GPS Carrier Phase Research Articles

GPS monitoring of the crustal motion in southwestern China

Through GPS carrier phases observation in southwestern China during 1991–1997, the velocity field within eastern Qinghai-Xizang (Tibet) and its neighbour regions has been established. The velocity of those sites in and west of Chuan-Dian block is mostly 5–10 mm · a™1 relative to the fiduciary station CHDU (Chengdu), and the motion in Chuan-Qing and Yangtze blocks east of the Xianshuihe-Xiaojiang fault is weak with a velocity of about 0–7 mm · a−1. The velocity vector in these areas indicates a clockwise rotation vortex rather than the so-called intensive eastward pushing or eastward escape. The main pattern of the crustal deformation is a clockwise rotation vortex structure and a differential slip along the boundary fault between different blocks.

Carrier-phase time transfer

We have conducted several time-transfer experiments using the phase of the GPS carrier rather than the code, as is done in current GPS-based time-transfer systems. Atomic clocks were connected to geodetic GPS receivers; we then used the GPS carrier-phase observations to estimate relative clock behavior at 6-minute intervals. GPS carrier-phase time transfer is more than an order of magnitude more precise than GPS common view time transfer and agrees, within the experimental uncertainty, with two-way satellite time-transfer measurements for a 2400 km baseline. GPS carrier-phase time transfer has a stability of 100 ps, which translates into a frequency uncertainty of about two parts in 10(-15) for an average time of 1 day.

Carrier Phase GPS Navigation to the North Pole

Over the last few years, on-the-fly integer ambiguity resolution for GPS has proven to be successful over short baselines (<20 km). However, the remaining challenge has been to extend the length of the baseline between the reference station and the mobile receiver, whilst still maintaining the capability of on-the-fly resolution and true carrier-based kinematic positioning. The goal has been to achieve centimetric level positioning at ranges of over 500 km. New techniques have been developed at the University of Nottingham to allow very long baseline integer ambiguity resolution, on-the-fly. A major problem with the use of carrier phase data is that posed by cycle slips. A technique for detecting and correcting cycle slips has been developed, and its use is discussed in this paper. The new technique has been proven through a series of trials, one of which included two flights to the North Pole, performing centimetric level positioning all the way to the pole. For many years, the GD Aero-Systems Course of the Air Warfare Centre based at RAF Cranwell executed a series of equipment flight trials to the North Pole, called the ARIES Flights. In May 1996, the authors were fortunate to take part in both flights, via Iceland and Greenland, to the North Pole. Based on reference stations at Thule Air Base, integer ambiguity resolution was accomplished, on-the-fly, and centimetric level navigation maintained throughout the flights. Earlier trials detailed in the paper demonstrate that the technique can resolve integer ambiguities on-the-fly within a few seconds over a baseline length of approximately 134 km, resulting in an accuracy of 12 cm. The majority of the residual error source for this being the ionosphere.

A Simple and Economical Algorithm for GPS Ambiguity Resolution on the Fly Using a Whitening Filter

In this paper, a whitening filter technique using Idl (lower diagonal lower) and udu (upper diagonal upper) factorizations is used to provide a simple carrier phase ambiguity resolution on-the-fly (OTF) technique. The technique proved to be very efficient for short baselines over short observation periods. It also performed very well in instantaneously recovering ambiguities after loss of lock. The ability to function without a search algorithm, combined with the simplicity of its implementation, makes the whitening filter a powerful tool to resolve GPS carrier phase ambiguities. The whitening filter can also be used with algorithms involving a search technique. This application is accomplished by applying the whitening filter right before the search; in this case, the search becomes more efficient. A MATLAB® implementation of the algorithm is given in the appendix.

Autonomous fault detection and removal using GPS carrier phase

This paper is focused on the use of carrier phase measurements and parity space methodology to investigate the limits of high-integrity and high-continuity satellite-based navigation performance. In this regard, a new algorithm for receiver autonomous fault detection and removal is developed with the specific goal of attaining the high levels of integrity and continuity required for aircraft precision approach and landing applications. Fault detection and removal algorithm performance is demonstrated through analysis and simulation, and the results of tests using deliberately induced failures in raw night data are presented.

