Accuracy Of Velocity Determination Research Articles

Evaluation of the performance of GNSS-based velocity estimation algorithms

Global Navigation Satellite System (GNSS) based velocity estimation is one of the most cost-effective and widely used methods in determining velocity in geodesy and transport applications. Highly accurate and reliable velocity measurements can be obtained by exploiting the raw Doppler, carrier phase, and pseudorange measurements with a GNSS receiver. There are several approaches to GNSS-based velocity determination. This paper investigates the characteristics of the approaches which are currently popular and applicable to the observations of Global Positioning System (GPS), BeiDou Navigation Satellite System (BDS), and their combination (GPS/BDS). Specifically, it evaluates the performance of the velocity estimated based on the Raw Doppler method, the Time-Differenced Pseudorange method, the Time-Differenced Carrier Phase method, and the Double-Differenced Carrier Phase method, in both static and dynamic modes and in open and urban scenarios. The experiments show that BDS has the advantages in delivering accurate velocity determinations over GPS in the Asia–Pacific region, and the effectiveness of the GPS/BDS in improving the overall accuracy of velocity determination in complex urban scenarios.

Investigation of high-precision non-linear crash reconstruction method basing on a ‘Mini’ vehicle class database

ABSTRACTIn the research concerning Mini NHTSA vehicle class there was presented the application of non-linear description of the bk coefficient depending on the precrash velocity Vt as a function of generalised body deformation coefficient Cs defined after crash test. The nonlinear relationship includes one independent parameter – vehicle mass. These two parameters – Cs and m – through quadric surface describe the value of the crash velocity Vt. Previously used linear model did not allow to achieve the accuracy of velocity determination in the range enabling performing the crash reconstructions. The non-linear model is more precise and hence represents the phenomenon occurring during body deformation. The value of relative error for the new method for the velocity Vt decreases. The authors present the relative error value as a function of the case number form the NHTSA database.

Aortic Stenosis assessment with a 3-directional phase contrast magnetic resonance technique. Comparison to transthoracic echocardiography

Background Transthoracic Doppler-echocardiography (TTE) is the standard clinical method for diagnosis and staging of aortic stenosis (AS). AS staging is based on measurement of aortic peak velocity, transvalvular gradient, and calculation of aortic valve area. Unidirectional throughplane phase-contrast magnetic resonance imaging (1DPC-MRI) has been widely applied in clinical imaging to quantify aortic peak velocities and flow. Nonetheless, 1DPC-MRI requires accurate positioning of imaging planes perpendicular to flow direction in order to avoid peak velocity underestimation, which can be challenging in patients with multiple or eccentric jets. Therefore PC techniques with multi-directional velocity quantification would likely improve the accuracy of velocity determination, and allow for more accurate grading of AS severity. The aim of this study is to determine whether a rapid technique that is able to capture 3 directions of velocity in a 2D image plane in a single breath-hold (3DPCMRI) provides more accurate estimation of diagnostic parameters compared with the traditional 1DPC-MRI, using TTE as the reference standard.

Errors in Radar CMP Velocity Estimates Due to Survey Geometry, and Their Implication for Ice Water Content Estimation

The accuracy of velocity determination from common mid-point (CMP) ground penetrating radar surveys has been assessed in the past and found to be sufficient for migration and depth determination. Increasingly, these velocities are also being used to quantify subsurface physical properties such as water content. This paper demonstrates that small errors in measured velocity can result in large errors in these derived properties. We have evaluated the size of some error sources with specific reference to a given glaciological model and common glaciological survey conditions. At worst, large static errors and 3% errors in measured offset result in interval velocity errors of [Formula: see text]. This error is large enough that derived water content has an error greater than 80% (e.g., [Formula: see text] volumetric % water). Common acquisition and processing practices result in [Formula: see text] interval velocity errors (corresponding to [Formula: see text] error in water content, e.g., [Formula: see text] volumetric %); best practices could result in errors as low as [Formula: see text] in interval velocity (corresponding to [Formula: see text] error in water content, e.g., [Formula: see text] volumetric %), but to achieve this level of precision requires a revision of common practice for CMP acquisition and processing. This revision would need to result in improved assignment of time zero and a consistent definition of reflection event arrival time (to provide travel time errors smaller than 0.5%), and accurate measurement of CMP geometry.

Automatic Ultrasonic Measurement of Sound Velocity in Liquids by a Phase Difference Method

The working of a novel ultrasonic technique for measuring the sound velocity in liquids, which automatically cancels the dependence of temperature by a phase difference method is described in this paper. This technique uses a very simple circuit system which treats only the continuous sinusoidal waves and is constituted of only analog circuits. The temperature-compensation factor in the designing of the temperature-compensation circuit is derived from the equation obtained for the ultrasonic velocity in sea water. This measuring system is shown to yield a 0.01% accuracy of velocity determination, independent of the temperature variation of ±1.0°C around 25.4°C for the NaCl solution.