Determination of polar motion from satellite observations

Doppler observations of U.S. Navy Navigation Satellites have been used to determine the Earth's pole position for the period 1967 to July 1972. Recent results are competitive in accuracy with astronomic results and exhibit about 0".02 agreement with astronomic pole positions. The differences are no larger than those between independent calculations of pole positions based on astronomic data (BIHvs. ILS). For a two-day span of observations made by 18 Doppler stations the uncertainty in computed pole position corresponding to random errors in observation is 0".002. However, the results have systematic errors with various frequencies which are primarily due to uncertainties in the gravity coefficients. Since these errors are independent of those producing systematic errors in astronomic results, the two techniques are complementary. Recent results of computation of polar motion based on laser observations of artificial Earth satellites have also produced results having accuracies comparable to Doppler and astronomic results. The analysis of the laser observations is based on the effect of pole position on the apparent inclination of satellite orbits; on the other hand, since the Doppler observations are made on polar orbiting satellites, they are more sensitive to errors in the component of pole position which lies in the orbit plane. As a result of this difference, biases in Doppler and laser results may be different in size or character.     

Best-fitting tri-axial earth ellipsoid parameters derived from satellite observations

Résumé De l'ensemble des coefficients harmoniques du développement du géopotentiel [3, 6, 7], calculé à partir des variations des éléments orbitaux des satellites, on a calculé les paramètres de l'ellipso?de terrestre triaxial, représentant la surface du géo?de. La solution fut effectuée par méthode analytique sous la condition du minimum de l'intégrale du carré de l'écart du rayon vecteur du géo?de et de l'ellipso?de, de même que par calcul numérique à partir des valeurs discrètes 10°×10°.

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Address: Politickych vězňů 12, Praha 1-Nové Město.     

On the determination of satellite coordinates from doppler observations

The basic task of satellite geodesy is the construction of a unified 3 or 4 dimensional world-wide geodetic network. In this frame the station position, the parameters of the Earth's gravity field, and the orbital elements of the observed satellite would be known.The satellite observations by Doppler method are independent of weather and daylight conditions; they can be done fully automatically and no accumulation of errors occurs. For these reasons, the satellite observations by Doppler methods are getting more and more weight.A simple method is given for the determination of the satellite's position using Doppler shifts observed at several stations of known coordinates.     

Forty-five years of oceanographic and meteorological observations at a coastal station in the NW Mediterranean: a ground truth for satellite observations

Ocean Dynamics - Marine and atmospheric parameters, including temperature observations from surface to 80 m (at 6 depths) are measured since September 1973 on a higher-than-weekly...     

Parameters of the normal gravity field deduced from satellite observations

Summary The parameters of the normal gravity field were deduced from the harmonic coefficients[3, 4] upto n=6 and compared with the parameters used hitherto. The symbols used are the same as in papers[5, 6, 8] with which this paper connects up.     

Geopotential and gravity on external surfaces as derived from satellite observations

Résumé On déduit les expressions donnant le géopotentiel et la pesanteur sur un ellipso?de triaxial extérieur, de même que la pesanteur sur la surface de niveaux extérieure et les valeurs moyennes intégrales de ces grandeurs. On discute la convergence des séries et l'usage des formules déduites à la détermination des paramètres de la forme du corps terrestre.

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Address: Politickych vězŭů 12, Praha 1-Nové Město.     

Variations in the stratospheric ozone field inferred from Nimbus satellite observations

The ultraviolet Earth radiance data from the backscatter ultraviolet experiment on Nimbus 4 have been inverted to infer ozone profiles using a single Rayleigh scattering model. Two methods of solution give essentially the same results. Comparison of these profiles with simultaneous rocket sounding data shows satisfactory agreement at low and middle latitudes.Vertical cross-sections of ozone mixing ratio along the orbital tracks indicate that while the gross characteristics of the ozone field above 10 mb are under photochemical control, the influence of atmospheric motions can be found up to the 4 mb level.     