Quality aspects of a GPS reference network in Antarctica - a simulation study

GPS has become an essential tool for the precise determination of point positions. Since GPS campaigns for geodynamic purposes – such as the monitoring of recent crustal movements – require major financial efforts, it is essential to ensure already in the planning phase a good network quality and the attainment of the scientific goals in a reasonable time. The paper outlines an operationally oriented procedure for these purposes based on the simulation and processing of GPS carrier-phase observations. Sensitivity analysis techniques are applied to describe both the network strain as it may be induced by gross errors and the detectability of point movements between two sessions or two campaigns. In addition, the eigenvalue decomposition of the variance-covariance matrix of the GPS coordinates will be used to identify weakly determined network components. The design of the SCAR Epoch 95 Campaign GPS network is discussed throughout the paper. It was realized in the Antarctic summer 1994/1995 on the Antarctic peninsula.

First results of comparisons of PRARE TEC with TOPEX measurements and with ionospheric models

The German microwave satellite tracking system PRARE (Precise Range And Range Rate Equipment) has been operating onboard ERS-2 since May 1995 with the routine product generation starting on January 1st, 1996. PRARE provides very precise range and range-rate measurements between the space segment and a globally distributed network of ground station transponders. The measurements are used for orbit determination, point positioning, Earth rotation and gravity field parameter estimation. In addition, the total electron content (TEC) can be derived from the simultaneous PRARE X- and S-band measurements. The paper outlines two methods that are used to derive TEC and summarises first results to calibrate and validate the ionospheric data. Finally, the PRARE derived TEC data are compared with IRI95, with daily global ionospheric maps derived from GPS carrier phase data, and with TOPEX dual-frequency altimeter derived TEC data.

Mitigation of GPS Carrier Phase Multipath by Microwave Absorbing Material

Mitigation of GPS Carrier Phase Multipath by Microwave Absorbing Material

Kinematic Positioning with GPS Carrier Phases by Two Types of Wide Laning

To resolve the integer ambiguities of the GPS L1 and L2 carrier phases on the fly, two types of wide-lane phase combination are formed, resulting in 86.2 and 162.8 cm signal wavelengths, respectively. Large lane spacings facilitate the determination of a correct ambiguity vector by a least-squares trial-and-error approach, in which double-difference phases between the satellite and the receiver serve as a mathematical model. An algebraic relationship of extra-wide-lane integer ambiguity to wide-lane ambiguity is derived and used to advantage. Based on independently surveyed reference values of short baseline vectors (< 5.0 km), kinematic positioning accuracies on the order of 0.4-2.8 cm are achievable during low ionospheric activity.

Combined GPS/GLONASS LAAS flight trials

The use of GPS in aviation is now accepted, with extensive work being undertaken on the technological, precision and infrastructure requirements. Work has focused on providing a service that is able to operate continuously in all areas. GPS alone, however, is seen as being unable to satisfy the stringent requirements for some phases of flight. Of the many solutions proposed, the Russian GLONASS system has been regularly overlooked. The research described in this paper aims to present GLONASS as a realistic and proven augmentation to GPS for aircraft positioning. During October 1996 the Civil Aviation Authority (CAA) Institute of Satellite Navigation (ISN) at the University of Leeds, in conjunction with the National Air Traffic Services Ltd (NATS UK) and the Defence Evaluation and Research Agency (DERA), performed a series of landmark differential GPS/GLONASS flight tests using the DERA BAC 1-11 flying laboratory. A real-time differential system was constructed using two GPS/GLONASS receivers developed by the ISN and a C-band data link for the RTCA corrections. Integration onboard the aircraft with avionic sensors and flight management systems was achieved using the ARINC 429 protocol. Routes were designed and flown to evaluate the complete system over a variety of airborne dynamics for both en-route and approach situations. In total, over 16h of flying time was recorded, including 30 runway approaches over nine flights. A thorough evaluation of the accuracy and integrity of the positioning system was performed. Emphasis was made in comparing the flight statistics with recognized Required Navigation Performance (RNP) figures. The paper describes in detail the project development and the results achieved. An analysis of the results, showing that aircraft positioning with GPS/GLONASS augmentation in a local area augmentation system (LAAS) scenario can achieve accuracies that are both comparable with GPS-alone solutions and can satisfy up to CAT II precision approach criteria, is presented. Results are also given for position propagation using velocities derived from GPS and GLONASS carrier phase measurements.

