FAST INTEGER AMBIGUITY RESOLUTION IN GPS KINEMATIC POSITIONING USING LEFT NULL SPACE AND MULTI-TIME (INVERSE) PAIRED CHOLESKY DECORRELATION

Aiming at the problems that huge amount of computation in ambiguity resolution with multiple epochs and high-order matrix inversion occurred in the GPS kinematic relative positioning, a modified algorithm for fast integer ambiguity resolution is proposed. Firstly, Singular Value Decomposition (SVD) is applied to construct the left null space matrix in order to eliminate the baselines components, which is able to separate ambiguity parameters from the position parameters efficiently. Kalman filter is applied only to estimate the ambiguity parameters so that the real-time ambiguity float solution is obtained. Then, sorting and multi-time (inverse) paired Cholesky decomposition are adopted for decorrelation of ambiguity. After diagonal elements preprocessing and diagonal elements sorting according to the results of Cholesky decomposition, the efficiency of decomposition and decorrelation is improved. Lastly, the integer search algorithm implemented in LAMBDA method is used for searching the integer ambiguity. To verify the validity and efficacy of the proposed algorithm, static and kinematic tests are carried out. Experimental results show that this algorithm has good performance of decorrelation and precision of float solution, with computation speed also increased effectively. The final positioning accuracy result with static baseline error less than 1 cm and kinematic error less than 2 cm, which indicates that it can be used for fast kinematic positioning of high precision carrier

Near Real-Time Precise Orbit Determiation of Low Earth Orbit Satellites Using an Optimal GPS Triple-Differencing Technique

This report was prepared by Tae-Suk Bae under the supervision of Professor Dorota A. Grejner-Brzezinska, Department of Civil and Environmental Engineering and Geodetic Science, The Ohio State University. This report was originally submitted to the Graduate School of The Ohio State University in partial fulfillment of the requirements for the Ph.D. degree.This research was supported by the grants from NASA (NASA NIP Project, OSURF #740809).During the last decade, numerous Low Earth Orbit (LEO) satellites, including TOPEX/POSEIDON, CHAMP and GRACE, have been launched for scientific purposes at altitudes ranging from 400 km to 1300 km. Because of highly complex dynamics of their orbits, coming from the Earth gravity field and the atmospheric drag, accurate and fast LEO orbit determination has been a great research challenge, especially for the lowest altitudes. To support GPS meteorology that requires an accurate orbit in near realtime, efficient LEO orbit determination methods were developed using the tripledifferenced GPS phase observations, as presented in this dissertation. These methods include the kinematic, dynamic, and reduced-dynamic approach based on the wave algorithm. To test the developed algorithms, 24 hours of CHAMP data on February 15, 2003, which amounts to 15 revolutions, were used for each method. The EIGEN2 geopotential model was used with degree and order up to 120. Precise IGS orbits are used for the GPS satellites, and 43 IGS ground tracking stations were chosen using the algorithm developed in this study, based on the network optimization theory. The estimated orbit solutions were compared with the published Rapid Science Orbit (RSO) and the consistency testing was performed for the dynamic solution. In addition to the comparison with other orbit solutions, the SLR residuals were also computed as an independent validation of the methods presented here. The kinematic orbit solution depends on the satellite geometry and data quality. The absolute kinematic positioning solution, with an RMS error of ±26 meters in 3D, was used as an initial approximation for the kinematic orbit determination. Because of the inaccuracy of the initial approximated orbit, there is a bias up to a few hundred epochs in the kinematic solution. This bias is effectively removed with the backward filter by fixing the last epoch from the forward filter solution. After the forward and backward filtering, the kinematic approach shows accuracy better than ±20 cm in 3D RMS for a half day arc compared to the reference RSO. The dynamic approach requires careful modeling of the atmospheric drag force which is the most dominant nonconservative force at LEO’s altitude. In addition, the empirical force modeling, which is similar to the stochastic process noise in the reduceddynamic approach, absorbs most of the remaining unmodeled forces. The two frequencies of the empirical forces, that is, once- and twice-per-revolution, are modeled in this study. Also after a thorough testing of the most suitable size of the arc length for the atmospheric drag parameters, the scaling factors for the drag force are estimated every iii hour. With this careful modeling, the dynamic solution shows an agreement within ±8 cm in position and ±0.12 mm/s in velocity of RSO. The computation time of the dynamic solution for the 24-hour arc is 2.5 hours on a 3 GHz PC platform. The wave algorithm, as implemented in this study, for the LEO precise orbit determination (POD) represents a new approach to the reduced-dynamic technique. This approach shows a better fit to RSO for each tested segment. However, there is slightly larger bias in its solution, thus, the overall RMS of fit is comparable to the dynamic orbit solution. This follows from the fact that the concept of the reduced-dynamic approach is already incorporated in the dynamic orbit determination in the form of the empirical force modeling. Therefore, there is no room for further improvement by the process noise modeling to take care of the unmodeled forces. A simplified force model is considered for future study in conjunction with the wave filter approach. The CHAMP orbit is successfully estimated in this study to support, for example, the GPS meteorology, using a new method that is accurate as well as fast and efficient. The applied wave algorithm shows the possibility of further improvement in the RMS of fit as long as the bias is modeled appropriately. The hypothesis testing indicates that the estimated dynamic solution of this study is consistent with the published RSO, thus, further accuracy improvement cannot be expected without other types of measurements, while its easy and time-effective implementation represents the major improvement, as compared to the existing solutions. Also, the SLR residual test shows that the CHAMP orbit solution estimated in this study is comparable to solutions determined by other analysis centers, such as JPL and GFZ

