Three-frequency BDS precise point positioning ambiguity resolution based on raw observables   总被引：1，自引：0，他引：1  

Pan Li  Xiaohong Zhang  Maorong Ge  Harald Schuh 《Journal of Geodesy》2018,92(12):1357-1369

All BeiDou navigation satellite system (BDS) satellites are transmitting signals on three frequencies, which brings new opportunity and challenges for high-accuracy precise point positioning (PPP) with ambiguity resolution (AR). This paper proposes an effective uncalibrated phase delay (UPD) estimation and AR strategy which is based on a raw PPP model. First, triple-frequency raw PPP models are developed. The observation model and stochastic model are designed and extended to accommodate the third frequency. Then, the UPD is parameterized in raw frequency form while estimating with the high-precision and low-noise integer linear combination of float ambiguity which are derived by ambiguity decorrelation. Third, with UPD corrected, the LAMBDA method is used for resolving full or partial ambiguities which can be fixed. This method can be easily and flexibly extended for dual-, triple- or even more frequency. To verify the effectiveness and performance of triple-frequency PPP AR, tests with real BDS data from 90 stations lasting for 21 days were performed in static mode. Data were processed with three strategies: BDS triple-frequency ambiguity-float PPP, BDS triple-frequency PPP with dual-frequency (B1/B2) and three-frequency AR, respectively. Numerous experiment results showed that compared with the ambiguity-float solution, the performance in terms of convergence time and positioning biases can be significantly improved by AR. Among three groups of solutions, the triple-frequency PPP AR achieved the best performance. Compared with dual-frequency AR, additional the third frequency could apparently improve the position estimations during the initialization phase and under constraint environments when the dual-frequency PPP AR is limited by few satellite numbers.  相似文献   

A Global Terrestrial Reference Frame from simulated VLBI and SLR data in view of GGOS     

Susanne Glaser  Rolf König  Dimitrios Ampatzidis  Tobias Nilsson  Robert Heinkelmann  Frank Flechtner  Harald Schuh 《Journal of Geodesy》2017,91(7):723-733

In this study, we assess the impact of two combination strategies, namely local ties (LT) and global ties (GT), on the datum realization of Global Terrestrial Reference Frames in view of the Global Geodetic Observing System requiring 1 mm-accuracy. Simulated Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) data over a 7 year time span was used. The LT results show that the geodetic datum can be best transferred if the precision of the LT is at least 1 mm. Investigating different numbers of LT, the lack of co-located sites on the southern hemisphere is evidenced by differences of 9 mm in translation and rotation compared to the solution using all available LT. For the GT, the combination applying all Earth rotation parameters (ERP), such as pole coordinates and UT1-UTC, indicates that the rotation around the Z axis cannot be adequately transferred from VLBI to SLR within the combination. Applying exclusively the pole coordinates as GT, we show that the datum can be transferred with mm-accuracy within the combination. Furthermore, adding artificial stations in Tahiti and Nigeria to the current VLBI network results in an improvement in station positions by 13 and 12%, respectively, and in ERP by 17 and 11%, respectively. Extending to every day VLBI observations leads to 65% better ERP estimates compared to usual twice-weekly VLBI observations.  相似文献   

On the consistency of the current conventional EOP series and the celestial and terrestrial reference frames     

Santiago Belda  Robert Heinkelmann  José M. Ferrándiz  Tobias Nilsson  Harald Schuh 《Journal of Geodesy》2017,91(2):135-149

Precise transformation between the celestial reference frames (CRF) and terrestrial reference frames (TRF) is needed for many purposes in Earth and space sciences. According to the Global Geodetic Observing System (GGOS) recommendations, the accuracy of positions and stability of reference frames should reach 1 mm and 0.1 mm year\(^{-1}\), and thus, the Earth Orientation Parameters (EOP) should be estimated with similar accuracy. Different realizations of TRFs, based on the combination of solutions from four different space geodetic techniques, and CRFs, based on a single technique only (VLBI, Very Long Baseline Interferometry), might cause a slow degradation of the consistency among EOP, CRFs, and TRFs (e.g., because of differences in geometry, orientation and scale) and a misalignment of the current conventional EOP series, IERS 08 C04. We empirically assess the consistency among the conventional reference frames and EOP by analyzing the record of VLBI sessions since 1990 with varied settings to reflect the impact of changing frames or other processing strategies on the EOP estimates. Our tests show that the EOP estimates are insensitive to CRF changes, but sensitive to TRF variations and unmodeled geophysical signals at the GGOS level. The differences between the conventional IERS 08 C04 and other EOP series computed with distinct TRF settings exhibit biases and even non-negligible trends in the cases where no differential rotations should appear, e.g., a drift of about 20 \(\upmu \)as year\(^{-1 }\)in \(y_{\mathrm{pol }}\) when the VLBI-only frame VTRF2008 is used. Likewise, different strategies on station position modeling originate scatters larger than 150 \(\upmu \)as in the terrestrial pole coordinates.  相似文献   

