On simulation of precise orbit determination of HY-2 with centimeter precision based on satellite-borne GPS technique

The HY-2 satellite carrying a satellite-borne GPS receiver is the first Chinese radar altimeter satellite, whose radial orbit determination precision must reach the centimeter level. Now HY-2 is in the test phase so that the observations are not openly released. In order to study the precise orbit determination precision and procedure for HY-2 based on the satellite- borne GPS technique, the satellite-borne GPS data are simulated in this paper. The HY-2 satellite-borne GPS antenna can receive at least seven GPS satellites each epoch, which can validate the GPS receiver and antenna design. What＇s more, the precise orbit determination processing flow is given and precise orbit determination experiments are conducted using the HY-2-borne GPS data with both the reduced-dynamic method and the kinematic geometry method. With the 1 and 3 mm phase data random errors, the radial orbit determination precision can achieve the centimeter level using these two methods and the kinematic orbit accuracy is slightly lower than that of the reduced-dynamic orbit. The earth gravity field model is an important factor which seriously affects the precise orbit determination of altimeter satellites. The reduced-dynamic orbit determination experiments are made with different earth gravity field models, such as EIGEN2, EGM96, TEG4, and GEMT3. Using a large number of high precision satellite-bome GPS data, the HY-2 precise orbit determination can reach the centimeter level with commonly used earth gravity field models up to above 50 degrees and orders.

A new interpolation method based on satellite physical character in using IGS precise ephemeris

Due to the deficiency of sliding Lagrange polynomial interpolation, the author proposes a new interpolation method, which considers the physical character of satellite movement in coordinate transformation and reasonable selection of interpolation function. Precision of the two methods is compared by a numerical example. The result shows that the new method is superior to the sliding Lagrange polynomial interpolation in interpolation and extrapolation, especially in extrapolation that is over short time spans.

High Precision Orbit Determination of CHAMP Satellite

The precision orbit determination of challenging minisatellite payload(CHAMP) satellite was done based on position and navigation data analyst(PANDA) software which is developed in Wuhan University, using the onboard GPS data of year 2002 from day 126 to 131. The orbit accuracy was assessed by analyzing the difference from GFZ post-processed science orbits (PSO), the GPS carrier and pseudo-range data residuals and the satellite laser ranging (SLR) residuals.

Research on HJ-1A/B satellite data automatic geometric precision correction design

Developed independently by China,HJ-1A/B satellites have operated well on-orbit for five years and acquired a large number of high-quality observation data.The realization of the observation data geometric precision correction is of great significance for macro and dynamic ecological environment monitoring.The paper analyzed the parameter characteristics of HJ-1 satellite and geometric features of HJ-1 satellite level 2 data(systematic geo- corrected data).Based on this,the overall HJ- 1 multi- sensor geometric correction flow and charge-coupled device(CCD) automatic geometric precision correction method were designed.Actual operating data showed that the method could achieve good result for automatic geometric precision correction of HJ-1 satellite data,automatic HJ-1 CCD image geometric precision correction accuracy could be achieved within two pixels and automatic matching accuracy between the images of same satellite could be obtained less than one pixel.

Reference satellite selection method for GNSS high-precision relative positioning

Selecting the optimal reference satellite is an important component of high-precision relat/ve positioning because the reference satellite directly influences the strength of the normal equation. The reference satellite selection methods based on elevation and positional dilution of precision （PDOP） value were compared. Results show that all the above methods cannot select the optimal reference satellite. We introduce condition number of the design matrix in the reference satellite selection method to improve structure of the normal equation, because condition number can indicate the ill condition of the normal equation. The experimental results show that the new method can improve positioning accuracy and reliability in precise relative positioning.

Improving the spaceborne GNSS-R altimetric precision based on the novel multilayer feedforward neural network weighted joint prediction model

Global navigation satellite system-reflection(GNSS-R)sea surface altimetry based on satellite constellation platforms has become a new research direction and inevitable trend,which can meet the altimetric precision at the global scale required for underwater navigation.At present,there are still research gaps for GNSS-R altimetry under this mode,and its altimetric capability cannot be specifically assessed.Therefore,GNSS-R satellite constellations that meet the global altimetry needs to be designed.Meanwhile,the matching precision prediction model needs to be established to quantitatively predict the GNSS-R constellation altimetric capability.Firstly,the GNSS-R constellations altimetric precision under different configuration parameters is calculated,and the mechanism of the influence of orbital altitude,orbital inclination,number of satellites and simulation period on the precision is analyzed,and a new multilayer feedforward neural network weighted joint prediction model is established.Secondly,the fit of the prediction model is verified and the performance capability of the model is tested by calculating the R2 value of the model as 0.9972 and the root mean square error(RMSE)as 0.0022,which indicates that the prediction capability of the model is excellent.Finally,using the novel multilayer feedforward neural network weighted joint prediction model,and considering the research results and realistic costs,it is proposed that when the constellation is set to an orbital altitude of 500 km,orbital inclination of 75and the number of satellites is 6,the altimetry precision can reach 0.0732 m within one year simulation period,which can meet the requirements of underwater navigation precision,and thus can provide a reference basis for subsequent research on spaceborne GNSS-R sea surface altimetry.

