Interferometric Baseline Performance Estimations for Multistatic Synthetic Aperture Radar Configurations Derived from GRACE GPS Observations     

A. O. Kohlhase  R. Kroes  S. D’Amico 《Journal of Geodesy》2006,80(1):28-39

Recent studies have demonstrated the usefulness of global positioning system (GPS) receivers for relative positioning of formation-flying satellites using dual-frequency carrier-phase observations. The accurate determination of distances or baselines between satellites flying in formation can provide significant benefits to a wide area of geodetic studies. For spaceborne radar interferometry in particular, such measurements will improve the accuracy of interferometric products such as digital elevation models (DEM) or surface deformation maps. The aim of this study is to analyze the impact of relative position errors on the interferometric baseline performance of multistatic synthetic aperture radar (SAR) satellites flying in such a formation. Based on accuracy results obtained from differential GPS (DGPS) observations between the twin gravity recovery and climate experiment (GRACE) satellites, baseline uncertainties are derived for three interferometric scenarios of a dedicated SAR mission. For cross-track interferometry in a bistatic operational mode, a mean 2D baseline error (1σ) of 1.4 mm is derived, whereas baseline estimates necessary for a monostatic acquisition mode with a 50 km along-track separation reveal a 2D uncertainty of approximately 1.7 mm. Absolute orbit solutions based on reduced dynamic orbit determination techniques using GRACE GPS code and carrier-phase data allows a repeat-pass baseline estimation with an accuracy down to 4 cm (2D 1σ). To assess the accuracy with respect to quality requirements of high-resolution DEMs, topographic height errors are derived from the estimated baseline uncertainties. Taking the monostatic pursuit flight configuration as the worst case for baseline performance, the analysis reveals that the induced low-frequency modulation (height bias) fulfills the relative vertical accuracy requirement (σ<1 m linear point-to-point error) according to the digital terrain elevation data level 3 (DTED-3) specifications for most of the baseline constellations. The use of a GPS-based reduced dynamic orbit determination technique improves the baseline performance for repeat-pass interferometry. The problem of fulfilling the DTED-3 horizontal accuracy requirements is still an issue to be investigated. DGPS can be used as an operational navigation tool for high-precision baseline estimation if a geodetic-grade dual-frequency spaceborne GPS receiver is assumed to be the primary instrument onboard the SAR satellites. The possibility of using only single-frequency receivers, however, requires further research effort.Deutsche Forschungsgemeinschaft (DFG) research fellow until Sept. 2004 at the Microwaves and Radar Institute, Deutsche Zentrum für Luft- und Raumfahrt (DLR) e.V., 82234 Weßling, Germany  相似文献   

Harmonic analysis of the Earth's gravitational field by means of semi-continuous ephemerides of a low Earth orbiting GPS-tracked satellite. Case study: CHAMP   总被引：1，自引：0，他引：1  

T. Reubelt  G. Austen  E.W. Grafarend 《Journal of Geodesy》2003,77(5-6):257-278

An algorithm for the determination of the spherical harmonic coefficients of the terrestrial gravitational field representation from the analysis of a kinematic orbit solution of a low earth orbiting GPS-tracked satellite is presented and examined. A gain in accuracy is expected since the kinematic orbit of a LEO satellite can nowadays be determined with very high precision, in the range of a few centimeters. In particular, advantage is taken of Newton's Law of Motion, which balances the acceleration vector with respect to an inertial frame of reference (IRF) and the gradient of the gravitational potential. By means of triple differences, and in particular higher-order differences (seven-point scheme, nine-point scheme), based upon Newton's interpolation formula, the local acceleration vector is estimated from relative GPS position time series. The gradient of the gravitational potential is conventionally given in a body-fixed frame of reference (BRF) where it is nearly time independent or stationary. Accordingly, the gradient of the gravitational potential has to be transformed from spherical BRF to Cartesian IRF. Such a transformation is possible by differentiating the gravitational potential, given as a spherical harmonics series expansion, with respect to Cartesian coordinates by means of the chain rule, and expressing zero- and first-order Ferrer's associated Legendre functions in terms of Cartesian coordinates. Subsequently, the BRF Cartesian coordinates are transformed into IRF Cartesian coordinates by means of the polar motion matrix, the precession–nutation matrices and the Greenwich sidereal time angle (GAST). In such a way a spherical harmonic representation of the terrestrial gravitational field intensity with respect to an IRF is achieved. Numerical tests of a resulting Gauss–Markov model document not only the quality and the high resolution of such a space gravity spectroscopy, but also the problems resulting from noise amplification in the acceleration determination process.  相似文献   

