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Precise orbit determination for LEO satellites:single-receiver ambiguity resolution using GREAT products

Geo-Spatial Information Science 2022年第1期25卷 63-73页

作者： Xingxing Li Yujie Qin Keke Zhang Jiaqi Wu Wei Zhang Qian Zhang Hongmin Zhang School of Geodesy and geomatics Wuhan UniversityWuhanHubeiChina Department of Geodesy and Remote Sensing of the German Research centre for Geosciences(GFZ) PotsdamGermany

In recent years,the large Low Earth Orbit(LEO)constellations have become a hot topic due to their great potential to improve the Global Navigation Satellite Systems(GNSS)positioning performance.One of the important focus is how to obtain the accurate and reliable orbits for these constellations with dozens of LEO satellites.The GNSS-based Precise Orbit Determination(POD)will be exclusively performed to achieve this goal,where the Integer Ambiguity Resolution(IAR)plays a key role in acquiring high-quality orbits.In this study,we present a comprehensive analysis of the benefit of the single-receiver IAR in LEO POD and discuss its implication for the future LEO constellations.We perform ambiguity-fixed LEO POD for four typical missions,including Gravity Recovery and Climate Experiment(GRACE)Follow-On(GRACE-FO),Swarm,Jason-3 and Sentinel-3,using the Uncalibrated Phase Delay(UPD)products generated by our GREAT(GNSS+REsearch,Application and Teaching)software.The results show that the ambiguity fixing processing can significantly improve the accuracy of LEO orbits.There are negligible differences between our UPD-based ambiguity-fixed orbits and those based on the Observable Signal Bias(OSB)and Integer Recovery Clock(IRC)products,indicating the good-quality of UPD products we generated.Compared to the float solution,the fixed solution presents a better consistency with the external precise science orbits and the largest accuracy improvement of 5 mm is achieved for GRACE-FO satellites.Meanwhile,the benefit can be observed in laser ranging residuals as well,with a Standard Deviation(STD)reduction of 3–4 mm on average for the fixed solutions.Apart from the absolute orbits,the relative accuracy of the space baseline is also improved by 20–30%in the fixed solutions.The result demonstrates the superior performance of the ambiguity-fixed LEO POD,which appears as a particularly promising technique for POD of future LEO constellations.

关键词： Precise orbit determination single-receiver ambiguity resolution onboard GPS observation LEO

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A comparative analysis of five global cropland datasets in china

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Science china Earth Sciences 2016年第12期59卷 2307-2317页

作者： LU Miao WU WenBin ZHANG Li LIAO AnPing PENG Shu TANG HuaJun Key Laboratory of Agri-informatics Ministry of Agriculture/Institute of Agricultural Resources and Regional PlanningChinese Academy of Agricultural Sciences National Geomatics Centre of China

Accurate information of cropland area and spatial location is critical for studies of national food security, global environmental change, terrestrial ecosystem geophysics and the geochemical cycle. In this paper, we compared five global cropland datasets in circa 2010 of china from in terms of cropland area and spatial location, including Global Land30, FROM-GLC, Glob Cover, MODIS Collection 5, and MODIS Cropland. The results showed that the accuracies of cropland area and spatial location of Globe Land30 were higher than the other four products. The cropland areas of the five products varied in most of the provinces. Compared with the statistical data, the best goodness of fit was obtained using Globe Land30, followed by MODIS Collection 5 and FROM-GLC, with MODIS Cropland and Glob Cover having the poorer accuracies. Regarding the spatial location of cropland, Globe Land30 achieved the best accuracy, followed by FROM-GLC and MODIS Collection 5, with Glob Cover and MODIS Cropland having the poorer accuracies. In addition, the spatial agreement of the five datasets was reduced from agricultural production area to pastoral area and significantly affected by elevation and slope factors. Although the spatial resolution of MODIS Collection 5 was the lowest, accuracies of the cropland area and spatial location were better than those of Glob Cover and MODIS Cropland. Therefore, high spatial resolution remote sensing images can help to improve the accuracy of the dataset during land cover mapping, while it is also important to select a suitable classification method. Furthermore, in northwestern and southeastern china, spectral mixing pixels are universal because of the complicated landscape and fragmentized topography and result in uncertainty and poor consistency when using the five products. Therefore, these regions require additional attention in future cropland mapping studies.

