Angle Measurement Error Research Articles

Tracking Filters for Radar Systems with Correlated Measurement Noise

where the tracking system model presumes white process and measurement noise. In practice, the measurement noise may not be white. Its bandwidth may be on the order of several hertz. For example, target scintillation (or glint) causes the range and angle measurement errors to have a finite bandwidth. Another example of correlated measurement error is the radial velocity measurement error appearing as a result of radar frequency instability and target velocity fluctuations.When the measurement frequency is much smaller than the error bandwidth, the errors of successive measurements are approximately uncorrelated and can be treated as white noise. However, the measurement frequency of some modern radars is sufficiently high and the correlation cannot be ignored without tracking accuracy deterioration.A possible approach to circumvent the effect of colored noise is the target state augmentation technique.

Precision angle measurement in a diffractional spectrometer by means of a ring laser

The measurement of radiation diffraction angles in spectrometers is usually carried out by means of optical encoders or laser interferometers. An angle measurement system based on a ring laser (RL) is described in this paper. The main feature of the RL is that a standing electromagnetic wave in the RL cavity can be considered as a high-precision circular scale. Systems incorporating RLs usually provide an accuracy of angle measurements of several hundredths of an arcsecond in the measurement range 0-. The system described here consists of a RL and an optical interference null-indicator located on a rotary platform optically connected to the crystal of the diffractional spectrometer. An analysis of the measurement principle and measurement errors is presented. It is shown that the main sources of error are the random drift of the phase of the RL output signal and the wideband fluctuation of the null-indicator output signal. Results of measurements of the x-ray line of radiation with an energy of radiation E = 17.47334 keV and corresponding wavelength Å are shown. The angle measurement error of the described system turned out to be about 0.05 arcsecond.

Unbiased converted measurements for tracking

The exact compensation for the bias in the classical polar-to-Cartesian conversion is shown to be multiplicative and to depend on the statistics of the cosine of the angle measurement errors. An unbiased conversion is presented. A comparison between this unbiased conversion and the previously presented debiased conversion is made. The unbiased spherical-to-Cartesian conversion is also presented and evaluated.

The optimal detector surface of a fixed target RICH with a tilted mirror

The origin of the optical error in the Cherenkov angle measurement in the case of a tilted RICH mirror geometry is described together with possible reductions of this error. It is shown that by suitably adjusting the detector form, the resulting contribution to the overall error in Cherenkov angle measurement can be made negligible.

Distortion of intravascular ultrasound images because of nonuniform angular velocity of mechanical-type transducers

The purpose of this study was to quantify nonuniform rotation in a current mechanical intravascular ultrasound (IVUS) instrument and its effect on arc, area, and diameter measurements. The accurate reconstruction of IVUS two-dimensional images is dependent on uniform rotation of the catheter tip. Prior investigations suggested that bends in the catheter driveshaft may be responsible for poor torque transmission, nonuniform rotation, and consequent errors in IVUS measurements. Eight 30 MHz mechanically driven IVUS catheters were evaluated in a model simulating the catheter course through the aorta and coronary ostium in a clinical study. Angular velocity and position profiles of the transducer, image angle, and diameter and area measurement errors were obtained from each catheter by imaging a vascular phantom with eight equispaced echogenic markers from concentric and eccentric positions. Six catheters also were tested for comparison in a simple curvature model. Rotational error was found in all catheters tested and worsened in the aortic model. Maximal angular error, defined as the largest angle between actual and presumed transducer direction, increased when measured in the aortic model as compared with the simple curvature model (17 ± 12 degrees to 45 ± 25 degrees; p < 0.05). Angles of 45 degrees were misrepresented with a mean range of values of 26 to 63 degrees. With eccentric catheter placement, area and diameters had average maximal absolute errors of 26% ± 7.8% and 23% ± 10%, respectively. In conclusion, nonuniform rotation of mechanical IVUS transducers constitutes a significant potential source of error in IVUS measurement of arcs of calcification, and lumen shape, area, and diameter.

Two-colour compensation method for measuring unsteady vertical force of an insect in a wind tunnel

A two-colour compensation (TCC) method was developed for measuring the tilt angle of a gauge block generated by the beating motion of a dragonfly in a wind tunnel. In this method, a wavelength correlation was used to compensate the error due to beam fluctuations induced by air turbulence. The repeatability and resolution of the TCC method were determined by using a piezo translator (PZT) to generate the tilt angle variation. The results show that by using the TCC method the error in tilt angle measurement due to air turbulence can be decreased by about 50% compared with that using a one-wavelength method. The TCC method was then applied to measure the tilt angle variation caused by the beating motion of a dragonfly attached to one end of a gauge block in a wind tunnel for a wind velocity of . The results confirmed the effectiveness of this new method.

