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The total electron content (TEC) of the ionosphere is an important parameter to describe the ionosphere, and it is a great significance to monitor and predict it accurately. In this paper, a hybrid ionospheric TEC prediction model based on the least squares support vector machine (LSSVM) and the Moth-Flame Optimization (MFO) algorithm is proposed. The parameters of the LSSVM model are optimized by the MFO algorithm. We use observation data of 15 GNSS stations from the Crustal Movement Observation Network of China (CMONOC) to extract ionospheric TEC from 2012 to 2019. The ionospheric TEC is forecasted using solar and geomagnetic activity indices in both the low solar activity year (2019) and the high solar activity year (2015). The results show that the prediction performance of the MFO_LSSVM model is significantly better than that of the IRI model, SVM model, and LSSVM model. Compared with the other three models, there are more stable prediction results in the low and high solar activity years. At the same time, the predicted value of the MFO_LSSVM model has a good correlation with the measured value, and it also has good prediction potential in areas with active geomagnetic activity. The comparison with the Long Short-Term Memory (LSTM) model shows that the MFO_LSSVM model has better performance than the single LSTM model. In conclusion, the MFO_LSSVM model can accurately predict ionospheric TEC in China, and has better accuracy than traditional long-term and short-term models. [ABSTRACT FROM AUTHOR]

High precision ionospheric Total Electron Content(TEC) prediction is of great significance for improving the accuracy of Global Navigation Satellite System(GNSS), preventing natural disasters, and ensuring wireless communication. Given the varying frequencies of TEC signals, a hybrid CEEMDAN-BiLSTM-PSO-LSSVM-FE model for predicting ionospheric TEC content is proposed in this paper. Firstly, complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) is used to decompose the extracted hourly TEC sequence and calculate the fuzzy entropy (FE) of the subsequences. Then, the signal is divided into high-frequency and low-frequency parts based on the fuzzy entropy value, for the high-frequency component, Bidirectional Long Short-Term Memory network (BiLSTM) is used for prediction; for the low-frequency component, Particle Swarm Optimization-based Least Squares Support Vector Machine (PSO-LSSVM) is used for prediction. The hourly TEC values collected from six evenly distributed GPS stations in China are used as the main input variable for the proposed model, with solar and geomagnetic activity data used as auxiliary data, using the TEC data from the previous 48 h to forecast the TEC content for the next hour. The performance of the model is evaluated by comparing it with other models under different geographical locations, seasons, solar and geomagnetic activity conditions. Experimental results show that the proposed hybrid model outperforms other models, with a correlation coefficient R2 and root mean square error (RMSE) of 0.99 and 0.20 TECU, respectively. The model effectively overcomes the problem of low TEC prediction accuracy and can provide more precise ionospheric delay correction services. [ABSTRACT FROM AUTHOR]

• Variable stiffness design for a 3-legged asteroid probe. • Landing dynamics for soft landing on the 2016HO3 asteroid is modeled. • Response surface surrogate model is established for optimization. • Variable stiffness leg and pressing force are optimized. China plans to launch a probe to detect and sampling on the near-Earth asteroid 2016HO3 around 2025. In view of this, this paper discusses an alternative landing strategy with passive variable stiffness landing gears, which help to land the probe stably on the asteroid for sufficient sampling time. First, a three-legged lander is introduced, following which, a four-bar-linkage-based variable stiffness leg is designed considering the design constraint of landing clearance. Then, a numerical model of the probe for landing simulation is established. Moreover, a surrogate model is obtained using the second-order response surface method (RSM) to improve computational efficiency. Based on the surrogate, the variable stiffness leg and the pressing force are optimized to reduce the impact forces at touchdown and the landing time. Finally, the optimal solution is validated using the dynamics analysis model. [ABSTRACT FROM AUTHOR]

Satellite Laser Ranging (SLR) technology is one of the main technologies in the field of space geodesy, it has played an extremely important role in laser ranging data application and research. As a commonly used geodynamic satellites, the main contribution of LAGEOS and LAGEOS-2 is the solution of orbit determination and station coordinates. At present, there are 8 analysis centers of the International Laser Ranging Service (ILRS) to release the precise orbit products for the two LAGEOS satellites. However, there is currently no relevant research on the analysis of the consistency of these orbits. So, the authors would evaluate the accuracies of them, and the results show that the orbital accuracies of the two LAGEOS satellites are 3 ∼ 5 cm. SLR is regarded as one of the important input data of the International Terrestrial Reference Frame (ITRF), the analysis center of ILRS provides weekly solutions of station coordinates for ITRF. But, due to the limitation of SLR observation conditions, for example most observations of Chinese SLR stations can be made at night, and laser ranging test cannot be conducted in rainy days, the orbit solution of the seven-day arc may have the problem of less data. Therefore, this paper proposed a method for computing the station coordinates based on long arc orbit determination, and we developed the LAODGEO software (Long Arc Orbit Determination Software for Geodynamic Satellite), which is used to solve the orbits of two LAGEOS satellites and station coordinates of five SLR stations in China. The results show that the obtained orbital precision is basically superior to 3.70 cm, and the 3DRMS values between station coordinates solved by us and the coordinates published by SLRF2014 are mostly smaller than 0.013 m, which is consistent with research results domestic and overseas. [ABSTRACT FROM AUTHOR]

Many studies have investigated the spatial variations of the ionosphere, but the quantitative characteristics of the ionosphere are rarely reported. In this paper, we utilize the total electron content (TEC) data to evaluate the latitudinal gradient of the ionosphere within 10°-50° N over the China sector. It is found that the magnitudes of latitudinal gradient are significantly higher within 10°-40° N and 45°-50° N, respectively. The database of TEC from 1 November 2018 to 31 October 2022 is processed to figure out the local time, seasonal, and solar activity dependency of the latitudinal gradient. The results suggest that the gradient within 10°-40° N is higher in the daytime and during high solar activity period. They are more noticeable in the spring and autumn, and least visible in the summer. Conversely, the gradient within 45°-50° N strengthens in the nighttime and under lower solar activity, and has larger values in the summer months. Furthermore, the International Reference Ionosphere (IRI-2020) model is assessed in terms of the reproducibility of latitudinal gradient. The IRI-2020 basically represents the latitudinal gradient within 10°-40° N, whereas it overestimates the gradient in the low solar activity period and misses the gradient features near 45°–50° N. [ABSTRACT FROM AUTHOR]

This paper investigates the ionospheric responses to the February and April 2023 geomagnetic storms using Total Electron Content (TEC) derived from the 10 Global Navigation Satellite System (GNSS) stations at the transition of low to mid-latitudes (Approx. 20 ∼ 30°N) across different longitudes in the American and Asian sectors. Significant variations in both sectors were recorded during the recovery phase and were mainly attributed to the Prompt Penetration Electric Field (PPEF), Disturbance Dynamo Electric Field (DDEF) and the thermospheric neutral composition changes as O/N 2 depletion. Similarly, the American and Asian sectors showed TEC enhancements, primarily attributed to the PPEF, during the main phase of the April storm. The negative TEC variations during the recovery phase were observed due to the DDEF and changes in O/N 2. In the Asian sector, positive and negative variations were recorded over Pakistan and China, respectively, during the main phase of the April storm. These variations resulted in high and low concentrations of the O/N 2 ratio due to Magnetosphere-Ionosphere-Thermosphere coupling. [ABSTRACT FROM AUTHOR]

