CENTRE DE DOCUMENTATION DE L INSTITUT GEOGRAPHIQUE NATIONAL. Bibliographie : Positionnement RTK et PPP

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1 CENTRE DE DOCUMENTATION DE L INSTITUT GEOGRAPHIQUE NATIONAL centrededocumentationdel'igncentrededocumentationdel'igncentrededocumentationdel'igncentrededocumentationdel'igncentrededo cumentationdel'igncentrededocumentationdel'igncentrededocumentationdel'igncentrededocumentationdel'igncentrededocumentatio ndel'igncentrededocumentationdel'igncentrededocumentationdel'igncentrededocumentationdel'igncentrededocumentationdel'ignce Bibliographie : Positionnement RTK et PPP Mars 2012 DOCUMENTS DISPONIBLES AU CENTRE DE DOCUMENTATION centrededocumentationdel'igncentrededocumentationdel'igncentrededocumentationdel'igncentrededocumentationdel'igncentrededo CENTRE DE DOCUMENTATION DE L'INSTITUT GEOGRAPHIQUE NATIONAL 6/8 Avenue Blaise Pascal - Cité Descartes - Champs sur Marne Marne la Vallée cedex 2 Tél. : Télécopie : Mél : cdoc@ensg.eu Site Web : centrededocumentationdel'igncentrededocumentationdel'igncentrededocumentationdel'igncentrededocumentationdel'igncentrededo

2 Cette bibliographie a été préparée à l occasion du forum PPMD (Photogrammétrie, positionnement et mesure de déformation) : Prises de vues et positionnement cinématique : interactions et modernisation des techniques, du 20 mars 2012 organisé par la promotion du Mastère PPMD à l ENSG, Marne-la-Vallée. Cette bibliographie ne prétend pas à l exhaustivité. Elle ne porte que sur les dix dernières années pour les monographies et les six dernières années pour les articles. Les références bibliographiques souvent assorties d un résumé, sont présentées par thème, puis par type de document, et par date de parution. Les documents sont en français, sauf indication contraire. Le catalogue du Centre est accessible par Internet. Table des matières : 1- Monographies Articles Monographies Ein integritätswahrendes Messsystem für kinematische Anwendungen = [un système de mesure intégré pour des applications cinématiques] Auteur(s) STEMPFHUBER (W.) Edition Munich : BAYERISCHE AKADEMIE DER WISSENSCHAFTEN, 2004 Collection DGK - C, 576 Allemand Collation 128 pages Mots clés AGRICULTURE DE PRECISION, ETALONNAGE D'INSTRUMENT, GPS EN MODE CINEMATIQUE, GPS EN MODE DIFFERENTIEL, GUIDAGE DE VEHICULES, LEVER TACHEOMETRIQUE, POSITIONNEMENT CINEMATIQUE EN TEMPS REEL, TACHEOMETRE ELECTRONIQUE N notice Cote Résumé d auteur By combining individual components with intelligent analytical algorithms, modern measuring systems such as robot tacheometer or the GPS allow many new areas of application in modern engineering surveying. Use of this equipment is initially limited to static, quasi-static or stop-and-go techniques. Today, these efficient measuring sensors are used increasingly for kinematic measuring tasks. Different applications for the precise description of the movement track and for optimizing the horizontal and vertical availability require a combination of these measuring sensors, which operate separately. Normally both these measuring instruments cannot be combined without changing hardware or software (firmware). This thesis presents a method that allows a synchronization of independent measuring systems without a common basis through a comprehensive observation of all factors of disturbance and influence. Calibration of terrestrial and global measuring sensors for kinematic applications is also discussed in detail. With respect to the description of dynamic movement processes, a calibration of this kind of kinematic measuring sensors requires an expansion of conventional geodetic strategies. Based on static characteristics, these sensors must be tested using kinematic testing methods relating to the type, size and behavior of target points affected by measuring uncertainty. In addition, the real time capability of the measuring system and the synchronization of individual subsystems must be verified and, if required, minimized by corresponding calibration functions. The result is a hybrid measuring system for kinematic applications that, independent of the type of movement, allows a precise derivation of the movement path based on discrete measuring points on a millimeter scale. For example, these hybrid measuring systems can be employed for the following: 1- as a high precision positioning system for navigation and control of process flows in road and railways track construction (machine guidance), 2- for special applications Bibliographie du centre de documentation de l IGN mars Page 2

3 involving maximum availability and accuracy requirements for land and water vehicles or aircraft, 3- as a reference system to verify the feasible accuracy of positioning and application techniques, and 4- to analyze technical reaction times of partial and overall systems in the precision farming sector. The descriptions of selected applications in this thesis are limited to testing of section specific land use with the " Landwirtschaftlichen BUS System LBS, (DIN 9684 and ISO 11783) " with respect to position accuracy, precision, quality, and size of disturbances occurring. Investigations have been partly funded by a joint research project within the " Forschungsverbund Agrarökosysteme München, (FAM) " research alliance, which took place at the Chair for Geodesy in cooperation with the Department for Bio Resources and Land Use Technology, Crop Production Engineering (both at the Technical University of Munich). Pilotage d'un projet expérimental de lèves topographiques par méthodes GPS dans le cadre des opérations de récolement des travaux et partenariats liés à ces données *= Mémoire de fin de stage, DEA sciences de l'information géographique Auteur(s) LE VOUEDEC (E.) Edition Noisy-le-Grand : UNIVERSITÉ DE MARNE-LA-VALLÉE, 2005 Collation 34 pages Mots clés BASE DE DONNEES LOCALISEES, GPS EN MODE CINEMATIQUE, GPS EN MODE DIFFERENTIEL, LEVER TOPOMETRIQUE, ORPHEON, CANALISATION, POSITIONNEMENT CINEMATIQUE EN TEMPS REEL, POSITIONNEMENT PAR GPS, PRECISION CENTIMETRIQUE, RESEAU D'ASSAINISSEMENT, RESEAU DE DISTRIBUTION D'EAU, TERIA, STATION VIRTUELLE, SYSTEME D'INFORMATION GEOGRAPHIQUE, S@T-INFO Mots clés géog ILE-DE-FRANCE N notice Cote Résumé d auteur DSIG Le SEDIF a engagé en 1992 un projet de développement d'un SIG afin d'étudier les aspects d'un système d'information géographique comme moyen d'aide à la décision, partie maîtrise d'ouvrage pour le Syndicat, et moyen d'aide à l'exploitation, partie maîtrise d'œuvre pour le Régisseur, la Compagnie Générale des Eaux. Les résultats furent jugés très encourageants et la généralisation du SIG à la totalité du territoire syndical est en cours de mise en œuvre depuis 1999 et doit s'achever fin La vocation première de ce SIG est la cartographie du réseau (8 700 km) et la gestion de la base de données associée (types de canalisations, données cadastrales, données d'exploitation, etc...) pour répondre aux besoins