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Li J.,CAS National Astronomical Observatories | Li J.,University of Chinese Academy of Sciences | Ma G.,CAS National Astronomical Observatories | Maruyama T.,Japan National Institute of Information and Communications Technology | And 2 more authors.
Journal of Geophysical Research: Space Physics | Year: 2012

Post-sunrise intense ionospheric irregularities at low to mid-latitudes are reported for the first time. A method based on spaced-receiver technique is proposed to estimate the apparent drift velocity of the irregularities by using the correlation of the slant total electron content (TEC) from 3 GPS receivers. The irregularities were detected at 23∼45°N by the GPS Earth Observation Network (GEONET) of Japan from ∼0455 LT to ∼1051 LT on 21 March 2001 during the recovery phase of the magnetic storm. At the corresponding time spread F was observed with 3 ionosondes located meridionally at Okinawa (127.8°E, 26.3°N; 20.7°N magnetic latitude), Kokubunji (139.5°E, 35.7°N; 30.0°N magnetic latitude) and Wakkanai (141.7°E, 45.4°N; 40.5°N magnetic latitude), while an intense negative ionospheric storm was processing and propagating from mid to lower latitudes. The irregularities were seen as plasma bubbles by the Defense Meteorological Satellite Program (DMSP) in-situ measurements. Westward drift with the speed of ∼100 m/s was estimated by spaced receivers from GEONET and confirmed by DMSP during the evolution of the irregularities. The plasma bubbles at mid-latitude sustained ∼1.5 hour after sunrise, and at the lower latitudes they survived more than 4 hours after sunrise. The observations suggested that the irregularities were generated by an eastward electric field associated with the disturbance dynamo, and the long time existence of the irregularities after sunrise seemed to be related to the daytime intense negative ionospheric storm on 21 March. © 2012. American Geophysical Union. All Rights Reserved. Source


Wang Y.,National University of Defense Technology | Zheng W.,National University of Defense Technology | Sun S.,Xian Jiaotong University | Li L.,Science and Technology on Aerospace Flight Dynamics Laboratory
Aerospace Science and Technology | Year: 2014

In order to reduce the composite impacts of the systematic biases in the X-ray pulsar-based navigation system, an innovative navigation method is proposed. The proposed method employs the time-differenced measurement which is the difference between the measurements at the neighbor epochs. For Earth-orbiting satellite, the systematic biases vary slowly over the navigation period, and the time-differenced measurement can greatly reduce the major part of systematic biases. Through observability analysis, the corresponding navigation system is demonstrated to be completely observable. In order to solve the correlation between the process and measurement noises in the proposed method, a modified unscented Kalman filter is derived. In addition, the modified unscented Kalman filter propagates the selected sigma points to generate the time-differenced measurement model without involving linearization error. The results of simulations have shown that the proposed method can effectively reduce the composite impacts of systematic biases including the pulsar angular position error, pulsar distance error, Earth ephemeris error, and satellite-borne clock error. © 2014 Elsevier Masson SAS. All rights reserved. Source


Wang Y.,National University of Defense Technology | Sun S.,Xian Jiaotong University | Li L.,Science and Technology on Aerospace Flight Dynamics Laboratory
Journal of Guidance, Control, and Dynamics | Year: 2014

A study was conducted to propose a adaptively robust Kalman filter (ARKF) for tracking a maneuvering vehicle. The ARUKF had the potential to reduce the effect of the dynamics model error and the measurement model error simultaneously. The fading factor based on the innovation sequence orthogonal principle was derived to overcome the limitation of the ARKF. The ARKF had the potential to reduce the effect of the dynamics model error, with fewer iterations. The cost function of an improved adaptively robust Kalman filter (IARKF) was derived and the procedure in embedding the structure of the IARKF into the unscented Kalman filter (UKF) framework was discussed. The method of forming the fading factor based on the innovation sequence orthogonal principle was also provided. The ARUKF effectively tracked the movement of the vehicle when the orbital maneuver, measurement outlier, and contaminated noise occurred simultaneously. Source


Wang Y.,National University of Defense Technology | Zheng W.,National University of Defense Technology | Sun S.,Xian Jiaotong University | Li L.,Science and Technology on Aerospace Flight Dynamics Laboratory
Advances in Space Research | Year: 2013

The objective of this paper is to investigate and reduce the impact of the errors in the planetary ephemerides on X-ray pulsar-based navigation system for Earth-orbiting satellite. Expressions of the system biases caused by the errors in the planetary ephemerides are derived. The result of investigation has shown that the impact of the error in Earth's ephemeris is must greater than the errors in the other ephemerides and would greatly degrade the performance of X-ray pulsar-based navigation system. Moreover, the system bias is modeled as a slowly time-varying process, and is handled by including it as a part of navigation state vector. It has been demonstrated that the proposed navigation system is completely observable, and some simulations are performed to verify its feasibility. © 2013 COSPAR. Published by Elsevier Ltd. All rights reserved. Source


Tang J.,Nanjing University | Tang J.,Science and Technology on Aerospace Flight Dynamics Laboratory | Cheng H.,CAS National Astronomical Observatories | Liu L.,Nanjing University | Liu L.,Science and Technology on Aerospace Flight Dynamics Laboratory
Water Resources Research | Year: 2014

Heavy droughts have frequently struck Southwestern China in recent years. A major consequence of these droughts is the loss of terrestrial water storage (TWS) which affects agriculture, civil life, and industry production and results in serious social and economic losses. The satellite gravimetry has been proved an effective way to estimate hydrological variations over the globe, and we use the monthly gravity solutions from the Gravity Recovery and Climate Experiment (GRACE) satellite mission and extract the hydrological variations from the regional gravity signal. Here we show that the recent heavy droughts in Southwestern China have caused observable nonseasonal gravity changes in the monthly GRACE solutions. Two heavy droughts in September 2009 to May 2010 and August 2011 to January 2012 have resulted in significant TWS deficit up to hundreds of gigatons in Southwestern China. It is found that the latter drought in 2011-2012 is the most severe one in Southwestern China over the decade, hitting large areas, and causing heavy TWS deficit. Affected by the recent droughts, the GRACE estimate shows a gradual decrease in the regional TWS during the recent 4 years in Southwestern China with a nominal rate of-13.3-±-7.5 mm/yr, which indicates the severity of the TWS deficit in this area. Key Points GRACE is capable to capture recent heavy droughts in Southwestern China The TWS is gradually decreasing in Southwestern China due to recent droughts The TWS change is mainly controlled by rainfall and affected by global climate © 2014. American Geophysical Union. All Rights Reserved. Source

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