The Global Positioning System (GPS) has been used for more than a decade for the accurate determination of position on the earth's surface, as well as navigation. The system consists of approximately thirty satellites, managed by the US Department of Defense, orbiting at an altitude of 20 200 kilometres, as well as thousands of stationary ground-based and mobile receivers. It has become apparent from numerous studies that the delay of GPS signals in the atmosphere can also be used to study the amosphere, particularly to determine the precipitable water vapour (PWV) content of the troposphere and the total electron content (TEC) of the ionosphere. This dissertation gives an overview of the mechanisms that contribute to the delay of radio signals between satellites and receivers. The dissertation then focuses on software developed at the Hartebeesthoek Radio Astronomy Observatory's (HartRAO's) Space Geodesy Programme to estimate tropospheric delays (from which PWV is calculated) in near real-time. In addition an application of this technique, namely the improvement of tropospheric delay models used to process satellite laser ranging (SLR) data, is investigated. The dissertation concludes with a discussion of opportunities for future work. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2004.

The Global Positioning System (GPS) has been used for more than a decade for the accurate determination of position on the earth's surface, as well as navigation. The system consists of approximately thirty satellites, managed by the US Department of Defense, orbiting at an altitude of 20 200 kilometres, as well as thousands of stationary ground-based and mobile receivers. It has become apparent from numerous studies that the delay of GPS signals in the atmosphere can also be used to study the amosphere, particularly to determine the precipitable water vapour (PWV) content of the troposphere and the total electron content (TEC) of the ionosphere. This dissertation gives an overview of the mechanisms that contribute to the delay of radio signals between satellites and receivers. The dissertation then focuses on software developed at the Hartebeesthoek Radio Astronomy Observatory's (HartRAO's) Space Geodesy Programme to estimate tropospheric delays (from which PWV is calculated) in near real-time. In addition an application of this technique, namely the improvement of tropospheric delay models used to process satellite laser ranging (SLR) data, is investigated. The dissertation concludes with a discussion of opportunities for future work. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2004.

Radio signals from Global Navigation Satellite Systems (GNSS) satellites suffer delay as they propagate through the atmosphere (neutral and non-neutral) and this delay is partially driven by the water vapour content in the atmosphere. The delay component due to the non-neutral atmosphere (ionosphere) is removed through the use of dual frequency GNSS receivers. The main tropospheric parameter is the zenith tropospheric (or total) delay (ZTD), which is a widely accepted parameter with which to express the total delay in the signal from all satellites due to the neutral atmosphere. The ZTD is a measure of the integrated tropospheric condition over a GNSS receiver station. Accordingly, the integrated water vapour or precipitable water vapour (PWV) can be obtained from a portion of the ZTD, if the atmospheric pressure and temperature at the station are known through a concept often referred to as GNSS meteorology. A number of GNSS receivers have been deployed for mapping and geodetic services in Nigeria under the African reference frame initiative, but unfortunately most of these receivers do not have co-located meteorological sensors for pressure and temperature measurements. The prospect of incorporating GNSS meteorology into weather monitoring and climate analysis in Nigeria was investigated and is reported in this thesis. During the first task of this research, the technical basis for ground-based GNSS meteorology was reviewed and the potentials and challenges of the approach to meteorological activities in Africa (including Nigeria) were identified. Thereafter an in-depth analysis of the spatial and temporal variability of ZTD over Nigeria for the period of 2010-2014 was conducted; results revealed weak spatial dependence among the stations. Tidal oscillations (of the diurnal and semidiurnal components) were observed at the GNSS stations of which the diurnal ZTD cycles exhibited significant seasonal dependence, affirming the prospective relevance of ground-based GNSS data to atmospheric studies. Also in this research, the accuracy and suitability of using reanalysis datasets (ERA-Interim and NCEP/NCAR) and a GPT2 neutral model in retrieving PWV from GNSS observations over Nigeria were investigated; results showed that PWV can be retrieved to within a precision of about 1 mm, provided GNSS-derived ZTD is of high precision. A fundamental issue for GNSS meteorology in the West African region was yet again addressed in this research; this is the development of a weighted tropospheric mean temperature model for use in current and future GNSS meteorology activities in the region. A multitechnique comparison of PWV estimates showed good agreement between GNSS estimates and other techniques (i.e. the atmospheric infrared sounder, and ERAInterim reanalysis). This result is suggestive of the potential of assimilating GNSS atmospheric products into reanalysis and climate models. Diurnal and seasonal variability of GNSS PWV estimates exhibits strong correlation with weather events that influence the region (i.e. solar activity and rainfall events); this further demonstrated the immense contribution of the approach to efficient weather forecasting and climate monitoring for Nigeria. / Thesis (PhD)--University of Pretoria, 2017. / Geography, Geoinformatics and Meteorology / PhD / Unrestricted