我国发射射电卫星的作用及关键技术研究   总被引：1，自引：0，他引：1  

刘经南  魏二虎 《武汉大学学报(信息科学版)》2005,30(10):847-852

论述了我国发射射电卫星对于天文学和射电天文方法的发展、我国月球及深空探测计划、大地测量和天文地球动力学的研究和发展等方面的意义;根据VLBI卫星的技术和应用特点,分析了射电望远镜及相关设施的技术要求和指标,比较全面地分析和总结了VLBI卫星及相关设施的关键技术和方法。  相似文献   

Sensor Calibration in Support for NOAA’s Satellite Mission     

Xiangqian WU  Changyong CAO 《大气科学进展》2006,23(1):80-90

Sensor calibration, including its definition, purpose, traceability options, methodology, complexity, and importance, is examined in this paper in the context of supporting NOAA’s satellite mission. Common understanding of sensor calibration is essential for the effective communication among sensor vendors, calibration scientists, satellite operators, program managers, and remote sensing data users, who must cooperate to ensure that a nation’s strategic investment in a sophisticated operational environmental satellite system serves the nation’s interest and enhances the human lives around the world. Examples of calibration activities at NOAA/NESDIS/ORA are selected to further illustrate these concepts and to demonstrate the lessons learned from the past experience.  相似文献   

Ringlet–satellite interactions     

F. Namouni 《Monthly notices of the Royal Astronomical Society》1998,300(3):915-930

We study the interaction of a satellite and a nearby ringlet on eccentric and inclined orbits. Secular torques originate from mean motion resonances and the secular interaction potential which represents the m  = 1 global modes of the ring. The torques act on the relative eccentricity and inclination. The resonances damp the relative eccentricity. The inclination instability owing to the resonances is turned off by a finite differential eccentricity of the order of 0.27 for nearly coplanar systems. The secular potential torque damps the eccentricity and inclination and does not affect the relative semi-major axis; also, it suppresses the inclination instability that persists at small differential eccentricities. The damping of the relative eccentricity and inclination forces an initially circular and planar small mass ringlet to reach the eccentricity and inclination of the satellite. When the planet is oblate, the interaction of the satellite damps the proper precession of a small mass ringlet so that it precesses at the satellite's rate independently of their relative distance. The oblateness of the primary modifies the long-term eccentricity and inclination magnitudes and introduces a constant shift in the apsidal and nodal lines of the ringlet with respect to those of the satellite. These results are applied to Saturn's F-ring, which orbits between the moons Prometheus and Pandora.  相似文献   

A CCD OBSERVATIONAL METHOD TO DETERMINE PRECISELY THE BARYCENTRICPOSITIONS OF THE OUTER PLANETS(SATURN-NEPTUNE)     

Peng Qing-yu Mao Wei 《紫金山天文台台刊》1998,(2)

This paper presents a new method to determine precisely the barycentric positions of the outer planets(Saturn - Neptune)by optical observations. It requires the CCD observations from a long focal distance telescope which is used to observe a planet and its satellites and ones from a meridian circle when it works in a CCD drift scanning manner. The key part of the method is tested by the observations with 1 meter telescope of Yunnan Observatory. The result shows that the new method is feasible to carry out.  相似文献   

Optical identifications of southern rosat EUV and soft X-ray sources     

David A. H. Buckley  Kazuhiro Sekiguchi  Darragh O'Donoghue  Walter W. Wargau 《Astrophysics and Space Science》1995,230(1-2):117-130

