A Guideline to Establish DGPS Reference Station Requirements

2007 ◽  
Vol 61 (1) ◽  
pp. 99-114 ◽  
Author(s):  
Changdon Kee ◽  
Byungwoon Park ◽  
Jeonghan Kim ◽  
Allen Cleveland ◽  
Michael Parsons ◽  
...  
Keyword(s):  
Measurement Errors ◽  
Satellite Orbit ◽  
Maximum Size ◽  
Coast Guard ◽  
Rate Of Change ◽  
Reference Station ◽  
Baud Rate ◽  
Gps Measurement ◽  
Message Broadcasting ◽  
Noise Statistics

After Selective Availability (SA) was turned off, the rate of change with time of the DGPS common errors (atmospheric delay, satellite orbit and clock error) became quite slow. This inevitably leads to a requirement to modify various configurations of DGPS correction message broadcasting, and reference station (RS) managers need to examine the characteristics of GPS measurement errors with SA-off. GPS error sources are temporally and spatially decorrelated, so the DGPS user position accuracy is varied by the baud-rate of the RS, the distance between the user and the station, and the noise statistics of the receiver. We identify the minimum and maximum size of correction data, interval time, the coverage range and the baud-rate that are required to maintain the existing DGPS service. Moreover, the compatibility and accuracy can be assessed to meet the users' requirements without measurements being needed. The results in this paper are used in the study and testing for the redesign of United States Coast Guard (USCG) RS. We hope that our study will be a great help in determining the flexible factors of both the RS and the user.

Integration of INS and Un-Differenced GPS Measurements for Precise Position and Attitude Determination

2007 ◽  
Vol 61 (1) ◽  
pp. 87-97 ◽  
Author(s):  
Yufeng Zhang ◽  
Yang Gao
Keyword(s):  
Measurement Errors ◽  
Attitude Determination ◽  
Signal Transmission ◽  
Control Point ◽  
Satellite Orbit ◽  
Double Difference ◽  
Gps Measurements ◽  
Gps Receivers ◽  
Precise Position ◽  
Gps Measurement

The integration of GPS and INS observations has been extensively investigated in recent years. Current systems are commonly based on the integration of INS data and the double differenced GPS measurements from two GPS receivers in which one is used as a reference receiver set up at a precisely surveyed control point and another is as the rover receiver whose position is to be determined. The requirement of a base receiver is to eliminate the significant GPS measurement errors related to GPS satellites, signal transmission and GPS receivers by double differencing measurements from the two receivers. With the advent of precise satellite orbit and clock products, the un-differenced GPS measurements from a single GPS receiver can be applied to output accurate position solutions at centimetre level using a positioning technology known as precise point positioning (PPP). This then opens an opportunity for the integration of un-differenced GPS measurements with INS for precise position and attitude determination. In this paper, a tightly coupled un-differenced GPS/INS system will be developed and described. The mathematical models for both INS and un-differenced GPS measurements will be introduced. The methods for mitigating GPS measurement errors will also be presented. A field test has been conducted and the results indicate that the integration of un-differenced GPS and INS observations can provide position and velocity solutions comparable with current double difference GPS/INS integration systems.

An Advanced Receiver Autonomous Integrity Monitoring (ARAIM) Ground Monitor Design to Estimate Satellite Orbits and Clocks

2020 ◽  
Vol 73 (5) ◽  
pp. 1087-1105
Author(s):  
Yawei Zhai ◽  
Jaymin Patel ◽  
Xingqun Zhan ◽  
Mathieu Joerger ◽  
Boris Pervan
Keyword(s):  
Measurement Errors ◽  
Satellite Orbit ◽  
Global Navigation Satellite Systems ◽  
Estimation Accuracy ◽  
Satellite Orbits ◽  
Integrity Monitoring ◽  
Satellite Systems ◽  
Receiver Autonomous Integrity Monitoring ◽  
The Impact ◽  
Advanced Receiver

This paper describes a method to determine global navigation satellite systems (GNSS) satellite orbits and clocks for advanced receiver autonomous integrity monitoring (ARAIM). The orbit and clock estimates will be used as a reference truth to monitor signal-in-space integrity parameters of the ARAIM integrity support message (ISM). Unlike publicly available orbit and clock products, which aim to maximise estimation accuracy, a straightforward and transparent approach is employed to facilitate integrity evaluation. The proposed monitor is comprised of a worldwide network of sparsely distributed reference stations and will employ parametric satellite orbit models. Two separate analyses, covariance analysis and model fidelity evaluation, are carried out to assess the impact of measurement errors and orbit model uncertainty on the estimated orbits and clocks, respectively. The results indicate that a standard deviation of 30 cm can be achieved for the estimated orbit/clock error, which is adequate for ISM validation.

