Digital Error Research Articles

The impact of different gridding methods on catchment geomorphology and soil erosion over long timescales using a landscape evolution model

AbstractMany digital elevation models are gridded from irregularly spaced data. This study examines differences in catchment geomorphology and hydrology as a result of kriging and Delaunay triangulation gridding methods. Both methods have been widely used as tools for placing irregularly spaced data onto a regular grid. In the past, numerical modelling has been performed with little assessment of model input variability and the variability produced by different gridding methods has not been fully assessed. Given the importance of the impact of digital elevation model error and potential impact on model output, little work has been done to understand the impact of this type of potential error. Examination of the different catchment realizations demonstrates that when using kriging (point or block) or Delaunay triangulation there are subtle differences in catchment area and elevation as well as networking properties. Subtle differences also exist in hillslope profile. Nevertheless, when comparing catchment descriptors such as the hypsometric curve, area–slope relationship and cumulative area distribution there is little hydrological and geomorphological difference between these catchments. Further, when these digital elevation models are used as landscape input in a long‐term landscape evolution model (i.e. SIBERIA) there is little geomorphological difference or hydrological difference between the two digital elevation models after a 50 000 year modelled period. Consequently either method is appropriate for the study catchment. These findings provide confidence in the conversion of irregularly spaced data onto a regular grid using kriging or Delaunay triangulation and that either method can be used. Copyright © 2006 John Wiley & Sons, Ltd.

Bench-top setup for validation of real time, digital periodic error correction

This paper provides experimental validation of the digital first-order periodic error reduction scheme described by Chu and Ray. A bench-top setup of a single-pass, heterodyne Michelson interferometer, designed to minimize common error contributors such as Abbe, dead path and environment, is described. Linear, reciprocating motion generation is achieved using a parallelogram, leaf-type flexure. Periodic error amplitude is varied through independent rotation of a half wave plate and polarizer. Experimental results demonstrate that the correction algorithm can successfully attenuate first-order error to sub-nm levels for a wide range of frequency mixing conditions.

Effects of Digital Elevation Model Errors on Spatially Distributed Seismic Slope Stability Calculations: An Example from Seattle, Washington

More than 1,600 centimeter-accurate differential GPS measurements show that elevation errors in a 10-m digital elevation model (DEM) covering an 18-km 2 portion of Seattle can have significant effects on calculated values of slope angle, static factor of safety, Newmark acceleration, and slope displacement. Declustered error data from the study area have a mean of ! 0.92 m and a standard deviation of 62.36 m, comparable to results reported by others. Conditional Gaussian simulation and normal score back-transformation were used to create 25 error realizations with the same statistical distribution and spatial correlation as the measured errors, and the error realizations were subsequently used to create elevation, slope angle, static factor of safety, Newmark acceleration, and displacement realizations. The maximum slope angle uncertainty magnitude decreases frommorethan108toabout48asslopeangleincreases, but the minimum slope angle uncertainty varies between 618 and 628 regardless of slope angle. Typical slope angle standard deviations arising from DEM errors are in the range of 638 to 648. The resulting uncertainties in calculated Newmark displacements as the consequence of a hypothetical large earthquake affecting the study area (Arias intensity of 4 m/s) are in most cases less than 63 cm, but some values are greater than 610 cm. If the acceptable maximum probability of misclassifying a potentially unstable area as stable is decreased from 50 to 5 percent, incorporation of displacement uncertainty into the calculusofhazardincreasesfrom0.6to4.1percentthe portion of the study area that may be susceptible to landsliding as a result of the hypothetical earthquake.

A117 CGで描画した投影図からの窓面入射光壁面分布の高速計算

In the numerical analysis of the indoor thermal environment with windows through which solar radiation is incident, it requires much computational time to identify irradiated surfaces. This paper shows the fast algorithm to calculate the wall surface distribution of the solar radiation through the window using the CG technique for the purpose of a prediction of the indoor thermal environment. We developed the fast calculation method of the direct solar radiation using parallel images made by graphics hardware at high speed. The diffuse solar radiation can be calculated by applying PPM (Pyramid Projection Method) that is the fast calculation method of view factors. PPM that we developed before uses perspective CG images. The errors of this algorithm are mainly derived from digitization errors of digital images. It was verified that this algorithms had a possibility to become an effective tool for the analysis of the indoor thermal environments with solar radiation.

