This paper evaluates the performance of a tightly coupled GPS/INS integrated system based on low cost MEMS IMUs in dense urban areas, and investigates two different methods to improve its performance. The first method used is to derive observations from two different constraint equations reflecting the behavior of a typical land vehicle. The first constraint equation is derived assuming that the vehicle does not slip and always remains in contact with the ground. If these assumptions are true the velocity of the vehicle in the plane perpendicular to the forward direction should be zero. The second constraint equation is derived from the fact that the height does not change much in a short time interval in a land vehicular environment. Thus, when a GPS outage occurs (partial/complete), the integrated system combines the INS and constraints-derived virtual measurements to keep the position and velocity errors bounded. This method is suitable for use in real-time applications. The second method is specifically suitable for a post-mission application and involves the use of Rauch-Tung-Striebel (RTS) smoother. The designed system performance is evaluated using two data sets collected in dense urban areas. The obtained results demonstrate the effectiveness of different algorithms considered, in controlling the INS error growth, and indicates the potential of MEMS IMUs for use in land vehicle navigation applications.

GPS/MEMS INS integrated system for navigation in urban areas

............................................................................................................................iii Acknowledgements........................................................................................................... iv Dedication .........................................................................................................................vi Table of

Improving the accuracy and resolution of SINS/DGPS airborne gravimetry

A method of generating post-mission position and orientation data comprises generating position and orientation data representing positions and orientations of a mobile platform, based on global navigation satellite system (GNSS) data and inertial navigation system (INS) data acquired during a data acquisition period by the mobile platform, using a network real-time kinematic (RTK) subsystem to generate correction data associated with the data acquisition period, and correcting the position and orientation data based on the correction data. The RTK subsystem may implement a virtual reference station (VRS) technique to generate the correction data.

Post-mission high accuracy position and orientation system

The goal of this case study is to answer four research questions related to fatigue through features derived from wearable sensors to measure patterns in steps: (1) How do important gait parameters...

Monitoring worker fatigue using wearable devices: A case study to detect changes in gait parameters

Airborne gravimetry has during the last decade become a really operational way to map the Earths gravity field, mainly because of improvements in GPS technology. Improved inertial sensors have been employed for airborne gravity recovery during the last few years and show some promising results, but the far biggest volume of airborne gravity mapping are done with spring type gravimeters mounted on stabilized platforms, even this sensor technology is quite old. This paper addresses possible improvements in the processing of airborne gravimetry from such a spring type gravimeter system. One of the biggest advantages of the spring type gravimeter compared to inertial sensors is its superior long-term stability. A new algorithm to correct for platform off-leveling errors is derived and it is shown that this new algorithm in combination with the good drift characteristic for the spring type gravimeter yields virtual bias free data. This is an important point when it comes to geodetic use of the acquired data. The near bias free nature of the data from our system is underlined by the fact that no crossover adjustment procedures are involved in the data reduction. Also routines to identify and correct for some GPS related errors are outlined. Unfiltered gravity estimates have proven to be a good indicator for artifact accelerations coming from GPS ambiguity fixing problems, especially under smooth flight conditions. The resolution of the airborne gravity system is optimized through an analysis of the vertical sensor response. Concepts as apparent K-factor and filter-optimized K-factor are introduced in order to access the combined response of the gravimeter beam and the GPS positioning system. It is shown that the analyzed system maps gravity with an accuracy of 1.3 mgal at 6 km resolution. This performance may degrade during periods with air turbulence. The noise estimates for four consecutive years of airborne measurements in Greenland ranged from 1.3 to 2.0 mgal. It should be noticed that 6 km is a conservative estimate for the resolution. The filter can under low-turbulent conditions be shortened considerably and still yield virtual the same data accuracy.

Airborne Scalar Gravimetry for Regional Gravity Field Mapping and Geoid Determination

The gravity field may be determined using different techniques, but airborne gravity surveying is becoming a powerful tool mainly due to its potential in remote areas.