In recent years, extreme rainfall events have frequently occurred frequently, and heavy rainfall can cause drastic changes in the troposphere. Therefore, achieving to achieve real-time high-precision numerical prediction of key tropospheric parameters during heavy rainfall has become a major problem in global navigation satellite system (GNSS) meteorology. In this paper, two extreme rainfall events in southern China (Guangdong region) and northern China (Shandong region) in 2022 are used as case studies. Twenty-four-hour real-time numerical forecasts of key tropospheric parameters (atmospheric weighted mean temperature (Tm), precipitable water vapor (PWV), and GNSS zenith tropospheric delay (ZTD)) are obtained using three models, namely, the HGPT2, GPT3, and WRF models. Two optimization models, i.e., WRFDA (am) and WRFDA (pre), are then constructed by assimilating two types of data (global upper air and surface weather observations and daily advanced microwave sounding unit A (AMSU-A) brightness temperature) based on the WRF model. The experimental results for heavy rainfall show that (1) the WRF model predicts the key tropospheric parameters with better accuracy than the HGPT2 and GPT3 models, and the WRFDA (pre) model predicts PWV and ZTD with the highest accuracy; (2) the WRFDA (pre) model achieves a higher accuracy than the WRF model in predicting PWV and ZTD, where the PWV prediction accuracy is improved relative to the WRF model (in the south: MAE: 32.7 %; RMSE: 33.9 %; MAPE: 36.8 %; in the north: MAE: 27.3 %; RMSE: 24.2 %; MAPE: 28.0 %); this model achieves an MAE of 2.17 cm and an RMSE of 2.70 cm in 24-h ZTD prediction in the south, while the MAE reaches 2.48 cm, and the RMSE is 3.18 cm in the north; (3) the models provide a higher forecast accuracy in the southern region than in the northern region for heavy rainfall. The WRFDA (pre) model provides a favourable ZTD accuracy at GNSS stations near the ocean, while the WRFDA (am) model provides a satisfactory ZTD accuracy at inland GNSS stations, and the WRFDA (am) model provides the highest ZTD prediction accuracy at GNSS stations above 100 m. [ABSTRACT FROM AUTHOR]

The ionospheric foF2 prediction model GWO-ALSTM is proposed in this paper, which combines the Gray Wolf Optimization (GWO) algorithm and the attention mechanism based on the long short-term memory (LSTM) model. The datasets used in this model were obtained from the oblique ionosondes of the China Ground-based Seismo-ionospheric Monitoring Network. The data from 2010 to 2012 was used for training, and the data of 2013 was used for verification. The input parameters of the model include local time, day number, sunspot number, F10.7 solar flux, Ap index, Dst index, and foF2 at the previous moment, and the output parameter is foF2 at the current moment. The IRI2016 model, GABP model, LSTM model and GWO-ALSTM model were compared with the observed results for analysis. The results show that the GWO-ALSTM model is superior to the LSTM model, the GABP model and the IRI2016 model. Meanwhile, the comparative analyses of the diurnal variations of foF2 show that the curve of the GWO-ALSTM model fits the observed values more closely than the curve of any other model under the geomagnetic quiet and storm conditions. [ABSTRACT FROM AUTHOR]

The rapid growth of China's national resources in the space domain may change the gap in power between China and the United States in relevant international rulemaking. This article proposes an analytical framework for identifying, comparing, and analyzing states' power resources critical to international rulemaking and uses the framework to compare the relevant resources between China and the United States in the space domain. First, this paper develops a method for identifying resources crucial to international rulemaking in outer space. The relevant resources of the two countries are then compared in this article. Finally, the article explores comparative advantages, consensus, differences, and cooperation possibilities of the two countries in specific international space rules. The framework could be adapted to compare diverse nations' resources critical to international rulemaking in other fields; it contributes to research on space law, international legislation, and national power. [ABSTRACT FROM AUTHOR]

Short Message Communication (SMC) is a featured service of BeiDou Navigation Satellite System (BDS). After its successful deployment in 2003, Regional Short Message Communication (RSMC) service has been continuously serving China and its neighboring countries and regions, especially in life safety scenarios. In this paper, the architecture of the Global Short Message Communication (GSMC) system is proposed based on the medium earth orbit (MEO) constellation and the crosslinks of the global BeiDou navigation system (BDS-3). Three subtypes of GSMC service, i.e. positioning report, emergency search and rescue (SAR) and regular SMC are designed in accordance with the technical characteristic of integration of navigation and communication in BDS-3, which supports future wide applications of GSMC. The performance of the designed GSMC system is analyzed by numerical calculations. As BDS-3 was officially announced completion on July 31, 2020, GSMC has been providing initial service. First test results of the in orbit GSMC payloads are also presented in the paper to verify the designed capabilities. Preliminary results also show that the requirements of Global Maritime Distress and Safety System (GMDSS) can also be fulfilled. [ABSTRACT FROM AUTHOR]

China's Chang'E-4 (CE-4) probe has started its exploration on the far side of the Moon thanks to the relay satellite---Queqiao---which is around the Earth-Moon collinear libration point L 2 and provides continuous communication links between the lander and ground stations. The triangular libration points of the Earth-Moon system, L 4 and L 5 , have long been considered as potential locations for future space applications. As a possible extension of Queqiao or other future missions around L 2 , the work presented here contributes to constructing transfers from the collinear libration point ( L 2 ) to the triangular libration points. Taking the L 4 point as an example, two types of two-maneuver transfers from a planar Lyapunov orbit around L 2 to the periodic orbit around L 4 are investigated in the planar Earth-Moon system and compared with each other, including the type-I transfer utilizing invariant manifolds along with powered lunar gravity assist and the type-II transfer using the Jacobi integral. Our studies indicate that type-I transfer saves more Δ v cost than type-II transfer. For the cases studied by us, the minimum Δ v cost is about 0.1636 km/s for type-I transfer, with a corresponding transfer time of 169.84 days. For type-II transfer and the cases studied by us, the corresponding values are 0.4745 km/s and 137.19 days. At the end of the paper, the type-I transfer is generalized (with some modifications) to the ephemeris model and some example transfer trajectories are given. Although only the transfer from L 2 to L 4 is studied in this paper, the same orbit design strategy can be generalized to the transfer to the triangular libration point L 5 , and the transfers from the collinear libration point L 1 to triangular libration points. [ABSTRACT FROM AUTHOR]

Tianwen-1 is China's first deep space probe to explore Mars with the goal of orbiting, landing and roving. This paper presents the orbit determination process and result of the probe in the phase of Earth-Mars trajectory in detail. Orbit determination is carried out based on the tracking data obtained by CDSN (Chinese Deep Space Network) and CVN (Chinese VLBI Network). The results show that the residual RMS of range, Doppler, VLBI delay and delay rate data are about 0.28 m, 0.10 mm/s, 0.12 ns and 0.34 ps/s, respectively. Compared with the previous missions in Chinese Lunar Exploration Program (CLEP), the accuracy of VLBI data is significantly improved. The analysis shows that the prediction error of EOP (Earth Orientation Parameter) and the planetary ephemerides lead to the difference of orbit solution. With the increasing distance between the spacecraft and Earth, the EOP prediction error has a certain influence to the orbit determination accuracy. The difference in orbit solutions due to EOPs' prediction error before MOI (Mars Orbit Insertion) is about 300 m. Moreover, the orbit difference is about 200 m using different planetary ephemerides (DE421/DE436). Orbit overlapping results show the position and velocity error of Tianwen-1 are less than 2 km and 1 cm/s, respectively. During the approaching phase, the error ellipse in B-plane shows that σ SMAA = 389.40 m, σ SMIA = 140.88 m (1σ). [ABSTRACT FROM AUTHOR]

