Quality assessment of onboard GPS receiver and its combination with DORIS and SLR for Haiyang 2A precise orbit determination

The GPS,DORIS,and SLR instruments are installed on Haiyang 2A(HY2A)altimetry satellite for Precise Orbit Determination(POD).Among these instruments,the codeless GPS receiver is the state-of-art Chinese indigenous onboard receiver,and it is the first one successfully used for Low Earth Orbit(LEO)satellite.Firstly,the contribution assesses the performance of the receiver through an analysis of data integrity,numbers of all tracked and valid measurements as well as multipath errors.The receiver generally shows good performance and quality despite a few flaws.For example,L2 observations are often missing in low elevations,particularly during the ascent of GPS satellites,and the multipath errors of P1 show a slightly abnormal pattern.Secondly,the PCO(Phase Center Offset)and PCV(Phase Center Variation)of the antenna of the GPS receiver are determined in this contribution.A significant leap for Z-component of PCO up to-1.2 cm has been found on 10 October 2011.Thirdly,the obtained PCO and PCV maps are used for GPS only POD solutions.The post-fit residuals of ionosphere-free phase combinations reduce almost 50%,and the radial orbit differences with respect to CNES(Centre National d’Etudes Spatiales)Precise Orbit Ephemeris(POEs)improve about 13.9%.The orbits are validated using the SLR data,and the RMS of SLR Observed minus Computed(O-C)residuals reduces from 17.5 to 15.9 mm.These improvements are with respect to the orbits determined without PCO and PCV.Fourthly,six types of solutions are determined for HY2A satellite using different combinations of GPS,DORIS,and SLR data.Statistics of SLR O-C residuals and cross-comparison of orbits obtained in the contribution and the CNES POEs indicate that the radial accuracy of these orbits is at the 1.0 cm level for HY2A orbit solutions,which is much better than the scientific requirements of this mission.It is noticed that the GPS observations dominate the achievable accuracy of POD,and the combination of multiple types of observations can reduce orbit errors caused by data gaps and maintain more stable and continuous orbits.     

On precise orbit determination of HY-2 with space geodetic techniques

As the first radar altimetric satellite of China, HY-2 requires the precise orbit determination with a higher accuracy than that of other satellites. In order to achieve the designed radial orbit with the accuracy better than 10 cm for HY-2, the methods of precise orbit determination for HY-2 with the centimeter-level accuracy based on space geodetic techniques (DORIS, SLR, and satellite-borne GPS) are studied in this paper. Perturbations on HY-2 orbit are analyzed, in particular those due to the non-spherical gravitation of the earth, ocean tide, solid earth tide, solar and earth radiation, and atmospheric drag. Space geodetic data of HY-2 are simulated with the designed HY-2 orbit parameters based on the orbit dynamics theory to optimize the approaches and strategies of precise orbit determination of HY-2 with the dynamic and reduced-dynamic methods, respectively. Different methods based on different techniques are analyzed and compared. The experiment results show that the nonspherical perturbation modeled by GGM02C causes a maximum perturbation, and errors caused by the imperfect modeling of atmospheric drag have an increasing trend on T direction, but errors are relatively stable on the other two directions; besides, the methods with three space geodetic techniques achieve the radial orbit with the precision better than 10 cm.     

基于星载GPS的HY-2卫星高精度精密定轨模拟研究(英文)

HY-2卫星是我国第一颗测高卫星,其径向定轨精度要求厘米量级,搭载了星载GPS接收机。目前HY-2还处于测试阶段,没有公布观测数据。为了确定基于星载GPS的HY-2精密定轨流程及其定轨精度,本文模拟了HY-2卫星星载GPS观测数据,结果表明HY-2星载GPS天线每个历元至少观测7颗GPS卫星。给出了基于星载GPS的精密定轨流程,分别采用简化动力学方法和动态几何法进行了精密定轨实验。对于相位1mm和3mm随机误差的相位观测数据,简化动力学法和动态几何法定轨都能够实现厘米量级的径向精密定轨,几何法定轨精度略低于简化动力定轨。地球重力场模型是影响HY-2卫星精密定轨的重要因素,本文对不同阶次的重力场模型EIGEN2、EGM96、TEG4和GEMT3进行了简化动力学定轨实验,高于50阶次的重力场模型都能够实现厘米级径向精密定轨,主要原因在于大量的高精度星载GPS观测数据和重力场模型精度的提高。     