Resilient design of discrete-time observers with general criteria using LMIs

Much of the recent work on robust control or observer design has focused on preservation of stability of the controlled system or the convergence of the observer in the presence of parameter perturbations in the plant equations. The present work addresses the important problem of resilience or nonfragility which is the maintenance of convergence or performance when the observer is erroneously implemented due possibly to computational errors, e.g., round off errors in digital implementation or sensor errors. A linear matrix inequality approach is presented that maximizes performance in the implementation based on the knowledge of an upper bound on the error in the observer gain. Some design examples are provided for illustration purposes.

RELIABILITY OF THE ERROR CODE FROM THE BEST TRIAL AS AN INDICATOR OF SPIROMETRIC TEST QUALITY USING AMERICAN THORACIC SOCIETY (ATS) CRITERIA

PURPOSE: Assessment of spirometric test quality is important in the interpretation of an individual patient's study, in determining the overall quality of tests being performed by technologists, and when using the data in research. The 1994 ATS criteria for spirometry require three acceptable trials, two of which are reproducible. Computerized testing equipment often provide a five or six digit error code which summarizes whether these criteria have been met. The system in use at our institution provides an error code that identifies whether the reproducibility criteria have been met, yet reports acceptability only for the designated single best trial.

A new method for decaying dc offset removal for digital protective relays

Voltage and current signals used in protection devices may contain harmonics and decaying dc offset in transient states. Because of this, protection devices must contain filters to remove the part of the signal which is not of interest and estimate the value of the component or components which are to be used for protection functions. Traditionally, the discrete Fourier transform (DFT) filter has been used in digital protection devices. This filter has the advantage of being easily applied, but the disadvantage that when an exponentially decaying component is present the results obtained are incorrect. Because of this, different algorithms based on the DFT have been developed in order to remove the decaying dc offset and reduce digital processing errors. This paper describes a new method for removing the exponential component associated with electrical signals in transient states. Its ease of application results in a low computational load as compared with other methods. This characteristic, together with the accuracy of results, makes this new method suitable for application in real time on protection devices.

An LMI approach to discrete-time observer design with stochastic resilience

Much of the recent work on robust control or observer design has focused on preservation of stability of the controlled system or the convergence of the observer in the presence of parameter perturbations in the plant or the measurement model. The present work addresses the important problem of stochastic resilience or non-fragility of a discrete-time Luenberger observer which is the maintenance of convergence and/or performance when the observer is erroneously implemented possibly due to computational errors i.e. round off errors in digital implementation or sensor errors, etc. A common linear matrix inequality framework is presented to address the stochastic resilient design problem for various performance criteria in the implementation based on the knowledge of an upper bound on the variance of the random error in the observer gain. Present results are compared to earlier designs for stochastic robustness. Illustrative examples are given to complement the theoretical results.

Direction finding and antenna calibration through analytical inversion of radio measurements performed using a system of two or three electric dipole antennas on a three‐axis stabilized spacecraft

We present an analytical inversion method to achieve direction‐finding (DF) (i.e., retrieve the direction of arrival of an incoming electromagnetic wave, its flux, and its full polarization state) using radio measurements performed using a system of two or three electric dipole antennas on a three‐axis stabilized spacecraft. The Radio and Plasma Wave Science (RPWS) radio receiver on board Cassini includes such instantaneous DF capabilities, and so does the Solar Terrestrial Relations Observatory (STEREO) Waves radio receiver. We also present an analytical solution of the inverse problem which consists of calibrating the electric dipole orientations and effective lengths using a known radio source. Error sources (imperfect knowledge of antenna parameters, digitization errors, signal to noise ratio, etc.) and their propagation through the analytical inversion have been studied. The typical expected accuracy of our DF inversion is 1 dB [V2/Hz] for flux measurements, about 1–2° for source position and a few percent for degrees of polarization. For the antenna calibration procedure the expected accuracy is of the order of 2° on antenna direction and of 1% on antenna length. We define the data selection criteria to be used during both DF analysis and antenna calibration. We also discuss the limitations of the methods and the ways to improve their accuracy.

Digital Timing Error Correction in Discrete Multitone Systems

When a fixed free-running crystal is used for sampling time generation at a DMT receiver, Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI) are introduced by sampling time error. The ICI becomes more serious as the DMT symbol length increases. In this letter, the effects of sampling clock offset are investigated in the time domain using a new notion of Inter-sample Interference (IsI) instead of ISI and ICI. Based on the IsI analysis, we propose a new frequency domain timing error correction scheme.