关键词： Land cover Cropland area Spatial location Accuracy Spatial agreement

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An Improved Extreme Learning Machine Prediction Model for Ionospheric Total Electron Content

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Journal of Geodesy and Geoinformation Science 2023年第1期6卷 1-10页

作者： Jianmin WANG Jiapeng HUANG School of geomatics Liaoning Technical UniversityFuxin 123000China

Earth’s ionosphere is an important medium for navigation,communication,and radio wave transmission.Total Electron Content(TEC)is a descriptive quantify for ionospheric research.However,the traditional empirical model could not fully consider the changes of TEC time series,the prediction accuracy level of TEC data performed not high.In this study,an improved Extreme Learning Machine(ELM)model is proposed for ionospheric TEC prediction.Improvements involved the use of Empirical Mode Decomposition(EMD)and a Fuzzy C-Means(FCM)clustering algorithm to pre-process data used as input to the ELM model.The proposed model fully uses the TEC data characteristics and expected to perform better prediction accuracy.TEC measurements provided by the centre for Orbit Determination in Europe(CODE)were used to evaluate the performance of the improved ELM model in terms of prediction accuracy,applicable latitude,and the number of required training samples.Experimental results produced a Mean Relative Error(MRE)and a Root Mean Square Error(RMSE)of 8.5%and 1.39 TECU,respectively,outperforming the ELM algorithm(RMSE=2.33 TECU and MRE=17.1%).The improved ELM model exhibited particularly high prediction accuracy in mid-latitude regions,with a mean relative error of 7.6%.This value improved further as the number of available training data increased and when 20-doys data were trained,achieving a mean relative error of 4.9%.These results suggest the proposed model offers higher prediction accuracy than conventional algorithms.

关键词： ELM model EMD FCM incentive function ionospheric TEC prediction

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Development and evaluation of the refined zenith tropospheric delay(ZTD)models

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Satellite Navigation 2021年第1期2卷 296-304页

作者： Fei Yang Xiaolin Meng Jiming Guo Debao Yuan Ming Chen College of Geoscience and Surveying Engineering China University of Mining and Technology-Beijing100083 BeijingChina Global Geospatial Engineering Ltd. The Sino-UK Geospatial Engineering Centre18 Radford Bridge RoadNottingham NG81NAUK School of Geodesy and geomatics Wuhan University129 Luoyu RoadWuhan 430079China national geomatics Center of china Beijing 100830China.

The tropospheric delay is a significant error source in Global Navigation Satellite System(GNSS)positioning and navigation.It is usually projected into zenith direction by using a mapping function.It is particularly important to establish a model that can provide stable and accurate Zenith Tropospheric Delay(ZTD).Because of the regional accuracy difference and poor stability of the traditional ZTD models,this paper proposed two methods to refine the Hopfield and Saastamoinen ZTD models.One is by adding annual and semi-annual periodic terms and the other is based on Back-Propagation Artificial Neutral Network(BP-ANN).Using 5-year data from 2011 to 2015 collected at 67 GNSS reference stations in china and its surrounding regions,the four refined models were constructed.The tropospheric products at these GNSS stations were derived from the site-wise Vienna Mapping Function 1(VMP1).The spatial analysis,temporal analysis,and residual distribution analysis for all the six models were conducted using the data from 2016 to 2017.The results show that the refined models can effectively improve the accuracy compared with the traditional models.For the Hopfield model,the improvement for the Root Mean Square Error(RMSE)and bias reached 24.5/49.7 and 34.0/52.8 mm,respectively.These values became 8.8/26.7 and 14.7/28.8 mm when the Saastamoinen model was refined using the two methods.This exploration is conducive to GNSS navigation and positioning and GNSS meteorology by providing more accurate tropospheric prior information.

