scholarly journals Investigation and Validation of the Time-Varying Characteristic for the GPS Differential Code Bias

2019 ◽  
Vol 11 (4) ◽  
pp. 428 ◽  
Author(s):  
Haojun Li ◽  
Jingxin Xiao ◽  
Weidong Zhu
Keyword(s):  
Single Point ◽  
Time Varying ◽  
International Gnss Service ◽  
Data Set ◽  
Differential Code Bias ◽  
Triple Frequency ◽  
Code Bias ◽  
Constant Part ◽  
The Difference ◽  
Better Than

The time-varying characteristic of the bias in the GPS code observation is investigated using triple-frequency observations. The method for estimating the combined code bias is presented and the twelve-month (1 January–31 December 2016) triple-frequency GPS data set from 114 International GNSS Service (IGS) stations is processed to analyze the characteristic of the combined code bias. The results show that the main periods of the combined code bias are 12, 8, 6, 4, 4.8 and 2.67 h. The time-varying characteristic of the combined code bias, which is the combination of differential code bias (DCB) (P1–P5) and DCB (P1–P2), shows that the real satellite DCBs are also time-varying. The difference between the two sets of the computed constant parts of the combined code bias, with the IGS DCB products of DCB (P1–P2) and DCB (P1–P2) and the mean of the estimated 24-h combined code bias series, further show that the combined code bias cannot be replaced by the DCB (P1–P2) and DCB (P1–P5) products. The time-varying part of inter-frequency clock bias (IFCB) can be estimated by the phase and code observations and the phase based IFCB is the combinations of the triple-frequency satellite uncalibrated phase delays (UPDs) and the code-based IFCB is the function of the DCBs. The performances of the computed the IFCB with different methods in single point positioning indicate that the accuracy for the constant part of the combined code bias is reduced, when the IGS DCB products are used to compute. These performances also show that the time-varying part of IFCB estimated with phase observation is better than that of code observation. The predicted results show that 98% of the predicted constant part of the combined code bias can be corrected and the attenuation of the predicted accuracy is much less evident. However, the accuracy of the predicted time-varying part decreases significantly with the predicted time.

scholarly journals A New Geometric Metric in the Shape and Size Space of Curves in R n

Mathematics ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1691
Author(s):  
Irene Epifanio ◽  
Vicent Gimeno ◽  
Ximo Gual-Arnau ◽  
M. Victoria Ibáñez-Gual
Keyword(s):  
Nearest Neighbor ◽  
Simulated Data ◽  
Shape Space ◽  
Data Set ◽  
Scale Size ◽  
The Difference ◽  
Active Research ◽  
First Time ◽  
Shape And Size ◽  
Better Than

Shape analysis of curves in Rn is an active research topic in computer vision. While shape itself is important in many applications, there is also a need to study shape in conjunction with other features, such as scale and orientation. The combination of these features, shape, orientation and scale (size), gives different geometrical spaces. In this work, we define a new metric in the shape and size space, S2, which allows us to decompose S2 into a product space consisting of two components: S4×R, where S4 is the shape space. This new metric will be associated with a distance function, which will clearly distinguish the contribution that the difference in shape and the difference in size of the elements considered makes to the distance in S2, unlike the previous proposals. The performance of this metric is checked on a simulated data set, where our proposal performs better than other alternatives and shows its advantages, such as its invariance to changes of scale. Finally, we propose a procedure to detect outlier contours in S2 considering the square-root velocity function (SRVF) representation. For the first time, this problem has been addressed with nearest-neighbor techniques. Our proposal is applied to a novel data set of foot contours. Foot outliers can help shoe designers improve their designs.

scholarly journals Evaluation of differences in health-related quality of life in patients receiving conventional versus newer anti-epileptic drugs

2020 ◽  
Vol 9 (2) ◽  
pp. 342
Author(s):  
Kavisha S. Goswami ◽  
Devang A. Rana ◽  
Shalin Shah ◽  
Supriya D. Malhotra
Keyword(s):  
Quality Of Life ◽  
Single Point ◽  
Health Related Quality ◽  
Cross Sectional ◽  
Male Predominance ◽  
Related Quality ◽  
Health Related ◽  
The Difference ◽  
Better Than