Dynamic compensation of HMM variances using the feature enhancement uncertainty computed from a parametric model of speech distortion

This paper presents a new technique for dynamic, frame-by-frame compensation of the Gaussian variances in the hidden Markov model (HMM), exploiting the feature variance or uncertainty estimated during the speech feature enhancement process, to improve noise-robust speech recognition. The new technique provides an alternative to the Bayesian predictive classification decision rule by carrying out an integration over the feature space instead of over the model-parameter space, offering a much simpler system implementation, lower computational cost, and dynamic compensation capabilities at the frame level. The computation of the feature enhancement variances is carried out using a probabilistic and parametric model of speech distortion, free from the use of any stereo training data. Dynamic compensation of the Gaussian variances in the HMM recognizer is derived, which is simply enlarging the HMM Gaussian variances by the feature enhancement variances. Experimental evaluation using the full Aurora2 test data sets demonstrates a significant digit error rate reduction, averaged over all noisy and signal-to-noise-ratio conditions, compared with the baseline that did not exploit the enhancement variance information. When the true enhancement variances are used, further dramatic error rate reduction is observed, indicating the strong potential for the new technique and the strong need for high accuracy in estimating the variances associated with feature enhancement. All the results, using either the true variances of the enhanced features or the estimated ones, show that the greatest contribution to recognizer's performance improvement is due to the use of the uncertainty for the static features, next due to the delta features, and the least due to the delta-delta features.

A study of the real-time deconvolution of digitized waveforms with pulse pile up for digital radiation spectroscopy

Two new real-time approaches have been developed and compared to the least-squares fit approach for the deconvolution of experimental waveforms with pile-up pulses. The single pulse shape chosen is typical for scintillators such as LSO and NaI(Tl). Simulated waveforms with pulse pile up were also generated and deconvolved to compare these three different approaches under cases where the single pulse component has a constant shape and the digitization error dominates. The effects of temporal separation and amplitude ratio between pile-up component pulses were also investigated and statistical tests were applied to quantify the consistency of deconvolution results for each case. Monte Carlo simulation demonstrated that applications of these pile-up deconvolution techniques to radiation spectroscopy are effective in extending the counting-rate range while preserving energy resolution for scintillation detectors.

Optimum Solution of On-Chip A/D Converter for Cooled Type Infrared Focal Plane Array

Transferring the image information in analog form between the focal plane array (FPA) and the external electronics causes the disturbance of the outside noise. On-chip analog-to-digital (A/D) converter into the readout integrated circuit (ROIC) can eliminate the possibilities of the cross-talk of noise. Also, the information can be transported more efficiently in power in the digital domain compared to the analog domain. In designing on-chip A/D converter for cooled type high density infrared detector array, the most stringent requirements are power dissipation, number of bits, die area and throughput. In this study, pipelined type A/D converter was adopted because it has high operation speed characteristics with medium power consumption. Capacitor averaging technique and digital error correction for high resolution was used to eliminate the error which is brought out from the device mismatch. The readout circuit was fabricated using 0.6 μm CMOS process for 128 x 128 mid-wavelength infrared (MWIR) HgCdTe detector array. Fabricated circuit used direct injection type for input stage, and then S/N ratio could be maximized with increasing the integration capacitor. The measured performance of the 14 b A/D converter exhibited 0.2 LSB differential non-linearity (DNL) and 4 LSB integral non-linearity (INL). A/D converter had a 1 MHz operation speed with 75 mW power dissipation at 5 V. It took the die area of 5.6 mm 2 . It showed the good performance that can apply for cooled type high density infrared detector array.

The Recovery of Posterior Cornea and Anterior Lens Radii by a Novel Ray-Tracing Method