In the early morning on December 17, 2020 Beijing time, China's chang'E-5 probe successfully returned to the Earth with 1731 g of lunar samples after completing drilling, shoveling, packaging of lunar soil and scientific exploration on lunar surface. It is the successful completion of the third phase of China's lunar exploration project, namely "circling, landing and returning to the moon". The scientific objectives of CE-5 mission are to carry out in situ investigation and analysis of the lunar landing region, laboratory research and analysis of lunar return samples. This paper analyzes scientific exploration tasks of CE-5 mission conducted on the lunar surface, and carries out the scientific payload system architecture design and individual scientific payload design with the scientific exploration task requirements as the target, and proposes the working mode and main technical index requirements of the scientific payloads. Based on the preliminary geological background study of the Mons Ruemker region which is the landing region of CE-5, the lunar scientific exploration and the laboratory physicochemical characterization of the return samples are of great scientific significance for our in-depth understanding of the formation and evolution of the Earth-Moon system and the chemical evolution history of the lunar surface. [ABSTRACT FROM AUTHOR]

The annual periodic deformation of Earth's surface can be obtained indirectly using existing models. However, model reliability is affected by numerous uncertain factors such as indirect observation, inversion algorithms, and other factors. In this study, a model of annual vertical surface displacements of mainland China is built based on the direct observation of deformation by 234 continuous Global Positioning System (GPS) stations and unified data processing using the multisurface function method (referred to as the GPS model). The GPS model shows that the weighted root mean square (WRMS) is reduced for 97% of the GPS stations after applying the model correction. The average, maximum, and minimum reductions in the WRMS are 11.6%, 37.2%, and −3.6%, respectively. The slope of the fit lines are 0.40 and 0.61 for the GPS/SLM and GPS/GRACE annual periodic amplitudes, respectively, while a slope of 0.79 for GPS/GPS model from this paper, showing the advantage of GPS model in the representing of surface displacement. Additionally, the GPS model can accurately reflect the detailed motion characteristics of mainland China, particularly in areas between large and small hydrological changes. The difference between models and GPS observation in mainland China may be related to the leakage errors in the GRACE data processing and large uncertainty in the land water storage in SLM, indicating that GPS model may provide more realistic load estimates in mainland China. The GPS model can accurately describe the annual signal, which will be extremely important for practical applications and geoscience research in the future. [ABSTRACT FROM AUTHOR]

In this paper, the China's first global ocean Climate Data Records (CDRs) are used to analyze and predict the sea level changes in the Yellow Sea with obvious seasonal changes. Based on the singular spectrum analysis (SSA) method, the spatiotemporal and time series of sea level anomalies (SLAs) in the Yellow Sea are decomposed and de-noised. Then the long short-term memory (LSTM) neural network is combined with the SSA to establish the SSA-LSTM combined model to predict the sea level trends of the Yellow Sea. Compared with the traditional methods, the prediction accuracy of SSA-LSTM combined model is significantly improved with minimum 35.04 mm RMSE values for the SLA time series prediction. For the one-year prediction of spatiotemporal series of SLA, the minimum RMSE values are only 19.68 mm. The law of spatial and temporal differentiation of the sea level change in the Yellow Sea is also analyzed by temporal empirical orthogonal function. It is found that the sea level trend of the Yellow Sea is highly consistent and significantly related to the season and latitude. According to the SSA-LSTM combined model, the sea level rise rate of the Yellow Sea will remain at 3.65 ± 0.79 mm/year in the next ten years. [ABSTRACT FROM AUTHOR]

Monitoring river water level is of great importance to understand hydrological and hydraulic processes and evaluate flood and landslide risk. This paper proposes a method for estimating river water levels under bridges using multi-temporal high-resolution synthetic aperture radar (SAR) intensity images. Due to the side-looking characteristics of SAR data acquisitions, bridges crossing over rivers usually exhibit multiple bounce echoes in SAR images caused by the multipath scattering. The range difference of the multiple returns is proportional to the clearance between the water surface and the bridge. In this study, the water level oscillation of Yangtze River under Badong Yangzte River Bridge (China) was calculated by estimating the range pixel distances of the multiple bounces in ALOS-2 PALSAR-2 images using cross correlation algorithm. Besides, a linear correlation between the range pixel distance of the multiple bounces and in situ water level measurements was found, with a coefficient of determination equal to 0.9985. This relationship allowed estimating the river water level in each SAR acquisition, with an average error equal to −0.39 m and root mean square error of 0.51 m, and the elevation of the bridge, with an error of about 0.5 m, which is smaller than the theoretical uncertainty of the method (1.24 m). The obtained results show the efficiency of the method in estimating river water levels. [ABSTRACT FROM AUTHOR]

Precise mapping and forecasting of rice cropping systems are essential for guaranteeing regional and even global food security. The central areas of China are the dominant Chinese rice-producing areas. However, due to limited land and a scarcity of skilled rural labourers in China, it has been difficult to meet the growing demand for rice production in recent years. Furthermore, the complex topography and climate in central China make it difficult to map paddy rice accurately. This paper maps the spatial pattern of rice in central China by using multiple data sources and a phenology-based time-series similarity approach, explores the driving forces for rice patterns through grey relational analysis (GRA), and presents a simulated future rice cropping system map by adding socio-economic factors to a cellular automata-Markov (CA-Markov) model. This study concluded that for 2015, the overall classification accuracy of rice was 88.12%, with a Kappa coefficient of 0.90. The planting acreage accuracies for single- and double-season rice in 2015 were 89.51% and 77.00%, respectively, and the corresponding R2 value for both were 0.80. From 2005 to 2015, the planting acreage of single-season rice significantly increased, while the planting acreage of double-season rice generally decreased. The planting acreage of total rice exhibited an overall increasing trend during 10 years. The cumulative temperature, slope and distance to water bodies were key influencing factors for the spatial distribution of rice. Compared with that for 2015, the simulated total planting area of rice for 2030 was slightly higher, and the spatial pattern of double-season rice exhibited an obvious southward trend. These findings show that the proposed rice mapping and forecasting method is effective. This method allows us to predict future rice patterns precisely under the influence of human activities in complex cropping conditions and various rice cropping systems. [ABSTRACT FROM AUTHOR]

China's BeiDou Navigation Satellite System (BDS) can provide real-time precise point positioning (PPP) service for users in China and surrounding areas with PPP-B2b signal. In this paper, real-time PPP is assessed and studied based on 8 days of PPP-B2b and BDS/GPS broadcast messages. Real-time precise ephemerides are compared against Multi-GNSS Experiment (MGEX) final products and the positioning performance of real-time PPP is evaluated with MGEX/iGMAS stations. Results show that the real-time orbit accuracy is about 0.0725, 0.2479 and 0.2587 m in directions of radial (R), along (A) and cross (C) for BDS-3 satellites, and 0.0729, 0.3098 and 0.2193 m for GPS satellites. The standard deviation values of the clock offset errors are about 0.05–0.18 ns for BDS-3 satellites, and 0.05–0.15 ns for GPS satellites. In addition, the differential code bias (DCB) parameters of PPP-B2b agree well with parameters of MGEX DCB and time group delay (TGD), with the differences less than 2 and 0.15 ns, respectively. Furthermore, for the positioning experiments, the average positioning accuracies of BDS and GPS integrated real-time PPP are about 1.07, 2.69 and 2.25 cm in north (N), east (E), and up (U) directions for static mode; and about 3.6, 5.9 and 9.4 cm for kinematic mode. Moreover, the convergence times for an accuracy level of 20 cm in N, E and U components are about 8–22 min, and 10–8 min, for static mode and kinematic mode, respectively. [ABSTRACT FROM AUTHOR]

