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Joint statistical correction of clutters, spokes and beam height for a radar derived precipitation climatology in southern Germany

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HYDROLOGY AND EARTH SYSTEM SCIENCES 2012年第11期16卷 4101-4117页

作者： Wagner, A. Seltmann, J. Kunstmann, H. German Met Serv DWD Meteor Observ Hohenpeissenberg Germany Univ Augsburg Inst Geog Reg Climate & Hydrol D-86159 Augsburg Germany Karlsruhe Inst Technol Inst Meteorol & Climate Res IMK IFU Garmisch Partenkirchen Germany

First results of radar derived climatology have emerged over the last years, as datasets of appropriate extent are becoming available. Usually, these statistics are based on time series lasting up to ten years as continuous storage of radar data was often not achieved before. This kind of climatology demands a high level of data quality. Small deviations or minor systematic under- or overestimations in single radar images become a major cause of error in statistical analysis. Extensive corrections of radar data are a crucial prerequisite for radar derived climatology. We present a new statistical post-correction scheme based on a climatological analysis of seven years of radar data of the Munich weather radar (2000-2006) operated by DWD (German Weather Service). Original radar products are used subject only to corrections within the signal processor without any further corrections on single radar images. The aim of this statistical correction is to make up for the average systematic errors caused by clutter, propagation, or measuring effects but to conserve small-scale natural variations in space. The statistical correction is based on a thorough analysis of the different causes of possible errors for the Munich weather radar. This analysis revealed the following basic effects: the decrease of rain amount as a function of height and distance from the radar, clutter effects such as clutter remnants after filtering, holes by eliminated clutter or shading effects from obstacles near the radar, visible as spokes, as well as the influence of the bright band. The correction algorithm is correspondingly based on these results. It consists of three modules. The first one is an altitude correction which minimises measuring effects. The second module corrects clutter effects and disturbances and the third one realises a mean adjustment to selected rain gauges. Two different sets of radar products are used. The statistical analysis as well as module 1 and module 2 of the corre

关键词： rain gauges radar clutter Climatology SPOKE Data Quality correction algorithm Radar images signal processor radar data

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A proposal of AHRS yaw angle correction with the use of roll angle

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AIRCRAFT ENGINEERING AND AEROSPACE TECHNOLOGY 2023年第9期95卷 1435-1443页

作者： Kopecki, Grzegorz Banicki, Michal Rzeszow Univ Technol Dept Av & Control Syst Rzeszow Poland

PurposeAttitude and heading are very important measurements on board aircraft. In modern solutions they are measured by the attitude and heading reference system (AHRS). In some small unmanned systems, the GPS track angle is used for heading corrections instead of the magnetometer;then, the system measures the track angle instead of heading. With a temporary lack of correction signals, the measurement error increases very quickly. Similarly, a quick increase in the measurement error is observed when a magnetic heading sensor used for correction stops working properly. This study aims to propose measurement of the roll angle for yaw angle correction. Design/methodology/approachAHRS algorithms were designed;typical maneuvers were analyzed. The method was verified by simulation and in flight testing analysis. For quantitative analyses, a performance index was proposed. FindingsThe method enables reduction of the yaw angle error caused by the gyros bias error. This study presents the idea, results of simulations and flight testing data analysis and discusses advantages and limitations of the presented method. Practical implicationsThe presented methodology can be implemented in AHRS systems for manned and unmanned aircraft. Originality/valueThis study enables more accurate measurement of the yaw angle in the case of missing correction signals.

关键词： AHRS correction algorithm Heading measurement

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Atmospheric correction of SeaWiFS imagery for turbid coastal and inland waters

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APPLIED OPTICS 2000年第6期39卷 897-912页

作者： Ruddick, KG Ovidio, F Rijkeboer, M Math Models N Sea Management Unit B-1200 Brussels Belgium Free Univ Amsterdam Inst Environm Studies NL-1081 HV Amsterdam Netherlands

The standard SeaWiFS atmospheric correction algorithm, designed for open ocean water, has been extended for use over turbid coastal and inland waters. Failure of the standard algorithm over turbid waters can be attributed to invalid assumptions of zero water-leaving radiance for the near-infrared bands at 765 and 865 nm. In the present study these assumptions are replaced by the assumptions of spatial homogeneity of the 765:865-nm ratios for aerosol reflectance and for water-leaving reflectance. These two ratios are imposed as calibration parameters after inspection of the Rayleigh-corrected reflectance scatterplot. The performance of the new algorithm is demonstrated for imagery of Belgian coastal waters and yields physically realistic water-leaving radiance spectra. A preliminary comparison with in situ radiance spectra fbr the Dutch Lake Markermeer shows significant improvement over the standard atmospheric correction algorithm. An analysis is made of the sensitivity of results to the choice of calibration parameters, and perspectives for application of the method to other sensors are briefly discussed. (C) 2000 Optical Society of America.