propres du Syndicat et de son exploitant. Dans un premier temps, la constitution de la base de données du réseau est effectuée à partir de plans sur papier, plus ou moins récents, avec une précision correspondant à l'échelle du 1/ Cependant, l'entretien et le développement du réseau ouvrent la voie à une description plus précise des ouvrages. Grâce à la technologie GPS, les plans de récolement des travaux courants peuvent être effectués à partir de relevés topographiques atteignant une précision centimétrique. En complément du schéma du réseau au 1/2 000, se pose ainsi la question d'une description plus fine des objets enfouis, indispensable pour les travaux opérationnels qui nécessitent de travailler avec une précision sub-décimétrique, au 1/200 (encore appelée «très grande échelle», par rapport aux «grandes échelles» que constituent le 1/1 000 ou le 1/2 000). Une réflexion doit donc être menée pour adapter les modalités de l'acquisition des données topographiques et les éventuels moyens à mettre en œuvre afin d'intégrer dans l'application SIG, ces données au 1/200 issues du récolement des travaux. Par ailleurs cette problématique exige d'étudier toute possibilité de partenariats avec les autres collectivités publiques, dont les communes du Syndicat, pour optimiser les coûts importants liés à l'enrichissement des SIG pour la précision 1/200. Ainsi le SEDIF a lancé en 2004 une opération expérimentale de levers topographiques par méthodes GPS dans le cadre des opérations de récolement des travaux. Cette expérimentation vise à comparer deux méthodes de levés topographiques utilisant les techniques du positionnement par satellite («RTK classique», «RTK VRS»), mais elle a également pour objectif de mesurer le positionnement économique de l'utilisation des outils GPS pour ces relevés de précision centimétrique. Auteur(s) Traitement et analyse des délais troposphériques issus des données d'un récepteur GPS bi fréquence embarqué sur un navire *= Rapport de stage de fin d'études, cycle des ingénieurs diplômés de L'ENSG 3ème année (IT3), mastère spécialisé photogrammétrie, positionnement et mesures de déformations EL YAHMADI (M.) Bibliographie du centre de documentation de l IGN mars Page 3

4 Edition Marne-la-Vallée : ENSG, 2009 Collation 94 pages Mots clés GPS EN MODE CINEMATIQUE, POSITIONNEMENT PONCTUEL PRECIS, PROPAGATION TROPOSPHERIQUE, RECEPTEUR GPS BIFREQUENCE, TRAITEMENT DE DONNEES GNSS N notice Cote MPPMD Résumé d auteur Ce stage se déroule à l'institut Géographique National au sein du Service de Géodésie et Nivellement. Il s'inscrit dans le cadre du projet VAPIMED (VAPeur d'eau, Pluie intense en MEDitérranée). L'objectif principal de ce stage est de déterminer le délai zénithal total à partir des données GPS collectées sur un bateau. Un outil a déjà été développé au sein du SGN permettant de faire du traitement ponctuel précis en mode cinématique. Pour traiter les données de toute la campagne, Il fallait donc paramétrer ce noyau de calcul, l'adapter au besoin et l'automatiser. La comparaison des résultats avec divers centres de calcul et avec les stations du RGP a permis de valider la méthode de calcul et d'évaluer la précision des résultats. GNSS: applications and methods Auteur(s) GLEASON (S.) et GEBRE-EGZIABHER (D.) Edition Londres, Washington : ARTECH HOUSE, 2009 Collection GNSS Technology and applications series, Collation 508 pages Mots clés CENTRALE INERTIELLE, COMPASS SATELLITE NAVIGATION SYSTEM, DETECTION DU SIGNAL, GALILEO, GEODESIE SPATIALE, GLOBAL NAVIGATION SATELLITE SYSTEM, GLOBAL POSITIONING SYSTEM, GNSS ASSISTE POUR LA NAVIGATION, GNSS EN MODE DIFFERENTIEL, GPS-INS, INTERFERENCE, LOGICIEL DE POST-TRAITEMENT GPS, LORAN (système), NAVIGATION AERIENNE, NAVIGATION INERTIELLE, NAVIGATION SPATIALE, OCCULTATION DU SIGNAL, POSITIONNEMENT DIFFERENTIEL, POSITIONNEMENT EN INTERIEUR, POSITIONNEMENT PAR GNSS, POURSUITE DE SATELLITE, RADIOFREQUENCE, RECEPTEUR GPS, SIGNAL GNSS, SIMULATION, SYSTEME DE NUMERISATION MOBILE, TRAITEMENT DU SIGNAL, TRANSMISSION DE DONNEES N notice Cote Résumé d éditeur Over the past few years, the growth of GNSS applications has been staggering. And, this trend promises to continue in the foreseeable future. Placing emphasis on applications development, this unique resource offers a highly practical overview of GNSS (global navigation satellite systems), including GPS. The applications presented in the book range from the traditional location applications to combining GNSS with other sensors and systems and into more exotic areas, such as remote sensing and space weather monitoring. Written by leading experts in the field, this book presents the fundamental underpinnings of GNSS and provides you with detailed examples of various GNSS applications. Moreover, the software included with the book contains valuable processing tools and real GPS data sets to help you rapidly advance your own work in the field. You will find critical information and tools that help give you a head start to embark on future research and development projects. 2- Articles Airborne kinematic positioning using precise point positioning methodology Auteur(s) GAO (Y.) et WOJCIECHOWSKI (A.) Source GEOMATICA, vol 59, n 1, [01/03/2005], pp Mots clés ANALYSE COMPARATIVE, GPS EN MODE CINEMATIQUE, GPS EN MODE DIFFERENTIEL, INSTRUMENT AEROPORTE, POSITIONNEMENT CINEMATIQUE, POSITIONNEMENT DIFFERENTIEL, PRECISION CENTIMETRIQUE, PRECISION DE LOCALISATION, POSITIONNEMENT PONCTUEL PRECIS N notice A Résumé d auteur Currently, high precision kinematic GPS positioning with centimetre-level accuracy can only be carried out using a differential GPS (DGPS) positioning approach which requires the deployment of a GPS receiver at each base station. The DGPS approach, spatially limits the operating range of the rover receiver to about 20 km from the base stations. As a result, it increases not only the operational cost of equipment and human resources but Bibliographie du centre de documentation de l IGN mars Page 4

