空间科学学报

LIU Congliang, KIRCHENGAST Gottfried, SUN Yueqiang, WANG Xin, LÜ Daren, BAI Weihua, DU Qifei, LÖSCHER Armin, SYNDERGAARD Stig, TIAN Longfei, ZHANG Zhihua

2020, 40(2): 151-168. doi: 10.11728/cjss2020.02.151

Abstract(1285) PDF 6103KB(138)

Abstract:
The Essential Climate Variables (ECVs), such as the atmospheric thermodynamic state variables and greenhouse gases, play an important role in the atmosphere physical processes and global climate change. Given the need of improvements in existing ground-based and satellite observations to successfully deliver atmosphere and climate benchmark data and reduce data ambiguity, the Climate and Atmospheric Composition Exploring Satellites mission (CACES) was proposed and selected as a candidate mission of the Strategic Priority Research Program of Chinese Academy Science (SPRPCAS). This paper presents an overview of the key scientific questions and responses of ECVs in relation to global change; the principles, algorithms, and payloads of microwave occultation using centimeter and millimeter wave signals between low Earth orbit satellites (LEO-LEO microwave occultation, LMO) as well as of the LEO-LEO infrared-laser occultation (LIO); the CACES mission with its scientific objectives, mission concept, spacecraft and instrumentation.

Parallel Computing Technology for CME Parameter Detection Model Based on MapReduce

YANG Shitong, CAI Yanxia, LU Guorui, WANG Jingjing

2020, 40(2): 169-175. doi: 10.11728/cjss2020.02.169

Abstract(1012) PDF 3204KB(108)

Abstract:
Space environment prediction model is an important part of space environment business. Coronal Mass Ejection (CME) is the source of many space events and near-Earth space environment disturbances. The CME parameter detection model is an important part of the solar wind forecasting process. In order to improve the accuracy of solar wind forecasting in space environment forecasting, it is necessary to improve the accuracy of CME parameter detection. However, the model runs in serial mode with low calculating efficiency, which leads to long operation time of the model and can not meet the requirement. Based on the parallel computing framework of MapReduce, according to the characteristics of CME parameter detection model, the calculation flow of CME parameter detection model is improved. A CDMR (CME Detection under MapReduce) method is presented, which can realize the parallel computing of CME parameter detection model. Moreover, the running time of the CME parameter detection model between serial computing and MapReduce parallel computing is compared. The experimental results show that the running time is reduced by using MapReduce parallel computing, and the detection accuracy and calculation efficiency of the model are improved.

Application of LSTM Neural Network in F_10.7 Solar Radio Flux Mid-term Forecast

YANG Xu, ZHU Yaguang, YANG Shenggao, WANG Xijing, ZHONG Qiuzhen

2020, 40(2): 176-185. doi: 10.11728/cjss2020.02.176

Abstract(1853) PDF 4297KB(143)

Abstract:
The F_10.7 index is an important input parameter for the empirical models of atmospheric density, and its prediction accuracy directly affects the accuracy of spacecraft orbit prediction. The solar activity exhibited an average of 11 years on a long-term scale and a 27-day periodic variation on a short-term scale. Based on this observational fact, a l Long and Short Term Memory (LSTM) recurrent neural network method is proposed to conduct the mid-term forecast of F_10.7 index for the next 27 days. Using a continuous long period of F_10.7 data as training data, the LSTM neural network training is constructed, and the upper and lower bounds of model parameters based on empirical formula are determined. The method of trial and error is used to select the optimal model parameters, and the prediction models to predict solar activity of high and low years F_10.7 index in the next 27 days are constructed. The results show that the average relative error of the 27th day F_10.7 index forecast for solar activity in the high year can reach about 10%, and can reach 2% or less in the low year. In 1998, the correlation coefficient between the predicted value of the F_10.7 index on the 27th day and the measured value was 0.60.