The spectrum of GPS measurement errors and the accuracy of airborne gravity measurements

Geophysics ◽  
1990 ◽  
Vol 55 (8) ◽  
pp. 1101-1104 ◽  
Author(s):  
D. R. Bower ◽  
J. Kouba ◽  
R. J. Beach
Keyword(s):  
Measurement Errors ◽  
Regional Scale ◽  
Vertical Motion ◽  
Airborne Gravity ◽  
Width Ratio ◽  
Noise Power ◽  
Power Spectral ◽  
Gps Measurement ◽  
Gravity Measurements ◽  
Allowable Error

Recent observations (Georgiadou and Kleusberg, 1987; Kleusberg et al., 1989) suggest that errors in GPS carrier phase observations at frequencies within the gravity passband of airborne gravity systems may be due mainly to multipath interference. Further, the power spectral density (PSD) of these errors has been found to fall off rapidly with increase in frequency throughout the anticipated gravity passband, in the manner of a red spectrum rather than a white (which remains constant). It is shown that this implies a much greater allowable error in GPS‐derived altitude reference than would be the case if the PSD of altitude errors (1) was white, (2) had the same shape as that of typical aircraft vertical motion, or (3) was dominated by a sinusoidal wave located near the high frequency limit of the gravity passband. This enhances the feasibility of airborne gravity for regional scale surveys and perhaps explains why actual measurements have been better than predicted. For example, given a uniform [Formula: see text] distribution of spectral noise power and a speed to grid‐width ratio of 60 per hour, an rms altitude error as large as 12 cm will still allow the computation of acceleration correction with an accuracy of 2 mGal. For the same conditions, the allowable rms altitude error given a white distribution of spectral noise power is 1.5 cm.

CLEAN HARBORS COOPERATIVE

1981 ◽  
Vol 1981 (1) ◽  
pp. 557-562
Author(s):  
Edward Wirkowski
Keyword(s):  
New York ◽  
Oil Spills ◽  
Practical Knowledge ◽  
Maximum Size ◽  
Coast Guard ◽  
Purchase Decisions ◽  
Oil Companies ◽  
Area Of Interest ◽  
Response Organization ◽  
Harbor Area

ABSTRACT Clean Harbors Cooperative is a nonprofit organization initiated by eight major oil companies whose purpose is to contain and clean up major oil spills effectively and efficiently throughout the Greater New York Harbor area. Initial efforts included defining the area of interest; determining the maximum size spill that is likely to occur; deciding the time to clean up the free oil on the water; determining the type and quantity of equipment required to contain and clean up the spill, where major spills are likely to occur, where the equipment should be located, and the means to finance the purchase of the equipment and the operation of the cooperative; and deciding who will store, operate, test, and maintain the equipment, and who will direct and handle the actual cleanup activities. These decisions were reached by discussions with company marine experts, by analyses of past major spills, by consultations with the U.S. Coast Guard (USCG) regarding its experiences and recommendations, by visits with other major cooperatives throughout the country, and by studies that simulated oil spills at various locations throughout New York Harbor (by means of Shell Oil Company's spill computer program and the USCG vector analysis program). Secondary efforts consisted of establishing a response organization team that will be available to direct and supervise the entire containment and cleanup effort, and developing a major contingency plan manual that includes cleanup plans and techniques, and data on sensitive areas, training, disposal, communications, wildlife, etc., in addition to call-out procedures and emergency phone numbers. Parameters covering both technical and practical aspects were developed and used in preparing equipment specifications. Purchase decisions were based primarily on visual observations, recommendations of knowledgeable users, and impartial test results. Cost was a secondary consideration. The capital equipment purchase program was divided into three 1-year periods and totalled 3.9 million dollars. In conclusion, Clean Harbors Cooperative believes that by using the best technical and practical knowledge and experiences available, the time and money will have been spent wisely, and they will be prepared to contain and clean up major oil spills efficiently and effectively anywhere in the Greater New York Harbor area.

Determination of upper-atmosphere air density and scale height from satellite observations

1959 ◽  
Vol 252 (1268) ◽  
pp. 16-27 ◽  
Keyword(s):  
Satellite Orbit ◽  
Major Axis ◽  
Scale Height ◽  
Rate Of Change ◽  
Satellite Observations ◽  
Upper Atmosphere ◽  
Semi Major Axis ◽  
Air Density ◽  
Standard Deviations

A solution is obtained for the rate of change of semi-major axis and perigee distance of a satellite orbit with time due to the resistance of the atmosphere. The logarithm of air density is assumed to vary quadratically with height, and the oblateness of the atmosphere is taken into account. The calculation of perigee air density in terms of the rate of change of satellite period is dealt with; and the method is applied to data at present available on six different satellites. The variation of air density with height is obtained as ln ρ = -28·59(±0·15) - ( h - 200 )/46(±5) + 0·028(±0·013) ( h - 200) 2 /(46) 2 for h in the range of approximately 170 to 700 km, where ρ is in grams/cm 3 , h is in kilometres and standard deviations are given in brackets.