• Wave processes act to vary reflection level heights within ±(40–50 km) limits. • Dusk (but not dawn) terminator and supertyphoon jointly enhance ionospheric wave activity. • Amplitude of F -region electron density variations was 30–60% for ∼60–120-min periods. • Amplitude of F -region electron density variations was 10–12% for ∼20-min periods. The purpose of the present paper is to describe the observations of the variations in the parameters of HF radio waves propagating through the ionosphere when the action of the super typhoon Hagibis on 6–13 October 2019 occurred. The observations have been made with the Harbin Engineering University (the People's Republic of China) multi-frequency multiple path radio system involving the software-defined technology. The action of the super typhoon has been shown to be accompanied by enhanced atmospheric wave activity acting to generate wave processes with periods of 10 to 120 min. Coupling in the atmosphere–upper-atmosphere–ionosphere system has been confirmed to be carried out with atmospheric gravity waves. The ionosphere underwent the greatest impact on those days when the supertyphoon had maximum energy, on 8, 10, and especially 9 October 2019, and when it was found to be in an ∼2,500–3,000-km distance range from the propagation path midpoints. Under the action of wave processes, the height of the reflection region was observed to oscillate within the ±(30–90 km) limits. The amplitude of the quasi-periodic variations in the ionospheric F -region electron density was estimated to be 10–12% for periods of ∼20 min, and 30–60% for periods of ∼60–120 min. The joint action of the dusk terminator and the supertyphoon has been confirmed to enhance wave activity in the ionosphere. Similar effects for the dawn terminator have not been detected. [ABSTRACT FROM AUTHOR]

This paper describes the scientific objectives and payloads of Tianwen-1, China's first exploration mission to Mars. An orbiter, carrying a lander and a rover, lifted-off in July 2020 for a journey to Mars where it should arrive in February 2021. A suite of 13 scientific payloads, for in-situ and remote sensing, autonomously commanded by integrated payload controllers and mounted on the orbiter and the rover will study the magnetosphere and ionosphere of Mars and the relation with the solar wind, the atmosphere, surface and subsurface of the planet, looking at the topography, composition and structure and in particular for subsurface ice. The mission will also investigate Mars climate history. It is expected that Tianwen-1 will contribute significantly to advance our scientific knowledge of Mars. [ABSTRACT FROM AUTHOR]

The quality and availability of Uncalibrated Phase Delay (UPD) solutions are crucial to the Precise Point Positioning (PPP) service, and the long-term temporal variability and its contributing factors should be better understood. In this paper, we comprehensively investigate the long-term time-varying characteristics of each UPD product respectively generated by a global and regional network and their interoperable application in PPP-AR (ambiguity resolution), the sampling of the WL and NL UPDs are daily and 30 s, respectively. Firstly, in terms of our 30 day Wide-Lane (WL) UPD products of 31 satellites, the Standard Deviation (STD) of each satellite WL UPDs ranges from 0.04 to 0.06 cycles, indicating that the long-term prediction accuracy of satellite WL UPD is sufficient for fixing Wide-Lane ambiguities. Secondly, when a satellite in eclipsing the discontinulity may corrupt the determination of Narrow-Lane (NL) UPD in form of offset, as a result of lacking or poor satellite attitude dynamic modeling. When the influence of discontinuity is removed, the STD of our estimated satellite NL UPDs is less than 0.05 cycles. Thirdly, the STD of our estimated receiver WL UPDs is mainly below 0.2 cycles, which implies that its stability is one order poorer that of the satellite. In addition, if they are used for stations in and around the network covered region, the stability of the UPD products from the CMONOC (Crustal Movement Observation Network of China) is better than that from a global network, benefit from the fact that all the CMONOC stations are equipped with the same receiver type. Finally, the PPP-AR results show that a rate of 82.9% for stations with a WL-ambiguity-fixed rate of over 90% while 69.5% for stations with an NL-ambiguity-fixed rate of over 80% can be achieved when using UPD from the global network, which is worse than that of using UPD from the CMONOC (85.7% for stations with a WL-ambiguity-fixed rate of over 90% while 75% for stations with an NL-ambiguity-fixed rate of over 80%). The results of the experiment on the UPD interoperable application in PPP show that the global network UPD products can provide a fast AR at any single station, and the convergence time is well below 25 min. Particularly, when the location of a station is in and around the regional network, our results show that the PPP results obtained using regional UPDs enable the consistent use of global UPDs. When the location of a station is far away from the regional network, using the regional UPDs can not achieve PPP-AR. Finally, the WL UPDs of the previous day is used for forecasting to estimate the NL UPDs, the stability analysis results of NL UPDs solution and positioning results are demonstrate the validity of forecasted UPD products. [ABSTRACT FROM AUTHOR]

The next-generation satellite-based augmentation system (SBAS) will follow the dual-frequency multi-constellation (DFMC) protocol and broadcast satellite clock-ephemeris corrections and integrity information via GPS L5-like signals to improve the accuracy and integrity for GNSS dual-frequency users. BeiDou Navigation Satellite System (BDS)-3 B1C/B2a dual-frequency users will obtain a higher positioning accuracy using DFMC clock-ephemeris corrections. This paper focuses on an approach for the generation of DFMC SBAS corrections and its preliminary results. Analyzing the signal-in-space ranging error characteristics of BDS-3 satellites reveals that it is impossible to obtain orbits that are more accurate than the broadcast orbits using regionally distributed SBAS monitoring stations. Therefore, a novel DFMC SBAS correction generation approach for BDS-3 satellites is proposed in which only clock offset corrections are calculated. The effectiveness of the proposed approach is validated using measurements from mainland China. By using clock corrections only, B1C/B2a dual-frequency users can obtain the best accuracy. The results of the BDS-3 B1C/B2a dual-frequency positioning experiment show that the user equivalent ranging error is reduced from 0.59 m to 0.37 m with clock corrections but is reduced to only 0.43 m with the addition of clock-ephemeris corrections. With clock corrections only, the 95% positioning errors are reduced from 3.57 m to 1.53 m and from 3.79 m to 2.24 m in the horizontal and vertical directions, respectively, indicating a 48% reduction in positioning errors compared to users without SBAS corrections; however, the error reduction is only 40% with clock-ephemeris corrections. [ABSTRACT FROM AUTHOR]

• A modeling method of real-time ionospheric scintillation maps are presented. • Comparisons indicate that maps are valid, showing better accuracy than GISM. • The maps can be considered as a tool to monitor and warn regional scintillation activities. Trans-ionospheric communication of radio waves can be affected by ionospheric scintillation which can lead to a complete loss of lock. Scintillation is more prevalent in the ionospheric equatorial anomaly region, and at high latitudes, which is one of the main concerns of space weather services. In this paper, we present the first time a technique to derive a near-real-time ionospheric scintillation index S4 regional mapping based on Kriging method using six low latitude stations in Southern China. The result is compared with the Global Ionospheric Scintillation Propagation Model (GISM) and ionospheric irregularity index represented by the rate of change total electron content index (ROTI) to assess the validation and accuracy of output of Kriging method. It shows that our map could reflect better the regional characteristic and variations of S4 in the Southern China. The lower mean absolute errors and the mean square errors indicate that the results of Kriging method are relatively true and reliable, which could be considered monitoring and warning regional ionospheric scintillation activities under disturbed space weather conditions. [ABSTRACT FROM AUTHOR]

