GPS-based Techniques Research Articles

Underreported trips, a non-negligible empirical effect of traditional survey methods – A new weighting procedure of data enriching to overcome this bias

Travel behavior surveys are essential for a fact based transport policy. But they suffer notoriously from unreported trips. Depending on the mode of transport the amount of underreported trips is estimated in the range up to 40%. An exact determination of underreporting is difficult, because the "underlying truth" is generally latent. One solution is to combine traditional travel survey methods with GPS-based techniques for a representative sub-sample. The result provides patterns of mobility both from the traditional survey for the whole sample as well as from the GPS-survey, which can be used for a weighting procedure to eliminate the bias.

Estimation of relation between moisture content of soil and reflectivity index using GPS signals

The irrigation system throughout the world is affected by the variations in water content due to different soil structure, textures and climate change. The irrigation system supplies sufficient water to the agricultural fields in order to fulfill the prerequisites. The measurement of soil moisture content (62%) is crucial for precision irrigation and sustainable agricultural system. Site specific agricultural system was utilized to overcome all issues related to soil water moisture contents in the paddock. Smart technology was utilized to record GPS signals utilizing the signals reflected on the Earth’s surface. The GPS was utilized to analyze dielectric soil properties and moisture content in proposed areas. The main objective of this study was to determine water content with stimulus soil type, ground cover and compaction on the irrigation system by utilizing the GPS-based techniques. The result indicated positive relation between soil moisture content and the signals reflected on the earth surface. All factors affecting the irrigation system were not related to the reflected signals and did not affect the soil moisture content. The reflectivity was not reduced by ground cover. Whereas, comparative relationship was found between soil moisture content and reflectivity index i.e. soil moisture contents were increased with reflectivity index up to 0.02 %. The results showed that GPS signals system have significant impact on estimation of soil moisture content in precise irrigation system.

Comparative Analysis of Stockpile Volume Estimation using UAV and GPS Techniques

Mining operations involve the extraction of minerals of economic value from the earth. In surface mining operations, overburdens need to be stripped in other to reach the ore. Large volumes of waste as well as ore is stripped in the process. Various technologies have been used to aid in stockpile volume estimation. Notable among them are the Total Stations and Global Positioning Systems (GPS). However, labour, safety and time has challenged the use of these technologies. Unmanned Aerial Vehicle (UAV), commonly known as drone is an emerging technology for stockpile volume computations in the Mine. UAV technology for data collection is less labour intensive, safer and faster. Therefore, this study applied the UAV technology in an open pit to estimate stockpile volumes from a Mine. For the purpose of this study, GPS and UAV data were collected for measuring stockpile volumes of materials mined. The actual volumes of stockpiles A, B, C, D (Case 2), produced differences of 0.05% for A, 0.05% for B, 0.08% for C, 0.07% for D and 0.03% for A, -0.03% for B, 0.03% for C and 0.04% for D, for the GPS-based and the UAV-based techniques, respectively. The GPS-based technique generated moderate accuracies for volume estimation, but was time consuming and labour intensive, compared to the UAV-based technique; which was faster and less labour intensive. The UAV-based technique was the most accurate, safest and is capable of mapping large areas rapidly. It is therefore recommended that UAV survey be incorporated in stockpile volume estimation.
 Keywords: UAV, GPS, Stockpile, Mine, Total Stations

Parametric study of sensor placement for vision-based relative navigation system of multiple spacecraft

In order to overcome the limited range of GPS-based techniques, vision-based relative navigation methods have recently emerged as alternative approaches for a high Earth orbit (HEO) or deep space missions. Therefore, various vision-based relative navigation systems use for proximity operations between two spacecraft. For the implementation of these systems, a sensor placement problem can occur on the exterior of spacecraft due to its limited space. To deal with the sensor placement, this paper proposes a novel methodology for a vision-based relative navigation based on multiple position sensitive diode (PSD) sensors and multiple infrared beacon modules. For the proposed method, an iterated parametric study is used based on the farthest point optimization (FPO) and a constrained extended Kalman filter (CEKF). Each algorithm is applied to set the location of the sensors and to estimate relative positions and attitudes according to each combination by the PSDs and beacons. After that, scores for the sensor placement are calculated with respect to parameters: the number of the PSDs, number of the beacons, and accuracy of relative estimates. Then, the best scoring candidate is determined for the sensor placement. Moreover, the results of the iterated estimation show that the accuracy improves dramatically, as the number of the PSDs increases from one to three.

High Accuracy GPS-Free Vehicle Localization Framework via an INS-Assisted Single RSU

Collision avoidance and road safety applications require highly accurate vehicle localization techniques. Unfortunately, the existing localization techniques are not suitable for road safety applications as they rely on the error-prone Global Positioning System (GPS). Likewise, cooperative localization techniques that use intervehicle communications experience high errors due to hidden vehicles and the limited sensing/communication range. Recently, GPS-free localization based on vehicle communication with a low cost infrastructure installed on the roadsides has emerged as a more accurate alternative. However, existing techniques require the vehicle to communicate with two roadside units (RSUs) in order to achieve high localization accuracy. In contrast, this paper presents a GPS-free localization framework that uses two-way time of arrival to locate the vehicles based on communication with a single RSU. Furthermore, our framework uses the vehicle kinematics information obtained via the vehicle's onboard inertial navigation system (INS) to further improve the accuracy of the vehicle location using Kalman filters. Our results show that the localization error of the proposed framework is as low as 1.8 meters. The resulting localization accuracy is up to 65% and 47.5% better than GPS-based techniques used without/with INS, respectively. This accuracy gain becomes around 73.3% when compared to existing RSU-based techniques.