Gravity anomalies from airborne measurements — experiments using a low cost IMU device

On the Integration of Inertial and GPS Data with an Odometer for Land Vehicles Navigation

Many airborne applications, such as altimetry or photogrammetry without ground control points, strongly rely on the precise evaluation of the aircraft’s attitude. This paper presents an approach to the attitude determination problem, where a system combining Litton’s LN-200 Inertial Measurement Unit (IMU) with differential GPS (DGPS) is described. The methodology is based on the integrated processing of raw inertial measurements and GPS data collected from at least two receivers on board the aircraft and one, or possibly more, reference stations. It is well known that GPS and inertial navigation systems have complementary operational characteristics that can be exploited in an integrated system for continuous tracking of the aircraft’s navigational parameters (attitude, velocity and position). The incorporation of DGPS observations of one of the aircraft’s GPS antennas, specifically absolute position and doppler velocity readings, improves the overall system accuracy, including the estimates of roll and pitch angles that result from filtered raw inertial measurements, since it enables the continuous alignment of the strapdown analytical platform. By processing carrier phase measurements in differential mode between a pair of the aircraft’s GPS antennas (without information from any reference station), good attitude observations, especially true heading, are obtained. This is critical to align the low cost inertial platform in heading, since azimuth errors are weakly coupled with velocity or position errors. In fact, by this method alignment is achieved in motion and very quickly. The inertial system also provides high rate (DGPS filtered) position and velocity estimates that can be valuable during GPS signal outages and in DGPS ambiguity fixing procedures that occur whenever a new satellite becomes visible or cycle slips are detected. The estimated accuracy is 0.01o (1s) for roll and pitch and 0.1o (1s) for heading. Should the reference station data be absent and stand-alone doppler and position estimates be used instead, some degradation of the roll and pitch accuracy are to be expected. Besides a description of the relevant theory, this paper also includes post-processing results from one of a series of flights that took place in the Azorean area during a gravimetric and altimetric survey. The present methodology was successfully employed to process all data from this campaign.

Integrating Multiple GPS Receivers With a Low Cost IMU For Aircraft Attitude Determination

This is a presentation of the techniques used to process inertial and GPS data collected during an airborne gravimetric and altimetric survey in order to obtain absolute position and attitude estimates of the sensors mounted on board the aircraft. For high precision gravimetry and altimetry, these navigational parameters are required, in the order of a decimeter for position and better than one arc-minute for attitude. The survey took place in the Portuguese Azorean area in October 1997. It consisted of flying a series of profiles with a set of instruments mounted in a military aircraft, covering a large area around the islands, mainly over the mid-Atlantic ridge. The instruments whose position and attitude had to be determined were a gravimeter and two altimeters (one laser and another radar). For this purpose, three GPS receivers and an Inertial Measurement Unit (IMU) were used. The basic idea was to have a relatively low cost system that would be able to supply position and attitude with a level of accuracy and reliability similar to other more expensive systems, like gimbaled and ring laser gyro based inertial systems. One other requirement was that it should be able to work in real time. This feature could be useful for repeating flight tracks and for many other applications. For this purpose, a radio link was established with the aircraft to supply GPS data from a ground reference station. The methodology for processing GPS and IMU raw data was implemented with an integrated feedback loop. The position determination is based on real time DGPS with L1 and L2 carrier phase ambiguity fixing, using online IMU processed data to validate and increase the positions reliability, especially during GPS outages and when the aircraft is far away from the nearest GPS reference station. For the attitude angles, the IMU raw data is processed using the absolute GPS position measurements for continuous alignment. The baseline between a pair of GPS antennas is also computed (without resorting to a reference station data), using L1 and L2 carrier phase and doppler measurements. This baseline is very helpful for the continuous alignment of the strapdown analytical platform in heading, since this angle estimate is weakly coupled to position updates, especially in the absence of high horizontal accelerations. The position and attitude values were obtained from all the measurements using an Extended Kalman filter. Besides the normal navigation states, the filter also includes extra states to account for the inertial sensor errors and the vertical gravity anomaly.

Position+Attitude from GPS+INS for RTK Airborne Sensoring

Telmo R. Cunha graduated in Electrical Engineering in the University of Porto, Portugal, in 1996. He is finishing his Ph.D. at the Faculty of Engineering of the University of Porto, and developing his work at the Astronomical Observatory of the University of Porto in the area of navigation and sensor positioning based on GPS/INS integration, with particular emphasis on realtime high-precision GPS positioning.

Reliability Analysis of a Quasi-Instantaneous Ambiguity Fixing Method

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