This paper discusses the first all-sky surveys of cosmic extreme ultra-violet and soft X-ray sources, discovered by ROSAT. Details of the surveys are presented, with comparisons made to previous selected surveys in the X-ray regime. The subsequent optical identification programs are described, and the major results summarized. We then discuss the main classes of EUV emitters: active chromosphere stars and hot white dwarfs, and describe the importance of EUV observations in understanding the astrophysics of these objects. Many bright, and relatively nearby, sources have been identified as hitherto unrecognized active stars, representing the extremes in chromospheric and coronal activity, be it binary or age related. Many new hot DA white dwarfs have also been indentified, and the most exciting result in this area is the discovery that significant traces of heavier elements (e.g. C, N, O, Si, Fe and Al) exist in their atmospheres, substantially increasing their EUV opacities. The importance of hot white dwarfs as standard candles in probing the local interstellar medium is also discussed. Miscellaneous counterparts (AGN, PNN, O-B stars and CVs) that make up the rest of the sample of EUV sources are also briefly mentioned. We finish with a discussion of the on-going ROSAT Galactic Plane Survey (RGPS) identification program.  相似文献   

Basis for integration of conventional observations of cloud into global nephanalyses   总被引：1，自引：0，他引：1  

A. Henderson-Sellers  K. McGuffie 《Journal of Atmospheric Chemistry》1990,11(1-2):1-25

Water vapour is the largest and, radiatively, the most important trace gas in the Earth's atmosphere. Cloud amount and cloud optical depth feedbacks are, as yet, poorly understood and improvements in model parameterization schemes await an adequate observational data base. Satellite retrievals do not, and will not for some time, provide more than snapshot (a few months to a few years) records. Conventional surface-based observations of cloudiness could complement the global coverage offered by satellite retrievals if a sound relationship between the two observational measurements could be found. Observations underline the importance of the vertical dimension of clouds which affects the observational geometries from satellites and the surface. A new basis for the relationship between the (vertical) earthview of cloud amount and the (whole dome) skycover of cloud amount has been sought. Over four and a half thousand all-sky camera photographs, representing a considerable range of seasonal and climatological conditions, have been analyzed to give rise to a database from which predictive relationships for earthview, E, and skycover, S, have been established.Cubic functions are the most soundly based both physically and empirically. We find: S=0.647+2.192E–0.461E ²+0.037E ³ and E=-0.001+0.082S+0.269S ²–0.019S ³ for the prediction of skycover from earthview and earthview from skycover, respectively. If earthview is required from skycover observations then ES could be used with little additional error. Hence, conventional surface observations of skycover could be compared directly with satellite-derived earthview values. More importantly, these results do not support the widespread assumption that conventional (surface) observations of cloud amount always exceed the earthview could retrieval. Furthermore, climate model predictions of total cloud amount may also be interpreted via these relationships. GCM-predicted layer cloud amounts can be synthesized into modelled E values using the random overlap formula and hence it is possible to construct modelled S values which are directly comparable with conventionally observed cloud climatologies. The baseline observation of skycover by clouds therefore provides a valuable validation tool for both satellite programmes and climate models.  相似文献   

关于土卫八运动的轨道解     

张伟  刘林 《紫金山天文台台刊》1999,18(1):9-17

为了适应星际探测的需求,本文建立了在新的精度要求下土星卫星运动对应的力学模型,具体讨论了土卫八的运动,并针对主要摄动源土卫六的引力作用,建立了轨道变化的分析解,以此表明建立了土卫运动理论该采取的途径和精密定轨宜采用以轨道根数作为状态量的数值定轨方法。  相似文献   

天王星卫星CCD观测的初步分析   总被引：2，自引：1，他引：1  

刘建荣 《紫金山天文台台刊》1999,18(4):371-374

１９９５ 年８ 月在上海天文台利用安装在１ ．５６ 米望远镜上的ＣＣＤ 探测器对天王星五颗主要卫星进行了定位试观测。将观测所得的位置资料与其理论值做了比较。结果表明：ＣＣＤ观测的位置精度优于照相观测的结果。这些资料对于卫星轨道的研究是有价值的。  相似文献