Thermospheric mass density derived from CHAMP satellite precise orbit determination data based on energy balance method

In this article, the energy balance method is used to retrieve thermospheric mass density from CHAMP satellite precise orbit determination(POD) data during 2007–2009. The retrieved thermospheric mass densities are compared with those from accelerometer data and an empirical model. The main conclusions are as follows:(1) Thermospheric mass density can be retrieved from POD data by the energy balance and semi-major axis decay methods, whose results are consistent.(2) The accuracy of the retrieved densities depends on the integration time period, and the optimal period for CHAMP density retrieval from POD data is about 20 minutes.(3) The energy balance method can be used to calibrate accelerometer data.(4) The accuracy of retrieving thermospheric density from POD data varies with satellite altitude and local time.     

基于DORIS数据的JASON-2卫星精密定轨分析

高精度的卫星轨道确定是卫星应用的基础和保证,本文以新一代DORIS接收机观测数据DORIS 3.0的相位观测数据为基础,研究了相位观测数据与传统的DORIS距离变化率数据的转换方法,并以JASON-2卫星为例,基于卫星动力学定轨原理,分析了不同数据类型、不同定轨方案得到的卫星轨道精度.结果表明,1)利用3天弧段的DORIS 2.2格式距离变化率数据和数据文件提供的相位中心偏差改正,或者采用模型对天线相位中心偏差进行改正并同时对地面测站进行偏心改正时,两种方案得到的轨道三维位置精度基本一致,均优于8.7cm,说明新一代DORIS接收机相位中心稳定,变化较小,采用模型进行偏差修正完全能够满足定轨精度要求.2)采用3.0格式的DORIS数据以及天线相位中心偏差修正模型和地面测站偏心改正模型时,得到的卫星定轨精度略有降低,大约为9.2cm;SLR校核残差约为6.5cm(均方根误差).3)采用2.2和3.0两种格式的DORIS数据,利用不同的定轨方案对JASON-2卫星进行精密定轨,均可以达到2cm左右的径向定轨精度,不同的定轨方案对径向定轨精度的影响可忽略不计.因此,对于最关心卫星径向定轨精度的海洋测高卫星而言,采用本文的数据格式转换方法和定轨方案,完全可以满足其定轨任务需求.     

卫星精密定轨与重力场建模的同解法

现代卫星跟踪卫星重力测量技术显著改善了地球重力场模型的中长波段信号,并拓展了重力场模型在相关科学研究中的应用.同解法作为卫星重力观测数据的主要处理手段之一,国内一直没有实质突破.本文从基本模型和关键技术的分析出发,剖析了同解法的特点,特别是在建立同解法与几何法(运动学)定轨、一般动力学方法关系的基础上,给出了一种同解法的实现路线.在已有的精细数据预处理和并行计算研究基础上,结合GRACE卫星的实测飞行数据,在国内首次获得了真实卫星任务数据条件下的同解法结果,并进行了动力法轨道的外部质量检核、卫星非保守力分析、重力场模型的GPS水准检验等.利用卫星激光测距数据检验,卫星精密轨道的径向精度优于2cm,同时建立了质量可靠的卫星重力场模型,充分展示了同解法的优点.数值结果及其分析表明,本文所提的同解法实施方案合理可行,已经掌握了实现同解法的关键技术,获得了从仿真研究到实际飞行数据处理的新进展.最后,本文对同解法今后的发展思路,以及如何进一步挖掘同解法的潜力,提出了见解和今后的工作方向.     