关键词： GNSS Tropospheric delay ZTD Refined model ANN

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Scattering and absorption characteristics of non-spherical cirrus cloud ice crystal particles in terahertz frequency band

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Chinese Physics B 2020年第7期29卷 120-127页

作者：谢涛陈梦婷陈健陆风安大伟 School of Remote Sensing and geomatics Engineering Nanjing University of Information Science and TechnologyNanjing 210044China School of Electronic and Information Engineering Nanjing University of Information Science and TechnologyNanjing 210044China national Satellite Meteorological centre China Meteorological AdministrationBeijing 100081China

We used discrete dipole approximation(DDA)to examine the scattering and absorption characteristics of spherical ice crystal particles.On this basis,we studied the scattering characteristics of spherical ice crystal particles at different frequencies and non-spherical ice crystal particles with different shapes,aspect ratios,and spatial orientations.The results indicate that the DDA and Mie methods yield almost the same results for spherical ice crystal particles,illustrating the superior calculation accuracy of the DDA method.Compared with the millimeter wave band,the terahertz band particles have richer scattering characteristics and can detect ice crystal particles more easily.Different frequencies,shapes,aspect ratios,and spatial orientations have specific effects on the scattering and absorption characteristics o f ice crystal particles.The results provide an important theoretical basis for the design of terahertz cloud radars and related cirrus detection methods.

关键词： scattering characteristics discrete dipole approximation terahertz non-sphericalice crystal particles

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Random Forest-Based Snow Cover Mapping in china Using Fengyun-3B VIRR Data

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Journal of Meteorological Research 2023年第5期37卷 666-689页

作者： Yuchen XIE Yonghong LIU Yeping ZHANG Fuzhong WENG Shanyou ZHU Zhaojun ZHENG Shihao TANG School of Remote Sensing&geomatics Engineering Nanjing University of Information Science&TechnologyNanjing 210044 CMA Earth System Modeling and Prediction centre China Meteorological Administration(CMA)Beijing 100081 State Key Laboratory of Severe Weather Chinese Academy of Meteorological SciencesChina Meteorological AdministrationBeijing 100081 national Satellite Meteorological centre China Meteorological AdministrationBeijing 100081

Currently,there is variability in the spectral band thresholds for snow cover recognition using remote sensing in different regions and for complex terrains.Using Fengyun-3B Visible and Infra-Red Radiometer(FY-3B VIRR)satellite data,we applied random forest(RF)methodology and selected 13 feature variables to obtain snow cover.A training set was generated,containing approximately 1 million snow and nonsnow samples obtained in china from the snow monitoring reports issued by the national Satellite Meteorological centre and four snow cover products from the Interactive Multi-sensor Snow and Ice Mapping System(IMS),the FY-3B Multi-Sensor Synergy(MULSS),the Moderate Resolution Imaging Spectroradiometer(MODIS)snow cover product(MYD10A1),and the national Cryosphere Desert Data Center(NCDC).This training set contained many different samples of cloud types and snow under forest cover to help effectively distinguish snow and clouds and improve the recognition rate of snow under forest cover.Then,two RF snow cover recognition models were constructed for the snow and nonsnow seasons and they were used to conduct daily snow cover recognition in china from 2011 to 2020.The results show that the RF models constructed based on FY-3B VIRR data have good recognition performance for shallow snow,understory snow,and snow on the Qinghai–Tibetan Plateau.The recognition accuracy against weather stations and the spatial consistency with the IMS product are better than the MULSS,MYD10A1,and NCDC products.The overall accuracy of the RF product is 90.6%,and the recall rate is 93.8%.The omission and commission errors are 6.2%and11.1%,respectively.Unlike other existing snow cover algorithms,the established RF model skips the complicated atmospheric correction and cloud identification processes and does not involve external auxiliary data;thus,it is more easily popularized and operationally applicable to generating long-time series snow cover products.