5 also the logistical complexity of many applications such as land and geodetic surveying, and airborne mapping. With the increased availabiliiy of precise GPS satellite orbit and clock data with reduced latency from the International GPS Service (IGS) and many other organizations, high precision kinematic at centimetre to decimetre-level is now possible using a single GPS receiver. This paper describes a method known as precise point positioning and its application to airborne kinematic positioning. Different from the conventional DGPS approach, the new method does not need a base station since the positioning determination is based on the processing of un-differenced code and carrierphase observations from a single GPS receiver. It therefore eliminates the dependency on base station and the rover range limitation associated with conventional methods, resulting in instant advantages in field operations. A software system that has been developed at the University of Calgary will also be described in this paper along with numerical results to demonstrate the positioning accuracy obtainable. GPS time transfer: using precise point positioning for clock comparisons Auteur(s) LAHAYE (F.), ORGIAZZI (D.), TAVELLA (P.) et CERRETTO (G.) Source GPS WORLD, vol 17, n 11, [01/11/2006], pp Mots clés ANALYSE COMPARATIVE, GLOBAL POSITIONING SYSTEM, PHASE GPS, PSEUDO- DISTANCE, RECEPTEUR GPS, RECEPTEUR GPS BIFREQUENCE, TEMPS ATOMIQUE INTERNATIONAL, POSITIONNEMENT PONCTUEL PRECIS N notice A Résumé doc. Les auteurs relatent les résultats d'une expérience menée avec la méthode de transfert de temps "Precise Point Positioning PPP" de post-traitement des données GPS par comparaison avec les mesures de transfert de temps et fréquence du satellite par 2 voies (Two-Way Satellite Time and Frequency Transfer TWSTFT). La méthode PPP permet une précision au niveau de la nano-seconde, sans avoir recours au réseau des stations. Code single point positioning using nominal GNSS constellations (future perception) Auteur(s) FARAH (A.) Source ARTIFICIAL SATELLITES, vol 42, n 3, [01/12/2007], pp Mots clés CONSTELLATION GALILEO, CONSTELLATION GLONASS, CONSTELLATION GPS, POSITIONNEMENT PONCTUEL PRECIS N notice A Résumé d auteur Global Navigation Satellite Systems (GNSS) have an endless number of applications in industry, science, military, transportation and recreation & sports. Two systems are currently in operation namely GPS (the USA Global Positioning System) and GLONASS (the Russian GLObal NAvigation Satellite System), and a third is planned, the European satellite navigation system GALILEO. The potential performance improvements achievable through combining these systems could be significant and expectations are high. The need is inevitable to explore the future of positioning from different nominal constellations. In this research paper, Bernese 5.0 software could be modified to simulate and process GNSS observations from three different constellations (GPS, Glonass and Galileo) using different combinations. This study presents results of code single point positioning for five stations using the three constellations and different combinations. Copyright Artificial satellites Improving long-range RTK: getting a better handle on the biases Auteur(s) KIM (D.) et LANGLEY (R.B.) Source GPS WORLD, vol 19, n 3, [01/03/2008], pp Mots clés CORRECTION ATMOSPHERIQUE, GPS EN MODE CINEMATIQUE, PHASE GPS, POSITIONNEMENT CINEMATIQUE EN TEMPS REEL, PROPAGATION IONOSPHERIQUE, PROPAGATION TROPOSPHERIQUE, RESOLUTION D'AMBIGUITE N notice A Résumé d éditeur Scientists and engineers continue to improve high-accuracy GPS positioning techniques - techniques pioneered a quarter of a century ago. The first GPS satellite, SVN01/PRN04, was launched from Cape Canaveral on February 22, And between 1978 and 1985, the U.S. Air Force orbited nine more prototype or Block I satellites to test key technologies before deploying the operational constellation. Surveyors and geodesists were among the earliest users of the Block I satellites. Using the satellite signals, they Bibliographie du centre de documentation de l IGN mars Page 5

6 developed accurate positioning techniques based on the use of carrier-phase observations - about two orders of magnitude more precise than code measurements. To reduce the effect of biases and errors in the measurements, they developed the concepts of between-satellite and between-receiver single differencing of the carrier-phase data as well as double and triple differencing. Raw measurements were recorded by receivers and then post-processed to obtain receiver coordinates. Clever approaches were developed to handle the integer ambiguity of the carrier phases. With the launch of the Block II satellites beginning in 1989, further improvements in positioning accuracy and efficiency became possible, including real-time carrier-phase based positioning with a radio link between a reference receiver and a remote receiver. This technique became known as real-time kinematic or RTK, as it permitted the remote receiver to rove and occupy different points in a single positioning exercise. But carrier-phase ambiguity resolution issues coupled with inaccurately modeled satellite orbit and atmospheric effects has limited consistent single-baseline RTK operation between reference and rover receivers to tens of kilometers. On longer baselines, inaccurate modeling can result in significant positioning errors. Network RTK, using simultaneously operating reference stations to better determine error corrections, can extend the area of coverage of RTK but it, too, has limitations. In this month's column, I am joined by my colleague Don Kim who has developed an innovative approach to long-range RTK. We describe how accurate modeling of atmospheric effects coupled with an ionosphere-free ambiguity resolution process results in successful long-range RTK that can be implemented in either singlebaseline or network mode. Has the ultimate RTK approach been developed? Probably not. But we're getting closer. Copyright Questex Media Group Inc Performance of GPS precise point positioning under conifer forest canopies Auteur(s) NAESSET (E.) et GJEVESTAD (J.G.) Source PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, vol 74, n 5, [01/05/2008], pp Mots clés ANTENNE GPS, CONIFERE, FORET, GPS EN MODE DIFFERENTIEL, POSITIONNEMENT PAR GPS, POSITIONNEMENT PONCTUEL PRECIS, PRECISION DU POSITIONNEMENT, PSEUDO- DISTANCE N notice A Résumé d auteur A 20-channel, dual-frequency GPS receiver collecting pseudorange and carrier phase observations was used as a stand-alone receiver to determine positional accuracy of 19 points under conifer tree canopies. The positions were determined utilizing precise satellite orbit and clock products from the International GNSS Service. The mean positional accuracy ranged from 0.27 to 0.88 m for an observation period of 120 minutes, and 0.95 to 3.48 m for 15 minutes. For the 15 minute observation period computed positions could not be found for 8 to 44 percent of the locations. Accuracy increased with decreasing forest stand density. Stand basal area (R2 = 0.11, p < 0.001) and number of tree stems (R2 = 0.07, p < 0.001) were significantly correlated with accuracy. The probability of determining a position increased with longer observation periods and decreasing number of tree stems. For natural resource applications where the costs associated with the length of the observation period on each site in field is a critical factor, differential GPS seems to be a more robust alternative than precise point positioning with GPS. Copyright ASPRS Comparaison du positionnement temps réel classique RTK et du positionnement GPS temps réel réseau : mise en oeuvre dans le réseau Orphéon Auteur(s) MOREL (L.) et DURAND (S.) Source XYZ, n 115, [01/06/2008], pp Mots clés ANALYSE COMPARATIVE, NORME RTCM, ORPHEON, POSITIONNEMENT CINEMATIQUE EN TEMPS REEL, POSITIONNEMENT PAR GNSS, STATION GPS, TEMPS REEL N notice A Résumé d auteur Plusieurs réseaux GPS temps réel poursuivent leur implantation sur le territoire national pour délivrer de nouveaux services de positionnement par GNSS. En s'appuyant sur les principes du RTK avec une seule station, cet article explicite le concept maître auxiliaire à la base de la nouvelle norme de transmission RTCM version 3. Nous présentons ensuite les résultats d'une campagne de mesures mettant en œuvre ces deux types de positionnement : le RTK classique et le RTK dans le réseau Orphéon. Afin de comparer ces deux modes de positionnement RTK, nous avons fait varier la distance à la station de référence utilisée pour le mode RTK classique, utilisé les mêmes observations pour les Bibliographie du centre de documentation de l IGN mars Page 6

