Accuracy of vertical velocity determination

Typical wind spectra taken at Poker Flat, Alaska, using the vertically oriented antenna show velocities of 10's of cm to meters per second and spectral widths winds of 0.5 to 1 m/s. The potential errors in such measurements can be broken down into three categories: (1) those due to instrumental parameters and data processing, (2) those due to specular returns from non-horizontal surfaces, and (3) those due to other physical effects. Error analysis in vertical velocity measurement is further discussed

GPS vertical axis performance enhancement for helicopter precision landing approach

Several areas were investigated for improving vertical accuracy for a rotorcraft using the differential Global Positioning System (GPS) during a landing approach. Continuous deltaranging was studied and the potential improvement achieved by estimating acceleration was studied by comparing the performance on a constant acceleration turn and a rough landing profile of several filters: a position-velocity (PV) filter, a position-velocity-constant acceleration (PVAC) filter, and a position-velocity-turning acceleration (PVAT) filter. In overall statistics, the PVAC filter was found to be most efficient with the more complex PVAT performing equally well. Vertical performance was not significantly different among the filters. Satellite selection algorithms based on vertical errors only (vertical dilution of precision or VDOP) and even-weighted cross-track and vertical errors (XVDOP) were tested. The inclusion of an altimeter was studied by modifying the PVAC filter to include a baro bias estimate. Improved vertical accuracy during degraded DOP conditions resulted. Flight test results for raw differential results excluding filter effects indicated that the differential performance significantly improved overall navigation accuracy. A landing glidepath steering algorithm was devised which exploits the flexibility of GPS in determining precise relative position. A method for propagating the steering command over the GPS update interval was implemented

Accuracy, reproducibility and vertical resolution of data from radiosondes

In a comparison of three radiosonde-systems typical data deviations as well as their reproducibility could be determined. Basic considerations regarding a possible vertical resolution are followed by a suggestion as to how the ascent velocity of the balloon could be utilized to determine vertical winds

Comparison of vertical velocities analyzed by a numerical model and measured by a VHF wind profiler

The use of wind profilers for measuring vertical velocities in the troposphere and lower stratosphere is potentially of great interest for verification of forecasts, diagnosis of mesoscale circulations, and studies of wave motions. The studies of profiler vertical velocities to date have shown that the observed patterns of ascent and subsidence are reasonable when compared to the synoptic conditions. However, difficulties arise when a direct verification of the profiler vertical winds is sought. Since no other technique can measure the vertical velocities over the same height range and with the same claimed accuracy as the profilers, direct comparisons are impossible. The only alternative is to compare the measurements to analyzed vertical velocity fields. Here, researchers compare vertical measurements made with the SOUSY VHF radar over a period of 11 days at the beginning of November 1981 to the analyzed vertical velocities produced by the European Center for Medium-range Weather Forecasting (ECMWF) model for grid points near the radar site

Galerkin Least-Squares Stabilization in Ice Sheet Modeling - Accuracy, Robustness, and Comparison to other Techniques

We investigate the accuracy and robustness of one of the most common methods used in glaciology for the discretization of the $\mathfrak{p}$-Stokes equations: equal order finite elements with Galerkin Least-Squares (GLS) stabilization. Furthermore we compare the results to other stabilized methods. We find that the vertical velocity component is more sensitive to the choice of GLS stabilization parameter than horizontal velocity. Additionally, the accuracy of the vertical velocity component is especially important since errors in this component can cause ice surface instabilities and propagate into future ice volume predictions. If the element cell size is set to the minimum edge length and the stabilization parameter is allowed to vary non-linearly with viscosity, the GLS stabilization parameter found in literature is a good choice on simple domains. However, near ice margins the standard parameter choice may result in significant oscillations in the vertical component of the surface velocity. For these cases, other stabilization techniques, such as the interior penalty method, result in better accuracy and are less sensitive to the choice of the stabilization parameter. During this work we also discovered that the manufactured solutions often used to evaluate errors in glaciology are not reliable due to high artificial surface forces at singularities. We perform our numerical experiments in both FEniCS and Elmer/Ice.Comment: 32 pages, 17 figure

Accuracy of digital panoramic radiographs on the vertical measurements of dental implants