高亚洲冰川质量变化趋势的卫星重力探测

利用高亚洲地区32个Mascon,基于GRACE RL05时变重力场模型频域和空域上的两种计算方法有效分离并提取出高亚洲冰川及其毗邻地区的等效水质量变化,得到2002—2013年期间高亚洲地区更为可靠的Mascon质量变化.高亚洲冰川质量变化的空间特征是:青藏高原内陆地区以正增长为主,边缘地区以负增长为主,在藏东南的最边缘地区冰川质量损失最为严重.天山地区、帕米尔和昆仑山地区、喜马拉雅山和喀喇昆仑山地区、青藏高原内陆地区冰川质量的平均变化趋势分别为-2.8±0.9 Gt/a、-3.3±1.5 Gt/a、-9.9±2.1 Gt/a和5.0±0.8 Gt/a, 高亚洲冰川质量整体的平均变化趋势为-11.0±2.9 Gt/a.印度等北部平原地区地下水平均变化趋势为-35.0±4.2 Gt/a,该地区地下水信号泄漏是影响GRACE研究高亚洲冰川质量变化的关键因素,频域法和空域法能有效改正该地区地下水信号泄漏的影响.     

山基GPS掩星与自动气象站观测结果比较

山基GPS掩星技术可以精确获得低层大气折射率信息,其观测原理是:在高山的山顶安装GPS接收机,跟踪GPS卫星的低仰角和负仰角信号,通过载波相位的变化求出大气折射造成的弯曲角剖面,从而利用科学反演方法获得观测点高度以下的大气折射率剖面.为了对山基掩星测量数据进行验证,2005年8月1日～29日,在河北雾灵山(40.60°N,117.48°E,2118m)开展了为期一个月的山基GPS掩星观测与其他探测的时比实验.实验所用的JAVAD双频GPS接收机共工作576小时,接收机朝南观测,记录到山基掩星事件1136次,其中上升掩星621次,下降掩星515次.实验期间,在雾灵山顶利用自动气象观测仪每天24小时观测当地的温度、湿度和气压,由此可计算大气折射率.本文利用雾灵山GPS掩星实验所获得的观测数据,成功反演得到大气折射率剖面,并将所得接收机高度的折射率与雾灵山顶自动气象站观测结果进行比对,分析结果表明:山基GPS掩星和自动气象站观测结果是一致的.山基GPS掩星观测可为低层大气环境监测提供大量数据,具有潜在的应用前景.     

基于重力卫星数据监测地表质量变化的三维点质量模型法

利用卫星重力测量手段监测全球质量变化取得了巨大成功,本文基于牛顿万有引力定律在三维空间直角坐标系中导出利用重力卫星观测数据监测全球质量变化的三维点质量模型法,该方法可直接利用重力卫星的轨道和星间观测数据或时变重力场模型计算全球质量变化,由于利用卫星观测数据计算地表质量变化的向下延拓过程以及观测数据噪声的影响,需要采用合适的空间约束方程或正则化技术对解算结果进行约束或平滑处理.利用合成全球质量变化模型模拟一个月的GRACE双星轨道和星间距离变率数据计算全球质量变化,对三维点质量模型法进行分析验证,采用零阶Tikhonov正则化技术处理病态问题.结果表明,三维点质量模型法可有效用于重力卫星观测数据监测全球质量变化,为利用重力卫星观测数据监测全球质量变化提供一种可选的途径.

     

Parameters of traveling ionospheric disturbances estimated from satellite beacon observations in low-earth orbit

Based on beacon sounding the ionosphere using coherent signals of low-orbiting navigation satellites, the following parameters of medium-scale traveling ionospheric disturbances have been determined: the effective thickness of the atmospheric waveguide and the altitude of its longitudinal axis, the horizontal spatial period, the velocity, the maximum amplitudes of disturbances, and the inclination of the disturbance phase front. It has been found that the horizontal spatial period of studied disturbances increases with increasing distance to an initiating impact location and its delay. In this case the minimum value of the horizontal spatial period always exceeds ∼150 km, and the disturbance amplitude increases with increasing horizontal period and distance from the initiating disturbance location and with decreasing altitude of the main ionization maximum. All disturbance parameters are independent of the initiating impact nature. It has been found that disturbances with relative amplitudes of 0.1–0.7 are often observed. Disturbances that are registered more often travel southward, and their absolute velocities are 7–60 m/s.     