Synthetically adaptive robust filtering for satellite orbit determination

The precise orbit information is the premise of the application of satellite, and the precise orbit deter- mination includes dynamic and geometric methods. The dynamic method estimates the position and veloc-ity of a satellite at one epoch by extending the obser-vational arc in order to include more observations of different epochs in it. It is realized by integrating the dynamic equation of the satellite so that the observa-tions at different epochs are related to the particular state. The dy…     

GRACE卫星精密定轨随机模型精化

合理的随机模型是确定高精度卫星轨道的前提条件,目前广泛应用于地面观测数据的随机模型主要有高度角模型和载噪比模型,本文通过对GRACE卫星实测数据的分析表明上述随机模型均不能很好地描述GRACE卫星星载GPS观测值的噪声特点,为此,文中提出了扩展的高度角模型和扩展的载噪比随机模型.利用自主研发的精密定轨软件,分别采用高度角模型、扩展的高度角模型、载噪比模型、扩展的载噪比模型对GRACE卫星进行了轨道确定.数值结果表明:(1)高度角模型的运动学轨道径向精度为3.4 cm,扩展的高度角模型的为3.3 cm;(2)载噪比模型的运动学轨道径向精度为4.9 cm,扩展的载噪比模型的则为3.4 cm,精度提高了1.5 cm.经比较分析,文中提出的扩展的高度角模型和载噪比模型能更好地描述GRACE卫星观测值噪声特点,并能取得更高的卫星定轨精度.     

基于轨道扰动引力谱分析的方法确定低低观测重力卫星反演重力场的空间分辨率

基于低低卫-卫跟踪重力卫星的轨道特性,从垂直和水平两个方向计算了重力卫星高空扰动引力,并根据其谱特性及星载加速度的测量噪声水平分析了重力卫星能反演重力场的阶数.利用EGM96重力场模型分别计算了400 km、450 km和500 km 轨道高度处重力卫星受到的扰动引力谱及扰动引力谱的平均量级,分析其垂直特性表明:在三个轨道高度处能分别能反演150、140和130阶的重力场模型.利用两颗同轨重力卫星相距220 km的特性,计算了400 km、450 km和500 km 轨道高度处纬度相差2°的两颗卫星纬向扰动引力差,即扰动引力水平分量,分析其谱特性,表明:重力卫星能反演至117阶的地球重力场模型.     

固定非差整数模糊度的PPP快速精密定位定轨

从GPS基本观测模型出发,给出并推导了分离相位小数偏差求解非差整数模糊度的精密单点定位数学模型和算法.利用少量IGS跟踪站组成服务端观测网计算未检校的相位小数偏差改正信息,用于改正用户端接收机的相位观测值,实现了固定非差整数模糊度的快速精密单点定位与定轨.试验结果表明: 利用30 min的地面动态或静态观测数据进行精密单点定位,非差模糊度固定成整数后,其定位结果较PPP浮点解有明显改善,水平方向提高了近一个数量级,可达到1 cm甚至毫米级的精度;高程方向与对流层延迟解算精度也改善了20%~60%.与浮点解相比,固定解能显著改善PPP的定轨精度,仅用15 min的短弧段观测数据,切向与法向的定轨精度可达到1 cm左右;径向方向为3~5 cm左右,较浮点解定轨精度改善了50%~70%.因此,固定非差整数模糊度后的PPP能够满足毫米至厘米级的快速精密定位和定轨的要求,这在GPS(准)实时应用与服务中具有很好的应用前景.     

Estimation of the elastic earth parameters using the SLR LAGEOS 1 and LAGEOS 2 data

We present results for the global elastic parameters (k ₂, k ₃) and (h ₂, l ₂) derived from the analysis of Satellite Laser Ranging (SLR) data. The SLR data for two satellites, LAGEOS 1 and LAGEOS 2, collected over a period of two years, from 1 January 2005 to 1 January 2007, from 18 globally distributed ground stations are analyzed using different approaches. The analysis is performed for the two satellites jointly, and the four elastic parameters are estimated. We carry out a sequential analysis and study the stability of the estimates as a function of the length of the data set used. The adjusted final values for k ₂ (0.3011±0.0001) and k ₃ (0.0896±0.0037) and those for h ₂ (0.6146±0.0006) and l ₂ (0.0883±0.0003) for LAGEOS 1 and LAGEOS 2 tracking data are compared to the estimates derived in other studies.     