NASA Geodynamics Program

Activities and achievements for the period of May 1983 to May 1984 for the NASA geodynamics program are summarized. Abstracts of papers presented at the Conference are inlcuded. Current publications associated with the NASA Geodynamics Program are listed

International global network of fiducial stations: Scientific and implementation issues

In this report, an ad hoc panel of the National Research Council's Committee on Geodesy, Board of Earth Sciences and Resources (1) evaluates the scientific importance of a global network of fiducial sites, monitored very precisely, using a combination of surface- and space-geodetic techniques; (2) examines strategies for implementing and operating such a network; and (3) assesses whether such a network would provide a suitable global infrastructure for geodetic and other geophysical systems of the next century. The panel concludes that a global network of fiducial sites would be a valuable tool for addressing global change issues and play a critical role in providing a reference frame for scientific Earth missions. The panel suggests that existing global networks be integrated and anticipates that such a network would grow from about 30 to the ultimate size of about 200 fiducial sites. It is noted that such a global network will provide a long-term infrastructure for geodetic and geophysical studies. The panel expects that these fiducial sites would evolve into terrestrial observatories or laboratories that would permit more comprehensive studies of the Earth than those now possible

Airborne Vector Gravimetry Using GPS/INS

This report was prepared by Jay Hyoun Kwon, a graduate student, Department of Civil and Environmental Engineering and Geodetic Science, under the supervision of Professor Christopher Jekeli.This research was supported by the National Imagery and Mapping Agency (NIMA); Contract No. NMA202-98-1-1110.It was submitted to the Graduate School of The Ohio State University in the Winter of 2000 in partial fulfillment of the requirements of the Doctor of Philosophy degree.Compared to the conventional ground measurement of gravity, airborne gravimetry is relatively efficient and cost-effective. Especially, the combination of GPS and INS is known to show very good performances in the range of medium frequencies (1-100 km) for recovering the gravity signal. Conventionally, gravity estimation using GPS/INS was analyzed through the estimation of INS system errors using GPS position and velocity updates. In this case, the complex navigation equations must be integrated to obtain the INS position, and the gravity field must be stochastically modeled as a part of the state vector. The vertical component of the gravity vector is not estimable in this case because of the instability of the vertical channel in the solution of the inertial navigation equations. In this study, a new algorithm using acceleration updates instead of position/velocity updates has been developed. Because we are seeking the gravitational field, that is, accelerations, the new approach is conceptually simpler and more straightforward. In addition, it is computationally less expensive since the navigation equations do not have to be integrated. It is more objective, since the gravity disturbance field does not have to be explicitly modeled as state parameters. An application to real test flight data as well as an intensive simulation study has been performed to test the validity of the new algorithm. The results from the real flight data show very good accuracy in determining the down component, with accuracy better than ±5 mGal. Also, a comparable result was obtained for the horizontal components with accuracy of ±6 to ±8 mGal. The resolution of the final result is about 10 km due to the attenuation with altitude. The inclusion of a parametric gravity model into the new algorithm is also investigated for theoretical reasons. The gravity estimates from this filter showed strong dependencies on the model and required extensive computation with no improvement over the approach without parametric gravity model

Geodetic measurement of tectonic deformation in central California

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1991.Includes bibliographical references (p. 203-222).by Kurt Lewis Feigl.Ph.D

Radar Technology

In this book “Radar Technology”, the chapters are divided into four main topic areas: Topic area 1: “Radar Systems” consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: “Radar Applications” shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: “Radar Functional Chain and Signal Processing” describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: “Radar Subsystems and Components” consists of design technology of radar subsystem components like antenna design or waveform design

Proceedings of the Sixth General Meeting of the International VLBI Service for Geodesy and Astrometry

This volume is the proceedings of the sixth General Meeting of the International VLBI Service for Geodesy and Astrometry (IVS), held in Hobart, Tasmania, Australia, February 7-13, 2010. The contents of this volume also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/gm2010. The keynote of the sixth GM was the new perspectives of the next generation VLBI system under the theme "VLBI2010: From Vision to Reality". The goal of the meeting was to provide an interesting and informative program for a wide cross-section of IVS members, including station operators, program managers, and analysts. This volume contains 88 papers. All papers were edited by the editors for usage of the English language, form, and minor content-related issues

Robot Manipulators

Robot manipulators are developing more in the direction of industrial robots than of human workers. Recently, the applications of robot manipulators are spreading their focus, for example Da Vinci as a medical robot, ASIMO as a humanoid robot and so on. There are many research topics within the field of robot manipulators, e.g. motion planning, cooperation with a human, and fusion with external sensors like vision, haptic and force, etc. Moreover, these include both technical problems in the industry and theoretical problems in the academic fields. This book is a collection of papers presenting the latest research issues from around the world