7 deux calculs en temps réel, considéré différents environnements (rural, semi-urbain, urbain). Nous avons également comparé les positions RTK à des positions RGF93 obtenues par post-traitement. Les principaux résultats montrent une précision du positionnement RTK réseau d'au moins aussi bonne qualité que le positionnement RTK classique et de l'ordre de 2 cm. Les temps d'initialisation sont également similaires et proches de 10 secondes en moyenne. Copyright AFT Resolution of GPS carrier-phase ambiguities in Precise Point Positioning (PPP) with daily observations Auteur(s) GE (M.), GENDT (G.), ROTHACHER (M.) et al. Source JOURNAL OF GEODESY, vol 82, n 7, [01/07/2008], pp Mots clés AMBIGUITE ENTIERE, DOUBLE DIFFERENCE, MESURAGE DE PHASE, POSITIONNEMENT PAR GNSS, RESOLUTION D'AMBIGUITE, SIMPLE DIFFERENCE, POSITIONNEMENT PONCTUEL PRECIS N notice A Résumé d auteur Precise Point Positioning (PPP) has been demonstrated to be a powerful tool in geodetic and geodynamic applications. Although its accuracy is almost comparable with network solutions, the east component of the PPP results is still to be improved by integer ambiguity fixing, which is, up to now, prevented by the presence of the uncalibrated phase delays (UPD) originating in the receivers and satellites. In this paper, it is shown that UPDs are rather stable in time and space, and can be estimated with high accuracy and reliability through a statistical analysis of the ambiguities estimated from a reference network. An approach is implemented to estimate the fractional parts of the singledifference (SD) UPDs between satellites in wide- and narrow-lane from a global reference network. By applying the obtained SD-UPDs as corrections to the SD-ambiguities at a single station, the corrected SD-ambiguities have a naturally integer feature and can therefore be fixed to integer values as usually done for the double-difference ones in the network mode. With data collected at 450 stations of the International GNSS Service (IGS) through days 106 to 119 in 2006, the efficiency of the presented ambiguity-fixing strategy is validated using IGS Final products. On average, more than 80% of the independent ambiguities could be fixed reliably, which leads to an improvement of about 27% in the repeatability and 30% in the agreement with the IGS weekly solutions for the east component of station coordinates, compared with the real-valued solutions. Copyright Springer Online precise point positioning: a new, timely service from Natural Resources Canada Auteur(s) MIREAULT (Y.), TETREAULT (P.), LAHAYE (F.) et al. Source GPS WORLD, vol 19, n 9, [01/09/2008], pp Mots clés SERVEUR WEB, TEMPS REEL, TRAITEMENT DE DONNEES GNSS, POSITIONNEMENT PONCTUEL PRECIS Mots clés géog CANADA N notice A Résumé d éditeur Meliora sequamur - let us strive to improve. The words that the Roman poet Virgil wrote some 2,000 years ago could well be the watchwords of those scientists and engineers who today work to improve the accuracy, coverage, and timeliness of GPS-based positioning. They are particularly appropriate for those seeking to improve the technique of precise point positioning or PPP. PPP is a single-receiver positioning technique just like conventional pseudorange-based positioning, which takes place inside a receiver. However, the similarity stops there. PPP uses the receiver's very precise undifferenced carrier-phase observations together with very precise (and accurate) satellite orbits and clocks to achieve positioning accuracies at the few centimeter level or better. And unlike differential techniques such as real-time kinematic (RTK) positioning, all of the physical phenomena affecting the measurements must be very accurately modeled. These include solid earth tides, ocean-tide loading, transmitting and receiving antenna phase-center offsets and variations, carrier-phase wind-up, relativistic effects, and so on. With differential techniques, such effects are greatly reduced and typically become insignificant, especially on short baselines. PPP can be used to process data collected at a fixed (static) site or along a trajectory in kinematic mode or a mixture of the two - "stop and go" PPP. Although introduced in the late 1990s, PPP has only become more Bibliographie du centre de documentation de l IGN mars Page 7

8 commonplace in the past few years, thanks, in part, to continued PPP development in government and university research labs. Several PPP processors are even available online. The precise satellite orbits and clocks required are provided by the International GNSS Service (IGS) and its worldwide tracking network and analysis centers. These products are supplied with some latency resulting in PPP normally being used as a postprocessing technique with observations being processed some time after they are collected. However, over the past year or so efforts have been made to reduce the latency of some high-precision products. In particular, the ultra-rapid orbit and clock product of the Geodetic Survey Division of Natural Resources Canada (NRCan) is now being produced with a delay of only 90 minutes. Coupled with NRCan's online PPP engine, it provides positioning accuracies almost as good as the IGS final product, which is only available with a delay of about two weeks. In this month's column, we take a look at this new, timely service from the Great White North. Copyright Questex Media Group Inc Deploying a Locata network to enable precise positioning in urban canyons Auteur(s) MONTILLET (J.P.), ROBERTS (G.W.), HANCOCK (C.) et al. Source JOURNAL OF GEODESY, vol 83, n 2, [01/02/2009], pp Mots clés CANYON URBAIN, GPS EN MODE CINEMATIQUE, MILIEU URBAIN, POSITIONNEMENT CINEMATIQUE EN TEMPS REEL, PROPAGATION DU SIGNAL, WIFI N notice A Résumé d auteur Locata is a new positioning technology developed by the Locata Corporation. At the beginning of 2007, the Institute of Engineering Surveying and Space Geodesy (IESSG) bought and received a network of Locata transceivers with two rovers. The purpose is to solve the challenges