Key Error Sources Research Articles

Evaluation of clear‐sky solar fluxes in GCMs participating in AMIP and IPCC‐AR4 from a surface perspective

Solar fluxes at the Earth's surface calculated in General Circulation Models (GCMs) contain large uncertainties, not only in the presence of clouds but, as shown here, even under clear‐sky (i.e., cloud‐free) conditions. Adequate observations to constrain the uncertainties in these clear‐sky fluxes have long been missing. The present study provides newly derived observational clear‐sky climatologies at worldwide distributed anchor sites with high‐accuracy measurements from the Baseline Surface Radiation Network (BSRN) and the Atmospheric Radiation Measurement Program (ARM). These data are used to systematically assess the performance of a total of 36 GCMs with respect to their surface solar clear‐sky fluxes. These models represent almost 2 decades of model development, from the atmospheric model intercomparison projects AMIP I and AMIP II to the state of the art models participating in the 4th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC‐AR4). Results show that earlier model versions tend to largely overestimate the surface insolation under cloud‐free conditions. This identifies an overly transparent cloud‐free atmosphere as a key error source for the excessive surface insolation in GCMs noted in previous studies. Possible origins are an underestimated water vapor absorption and a lack of adequate aerosol forcing. Similar biases remain in a number of current models with comparatively low atmospheric clear‐sky solar absorption (around 60 Wm−2 in the global mean). However, there are now several models participating in IPCC‐AR4 with higher atmospheric clear‐sky absorption (70 Wm−2 and up, globally averaged) and more realistic aerosol treatment, which are in excellent agreement with the newly derived observational clear‐sky climatologies. This underlines the progress made in radiative transfer modeling as well as in the observation and diagnosis of solar radiation under cloudless atmospheres and puts the most likely value of solar radiation absorbed in the cloud‐free atmosphere slightly above 70 Wm−2.

Uncertainty Assessment of Voc Emissions from Paint in the Netherlands Using the Nusap System

We demonstrate an innovative approach to uncertainty assessment known as the NUSAP system, to assess qualitative and quantitative uncertainty for the case of emissions of volatile organic compounds (VOC) from paint in The Netherlands. Using expert elicitation, we identified key sources of error, critical assumptions, and bias in the monitoring process. We assessed pedigree and probabilistic uncertainty of all input quantities. We used four pedigree criteria to assess the strength of the knowledge base: proxy representation, empirical basis, methodological rigour and degree of validation. Using Monte Carlo analysis, we assessed sensitivity and propagation of uncertainty. Results for sensitivity and pedigree were combined in a 'NUSAP Diagnostic Diagram', which effectively highlighted the assumption for VOC percentage of imported paint as the weakest spot in the monitoring of VOC emissions. We conclude that NUSAP facilitates systematic scrutinization of method and underlying assumptions and structures creative thinking on sources of error and bias. It provides a means to prioritise uncertainties and focus research efforts on the potentially most problematic parameters and assumptions, at the same time identifying specific weaknesses in the knowledge base. With NUSAP, nuances of meaning about quantities can be conveyed concisely and clearly, to a degree that is not possible with statistic methods only.

Direct sample positioning and alignment methodology for strain measurement by diffraction

An ISO (International Organization for Standardization) TTA (Technology Trends Assessment) was published in 2001 for the determination of residual stress using neutron diffraction which identifies sample alignment and positioning as a key source of strain measurement error. Although the measurement uncertainty by neutron and synchrotron x-ray diffraction for an individual measurement of lattice strain is typically of the order of 10–100×10−6, specimens commonly exhibit strain gradients of 1000×10−6mm−1 or more, making sample location a potentially considerable source of error. An integrated approach to sample alignment and positioning is described which incorporates standard base-plates and sample holders, instrument alignment procedures, accurate digitization using a coordinate measuring machine and automatic generation of instrument control scripts. The methodology that has been developed is illustrated by the measurement of the transverse residual strain field in a welded steel T-joint using neutrons.

An Experimental Study of Small-Scale Variability of Radar Reflectivity Using Disdrometer Observations

Abstract Analysis of data collected by four disdrometers deployed in a 1-km2 area is presented with the intent of quantifying the spatial variability of radar reflectivity at small spatial scales. Spatial variability of radar reflectivity within the radar beam is a key source of error in radar-rainfall estimation because of the assumption that drops are uniformly distributed within the radar-sensing volume. Common experience tells one that, in fact, drops are not uniformly distributed, and, although some work has been done to examine the small-scale spatial variability of rain rates, little experimental work has been done to explore the variability of radar reflectivity. The four disdrometers used for this study include a two-dimensional video disdrometer, an X-band radar-based disdrometer, an impact-type disdrometer, and an optical spectropluviometer. Although instrumental differences were expected, the magnitude of these differences clouds the natural variability of interest. An algorithm is applied to ...

Development and assessment of a single-image fringe projection method for dynamic applications

A single-image fringe projection profiling method suitable for dynamic applications was developed by combining an accurate camera calibration procedure and improved phase extraction procedures. The improved phase extraction process used a modified Hilbert transform with Laplacian pyramid algorithms to improve measurement accuracy. The camera calibration method used an accurate pinhole camera model and pixel-by-pixel calibration of the phase-height relationship. Numerical simulations and controlled baseline experiments were performed to quantify key error sources in the measurement process and verify the accuracy of the approach. Results from numerical simulations indicate that the resulting phase error can be reduced to less than 0.02 radians provided that parameters such as fringe spacing, random measured intensity noise, fringe contrast and frequency of spatial intensity noise are carefully controlled. Experimental results show that the effects of random temporal and spatial noise in typical CCD cameras for single fringe images limits the accuracy of the method to 0.04 radians in most applications. Quantitative results from application of the fringe projection method are in very good agreement with numerical predictions, demonstrating that it is possible to design both a fringe projection system and a measurement process to achieve a prespecified accuracy and resolution in the point-to-point measurement of the spatial (X, Y, Z) positions.