关键词： Water-leaving Radiance atmospheric correction Inland waters correction algorithm sea water SeaWiFS application methods

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Tomographic motion detection and correction directly in sinogram space

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PHYSICS IN MEDICINE AND BIOLOGY 2002年第8期47卷 1267-1284页

作者： Lu, WG Mackie, TR Univ Wisconsin Dept Med Phys Madison WI 53706 USA

Patient motion, especially respiratory motion, results in various artefacts such as blurring and streaks in tomographic images. The interplay of the movement of the beam aperture and variations of organ anatomy during delivery can create 'hot' and 'cold' spots throughout the field in intensity-modulated radiation therapy (IMRT). Detection and correction of patient motion is extremely important in tomographic imaging and IMRT. Tomographic projection data (sinogram) encode not only the patient anatomy information, but also the intra-scanning motion information. In this paper. we developed an algorithm to detect and correct the in-plane respiratory motion directly in sinogram space. The respiratory motion is modelled as time-varying scaling along the x and v directions. Its effects on the sinogram are discussed. Based on the traces of some nodal points in the sinogram, the intra-scanning motion is determined. The motion correction is also implemented in sinogram space. The motion-corrected sinogram is used for reconstruction by the filtered back-projection (FBP) method. Computer simulations validate the motion detection and correction algorithm. The reconstructed images from the motion-corrected sinogram eliminate the majority of the artefacts. The method could be applied to projection data used in CT and ECT, as well as in tomotherapy delivery modification and dose reconstruction.

关键词： correction algorithm Tomography sinogram Motion detection COLD SPOT Patient Motion Artifact

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Wideband quadrature error correction (using SVD) for stepped-frequency radar receivers

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IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS 1999年第4期35卷 1444-1449页

作者： Noon, DA Longstaff, ID Stickley, GF Univ Queensland Dept Comp Sci & Elect Engn Cooperat Res Ctr Sensor Signal & Informat Proc Brisbane Qld 4072 Australia

We present a new technique which corrects the wideband quadrature errors associated with homodyne stepped-frequency radar receivers. The correction algorithm is derived using singular value decomposition (SVD) which diagonalizes and scales the covariance matrix of a test signal while preserving the coherent phasor alignment across all frequency steps of the homodyne receiver. Using our technique, the wideband quadrature errors of a 1-2 GHz stepped-frequency radar receiver were corrected to within a 0.1 dB gain imbalance, and to within a 0.5 deg phase imbalance. The Hermitian images were shown to be suppressed by more than 50 dB below the main target peaks.

关键词： homodyne receiver new technique test signal Stepped frequency radar correction algorithm variance covariance matrix Receivers orthogonal deviation broadband

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A Time-to-Digital Converter-Based correction Method for Charge Measurement Through Area Integration

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IEEE TRANSACTIONS ON NUCLEAR SCIENCE 2018年第12期65卷 2883-2891页

作者： Zhang, Jiajin Zhao, Lei Dong, Ruoshi Deng, Peipei Ma, Cong Lu, Jiaming Liu, Shubin An, Qi Univ Sci & Technol China State Key Lab Particle Detect & Elect Hefei 230026 Anhui Peoples R China Univ Sci & Technol China Dept Modern Phys Hefei 230026 Anhui Peoples R China

A high-precision charge measurement can be achieved by the area integration of a digitized quasi-Gaussian signal after the signal passes through the shaper and analog-to-digital converter. The charge measurement contains an error due to the uncertainty of the first sampled point of a signal waveform. To reduce the error, we employ a time-to-digital converter to measure the uncertainty precisely, and we design correction algorithms to improve the resolution of the charge measurement. This paper includes analysis and simulations of the proposed algorithms and implementation of them in a field-programmable gate array device. In addition, the tests are also conducted to evaluate the performance of the correction method. Test results indicate that the resolution of the charge measurement is successfully improved from 2.31 to 1.26 by using a signal from the shaping circuit (with the amplitude of 2 V, and leading and trailing edges of about 80 and 280 ns, respectively) digitized at the sampling rate of 62.5 Msps.

关键词： Charge measurement correction algorithm fine time time-to-digital converter (TDC)

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Suppression correction and characteristic study in liquid chromatography/Fourier transform mass spectrometry measurements

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RAPID COMMUNICATIONS IN MASS SPECTROMETRY 2011年第4期25卷 551-557页

作者： Ma, Xuepo Hestilow, Travis J. Cui, Jian Zhang, Jianqiu Univ Texas San Antonio Dept Elect & Comp Engn San Antonio TX USA

Analysis of peptide profiles from liquid chromatography/Fourier transform mass spectrometry (LC/FTMS) reveals a nonlinear distortion in intensity. Investigation of the measured C-13/C-12 ratios comparing with theoretical ones shows that the nonlinearity can be attributed to signal suppression of low abundance peptide peaks. We find that the suppression is homogenous for different isotopes of identical peptides but non-homogenous for different peptides. We develop an iterative correction algorithm that corrects the intensity distortions for peptides with relatively high abundance. This algorithm can be applied in a wide range of applications using LC/FTMS. We also analyze the distortion characteristics of the instrument for lower abundance peptides, which should be considered when interpreting quantification results of LC/FTMS. Copyright (C) 2011 John Wiley & Sons, Ltd.