Hemispheric Distribution of Lower-band Chorus Waves Observed by Van Allen Probes

CHENG Xiaowei, GU Xudong, NI Binbin, ZHANG Yang

2020, 40(2): 186-196. doi: 10.11728/cjss2020.02.186

Abstract(1163) PDF 14865KB(43)

Abstract:
Whistler mode chorus waves are important electromagnetic emissions due to their dual roles in acceleration and loss processes of Earth’s radiation belt electrons. A detailed global survey of lower-band chorus is performed using EMFISIS data from Van Allen Probes in near-equatorial orbits. In addition to the confirmation of the positive correlation of chorus wave intensities to geomagnetic activity and dayside-nightside distribution asymmetry of wave amplitude and occurrence probability, the analysis results find that in statistics lower-band chorus emissions exhibit higher wave occurrence rates and larger normalized peak wave frequencies in the magnetically northern hemisphere but somehow stronger peak wave intensities in the magnetically southern hemisphere. While overall the differences between the two magnetically hemispheric distributions tend to be not significant, it is important to establish the magnetically hemispheric distribution profiles of lowerband chorus with respect to L-shell, magnetic local time, and geomagnetic latitude for improved understanding of chorus-induced dynamics of radiation belt electrons.

Analysis of Spatial Variation Characteristics of Regional Ionospheric TEC Grid Based on Crustal Movement Observation Network of China

LI Yongtao, ZHOU Wei, LI Jianwen, CHE Tongyu, JING Xin

2020, 40(2): 197-206. doi: 10.11728/cjss2020.02.197

Abstract(1637) PDF 4771KB(260)

Abstract:
In order to study the variation characteristics and the applicable accuracy range of ionospheric TEC in small-scale, high-resolution space in the Crustal Movement Observation Network of China (CMONOC) region of China, 260 CORS data of the CMONOC are used to generate the 731-day CMONOC ionospheric RIM grids from 2016 to 2017, and the accuracy is verified. In the same RIM grid, the TEC grid points with different latitudinal and longitudinal are analyzed in the longitude and latitude directions respectively. The results show that the maximum change rate of the TEC difference in the longitudinal direction of the CMONOC region is about 0.3TECU·(°)^-1, and the average rate of TEC change is about 0.11TECU·(°)^-1. When the longitude interval is 1°, the TEC difference is less than 2TECU. As the longitude interval increases, its TEC difference also increases and shows a certain half-year and annual variation. The maximum value of the TEC difference in the latitudinal direction is about 1.7TECU·(°)^-1. The average change rate of TEC is approximately 0.46TECU·(°)^-1. The ionospheric TEC in the CMONOC region increases with the decrease of latitude. When the latitude interval is 1°, 99.4% TEC differences are less than 4TECU. As the latitude interval increases, the TEC difference also increases. It also shows a certain half-year and annual variation law. In the case of the same degree of interval, the change of TEC in the latitudinal direction is larger than that in the longitudinal direction.

Seasonal Variations of Mesospheric Densities Observed by Rayleigh Lidar at Golmud, Qinghai

DAI Yaru, PAN Weilin, QIAO Shuai, HU Xiong, YAN Zhaoai, BAN Chao

2020, 40(2): 207-214. doi: 10.11728/cjss2020.02.207

Abstract(1068) PDF 4784KB(69)

Abstract:
From Aug. 2013 to Oct. 2015, a Rayleigh lidar has been used to study the middle atmosphere at Golmud (36.25°N, 94.54°E), Qinghai, located in the northeastern part of the Tibetan Plateau. Mesospheric density profiles from 50 to 90 km were retrieved based on 205 nights of lidar observation, with a total of 1616 hours of operation. We compared our lidar density measurements with SABER observations onboard TIMED satellite and MSIS-00 model data. The results showed that the annual mean density measured by lidar agreed well with SABER data, but both were lower than that of MSIS-00. All datasets exhibited dominant annual oscillation in the mesosphere. From 63 to 85 km, the annual amplitude of lidar density is larger than those of SABER and MSIS-00. PDD (Percentage of Density Difference) was calculated to investigate the mesospheric density climatology. The largest density variations of lidar, MSIS-00, and SABER occurred at around 72 km. Both lidar and SABER PDD reached their maximum in May, about one month earlier than the MSIS-00; while the minimum PDD appeared in late December for all datasets.