In this paper, a new index is established which is defined by the standard deviation of total electron content (TEC) fluctuation and denoted by the symbol σ tec. It is demonstrated that the index σ tec is equivalent to the phase scintillation index and can serve as an indicator of the strength of the phase scintillation. The receiver transiently loses lock on the signal, leading to cycle slips and jumps in the TEC time series. In order to obtain continuous TEC data in the situation of the disturbed ionosphere, a batch processing method is developed to detect and correct cycle slip. Based on the methods mentioned above, we investigate the statistical features of the phase scintillations and cycle slips by means of the data from a scintillation observation network in the south-central region of China during 2012–2015. The results show that the variations of phase scintillation occurrences with local time and season display very similar features to those of the cycle slip occurrences, implying that cycle slips are closely related to phase scintillations. Phase scintillations occur mainly during the night, most frequently before midnight and seldom in the daytime. It is found that phase scintillations occur mainly in equinox months but seldom in solstice months in the crest of the ionization equatorial anomaly and its adjacent regions, and an equinoctial asymmetry that phase scintillations occur more frequently in Spring than in Autumn is also found. Besides, a comparison of the TEC fluctuation index (σ tec) and amplitude scintillation index (S4) indicates that there is close relation between the σ tec and S4, indicating the co-existence of large and small scale irregularities in equatorial irregularity structures. [ABSTRACT FROM AUTHOR]

The bistatic radar system has been one of the effective methods to detect the space debris in low earth orbit (LEO). Tianlai radio array with cylindrical-parabolic antennas is designed for dark energy detection, which has large field of view and high sensitivity, offering a fan-beam during the observation. We propose a bistatic radar system, which consists of Tianlai radio array and an incoherent scattering radar (ISR) assumed as a transmitter in the Qujing city of China, to detect space debris. In this paper, we calculate and analyze the detection capabilities of this system. The results show the bistatic radar system has the potential to detect small space debris of less than 10 cm in LEO. We provide a space debris detection method to obtain the position of the cross-beam satisfying the observation requirement with the TLE data of the space debris. The method can solve the problem of space synchronization between the radio array and ISR. We used the long-short baseline method of the radio array to locate the space target. The relationship among positioning error, the azimuth and the elevation angle are also discussed. [ABSTRACT FROM AUTHOR]

In this paper we propose a network-based Kalman filter combined generalized simulated annealing algorithm approach to decompose a group of GPS position time series into secular trend, annual and semi-annual signals as well as noise components. This approach treats east, north and vertical components of the whole network separately and estimates network-average process-noise parameters to constrain the time variability of the seasonal signals and noise components. Each coordinate component for each station is modeled in state-space model (SSM) individually. The noise components are described as the combination of flicker noise (FN), random walk noise (RWN) and observation white noise (WN). Each component, except for the trend, is allowed to variate over the time, and their amplitudes are estimated by maximization of likelihood function using a generalized simulated annealing (GSA) algorithm. The proposed approach is applied to 10 reprocessed GPS position time series from the Tectonic and Environmental Observation Network of Mainland China (CMONOC II), and its output is compared with that of ordinary maximum likelihood estimation (MLE). The results show that the proposed approach is an effective tool for the decomposition of GPS position time series. Finally, the advantages and limitations of the proposed approach are also discussed. [ABSTRACT FROM AUTHOR]

A lander and a rover were placed on the Moon in China's Chang'E-4 Lunar exploration mission, which is the first lander on the far side of the Moon. To provide communication and telemetry between the Earth and the lander, the CE-4 relay satellite (Queqiao) was launched firstly to the Earth-Moon L2 region in May 2018. The orbit precision of the Chang'E-4 relay satellite is evaluated in this paper. The ground tracking data including Ranging, Doppler, VLBI delay and rate are processed using a batch least squares method. The results show that the residual RMS of ranging, Doppler, VLBI delay and VLBI delay rate based on S-band are about 0.53 m, 0.37 mm/s, 1.16 ns and 0.67 ps/s, respectively. Compared with the previous missions (CE-1/CE-2/CE-5T1) using S-band tracking systems, the measurement precision of the CE-4 relay satellite is significantly improved. Furthermore, the analysis shows that VLBI data can improve the precision of orbit determination and prediction of the halo orbit around the Earth-Moon L2 point: the position precision is better than 100 m and the velocity precision is better than 2 mm/s. Since the CE-4 relay satellite is less than 300 km away from the lunar surface when it flies by the Moon, the lunar non-spherical gravitation has a significant influence on the orbit determination, and the lunar gravity field need to be considered when the Earth is chosen as the central body. [ABSTRACT FROM AUTHOR]

The separation of clouds from snow is fundamentally very challenging because of their similar spectral signature. A new algorithm was proposed to detect clouds from snow in Landsat 8 imagery. Taking the Hetian District region, where there is frequent cloud and snow cover, in northwestern China as one of the typical case areas. The typical case is presented in detail to illustrate the approach produces and results. A band math method for cloud and snow discrimination index (CSDI) was firstly conducted in this paper, fractal digital number-frequency (DN-N) algorithm and hotspot analyses were applied to determine the threshold of the CSDI and eliminate false anomalies. The results showed that an overall accuracy exceeding 95% in areas with very bright land surfaces, which indicate that this algorithm is effective for detecting clouds in specific situations where the ground objects have some reflectance characteristics similar to cloud. [ABSTRACT FROM AUTHOR]

Abstract This paper studies the imaging scheduling issue for China's L-band differential interferometric synthetic aperture radar (InSAR) satellite formation which can work in different observation modes to satisfy different imaging requests. Previous imaging scheduling mainly focuses on maximizing the total revenue of selected targets but ignores that different types of targets actually have different demands. Therefore, a constraint satisfaction model which classifies targets into three types according to targets' size and number of observations is established, meanwhile, three objective functions are considered to satisfy demands of different types of targets. Furthermore, an imaging scheduling method based on improved non-dominated sorting genetic algorithm III (NSGA-III) is proposed to obtain a set of well-converged and well-diversified non-dominating solutions. New Niche-Preservation operation with the same penalty value for convergence and diversity performance is adopted in NSGA-III. Numerical comparison simulations on walking fish group (WFG) test suits and three imaging scheduling instances of different size show the superiority of the proposed methodology. [ABSTRACT FROM AUTHOR]

Abstract Air temperature is an important parameter affecting biosphere processes, air quality, regional climate, and human health, but is difficult to estimate, especially on a nationwide scale. Remote sensing provides high spatial resolution data that influence air temperature and can help overcome this problem in spatially heterogeneous environments. Generally, the simple linear relationships between air temperature, land surface temperature (LST), and auxiliary data, seldom consider the complex spatial variations in air temperature. The random forest (RF) regression model can characterize the complex temperature distribution by establishing the non-linear relationships among them. The main purpose of this paper is to present an RF regression method to estimate monthly average temperatures in China, using MODIS LST, normalized differential vegetation index (NDVI), night-time light, and a digital elevation model (DEM). Results based on cross-validation show that mean absolute error (MAE) and root mean square error (RMSE) at national level in different months ranged from 1.15 to 1.44 °C (mean ± standard deviation: 1.30 ± 0.10 °C) and from 1.57 to 1.99 °C (1.79 ± 0.13 °C), respectively. Potential sources of error and uncertainty were analyzed and investigated. Results show that regression model performs better in eastern (MAE: 0.68 ± 0.79 °C; RMSE: 0.75 ± 0.81 °C) and central China (MAE: 0.68 ± 0.41 °C; RMSE: 0.74 ± 0.41 °C). The model performance was strongly dependent on elevation, slope, land cover, and satellite data quality. In addition, the percentage increase in mean squared error from RF regression model was used to quantify the importance of variables. Positive importance scores indicated an improvement in accuracy with the assistance of NDVI, night-time lights, and the DEM. LST, and more auxiliary data sources, when integrated into an RF regression model, may be ways in which to improve the modeling of air temperature variations in the future. [ABSTRACT FROM AUTHOR]

