scholarly journals Evaluation of Tropospheric & Clock Errors for Precision GPS Positioning & Navigation

2019 ◽  
Vol 8 (2) ◽  
pp. 882-887
Keyword(s):  
Hopfield Model ◽  
Bias Error ◽  
Tropospheric Delay ◽  
Random Errors ◽  
Precise Position ◽  
Clock Error ◽  
Receiver Clock ◽  
Time Correction ◽  
Instrumental Bias ◽  
The Individual

Positional inaccuracies in GPS are caused by severalerrors such as Ionospheric, Tropospheric, Satellite Clock, Receiver Clock etc., Instantaneous correction of these error aids in precise navigation. In the present work Original Hopfield model is considered for the tropospheric correction. The instantaneous tropospheric correction results in more precise position using GPS. The decreasing order of components on basis of effect are Ionospheric delay, Tropospheric delay, Clock error, satellite bias error, Receiver error, multipath error, Ephymeris error, random errors etc. It is a time taken process to calculate the individual error separately.so in this paper we only concentrated on simulation and analysis the tropospheric delay, clock error, ephemeris error. We used Modified Hopfield model to analysis Tropospheric delay, receiver instrumental bias for analysis Clock error in between we eliminate Ephymeris error, after obtained results are compared with and without time correction in original Hopfield model

scholarly journals Adequacy of the In Situ Observing System in the Satellite Era for Climate SST

2006 ◽  
Vol 23 (1) ◽  
pp. 107-120 ◽  
Author(s):  
Huai-Min Zhang ◽  
Richard W. Reynolds ◽  
Thomas M. Smith
Keyword(s):  
High Resolution ◽  
Satellite Observations ◽  
Sea Surface ◽  
Bias Error ◽  
Random Errors ◽  
In Situ Data ◽  
Satellite Sst ◽  
Maximum Bias ◽  
Very High

Abstract A method is presented to evaluate the adequacy of the recent in situ network for climate sea surface temperature (SST) analyses using both in situ and satellite observations. Satellite observations provide superior spatiotemporal coverage, but with biases; in situ data are needed to correct the satellite biases. Recent NOAA/U.S. Navy operational Advanced Very High Resolution Radiometer (AVHRR) satellite SST biases were analyzed to extract typical bias patterns and scales. Occasional biases of 2°C were found during large volcano eruptions and near the end of the satellite instruments’ lifetime. Because future biases could not be predicted, the in situ network was designed to reduce the large biases that have occurred to a required accuracy. Simulations with different buoy density were used to examine their ability to correct the satellite biases and to define the residual bias as a potential satellite bias error (PSBE). The PSBE and buoy density (BD) relationship was found to be nearly exponential, resulting in an optimal BD range of 2–3 per 10° × 10° box for efficient PSBE reduction. A BD of two buoys per 10° × 10° box reduces a 2°C maximum bias to below 0.5°C and reduces a 1°C maximum bias to about 0.3°C. The present in situ SST observing system was evaluated to define an equivalent buoy density (EBD), allowing ships to be used along with buoys according to their random errors. Seasonally averaged monthly EBD maps were computed to determine where additional buoys are needed for future deployments. Additionally, a PSBE was computed from the present EBD to assess the in situ system’s adequacy to remove potential future satellite biases.

scholarly journals Bias Errors due to Leakage Effects When Estimating Frequency Response Functions

2012 ◽  
Vol 19 (6) ◽  
pp. 1257-1266 ◽  
Author(s):  
Andreas Josefsson ◽  
Kjell Ahlin ◽  
Göran Broman
Keyword(s):  
Frequency Response ◽  
Measurement Data ◽  
Approximate Expression ◽  
Bias Error ◽  
Systematic Bias ◽  
Response Functions ◽  
Random Errors ◽  
Frequency Response Functions ◽  
Rectangular Window ◽  
Wide Range