Practical Application of a Biaxial Goniometer to the Wrist Joint

The objectives of this study were: 1) to determine errors in wrist angle measurements from a commercially-available biaxial electrogoniometer and 2) to develop a calibration routine in order to correct for these errors. Goniometric measurements were simultaneously collected with true angular data using a fixture that allowed wrist movement in one plane while restricting motion in the orthogonal plane. These data were collected in two sets of trials: 1) flexion/extension with radial/ulnar deviation restricted and 2) radial/ulnar deviation with flexion/extension restricted. During these trials, discrete 30 degree increments of forearm rotation were studied. The results showed the expected cross talk and zero drift errors during forearm rotation. The application of mathematical equations that describe the effect of goniometer twist during forearm rotation resulted in significant error reduction for most trials. The calibration technique employs both a slope and a displacement transformation to improve the accuracy of angular data. The calibration technique may be used on data collected in the field if forearm rotation is measured simultaneously with the goniometer data.

Experiments on meso-optical fourier transform microscope with double focusing

There are described two experiments on meso-optical Fourier transform microscope with double focusing, one with nuclear emulsion, exposed by the accelerated Ne-nucleus, and another, in which the primary particles were the accelerated Oxigen-nucleus. It is shown that the measurement error of the orientation angle θ xy is equal to ±1.5 angular minutes. Three kinds of the geometrical distortions in the nuclear emulsion have been detected.

A new method for absolute calibration of high-sensitivity accelerometers and other graviinertial devices

Abstract To investigate the dynamic characteristics of high-sensitivity graviinertial devices (accelerometers, seismometers, and others) it seems advantageous to use for the input signal the gravitational acceleration produced by bodies with a known mass distribution. This eliminates the need for moving the transducer under investigation. Such motion is needed in the inertial acceleration reproduction as well as for inclining a measuring instrument in the Earth's gravity field. Error in measuring the parameters of the transducer motion is determined by the uncertainties of the length- and angle-measuring instruments being used. Particularly, it concerns the angle measurement errors when the gravity field effects have been taken into account. The existing methods for reproducing gravitational acceleration are based on the use of nonuniform fields of simple shape bodies (sphere, cylinder, and the like). These methods require calculation of the corresponding acceleration, taking into account the spatial mass distribution of the instrument sensing element. The commonly employed approximation results in a procedural error of the order of 10% and over. It is proposed to calibrate a measuring instrument using a uniform, flat gravity field of varying direction. The set-up designed to realize this method reproduces varying accelerations over the frequency range 0.01 to 0.3 Hz with amplitude less than 1.3 × 10−7 m/sec2. This enables calibration of seismometers of various types with a higher accuracy.

Random tropospheric effects in command guidance by multilateration and interferometry

Statistical models are developed for the random spatial variations in refractivity in the troposphere, and are used to derive spatial correlation functions for the errors in range measurement and interferometer angle measurement. These are then used to analyze the relative errors between two tracked targets, for application to command-guided intercept problems. It is shown that multilateration, using range measurements, yields much smaller relative errors than does the interferometer approach.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Space-based tactical ballistic missile launch parameter estimation

The author explores the influence of a priori uncertainties in launch time and trajectory fly-out profiles, along with sensor angle measurement errors, on the estimation of missile launch location and heading angle. An error model is developed to compute the statistics of the estimation errors using a single pair of angle measurements, one from each of two satellites, or both from the same satellite platform. The measurements and estimation methods are described, followed by a derivation of the estimation errors for the hypothetical case of perfect knowledge of trajectory and launch time. Using the ideal case as a framework, the errors are generalized to include trajectory and launch time uncertainties. The results are discussed with the aid of graphics which were run parametrically to highlight important dependencies and sensitivities.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Error sources in deferred heterodyne moire deflectometry: an analytical study

Effects of aperture size and shape of the photodetector and effects of the structure of the grating lines on the performance of deferred electronic heterodyne moire deflectometry are theoretically investigated. Deferred deflectometry is used for measurements of nonsteady phase objects for which it is difficult to complete the analysis of the field in real time. It has been shown that scanning of a moire fringe pattern parallel to an unshifted fringe yields periodical variations in the heterodyne phase and amplitude, which cause severe errors in the measurements. Theory indicates that these variations may be minimized by using a detector with square aperture of size rho/p = 1.0,2.0,3.0 ... or a circular detector with size rho/p =1.25,2.25,3.25... To minimize errors in deflection angle measurements, the fringe inclination due to the phase object should not exceed 15 degrees for a square detector and 13 degrees for a rho/p = 3.25 circular detector. Ronchi gratings with structure factor 0.5 less, similar q less, similar 0.7 are recommended.