利用Satmaster软件优化青海便携卫星站链路设计

介绍链路设计的基本知识,并以青海便携应急卫星站为例,利用Satmaster软件对该站点的卫星链路进行计算,使之能够在卫星信号覆盖较差的偏远地区进行正常的卫星通信。     

芬兰海岸带水域蓝藻水华遥感监测

MODIS-Terra和MERIS数据被用于芬兰湾蓝藻水华的监测,并对两者的性能进行了比较.研究结果表明:MODIS-Terra 波段设置主要针对一类大洋水体,缺乏预警藻蓝素的有效波段;MERIS传感器设置了620nm和665nm波段,基本对应藻蓝素的吸收峰(630nm)和反射峰(650nm),具有蓝藻水华探测的潜力,但在藻华未成型之前,海岸带水体不同优势藻类具有相似的叶绿紊特征,较难辨别蓝藻水华.总的来说,MODlS和MERIS数据比较困难实现蓝藻水华初期预警,但可以有效监测已成型的蓝藻水华.这一方法可以用于中国太湖或者海岸带水体藻华探测和监测研究.     

Vertical crustal motions from differential tide gauge observations and satellite altimetry in southern Italy

Our goal is to determine vertical crustal movement rates from tide gauge and satellite altimetry measurements. Tide gauges measure sea level, but as they are fixed to the crust, they sense both sea surface height variations and vertical crustal movements. The differential sea level rates of sufficiently nearby stations are a good means to determine differential crustal movement rates, when sea level height variations can be assumed to be homogeneous. Satellite altimetric measurements determine sea surface height variations directly and can be used to separate the crustal signal from the sea surface height variations in tide gauge measurements. The correction of the tide gauge sea level rates for the sea surface height contribution requires collocation of the satellite pass and the tide gauge station. We show that even if this is not the case, the satellite altimetric observations enable correction of differential tide gauge rates for the effects of sea surface rate inhomogeneities.     

Monitoring air pollution in China from geostationary satellite: A synthetic study using simulated observations

We simulated geostationary satellite observations to assess the potential for high spatial-and temporal-resolution monitoring of air pollution in China with a focus on tropospheric ozone(O_3), nitrogen dioxide(NO_2), sulfur dioxide(SO_2), and formaldehyde(HCHO). Based on the capabilities and parameters of the payloads onboard sun-synchronous satellites, we simulated the observed spectrum based on a radiative transfer model using a geostationary satellite model. According to optimal estimation theory, we analyzed the sensitivities and retrieval uncertainties of the main parameters of the instrument for the target trace gases. Considering the retrieval error requirements of each trace gas, we determined the major instrument parameter values(e.g., observation channel, spectral resolution, and signal-to-noise ratio). To evaluate these values, retrieval simulation was performed based on the three-dimensional distribution of the atmospheric components over China using an atmospheric chemical transportation model. As many as 90% of the experiments met the retrieval requirements for all target gases. The retrieval precision of total-column and stratospheric O_3 was 2%. In addition, effective retrieval of all trace gases could be achieved at solar zenith angles larger than 70°. Therefore, the geostationary satellite observation and instrument parameters provided herein can be used in air pollution monitoring in China. This study offers a theoretical basis and simulation tool for improving the design of instruments onboard geostationary satellites.     