Frequency response functions are often utilized to characterize a system's dynamic response. For a wide range of engineering applications, it is desirable to determine frequency response functions for a system under stochastic excitation. In practice, the measurement data is contaminated by noise and some form of averaging is needed in order to obtain a consistent estimator. With Welch's method, the discrete Fourier transform is used and the data is segmented into smaller blocks so that averaging can be performed when estimating the spectrum. However, this segmentation introduces leakage effects. As a result, the estimated frequency response function suffers from both systematic (bias) and random errors due to leakage. In this paper the bias error in theH1andH2-estimate is studied and a new method is proposed to derive an approximate expression for the relative bias error at the resonance frequency with different window functions. The method is based on using a sum of real exponentials to describe the window's deterministic autocorrelation function. Simple expressions are derived for a rectangular window and a Hanning window. The theoretical expressions are verified with numerical simulations and a very good agreement is found between the results from the proposed bias expressions and the empirical results.

The SRS Catalog of 20,488 Star Positions Culmination of an International Cooperative Effort

1990 ◽  
Vol 141 ◽  
pp. 457-463
Author(s):  
C. A. Smith ◽  
T. E. Corbin ◽  
J. A. Hughes ◽  
E. S. Jackson ◽  
E. V. Khrutskaya ◽  
...  
Keyword(s):  
Reference Star ◽  
Random Errors ◽  
Reduction Procedure ◽  
Cooperative Effort ◽  
International Effort ◽  
Present Discussion ◽  
Observational Material ◽  
Color Error ◽  
The Individual

A major international effort to observe and compile the results of observations from many transit circle programs into a single catalog of positions referred to the FK4 system came to a conclusion with the completion and distribution of the Southern Reference Star (SRS) catalog of 20,488 stars. Previous discussions focussed on the adjustments to the observational material to refer it to the FK4 system and on the random errors as estimated from residual differences. In the present discussion, we give the results of internal comparisons which have been made between the individual contributing catalogs and the final combined SRS catalog. Also, results of a comparison between the SRS catalog and the AGK3R catalog are given where they overlap in the declination zone from +5 to −5 degrees. The possibility of magnitude equation and color error in the SRS catalog is discussed.The reduction procedure used to transform the version of the SRS catalog based on the FK4/B1950.0 system to the version based on the FK5/J2000.0 system is given.

scholarly journals Calibration of Photometry from the Gemini Multi-Object Spectrograph on Gemini North

2009 ◽  
Vol 26 (1) ◽  
pp. 17-30 ◽  
Author(s):  
Inger Jørgensen
Keyword(s):  
Systematic Errors ◽  
Random Errors ◽  
Standard Star ◽  
Primary Mirror ◽  
Color Terms ◽  
User Community ◽  
Color Term ◽  
The Individual ◽  
Zero Points

AbstractAll available observations of photometric standard stars obtained with the Gemini Multi-Object Spectrograph at Gemini North in the period from August 2001 to December 2003 have been used to establish the calibrations for photometry obtained with the instrument. The calibrations presented in this paper are based on significantly more photometric standard star observations than usually used by the individual users. Nightly photometric zero points as well as color terms are determined. The color terms are expected to be valid for all observations taken prior to UT 2004 November 21 at which time the Gemini North primary mirror was coated with silver instead of aluminium. While the nightly zero points are accurate to 0.02 mag or better (random errors), the accuracy of the calibrations is limited by systematic errors from so-called ‘sky concentration’, an effect seen in all focal reducer instruments. We conclude that an accuracy of 0.035 to 0.05 mag can be achieved by using calibrations derived in this paper. The color terms are strongest for very red objects, e.g. for objects with (r′ – z′) = 3.0 the resulting z′ magnitudes will be ≈0.35 mag too bright if the color term is ignored. The calibrations are of importance to the large Gemini user community with data obtained prior to UT 2004 November 21, as well as future users of achive data from this period in time.

