External Global Positioning System Research Articles

A Low-Cost Test Platform for Performance Analysis of Phasor Measurement Units

In this paper, a customizable low-cost voltage waveform generator based on a real-time desktop PC and embedded data acquisition card synchronized with Coordinated Universal Time (UTC) is presented. A software approach to phase-locked loop synchronization with an external Global Positioning System (GPS) pulse signal is utilized to achieve a time uncertainty of ±1μs. This avoids expensive hardware modules for synchronization and timing purposes, which are commonly presented in literature. Besides the application for controlling the test platform, our own phasor data concentrator (PDC) application is running concurrently on the host PC. The latter is used for collecting and comparing the syncrophasor data from the test platform against the syncrophasor data measured by phasor measurement units (PMUs) under the test. The paper describes all procedures for generating reference test signals. Numerous case studies were performed, and experimental results for steady-state compliance as well as frequency ramp and phase modulation tests for dynamic compliance are presented in detail. All tests confirm that customizable test platform meets the requirements of IEEE/IEC standards. Compared to other calibrators, the cost as well as the specifications and point-by-point concept of data processing makes the described test platform suitable for performance analysis of PMU algorithms implemented on various development boards.

Assessing the Use of GACOS Products for SBAS-InSAR Deformation Monitoring: A Case in Southern California.

The Generic Atmospheric Correction Online Service (GACOS) products for interferometric synthetic aperture radar (InSAR) are widely used near-real-time and global-coverage atmospheric delay products which provide a new approach for the atmospheric correction of repeat-pass InSAR. However, it has not been determined whether these products can improve the accuracy of InSAR deformation monitoring. In this paper, GACOS products were used to correct atmospheric errors in short baseline subset (SBAS)-InSAR. Southern California in the U.S. was selected as the research area, and the effect of GACOS-based SBAS-InSAR was analyzed by comparing with classical SBAS-InSAR results and external global positioning system (GPS) data. The results showed that the accuracy of deformation monitoring was improved in the whole study area after GACOS correction, and the mean square error decreased from 0.34 cm/a to 0.31 cm/a. The improvement of the mid-altitude (15–140 m) point was the most obvious after GACOS correction, and the accuracy was increased by about 23%. The accuracy for low- and high-altitude areas was roughly equal and there was no significant improvement. Additionally, GACOS correction may increase the error for some points, which may be related to the low accuracy of GACOS turbulence data.

The Design of a Low Cost Phasor Measurement Unit

The widespread diffusion of Phasor Measurement Units (PMUs) is a becoming a need for the development of the “smartness” of power systems. However, PMU with accuracy compliant to the standard Institute of Electrical and Electronics Engineers (IEEE) C37.118.1-2011 and its amendment IEEE Std C37.118.1a-2014 have typically costs that constitute a brake for their diffusion. Therefore, in this paper, the design of a low-cost implementation of a PMU is presented. The low cost approach is followed in the design of all the building blocks of the PMU. A key feature of the presented approach is that the data acquisition, data processing and data communication are integrated in a single low cost microcontroller. The synchronization is obtained using a simple external Global Positioning System receiver, which does not provide a disciplined clock. The synchronization of sampling frequency, and thus of the measurement, to the Universal Time Coordinated, is obtained by means of a suitable signal processing technique. For this implementation, the Interpolated Discrete Fourier Transform has been used as the synchrophasor estimation algorithm. A thorough metrological characterization of the realized prototype in different test conditions proposed by the standards, using a high performance PMU calibrator, is also shown.

System for deployment of groups of unmanned micro aerial vehicles in GPS-denied environments using onboard visual relative localization

A complex system for control of swarms of micro aerial vehicles (MAV), in literature also called as unmanned aerial vehicles (UAV) or unmanned aerial systems (UAS), stabilized via an onboard visual relative localization is described in this paper. The main purpose of this work is to verify the possibility of self-stabilization of multi-MAV groups without an external global positioning system. This approach enables the deployment of MAV swarms outside laboratory conditions, and it may be considered an enabling technique for utilizing fleets of MAVs in real-world scenarios. The proposed visual-based stabilization approach has been designed for numerous different multi-UAV robotic applications (leader-follower UAV formation stabilization, UAV swarm stabilization and deployment in surveillance scenarios, cooperative UAV sensory measurement) in this paper. Deployment of the system in real-world scenarios truthfully verifies its operational constraints, given by limited onboard sensing suites and processing capabilities. The performance of the presented approach (MAV control, motion planning, MAV stabilization, and trajectory planning) in multi-MAV applications has been validated by experimental results in indoor as well as in challenging outdoor environments (e.g., in windy conditions and in a former pit mine).