[ES] El vapor de agua es la llave del ciclo hidrológico, del balance energético atmosférico y el principal gas natural de efecto invernadero. Su estudio, es, por tanto, esencial para entender la dinámica climática y para la previsión de fenómenos meteorológicos. El uso de las observaciones GNSS para obtenerlo, contribuye de forma notable a su estudio, dada su alta resolución espacial y temporal. Para que se pueda obtener el vapor de agua a partir de observaciones GNSS, estas deben procesarse de un modo que asegure una alta precisión en la obtención de la componente troposférica. En esta tesis, se muestra una estrategia de cálculo con el programa científico Bernese 5.2, basado en Dobles Diferencias de fase, y detallada con sus diferentes opciones. Esa estrategia se aplicó sobre un conjunto de estaciones GNSS situadas desde la ciudad de Vigo, hasta la ciudad francesa de Brest con un total de nueve estaciones principales, a las que se sumaron otras 8 para el diseño de la red de procesamiento. La estrategia fue validada con los productos oficiales de referencia, EPN REPRO2, con las 13 estaciones comunes entre la red de procesamiento y la red EUREF, obteniendo un valor de error medio cuadrático de aproximadamente 3 milímetros. Después se procedió al cálculo del vapor de agua precipitable, con el uso del modelo GPT3 completando cuatro años de datos. Para la validación de estas series de vapor de agua se usaron observaciones de radiosonda, de dos estaciones, situadas cerca de la estación de GNSS de A Coruña y de Santander. La comparación del vapor de agua, arrojó valores máximos de error medio cuadrático de 3 milímetros. Con las series de vapor de agua, se procedió al estudio de su caracterización espacial y temporal. Se constató la disminución del vapor de agua al ascender en la latitud. Así mismo, se observó en la variación temporal una componente anual mucho más significativa que la semianual, así como una distribución claramente estacional del vapor de agua, con valores en la estación de verano muy superiores a la estación de invierno. Las anomalías diarias mostraron ciertas similitudes, con un valor mínimo en la noche, ascendiendo hacia un pico o valor máximo, generalmente en la tarde. Su comportamiento también se mostró claramente estacional, con una variación mucho más significativa y de mayor amplitud en el verano que en el invierno. La serie de vapor de agua de la ciudad de A Coruña, junto con los datos de una estación meteorológica, se aplicaron al estudio de su relación con otras variables atmosféricas. En el caso de la temperatura y el vapor de agua, el estudio mostró una fuerte correlación. Sin embargo, el estudio de la relación entre el vapor de agua y precipitación no mostró ninguna relación entre ambas. Además, la serie de vapor de agua permitió estudiar el índice de Eficiencia de Precipitación, encontrándose una baja efectividad de los mecanismos que producen la precipitación más acusada en verano que en invierno, a pesar del nivel alto de vapor de agua en la estación estival. Además, se estudiaron nueve episodios de lluvia de diferentes estaciones climáticas, estudiando la evolución temporal del vapor de agua antes, durante y después del fenómeno. Esto permitió observar un patrón de comportamiento similar con un claro aumento del vapor de agua antes del comienzo de la lluvia y un fuerte descenso posterior, que fue parametrizado en forma de diferentes indicadores, en los que, de nuevo, se constató una fuerte componente estacional. Además, se pudo observar un comportamiento más significativo en la ventana de 12 horas previas a los episodios de lluvia. / [CA] El vapor d'aigua és la clau del cicle hidrològic, del balanç energètic atmosfèric i el principal gas natural d'efecte d'hivernacle. El seu estudi, és, per tant, essencial per a entendre la dinàmica climàtica i per a la previsió de fenòmens meteorològics. L'ús de les observacions GNSS per a obtindre'l, contribuïx de manera notable al seu estudi, donada la seua alta resolució espacial i temporal. Perquè es puga obtindre el vapor d'aigua a partir d'observacions GNSS, estes han de processar-se d'un mode que assegure una alta precisió en l'obtenció de la component troposfèrica. En esta tesi, es mostra una estratègia de càlcul amb el programa científic Bernese 5.2, basat en Dobles Diferències de fase, i detallada amb les seues diferents opcions. Eixa estratègia es va aplicar sobre un conjunt d'estacions GNSS situades des de la ciutat de Vigo, fins a la ciutat francesa de Brest amb un total de nou estacions principals, a les quals es van sumar