Methods for estimating ocular surface radii are typically based on paraxial vergence calculations, need to account for finite source positions, and require refocusing of the camera. This article describes (1) a telecentric ray-finding method; and (2) its application to the problem of determining posterior cornea (R2) and anterior lens (R3) radii by a regression procedure that addresses these issues. The ray-finding algorithm simulates Purkinje image heights Pj(h) (for j = 2, 3; for the Le Grand eye) for the expected range of Rj. A two-step cubic regression procedure fits this image data globally and then over a refined interval to estimate Rj locally. The goodness of fit is measured by the R statistic. A standard method is compared with the new method in simulation. Mean absolute errors and SD's are recorded for 10 randomly chosen R2 and R3. The effect of errors caused by (1) axial shift of the posterior cornea and anterior lens (axially up to +/-0.1 mm); and (2) camera digitization (pixel sizes of 20 microm) are simulated. The method can make use of general surface height information; therefore, it is tested on an eye with nonspherical cornea shape (a toroidal surface). The time to generate Rj is no more than 45 s (R3), with R > 0.9999. The errors for the unmodified eye are (1.3 +/- 2.1) x 10 mm (R2) and (2.4 +/- 1.6) x 10 mm (R3) (new) vs. (5.6 +/- 0.9) x 10 mm (R2) and (1.1 +/- 1.0) x 10 mm (R3) (standard). Digitization increases errors to 0.32 +/- 0.16 mm (R2) and 0.10 +/- 0.10 (R3) (new) vs. 0.45 +/- 0.33 mm (R2) and 0.48 +/- 0.13 mm (R3) (standard). Axial shift error for R2 is similar between methods, with a tendency toward lower error for the new method given digitization error. This trend is found for R3, although the new method now does consistently better with digitization error. Shift contributes the smaller proportion of total error (approximately 10 mm) compared with digitization (approximately 10 mm). The errors for the toroidal surface are (5.7 +/- 7.6) x 10 mm (R2) and (1.1 +/- 0.7) x 10 mm (R3) (new) compared with errors of 0.18 +/- 0.01 mm (R2) and 0.44 +/- 0.07 mm (R3) (standard). The new method produces better results in this case. A telecentric image-computing algorithm produces accurate image positions. A two-step cubic regression produces accurate estimates of R2 and R3 (errors approximately 10 mm). This error increases with axial shift (approximately 10 mm) and digitization (approximately 10 mm). The new method does better than a standard method ignoring all the errors and tends to handle digitization error better. The new method works well on a toroidal anterior cornea. Testing on model/real eyes is required. Efforts are continuing to refine methods for videophakometry.

Physically accurate haptic rendering with dynamic effects

We focus on the realism/transparency aspect of haptic rendering. We introduce a novel approach that enables physically correct and accurate simulation of contact wrench W/sub c/ for general rigid objects in real time, taking into account not only friction and gravity but also dynamic effects. Our method for contact force and moment simulation builds on the real-time identification of geometrically valid contact states despite digital errors. Our approach applies to general rigid bodies including both polyhedral and nonpolyhedral objects. For nonpolyhedral, curved objects, we build our contact state representation and contact force/moment model directly on the smooth and accurate representation of the object surfaces. Our approach's key idea is to solve for the contact force and moment analytically based on not only the contact configuration, but also the real-time identification of the exact type of the corresponding contact state, the type of instantaneous motion of the held object prior to reaching the contact configuration.

An Analog Checker with Input-Relative Tolerance for Duplicate Signals

We discuss the design of a novel analog checker that monitors two duplicate signals and provides a digital error indication when their absolute difference is unacceptably large. The key feature of the proposed checker is that it establishes a test criterion that is dynamically adapted to the magnitude of its input signals, thus enhancing the accuracy of assessing their relative discrepancy. Consequently, when this checker is utilized in concurrent error detection, it diminishes the probability of both false negatives and false positives. Likewise, when employed for off-line test purposes, the checker supports both high yield and high fault coverage. In contrast, checkers implementing a static test criterion may only be tuned to achieve efficiently one of the aforementioned objectives.

What is the adequate sampling interval of the ECG signal for heart rate variability analysis in the time domain?

Heart rate variability (HRV) analysis is considered a simple method for investigating neurocardiac regulation. However, measures of HRV may be corrupted by technical artifacts. In order to investigate the consequences of digitization errors on the time domain parameters, HRV measures from model tachograms resampled at different rates were compared. Two 375-element tachograms from human ECG tracings were shifted to a mean of 800 ms and stretched to standard deviations (SD) of 5–120 ms in 5 ms steps. All were resampled at 1–10 ms in 1 ms steps, 10 times repetitively at each interval. The mean, SD, relative accuracy error (RAE) and relative precision error (RPE) were calculated from the mean RR-interval, SD (SDNN), root mean square of successive RR-differences (RMSSD) and the percentage of consecutive RR-interval differences greater than 50 ms (pNN50). The RAE and RPE of the mean heart rate were below 0.1%. In the series with 5 ms SD, the SDNN–RAE exceeded 30% at 10 ms SI, its RPE was lower than 2% all through. Resampling the 15 ms SD tachogram at 1, 2, 4, or 10 ms resulted in RMSSD–RAE of 0.7%, 2.5%, 7.8% and 45.1%, respectively, while its RPE remained below 5%. The pNN50 shows poor accuracy and precision. An ECG sampling interval of 1 ms is recommended for HRV analysis without interpolation in order to get accurate time domain measures even in seriously reduced-variability samples. However, a lower sampling rate may be satisfactory in cases where higher variability is expected.