Tracking the North Korean nuclear explosion of 2006, using seismic data from Japan and satellite data from Taiwan

The location of the 2006 nuclear explosion in North Korea has been accurately imaged by back-projected regional Pn waves recorded by the Japanese Hi-net array. Based on the determined location, the nuclear explosion site can be identified from geo-referenced FORMOSAT-2 satellite images. The seismically determined epicenter is about 2.5 km northeast of the original estimate of its absolute location. Results indicate that a remote suspect event had been unambiguously detected and accurately located by a dense array within a regional distance. Employing ground truth correction, the satellite images can be referenced for shifting the array-determined epicenter to its absolute position. After correction, this event can be treated as a reference event for accurately locating future nuclear explosions. Our study utilizes public information from a dense seismic network and further demonstrates that commercial observation satellites can accurately monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty, as well as earthquake and tsunami hazards almost in real time.     

北斗卫星导航系统/美国全球定位系统载波相位相对定位全球精度分析

文章推导了载波相位相对定位精度的计算公式;分析了影响载波相位相对定位精度的各项因素;提出了频率精度衰减因子的概念,用以表达不同频率组合对定位精度的定量影响;在此基础上,计算并绘制了美国全球定位系统(GPS)、北斗二号(BDS2)、北斗三号(BDS3)及其融合系统的单天解、半小时解和单历元解的相对定位精度因子全球分布图;利用自主知识产权的处理软件(GCN和VENUS/ARSNet)解算了实测数据,检验了GPS和BDS2的单天解和单历元解的定位精度.分析表明:BDS的B1/B2频率定位精度优于GPS L1/L2频率; BDS2在其服务区内精度总体上与GPS相当; BDS3在亚太地区定位精度高于GPS.根据上述结论,文章在导航系统信号频率和全球定位系统(GPS)测量规范方面提出了优化建议,可为系统性能优化和制定标准提供参考.     

Global precision analysis of carrier phase relative positioning in BeiDou navigation satellite system and United States global positioning system

In this paper, we derived a high-efficiency formula for calculating the precision of carrier phase relative positioning,analyzed the various factors that affect the positioning accuracy using the carrier phase, and proposed the concept of using a frequency dilution of precision to describe the quantitative effect of different frequency combinations on the positioning precision. To this end, we computed and plotted the global spatial distribution map of the relative positioning dilution of precision for single-day solution, half-hour solution, and single-epoch solution of the global positioning system(GPS), regional Beidou navigation satellite system(BDS2), future global Beidou navigation satellite system(BDS3), and their fusion systems.Using processing software with autonomous intellectual property rights(GCN and VENUS/ARSNet), we solved the measurement data and examined the positioning precision of the single-day solution and single-epoch solution of GPS and BDS2.The analysis demonstrated that the B1/B2 frequency positioning precision of BDS2 was better than that of L1/L2 frequency positioning of GPS, but the positioning precision of the BDS2 is worse than that of GPS over most of the service region of the BDS2. Further, the positioning precision of BDS3 is better than that of GPS in the Asia-Pacific region, while it is the opposite in other regions. Based on these conclusions, we put forth some optimization recommendations regarding the signal frequency of the navigation system and GPS measurement standards to serve as references for optimizing the system performance and formulating standards.     

陆面微波比辐射率的卫星观测研究进展

复杂多变的陆地表微波比辐射率,造成陆面上星载微波观测反演大气参数较为困难,也使得许多卫星微波资料不易同化应用到数值模式,因此迫切需要提供准确可靠的陆面微波地表比辐射率信息.随着卫星观测技术的迅速发展,利用丰富的星载被动微波观测直接反演陆面微波比辐射率成为一种主要手段.国外针对星载微波成像仪和微波垂直探测器开展较为系统的陆面微波比辐射率研究,建立不同类型的地表比辐射率反演方法,开发地表比辐射率参数化方法并应用于辐射资料同化.对于卫星观测反演陆面微波比辐射率存在的问题,开展了评估分析和方法订正.国内利用卫星观测也开展了一些陆面微波比辐射率研究工作,尚需要系统、综合的提炼.对于地表特征复杂的中国地区,还需要评估认识不同陆面微波比辐射率反演方法在我国适用情况,需要增强陆面微波比辐射率数据质量的认识以及业务应用.