scholarly journals Effects of systematic and random errors on the retrieval of particle microphysical properties from multiwavelength lidar measurements using inversion with regularization

2013 ◽  
Vol 6 (11) ◽  
pp. 3039-3054 ◽  
Author(s):  
D. Pérez-Ramírez ◽  
D. N. Whiteman ◽  
I. Veselovskii ◽  
A. Kolgotin ◽  
M. Korenskiy ◽  
...  
Keyword(s):  
Optical Data ◽  
Physical Parameters ◽  
Random Errors ◽  
Additive Property ◽  
Nasa Goddard Space ◽  
Microphysical Properties ◽  
Fine Mode ◽  
Systematic And Random Errors ◽  
The Individual ◽  
Multiwavelength Lidar

Abstract. In this work we study the effects of systematic and random errors on the inversion of multiwavelength (MW) lidar data using the well-known regularization technique to obtain vertically resolved aerosol microphysical properties. The software implementation used here was developed at the Physics Instrumentation Center (PIC) in Troitsk (Russia) in conjunction with the NASA/Goddard Space Flight Center. Its applicability to Raman lidar systems based on backscattering measurements at three wavelengths (355, 532 and 1064 nm) and extinction measurements at two wavelengths (355 and 532 nm) has been demonstrated widely. The systematic error sensitivity is quantified by first determining the retrieved parameters for a given set of optical input data consistent with three different sets of aerosol physical parameters. Then each optical input is perturbed by varying amounts and the inversion is repeated. Using bimodal aerosol size distributions, we find a generally linear dependence of the retrieved errors in the microphysical properties on the induced systematic errors in the optical data. For the retrievals of effective radius, number/surface/volume concentrations and fine-mode radius and volume, we find that these results are not significantly affected by the range of the constraints used in inversions. But significant sensitivity was found to the allowed range of the imaginary part of the particle refractive index. Our results also indicate that there exists an additive property for the deviations induced by the biases present in the individual optical data. This property permits the results here to be used to predict deviations in retrieved parameters when multiple input optical data are biased simultaneously as well as to study the influence of random errors on the retrievals. The above results are applied to questions regarding lidar design, in particular for the spaceborne multiwavelength lidar under consideration for the upcoming ACE mission.

scholarly journals No Myth far and wide:

2018 ◽  
Vol 2 ◽  
Author(s):  
Joachim Hüffmeier ◽  
Stefan Krumm
Keyword(s):  
Reaction Time ◽  
Reaction Times ◽  
Reaction Time Data ◽  
Stopping Rule ◽  
Time Estimate ◽  
Time Data ◽  
Methodological Choices ◽  
Time Correction ◽  
The Individual ◽  
High Chance

Skorski, Extebarria, and Thompson (2016) aim at our article on relay swimmers (Hüffmeier, Krumm, Kanthak, & Hertel, 2012). We have shown that professional freestyle swimmers at relay positions 2 to 4 swam faster in the relay than in the individual competition if they had a high chance to win a relay medal. After applying a reaction-time correction that controls for different starting procedures in relay and individual competitions, Skorski et al. (2016) conclude that swimmers in relays do not swim faster. At first sight, their results appear to show this very pattern. However, we argue that the authors’ findings and conclusion—that our finding is a myth—are not warranted. First, we have also controlled for quicker reaction times in the relay competition. Our correction has been based on the swimmers’ own reaction time data rather than on a constant reaction time estimate and is, thus, more precise than theirs. Second, Skorski et al. treat data from international and national competitions equally although national relay competitions are less attractive for the swimmers than national individual competitions. This difference likely biases their data towards slower relay times. Third, the authors select a small and arbitrary sample without explicit power considerations or a clear stopping rule. Fourth, they unfavorably aggregate their data. We conclude that the reported results are most likely due to the methodological choices by Skorski et al. and do not invalidate our findings.

scholarly journals Irnss Orbit and Clock Bias Estimation using Navic Ground Receiver Data: Extended Kalman Filter