Highlights • FSF occurred more often after midnight. • RSF and scintillation appeared mainly during pre-midnight. • FSF occurrence rates mostly appeared during the summer months. • RSF and scintillation occurred mostly in the equinoctial months at low-latitudes. • Scintillation occurrence was usually associated with the appearance of RSF. Abstract The spread-F echo of ionograms and scintillation of satellite signal propagation along the Earth-space path are two typical phenomena induced by ionospheric irregularities. In this study, we obtained spread-F data from HF (high frequency) digital ionosonde and scintillation index (S4) data from L-band and UHF receivers at low- and mid-latitudes in China during the 24th solar cycle. These four sites were located at Haikou (HK) (20°N, 110.34°E), Kunming (KM) (25.64°N, 103.72°E), Qingdao (QD) (36.24°N, 120.42°E), and Manzhouli (MZL) (49.56°N, 117.52°E). We used these data to investigate spread-F and scintillation occurrence percentages and variations with local time, season, latitude and solar activity. A comparative study of spread-F and scintillation occurrence rates has been made. The main conclusions are as follows: (a) FSF occurred mostly during post-midnight, while RSF and scintillation appeared mainly during pre-midnight at HK and KM; (b) FSF occurrence rates were larger at QD and MZL than expected; (c) the FSF occurrence percentages were anti-correlated with solar activity at HK and KM; meanwhile RSF and scintillation occurrence rates increased with the increase of solar activity at this two sites; (d) the highest FSF occurrence rates mostly appeared during the summer months, while RSF and scintillation occurred mostly in the equinoctial months at HK and KM; (e) the scintillation occurrence was usually associated with the appearance of RSF, probably due to a different physical mechanism comparing with FSF. Some of these results verified the conclusions of previous papers, whereas some show slight difference. These results are important in understanding ionospheric irregularities variations characteristic at low- and mid-latitudes in China. [ABSTRACT FROM AUTHOR]

The present paper has used a comprehensive approach to study atmosphere pollution sources including the study of vertical distribution characteristics, the epicenters of occurrence and transport of atmospheric aerosol in North-West China under intensive dust storm registered in all cities of the region in April 2014. To achieve this goal, the remote sensing data using Moderate Resolution Imaging Spectroradiometer satellite (MODIS) as well as model-simulated data, were used, which facilitate tracking the sources, routes, and spatial extent of dust storms. The results of the study have shown strong territory pollution with aerosol during sandstorm. According to ground-based air quality monitoring stations data, concentrations of PM 10 and PM 2.5 exceeded 400 μg/m 3 and 150 μg/m 3 , respectively, the ratio PM 2.5 /PM 10 being within the range of 0.123–0.661. According to MODIS/Terra Collection 6 Level-2 aerosol products data and the Deep Blue algorithm data, the aerosol optical depth (AOD) at 550 nm in the pollution epicenter was within 0.75–1. The vertical distribution of aerosols indicates that the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) 532 nm total attenuates backscatter coefficient ranges from 0.01 to 0.0001 km −1  × sr −1 with the distribution of the main types of aerosols in the troposphere of the region within 0–12.5 km, where the most severe aerosol contamination is observed in the lower troposphere (at 3–6 km). According to satellite sounding and model-simulated data, the sources of pollution are the deserted regions of Northern and Northwestern China. [ABSTRACT FROM AUTHOR]

Water vapor plays an important role in climate change; thus, studying the spatial distribution and temporal variation of precipitable water vapor (PWV) in the coastal regions of China would help researchers to understand the climate characteristics of those regions. In this paper, 6-year 1-h interval PWV were derived from 27 Global Positioning System stations observations of Chinese coastal GPS observation network, surface meteorological data and European Center for Medium-Range Weather Forecasts (ERA-Interim) reanalysis products. The present study provides the use of these data to investigate the spatial-temporal variability of water vapor throughout the coastal regions of China. Latitude is the main factor affecting the spatial distribution of GPS-derived PWV; that is, PWV decreased by about 1.5 mm for each 1° increase of latitude. For regions at the same latitude, a region that is relatively close to the ocean will have a higher content of PWV. The PWV in the southeastern and southwestern coastal regions of China is significantly higher in summer; this may be influenced by the southeastern and southwestern water vapor inflow corridors. The PWV obviously varies monthly, reaching a minimum in January; however, the timing of the maximum varied but usually appeared in June, July or August and was affected by the monsoons. The PWV varies largely between summer and winter with a larger gradient of change in PWV with latitude in winter than in summer. The positive correlation coefficient between PWV and the surface temperature varied in different seasons; this is related to the changes of temperature and the horizontal motion of water vapor. Use of the Fast Fourier Transform method showed that the PWV time series data have multi-scale characteristics. The amplitude and phase of the PWV time series in annual, semiannual, four month and seasonal cycles were extracted through harmonic wave analysis. The amplitude of four month and seasonal cycles did not pass significance testing. The maximum amplitude of the annual PWV cycle is located in mid-latitudes with 22.09 mm, which gradually decreases towards high latitude and equator area. The peak time of annual PWV cycle occurs in July, which does not agree with the timing of the maximum monthly average PWV. The semiannual cycle amplitudes is between 0.42 and 6.32 mm, with no significant correlation between their distribution and latitude. The peak time of semiannual PWV cycles is during about January–March and July–September, and the peak time gradually becomes late from north to south. [ABSTRACT FROM AUTHOR]

The International Reference Ionosphere (IRI) is the most frequently used community empirical model. The latest version IRI2016 provides three options for the F2 peak height hmF2: AMTB2013, SHU-2015, and BSE-1979. In this paper, we used the hmF2 data derived by the ionosondes at Mohe, Beijing, Wuhan and Sanya ranging from year 2007 to 2016 to assess the performance of these three options in the model. The results show that the variability of the observed hmF2 versus local time, seasons and levels of solar activity could be reproduced well by the three options. However, the SHU-2015 option performs best at these four stations, followed by BSE-1979, and the AMTB2013 option is worst. Generally, the AMTB2013 and BSE-1979 options overestimate the hmF2 values, while the SHU-2015 option mainly underestimates the hmF2 values. This is the first evaluations of the three IRI2016 hmF2 options by manually scaled ionosonde data over China area to our knowledge. Overall, we recommend the usage of SHU-2015 hmF2 option over China region when using IRI2016 model in terms of hmF2 calculation. [ABSTRACT FROM AUTHOR]

As BeiDou Navigation Satellite System (BDS) has been operational in the whole Asia-Pacific region, it means a new GNSS system with a different satellite orbit structure will become available for deformation monitoring in the future. Conversely, GNSS deformation monitoring data are always processed with a regular interval to form displacement time series for deformation analysis, where the interval can neither be too long from the time perspective nor too short from the precision of determined displacements angle. In this paper, two experimental platforms were designed, with one being at mid-latitude and another at higher latitude in China. BDS data processing software was also developed for investigating the accuracy of continuous deformation monitoring using current in-orbit BDS satellites. Data over 20 days at both platforms were obtained and were processed every 2, 4 and 6 h to generate 3 displacement time series for comparison. The results show that with the current in-orbit BDS satellites, in the mid-latitude area it is easy to achieve accuracy of 1 mm in horizontal component and 2–3 mm in vertical component; the accuracy could be further improved to approximately 1 mm in both horizontal and vertical directions when combined BDS/GPS measurements are employed. At higher latitude, however, the results are not as good as expected due to poor satellite geometry, even the 6 h solutions could only achieve accuracy of 4–6 and 6–10 mm in horizontal and vertical components, respectively, which implies that it may not be applicable to very high-precision deformation monitoring at high latitude using the current BDS. With the integration of BDS and GPS observations, however, in 4-h session, the accuracy can achieve 2 mm in horizontal component and 4 mm in vertical component, which would be an optimal choice for high-accuracy structural deformation monitoring at high latitude. [ABSTRACT FROM AUTHOR]