BDS PPP技术在云南民航通信导航应用中的探索

北斗卫星导航系统(BDS)是我国重要空间战略基础设施。为探究北斗精密单点定位(BDS PPP)技术在云南地区民航通信导航中的应用前景,本文基于云南4个地基北斗站动态和静态结果进行评估。静态结果显示,北斗静态定位在北向、东向和天向误差平均为2.1 mm、2.2 mm和5.7 mm,相当于6.5 mm三维定位误差;动态结果显示,北斗动态定位在北向、东向和天向误差平均为0.8 cm、1.0 cm和2.4 cm,相当于2.7 cm三维定位误差。此外,利用北斗系统进行静态和动态定位精度均略优于GPS,可能与北斗系统在我国可见卫星数更充足有关。本文实验结果在一定程度上证明了高精度的BDS PPP技术在云南地区民航通信导航中的应用前景。

GPS/Galieo/BDS多频多模PPP定位性能评估

全球导航卫星系统(GNSS)的快速发展提供了多样化的数据,多频多模精密单点定位(PPP)是今后定位的重要趋势。现对4种不同组合(GPS+BDS/GPS+Galieo/BDS+Galieo/GPS+Galieo+BDS)多频多模PPP定位性能进行评估,借助MGEX跟踪站中12个观测站60d观测数据进行静态、动态实验。结果表明,4种不同组合多频多模PPP结果均为厘米级,GPS+BDS、GPS+Galieo和BDS+Galieo双系统组合定位在N、E、U方向定位精度基本相当,且在U方向定位精度最差,三系统(GPS+Galieo+BDS)PPP结果可提高静态、动态定位精度,其中静态定位在N、E、U方向上的平均定位精度分别提升10.98%、11.82%、9.18%,动态定位在N、E、U方向上平均定位精度分别提升10.96%、7.52%、8.23%,多频多模PPP对城市复杂环境定位精度有提升效果。

水田卫星平地机的研究进展

在现代农业中,土地平整作业的精度和效率直接影响着作物的生长质量,尤其在水田作业中尤为重要。卫星平地技术作为一种新型的精准土地平整手段,利用卫星导航系统,通过高精度的定位与实时数据传输,实现了对平地作业的精确控制。这一技术相较于传统的人工经验或简单机械操作,能够显著提高作业精度,克服地势复杂带来的挑战,尤其在大范围、起伏较大的地块上表现突出。近年来,卫星平地技术已在国内外取得了显著成果,尤其在提高土地利用效率、减少水资源浪费和增加作物产量方面展现了巨大潜力。本文深入探讨水田卫星平地技术的原理、发展现状及未来趋势,为农业现代化提供理论支持与实践指导。

BDS三频双无电离层组合PPP定位性能评估

为了对不同组合北斗卫星导航系统(BDS)三频双无电离层精密单点定位(PPP)的性能进行评估,推导出三频双无电离层组合PPP的数学模型,利用MGEX跟踪站中的5个观测站连续30d的观测数据进行静态、动态实验分析。实验结果表明,5个测站静态、动态PPP结果均显示为:N、E方向的定位精度相当,在U方向的定位精度较差;静态PPP模型在U方向上的误差优于3.0cm,在N方向上的误差优于1.5cm,在E方向上的误差优于2cm;动态PPP模型在U方向上的误差优于6.0cm,在N方向上的误差优于3.0cm,在E方向上的误差优于4.0cm;B1I-B2a-B3I、B1I-B2b-B3I、B1C-B2a-B3I和B1C-B2b-B3I四种三频组合在静态、动态PPP结果在三维N、E、U方向上的定位精度基本相当。

