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A new ZTD model based on permanent ground-based GNSS-ZTD data / M. Ding in Survey review, vol 48 n° 351 (October 2016)  

Public [article]  inSurvey review > vol 48 n° 351 (October 2016) . - pp 385 - 391 Titre : A new ZTD model based on permanent ground-based GNSS-ZTD data Type de document : Article/Communication Auteurs : M. Ding, Auteur ; W. Hu, Auteur ; X. Jin, Auteur ; L. Yu, Auteur Année de publication : 2016 Article en page(s) : pp 385 - 391 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes IGN] correction troposphérique [Termes IGN] données GNSS [Termes IGN] réseau neuronal artificiel [Termes IGN] retard troposphérique zénithal [Termes IGN] Russie Résumé : (Auteur) Tropospheric delay has a major effect on the accuracy of navigation and positioning when using the Global Navigation Satellite System (GNSS). Zenith tropospheric delay (ZTD) modelling has been used to weaken the influence of the atmosphere. The work reported here focused on ZTD modelling based on real-time surface meteorological parameters, traditionally represented by the Saastamoinen model. However, Saastamoinen accuracy only reaches scale of centimetres, even to scale of centimetres when the water vapour is active, whereas the scale of ground-based GNSS-ZTD data (i.e. ZTD derived from ground GNSS data) is on the millimetre scale and is considered to be the ‘true’ value. An important direction in GNSS studies is how to make good use of ground-based GNSS-ZTD data to improve the accuracy of the Saastamoinen model. Authors studied the residuals in the Saastamoinen model using high-precision GNSS-ZTD data provided by the International GNSS Service (IGS) product and then carried out modelling based on a back propagation neural network. A new ZTD model (ISAAS) based on real-time surface meteorological parameters is proposed based on this method. The ISAAS model has good accuracy: its BIAS and root mean square error (RMSE) at the test area in Russia were -4.4 and 20.4 mm, respectively, which are lower than the results obtained using the Saastamoinen model (-10.4 and 23.3 mm, respectively). The ISAAS model can improve the ZTD prediction accuracy by more than 12.4% and therefore has important implications for precision engineering measurements in Russia. Numéro de notice : A2016-821 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1179/1752270615Y.0000000034 En ligne : https://doi.org/10.1179/1752270615Y.0000000034 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=82636 [article]

A recursive procedure for computation and quality control of GPS differential corrections / X. Jin (1995)

Public Titre : A recursive procedure for computation and quality control of GPS differential corrections Type de document : Monographie Auteurs : X. Jin, Auteur Editeur : Delft [Pays-Bas] : Delft University of Technology Année de publication : 1995 Collection : LGR-SERIES num. 8 Importance : 83 p. Format : 21 x 30 cm Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] contrôle qualité [Termes IGN] correction du signal [Termes IGN] correction ionosphérique [Termes IGN] erreur moyenne quadratique [Termes IGN] erreur systématique [Termes IGN] filtre de Kalman [Termes IGN] GPS en mode différentiel [Termes IGN] modèle ionosphérique [Termes IGN] précision du positionnement [Termes IGN] propagation ionosphérique [Termes IGN] traitement de données GNSS Index. décimale : 30.61 Systèmes de Positionnement par Satellites du GNSS Résumé : (Auteur) The DGPS technique can considerably improve the accuracy of stand-alone GPS positioning, since biases inherent in the latter technique are greatly reduced or even eliminated. But the improvement depends on the distance between the user and the reference station (spatial correlation), the latency of differential corrections (temporal correlation), and the quality of differential corrections. Therefore, how to correctly generate differential corrections is one of the keys to the DGPS positioning technique. Currently, there already exist several algorithms for the generation of differential corrections, for instance, the algorithm based on carrier filtered code observations and the algorithm based on code observations and sequential differences of carrier observations. This research derives a new algorithm for generating differential corrections along with a recursive quality control procedure, which has some distinct features. First, it directly uses code and carrier observations in the measurement model of a Kalman filter, so that the measurements are not correlated in time if code and carrier observations can be assumed to have no time correlation. This makes it possible to use a simple stochastic observation model and to use the standard algorithm of the Kalman filter. Second, the algorithm accounts for biases like multipath errors and instrumental delays in code observations. It explicitly shows how code biases affect differential corrections when dual or single frequency data are used. Third, the algorithm can be easily integrated with a recursive quality control procedure, so that the quality of the estimated states can be guaranteed with certain probability. Fourth, in addition to the generation of differential corrections, it also produces the change of ionospheric delays and that of code biases with time. It can, therefore, be used to investigate properties of ionospheric delays and code biases. Finally, all state estimates including differential correction are not affected by the opposite influence of ionospheric delay on code and carrier observations. On the basis of data collected by TurboRogue SNR-8000, Trimble 4000 SSE and Trirable 4000 SST receivers, this research also investigates the relationship between satellite elevation and the accuracy of code observations. Since this investigation uses code predicted residuals, which are dominated by code observation noises, the estimation of code observation accuracy is not affected by systematic errors caused by, for example, multipath and instrumental delays in code observations. It turns out that the deterioration of GPS code accuracy with decreasing elevation is very obvious at low elevation. When satellite elevation increases, the accuracy becomes more and more stable. The change of the code accuracy with satellite elevation can quite well be modelled by an exponential function of the form y=ao+a1.exp{-x/xo}, where y (the RMS error), ao and a1 have units of metres, and x (elevation) and xo are in degrees. For different types of receivers and different types of code observables, the parameters ao, a1 and xo may be different. It is shown that by using code and carrier data with a sampling interval of one second, the dynamic behaviour of SA clock errors and that of ionospheric delays can well be modelled by quadratic and linear functions, respectively. The modelling accuracy is at least within a few millimetres. Biases in code measurements are found and they may behave linearly and periodically with time. By using the same receiver, code biases related to different observation conditions have different behaviours and those related to the same satellite but observed in different frequencies (i.e. L1 and L2) may also not be the same. Model testing experiments with simulated errors show that cycle slips as small as one cycle can be indeed successfully detected and identified in real time. The recursive quality control procedure allows for detection and identification of single as well as multiple model errors. But there exists a problem that the mean of the test statistic is always smaller than its expectation. It has been shown that this problem still remains after the relationship between satellite elevation and the accuracy of code observations is taken into account. Based on the differential corrections generated by the new algorithm, it is shown that with increasing differential-correction latencies, the accuracy of differential-correction prediction decreases quadratically when SA clock errors are present and linearly when SA clock errors are absent. For latencies up to 5, 10 and 15 seconds, the accuracies are usually within 0.05, 0.2 and 0.5 in, respectively. Using differential-correction acceleration in differential-correction prediction can improve or worsen the accuracy when SA clock errors are present or absent, respectively. But the deteriorated accuracies related to satellites without SA clock errors are still better than the improved ones related to satellites with SA clock errors. For latencies within 15 seconds, the accuracy of differential-correction prediction can usually be reduced to below 0.2 metres if differential-correction accelerations are used. Numéro de notice : 18210 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Monographie Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=55351