In this paper, the ionospheric total electron content (TEC) is derived from 250 Global Navigation Satellite Systems (GNSS) receivers over China. The GNSS TEC data are utilized to study the diurnal and day-to-day variability of ionosphere, ionospheric east–west differences and to construct regional ionospheric map. The GNSS–TEC curves clearly show sunrise and sunset enhancements in the diurnal variation. The peak value of TEC is lower in January 2015 than in May 2014. There is 2 h difference in the occurrence time of TEC maximum/minimum between May and January. Compared with the observations of Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS), the measurements from the Geostationary Earth Orbit (GEO) satellites of BeiDou Navigation Satellite System (BDS) clearly present the ionospheric day-to-day variability and east–west differences in a region with small longitude differences (3.52–11.31°). The east–west differences in TEC are more obvious in larger longitude differences at 11:30 local time on 23 January 2015. The maximum east–west difference in TEC is about 7 total electron content unit (TECU, 1 TECU = 10 16 el m −2 ) in longitude difference of 11.31°. Our analysis shows that the TEC for east–west small longitude differences may be associated with the east–west gradient of geomagnetic declination. Based on 250 GNSS stations, a regional TEC map constructed by Kriging method can well capture the main spatial structure of ionosphere in China. A comparison between TEC maps obtained by Kriging method and provided by Jet Propulsion Laboratory displays that there are large deviations in the North of China, which is mainly caused by the difference in the number of used GNSS stations. In addition, comprehensive investigation presents that GNSS has more advantages over GPS and GLONASS in the ionosphere research over China. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis of the Schumann resonance (SR) parameters observed at low latitude stations in China for the first time. Variations of SR peak frequency and intensity on different timescales (from minutes to years) are analyzed in detail. Diurnal and seasonal variations are shown and the source-observer distance is calculated to confirm the contributions of lightning activity. Differences in the profiles of SR intensity between the NS and EW components are due to the effects of the source-observer distance and the relative position of the observer to the sources. Diurnal frequency variations are more complicated and cannot be directly linked with the three thunderstorm centers. Seasonal variations are clear for intensity but not for frequency. The differences in the diurnal and seasonal variations between the SR intensity and frequency show that the greatest contributor to SR intensity is global lightning activity, while the SR frequency is not affected solely by lightning, as certain other factors involving ionosphere properties may play non-negligible roles. We also emphasize that our observations do not show a distinct day–night change in the SR parameters, and that the SR intensity does not show abrupt changes across terminators. This observation is consistent with previous simulations. Finally, the response of the SR to a solar flare is discussed. The flare leads to a sudden increase of about 0.2 Hz relative to the 2 σ level of the SR frequencies in the first three modes, which is in agreement with other works in the literature. This frequency enhancement is explained using theoretical calculations. [ABSTRACT FROM AUTHOR]

Five inclined geosynchronous orbit (IGSO) satellites with the inclination of about 55° in the Chinese BeiDou navigation system have been put in orbit until now. The Inter-Agency Space Debris Coordination Committee (IADC) has defined a geosynchronous orbit (GEO) protected region and recommended that the GEO satellite should be maneuvered to a disposal orbit high enough at end-of-mission to remain above the GEO protected region. The recommended disposal altitude is at least 235 km + ( 1000 · C R · A / M ) higher than the perigee altitude of the GEO satellite, where C R and A / M are radiation pressure coefficient and area-to-mass ratio respectively. Whether this recommendation is also adequate for the disposal of these IGSO satellites in the Chinese BeiDou navigation system at end-of-mission? And if not, is there any other possible strategy to do? In view of these considerations, the long-term dynamical evolution of these IGSO satellites is investigated by both theoretical analysis and numerical computation methods in this paper. Some qualitative orbital evolution characteristics and quantitative result of variation ranges of the semi-major axis a , the inclination i and the eccentricity e are presented respectively. Based on these results, a possible mitigation strategy to reduce the orbital lifetime of the IGSO satellites after end-of-mission is proposed. [ABSTRACT FROM AUTHOR]

The F2 layer critical frequency of the ionosphere ( f oF2) is one of the most significant parameters for studying the ionosphere. To investigate the large-scale characteristics of the ionosphere over particular regions, modeling f oF2 is an effective method. In this paper, we use both the Kriging (KG) and neural network (NN) methods to reconstruct f oF2 maps over North China. The neural network is trained by the genetic algorithm (GA) to avoid the ‘local minimum’ phenomenon in most NN applications. We then carry out a comparison between f oF2 provided by both the KG and NN methods with vertical model operation of ionosonde data including Beijing, Qingdao, Suzhou, and Changchun. All of the f oF2 data used in the comparison are obtained from the oblique and vertical mode operation of ionosonde from the China Ground-based Seismo-ionospheric Monitoring Network. To allow for a possible seasonal and diurnal variation, data obtained from summer, winter, and equinox months are applied in the present comparison. In addition, we make a comparison during a magnetic storm period. The results of our comparisons demonstrate that both the KG and NN methods are appropriate tools for modeling f oF2 maps. However, when the data set is spare, the performance of the NN method is better than the KG method. On the other hand, the KG method is more robust than the NN method during a magnetic storm. [ABSTRACT FROM AUTHOR]

Abstract: One of various mechanisms of pre-earthquake lithosphere–atmosphere–ionosphere coupling as possible explanation of the seismo-ionospheric effects is connected with the release of latent heat. Abnormal variations of ionospheric electromagnetic parameters possibly related to the 2007 Ms 6.4 Pu’er earthquake in China were reported. This paper attempts to examine whether there were abnormal changes of surface latent heat flux (SLHF) linked with this pre-earthquake ionospheric disturbances. The spatio-temporal statistical analyzes of multi-years SLHF data from USA NCEP/NCAR Reanalysis Project reveal that local SLHF enhancements appeared 11, 10 and 7days before the Pu’er earthquake, respectively. As contrasted to the formerly reported local ionospheric Ne enhancement 9days before the shock observed by DEMETER satellite, it is discovered that the SLHF and Ne anomalies are quasi-synchronous and have good spatial correspondence with the epicentre and the local active faults. This is valuable for understanding the seismogenic coupling processes and for recognizing earthquake anomaly with multiple parameters from integrated Earth observation system. [Copyright &y& Elsevier]

Abstract: The Ionospheric Laboratory of Wuhan University is interested in upgrading its instrumentation replacing the WIOBSS (Wuhan Ionospheric Oblique Backscattering Sounding System) with a more flexible and automatic ionosonde. Then the updated ionosonde WMI (Wuhan Multifunctional Ionosonde) with automatic ionogram scaling has been developed to satisfy future research. The new system not only inherited some classic techniques from WIOBSS, such as the pulse compression and the coherent integration techniques, but also made great improvements in hardware design and software updating. This paper mainly introduces evolutions of this new ionosonde in both digital transceiver and digital signal processing domain, and also presents some observations. [Copyright &y& Elsevier]

Abstract: ARGO-YBJ is a multipurpose experiment consisting in a dense sampling air shower array with 93% sensitive area located at very high altitude. The apparatus is in stable data taking since November 2007 at the YangBaJing Cosmic Ray Laboratory (Tibet, PR China, 4300ma.s.l., 606g/cm2). In this paper we report the main results in Gamma-Ray Astronomy and Cosmic Ray Physics after about 3years of operation. [Copyright &y& Elsevier]