altres 8 per al disseny de la xarxa de processament. L'estratègia va ser validada amb els productes oficials de referència, EPN REPRO2, amb les 13 estacions comunes entre la xarxa de processament i la xarxa EUREF, obtenint un valor d'error mig quadràtic d'aproximadament 3 mil·límetres. Després es va procedir al càlcul del vapor d'aigua precipitable, amb l'ús del model GPT3 completant quatre anys de dades. Per a la validació d'estes sèries de vapor d'aigua es van usar observacions de radiosonda, de dos estacions, situades prop de l'estació de GNSS de la Corunya i de Santander. La comparació del vapor d'aigua, va llançar valors màxims d'error mig quadràtic de 3 mil·límetres. Amb les sèries de vapor d'aigua, es va procedir a l'estudi de la seua caracterització espacial i temporal. Es va constatar la disminució del vapor d'aigua en ascendir en la latitud. Així mateix, es va observar en la variació temporal una component anual molt més significativa que la semianual, així com una distribució clarament estacional del vapor d'aigua, amb valors en l'estació d'estiu molt superiors a l'estació d'hivern. Les anomalies diàries van mostrar unes certes similituds, amb un valor mínim en la nit, ascendint cap a un pic o valor màxim, generalment en la vesprada. El seu comportament també es va mostrar clarament estacional, amb una variació molt més significativa i de major amplitud en l'estiu que en l'hivern. La sèrie de vapor d'aigua de la ciutat de la Corunya, juntament amb les dades d'una estació meteorològica, es van aplicar a l'estudi de la seua relació amb altres variables atmosfèriques. En el cas de la temperatura i el vapor d'aigua, l'estudi va mostrar una forta correlació. No obstant això , l'estudi de la relació entre el vapor d'aigua i precipitació no va mostrar cap relació entre ambdues. A més, la sèrie de vapor d'aigua va permetre estudiar l'índex d'Eficiència de Precipitació, trobant-se una baixa efectivitat dels mecanismes que produïxen la precipitació més acusada a l'estiu que a l'hivern, malgrat el nivell alt de vapor d'aigua en l'estació estival. A més, es van estudiar nou episodis de pluja de diferents estacions climàtiques, estudiant l'evolució temporal del vapor d'aigua abans, durant i després del fenomen. Això va permetre observar un patró de comportament similar amb un clar augment del vapor d'aigua abans del començament de la pluja i un fort descens posterior, que va ser parametritzat en forma de diferents indicadors, en els quals, de nou, es va constatar una forta component estacional. A més, es va poder observar un comportament més significatiu en la finestra de 12 hores prèvies als episodis de pluja. / [EN] Water vapour is the key of the hydrological cycle and the atmospheric energy balance and the most important natural greenhouse gas. Its study is therefore essential for understanding climate dynamics and for forecasting meteorological phenomena. The use of GNSS observations to obtain it contributes significantly to its study, given its high spatial and temporal resolution. In order to obtain water vapour from GNSS observations, these must be processed in a way that ensures high accuracy in obtaining the tropospheric component. In this thesis, a calculation strategy with the scientific programme Bernese 5.2, based on Double Phase Differences, is shown, and detailed with its different options. This strategy was applied on a set of GNSS stations located from the Spanish city of Vigo to the French city of Brest with a total of nine main stations, to which another 8 were added for the design of the Double Difference processing network. The strategy was validated with the official reference products, EPN REPRO2, with the 13 common stations between the processing network and the EUREF network, obtaining a mean square error value of approximately 3 millimetres. Then, four years series of precipitable water vapour was calculated, using the GPT3 model. For the validation of these water vapour series, radiosonde observations from two stations, located near the GNSS station of A Coruña and Santander were used. The comparison between both sets of water vapour information was performed yielding maximum values of mean square error of 3 millimetres. Using the water vapour series, the spatial and temporal characterisation of water vapour in the working area was studied. It was then possible to observe the decrease in water vapour with increasing latitude. Likewise, a much more significant annual component than the semi-annual one was observed in the temporal variation, as well as a clearly seasonal distribution of water vapour in the whole working area, with values in the summer season much higher than in the winter season. The daily anomalies showed some similarities, showing in general a minimum value at night, rising towards a peak or maximum value in the afternoon. Their behaviour was also clearly seasonal, with a much more significant variation and greater amplitude in the summer than in the winter. The water vapour series of the city of A Coruña, together with data from a meteorological station, were applied to the study of their relationship with other atmospheric variables. In the case of temperature and water vapour, the study showed a strong correlation. However, the study of