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Taylor expansion of GPS observations equations / X. Jin (1995)

Public Titre : Taylor expansion of GPS observations equations Type de document : Monographie Auteurs : X. Jin, Auteur Editeur : Delft [Pays-Bas] : Delft University of Technology Année de publication : 1995 Collection : LGR-SERIES num. 11 Importance : 48 p. Format : 21 x 30 cm Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] équation linéaire [Termes IGN] erreur systématique [Termes IGN] matrice de covariance [Termes IGN] phase GPS [Termes IGN] série de Taylor [Termes IGN] signal GPS [Termes IGN] stabilité [Termes IGN] système de référence céleste [Termes IGN] temps de propagation [Termes IGN] temps réel Index. décimale : 30.60 Géodésie spatiale Résumé : (Auteur) In addition to giving an alternative derivation of GPS carrier observation equations, this research aims mainly at deriving the Taylor expansion of GPS observation equations. The derivation of GPS carrier observation equations can be found in many literatures. The main difference between the alternative derivation of carrier observation equations and many others is that no assumptions in the former are made on the stability of the satellite clock. In addition. the alternative derivation can show clearly what the carrier observable ambiguity consists of, so that one can understand exactly what is cancelled in single, double or triple differences of carrier observations. In order to solve GPS observation equations, one needs to know the transmission time of the GPS signal which is usually determined by using iterations or code observations. Since using iterations is rather time consuming, one should try to avoid this approach, especially in real time GPS applications. This research shows by a real data set that as large as one millisecond gross error can be included in a code observation. Therefore using code observations to determine the travel time of the GPS signal will possibly lead to seriously biased results. In addition, the use of code observations leads to that the coefficients of linearized GPS observation equations are functions of code observations, which makes it difficult to correctly compute the covariance matrix of the estimates of unknowns. This research proves that GPS observation equations can be expanded in Taylor series which contains only up to first-order derivative quantities. Since the expansion does not contain the travel time of the GPS signal, solving it requires neither iterations nor code observations for the determination of the transmission time of the GPS signal. The use of the Taylor expansion of GPS observation equations can, therefore, save computing time and avoid the impacts of any gross errors in code observations on computed observations. Thus the expansion is particularly useful for real time high precision GPS applications. Additionally, the Taylor expansion of GPS observation equations makes it possible to show explicitly the exact coefficients of linearized GPS observation equations. Numéro de notice : 18212 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Monographie Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=55352

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