北斗卫星导航单点定位方法研究

目前,北斗卫星导航系统(BDS)在单点定位模式下,如忽视差分码偏差和误差修正方式不当,会导致定位性能下降。为了改善BDS的单点定位性能,创新性地定义与估计差分码偏差,检验差分码偏差估计值精度,深入分析精密单点定位误差,从而筛选接收机钟差与卫星钟差。应用非组合方式获取修正值,计算电离层延迟与对流层延迟以消除对冲值。基于差分码偏差估计值、误差修正值和大气参数消除对冲值,获取接收机伪距最终观测值。通过解算观测值获得接收机的位置信息(经纬度),实现北斗卫星导航单点定位。试验结果表明,在不同试验工况背景下,所获得的定位结果与接收机实际位置保持一致,并且定位收敛时间最小值为3 s。该方法应用性能较佳。

BDGIM模型对BDS-3/GPS单频精密单点定位性能影响分析

随着北斗全球导航卫星系统(BDS-3)的建成和北斗全球广播电离层延迟修正模型(BDGIM)的提出,基于低成本单频接收机的精密单点定位(PPP)性能有望得到提升。本文采用全球均匀分布的20个MGEX测站观测数据,分析BDGIM模型在全球范围内对BDS-3/GPS单频PPP定位性能的影响。结果表明,采用BDGIM模型的GPS单频PPP三维定位精度优于1.0m,随着BDS-3观测值的引入,GPS单频PPP三维定位精度可提高9.1%;在BDS-3/GPS组合单频PPP中,基于BDGIM模型的三维定位精度比GPS Klobuchar模型高出26.8%;当采用GIM模型时,双系统组合单频PPP定位性能达到最优,其三维定位精度优于0.5m,说明当前BDS-3/GPS单频定位已具备稳定、连续的分米级服务能力。

Magnetic field data processing methods of the China Seismo-Electromagnetic Satellite

The High Precision Magnetometer(HPM) on board the China Seismo-Electromagnetic Satellite(CSES) allows highly accurate measurement of the geomagnetic field; it includes FGM(Fluxgate Magnetometer) and CDSM(Coupled Dark State Magnetometer)probes. This article introduces the main processing method, algorithm, and processing procedure of the HPM data. First, the FGM and CDSM probes are calibrated according to ground sensor data. Then the FGM linear parameters can be corrected in orbit, by applying the absolute vector magnetic field correction algorithm from CDSM data. At the same time, the magnetic interference of the satellite is eliminated according to ground-satellite magnetic test results. Finally, according to the characteristics of the magnetic field direction in the low latitude region, the transformation matrix between FGM probe and star sensor is calibrated in orbit to determine the correct direction of the magnetic field. Comparing the magnetic field data of CSES and SWARM satellites in five continuous geomagnetic quiet days, the difference in measurements of the vector magnetic field is about 10 nT, which is within the uncertainty interval of geomagnetic disturbance.

A three-dimensional positioning method based on three satellites

A three-dimensional positioning method for global positioning system(GPS)receivers based on three satellites was proposed.In the method,the measurement equation used for positioning calculation was expanded by means of two measures.In this case,the measurement equation could be solved,and the function of positioning calculation could be performed.The detailed steps of the method and how to evaluate the positioning precision of the method were given,respectively.The positioning performance of the method was demonstrated through some experiments.It is shown that the method can provide the three-dimensional positioning information under the condition that there are only three useful satellites.

New Regional Satellite Positioning Constellation Scheme Discussion

The characteristics of present “Beidou” satellite positioning system are analyzed. In order to perfect our country regional satellite positioning system, the idea of “Beidou” geosychronous earth orbit （GEO） satellites combined with some middle earth orbit （MEO） satellites constellation is put forward. The details of general satellite constellation optimized method are described, using this method the multiple positioning constellation design results are gained. And those results belong to two type of sehems, one is 2 GEO plus some MEO satellites and the other is 3 GEO plus some MEO satellites. Through simulation and comparison, among those multiple design results, final optimized regional positioning constellation is given. In order to check the chosen constellation cover performance, the position dilution of preeision（PDOP） is calculated, and with ,satellite constellation simulation software Satlab many coverage performances of the chosen constellation substellar point track, elevation, azimuth and visible satellites number changing situation are also simulated.

Precision Analysis and Parameter Inversion in the Stepwise Deployment of a Mixed Constellation

Along with the planning and implementation of the COMPASS satellite navigation system, first as a regional then a global system, there is a need to probe into the positioning performance of the mixed constellation in the stepwise deployment scheme. Both the increase in the number of the MEO satellites in the constellation and the decrease in the user equivalent ranging error of the GEO satellites will improve the overall positioning performance of the system. Using the weighted dilution of precision as the evaluation criterion, we study the theoretical relationship between the internal parameters and the positioning precision during the evolution of the system. On one hand, the influence of each factor on the positioning performance is quantitatively analyzed under the circumstances of various constellation deployment schemes and user types. On the other hand, for given positioning performance indices, simulations are carried out to present the inversion of parameters. Our conclusions provide useful suggestions to the system design and stepwise deployment scheme of satellites.