Daytime Sodium Lidar Observations and Studies of the Tidal Characteristics in Winter over Beijingormalsize

LU Zhenghua, YANG Guotao, WANG Jihong, JIAO Jing, XUN Yuchang

2020, 40(2): 215-222. doi: 10.11728/cjss2020.02.215

Abstract(1068) PDF 2889KB(74)

Abstract:
Based on continuous observation of the sodium layer from lidar located in Yanqing, Beijing, the diurnal variation of the sodium layer and its relevant parameters can be analyzed. Comparing the phase information of sodium density from every altitude with the information from meridian wind at the same time, it can be found that the two diurnal phases are consistent with each other. Although the two semi-diurnal phases exist a little bit difference, as a whole, they two agree very well. Extracting the phase and amplitude from continuous sodium observation data from October to January from 2014 to 2016, tidal characters in fall over Beijing can be studied. The results show diurnal tide phases have unobvious seasonal variation and propagate upward with vertical wavelengths between 30 and 50km. Besides, the diurnal tide is stronger than the semidiurnal tide.

Study on Charge of Dust Particles in Lower Polar Region of Double Maxwell Distributionormalsize

PATIMAN A, WANG Yantong, SHI Yanxiang

2020, 40(2): 223-226. doi: 10.11728/cjss2020.02.223

Abstract(1505) PDF 1151KB(48)

Abstract:
Polar Mesosphere Summer Echoes (PMSE) will disappear immediately under the condition of high power microwave irradiation, which is called heating phenomenon in the polar mesosphere. When the high power microwave irradiate the polar mesosphere, the directional motion velocity of the electrons under the acceleration of microwave electric field can be compared with the thermal motion velocity, and the dust plasma in the polar mesosphere obeys the dual Maxwell distribution. The charge distribution of dust particles in the polar mesosphere is given based on the charge theory of dust particles under double Maxwell distribution. The charge changes of dust particles and the electron concentration are compared before and during the high power microwave heating the polar mesosphere. The results show that heating the polar mesosphere with a high-power microwave device will affect the charge of electrons to dust particles and lead to the change of electron concentration, which is of great significance to further explain the phenomenon of heating in the polar mesosphere.

Assimilation of Near Space Temperature Data from SABER and MLS Observations into the Whole Atmosphere Community Climate Model and Data Assimilation Research Test-bed

JING Wenqi, CUI Yuanyuan, WANG Yegui, JIANG Huiming, CAI Qifa, LAN Weiren

2020, 40(2): 227-241. doi: 10.11728/cjss2020.02.227

Abstract(1548) PDF 9004KB(102)

Abstract:
This study performs SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) and MLS (Microwave Limb Sounder) temperature data assimilation experiments to simulate a SSW (Stratospheric Sudden Warming) process occurred in February 2016, based on WACCM+DART (Whole Atmosphere Community Climate Model, Data Assimilation Research Test-bed). The following main conclusions are obtained. First, assimilating SABER and MLS temperature observations significantly reduces WACCM's forecast error of temperature fields in mesosphere and middle-upper stratosphere (0.001～10hPa), and effectively improves control experiment's several discrepancies with observations and reanalysis, such as colder mesosphere during SSW, lower layer height that zonal wind direction firstly changes when SSW occurs, east zonal wind layers in 0.1～10hPa prematurely vanishing, stronger zonal wind and higher stratopause height during SSW recovery phase. The verification based on ERA5 reanalysis suggests that assimilating SABER and MLS temperature observations is in favor of reducing analysis error of zonal wind in low mesosphere and middle-upper stratosphere (0.1～14hPa) and temperature in stratosphere and middle-lower mesosphere (0.01～100hPa) above high-latitude areas (60°-90°N)in the northern hemisphere. In addition, assimilating low atmospheric observations is also beneficial for reducing analysis error of zonal wind in 0.1～14hPa and temperature in 0.01～100hPa, but this reduction effect is not as significant as that of assimilating SABER and MLS temperature observations.