The extension of the parametrization of the radio source coordinates in geodetic VLBI and its impact on the time series analysis     

Maria Karbon  Robert Heinkelmann  Julian Mora-Diaz  Minghui Xu  Tobias Nilsson  Harald Schuh 《Journal of Geodesy》2017,91(7):755-765

The radio sources within the most recent celestial reference frame (CRF) catalog ICRF2 are represented by a single, time-invariant coordinate pair. The datum sources were chosen mainly according to certain statistical properties of their position time series. Yet, such statistics are not applicable unconditionally, and also ambiguous. However, ignoring systematics in the source positions of the datum sources inevitably leads to a degradation of the quality of the frame and, therefore, also of the derived quantities such as the Earth orientation parameters. One possible approach to overcome these deficiencies is to extend the parametrization of the source positions, similarly to what is done for the station positions. We decided to use the multivariate adaptive regression splines algorithm to parametrize the source coordinates. It allows a great deal of automation, by combining recursive partitioning and spline fitting in an optimal way. The algorithm finds the ideal knot positions for the splines and, thus, the best number of polynomial pieces to fit the data autonomously. With that we can correct the ICRF2 a priori coordinates for our analysis and eliminate the systematics in the position estimates. This allows us to introduce also special handling sources into the datum definition, leading to on average 30 % more sources in the datum. We find that not only the CPO can be improved by more than 10 % due to the improved geometry, but also the station positions, especially in the early years of VLBI, can benefit greatly.  相似文献   

GPS/BDS short-term ISB modelling and prediction     

Jiang  Nan  Xu  Yan  Xu  Tianhe  Xu  Guochang  Sun  Zhangzhen  Schuh  Harald 《GPS Solutions》2017,21(1):163-175

GPS Solutions - The Chinese BeiDou Navigation Satellite System (BDS) has completed its first milestone by providing coverage of the Asia–Pacific area navigation service since December 27,...  相似文献   

Emissions of Volatile Organic Compounds from Sunflower and Beech: Dependence on Temperature and Light Intensity   总被引：11，自引：0，他引：11  

G. Schuh  A. C. Heiden  Th. Hoffmann  J. Kahl  P. Rockel  J. Rudolph  J. Wildt 《Journal of Atmospheric Chemistry》1997,27(3):291-318

Emissions of volatile organic compounds (VOCs) from sunflower (Helianthus annuus L. cv. giganteus) were measured in a continuously stirred tank reactor. The compounds predominantly emitted from sunflower were: isoprene, the monoterpenes -pinene, -pinene, sabinene, 3-carene and limonene, an oxygenated terpene, not positively identified so far and the sesquiterpene -caryophyllene. Emission rates ranged from 0.8 x 10^–16 to 4.3 x 10 ^–15 mol cm^–2 s^–1 at a temperature of 25°C and at a light intensity of 820 µEm^–2 s^–1. A dependence of the emission rates on temperature as well as on light intensity was observed. The emission rates of -pinene, sabinene and thujene from beech (Fagus sylvatica L.) were also affected by temperature as well as by light intensity. Our results suggest that an emission algorithm for all compounds emitted from sunflower and beech has to consider temperature and light intensity simultaneously. The observations strongly indicate that the emissions of VOCs from sunflower and beech are in part closely coupled to the rate of biosynthesis and in part originate from diffusion out of pools. The emission rates can be described by an algorithm that combines the model given by Tingey and coworkers with the algorithm given by Guenther and coworkers after slight modification.  相似文献   

Die Bedeutung der Atmosphärischen Wasserzirkulation für das Klima der Vorzeit     

Friedrich Schuh 《International Journal of Earth Sciences》1952,40(1):179-180

Ohne ZusammenfassungAuf der Heimfahrt von der Jahresversammlung der Geologischen Vereinigung in Köln, auf der das Thema Klima der Vorzeit behandelt wurde, drängte sich mir bei meinen rückschauenden Betrachtungen ein Klimafaktor auf, der bei der Tagung nicht erwähnt worden war und auch sonst wohl kaum in die Diskussion gezogen wurde, der mir aber doch beachtenswert scheint. So sollen die folgenden Zeilen gewissermaßen als nachträgliche Diskussionsbemerkung gewertet werden.  相似文献   