Solar Radiation Pressure Modeling and Application of BDS Satellites

Solar radiation pressure(SRP)model is the basis of high precise orbit determination and positioning of navigation satellites.At present,it is common to see the study of SRP model of BDS satellites.However,the establishment and application of a comprehensive analytical SRP model based on satellite physical parameters are rare.Different from other conservative forces and non-conservative forces,SRP is closely related to the satellite’s physical parameters and in-orbit state.On the basis of the physical mechanism of solar radiation,BDS satellite physical parameters,in-orbit attitude control mode,and so on,a comprehensive analytical model has been studied in this paper.Based on precise ephemeris and satellite laser ranging(SLR)data,the precision of a comprehensive analytical model has been verified.And the precision of orbit determination is at the decimeter level using this comprehensive analytical SRP model.According to the satellite conservation theorem of angular momentum and change of in-orbit telemetry parameters,the difference between a comprehensive analytical model and the actual in-orbit interference force has been analyzed and calculated.The addition of empirical items on the comprehensive analytical model has been proposed.SLR validations demonstrated that the orbit precision of BDS C08 and C10 can be achieved at 0.078 m and 0.084 m respectively.Compared with using the improved CODE empirical model,precision orbit accuracy of them has increased by 0.021 m and 0.045 m respectively.

A 16-parameter GEO Broadcast Ephemeris

Currently,the broadcast ephemerides used in GEOs are same as those of the MEOs and IGSOs in the BeiDou navigation constellation.However,a trade-off strategy,i.e.an orbital inclination of 5°rotation,is needed in the fitting algorithm to solve the ephemeris parameters as well as the user satellite position computation for GEOs.Based on the standard broadcast ephemerides,the representations of both the orbit and its perturbation were revised according to the second class of nonsingular orbital elements.In this research,a 16-parameter broadcast ephemeris is presented specifically for GEOs,and user satellite position computation formulas were derived correspondingly.Fit simulations show that the root of mean squares(RMS)of user range error(URE)with two hour and three hour data sets are better than 0.05 m and 0.1 m,respectively.

Modeling and Prediction of Inter-System Bias for GPS/BDS-2/BDS-3 Combined Precision Point Positioning

The combination of Precision Point Positioning(PPP)with Multi-Global Navigation Satellite System(MultiGNSS),called MGPPP,can improve the positioning precision and shorten the convergence time more effectively than the combination of PPP with only the BeiDou Navigation Satellite System(BDS).However,the Inter-System Bias(ISB)measurement of Multi-GNSS,including the time system offset,the coordinate system difference,and the inter-system hardware delay bias,must be considered for Multi-GNSS data fusion processing.The detected ISB can be well modeled and predicted by using a quadratic model(QM),an autoregressive integrated moving average model(ARIMA),as well as the sliding window strategy(SW).In this study,the experimental results indicate that there is no apparent difference in the ISB between BDS-2 and BDS-3 observations if B1I/B3I signals are used.However,an obvious difference in ISB can be found between BDS-2 and BDS-3 observations if B1I/B3I and B1C/B2a signals are used.Meanwhile,the precision of the Predicted ISB(PISB)on the next day of all stations is about 0.1−0.6 ns.Besides,to effectively utilize the PISB,a new strategy for predicting the PISB for MGPPP is proposed.In the proposed strategy,the PISB is used by adding two virtual observation equations,and an adaptive factor is adopted to balance the contribution of the Observed ISB(OISB)and the PISB to the final estimations of ISB.To validate the effectiveness of the proposed method,some experimental schemes are designed and tested under different satellite availability conditions.The results indicate that in open sky environment,the selective utilization of the PISB achieves almost the same positioning precision of MGPPP as the direct utilization of the PISB,but the convergence time of MGPPP is reduced by 7.1%at most in the north(N),east(E),and up(U)components.In the blocked sky environment,the selective utilization of the PISB contributes to more significant improvement of the positioning precision and convergence time than that in the open sky environment.Compared with the direct utilization of the PISB,the selective utilization of the PISB improves the positioning precision and convergence time by 6.7%and 12.7%at most in the N,E,and U components,respectively.

Progress on the use of satellite technology for gravity exploration

In this paper, the technological progress on Chinese gravity exploration satellites is presented. Novel features such as ultra-stable structure, high accurate thermal control, drag-free and attitude control, micro-thrusters, aerodynamic configuration, the ability to perform micro-vibration analyses, microwave ranging system and mass center trimmer are described.