The influence of soccer match play on physiological and physical performance measures in soccer referees and assistant referees

ABSTRACTThe aim of this study was to quantify the acute impact of soccer match officiating on selected physiological and physical performance measures. Twenty-four officials from the Spanish National 3rd Division participated in this study. External global positioning system and internal (heart rate) load data were collected for each match official during 8 official matches. Pre- and post-matches, the referees were assessed for tympanic temperature, blood lactate, 15- and 30-m sprint speeds and unilateral (dominant and non-dominant legs) and bilateral vertical jump performances. For referees, the acute physiological and physical performance effects of officiating (post-match value minus pre-match value) were large increases in blood lactate (1.7 mmol · l−1; ±90% confidence limit, 0.9 mmol · l−1; effect size, ES = 4.35), small increases in 15-m sprint (0.09; ±0.04 s; ES = 0.53) and 30-m sprint speeds (0.14; ±0.08 s; ES = 0.39) and a small increase in non-dominant leg jump performance (2.1; ±1.4 cm; ES = 0.31). For assistant referees, there was a small decrease in tympanic temperature (−0.3°C; ±0.2°C; ES = −0.65) and small increases in blood lactate (0.4; ±0.3 mmol · l−1; ES = 0.66), 15-m sprint speed (0.06; ±0.04 s; ES = 0.47), 30-m sprint speed (0.11; ±0.16 s; ES = 0.49) and bilateral countermovement jump height (3.4; ±1.5 cm; ES = 0.45). Taken together, these data demonstrate that the physical demands of soccer officiating are sufficient to elicit increases in blood lactate and small decrements in sprint performance and, thereby, provide some evidence for match-related fatigue.

Underwater Doppler Navigation with Self-calibration

Precise autonomous navigation remains a substantial challenge to all underwater platforms. Inertial Measurement Units (IMU) and Doppler Velocity Logs (DVL) have complementary characteristics and are promising sensors that could enable fully autonomous underwater navigation in unexplored areas without relying on additional external Global Positioning System (GPS) or acoustic beacons. This paper addresses the combined IMU/DVL navigation system from the viewpoint of observability. We show by analysis that under moderate conditions the combined system is observable. Specifically, the DVL parameters, including the scale factor and misalignment angles, can be calibrated in-situ without using external GPS or acoustic beacon sensors. Simulation results using a practical estimator validate the analytic conclusions.

Extracting gravity vectors from the integration of global positioning system and inertial navigation system data

Consulting records of a past flight, 1‐Hz trajectory, and (roll, pitch, yaw) motion profiles were adopted for a simulated 7.5‐hour balloon flight over New Mexico. The assumed pay load of the balloon was an inertial ring laser gyro strap‐down system and a three‐antenna, minimum 12‐channel Global Positioning System (GPS) receiver. The adopted trajectory was assumed to be GPS determined and interferometric in nature reflecting a second, ground‐fixed receiver. Owing to the strap‐down Inertial Navigation System (INS), a corresponding 1‐Hz profile of accelerometer specific force outputs (total (GPS sensitive) inertially referenced accelerations less gravitational accelerations present) was also required to conduct a covariance error analysis. The gravitational accelerations were computed by a spherical harmonic expansion through n = m = 360. A 36‐state, 40‐noise process, open‐loop Kaiman filter integrating GPS and INS data was constructed. A full constellation of 18 GPS satellites was simulated. Related to the two receivers, external GPS updating observation types used were pseudorange differences, single differenced carrier phases, and single differenced phase rates. A fourth type of updating observation used was the error in the INS's estimation of phase differences between GPS antenna pairs (an equilateral triangle balloon‐borne configuration was assumed with 1‐m baselines). The filter cycle and update frequency were both set at 1 Hz. A postmission covariance analysis based Kaiman filter mechanization was executed, taking into account the major initial INS and GPS error sources. Hybrid alignment errors were reduced to 0.4 arc sec about the north and east axes (leveling errors) and to 0.7 arc sec about the down axis (heading error). Hybrid positioning and velocity errors were held to the 1–2 cm and 1–2 mm\s range, respectively, and were highly correlated to the corresponding position dilution of precision satellite geometry. The benign motions of the balloon allowed for a smooth time behavior of the states. Assuming the accelerometer errors are essentially bias states that can be calibrated in flight based on very accurate GPS observations, the leveling uncertainties are the main error sources in obtaining the three components of the balloon‐ borne gravity vector. The alignment errors mentioned above contribute a 2.5‐mGal error to the computed horizontal components and a 0.05‐mGal error to the vertical. Limiting the misalignment contributions to the deflection error budgets to 1 mGal will require leveling errors of 0.2 arc sec. Gravity components obtained from a hybrid system can be compared to upward continued (from extensive ground gravity data) components to validate continuation models and to establish instrumental proof of concept. A successful balloon experiment would be a strong argument for a “high‐low” satellite tracking mission involving the GPS constellation and a dedicated, polar orbit, low satellite (altitude ε (160 km, 300 km)) possessing the same payload. At such an altitude the leveling concerns are less pronounced. Such a spaceborne mission would allow for a downward continued gravity mapping over all heretofore inaccessible Earth surface regions.