A Bayesian nonlinear inversion of seismic body-wave attenuation factors

1997 ◽  
Vol 87 (4) ◽  
pp. 961-970
Author(s):  
S. Gao
Keyword(s):  
Measurement Errors ◽  
Numerical Experiments ◽  
Spectral Ratio ◽  
Synthetic Seismograms ◽  
Reference Station ◽  
Ratio Method ◽  
Nonlinear Inversion ◽  
Amplification Factors ◽  
Spectral Ratio Method ◽  
T Values

Abstract It is a well-known fact that the uncertainties in measuring relative attenuation factors within a local or regional seismic network are usually high, due to noise of different kinds and unrealistic assumptions. Numerical experiments using nine synthetic seismograms, created using t* values ranging from 0.1 to 0.9 sec, reveal that the commonly used spectral ratio method is strongly affected by the selection of data processing parameters such as width of the spectral smoothing window, reference station, and so on. The numerical experiments demonstrate that a Bayesian nonlinear inversion approach that directly matches the spectra is better at finding the correct parameters used to generate the synthetic seismograms. The Bayesian inversion approach uses a priori information to simultaneously search for the t* values, the common spectrum for all the records from an event, and the near-receiver amplification factors by using all the recordings from an event. When z, the ratio of Gaussian noise to signal, ≦ 0.1, the spectral ratio and Bayesian methods yield similar results with mean t* measurement errors <0.05 sec. For 0.1 < z ≦ 0.8, the mean errors of the spectral ratio method are larger than 0.1 sec and in some cases as large as 0.6 sec, while those of the Bayesian method are less than 0.08 sec. Frequency-independent t* and near-receiver amplification factors are assumed. A multi-step procedure is proposed to reject records with a large misfit.

L2 GRIT

2021 ◽  
pp. 1-28
Author(s):  
Majid Elahi Shirvan ◽  
Tahereh Taherian ◽  
Elham Yazdanmehr
Keyword(s):  
Latent Variables ◽  
Measurement Errors ◽  
Second Order ◽  
Rate Of Change ◽  
Cross Sectional ◽  
Domain Specific ◽  
Confirmatory Factor ◽  
L2 Learners ◽  
Measure Change ◽  
Over Time

Abstract Given the longitudinal nature of L2 grit, the use of conventional research methodologies with cross-sectional data to examine the validity of L2 grit scale seems inadequate. The present research was an attempt to extend the domain-specific phase of research on L2 grit, with the pursuit of long-term goals at its core, into a dynamic one. Thus, we adopted a longitudinal confirmatory factor analysis-curve of factors model (LCFA-CFM) approach to trace changes in L2 learners’ grit at different points of time in an EFL course. LCFA-CFM ensures measurement invariance over time, deals with second-order latent variables, takes into account measurement errors, and is capable of assessing interindividual differences. With this in mind, we, first, employed LCFA to test the factor invariance of L2 grit based on a bifactor CFA model over time and, second, used CFM to measure change of L2 grit during an L2 course. To do so, we collected data from 437 adult EFL learners in Iran in four time phases using the L2 grit scale and analyzed them using Mplus 7.4. The model fit was accepted and invariance of the latent factor of L2 grit was confirmed over time. Also, the negative covariance between initial level of L2 grit and its rate of change over time (second-order latent variables) suggested a steeper increase in the construct over time for learners with lower initial scores of the construct. That is, L2 learners who started at a higher level of L2 grit experienced less change in L2 grit over time. The LCFA-CFM ensured that the factor structure of L2 grit is invariant over time and provided insights into how L2 grit changes over an L2 course.