the relationship between water vapour and precipitation showed no relationship between the two. In addition, the water vapour series allowed the study of the Precipitation Efficiency index, finding a low effectiveness of the mechanisms that produce precipitation more pronounced in summer than in winter, despite the high level of water vapour in the summer season. Finally, nine rainfall events were studied in different climatic seasons, studying the temporal evolution of water vapour before, during and after the event. This allowed a similar pattern of behaviour to be observed, with a clear increase in water vapour before the onset of the rain and a sharp decrease afterwards, which was parameterised in the form of different indicators, in which, once again, a strong seasonal component was observed. In addition, a more significant behaviour was observed in the 12-hour window prior to rainfall events. / Perdiguer López, R. (2024). Estrategia de cálculo del vapor de agua a partir de las observaciones GNSS para su caracterización y aplicación climática [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/205795

An important goal in modern weather prediction is to improve short-term weather forecasts, especially of severe weather and precipitation. However, the ability to achieve this goal is hindered by the lack of timely and accurate observations of atmospheric water vapour, which is one of the most poorly measured and least understood constituents of the Earth's atmosphere due to its high temporal and spatial variability. This situation is being addressed by the Global Positioning System (GPS) technology. GPS radio signals are slowed and bent by changes in temperature, pressure and water vapour in the atmosphere. Traditionally, the GPS signal propagation delay is considered a nuisance parameter that is an impediment to obtaining precise coordinates using GPS. Recent development in GPS precise positioning and orbit determination has enabled the atmospheric parameters to be determined to a high degree of accuracy on a routine basis, using continuous tracking data from ground-based GPS receivers. The aim of this research is to address several critical scientific challenges in estimating the atmospheric water vapour content in near-real-time (NRT) in Australia. Contributions are made to the field of GPS meteorology in the following five areas: First of all, research efforts were made to develop a technical platform for the ground-based GPS meteorology studies and demonstration of GPS Precipitable Water Vapour (PWV) estimation using observations from Australian Regional GPS Networks (ARGN). Methods of estimation of water vapour from GPS and radiosonde data have been developed and tested. GAMIT-based GPS data processing strategies and compare analysis with radiosonde water vapour solutions from the Australia Upper Air Network (AUAN) were undertaken, providing an effective technical basis for further studies. Secondly, the research has developed techniques to allow estimation of atmospheric water vapour from GPS data and surface meteorological observations collected around the GPS sites. Ideally a dedicated meteorological sensor is installed adjacent to the GPS antenna. However, meteorological sensors are normally not installed at most Australian GPS stations. Installing a new meteorological sensor at each GPS station would involve additional cost at the level of one-third or half of the geodetic GPS receiver cost. We have experimentally developed and demonstrated interpolation methods for making use of hourly collected surface meteorological data from the Australian Automatic Weather Station (AWS) network operated by the Bureau of Meteorology (BOM) to estimate atmospheric water vapour. Thirdly, the research has studied ocean tidal loading and its effects on GPS derived precipitable water vapour estimates. The periodic motion of the Earth's surface due to ocean loading is one of the largest periodic motions. However, very little work has been done to quantify their effects on GPS-derived solutions at the GPS sites in the Australian region surrounded by ocean waters. The research presents the theoretical analysis and experimental results from the ARGN network, focusing on ocean loading and its effects on GPS derived precipitable water vapour estimates. The fourth important effort was the development of techniques for estimating highrate Slant Water Vapour (SWV) values for future operational meteorological applications in Australia, including addressing such issues as slant-path delay recovery from post-fit double-difference residuals, and overcoming site multipath effects. The experimental results have demonstrated the efficiency of the proposed methods. Finally, in order to address the meteorological applications with the existing and anticipated GPS reference stations in the Australian region, and measure the atmospheric water vapour content in near-real-time, the technical issues to implement NRT GPS water vapour estimation were identified and discussed, including the data requirements for meteorological and climate applications, NRT data processing and quality control procedures for GPS orbits. The experimental GPS PWV results from NRT and post data processing are compared and presented.