Background: Epilepsy is associated with stigma and bad health-related quality of life (HR-QOL) due to this, and side effects of the drug therapy. Newer anti-epileptics are claimed to be better than the conventional. We evaluated this based on comparison of HR-QOL in patients taking the respective therapy.Methods: An observational, cross-sectional, single point study involved 127 consenting patients from Neurology OPD at V.S. General Hospital. Quality of life in epilepsy-10 (QOLIE-10) questionnaire was used to measure HR-QOL in patients. SPSS software and Graphpad prism were used to analyze the variables.Results: Patients of 20-30 age group were commonly affected (37.80%) with a male predominance (56.69%). 41.73% were unemployed. The difference in HR-QOL between patients and controls in all three domains (epilepsy effects, mental effects, role function domains) of QOLIE-10 was significant (p=0.0002), indicating better HR-QOL in controls. The worst HR-QOL scores were found in Epilepsy effects domain. Metabolic adverse effects (38.58%) were the common ADRs. Sodium valproate was the most effective in controlling seizures (last seizure episode: 15 months). HR-QOL correlation between patients receiving monotherapy and polytherapy was significant (p=0.026) with monotherapy rendering a better HR-QOL. Comparison of HR-QOL between patients taking the conventional and the newer drugs was not significant (p=0.1768).Conclusions: Our study nullifies the claims that newer drugs are better than the conventional since no such benefit was seen in HR-QOL as well as ADRs. Our findings ruled out the belief that cases of epilepsy are better controlled with polytherapy.

Multi-GNSS triple-frequency differential code bias (DCB) determination with precise point positioning (PPP)

2018 ◽  
Vol 93 (5) ◽  
pp. 765-784 ◽  
Author(s):  
Teng Liu ◽  
Baocheng Zhang ◽  
Yunbin Yuan ◽  
Zishen Li ◽  
Ningbo Wang
Keyword(s):  
Precise Point Positioning ◽  
Differential Code Bias ◽  
Triple Frequency ◽  
Code Bias ◽  
Point Positioning

Impact of GPS differential code bias in dual- and triple-frequency positioning and satellite clock estimation

GPS Solutions ◽  
2016 ◽  
Vol 21 (3) ◽  
pp. 897-903 ◽  
Author(s):  
Haojun Li ◽  
Bofeng Li ◽  
Lizhi Lou ◽  
Ling Yang ◽  
Jiexian Wang
Keyword(s):  
Satellite Clock ◽  
Differential Code Bias ◽  
Triple Frequency ◽  
Code Bias ◽  
Clock Estimation

scholarly journals MGR-DCB: A Precise Model for Multi-Constellation GNSS Receiver Differential Code Bias

2015 ◽  
Vol 69 (4) ◽  
pp. 698-708 ◽  
Author(s):  
Mohamed Abdelazeem ◽  
Rahmi N. Çelik ◽  
Ahmed El-Rabbany
Keyword(s):  
Total Electron Content ◽  
Satellite System ◽  
Mean Difference ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
International Gnss Service ◽  
Total Electron ◽  
Differential Code Bias ◽  
Gnss Receiver ◽  
Code Bias

In this study, we develop a Multi-constellation Global Navigation Satellite System (GNSS) Receiver Differential Code Bias (MGR-DCB) model. The model estimates the receiver DCBs for the Global Positioning System (GPS), BeiDou and Galileo signals from the ionosphere-corrected geometry-free linear combinations of the code observations. In order to account for the ionospheric delay, a Regional Ionospheric Model (RIM) over Europe is developed. GPS observations from 60 International GNSS Servoce (IGS) and EUREF reference stations are processed in the Bernese-5·2 Precise Point Positioning (PPP) module to estimate the Vertical Total Electron Content (VTEC). The RIM has spatial and temporal resolutions of 1° × 1° and 15 minutes, respectively. The receiver DCBs for three stations from the International GNSS Service Multi-GNSS Experiment (IGS-MGEX) are estimated for three different days. The estimated DCBs are compared with the MGEX published values. The results show agreement with the MGEX values with mean difference and Root Mean Square Error (RMSE) values less than 1 ns. In addition, the combined GPS, BeiDou and Galileo VTEC values are evaluated and compared with the IGS Global Ionospheric Maps (IGS-GIM) counterparts. The results show agreement with the GIM values with mean difference and RMSE values less than 1 Total Electron Content Unit (TECU).

scholarly journals Two decades of satellite observations of AOD over mainland China

2017 ◽  
Author(s):  
Gerrit de Leeuw ◽  
Larisa Sogacheva ◽  
Edith Rodriguez ◽  
Konstantinos Kourtidis ◽  
Aristeidis K. Georgoulias ◽  
...  
Keyword(s):  
Time Series ◽  
Mainland China ◽  
Satellite Observations ◽  
Data Series ◽  
Data Sets ◽  
Data Set ◽  
Modis Aod ◽  
The Difference ◽  
Aerosol Properties ◽  
Better Than