2019 ◽  
Vol 9 (2) ◽  
pp. 713-717
Keyword(s):  
Kalman Filter ◽  
Extended Kalman Filter ◽  
Orbit Determination ◽  
Sequential Estimation ◽  
Estimation Algorithm ◽  
Time Instant ◽  
Tropospheric Delay ◽  
Bias Estimation ◽  
Satellite Clock ◽  
Clock Error

The aim of this work is to precisely estimate the IRNSS satellite’s orbit and clock errors using NavIC receiver data. Orbit determination is required to precisely calculate the user/receiver position on the Earth. In this study, Bengaluru, Surat, Kolkata, and Hyderabad’s NavIC ground receivers’ data is considered for orbit estimation. The pseudo-range measurements received by the ground receivers have multiple errors added due to ionospheric delay, tropospheric delay, multipath delays, satellite clock errors, and some unmodeled effects. But, the major factor accounting for errors is the satellite clock error. Hence, along with position and velocity of the satellite, even the clock correction is estimated using Extended Kalman Filter (EKF). EKF is a sequential estimation algorithm which estimates satellite position, velocity and clock error at each time instant. In this paper, results of all seven IRNSS satellite’s orbit determination are discussed.

Systematic and Random Errors Associated with Johnston's Cephalometric Analysis

1993 ◽  
Vol 20 (2) ◽  
pp. 101-107 ◽  
Author(s):  
Stephen D. Keeling ◽  
Sal R. Cabassa ◽  
Gregory J. King
Keyword(s):  
Random Error ◽  
Error Variance ◽  
Individual Case ◽  
Base Change ◽  
Mixed Dentition ◽  
Random Errors ◽  
Angular Measure ◽  
Basal Bone ◽  
Systematic And Random Errors ◽  
The Individual

This study examined intra- and interexaminer systematic and random errors associated with Johnston's cephalometric method of assessing skeletal and dental changes from pairs of radiographs. Data were obtained from the tracings of radiographs of 30 mixed dentition subjects, who had been treated to correct a Class II malocclusion. Measurements included molar and incisor crown movements relative to basal bone, apical base change, maxillary and mandibular displacement relative to the cranial base, and total molar and overjet reduction. In addition, the change in axial inclination of the incisors and molars was determined. A paired t- test for each pair of replicates for each measure was performed to examine inter- and intra-examiner bias. Estimates of the random error, the coefficient of reliability, and confidence limits (95 per cent level) of a single determination were undertaken. No systematic errors occurred between/within examiners for any linear or angular measure. Interexaminer random errors, based on the standard deviation of the mean difference between replicates, were greater than intra-examiner random errors for 12 out of 13 parameters. Measures assessing molar correction and overjet reduction had the least amount of random error variance within and across judges, while changes in mandibular position had the greatest. Because considerable random errors occurred, the Johnston analysis when used to assess skeletal changes, as well as individual molar and incisor movements, may have limited utility in clinical practice for the individual case.

SET UP ERRORS AND RECOMMENDED SAFETY MARGINS IN THE PELVIC RADIOTHERAPY FIELDS OF CANCER CERVIX PATIENTS: AN INSTITUTIONAL EXPERIENCE

2016 ◽  
Vol 1 (2) ◽  
Author(s):  
Jitendra Nigam ◽  
Piyush Kumar ◽  
Uthya Balan
Keyword(s):  
Safety Margin ◽  
Conformal Radiotherapy ◽  
Systematic Errors ◽  
Random Errors ◽  
Cancer Cervix ◽  
Lateral Field ◽  
Bony Landmarks ◽  
Safety Margins ◽  
Set Up ◽  
The Individual

