Subjects: Astronomy submitted time 2024-04-12 Cooperative journals: 《天文学报》
KANG Zhe
NIU Bing-li
LI Zhen-wei
SUN Jian-nan
LV You
ZHU Cheng-wei
DENG Shi-yu
LIU De-long
YANG Wen-bo
ZHANG Nan
LIU Ming
SUN Ming-guo
LIU Cheng-zhi
Abstract： Ground-based optical astronomical telescopes are one of the most important instruments for human exploration and research of the universe. Monitoring and analysis of the optical observation environment of the existing ground-based optical station can provide a reference for the targeted modification of equipment and the adjustment of observation strategies of observers, which is of great significance for improving the observation efficiency of ground-based optical equipment. Jilin Astronomical Observatory (hereinafter referred to as the ``Base'') is located about 5 kilometers (126.3$^{\circ}$ E, 43.8$^{\circ}$ N, 313 meters above sea level) in Nangou, Xiaosuihe Village, Dasuihe Town, Jilin City, Jilin Province, which is affiliated to the Changchun Observatory, National Astronomical Observatories, Chinese Academy of Sciences. The mean value of seeing of the base is about 1.3$''$--1.4$''$, the night sky brightness in the V band near the zenith is 20.64\;mag\,$\cdot$\,arcsec$^{-2}$, and the maximum number of clear nights is better than 270 days per year, which shows the good astronomical observation conditions. Jilin Astronomical Observatory, which was put into operation in 2016, has several photoelectric telescopes, including the 1.2-meter photoelectric telescope, the Mini Optoelectronic Telescope Array, the large field of view photoelectric telescope array, and the advanced multi-functional array-structured photoelectric detector. With the equipments mentioned above, we have carried out relevant research mainly on space target detection and recognition, precision orbit determination, new photoelectric detection methods and multicolor photometry of variables, and so forth. We have maintained a good cooperative relationship with a number of domestic universities and scientific research institutes.
Subjects: Astronomy submitted time 2024-01-31 Cooperative journals: 《天文学报》
Abstract： The features of upper atmospheric midnight density maximum (MDM) around low geographic latitudes are studied based on neutral mass densities data at altitudes 360--480\;km, derived from the accelerometer measurements aboard on the three polar orbiting satellites CHAMP (CHAllenging Minisatellite Payload), GRACE-A (Gravity Recovery and Climate Experiment-A) and SWARM-C (The Earth's Magnetic Field and Environment Explorers-C). The MDM appears during the local times from 23:00 to 02:00\;LT, whose peak locates at the low latitudes within ${15}^\circ$ and two valleys locate at the middle latitudes between ${35}^\circ$ and ${45}^\circ$ on both hemispheres separately. The structure of MDM drifts toward the southern hemisphere overall. The MDM's amplitude decreases with increases in altitude and solar radiation level. The seasonal effect weakens the MDM's amplitudes around the summer and winter solstices, while the amplitudes around the spring and autumn equinoxes are extremely significant due to the slight seasonal difference between both hemispheres. Three atmospheric density models DTM2000 (Drag Temperature Model 2000), NRLMSISE00 (Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Extended atmosphere model) and JB2008 (Jacchia-Bowman 2008 model) are used to simulate the MDM along these three satellites' orbits, and compared with the observations. It is found that the JB2008 model is failed to describe the MDM, and the other two models underestimate the MDM's amplitudes at altitudes 360 km and 480 km: the simulated amplitudes by the DTM2000 model are 46\% and 53\% of the observed amplitudes respectively, and only 33\% and 26\% for the NRLMSISE00 model. These three models are also failed to depict the MDM's variation with altitude, solar radiation level and seasonal effects. In order to correct the model prediction, a 6th-order Legendre polynomial of geographic latitude, coupled with arguments of local time and altitude, is designed to fit the MDM signals from the three satellites' observations. In terms of amplitude and phase of the MDM, the fitting results agree with the observations very well, and the correlation coefficient is 0.923. It indicates that this empirical polynomial could be helpful to the density model correction and high accuracy prediction of spacecrafts in low Earth orbits.}
Subjects: Astronomy submitted time 2023-10-07 Cooperative journals: 《天文学报》
Abstract： The data-fusion orbit determination software SPODFMD (Space debris Precise Orbit Determination fusing Multi-source Data) is developed with the purpose of cataloging space debris, characterized by integrating pure numerical integrators and given birth in the lab of SPOD (Satellite Precise Orbit Determination) at PMO (Purple Mountain Observatory). At the initial stage of the birth, developers fully investigated national space debris monitoring equipment, fully understood the orbit and physical complexity of numerous space debris, fully recognized the requirement for high efficiency when renewing orbits for lots of debris, and fully considered the robustness requirement in engineering. In addition, SPODFMD integrates several algorithms with indigenous intellectual property rights, including a rapid and non-singular algorithm for computing the Earth's gravitational potential and its derivatives, analytical and non-singular expressions for the DTM94 thermosphere model and its derivatives, an accurate and efficient method for calculating dense ephemeris of high-eccentricity orbit, and a robust adaptive weighting method. Integrating these advanced algorithms by applying software engineering theory, SPODFMD can freely fuse observation data from 14 kinds of equipment, achieving a second-level computation efficiency in a majority of typical orbit determination cases. Moreover, the software shows similar performance for GEO (Geosynchronous Equatorial Orbit), MEO (Medium Earth Orbit), LEO (Low Earth Orbit), and HEO (Highly Elliptical Orbit) objects without computation and pole singularity. It is tested and proved to be multi-source, efficient, general, and robust.
Subjects: Astronomy submitted time 2023-10-07 Cooperative journals: 《天文学报》
Abstract： This paper proposes a new method of deriving the launch and landing locations based on the orbital motion characteristics of the missiles and elevation database. In this method, the DEM support is introduced to change the assumption of the earth from the reference ellipsoid to a more real shape. The method to improve the prediction accuracy of the position and time of the launch and landing points is discussed. The results with DEM (Digital Elevation Model) indicate the accuracy can be improved by adding a few elevation iterations on the original method. The higher the elevation of the starting and landing points, the better the result would be.
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