An initial scoping of transitional justice for global climate governance     

Sonja Klinsky 《Climate Policy》2018,18(6):752-765

Geopolitical changes combined with the increasing urgency of ambitious climate action have re-opened debates about justice and international climate policy. Tensions about historical responsibility have been particularly difficult and could intensify with increased climate impacts and as developing countries face mounting pressure to take mitigation action. Climate change is not the only time humans have faced historically rooted, collective action challenges involving justice disputes. Practices and tools from transitional justice have been used in over 30 countries across a range of conflicts at the interface of historical responsibility and imperatives for collective futures. Central to this body of theory and experience is the need to reflect both backwards- and forwards-oriented elements in efforts to build social solidarity. Lessons from transitional justice theory and practice have not been systematically explored in the climate context. This article conceptually examines the potential of transitional justice practices to inform global climate governance by looking at the structural similarities and differences between the global climate regime and traditional transitional justice contexts. It then identifies a suite of common transitional justice practices and assesses their potential applicability in the climate context.

POLICY RELEVANCE

• Justice disputes, including about historical responsibility and future climate actions, are long-standing in the climate context and could intensify with increased climate impacts and broadened mitigation pressures.

• Lessons from efforts to use transitional justice mechanisms could provide insight into strategies for balancing recognition of harms rooted in the past, while creating stronger future-oriented collective action.

• Several areas of transitional justice practice including: the combination of amnesties and litigation, truth commissions, reparations and institutional change could provide useful insights for the climate context.

  相似文献   

Approximating covariance matrices estimated in multivariate models by estimated auto- and cross-covariances   总被引：1，自引：1，他引：0  

K. R. Koch  H. Kuhlmann  W.-D. Schuh 《Journal of Geodesy》2010,84(6):383-397

Quantities like tropospheric zenith delays or station coordinates are repeatedly measured at permanent VLBI or GPS stations so that time series for the quantities at each station are obtained. The covariances of these quantities can be estimated in a multivariate linear model. The covariances are needed for computing uncertainties of results derived from these quantities. The covariance matrix for many permanent stations becomes large, the need for simplifying it may therefore arise under the condition that the uncertainties of derived results still agree. This is accomplished by assuming that the different time series of a quantity like the station height for each permanent station can be combined to obtain one time series. The covariance matrix then follows from the estimates of the auto- and cross-covariance functions of the combined time series. A further approximation is found, if compactly supported covariance functions are fitted to an estimated autocovariance function in order to obtain a covariance matrix which is representative of different kinds of measurements. The simplification of a covariance matrix estimated in a multivariate model is investigated here for the coordinates of points of a grid measured repeatedly by a laserscanner. The approximations are checked by determining the uncertainty of the sum of distances to the points of the grid. To obtain a realistic value for this uncertainty, the covariances of the measured coordinates have to be considered. Three different setups of measurements are analyzed and a covariance matrix is found which is representative for all three setups. Covariance matrices for the measurements of laserscanners can therefore be determined in advance without estimating them for each application.  相似文献   

A Tailored Computation of the Mean Dynamic Topography for a Consistent Integration into Ocean Circulation Models     

S. Becker  M. Losch  J. M. Brockmann  G. Freiwald  W.-D. Schuh 《Surveys in Geophysics》2014,35(6):1507-1525

Geostrophic surface velocities can be derived from the gradients of the mean dynamic topography—the difference between the mean sea surface and the geoid. Therefore, independently observed mean dynamic topography data are valuable input parameters and constraints for ocean circulation models. For a successful fit to observational dynamic topography data, not only the mean dynamic topography on the particular ocean model grid is required, but also information about its inverse covariance matrix. The calculation of the mean dynamic topography from satellite-based gravity field models and altimetric sea surface height measurements, however, is not straightforward. For this purpose, we previously developed an integrated approach to combining these two different observation groups in a consistent way without using the common filter approaches (Becker et al. in J Geodyn 59(60):99–110, 2012; Becker in Konsistente Kombination von Schwerefeld, Altimetrie und hydrographischen Daten zur Modellierung der dynamischen Ozeantopographie 2012). Within this combination method, the full spectral range of the observations is considered. Further, it allows the direct determination of the normal equations (i.e., the inverse of the error covariance matrix) of the mean dynamic topography on arbitrary grids, which is one of the requirements for ocean data assimilation. In this paper, we report progress through selection and improved processing of altimetric data sets. We focus on the preprocessing steps of along-track altimetry data from Jason-1 and Envisat to obtain a mean sea surface profile. During this procedure, a rigorous variance propagation is accomplished, so that, for the first time, the full covariance matrix of the mean sea surface is available. The combination of the mean profile and a combined GRACE/GOCE gravity field model yields a mean dynamic topography model for the North Atlantic Ocean that is characterized by a defined set of assumptions. We show that including the geodetically derived mean dynamic topography with the full error structure in a 3D stationary inverse ocean model improves modeled oceanographic features over previous estimates.  相似文献