Cloud tracking using satellite data for predicting the probability of heavy rainfall events in the Mediterranean area

The use of cloud tracking techniques and storm identification procedures is proposed in this paper with the aim of predicting the evolution of cloud entities associated with the highest rainfall probability within a given meteorological scenario. Suitable algorithms for this kind of analysis are based on the processing of digital images in the thermal infrared (IR) band from geostationary satellites: a selection of such algorithms is described in some detail together with a few real case applications. Three heavy rainfall events have been selected for this purpose with reference to the extreme meteorological situation observed during Fall 1992 and 1993 over the Mediterranean area. A window from 30 to 60 °N and from 20 °W to 30 °E has been identified for the analysis of data from the radiometer on board the ESA Meteosat platform. In conclusion, the suitability of cloud tracking techniques for predicting the probability of heavy rainfall events is discussed provided that the former are associated with proper modeling of small scale rainfall distribution.     

Improvement of ERS-1 orbits using along-track accelerations from DORIS data on SPOT2

In long-arc precise orbit determinations of altimetric satellites such as ERS-1, large errors may occur from mismodelling of aerodynamic drag and solar radiation pressure. Such surface forces for non-spherical satellites require accurate modelling of the effective area and particle-surface interactions, but the dominant source of error is neutral air density as derived from thermospheric models for aerodynamic drag. Several techniques can be employed to alleviate air-drag mismodelling but all require the solution of additional parameters from the tracking data. However, for ERS-1 the sparsity of laser range data limits the application of such empirical techniques. To overcome this, use can be made of the dense DORIS Doppler tracking for SPOT2 which is in a similar orbit to ERS-1. A recent investigation by CNES examined the use of drag scale factors from SPOT2 to constrain the ERS-1 orbit. An improvement to that methodology is to consider along-track mismodelling as observed by timing errors in the Doppler data for each pass of SPOT2. The along-track correction to the acceleration as derived from SPOT2 can then be applied to ERS-1 orbits, solving for a scale factor to absorb systematic errors - particularly that arising from the 50 km altitude difference. Results are presented of the associated improvement in ERS-1 orbits as derived from concurrent SPOT2 arcs. It will be seen that the procedure not only improves the laser range fit, but more importantly, leads to more precise radial positioning as evident in the altimeter and crossover residuals.     

Evapotranspiration in the Pampean Region using field measurements and satellite data

Evapotranspiration (LE) is an important factor for monitoring crops, water requirements, and water consumption at local and regional scale. In this paper, we applied the semi-empirical model to estimate the daily latent heat flux (LE_d = Rn_d + A − B(Ts − Ta)). LE_d has been estimated using satellite images (Thematic Mapper sensor) and a local dataset (incoming and outgoing short- and long-wave radiation) measured during three years. We first estimated the daily net Radiation (Rn_d) from a linear equation derived from the instantaneous net Radiation (Rn_d = CRn_i + D). Subsequently, coefficients A and B have been estimated for two different cover vegetations (pasture and soybean). For each vegetation cover, an error analysis combining Rn_d, A, B, and surface and air temperatures has been calculated. Results showed that Rn_d had good performance (nonbias and low RMSE). LE_d errors for pasture and soybean were ±28 W m⁻² and ±40 W m⁻² respectively.     

星间加速度解算模式的模拟与分析

低低卫星跟踪卫星的观测量是两低轨卫星的星间距离或星间速度,星间加速度由星间速度通过数值微分导出,用星间加速度作为观测量可以避免解算卫星运动的变分方程,简化观测方程的建立,但数值微分会使观测噪声放大,从而影响重力位的解算精度.为了定量给出星间加速度观测模式的精度,本文分析并模拟验证了数值微分公式计算星间加速度的精度,导出了基于星间加速度的一般形式的观测方程,模拟计算了基于星间加速度的重力位模型.结果表明,采用星间加速度观测模式的解算精度要明显低于星间速度观测模式的解算精度.     