Abstract. The retrieval of aerosol properties from satellite observations provides their spatial distribution over a wide area in cloud-free conditions. As such, they complement ground-based measurements by providing information over sparsely instrumented areas, albeit that significant differences may exist in both the type of information obtained and the temporal information from satellite and ground-based observations. In this paper, information from different types of satellite-based instruments is used to provide a 3-D climatology of aerosol properties over mainland China, i.e. vertical profiles of extinction coefficients from CALIOP, a lidar flying on board the CALIPSO satellite, and the column-integrated extinction (AOD), available from three radiometers: ESA’s ATSR-2, AATSR (together referred to as ATSR) and NASA's MODIS/Terra, together spanning the period 1995–2015. AOD data are retrieved from ATSR using the ADV v2.31 algorithm while for MODIS the Collection 6 (C6) DTDB merged AOD data set is used. These data sets are validated and differences are compared using AERONET version 2 L2.0 AOD data as reference. The results show that, over China, MODIS slightly overestimates the AOD and ATSR slightly underestimates the AOD. Consequently, MODIS AOD is overall higher than that from ATSR, and the difference increases with increasing AOD. The comparison also shows that none of the ATSR and MODIS AOD data sets is better than the other one everywhere. However, ATSR ADV has limitations over bright surfaces where the MODIS DB was designed for. To allow for comparison of MODIS C6 results with previous analyses where MODIS Collection 5.1 (C5.1) data were used, also the difference between the C6 and C5.1 DTDB merged data sets from MODIS/Terra over China is briefly discussed. The AOD data sets show strong seasonal differences and the seasonal features vary with latitude and longitude across China. Two-decadal AOD time series, averaged over the whole mainland China, are presented and briefly discussed. Using the 17 years of ATSR data as the basis and MODIS/Terra to follow the temporal evolution in recent years when ENVISAT was lost requires a comparison of the data sets for the overlapping period to show their complementarity. ATSR precedes the MODIS time series between 1995 and 2000 and shows a distinct increase in the AOD over this period. The two data series show similar variations during the overlapping period between 2000 and 2011, with minima and maxima in the same years. MODIS extends this time series beyond the end of the ENVISAT period in 2012, showing decreasing AOD.

Service and Evaluation of the GPS Triple-Frequency Satellite Clock Offset

2018 ◽  
Vol 71 (5) ◽  
pp. 1263-1273
Author(s):  
Haojun Li ◽  
Weidong Zhu ◽  
Rungen Zhao ◽  
Jiexian Wang
Keyword(s):  
Global Positioning System ◽  
Single Point ◽  
Satellite Clock ◽  
Service Strategy ◽  
North East ◽  
Triple Frequency ◽  
Global Positioning ◽  
Code Bias ◽  
Clock Offset ◽  
Gps Observations

This paper considers the effect of the biases in Global Positioning System (GPS) observations on satellite clock offset estimation. GPS triple-frequency satellite clock and reference observations are discussed. When the reference observation is selected and the corresponding satellite clock offset is computed, satellite clock offsets for all observations are obtained based on the computed satellite clock offset and the biases between the reference observation and other observations. The characteristics of these biases are analysed, and a service strategy for the GPS triple-frequency satellite clock offset is presented. To evaluate the computed GPS satellite clock offset, the performance in single-point positioning is validated. The positioning results show that the average relative improvements are about 20%, 28% and 19% for north, east and vertical components, when the Differential Code Bias (DCB) (P1-P2), DCB (P1-P5) and modelled Inter-Frequency Clock Bias (IFCB) are corrected. The effect of DCB (P1-P2), DCB (P1-P5) and modelled IFCB on the altitude direction is more evident than on the horizontal directions.

scholarly journals Impact of flex power on GPS Block IIF differential code biases

GPS Solutions ◽  
2020 ◽  
Vol 24 (4) ◽  
Author(s):  
Özge Gizem Esenbuğa ◽  
André Hauschild
Keyword(s):  
Density Ratio ◽  
Bias Estimation ◽  
International Gnss Service ◽  
Transmit Power ◽  
Differential Code Bias ◽  
Regional Area ◽  
Code Bias ◽  
Block Iif ◽  
German Aerospace ◽  
Gps Block Iif

Abstract GPS Block IIF satellites are able to redistribute the transmit power between the signal components. This ability is called flex power, and it has been developed as a remedy against jamming. Since it is operationally not possible to increase the transmit power for all signal components simultaneously, a redistribution between them is necessary under certain operational situations. Flex power has been active on Block IIF satellites since January 2017 over a specific regional area and has an impact on differential code bias estimation as well as the signal-to-noise density ratio. A network of the International GNSS Service stations containing only Septentrio PolaRx5 and PolaRx5TR receivers between August 1 and November 21, 2019 has been used for differential code bias estimation using GPS L1 C/A, L1 P(Y), L2 P(Y), and L2C signals with and without consideration of the flex power in the estimation process for Block IIF satellites. The estimation results are compared with the German Aerospace Center as well as the Chinese Academy of Sciences DCB products to validate the results.

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