identified when surveying in dense multipath areas (i.e. urban canyons). In this paper, the technology is tested in an urban canyon scenario on the University park at the University of Nottingham. By comparing Locata position solutions with the true positions calculated with a total station and a carrier-phase GPS, the results show that centimetre-level accuracy is achievable in difficult environments in the presence of Wi-Fi signals. The rover s estimated coordinates may diverge in some cases. Finally, a comparison study shows that Real Time Kinematic GPS and Locata technologies have similar accuracy when both are available. Copyright Springer Testing of Global Pressure-Temperature (GPT) Model and Global Mapping Function (GMF) in GPS analyses Auteur(s) KOUBA (J.) Source JOURNAL OF GEODESY, vol 83, n 3, [01/03/2009], pp Mots clés ANALYSE COMPARATIVE, DONNEES GPS, DONNEES METEOROLOGIQUES, MODELE ATMOSPHERIQUE, MODELE METEOROLOGIQUE, POSITIONNEMENT PAR GPS, POSITIONNEMENT PONCTUEL PRECIS, PRESSION ATMOSPHERIQUE, PROPAGATION DU SIGNAL, TEMPERATURE N notice A Résumé d auteur Several sources of a priori meteorological data have been compared for their effects on geodetic results from GPS precise point positioning (PPP). The new global pressure and temperature model (GPT), available at the IERS Conventions web site, provides pressure values that have been used to compute a priori hydrostatic (dry) zenith path delay z h estimates. Both the GPT-derived and a simple height-dependent a priori constant z h performed well for low- and mid-latitude stations. However, due to the actual variations not accounted for by the seasonal GPT model pressure values or the a priori constant z h, GPS height solution errors can sometimes exceed 10 mm, particularly in Polar Regions or with elevation cutoff angles less than 10 degrees. Such height errors are nearly perfectly correlated with local pressure variations so that for most stations they partly (and for solutions with 5-degree elevation angle cutoff almost fully) compensate for the atmospheric loading displacements. Consequently, unlike PPP solutions utilizing a numerical weather model (NWM) or locally measured pressure data for a priori z h, the GPT-based PPP height repeatabilities are better for most stations before rather than after correcting for atmospheric loading. At 5 of the 11 studied stations, for which measured local meteorological data were available, the PPP height errors caused by a priori z h interpolated from gridded Vienna Mapping Function-1 (VMF1) data (from a NWM) were less than 0.5 mm. Height errors due to the global mapping function (GMF) are even Bibliographie du centre de documentation de l IGN mars Page 8

9 larger than those caused by the GPT a priori pressure errors. The GMF height errors are mainly due to the hydrostatic mapping and for the solutions with 10-degree elevation cutoff they are about 50% larger than the GPT a priori errors. Copyright Springer Contrôle de l'intégrité GPS en temps réel et géoréférencement direct par RTK-GPS pour le levé laser aéroporté Auteur(s) STEBLER (Y.) Source GÉOMATIQUE SUISSE, vol 107, n 3, [01/03/2009], pp Mots clés CONTROLE QUALITE, GEOREFERENCEMENT DIRECT, GPS EN MODE CINEMATIQUE, LASERGRAMMETRIE, POSITIONNEMENT CINEMATIQUE EN TEMPS REEL, QUALITE DES DONNEES, SEMIS DE POINTS, TELEMETRE LASER AEROPORTE, TELEMETRIE LASER AEROPORTE, TEMPS REEL N notice A Résumé d auteur Le manque d'informations sur la fiabilité des données acquises durant le vol constitue l'un des problèmes majeurs des systèmes laser aéroportés (ALS) actuels. Des erreurs ou des dégradations inacceptables de la qualité des données GPS/INS/Lidar ne sont ainsi détectées que plus tard, lorsque plus aucune réaction n'est possible. En particulier, la qualité de la solution GPS utilisée pour l'intégration avec les données inertielles, puis pour le géoréférencement du nuage de points est essentielle en vue de l'élaboration d'un produit final de haute qualité. Dans le contexte du levé ALS où la solution GPS finale est calculée en post-traitant la phase-porteuse différentielle, les éventuelles dégradations affectant le code et/ou la phase du signal GPS n'apparaissent que lors de l'étape du posttraitement de la phase (PT). Les solutions restantes consistent alors, soit à accepter une forte dégradation de la qualité du produit final, soit à répéter le vol. Il est évident que ces deux solutions sont inacceptables d'un point de vue économique et que des solutions de détection de problèmes en amont du PT doivent être trouvées. Cet article traite de la problématique du suivi et du contrôle en temps réel (TR) de la qualité des observations GPS uniquement. En outre, il présente les premiers résultats obtenus pour le géoréférencement direct de données ALS par RTK-GPS/INS. Le contrôle de fiabilité des observations acquises par les capteurs inertiels et Lidar font l'objet d'autres recherches au sein du laboratoire de Topométrie de l'epfl (Schaer et al., 2008). Precise point positioning: a powerful technique with a promising future Auteur(s) BISNATH (S.) et GAO (Y.) Source GPS WORLD, vol 20, n 4, [01/04/2009], pp Mots clés POSITIONNEMENT CINEMATIQUE EN TEMPS REEL, POSITIONNEMENT PAR GPS, POSITIONNEMENT PONCTUEL PRECIS N notice A Résumé d éditeur [...] In the intervening decade, RTK - or real time kinematic- positioning has become an industry standard procedure in surveying, machine control, and other high-precision applications. RTK makes use of carrier-phase and pseudorange measurements recorded at a (usually) fixed reference location with known coordinates and transmitted in real time to user's rover receivers using a radio link of some kind. [...] In this month 's colomn, we take a look at the technique of precise point positioning (PPP). Like RTK, PPP makes use of ambiguous carrier-phase measurements but only from the user's receiver. Rather than measurements from a reference receiver, it needs ultra-precise (and accurate) satellite orbit and clock information such as that provided by the international GNSS Service. Currently, there are issues with how long solutions takes to converge and the difficulty in resolving the ambiguities, for example, but research is targeting these and other practical issues. How close is PPP to prime time? Read on. Copyright Questex Media Group The application of GPS precise point positioning technology in aerial triangulation Auteur(s) YUAN (X.), FU (J.), SUN (H.) et TOTH (C.) Source ISPRS JOURNAL OF PHOTOGRAMMETRY AND REMOTE SENSING, vol 64, n 6, [01/11/2009], pp Mots clés AEROTRIANGULATION NUMERIQUE, ANALYSE COMPARATIVE, COMPENSATION PAR FAISCEAUX, ERREUR ALEATOIRE, ERREUR SYSTEMATIQUE, GPS EN MODE DIFFERENTIEL, POSITIONNEMENT PONCTUEL PRECIS N notice A Résumé d auteur In traditional GPS-supported aerotriangulation, differential GPS (DGPS) positioning technology is used to determine the 3-dimensional coordinates of the perspective centers Bibliographie du centre de documentation de l IGN mars Page 9