基于B-spline和正则化算法的低轨卫星轨道平滑

本文提出了一个利用纯几何轨道和力模型的新算法来计算精确且相对平滑的卫星轨道. 该法将一个纯几何轨道表达为一个B-spline的线性组合,线性组合的系数可以由最小二乘法估计获得. 力模型通过计算加速度来附加约束. 为了平衡几何轨道的点位误差和加速度的不精确,一个基于“广义交互确认（GCV,generalized cross-validation）”的正则化算法运用其中. 由于B-spline的本地控制性,该方法的计算效率相当高. 本文的数值分析表明了该法的有效性. 模拟计算的结论是：带加速度约束较不带加速度约束的平滑效果好. 力模型越精确,平滑的轨道就越精确. 三个月的CHAMP实测轨道数据处理结果表明,平滑后的轨道改进了重力场模型.     

行星内部地震波及其对卫星轨道的影响

本文指出地震学在天文和行星学科里的重要作用.我们主要介绍最近提出的“潮汐—地震波共振”(tidal-seismic resonance)效应,并且讨论它对卫星轨道演化的作用.当在同步轨道以下周期运动的卫星引起的引潮力的频率和行星内部自由震荡频率吻合时,就会发生潮汐—地震波共振.此时,行星内部的地震波将被激发并引起行星表面的显著位移.升高和下降的地面会对卫星产生一个力矩从而使得卫星轨道下降.因为潮汐共振引起的动态地面位移可以比单纯引潮力引起的位移大两个数量级,所以潮汐共振会显著加速卫星下降速率.我们用我们开发的三维地震波场模拟程序AstroSeis数值计算了潮汐—地震波共振对轨道的影响,进而推测这一共振效应可能对行星早期吸积速度有显著影响.另外,因为行星内部的Q值和S波的波速对潮汐共振影响很大,未来研究微重力环境下的小行星或陨石内部地震波的速度和Q值对研究行星演化和太阳系的形成至关重要.     

Construction of the spatial-temporal model of the main geomagnetic field using satellite data

The spatial-temporal model of the geomagnetic field has been constructed using the data of the high-accuracy survey of the CHAMP German satellite, obtained during its operation from May 2001 to September 2007. The daily average spherical harmonic models calculated at an interval of four days are used as initial data in order to expand these models by the method of natural orthogonal components (NOCs). It has been indicated that the obtained NOC series rapidly converges. The secular variations, secular acceleration, and Dst variation are distinguished as individual NOC components, which makes it possible to construct the spatial-temporal field model. In addition, the models-predictions have been constructed for the year 2008 based on the candidate models of the main field and the secular variation for the year 2005, which were used to obtain the IGRF2005 international model. A comparison of the models-predictions with the model constructed for the year 2008 using our method indicated that the accuracy of our model is not lower than that of the models, obtained by other scientific groups using the traditional method.     

Estimation of the eddy-diffusion coefficients in the plasma sheet using THEMIS satellite data

We have studied the turbulent processes in the central plasma sheet using the tailward alignments of THEMIS satellites. Fluctuations of the plasma bulk velocity and corresponding eddy-diffusion coefficients were calculated using the simultaneous data obtained by THEMIS satellites situated inside the central plasma sheet between approximately 5 and 30 Earth's radii. The instantaneous profiles of eddy-diffusion coefficients show an increase with distance from the Earth in the tailward direction. This result agrees with previous statistical studies, and it is relevant for the understanding of the dynamics of the turbulent plasma sheet.     

A method for assessing lake morphometric characteristics with the use of satellite data

A method is proposed for assessing the main morphometric characteristics of lakes based on satellite data and relationships derived from the analysis of data from WORLDLAKE database.