Correcting GPS measurement errors induced by system motion over uneven terrain

2003 ◽  
Author(s):  
Stacy L. Tantum ◽  
Leslie M. Collins ◽  
Nagi Khadr ◽  
Bruce J. Barrow
Keyword(s):  
Measurement Errors ◽  
Uneven Terrain ◽  
Gps Measurement

scholarly journals Assessment of Centre National d’Études Spatiales Real-Time Ionosphere Maps in Instantaneous Precise Real-Time Kinematic Positioning over Medium and Long Baselines

Sensors ◽  
2020 ◽  
Vol 20 (8) ◽  
pp. 2293 ◽  
Author(s):  
Dariusz Tomaszewski ◽  
Paweł Wielgosz ◽  
Jacek Rapiński ◽  
Anna Krypiak-Gregorczyk ◽  
Rafał Kaźmierczak ◽  
...  
Keyword(s):  
Real Time ◽  
A Priori ◽  
Satellite Orbit ◽  
Satellite System ◽  
Ionospheric Delay ◽  
Reference Station ◽  
Atmospheric Effects ◽  
International Gnss Service ◽  
Real Time Kinematic ◽  
Global Navigation Satellite

Precise real-time kinematic (RTK) Global Navigation Satellite System (GNSS) positioning requires fixing integer ambiguities after a short initialization time. Originally, it was assumed that it was only possible at a relatively short distance from a reference station (<10 km), because otherwise the atmospheric effects prevent effective ambiguity fixing. Nowadays, through the use of VRS, MAC, or FKP corrections, the distances to the closest reference station have been increased to around 35 km. However, the baselines resolved in real time are not as far as in the case of static positioning. Further extension of the baseline requires the use of an ionosphere-weighted model with ionospheric delay corrections available in real time. This solution is now possible thanks to the Radio Technical Commission for Maritime (RTCM) stream of SSR corrections from, for example, Centre National d’Études Spatiales (CNES), the first analysis center to provide it in the context of the International GNSS Service. Then, ionospheric delays are treated as pseudo-observations that have a priori values from the CLK RTCM stream. Additionally, satellite orbit and clock errors are properly considered using space-state representation (SSR) real-time radial, along-track, and cross-track corrections. The following paper presents the initial results of such RTK positioning. Measurements were performed in various field conditions reflecting realistic scenarios that could have been experienced by actual RTK users. We have shown that the assumed methodology was suitable for single-epoch RTK positioning with up to 82 km baseline in solar minimum (30 March 2019) mid and high latitude (Olsztyn, Poland) conditions. We also confirmed that it is possible to obtain a rover position at the level of a few centimeters of precision. Finally, the possibility of using other newer experimental IGS RT Global Ionospheric Maps (GIMs), from Chinese Academy of Sciences (CAS) and Universitat Politècnica de Catalunya (UPC) among CNES, is discussed in terms of their recent performance in the ionospheric delay domain.

scholarly journals Dent Overlap in Hailpads: Error Estimation and Measurement Correction

2011 ◽  
Vol 50 (5) ◽  
pp. 1073-1087 ◽  
Author(s):  
Covadonga Palencia ◽  
Amaya Castro ◽  
Dario Giaiotti ◽  
Fulvio Stel ◽  
Roberto Fraile
Keyword(s):  
Kinetic Energy ◽  
Error Estimation ◽  
Measurement Errors ◽  
Maximum Size ◽  
Slope Parameter ◽  
Size Distributions ◽  
Final Measurement ◽  
Computerized Simulation ◽  
The Impact ◽  
Exponential Size

AbstractThe measurement of the physical characteristics of hailstones reaching the ground is usually carried out by means of hailpads, on which the impact of hailstones leaves dents. Hailstone dents provide information about parameters, such as the number N of hailstones, their size M, and their kinetic energy E. In the case of intense hailfalls, however, the dents often overlap and the final measurement may not be totally reliable. This paper presents a computerized simulation with the aim of assessing measurement errors caused by dent overlap. The simulated dents represent several random hailfalls with both exponential size distributions and monodispersed size distributions. The simulated hailpads were measured following the procedure employed in the case of hailpads exposed to authentic hailfalls, and it was thus possible to assess the error due to dent overlap. The results show that dent overlap makes it impossible to measure all the dents, which means that in a real hailfall the number of hailstones registered will often be lower than the number of hailstones that actually hit the ground (up to 25% may go undetected). Consequently, the energy and mass of the hailstones are also underestimated (they may be up to 50% higher than the values registered on a hailpad). The maximum size registered, however, does not depend on the degree of overlapping and neither does the slope parameter λ of the exponential distribution, except when λ takes higher values. Finally, the authors suggest a heuristic correction of the data obtained by real hailpads based on the results of the simulations. An example is provided that applies these corrections to the 228 hailfalls registered by the Italian hailpad network over a period of 10 yr. The results show that, on average, the correction applied because of overlapping increases the number of hailstones in 3.2%, the mass in 1.9%, and the energy in 5.4%. However, there are cases in which these corrections reached much higher values of up to 6.9% in N and M, and up to 25.2% in E. It is therefore advisable to correct dent overlap before carrying out a regional climatic study of hail, since this study would certainly be affected by the errors accumulated by all the hailpads.

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