10 at exposure time with an accuracy of centimeter to decimeter level. This method can significantly reduce the number of ground control points (GCPs). However, the establishment of GPS reference stations for DGPS positioning is not only labor-intensive and costly, but also increases the implementation difficulty of aerial photography. This paper proposes aerial triangulation supported with GPS precise point positioning (PPP) as a way to avoid the use of the GPS reference stations and simplify the work of aerial photography. Firstly, we present the algorithm for GPS PPP in aerial triangulation applications. Secondly, the error law of the coordinate of perspective centers determined using GPS PPP is analyzed. Thirdly, based on GPS PPP and aerial triangulation software self-developed by the authors, four sets of actual aerial images taken from surveying and mapping projects, different in both terrain and photographic scale, are given as experimental models. The four sets of actual data were taken over a flat region at a scale of 1:2500, a mountainous region at a scale of 1:3000, a high mountainous region at a scale of 1:32000 and an upland region at a scale of 1:60000 respectively. In these experiments, the GPS PPP results were compared with results obtained through DGPS positioning and traditional bundle block adjustment. In this way, the empirical positioning accuracy of GPS PPP in aerial triangulation can be estimated. Finally, the results of bundle block adjustment with airborne GPS controls from GPS PPP are analyzed in detail. The empirical results show that GPS PPP applied in aerial triangulation has a systematic error of half-meter level and a stochastic error within a few decimeters. However, if a suitable adjustment solution is adopted, the systematic error can be eliminated in GPS-supported bundle block adjustment. When four full GCPs are emplaced in the corners of the adjustment block, then the systematic error is compensated using a set of independent unknown parameters for each strip, the final result of the bundle block adjustment with airborne GPS controls from PPP is the same as that of bundle block adjustment with airborne GPS controls from DGPS. Although the accuracy of the former is a little lower than that of traditional bundle block adjustment with dense GCPs, it can still satisfy the accuracy requirement of photogrammetric point determination for topographic mapping at many scales. Copyright 2009 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS). Real-time registration of airborne laser with sub-decimeter accuracy Auteur(s) SKALOUD (J.), SCHAER (P.), STEBLER (Y.) et TOME (P.) Source ISPRS JOURNAL OF PHOTOGRAMMETRY AND REMOTE SENSING, vol 65, n 2, [01/03/2010], pp Mots clés COVARIANCE, DONNEES LIDAR, DONNEES LOCALISEES 3D, GPS EN MODE DIFFERENTIEL, GPS-INS, LASERGRAMMETRIE, MESURAGE DE PHASE, POSITIONNEMENT CINEMATIQUE EN TEMPS REEL, PRECISION ABSOLUE, PRECISION DECIMETRIQUE, PRECISION DU POSITIONNEMENT, SEMIS DE POINTS, TELEMETRIE LASER AEROPORTE, TEMPS REEL N notice A Résumé d auteur This paper presents a methodology for the precise registering of airborne laser data directly in flight with an accuracy that is sufficient for the majority of derived products, such as digital terrain models. We first present the strategy that integrates GPS/INS/LiDAR data for generating laser point clouds directly in flight and analyzes their accuracy. The latter requires the implementation of a functional covariance propagation on-line for all the system components (i.e. trajectory, laser, system calibration) to which influences of scanning geometry are added at the end of a flight line. The study of scanning geometry necessitates the classification of vegetation and coarse estimation of the terrain normal. This is achieved by a method that we formerly proposed for off-line quality analysis. The second part of the paper focuses on the positioning component. In high resolution scanning performed close to the terrain, the absolute accuracy of the resulting point cloud depends mainly on the quality of the trajectory which is related to the type of GPS solution (e.g. absolute positioning, DGPS, RTK). To reach sub-decimeter accuracy for the point cloud in the real-time, an RTK-GPS solution is needed. This requires the establishment of a communication link for the transmission of GPS corrections (or measurements). We analyze the usability of RTK-GPS/ALS acquired during several flights using different communication methods in the particular context of helicopter based missions. We focus mainly on the exploitation of nation-wide reference GNSS networks and confirm experimentally that the real-time registration of airborne laser data is feasible with sub-decimeter accuracy. Such quality is sufficient not only for a Bibliographie du centre de documentation de l IGN mars Page 10

11 wide range of applications, but it also opens new opportunities for monitoring missions that require a short reaction time. Finally, we concentrate on situations when the phase and code corrections cannot be transmitted, and the quality of the differential carrierphase positioning needs to be predicted. We validate the previously introduced indicators of positioning quality by simulated degradation of the input data. Copyright ISPRS Single receiver phase ambiguity resolution with GPS data Auteur(s) BERTIGER (W.), DESAI (S.), HAINES (B.) et al. Source JOURNAL OF GEODESY, vol 84, n 5, [01/05/2010], pp Mots clés DONNEES GPS, GIPSY-OASIS, MESURAGE DE PHASE, PHASE GPS, POSITIONNEMENT CINEMATIQUE, POSITIONNEMENT PAR GPS, POSITIONNEMENT PONCTUEL PRECIS, POSITIONNEMENT STATIQUE, RESOLUTION D'AMBIGUITE, TRAITEMENT DE DONNEES GNSS N notice A Résumé d auteur Global positioning system (GPS) data processing algorithms typically improve positioning solution accuracy by fixing double-differenced phase bias ambiguities to integer values. These double-difference ambiguity resolution methods usually invoke linear combinations of GPS carrier phase bias estimates from pairs of transmitters and pairs of receivers, and traditionally require simultaneous measurements from at least two receivers. However, many GPS users point position a single local receiver, based on publicly available solutions for GPS orbits and clocks. These users cannot form double differences. We present an ambiguity resolution algorithm that improves solution accuracy for single receiver point-positioning users. The algorithm processes dualfrequency GPS data from a single receiver together with wide-lane and phase bias estimates from the global network of GPS receivers that were used to generate the orbit and clock solutions for the GPS satellites. We constrain (rather than fix) linear combinations of local phase biases to improve compatibility with global phase bias estimates. For this precise point positioning, no other receiver data