关键词： correction algorithm Mass spectroscopy Nonlinear distortion Peptides wide-range liquids Transform nonlinearity

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Apparent resistivity for transient electromagnetic induction logging and its correction in radial layer identification

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JOURNAL OF APPLIED GEOPHYSICS 2018年 151卷 328-342页

作者： Meng, Qingxin Hu, Xiangyun Pan, Heping Xi, Yufei Hebei GEO Univ Coll Explorat Technol & Engn Shijiazhuang 050031 Hebei Peoples R China China Univ Geosci Inst Geophys & Geomat Wuhan 430074 Hubei Peoples R China Chinese Acad Geol Sci Inst Hydrogeol & Environm Geol Shijiazhuang 050061 Hebei Peoples R China

We propose an algorithm for calculating all-time apparent resistivity from transient electromagnetic induction logging. The algorithm is based on the whole-space transient electric field expression of the uniform model and Halley's optimisation. In trial calculations for uniform models, the all-time algorithm is shown to have high accuracy. We use the finite-difference time-domain method to simulate the transient electromagnetic field in radial two-layer models without wall rock and convert the simulation results to apparent resistivity using the all-time algorithm. The time-varying apparent resistivity reflects the radially layered geoelectrical structure of the models and the apparent resistivity of the earliest time channel follows the true resistivity of the inner layer;however, the apparent resistivity at larger times reflects the comprehensive electrical characteristics of the inner and outer layers. To accurately identify the outer layer resistivity based on the series relationship model of the layered resistance, the apparent resistivity and diffusion depth of the different time channels are approximately replaced by related model parameters;that is, we propose an apparent resistivity correction algorithm. By correcting the time-varying apparent resistivity of radial two-layer models, we show that the correction results reflect the radially layered electrical structure and the corrected resistivities of the larger time channels follow the outer layer resistivity. The transient electromagnetic fields of radially layered models with wall rock are simulated to obtain the 2D time-varying profiles of the apparent resistivity and corrections. The results suggest that the time-varying apparent resistivity and correction results reflect the vertical and radial geoelectrical structures. For models with small wall-rock effect, the correction removes the effect of the low resistance inner layer on the apparent resistivity of the larger time channels. (C) 2018 Elsevier

关键词： Transient electromagnetic induction logging Radial layer Apparent resistivity correction algorithm Halley's optimization

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ERROR ANALYSIS AND correction IN A BEAM PROFILE MONITOR

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NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 1995年第1期364卷 19-26页

作者： GRAVES, WS FERMILAB NATL ACCELERATOR LAB BATAVIAIL

An analysis of the accuracy and sources of error of transverse beam profile measurements made with an ion profile monitor in the Fermilab booster is presented. Two dimensional computer simulations are compared with experiment to determine the magnitude of the errors and a correction algorithm that uses beam size and charge as parameters is developed.

关键词： Beams and girders amplitude error BEAM PROFILES Error analysis Computer Simulation correction algorithm BEAM Contour measurement accuracy analysis MONITOR

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A regression-based statistical correction of mesoscale simulations for near-surface wind speed using remotely sensed surface observations

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ASIA-PACIFIC JOURNAL OF ATMOSPHERIC SCIENCES 2012年第4期48卷 449-456页

作者： Kim, Do-Yong Kim, Jin-Young Kim, Jae-Jin Pukyong Natl Univ Dept Environm Atmospher Sci Pusan 608737 South Korea Pukyong Natl Univ Brain Korea Grad Sch Earth Environm Syst 21 Pusan 608737 South Korea

Wind speed is an important meteorological variable for various scientific communities. In this study, numerical mesoscale simulations were performed over the Republic of Korea in 2006, to produce wind information distributed homogeneously with space. Then, an attempt was made to statistically correct the simulated nearsurface wind speed using remotely sensed surface observations. The weak wind season (WWS, from May to October) and strong wind season (SWS, from November to April) were classified on the basis of the annual mean wind speed. Although the spatial features and monthly variation pattern of the near-surface wind speed were reasonably simulated in the Weather Research and Forecasting (WRF) model, the simulations overestimated the observed values. To correct the simulated wind speeds, a regression-based statistical algorithm with different constants and coefficients for WWS and SWS was developed using match-up datasets of wind observations and satellitederived variables (land surface temperature and normalized difference water index). The corrected wind speeds showed reasonable performance for both WWS and SWS with respect to observed values. The monthly variation in the corrected wind speeds over the Republic of Korea also matched better with observations throughout the year, within a monthly bias range of approximately +/- 0.2 m s(-1). The proposed algorithm using remotely sensed surface observations may be useful for correcting simulated near-surface wind speeds and improving the accuracy of wind assessments over the Republic of Korea.

关键词： Wind speed mesoscale simulation satellite remote sensing correction algorithm

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