Adaptability Analysis of GPT2w Model in High Latitudes

YAO Xiang, CHEN Mingjian, WANG Jianguang, CHEN Rui

2020, 40(2): 242-249. doi: 10.11728/cjss2020.02.242

Abstract(1630) PDF 2503KB(87)

Abstract:
The GPT2w model is the most accurate zenith tropospheric model in current, but there exists large error at high latitudes. In order to better ensure the high-precision application of satellite navigation and positioning system in high latitudes, the accuracy of GPT2w model in high latitudes is evaluated, and GPT2w model is used to obtain zenith tropospheric wet delay, dry delay and total delay, and the impact of GPT2w model correction on precise point positioning is explored. The test results show that the accuracy of GPT2w model in high latitudes is in the centimeter level, which is better than that in the middle and low latitudes. The zenith tropospheric delay in the Antarctic and Arctic regions has obvious seasonal variation characteristics and regional consistency characteristics. The total tropospheric delay in summer is higher than that in winter. The tropospheric delay in the Arctic region is significantly higher than that in the Antarctic region, and the zenith tropospheric delay in the Arctic region varies with the seasons more than the Antarctic region. The PPP test results show that the GPT2w model can effectively improve the positioning accuracy and adapt to high-precision positioning in high latitudes.

Electric Fields Distribution of Zhinyu Crater in Chang’E-4 Landing Area

GAN Hong, LI Xiongyao, WEI Guangfei

2020, 40(2): 250-263. doi: 10.11728/cjss2020.02.250

Abstract(1180) PDF 7732KB(57)

Abstract:
Solar radiation and solar wind create a complex dust-plasma environment in lunar crater. Based on the elevation data obtained from the Lunar Orbiter Laser Altimeter (LOLA) onboard Lunar Reconnaissance Orbiter (LRO), we constructed a three-dimensional model of Zhinyu crater which located in the Chang'E-4 landing area, and then calculated the effective solar irradiance and the percentage of illuminated area at different local time in the lunar daytime. The results show that the crater self-shading effect plays an important role in crater illumination conditions, and the percentage of illuminated area reaches 100% only during 10:30LT-13:30LT. In addition, we calculated the distributions of equilibrium surface potential, Debye length and electric field at different local time, which were found to be highly dependent on the crater self-shading effect. Finally, we discussed the relationship of equilibrium surface potential, Debye length and electric field at the bottom of Zhinyu-like crater with local time and latitude. The results show that the distributions of equilibrium surface potential, Debye length and electric field are symmetric along the time of 12:00LT and lunar equator. These values almost remain unchanged on the shadow areas and change slightly on the sunlit areas, but change dramatically at the dead zone.

Characteristics of Moonquake and Its Comparison with Earthquakeormalsize

ZHAO Na

2020, 40(2): 264-272. doi: 10.11728/cjss2020.02.264

Abstract(3163) PDF 5408KB(188)

Abstract:
The study on lunar internal structure is the hot issue. Seismology is one of the best methods for studying lunar internal structure. In this paper, the moonquake data and parameters are reanalyzed, and the characteristics of moonquake signal, distribution and mechanism are discussed in detail and compared with earthquake. By combining with previous studies, it is concluded that the moonquake is quite different from earthquake. Moonquake signals are typically of very long duration. Deep moonquakes and thermal moonquakes show evident wave form matching feature. Most of moonquakes detected are deep moonquakes which mainly distribute on the nearside of the Moon. The largest number of deep moonquakes which emanate from source nest are caused by tidal. Thermal moonquake also occurs periodically, resulting from temperature variation during one lunation.