关键词： snow identification random forest Fengyun-3B Visible and Infra-Red Radiometer feature selection

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Precise Orbit Determination for the FY-3C Satellite Using Onboard BDS and GPS Observations from 2013, 2015, and 2017

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Engineering 2020年第8期6卷 904-912页

作者： Xingxing Li Keke Zhang Xiangguang Meng Wei Zhang Qian Zhang Xiaohong Zhang Xin Li School of Geodesy and geomatics Wuhan UniversityWuhan 430079China German Research centre for Geosciences(GFZ) Potsdam 14473Germany national Space Science Center Chinese Academy of SciencesBeijing 100190China Beijing Key Laboratory of Space Environment Exploration Beijing 100190China

Using the FengYun-3C(FY-3C)onboard BeiDou Navigation Satellite System(BDS)and Global Positioning System(GPS)data from 2013 to 2017,this study investigates the performance and contribution of BDS to precise orbit determination(POD)for a low-Earth orbit(LEO).The overlap comparison result indicates that code bias correction of BDS can improve the POD accuracy by 12.4%.The multi-year averaged one-dimensional(1D)root mean square(RMS)of the overlapping orbit differences(OODs)for the GPS-only solution is 2.0,1.7,and 1.5 cm,respectively,during the 2013,2015,and 2017 periods.The 1D RMS for the BDS-only solution is 150.9,115.0,and 47.4 cm,respectively,during the 2013,2015,and 2017 periods,which is much worse than the GPS-only solution due to the regional system of BDS and the few BDS channels of the FY-3C receiver.For the BDS and GPS combined solution(also known as the GC combined solution),the averaged 1D RMS is 2.5,2.3,and 1.6 cm,respectively,in 2013,2015,and 2017,while the GC combined POD presents a significant accuracy improvement after the exclusion of geostationary Earth orbit(GEO)satellites.The main reason for the improvement seen after this exclusion is the unfavorable satellite tracking geometry and poor orbit accuracy of GEO satellites.The accuracy of BDS-only and GC combined solutions have gradually improved from 2013 to 2017,thanks to improvements in the accuracy of International GNSS Service(IGS)orbit and clock products in recent years,especially the availability of a high-frequency satellite clock product(30 s sampling interval)since 2015.Moreover,the GC POD(without GEO)was able to achieve slightly better accuracy than the GPS-only POD in 2017,indicating that the fusion of BDS and GPS observations can improve the accuracy of LEO POD.GC combined POD can significantly improve the reliability of LEO POD,simply due to system redundancy.An increased contribution of BDS to LEO POD can be expected with the launch of more BDS satellites and with further improvements in the accuracy of BDS satellite products in the ne

关键词： FengYun-3C LEO precise orbit determination(POD) Onboard BDS and GPS BDS code bias BDS/GPS combined POD

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Refining the ERA5-based global model for vertical adjustment of zenith tropospheric delay

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Satellite Navigation 2022年第3期3卷 221-230,I0005页

作者： Ge Zhu Liangke Huang Yunzhen Yang Junyu Li Lv Zhou Lilong Liu College of geomatics and Geoinformation Guilin University of TechnologyGuilin541004China College of Resources and Environment Beibu Gulf UniversityQinzhou535011China

Tropospheric delay is an important factor affecting high precision Global Navigation Satellite System(GNSS)positioning and also the basic data for GNSS atmospheric research.However,the existing tropospheric delay models have some problems,such as only a single function used for the entire atmosphere.In this paper,an ERA5-based(the fifth generation of European centre for Medium-Range Weather Forecasts Reanalysis)global model for vertical adjustment of Zenith Tropospheric Delay(ZTD)using a piecewise function is developed.The ZTD data at 611 radiosonde stations and the MERRA-2(second Modern-Era Retrospective analysis for Research and Applications)atmospheric reanalysis data were used to validate the model reliability.The Global Zenith Tropospheric Delay Piecewise(GZTD-P)model has excellent performance compared with the Global Pressure and Temperature(GPT3)model.Validated at radiosonde stations,the performance of the GZTD-P model was improved by 0.96 cm(23%)relative to the GPT3 model.Validated with MERRA-2 data,the quality of the GZTD-P model is improved by 1.8 cm(50%)compared to the GPT3 model,showing better accuracy and stability.The ZTD vertical adjustment model with different resolutions was established to enrich the model's applicability and speed up the process of tropospheric delay calculation.By providing model parameters with different resolutions,users can choose the appropriate model according to their applications.