Frequency Domain Error Correction for Monopulse Radar Signals

Angle-measurement error of a coherent monopulse radar signalresulting from imbalances between in-phase and quadraturecomponents, as well as between sigma and delta channels, arecorrected in a simple procedure. No correction is needed for I,Qimbalances in the time domain [1]. Instead, a postintegrationcorrection is performed. This reduces the number of calibrationoperations of the monopulse signal by a factor X, 2 ≤ X ≤ N (N isthe number of DFT samples), depending on the degree of filtering.It also reduces the number of numerical operations necessary forthe production of the correction term by a factor of three. A firstorderrder estimation is made of the residual error after correction, dueto bias and image sidelobes.

Acceptable errors in angle measurement

Acceptable errors in angle measurement

Adaptive, high precision, satellite attitude control for microprocessor implementation

A control system is presented for three-axis, gas jet, satellite attitude control having application to any spacecraft where precise pointing is required within stringent mass and power limitations. Several novel features are incorporated as follows: parabolic switching boundaries are employed with parameters which adapt to a disturbing acceleration estimate in order to achieve a zero offset steady-state limit cycle of preset amplitude in the arcsecond region which minimizes both fuel consumption and thruster operation frequency. The disturbing acceleration estimate is obtained from a third-order state estimator, together with angle error and rate estimates using an angle error measurement from a rate integrating gyro and a jet drive input. Time optimal recovery from large initial angle errors and rapid response to step changes in disturbing acceleration are achieved. In addition, stable control is obtained with disturbing acceleration approaching the control jet acceleration. A slew control algorithm is incorporated which enables the same control law to be utilized for fuel optimal slewing through unlimited angles, one axis at a time. Simulation results are presented, including demonstration of stochastic performance with gyro and jet noise.

Registration errors in compound B-scans.

The effect of B-scanner articulated arm angle measurement errors on B-mode registration is considered. For a single-angle articulated arm model, a mathematical equation predicting B-mode misregistration as a function of angular errors and compound scan angle is derived and discussed. This model accurately predicts registration errors for transducer connector/acoustic axis misalignment or third arm angle errors.

An Adaptive, High Precision, Gas Jet Satellite Attitude Control System for Microprocessor Implementation

A control system is presented for three axis gas jet satellite attitude control employing parabolic switching boundaries with parameters which adapt to a disturbing acceleration estimate in order to achieve a steady state limit cycle of preset amplitude in the arc second region without zero offset, also minimizing fuel consumption and thruster operation frequency. The control law accepts angle error, rate and disturbing acceleration estimates obtained from a third order state estimator with an angle error measurement from a rate integrating gyro and an acceleration input derived from the jet drive. Time optimal recovery from large initial angle errors and rapid response to step changes in disturbing acceleration are achieved. In addition, stable control is obtained with disturbing accelerations approaching the control jet acceleration. A slew control algorithm is incorporated which enables the same control law to be utilized for fuel optimal slewing through unlimited angles, about one axis at a time. Simulation results are presented including demonstration of stochastic performance with gyro and jet noise. The technique has application to scientific spacecraft where precise pointing is required within stringent mass and power limitations. A good example is the application to ESA's EXOSAT spacecraft which carries scientific instruments with ultimate angular accuracies of about 5 arc seconds.

Effect of nonlinear distortions in frequency doublers on angle-measurement errors

Effect of nonlinear distortions in frequency doublers on angle-measurement errors

A note on run - error and the error of half - interval in mean - reading theodolites

Abstract It is recommended that the run-errors of mean-reading theodolites be determined from results of measurements of angles of known size rather than by following classical procedures. It is also shown that a difference between the magnifications of the diametral images of the circle-graduations can lead to a systematic error in angle measurements.

Measurement of angle errors of mutual inductance coils by means of an alternating current bridge

In using the described method for the measurement of angle errors of mutual inductance coils, it should be kept in mind that the error is determined by a number of factors, of which eddy currents in windings and the distributed capacitance are the most important. The presence of distributed capacitance leads to a situation where, in transition from the accordant connection of windings to connection in opposition, the leakage current changes. Therefore, the measured value of the angle error can be, generally speaking, substantially different from the value obtained if the given coil is used as an actual measure of the 90° phase shift. Consequently, the described method of measuring the angle error is suitable for those mutual inductance coils where the capacitance leakage is sufficiently small or does not change to a great extent when the coil connections are interchanged.