Performance Analysis of BDS/GPS Single Frequency RTK Based on MLAMBDA Methodormalsize

SHEN Xiaoyun, BAO Ningxin, JIAO Weidong, WANG Wei

2020, 40(2): 273-279. doi: 10.11728/cjss2020.02.273

Abstract(1868) PDF 2969KB(86)

Abstract:
GNSS RTK technology is widely used in aerospace, high-precision mapping, transportation and other industries due to its high precision, high efficiency and real-time performance. At present, dual-frequency RTK technology is very mature and widely used. Single-frequency GNSS RTK has difficulties in data quality control and positioning error processing. Therefore, the accuracy of single-frequency RTK service may be limited, and its positioning performance remains to be studied. Based on the extended Kalman filter model, the MLAMBDA ambiguity search method and the ratio test method are combined with the measured data to compare and analyze the single-frequency RTK positioning performance of BDS, GPS and BDS/GPS. The results show that the single-frequency RTK positioning accuracy of the three modes is in the centimeter level in the static scene, which can meet the high-precision positioning requirements. In the dynamic scene, the ambiguity fixed rate of the three modes is above 70%, which can meet the daily positioning requirements. Regardless of static or dynamic application scenes, BDS has the highest fixed rate of ambiguity, and the time used for ambiguity resolution is short, which can enable fast RTK positioning.

Design and Implementation of Signal Processing System for Radio Spectrometer Based on Casper and Simulink

ZHAO Cuixia, ZHAO Fei, YAN Jingye

2020, 40(2): 280-288. doi: 10.11728/cjss2020.02.280

Abstract(1399) PDF 4715KB(72)

Abstract:
The digital system of radio telescope based on Casper library is being widely used. In the Simulink, complex digital signal design can be realized by calling the Casper module. This module enables the development of signal processing functions in the Simulink graphical environment with the help of the System Generator tool, greatly improving the development efficiency of radio astronomy equipment. The Casper and Xilinx modules in Simulink are used to design the digital signal processing unit of the radio telescope unit prototype, and realize the sub-band extraction, down-conversion and overall spectrum analysis. The simulation of related functions are realized on the Casper general hardware platform ZYNQ7020, which verifies the feasibility and high efficiency for designing the digital signal processing system of radio telescope unit prototype based on FPGA by using Casper and Xilinx module.

Contour Detection of Disk Resolved Objects in Cassini ISS Image Using Deep Neural Network

ZHANG Qingfen, ZHENG Yang, CHENG Guohao, LU Zhicong, ZHOU Xiaomei, WANG Yuchen

2020, 40(2): 289-295. doi: 10.11728/cjss2020.02.289

Abstract(1745) PDF 2363KB(126)

Abstract:
In the astrometry of CCD image, it is important to match image stars with catalogue stars to correct the camera's pointing. The onboard Imaging Science Subsystem (ISS) in Cassini orbiter has taken a large number of images of targets which are disk resolved. In the astrometry of these images, the false image stars are often detected in the disk. It disturbs the pointing correction of camera and decline the precision of the astrometry. Therefore, it is helpful to find the contours of the disk to remove the false image stars. One method based on deep learning is proposed to detect the contour of disk resolved object in ISS images. A convolutional neural network was set up by the framework TensorFlow, in which the input is the nine features of each pixel, and the output is the classification of each pixel: contour pixel or non-contour pixel. The neural network is trained by about 36000 pixels, and then it is used to detect the contour pixels in 380 ISS images. Compared with the contour pixels labeled by hand, the contour pixels detected by neural network have the precision of 78.26% and the recall ratio of 73.32%. It proved that the proposed method is available to find the contour of disk resolved target in ISS images.

2020 Vol. 40, No. 2

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