using half-year data of the BeiDou navigation satellite system (BDS) broadcast ephemeris and precise post-processed products. The bias differs at each satellite on each frequency and shows a general systematic difference between BDS-2 and BDS-3. We attribute this to the satellite-dependent TGD bias of the BDS broadcast ephemeris, which is subsequently calibrated. Moreover, to calibrate the bias independently, a network solution strategy is proposed based on 87 globally distributed multi-GNSS experiment (MGEX) stations spanning 25 weeks. The estimated bias shows good agreement with the values observed from the orbit and clock comparison. For the validation of the bias, we compared the signal-in-space range error (SISRE) performance with and without the TGD bias correction. The results show that the SISRE of the BDS improved from 0.71, 0.81, and 1.40 m to 0.64, 0.66, and 0.64 m in the B1I, B3I, and B1I/B3I frequencies. For BDS-3, the SISRE is well within 0.50 m after the bias correction. To further validate the bias, a week's data were collected at 97 globally distributed MGEX stations. When the TGD bias is corrected, the root mean square (RMS) of single point positioning (SPP) can be improved by 5.6, 8.4, and 21.6% in the B1I, B3I, and B1I/B3I frequencies. Meanwhile, the SISRE and SPP assessment results also indicate that the TGD bias should be corrected by each satellite rather than only corrected between BDS-2 and BDS-3.2021-09-26T02:47:58ZThe Splash without a MergerAmarante, Joao A. S.Beraldo e Silva, LeandroDebattista, Victor P.Smith, Martin C.http://ir.bao.ac.cn:80/handle/114a11/545562021-09-26T02:47:57Z2021-09-26T02:47:57ZTitle: The Splash without a Merger
Authors: Amarante, Joao A. S.; Beraldo e Silva, Leandro; Debattista, Victor P.; Smith, Martin C.
Description: The Milky Way's progenitor experienced several merger events that left their imprints on the stellar halo, including the Gaia-Sausage/Enceladus. Recently, it has been proposed that this event perturbed the proto-disk and gave rise to a metal-rich ([Fe/H] > -1), low angular momentum (v < 100 km s(-1)) stellar population. These stars have dynamical and chemical properties different from the accreted stellar halo, but are continuous with the canonical thick disk. In this Letter, we use a hydrodynamical simulation of an isolated galaxy that develops clumps that produce a bimodal thin+thick disk chemistry to explore whether it forms such a population. We demonstrate that clump scattering forms a metal-rich, low angular momentum population, without the need for a major merger. We show that, in the simulation, these stars have chemistry, kinematics, and density distribution in good agreement with those in the Milky Way.2021-09-26T02:47:57Z3-D Gravity Anomaly Inversion Based on Improved Guided Fuzzy C-Means Clustering AlgorithmLiu, ShengJin, Shuanggenhttp://ir.bao.ac.cn:80/handle/114a11/545592021-09-26T02:47:57Z2021-09-26T02:47:57ZTitle: 3-D Gravity Anomaly Inversion Based on Improved Guided Fuzzy C-Means Clustering Algorithm
Authors: Liu, Sheng; Jin, Shuanggen
Description: The geophysical inversion with combining prior information is very important for resource exploration and studies of the Earth's internal structure. Guided fuzzy C-means clustering inversion (FCM) is normally applied for the Tikhonov regularized inversion, but has the shortcoming of uniform model parameter shrinkage, leading to inaccuracy. In this paper, an improved guided fuzzy clustering algorithm is proposed by adding a fuzzy entropy term to the original guided FCM. This method not only enforces the discrete values to a high degree of approximation by guiding the recovered model to cluster tightly around the known petrophysical property values, but also calculates the distributed characteristics of the model parameter set. Based on this method, the shortcoming of uniform shrinkage of the original guided FCM clustering algorithm is improved, and more accurate inversion results are obtained, making the FCM method more efficient and broadly applicable. Furthermore, a new parameter search algorithm is proposed to accelerate the search speed. The results recovered by using this method with three kinds of theoretical gravity anomaly data show more accurate density anomalies compared with the results generated from the original guided FCM clustering inversion and greater efficiency in the parametric search process when using the new parameter search algorithm. The improved FCM clustering algorithm could enable more extensive and efficient use of gravity inversion.2021-09-26T02:47:57ZBIS National E-infrastructure capital grant[ST/J005673/1]http://ir.bao.ac.cn:80/handle/114a11/545512021-09-26T02:47:56Z2021-09-26T02:47:56ZTitle: BIS National E-infrastructure capital grant[ST/J005673/1]2021-09-26T02:47:56ZSTFC DiRAC Operations grant[ST/K00333X/1]http://ir.bao.ac.cn:80/handle/114a11/545532021-09-26T02:47:56Z2021-09-26T02:47:56ZTitle: STFC DiRAC Operations grant[ST/K00333X/1]2021-09-26T02:47:56ZSTFC Consolidated grant[ST/R000786/1]http://ir.bao.ac.cn:80/handle/114a11/545502021-09-26T02:47:56Z2021-09-26T02:47:56ZTitle: STFC Consolidated grant[ST/R000786/1]2021-09-26T02:47:56Z