Développé initialement pour la correction du retard humide des signaux GPS, le lidar Raman vapeur d’eau de l’Institut National de l’information Géographique et forestière (IGN) pourrait aujourd’hui servir pour d’autres applications telles que la climatologie et la météorologie. Cependant, quelle que soit l’application visée, il est primordial d’assurer une très bonne précision de la mesure. Un étalonnage fiable et stable de l’instrument est alors requis. Lors de la dernière campagne de mesures (Démévap) qui consistait à inter-comparer différentes techniques d’étalonnage, une dérive du coefficient d’étalonnage du lidar a été observée. Ce travail revient alors sur cette dérive et explore, dans un premier temps, les signaux enregistrés durant cette campagne. En découle alors un inventaire de sources d’erreurs et de variations pouvant expliquer ces résultats. Trois sources majeures de variations seront ensuite étudiées de manière approfondie : la dépendance en température des sections efficaces Raman induite par l’usage de filtres étroits, l’impact du choix des optiques de transmission et détection du signal et les problèmes liés à l’électronique de détection. À l’aide de simulations numériques, modélisations et tests en laboratoire, on s’est efforcés de mettre en évidence et de quantifier les variations. Des solutions permettant de minimiser ces instabilités ont aussi été proposées et testées. Finalement, le système lidar a été remonté entièrement et une campagne de validation des améliorations a été menée à Saint-Mandé. Sur une période de cinq mois, on a pu contrôler la stabilité instrumentale et étudier l’étalonnage du lidar à l’aide de capteurs d’humidité placés au sol. / The IGN (Franch Mapping Institut) water vapor Raman lidar has been developed in order to correct the wet delay of GPS signals. Today, the goal is to open up to other applications such as meteorology and climatology. Regardless the applications, high accuracy is and will be completed with a reliable calibration of the instrument. The latest campaign, during which the IGN Raman was experimented, was Demevap. Several lidar calibration techniques were compared, and results showed a common drift all along the campaign. The work presented here starts with a detailed investigation of the Demavap absolute signals. This first step allowed listing different likely sources of errors and instabilities in the system which lead to fluctuations of the calibration coefficient. Among them, we chose to study thoroughly three subsystems which appear to have a major influence on the calibration coefficient variations: the temperature dependence of the Raman cross sections induced by the use of narrowband interference filters, the effect of the optical configuration of the detection part of the lidar and problems linked to the electronic part of the detection. We strive to highlight and quantify the variations by means of numerical simulations, models and laboratory experiments. Furthermore, we proposed theoretical, empirical and instrumental solutions for the mitigation of these variations. Eventually, long term calibration coefficient stability of the overall system will be assessed with regular water vapor profile recordings and calibration measurements spread over several months.

A software GPS receiver is a functional GPS receiver in software. It has several advantages compared to its hardware counterparts. For instance, improvements in receiver architecture as well as GPS system structure can be easily adapted to it. Furthermore, interaction between nearby sensors can be coordinated easily. In this thesis, a SGR (software GPS receiver) is presented from a practical point of view. Major components of the SGR are implemented in Matlab environment. Furthermore, some alternative algorithms are implemented. SGR implementation is considered in two main sections namely a signal processing section and a navigation section. Signal processing section is driven by the raw GPS signal samples obtained from a GPS front-end of NordNavTM R-25 instrument. The conventional and the block adjustment of synchronizing signal (BAAS) processing methods are implemented and their performances are compared in terms of their speed and outputs. Signal processing section outputs raw GPS measurements and navigation data bits. Since the output data length is insufficient in our case, navigation section input is fed from AshtechTM GPS receiver for a moving platform and TrimbleTM GPS Receiver for a stationary platform. Satellite position computation, pseudorange corrections, Kalman filter and LSE (least squares estimation) are implemented in the navigation section. Kalman filter and LSE methods are compared in terms of positioning accuracy for a moving as well as a stationary platform. Results are compared with the commercial GPS outputs. This comparison shows that the software navigation section is equivalent to the commercial GPS in terms of positioning accuracy.

The Global Positioning System (GPS) satellite signals provide not only traditional radionavigation service but inexpensive and convenient radio beacons for signal propagation studies on ionosphere and atmosphere. This thesis describes the development and testing of a specialized GPS sensor which measures, plots and records real-time high-resolution L1 (1575.42MHz) GPS signal strength at a data rate of up to 10Hz. The instrument is based on an open architecture GPS receiver development kit that can be modified and rebuilt. The signal strength is defined as mean-square signal strength in the thesis. The coarse/acquisition code (C/A-code) correlation is applied and the raw correlation data from a GPS correlator chip is obtained to calculate the signal strength. The gain variation of the automatic gain control (AGC) in the GPS signal link is considered, and a model is designed and implemented in data post-processing to reduce the AGC distortion to GPS signal strength measurements. Speed limitation of 1,000 knots and height limitation of 60,000 feet are removed so that it can track spacecraft such as low earth orbit (LEO) satellite. Four testing plans are developed and conducted to test the GPS signal strength sensor. A GPS simulator is used and the testing results prove that the space-borne sensor is fully operational and the signal strength resolution can be smaller than 0.05dB. Additionally, a COM-port-to-TCP/IP GPS simulation remote control gateway is designed and implemented for the senor and the GPS simulator to conduct formation flying. A graphic user interface (GUI) program is also built to retrieve data from a commercial high-performance space-borne GPS receiver for comparison. A Red Hat Linux signal strength sensor based on the National Aeronautics and Space Administration (NASA) PiVoT GPS receiver is achieved by modifications. The NASA PiVoT sensor, working together with the former signal strength sensor and the commercial space-borne GPS receiver, will strengthen our academic research strength in the studies on the ionospheric and atmospheric effects and irregularities which cause GPS signal degradation and scintillations. / Master of Science

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