Since many years the Global Navigation Satellite System (GNSS) has been regarded by the meteorological community as one of the systems for athmospheric water vapour remote sensing. In order to achieve millimiter level positioning accuracies, GNSS signal delays due to the interaction with atmosphere have in fact to be taken into account. Among these there is the tropospheric delay, caused by the water vapour present in the lower part of the atmosphere. Its effect on signal propagation can be modelled and removed in terms of a quantity called Zenith Tropospheric (or Total) Delay (ZTD), namely the delay experienced by the signal propagating along the zenith direction above a GNSS station. If surface temperature and pressure values near the GNSS station are known, it is possible to exploit ZTD to monitor the presence of water vapour in the atmosphere. ZTD is the sum of two quantities: the Zenith Hydrostatic Delay (ZHD) and the Zenith Wet Delay (ZWD). From the latter is possible to trace back the Precipitable Water Vapour (PWV), an important meteorological variable difficult to be modelled or predicted. In the present work ZTD parameters estimated from the data collected by some permanent stations are validated against independent values derived from radiosonde observations (RAOBS). The comparisons is done both in terms of ZTD and in terms of PWV values, obtained with different approaches. All results confirm a good agreement between the water vapor products, with differences within 2 mm standard deviation in terms of PWV and a 1-2 cm level standard deviation in terms of ZTD. The first two chapters of this work introduce some basic information about atmospheric phenomena and GNSS principles. The third one is about GNSS meteorology while the fourth presents the case study, the tools on which the entire work is based and extensively explains the data processing. The results are shown in the fifth chapter, followed by the conclusions.
Da molti anni il Global Satellite Navigation System (GNSS) viene considerato dalla comunità meteorologica come uno dei sistemi per il monitoraggio del vapor d’acqua atmosferico. Per raggiungere accuratezze millimetriche nel posizionamento è stato necessario correggere le osservazioni GNSS dai ritardi nella propagazione del segnale causati dall’interazione con l’atmosfera. Tra questi c’è il ritardo troposferico, causato dal vapore acqueo presente nello strato più basso dell’atmosfera. Il suo effetto sulla propagazione del segnale viene modellizzato e rimosso in termini di una quantità chiamata ritardo troposferico zenitale (ZTD), cioè il ritardo nella propagazione del segnale lungo la direzione zenitale sopra la stazione GNSS. Se i valori di pressione e temperatura superficiali nei pressi della stazione GNSS sono noti, è possibile ricavare dal ritardo stimato la quantità di vapor acqueo presente in atmosfera in termini di vapor acqueo precipitabile PWV, un’importante variabile meteorologica difficilmente modellabile e predicibile. In questo lavoro i valori di ZTD stimati a partire dai dati raccolti da alcune stazioni GNSS permanenti sono validati rispetto a valori indipendenti derivati da osservazioni di radiosondaggi (RAOBS). Il confronto è stato fatto sia in termini di ZTD che in termini di PWV, ricavati con approcci differenti. Tutti i risultati confermano una buona concordanza tra i valori di vapore acqueo da GNSS e da radiosonde, con differenze dell’ordine di 2 mm di scarto quadratico medio in termini di PWV e di 1-2 cm in termini di ZTD. Nei primi due capitoli di questo lavoro vengono introdotte alcune informazioni base sui fenomeni atmosferici e i principi del posizionamento GNSS. Il terzo è sulla meteorologia GNSS mentre nel quarto viene presentato il caso studio, con una descrizione dettagliata dei dati utilizzati e della loro elaborazione. I risultati sono riportati nel quinto capitolo, seguiti dalle conclusioni.
Experimental study on the relation between GNSS-derived and radiosonde-derived water vapour variations
KARAKUS, YUCEL
2017/2018
Abstract
Since many years the Global Navigation Satellite System (GNSS) has been regarded by the meteorological community as one of the systems for athmospheric water vapour remote sensing. In order to achieve millimiter level positioning accuracies, GNSS signal delays due to the interaction with atmosphere have in fact to be taken into account. Among these there is the tropospheric delay, caused by the water vapour present in the lower part of the atmosphere. Its effect on signal propagation can be modelled and removed in terms of a quantity called Zenith Tropospheric (or Total) Delay (ZTD), namely the delay experienced by the signal propagating along the zenith direction above a GNSS station. If surface temperature and pressure values near the GNSS station are known, it is possible to exploit ZTD to monitor the presence of water vapour in the atmosphere. ZTD is the sum of two quantities: the Zenith Hydrostatic Delay (ZHD) and the Zenith Wet Delay (ZWD). From the latter is possible to trace back the Precipitable Water Vapour (PWV), an important meteorological variable difficult to be modelled or predicted. In the present work ZTD parameters estimated from the data collected by some permanent stations are validated against independent values derived from radiosonde observations (RAOBS). The comparisons is done both in terms of ZTD and in terms of PWV values, obtained with different approaches. All results confirm a good agreement between the water vapor products, with differences within 2 mm standard deviation in terms of PWV and a 1-2 cm level standard deviation in terms of ZTD. The first two chapters of this work introduce some basic information about atmospheric phenomena and GNSS principles. The third one is about GNSS meteorology while the fourth presents the case study, the tools on which the entire work is based and extensively explains the data processing. The results are shown in the fifth chapter, followed by the conclusions.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/138890