关键词： Piecewise function Vertical adjustment ZTD GNSS Tropospheric delay

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Impacts of the Urban Spatial Landscape in Beijing on Surface and Canopy Urban Heat Islands

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Journal of Meteorological Research 2022年第6期36卷 882-899页

作者： Yonghong LIU Yongming XU Yeping ZHANG Xiuzhen HAN Fuzhong WENG Chunyi XUAN Wenjun SHU CMA Earth System Modeling and Prediction centre China Meteorological Administration(CMA)Beijing 100081 State Key Laboratory of Severe Weather Chinese Academy of Meteorological SciencesChina Meteorological AdministrationBeijing 100081 School of Remote Sensing and geomatics Engineering Nanjing University of Information Science&TechnologyNanjing 210044 national Satellite Meteorological centre China Meteorological AdministrationBeijing 100081 Beijing Municipal Climatecentre Beijing Meteorological ServiceBeijing 100089

How does the urban spatial landscape(USL)pattern affect the land surface urban heat islands(SUHIs)and canopy urban heat islands(CUHIs)?Based on satellite and meteorological observations,this case study compares the impacts of the USL pattern on SUHI and CUHI in the central urban area(CUA)of Beijing using the satellite land-surface-temperature product and hourly temperature data from automatic meteorological stations from 2009 to 2018.Eleven USL metrics—building height(BH),building density(BD),standard deviation of building height(BSD),floor area ratio(FAR),frontal area index(FAI),roughness length(RL),sky view factor(SVF),urban fractal dimension(FD),vegetation coverage(VC),impervious coverage(IC),and albedo(AB)—with a 500-m spatial resolution in the CUA are extracted for comparative analysis.The results show that SUHI is higher than CUHI at night,and SUHI is only consistent with CUHI at spatial-temporal scales at night,particularly in winter.Spatially,all 11 metrics are strongly correlated with both the SUHI and CUHI at night,with stronger correlation between most metrics and SUHI.VC,AB,and SVF have the greatest impact on both the SUHI and CUHI.High SUHI and CUHI values tend to appear in areas with BD≥0.26,VC≤0.09,AB≤0.09,and SVF≤0.67.In summer,most metrics have a greater impact on the SUHI than CUHI;the opposite is observed in winter.SUHI variation is affected primarily by VC in summer and by VC and AB in winter,which is different for the CUHI variation.The collective contribution of all 11metrics to SUHI spatial variation in summer(61.8%)is higher than that to CUHI;however,the opposite holds in winter and for the entire year,where the cumulative contribution of the factors accounts for 66.6%and 49.6%,respectively,of the SUHI variation.

关键词： surface urban heat island canopy urban heat island vegetation coverage albedo sky view factor building density Beijing

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3D visualization model and key techniques for digital mine

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中国有色金属学会会刊：英文版 2011年第S3期21卷 748-752页

作者： JIN Bao-xuan1,FANG Yuan-min2,SONG Wei-wei2 1. Yunnan Provincial geomatics centre, Kunming 650034, china 2. Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093, china Yunnan Provincial geomatics centre Kunming 650034 China Faculty of Land Resource Engineering Kunming University of Science and Technology Kunming 650093 China

Digital mine is the inevitable outcome of the information processing, and is also a complicated system engineering. Firstly, for the 3D visualization application of the digital mine, the ground and underground integrative visualization framework model was proposed based on the mine entity database. So, the visualization problem was availably resolved, as well as the professional analytical ability was improved. Secondly, aiming at the irregularities, non-uniformity, dynamics of mine entities, mix modeling method based on the entity character was put forward, in which 3D expression of mine entities was realized. Lastly, the 3D visualization project for a copper mine was experimentally studied. Satisfactory results were acquired, and the rationality of visualization model and feasibility of 3D modeling were validated.

关键词： digital mine three dimension visualization framework model spatial data modeling

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