Amaç: Panoramik radyografi (PR), dental ve iliskili yapilari degerlendirmek için en sik kullanilan tekniktir. Bu çalismanin amaci, dental implant tedavisinin planlanmasinda panoramik radyografik görüntülerin (PRI) dogrulugunu ve anterior, premolar ve posterior bölgeler için bir panoramik cihazin büyütme oranini belirlemekti. Gereç ve Yöntem: Implant cerrahisi sonrasi PRI'lari alinmis olan 83 hasta çalismaya dahil edildi. önceden dikey uzunluklari bilinen toplam 240 adet dental implant (53 anterior, 69 premolar ve 118 molar bölge), PRI'nin büyütme oranini ve dogrulugunu belirlemek için, panoramik sistemin ölçüm araçlari kullanilarak ameliyat sonrasi radyografik görüntüler üzerinde tekrar ölçüldü. Verilerin normal dagilima sahip olmasi nedeniyle, istatistiksel analiz için eslestirilmis t testi kullanildi (p < 0,05). üç bölgenin büyütme orani, implantlarin ölçülen dikey uzunlugunun, implantlarin gerçek dikey uzunluguna orani bulunarak hesaplandi. Bulgular: Implantlarin gerçek dikey uzunlugu ve PRI'dan ölçülen dikey uzunlugu arasinda istatistiksel olarak anlamli fark bulundu (p < 0,05). Bununla birlikte, korelasyon orani tüm bölgeler için 1'e yakin bulundu. Implantlarin gerçek dikey uzunlugu ve PRI'den ölçülen dikey uzunlugu arasindaki fark, ön bölge için 0.50 mm, premolar bölge için 0,97 mm ve molar bölge için 0,83 mm idi. Cliniview™ (Instrumentarium Sti., Tuusula, FINLANDIYA) yazilimi tarafindan düzeltilen panoramik sistemin büyütme orani, tüm bölgeler için 1 civarinda bulundu. Sonuçlar: PRI'lar, kolay ulasilabilir olmalari ve düsük radyasyon dozlari sayesinde, implant cerrahisi planlamasindaki dikey ölçümler için 1 mm'lik güven araligi ile kullanilabilir. © Cumhuriyet University Faculty of Dentistry 2018.Objectives: Panoramic radiography (PR) is the most commonly used technique to evaluate the dental and associated structures. The aim of this study was to determine the accuracy of panoramic radiographic images (PRIs) in planning the dental implant treatment and the magnification rate of a panoramic device for anterior, premolar and posterior regions. Materials and Methods: Eighty-eight patients with PRIs were taken after implant surgery were included to the study. A total of 240 dental implants (53 anterior, 69 premolar, and 118 molar regions) of which actual vertical lengths were known, were re-measured on post-operative radiographic images using the scaling tools of the panoramic system to determine the magnification rate and the accuracy of PRIs. Because the data had normal distribution, the paired t test was used for the statistical analysis (p < 0.05). The magnification rates of the three regions were calculated as the ratio of the radiographically measured vertical length of the implants to the actual vertical length of the implants. Results: A statistically significant difference was found between the actual and measured vertical length of the implants on the PRI (p < 0.05). However, the correlation rate was found close to 1 for all regions. The difference between the actual and measured vertical length of the implants on the PRI was 0.50 mm for the anterior region, 0.97 mm for the premolar region, and 0.83 mm for the molar region. The magnification rate of the panoramic system corrected by Cliniview™ (Instrumentarium Corp., Tuusula, FINLAND) software was found around 1 for all the regions. Conclusions: Due to their readily accessible nature and low radiation dose, PRIs can be used in implant surgery for vertical measurements with 1 mm confidence interval. © Cumhuriyet University Faculty of Dentistry 2018

Applicability of APT aided-inertial system to crustal movement monitoring

The APT system, its stage of development, hardware, and operations are described. The algorithms required to perform the real-time functions of navigation and profiling are presented. The results of computer simulations demonstrate the feasibility of APT for its primary mission: topographic mapping with an accuracy of 15 cm in the vertical. Also discussed is the suitability of modifying APT for the purpose of making vertical crustal movement measurements accurate to 2 cm in the vertical, and at least marginal feasibility is indicated

Inventory of available data elements for the San Bernardino, California region

Elements of data sets that are available to be integrated for the San Bernardino vertical data integration project are given. Each of the data sets has specified for it the ownership, validity, accuracy and technical requirements for integration

A comparison of vertical velocities measured from specular and nonspecular echoes by a VHF radar

For a number of years, there have been doubts about the accuracy of vertical wind velocities measured with quasi-specular reflections from mesosphere-stratosphere-troposphere (MST) radar. The concern has been that the layers producing the quasi-specular reflection process this hypothetical tilt. Because of the quasi-specular reflection process, this hypothetical tilt would control the effective zenith angle of the radar antenna beam so that a small component of the horizontal velocity would be included in what was assumed to be a truly vertical beam. The purpose here is to test the hypothesis that there is an effect on the wind velocities measured on a vertical antenna beam due to a long-term tilting of the stable atmospheric layers that cause quasi-specular reflection. Gravity waves have been observed to cause short-term tilting of turbulent layers and specularly reflecting layers. In both cases, the effect was a wave-like deformation atmospheric layers with a period of a few minutes. This geometry is shown. Because of this influence of gravity waves, it was expected that there would be short-term variations in the vertical velocity

Calibration and accuracy assessment of Leica ScanStation C10 terrestrial laser scanner

Requirement of high accuracy data in surveying applications has made calibration procedure a standard routine for all surveying instruments. This is due to the assumption that all observed data are impaired with errors. Thus, this routine is also applicable to terrestrial laser scanner (TLS) to make it available for surveying purposes. There are two calibration approaches: (1) component, and (2) system calibration. With the intention to specifically identify the errors and accuracy of the Leica ScanStation C10 scanner, this study investigates component calibration. Three components of calibration were performed to identify the constant, scale error, accuracy of angular measurement and the effect of angular resolution for distance measurement. The first calibration has been processed using closed least square solutions and has yielded the values of constant (1.2 mm) and scale error (1.000008879). Using variance ratio test (F-Test), angles observation (horizontal and vertical) for Leica C10 scanner and Leica TM5100A theodolite have shown significance difference. This is because the accuracy of both sensors are not similar and these differences are 0.01 and 0.0075º for horizontal and vertical measurements, respectively. Investigation on the resolution setting for Leica C10 scanner has highlighted the drawback of the tilt-and-turn target. Using the highest resolution, Leica Cyclone software only able to recognize the tilt-and-turn target up to 10 m distance compare to 200 m for the black and white target