Evaluation of the Accuracy and Automation of Travel Time and Delay Data Collection Methods

Travel time and delay are among the most important measures for gauging a transportation system’s performance. To address the growing problem of congestion in the US, transportation planning legislation mandated the monitoring and analysis of system performance and produced a renewed interest in travel time and delay studies. The use of traditional sensors installed on major roads (e.g. inductive loops) for collecting data is necessary but not sufficient because of their limited coverage and expensive costs for setting up and maintaining the required infrastructure. The GPS-based techniques employed by the University of Delaware have evolved into an automated system, which provides more realistic experience of a traffic flow throughout the road links. However, human error and the weaknesses of using GPS devices in urban settings still have the potential to create inaccuracies. By simultaneously collecting data using three different techniques, the accuracy of the GPS positioning data and the resulting travel time and delay values could be objectively compared for automation and statistically compared for accuracy. It was found that the new technique provided the greatest automation requiring minimal attention of the data collectors and automatically processing the data sets. The data samples were statistically analyzed by using a combination of parametric and nonparametric statistical tests. This analysis greatly favored the GeoStats GPS method over the rest methods.

Field Measurements of Wind Turbine Wakes with Lidars

AbstractField measurements of the wake flow produced from a 2-MW Enercon E-70 wind turbine were performed using three scanning Doppler wind lidars. A GPS-based technique was used to determine the position of the wind turbine and the wind lidar locations, as well as the direction of the laser beams. The lidars used in this study are characterized by a high spatial resolution of 18 m, which allows the detailed characterization of the wind turbine wake. Two-dimensional measurements of wind speed were carried out by scanning a single lidar over the vertical symmetry plane of the wake. The mean axial velocity field was then retrieved by averaging 2D scans performed consecutively. To investigate wake turbulence, single lidar measurements were performed by staring the laser beam at fixed directions and using the maximum sampling frequency. From these tests, peaks in the velocity variance are detected within the wake in correspondence of the turbine top tip height; this enhanced turbulence could represent a source of dangerous fatigue loads for downstream turbines. The spectral density of the measured velocity fluctuations shows a clear inertial-range scaling behavior. Then, simultaneous measurements with two lidars were performed in order to characterize both the axial and the vertical velocity components. For this setup, the two velocity components were retrieved only for measurement points for which the two laser beams crossed nearly at a right angle. Statistics were computed over the sample set for both velocity components, and they showed strong flow fluctuations in the near-wake region at turbine top tip height, with a turbulence intensity of about 30%.

A comparison of total precipitable water measurements from radiosonde and sunphotometers

Atmospheric water vapour is an essential component of the terrestrial atmosphere and must be known precisely in a wide range of applications such as radiative transfer modelling or weather forecasting to mention just a few examples. Vertically integrated measurements, or total precipitable water (TPW) equivalent amounts traditionally derived from radiosonde measurements, are needed in many of these applications and can also be obtained from other methodologies such as sunphotometers or GPS-based techniques. This paper presents a study comparing different measurements of TPW from radiosonde and sunphotometer data recorded from 2001 to 2004 in Barcelona, Spain. Three collocated instruments were employed in this study: RS-80A Vaisala sondes and two types of commonly used sunphotometers (Cimel 318N-VBS7 and Microtops II). A cloud screening filter was applied to photometer data based on the quality control procedure of the AERONET database. A systematic comparison among the measurements indicates that bivariate correlations between different instruments were high, with correlation factors ( r 2) above 0.8 in all cases. Measurements covered all seasons allowing examining intra-annual variability, which generally did not exhibit statistically significant differences. Examination of 57 concurrent measurements of the three instruments indicated that radiosonde TPW measurements were the highest (15 mm on average) and Cimel and Microtops presented similar values (12 mm and 11 mm respectively).

MONITORING OF STRUCTURES USING THE GLOBAL POSITIONING SYSTEM.

Keywords BRUNEL UNIVERSITY, NOTTINGHAM UNIVERSITY, HUMBER BRIDGE BOARD STRUCTURES, MONITORING, GPS, GLOBAL, POSITIONING, SYSTEMS, MODELS, VALIDATION, FINITE ELEMENTS, BRIDGES, HUMBER BRIDGE, DEFLECTION, MEASUREMENT, LOADING, LOADS, PREDICTION, RESONANT, FREQUENCIES, TESTS, EXPERIMENTS, DATA, SIGNALS, DISPLACEMENT, STEEL, SURVEYING, APPLICATIONS, METHODS, SENSORS, MOVEMENT, TECHNOLOGY, DYNAMICS, RESPONSES HUMBER BRIDGE UK... Show All