Etude d'une méthode de sondage de la vapeur d'eau dans la troposphère appliquée à la correction de mesures GPS pour l'altimétrie de haute précision

Abstract : Since 1999, IGN (Institut Géographique National) aims at improving the accuracy of the vertical component of GPS coordinates. IGN is interested in improving GPS components accuracy for applications such as leveling network, when both short baselines and short observation sessions are involved, and more generally, for traditional GPS network in geodetic applications. The GPS signal belongs to the microwave band. As it propagates through the atmosphere, it is affected by the variation of the refractivity index of the air. Once major error sources (ionospheric delay, GPS receiver and receiver clocks, a priori variation of antenna phase center) have been corrected, the tropospheric delay remains the major error source in the GPS data processing. This tropospheric delay is divided into two contributions: the dry delay, related to the pressure an temperature variations of the dry air, and the wet delay, related to temperature and water vapor density variations. Consequently, to correct the GPS signal from the tropospheric wet delay, the water vapor distribution has to be precisely known in time and place around each GPS station to be processed. Since water vapor is both temporally and spatially variable, we chose to develop an high sensitive water vapor sensor, collocated to the GPS station to be positioned, in order to sound tropospheric water vapor variation simultaneously to GPS measurements. We chose to develop a Raman lidar which is a high spatially resolved remote sensing system. This lidar is the fruit of a collaboration between IGN/LOEMI, a laboratory specialized in instrumentation, and SA (Service d'Aéronomie, from CNRS), which deals with atmospheric dynamic and meteorology questions.

The first part of this work deals with the atmospheric water vapor, mainly its singular role in the atmosphere and its influence on the microwave signal propagation. After a review of major means of detecting water vapor, we take a particular interest in the relation between GPS and water vapor, since water vapor is not only a error source for GPS signal, but can also be a product of GPS data processing.

In a second part, we describe the lidar technique in general. After a review of the major water vapor lidar systems in action in the world, our Raman lidar is described in particular. Direct problem and precise inversion procedure are presented. Relative calibration and efforts in an absolute calibration aspects (aerosol content, overlap effect, instrumental and optical calibration) of the system are treated in detail.

In a last part, the first results obtained during the ESCOMPTE 2001 campaign and AIRS 2002 validation campaign are presented. The water vapor profiles determined from our Raman lidar are compared to other collocated water vapor measurements (WVR, Solar Spectrometer and RS). The variability of the water vapor field is analyzed and its impact on GPS signals and coordinates estimates is evaluated. We conclude on the strategy to apply for collocated measurements with GPS and a Raman lidar for high accuracy positioning. We discuss also the perspectives for the Raman lidar accuracy and other applications, such as the coupling between Raman lidar and GPS for the retrieved of water vapor in the lower troposphere (tomography).
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Submitted on : Monday, March 13, 2006 - 12:43:06 PM
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Jérôme Tarniewicz. Etude d'une méthode de sondage de la vapeur d'eau dans la troposphère appliquée à la correction de mesures GPS pour l'altimétrie de haute précision. Autre. Université de Versailles-Saint Quentin en Yvelines, 2005. Français. ⟨tel-00011934⟩

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