Combined GPS/GLONASS LAAS flight trials

The use of GPS in aviation is now accepted, with extensive work being undertaken on the technological, precision and infrastructure requirements. Work has focused on providing a service that is able to operate continuously in all areas. GPS alone, however, is seen as being unable to satisfy the stringent requirements for some phases of flight. Of the many solutions proposed, the Russian GLONASS system has been regularly overlooked. The research described in this paper aims to present GLONASS as a realistic and proven augmentation to GPS for aircraft positioning. During October 1996 the Civil Aviation Authority (CAA) Institute of Satellite Navigation (ISN) at the University of Leeds, in conjunction with the National Air Traffic Services Ltd (NATS UK) and the Defence Evaluation and Research Agency (DERA), performed a series of landmark differential GPS/GLONASS flight tests using the DERA BAC 1–11 flying laboratory. A real-time differential system was constructed using two GPS/GLONASS receivers developed by the ISN and a C-band data link for the RTCA corrections. Integration onboard the aircraft with avionic sensors and flight management systems was achieved using the ARINC 429 protocol. Routes were designed and flown to evaluate the complete system over a variety of airborne dynamics for both en-route and approach situations. In total, over 16 h of flying time was recorded, including 30 runway approaches over nine flights. A thorough evaluation of the accuracy and integrity of the positioning system was performed. Emphasis was made in comparing the flight statistics with recognized Required Navigation Performance (RNP) figures. The paper describes in detail the project development and the results achieved. An analysis of the results, showing that aircraft positioning with GPS/GLONASS augmentation in a local area augmentation system (LAAS) scenario can achieve accuracies that are both comparable with GPS-alone solutions and can satisfy up to CAT II precision approach criteria, is presented. Results are also given for position propagation using velocities derived from GPS and GLONASS carrier phase measurements. © 1997 John Wiley & Sons, Ltd.

On-line detection of abrupt changes in the carrier-phase measurements of GPS

The detection of cycle slips in carrier-phase data, outliers in phase rate or in code ranges, or any other type of disorder in the measurements of the GPS system, is one of the major quality-control problems that needs to be addressed, especially where GPS is used for real-time applications or for those applications that require continuous and reliable positioning results. This study is concerned with designing algorithms to detect failures or changes of small magnitude, in order to monitor and control the quality of GPS measurements for critical real-time and/or deformation applications. In this regard, the statistical technique known as the cumulative-sum test is described for the detection of abrupt changes in the GPS carrier-phase measurements. Real GPS data have been used to test and evaluate the algorithm.

Efficient technique to fix GPS carrier phase integer ambiguity on-the-fly

A new and fast method to fix integer ambiguity of GPS carrier phase measurement on-the-fly is proposed. The method is distinguished from other methods in that the relationship between integer ambiguities is found and used in a constraint equation for fixing integer ambiguity. Thus the method does not require positioning for every candidate and only three independent elements of the integer ambiguities are searched; the remaining dependent elements can be obtained from the constraint equation. This may greatly reduce the computational burden. Accurate relative positioning on a move also can be accomplished by adopting the proposed method. The technique is applied to two different types of real data to show its effectiveness. Experimental results show that the proposed method is fast and efficient for relative positioning of a moving user. The method may be used in areas requiring accurate positioning such as navigation and geodesy.

GPS kinematic carrier phase measurements for aerial photogrammetry

GPS kinematic positioning with carrier phase measurements is an effective method that can acquire required point accuracies for aerial photogrammetry. From late April to early May, 1994, airborne GPS carrier phase measurements with multi-reference stations were executed with four Trimble 4000SST receivers and an airborne Wild RC20 camera on board a Lear 36A Jet aircraft. The airborne GPS data were sampled at the flight altitudes of 0.45, 2.3 and 10.8 km. The furthest distance reached in the flight operation from the reference station was 453 km. It is known from the precision of the closure of the kinematic figure that GPS test data gathered at these three altitudes are of a high quality, so that the real-time positions and 3D velocities of the airborne GPS antenna can be solved accurately by our DDKIN software. This paper describes the air test results and discusses the practical problems of accurately surveying with airborne GPS.

High-Rate Precise Real-Time Positioning Using Differential Carrier Phase

Differential carrier-phase positioning overcomes some of the operational limitations of carrier-phase kinematic positioning in a real-time environment. Unlike kinematic positioning, differential carrier-phase positioning does not require time matching of reference and remote station data. The observation time matching adds the data link delay to the position latency and prevents positioning when the reference data transmission is interrupted. The differential carrier-phase algorithm is based on determining and then applying the GPS carrier-phase errors instead of direct observation differencing. The differential carrier-phase method enables several-centimeter positioning at a high rate dependent on the remote receiver observation rate, but relatively independent of the data link transmission rate. This paper discusses the design, successful implementation, and test results of a real-time differential carrier-phase system.