Estimating manipulation errors in finite element analysis part II

With the increasing use of microcomputers for engineering research and production analyses, control of round-off error is of increasing concern. An essential ingredient in control is the ability to estimate the errors. Part I of this paper described the errors in processing numbers with digital computers [4]. This part, Part II, presents and illustrates the effectiveness of error estimation for three goals: pre-estimating, measuring actual errors, and identifying the error source. Pre-estimation is intended to eliminate analyses whose results would be inaccurate. Measurement of actual errors qualifies the accuracy of calculations. Error source identification leads to selection of error reduction methods. The authors conclude that bound estimates of lost precision are excessively high, do not correlate with actual round-off errors, and are not reliable in identifying the key sources of error. Experiments show that the closure measure provides excellent estimates of maximum error in stress predictions. This fact suggests a conservative approach to protect against use of inaccurate analysis results.

Tests of published mechanisms by comparison with measured laminar flame structure in fuel-rich acetylene combustion

Mole-fraction data from a laminar, premixed, C 2 H 2 /O 2 /5% Ar flame were used to test predictions of combustion-chemistry mechanisms from Miller et al., Warnatz, Westbrook, and Westbrook and Dryer. Profiles of mole fraction vs. distance were measured for 38 species at conditions of o=2.40 (slightly sooting), 2.67 kPa, and 0.5 m·s −1 cold-gas velocity using molecular-beam mass spectrometry. Profiles for 25 of these species were predicted using each of the mechanisms in a one-dimensional flame model, and the importance of individual reactions were assessed using Reaction-Path Analysis. Products and rate constants for destruction reactions of CH 2 , C 2 H 3 , C 3 H 2 , C 3 H 3 , C 3 H 4 , and C 4 H 2 proved to be key sources of error. Including C 3 H 6 chemistry is a key to the good prediction of C 2 H 3 by the Westbrook and Dryer mechanism, but using the incorrect reaction C 2 H 3 +O 2 →C 2 H 2 +HO 2 causes poor prediction of C 2 H 3 by the other mechanisms. A reversible Warnatz mechanism gave the largest number of satisfactory predictions, emphasizing the importance of reversibility.

Job knowledge, ratee familiarity, conceptual similarity and halo error: An exploration.

Abstract : The results of numerous social perception studies have led researchers to conclude that raters' implicit cognitive schemes regarding trait and behavior covariance may play a crucial role in the rating judgement process. Cooper (1981a, 1981B) proposed one such cognitive scheme, semantic conceptual similarity, as a key source of halo error in job performance ratings, but was unable to reproduce the results of previous social perception research (e.g., Shweder, 1975). This study employed baseball studies as target ratees to examine the effects of job and ratee knowledge on the relationships of raters' conceptual similarity schemes with rating and true score covariance. The results were consistent with the systemic distortion hypothesis (Shweder, 1975): The association between conceptual similarity and rating covariance was significantly greater when raters lacked sufficient job and/or ratee knowledge. Moreover, the degree of halo was also significantly greater when raters lacked relevant job or ratee knowledge. The potential advantages of using objective measures of actual performance as true score estimates in the study of rater cognitive process, as opposed to the widely videotape simulations, are discussed. Keywords: Performance appraisal, rating errors, and halo errors.

Low earth orbit navigation in the tracking and data acquisition system era

Several alternatives are addressed for meeting spacecraft orbit and time determination requirements in the 1990s with the proposed follow-on to the Tracking and Data Relay Satellite System. Key objectives are to reduce ground requirements for routine two-way tracking, support onboard navigation, and satisfy projected user accuracy goals down to 10 m (position) and 1 /*s (time). This paper focuses primarily on three one-way range and Doppler tracking techniques based on 1) onboard processing of navigation beacon signals broadcast continuously, 2) onboard processing of scheduled tracking signals, and 3) ground-based processing of scheduled, usergenerated tracking signals. System configurations and requirements to support each method are compared and preliminary results of navigation performance evaluations are presented as a function of user orbit, relay satellite constellation, and other parameters. Comparison of results with the accuracy requirements in a 1990-2005 mission model indicate that essentially all can be satisfied with beacon tracking based on projected reductions in key error sources. The scheduled tracking alternatives are also applicable except in low-altitude orbits where performance is more sensitive to drag uncertainty, tracking frequency, and/or navigation data upload rates. ,

Analysis of Alternate Borehole Survey Systems

Conventional borehole survey technology, involving the use of either magnetic or gyroscopic instruments, provides at best a lateral position uncertainty of 1% of measured well depth. The conventional tools also exhibit severe accuracy degradation in inclined boreholes. Preliminary test programs have indicated that an order-of-magnitude improvement over conventional technology can be achieved by adapting modern inertial navigation and guidance techniques to the development of an improved gyroscopic survey instrument. The objective of this paper is to analyze the performance characteristics of certain gyroscopic tools currently in development and outline major system error sensitivities. Mathematical error models have been developed for several different gyroscopic tools, which can be grouped into three general categories: Gyrocompass, Attitude Reference System and Inertial Navigation System. These models are used as the basis for a series of computer error simulations which characterize the statistical survey accuracy of the various tool designs as a function of time and displacement. The analysis also identifies the major operational limitations of each design and establishes the sensitivities to key error sources.

Some Key Sources of Error in Test Administration

(1959). Some Key Sources of Error in Test Administration. The Clearing House: A Journal of Educational Strategies, Issues and Ideas: Vol. 34, No. 3, pp. 161-164.