Errors in thermochromic liquid crystal thermometry

This article experimentally investigates and assesses the errors that may be incurred in the hue-based thermochromic liquid crystal thermochromic liquid crystal (TLC) method, and their causes. The errors include response time, hysteresis, aging, surrounding illumination disturbance, direct illumination and viewing angle, amount of light into the camera, TLC thickness, digital resolution of the image conversion system, and measurement noise. Some of the main conclusions are that: (1) The 3×8 bits digital representation of the red green and blue TLC color values produces a temperature measurement error of typically 1% of the TLC effective temperature range, (2) an eight-fold variation of the light intensity into the camera produced variations, which were not discernable from the digital resolution error, (3) this temperature depends on the TLC film thickness, and (4) thicker films are less susceptible to aging and thickness nonuniformities.

A novel rodent neck pain model of facet-mediated behavioral hypersensitivity: implications for persistent pain and whiplash injury

Clinical, epidemiological, and biomechanical studies suggest involvement of cervical facet joint injuries in neck pain. While bony motions can cause injurious tensile facet joint loading, it remains speculative whether such injuries initiate pain. There is currently a paucity of data explicitly investigating the relationship between facet mechanics and pain physiology. A rodent model of tensile facet joint injury has been developed using a customized loading device to apply two separate tensile deformations ( low, high; n=5 each) across the C6/C7 joint, or sham ( n=6) with device attachment only. Microforceps were rigidly coupled to the vertebrae for distraction and joint motions tracked in vivo. Forepaw mechanical allodynia was measured postoperatively for 7 days as an indicator of behavioral sensitivity. Joint strains for high (33.6±3.1%) were significantly elevated ( P<0.005) over low (11.1±2.3%). Digitization errors (0.17±0.20%) in locating bony markers were small compared to measured strains. Allodynia was significantly elevated for high over low and sham for all postoperative days. However, allodynia for low injury was not different than sham. A greater than three-fold increase in total allodynia resulted for high compared to low, corresponding to the three-fold difference in injury strain. Findings demonstrate tensile facet joint loading produces behavioral sensitivity that varies in magnitude according to injury severity. These results suggest that a facet joint tensile strain threshold may exist above which pain symptoms result. Continued investigation into the relationship between injury mechanics and nociceptive physiology will strengthen insight into painful facet injury mechanisms.

Use of relaxation-edited one-dimensional and two dimensional nuclear magnetic resonance spectroscopy to improve detection of small metabolites in blood plasma

The 1H nuclear magnetic resonance (NMR) spectra of biological samples, such as blood plasma and tissues, are information rich but data complex owing to superposition of the resonances from a multitude of different chemical entities in multiple-phase compartments, hampering detection and subsequent resonance assignments. To overcome these problems, several spectral-editing NMR experiments are described here, combining spin-relaxation filters (based on T 1, T ρ, and T 2) with both one-dimensional and two-dimensional (2D) NMR spectroscopy. These techniques enable the separation of NMR resonances based on their relaxation times and allow simplification of the complex spectra. In this paper, the approach is exemplified using a control human blood plasma, which is a complex mixture of proteins, lipoproteins, and small-molecule metabolites. In the case of T 1ρ- and T 2-edited 2D NMR experiments, a “flip-back” pulse was introduced after the relaxation editing to make the phase cycling of the “relaxation filter” and the 2D NMR part independent, thus enabling easy implementation of the phase-sensitive 2D NMR experiments. These methods also permit much higher receiver gains to be used to reduce digitization error, in particular, for the small resonances, which are sometimes vitally important for metabonomics studies. Both pulse sequences and experimental results are discussed for T 1-, T 1ρ-, and T 2-filtered COSY, T 2-filtered phase-sensitive DQF-COSY, and T 1, T 1ρ-, and T 2-filtered TOCSY NMR.