are required. When tested, our algorithm significantly improved repeatability of daily estimates of ground receiver positions, most notably in the east component by approximately 30% with respect to the nominal case wherein the carrier biases are estimated as real values. In this static test for terrestrial receiver positions, we achieved daily repeatability of 1.9, 2.1 and 6.0 mm in the east, north and vertical (ENV) components, respectively. For kinematic solutions, ENV repeatability is 7.7, 8.4, and 11.7 mm, respectively, representing improvements of 22, 8, and 14% with respect to the nominal. Results from precise orbit determination of the twin GRACE satellites demonstrated that the inter-satellite baseline accuracy improved by a factor of three, from 6 to 2 mm up to a long-term bias. Jason- 2/Ocean Surface Topography Mission precise orbit determination tests results implied radial orbit accuracy significantly below the 10 mm level. Stability of time transfer, in low- Earth orbit, improved from 40 to 7 ps. We produced these results by applying this algorithm within the Jet Propulsion Laboratory s (JPL s) GIPSY/OASIS software package and using JPL s orbit and clock products for the GPS constellation. These products now include a record of the wide-lane and phase bias estimates from the underlying global network of GPS stations. This implies that all GIPSY OASIS positioning users can now benefit from this capability to perform single-receiver ambiguity resolution. Integer ambiguity resolution in precise point positionning : method comparison Auteur(s) GENG (J.), MENG (X.), DODSON (A.) et TEFERLE (F.) Source JOURNAL OF GEODESY, vol 84, n 9, [01/09/2010], pp Mots clés AMBIGUITE ENTIERE, ANALYSE COMPARATIVE, POSITIONNEMENT PAR GNSS, POSITIONNEMENT PONCTUEL PRECIS, PRECISION MILLIMETRIQUE, RESOLUTION D'AMBIGUITE N notice A Résumé d auteur Integer ambiguity resolution at a single receiver can be implemented by applying improved satellite products where the fractional-cycle biases (FCBs) have been separated from the integer ambiguities in a network solution. One method to achieve these products is to estimate the FCBs by averaging the fractional parts of the float ambiguity estimates, and the other is to estimate the integer-recovery clocks by fixing the undifferenced ambiguities to integers in advance. In this paper, we theoretically prove the equivalence of the ambiguity-fixed position estimates derived from these two methods by assuming that the FCBs are hardware-dependent and only they are assimilated into the Bibliographie du centre de documentation de l IGN mars Page 11

12 clocks and ambiguities. To verify this equivalence, we implement both methods in the Position and Navigation Data Analyst software to process 1 year of GPS data from a global network of about 350 stations. The mean biases between all daily position estimates derived from these two methods are only 0.2, 0.1 and 0.0 mm, whereas the standard deviations of all position differences are only 1.3, 0.8 and 2.0 mm for the East, North and Up components, respectively. Moreover, the differences of the position repeatabilities are below 0.2 mm on average for all three components. The RMS of the position estimates minus those from the International GNSS Service weekly solutions for the former method differs by below 0.1 mm on average for each component from that for the latter method. Therefore, considering the recognized millimeter-level precision of current GPS-derived daily positions, these statistics empirically demonstrate the theoretical equivalence of the ambiguity-fixed position estimates derived from these two methods. In practice, we note that the former method is compatible with current official clock-generation methods, whereas the latter method is not, but can potentially lead to slightly better positioning quality. Rapid re-convergences to ambiguity-fixed solutions in precise point positioning Auteur(s) GENG (J.), MENG (X.), DODSON (A.) et al. Source JOURNAL OF GEODESY, vol 84, n 12, [01/12/2010], pp Mots clés AMBIGUITE ENTIERE, CONVERGENCE, CORRECTION IONOSPHERIQUE, POSITIONNEMENT PAR GPS, POSITIONNEMENT PONCTUEL PRECIS, PROPAGATION IONOSPHERIQUE, RESOLUTION D'AMBIGUITE, TEMPS REEL Mots clés géog SUISSE N notice A Résumé d auteur Integer ambiguity resolution at a single receiver can be achieved if the fractional-cycle biases are separated from the ambiguity estimates in precise point positioning (PPP). Despite the improved positioning accuracy by such integer resolution, the convergence to an ambiguity-fixed solution normally requires a few tens of minutes. Even worse, these convergences can repeatedly occur on the occasion of loss of tracking locks for many satellites if an open sky-view is not constantly available, consequently totally destroying the practicability of real-time PPP. In this study, in case of such re-convergences, we develop a method in which ionospheric delays are precisely predicted to significantly accelerate the integer ambiguity resolution. The effectiveness of this method consists in two aspects: first, wide-lane ambiguities can be rapidly resolved using the ionospherecorrected wide-lane measurements, instead of the noisy Melbourne Wübbena combination measurements; second, narrow-lane ambiguity resolution can be accelerated under the tight constraints derived from the ionosphere-corrected unambiguous wide-lane measurements. In the test at 90 static stations suffering from simulated total loss of tracking locks, 93.3 and 95.0% of re-convergences to wide-lane and narrow-lane ambiguity resolutions can be achieved within five epochs of 1-Hz measurements, respectively, even though the time latency for the predicted ionospheric delays is up to 180 s. In the test at a mobile van moving in a GPS-adverse environment where satellite number significantly decreases and cycle slips frequently occur, only when the predicted ionospheric delays are applied can the rate of ambiguity-fixed epochs be dramatically improved from 7.7 to 93.6% of all epochs. Therefore, this method can potentially relieve the unrealistic requirement of a continuous open sky-view by most PPP applications and improve the practicability of real-time PPP. Regional reference network augmented precise point positioning for instantaneous ambiguity resolution Auteur(s) LI (X.), ZHANG (X.) et GE (M.) Source JOURNAL OF GEODESY, vol 85, n 3, [01/03/2011], pp Mots clés AMBIGUITE ENTIERE, POSITIONNEMENT CINEMATIQUE EN TEMPS REEL, POSITIONNEMENT PONCTUEL PRECIS, RESEAU GEODESIQUE LOCAL, RESOLUTION D'AMBIGUITE N notice A Résumé d auteur Integer ambiguity fixing can significantly shorten the initialization time and improve the accuracy of precise point positioning (PPP), but it still takes approximate 15 min of time to achieve reliable integer ambiguity solutions. In this contribution, we present a new strategy to augment PPP estimation with a regional reference network, so that Bibliographie du centre de documentation de l IGN mars Page 12