A New Motion-Based Algorithm for GPS Attitude Integer Resolution

Carrier-phase GPS techniques are capable of measuring positions with subcentimeter accuracy. With several antennae, carrier-phase GPS can be used to determine attitude. This paper presents a motion-based algorithm for resolving the integer ambiguities that is suitable for conditions of poor satellite visibility. In particular, this algorithm can use baselines with fewer than three common satellites visible. This algorithm was used very successfully in practice as the attitude sensor for an autonomous model helicopter and aircraft.

An optimized GPS carrier phase ambiguity search method focusing on speed and reliability

An optimized ambiguity search method is described in this paper focusing on speed and reliability. The method has incorporated several existing fast ambiguity search concepts and the ambiguity search speed can be further improved. In addition to the improvement of the ambiguity search speed, special attention has been paid to the improvement of the reliability of the ambiguity search process. Several theoretical and practical aspects involved in an ambiguity search algorithm are also addressed which have not been explored in previous literatures.

Horizontal acceleration corrections in airborne gravimetry

The stabilized platforms used in marine and airborne gravimeters behave like damped long‐period pendulums. When subjected to horizontal accelerations they tilt, resulting in gravimeter reading errors. The amount of tilt depends on the ratio of the period of the horizontal motion to that of the platform and is negligible if this ratio is less than about 0.1 (LaCoste, 1967). This condition can be achieved in straight and level flight using an auto pilot, provided the platform period is set to a sufficiently long period (Brozena and Peters, 1988). Course changes are sometimes unavoidable, however, resulting in lost data (Bell et al., 1991; Brozena, 1984). The aim of this paper is to show that such data loss is unnecessary since the tilt, and hence the gravimeter error, can be accurately modeled from the horizontal accelerations. Moreover the technique will improve data quality whenever long period horizontal accelerations occur. Measuring these accelerations is now straightforward with differential carrier phase GPS.

Dynamic orbit determination using GPS measurements from TOPEX/POSEIDON

The GPS data acquired by the TOPEX/POSEIDON (T/P) Demonstration Receiver (DR) have been used in a dynamic orbit determination, which was based on the description of the gravitational and nongravitational forces in the equations of motion. The GPS carrier phase data were processed in a double difference mode to remove clock errors, including the effects of Selective Availability. Simultaneous estimation of the T/P orbit and GPS orbits was performed using five 10‐day cycles in the interval between December (1992) and April (1993). The resulting T/P orbits have been compared with the orbits determined from Satellite Laser Ranging, the French one‐way Doppler tracking system, DORIS, and with the JPL reduced dynamic orbits obtained from the GPS/DR data. Using similar dynamic orbit determination strategies and force models with the GPS/DR to those used with SLR/DORIS, the radial component of the T/P orbit (based on JGM‐2) was found to agree to better than 30 mm (rms) and 35 mm with the JPL reduced dynamic orbit. An experimental gravity tuning was accomplished using four cycles of GPS/DR data. The resulting GPS/DR‐orbits, determined by the dynamic technique with the experimental gravity field, are in better agreement with the JPL reduced dynamic orbits in both the radial component (21–25 mm) and altimeter crossover residuals than the JGM‐2 orbits.

Real-Time on-the-Fly Kinematic GPS System Results

The development of a real-time positioning system using GPS carrier phase was formally initiated by the U. S. Army Corps of Engineers in 1988. The end goal of this effort was to have ready by 1993 an operational prototype capable of subdecimeter positions in three dimensions in real time. This goal has been met. Testing of this prototype began in March 1993. The first demonstration was in August 1993, with the first public demonstration following in October. The system typically resolves integer ambiguities on-the-fly (OTF) in 15 s or less, and requires no static initialization. It is robust and reliable to use for precisely positioning any mobile platform out to approximately 20 km. Testing has been performed under varying operating conditions to evaluate the limits of OTF ambiguity resolution for precisely positioning moving platforms. This paper summarizes the results of those tests. Early real-time tests performed have shown accuracies of l-3 cm in all three dimensions. Design of the final real-time system and its integration with hydrographic survey platforms are also discussed.