INTRODUCTION: Uncertainty exists in radiotherapy delivery due to daily patients set up errors resulting in a difference between planned and delivered dose. The conformal radiotherapy requires reduced margins around the clinical target volume (CTV) with respect to traditional radiotherapy technique and hence these positioning errors are accounted in CTV-PTV margin calculations. The primary aim of this study is to evaluate the set up errors and find out the optimum safety margins for the anterior and lateral fields of pelvis in the patients of cancer cervix treated with 3DCRT by four field box technique. The secondary objective was to study the adequacy of safety margin using the dosimetric and volumetric DVH data. METHODS AND MATERIALS: Study was conducted on twenty one patients of cancer cervix. All patients were immobilsed by full body Vaclok cushions. The radiotherapy to whole pelvis was planned by four field (Anterio-posterior, Posterio-anterior and two laterals) box technique with shielding of corners using multieaf collimators in Varian CLINAC 2300C/D. Weekly EPID images were acquired with Varian aS500 for each patient and were compared with the DRR images using the Portal Vision (Version 7.3.10). The displacement of EPID image from the DRR image was measured by defining reproducible bony landmarks in directions- X (Left to right (LR)), Z (Superior to inferior (SI)) in Anterio-posterior field, and Y (Anterior to posterior (AP)) in lateral field. The systematic and random set up errors for individual and population were calculated. Then the adequate safety margins were calculated by Stroom’s formula. RESULTS: A total of 242 images (42 DRR images and 200 portal images) and 363 match points were evaluated. Set up errors were -7.9 to 8.1mm (LR), -7.3 to 7.3mm (AP) and -9.9 to 8.2mm (SI). The individual systematic errors ranged from -6.6 to 4.9mm (LR), -4.9 to 3.5mm (AP) and -6.3 to 6.5mm (SI) while the individual random errors ranged from 0.5 to 8.3mm (LR), 0.7 to 5.2mm (AP) and 1.1 to 4.6mm (SI). The adequate safety margins which ensures at least 95% of prescribed dose to 99% of the CTV calculated by using Stroom’s formula were 7.9mm (LR), 7.0mm (AP) and 9.1mm (SI). The effect of dose was calculated by simulating a plan by shifting the isocenter along the three axes, where each shift corresponds to the displacement. Dose received by 99% of CTV volume for treatment plans with and without shifts was 99.51±0.81 and 98.63±1.46 respectively. CONCLUSION: In this study, the effect of the systematic errors and the random errors on dose distribution shows that the safety margin of 1 cm appears to be adequate for all the patients.

Mise au point d'un tarif de cubage général pour les forêts québécoises : une approche pour mieux évaluer l'incertitude associée aux prévisions

2007 ◽  
Vol 83 (5) ◽  
pp. 754-765 ◽  
Author(s):  
Mathieu Fortin ◽  
Josianne DeBlois ◽  
Sylvain Bernier ◽  
Georges Blais
Keyword(s):  
Mixed Model ◽  
Random Effect ◽  
Tree Height ◽  
Sample Plot ◽  
Random Errors ◽  
Basic Premise ◽  
Volume Assessment ◽  
Detailed Assessment ◽  
Cruise Line ◽  
The Individual

Merchantable volume assessment is of prime importance in forest management and for the estimation of wood production in Quebec Crown forests. Currently, this assessment is undertaken at the individual stem level according to a statistical model commonly identified as the Perron general stock table. This polynomial model is based on tree diameter at breast height and tree height. However, the mathematical model form and the method used to calibrate it do not enable a correct and detailed assessment of the uncertainty associated with volume assessments. This study describes a new model which, accounts for errors associated with the use of estimated height in volume forecasts and also limits the propogation of errors to sample plot and cruise line. Random effects have been specified in the model in order to take into account spatial correlation between observations made at the sample plot and cruise line level. Results indicate sample plot and cruise line random errors constitute components of model error, which individually range from 2 % to 4 % of volume assessment. Consequently, the basic premise that errors associated with volume assessment of individual stems are compensated by volume summations at the sample plot level is not valid. Key words: mixed model, random effect, error propagation, variance

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