13 instantaneous ambiguity fixing is achievable for users within the network coverage. In the proposed method, precise zero-differenced atmospheric delays are derived from the PPP fixed solution of the reference stations, which are disseminated to, and interpolated at user stations to correct for L1, L2 phase observations or their combinations. With the corrected observations, instantaneous ambiguity resolution can be carried out within the user PPP software, thus achieving the position solutions equivalent to the network realtime kinematic positioning (NRTK). The strategy is validated experimentally. The derived atmospheric delays and the interpolated corrections are investigated. The ambiguity fixing performance and the resulted position accuracy are assessed. The validation confirms that the new strategy can provide comparable service with NRTK. Therefore, with this new processing strategy, it is possible to integrate PPP and NRTK into a seamless positioning service, which can provide an accuracy of about 10 cm anywhere, and upgrade to a few centimeters within a regional network. Doppler-aided positioning: Improving single-frequency in the urban environment Auteur(s) BAHRAMI (M.) et ZIEBART (M.) Source GPS WORLD, vol 22, n 5, [01/05/2011], pp Mots clés DONNEES DOPPLER, EFFET DOPPLER, LISSAGE DE DONNEES, MILIEU URBAIN, POSITIONNEMENT CINEMATIQUE EN TEMPS REEL, PSEUDO-DISTANCE, RECEPTEUR GPS MONOFREQUENCE N notice A Résumé d éditeur What does a GPS receiver, a policeman s speed gun, a weather radar, and some medical diagnostic equipment have in common? Give up? They all make use of the Doppler effect. First proposed in 1842 by the Austrian mathematician and physicist, Christian Doppler, it is the change in the perceived frequency of a wave when the transmitter and the receiver are in relative motion. Doppler introduced the concept in an attempt to explain the shift in the color of light from certain binary stars. Three years later, the effect was tested for sound waves by the Dutch scientist Christophorus Buys Ballot. [...] The beginning of the space age heralded a new application of the Doppler effect. By measuring the shift in the received frequency of the radio beacon signals transmitted by Sputnik 1 from a known location, scientists were able to determine the orbit of the satellite. And shortly thereafter, they determined that if the orbit of a satellite was known, then the position of a receiver could be determined from the shift. That realization led to the development of the United States Navy Navigation Satellite System, commonly known as Transit, with the first satellite being launched in Initially classified, the system was made available to civilians in 1967 and was widely used for navigation and precise positioning until it was shut down in The Soviet Union developed a similar system called Tsikada and a special military version called Parus. These systems are also assumed to be no longer in use at least for navigation. GPS and other global navigation satellite systems use the Doppler shift of the received carrier frequencies to determine the velocity of a moving receiver. Doppler-derived velocity is far more accurate than that obtained by simply differencing two position estimates. But GPS Doppler measurements can be used in other ways, too. In this month s column, we look at how Doppler measurements can be used to smooth noisy code-based pseudoranges to improve the precision of autonomous positioning as well as to improve the availability of single-frequency real-time kinematic positioning, especially in urban environments. GNSS algebraic structures Auteur(s) LANNES (A.) et TEUNISSEN (P.) Source JOURNAL OF GEODESY, vol 85, n 5, [01/05/2011], pp Mots clés DOUBLE DIFFERENCE, ERREUR SYSTEMATIQUE, ETALONNAGE D'INSTRUMENT, MESURAGE DE PHASE, PHASE GNSS, POSITIONNEMENT CINEMATIQUE EN TEMPS REEL, POSITIONNEMENT PAR GNSS, POSITIONNEMENT PONCTUEL PRECIS N notice A Résumé d auteur The first objective of this paper is to show that some basic concepts used in global navigation satellite systems (GNSS) are similar to those introduced in Fourier synthesis for handling some phase calibration problems. In experimental astronomy, the latter are at the heart of what is called phase closure imaging.' In both cases, the analysis of the related structures appeals to the algebraic graph theory and the algebraic number theory. For example, the estimable functions of carrier-phase ambiguities, which were introduced Bibliographie du centre de documentation de l IGN mars Page 13

14 in GNSS to correct some rank defects of the undifferenced equations, prove to be closure-phase ambiguities:' the so-called closure-delay' (CD) ambiguities. The notion of closure delay thus generalizes that of double difference (DD). The other estimable functional variables involved in the phase and code undifferenced equations are the receiver and satellite pseudo-clock biases. A related application, which corresponds to the second objective of this paper, concerns the definition of the clock information to be broadcasted to the network users for their precise point positioning (PPP). It is shown that this positioning can be achieved by simply having access to the satellite pseudo-clock biases. For simplicity, the study is restricted to relatively small networks. Concerning the phase for example, these biases then include five components: a frequency-dependent satellite-clock error, a tropospheric satellite delay, an ionospheric satellite delay, an initial satellite phase, and an integer satellite ambiguity. The form of the PPP equations to be solved by the network user is then similar to that of the traditional PPP equations. As soon as the CD ambiguities are fixed and validated, an operation which can be performed in real time via appropriate decorrelation techniques, estimates of these float biases can be immediately obtained. No other ambiguity is to be fixed. The satellite pseudo-clock biases can thus be obtained in real time. This is not the case for the satellite-clock biases. The third objective of this paper is to make the link between the CD approach and the GNSS methods based on the notion of double difference. In particular, it is shown that the information provided by a maximum set of independent DDs may not reach that of a complete set of CDs. The corresponding defect is analyzed. One of the main results of the corresponding analysis concerns the DDCD relationship. In particular, it is shown that the DD ambiguities, once they have been fixed and validated, can be used as input data in the undifferenced CD equations.' The corresponding algebraic operations are described. The satellite pseudo-clock biases can therefore be also obtained via particular methods in which the notion of double differencing is involved. Bibliographie du centre de documentation de l IGN mars Page 14