Abstract: All countries around the world and many international bodies, including the United Nations Development Program (UNDP), United Nations Food and Agricultural Organization (FAO), the International Fund for Agricultural Development (IFAD) and the International Labor Organization (ILO), have to eliminate rural poverty. Estimation of regional poverty level is a key issue for making strategies to eradicate poverty. Most of previous studies on regional poverty evaluations are based on statistics collected typically in administrative units. This paper has discussed the deficiencies of traditional studies, and attempted to research regional poverty evaluation issues using 3-year DMSP/OLS night-time light satellite imagery. In this study, we adopted 17 socio-economic indexes to establish an integrated poverty index (IPI) using principal component analysis (PCA), which was proven to provide a good descriptor of poverty levels in 31 regions at a provincial scale in China. We also explored the relationship between DMSP/OLS night-time average light index and the poverty index using regression analysis in SPSS and a good positive linear correlation was modelled, with R2 equal to 0.854. We then looked at provincial poverty problems in China based on this correlation. The research results indicated that the DMSP/OLS night-time light data can assist analysing provincial poverty evaluation issues. [Copyright &y& Elsevier]

Abstract: GNSS (Global Navigation Satellite System) radio occultation mission for remote sensing of the Earth’s atmosphere will be performed by GNOS (GNSS Occultation Sounder) instrument on China FengYun-3 (FY3) 02 series satellites, the first of which FY3-C will be launched in the year 2013. This paper describes the FY3 GNOS mission and presents some results of measurement simulation. The key designed specifications of GNOS are also shown. The main objective of simulation is to provide scientific support for GNOS occultation mission on the FY3-C satellites. We used EGOPS software to simulate occultation measurements according to GNOS designed parameters. We analyzed the accuracy of retrieval profiles based on two typical occultation events occurring in China South–East area among total simulated events. Comparisons between the retrieval atmospheric profiles and background profiles show that GNOS occultation has high accuracy in the troposphere and lower stratosphere. The sensitivities of refractivity to three types of instrumental error, i.e. Doppler biases, clock stability and local multipath, were analyzed. The results indicated that the Doppler biases introduced by along-ray velocity error and GNOS clock error were the primary error sources for FY3-C occultation mission. [Copyright &y& Elsevier]

Abstract: The Crustal Movement Observation Network of China (CMONOC) is one of the major scientific infrastructures, mainly using Global Positioning System (GPS) measurements, to monitor crustal deformation in the Chinese mainland. In this paper, decade-long coordinate time series of 26 continuous GPS sites of CMONOC are analyzed for their noise content using maximum likelihood estimation (MLE). We study the noise properties of continuous GPS time series of CMONOC for the unfiltered, filtered solutions and also the common mode signals in terms of power law plus white noise model. In the spatial filtering, we remove for every time series a common mode error that was estimated from a modified stacking of position residuals from other sites within ∼1000km of the selected site. We find that the common mode signal in our network has a combination of spatially correlated flicker noise and a common white noise with large spatial extent. We demonstrate that for the unfiltered solutions of CMONOC continuous GPS sites the main colored noise is a flicker process, with a mean spectral index of ∼1. For the filtered solutions, the main colored noise is a general power law process, indicating that a major number of the filtered regional solutions have a combination of noise sources or local effects. The velocity uncertainties from CMONOC continuous GPS coordinate time series may be underestimated by factors of 8–16 if a pure white noise model is assumed. In addition, using a white plus flicker noise model, the median values of velocity errors for the unfiltered solutions are 0.16 (north), 0.17 (east) and 0.58 (vertical)mm/yr, and the median values for the filtered solutions are 0.09 (north), 0.10 (east) and 0.40 (vertical)mm/yr. [Copyright &y& Elsevier]

Abstract: The problems of physical explanation and possible mechanisms of the seismo-ionospheric effects formation are under discussion now. There are proposed different mechanisms of such effects, for example, large- and small-scale internal gravity waves (IGWs), atmospheric electric field, electromagnetic fields and emissions. However, the appearance of local large-scale seismo-ionospheric anomalies in Total Electron Content (TEC) is possible to explain only by two mechanisms: an atmospheric electric field and/or small-scale IGWs. In this paper, the simulation results for reproduction of the observed seismo-ionospheric great positive effects in TEC prior to strong Wenchuan earthquake are presented. The obtained results confirm the proposed mechanism of seismo-ionospheric effects formation by the penetration of the seismogenic electric field from the atmosphere into the ionosphere. It is suggested that so great TEC enhancement observed 3days prior to Wenchuan earthquake could be explained by combined action of seismogenic vertical electric field and IGWs generated by the solar terminator. [Copyright &y& Elsevier]

Abstract: This paper uses principal component analysis (PCA) to determine the spatial pattern of total electron content (TEC) anomalies in the ionosphere post the China’s Wenchuan Earthquake of 12 May, 2008 (UTC) (Mw =7.9). PCA and image processing are applied to the global ionospheric map (GIM) with transforms conducted for the time period 08:00–10:00UT on 12 May 2008. Results show that at a height of approximately 200km the anomaly is widespread and less intense; however, it becomes more localized with height reaching maximum intensity and localization at an altitude of 300km. The spatial distribution is remarkably similar to that reported for a TEC anomaly previously identified as a precursor anomaly on May 9, 2008 for the same time period. Potential causes of the results are discussed with emphasis given to vertical acoustic gravity waves based on the spatial pattern identified. [Copyright &y& Elsevier]

Abstract: In this paper a method based on in situ measured reflectance spectra was developed for accurately mapping salt fields in the Taibei Salt Farm in Lianyungang City of East China. After radiometric correction and geometric rectification, six multispectral ETM+ bands were fused with the panchromatic band via principal components analysis (PCA). The fused data were used to map salt fields in the farm. Salt fields were mapped 91.95% correctly in comparison with ground statistics from raw multispectral bands. This accuracy level rose to 96.4% with the use of the panchromatic band (15m resolution). However, PCA-fused data produced the highest accuracy of 98.8%. At the zone level, coarse resolution data resulted in an accuracy of 98.93% for crystallization ponds, but only 82.68% for condensation ponds. Use of the panchromatic band alone improved the accuracy for condensation ponds but decreased the accuracy for crystallization and evaporation ponds. Results derived from PCA-fused data are highly consistent with the ground statistics at a discrepancy between 0.35% for evaporation zone and 1.80% for condensation zone. It is concluded that a fine spectral resolution is important to separation of ponds of a varying salt content while a fine spatial resolution is important to their mapped area. Ponds of a lower salt content can be mapped more accurately from fused data than from raw spectral bands. [Copyright &y& Elsevier]

Abstract: The study of Hamiltonian systems is important for space physics and astrophysics. In this paper, we study local behavior of an isolated nilpotent critical point for polynomial Hamiltonian systems. We prove that there are exact three cases: a center, a cusp or a saddle. Then for quadratic and cubic Hamiltonian systems we obtain necessary and sufficient conditions for a nilpotent critical point to be a center, a cusp or a saddle. We also give phase portraits for these systems under some conditions of symmetry. [Copyright &y& Elsevier]

Abstract: Based on observations of two ionosondes at Wuhan and Kokubunji, this paper presents effects of TADs on the daytime mid-latitude ionosphere during the intense geomagnetic storm on March 31, 2001. During a positive ionospheric storm, the start of the enhancement of the foF2 (F2 peak plasma frequency) at Wuhan lags that at Kokubunji by 15min, which corresponds to the time interval of traveling atmospheric disturbances (TADs’) propagation from Kokubunji to Wuhan. Associated with the uplifting of the hmF2 (height of F2 peak) caused by TADs, it is observed by the two ionosondes that the F1 cusp becomes better developed. Therefore, during a geomagnetic storm, TADs originating from the auroral oval may have a strong influence on the shape of the electron density profile in the F1 region ionosphere at middle latitudes. It is highly likely that TADs are responsible for the evolution of the F1 cusp. [Copyright &y& Elsevier]