POSTER ID: G23B-10 The impact of interpolation of meteorological measurements in the quality of IWV-GNSS values Mariana Dias Chaves*, Luiz Fernando Sapucci**, João Francisco Galera Monico* [email protected] ; [email protected] ; [email protected] *Faculdade de Ciências e Tecnologia (FCT) – Universidade Estadual Paulista (UNESP) – Presidente Prudente – SP, Brazil **Centro de Previsão de Tempo e Estudos Climáticos (CPTEC), Instituto Nacional de Pesquisas Espaciais (INPE) - Cachoeira Paulista - SP, Brazil. Geodesic positioning using GNSS (Global Navigation Satellite System) has as basic observables the distances between the artificial satellites and receivers antennas, which are based on the radio-frequency signals. One of the errors source associated to this measurements type is the electrically neutral layer of the terrestrial atmosphere (Troposphere), which causes the so-called Tropospheric Delay (Dtrop) in the GNSS signals. This delay estimated along with the minimization of the additional observable sources of errors, when treated in the zenithal direction (Zenithal Tropospheric Delay-ZTD) can be converted to IWV (Integrated Water Vapor) (Section 1). Nowadays, the assimilation of GNSS-IWV is under investigation in the Center for Weather Forecast and Climate Studies (CPTEC), from the National Institute for Space Research (INPE). The use of continuous monitoring GNSS network, like in this case, that the Brazilian Continuous GNSS Monitoring Network (RBMC) was used, requires that measurements of atmospheric pressure and temperature are taken close to the GNSS antenna to guarantee the maximum accuracy in the IWV values (Section 2). In the absence of such measurements, some alternatives can be the use of data collected by the Meteorological Data Collection Platform (DCP) or from the conventional meteorological stations. Although, the DCP has automated collection measurement, the accuracy of the barometers is low (1hPa) (Section 3). The minimization of the problem requires temporal and spatial interpolation in the measurements. In both options there is a problem, because the density of stations is not enough and thus, there are GNSS stations with the closest meteorological stations located at several kilometers away, demanding a measurement correction in function of the distance. Section 3: Experiment Section 2: Data Analyzes Section 4: Further steps in the research Section 1: Definition and Propagation IWV IWV is of potential benefit to the Numerical Weather Predictions (NWP) model, since its assimilation improves the vertical water vapor structure, and, as consequence, it is possible to obtain a better initial state for the NWP model. It is estimated and expressed as function of measurements that are dispersed around a value, providing the variances. The evaluation of them, in terms of calculated quantities and correlations as functions of the dispersions from measurements, is realized as function of the Variance-Covariance-Propagation (Error-Propagation). To analyze the measurements obtained from a data collection and confirm the importance of the determination from IWV variance-covariance propagation, meteorological station data and GNSS measurements were organized and analyzed from two aspects: impact of dependency on the latitude and height of the following stations: BELE, RECF, RIOD, SMAR and RIOD, SAOP, PPTE, BRAZ stations. Objectives The aim of this work is to investigate appropriated methodologies of temporal and spatial meteorological data interpolation to convert the zenithal troposphere delay in IWV (Section 4). Results from the data collection experiment were compared to verify the impact on IWV-GPS by using meteorological stations near and far. way from a GPS station The Radiometer station was adopted as reference to make possible the comparison between the Radar and Radiometer stations (Fig. 5), since the data from these two stations had similar results for the temporal pressure and temperature series. The next studies to be realized in this project aim to investigate the impact of such interpolations and corrections in the final quality of the IWV obtained via GNSS based on measurements to be carried out in an experiment involving several high-accuracy meteorological sensors. The data collection at different stations will be compared with measurements from the station located near CHPI station (Fig. 7), where several equipments are available to test the results. After checking its consistency, in spite of showing good results of the temperature would be not suitable for use in collecting pressure. This happens because the INPE measurements obtained in the conventional stations are performed by operators and consequently, the collection rate is low and not uniform station. From this figure it is possible to see that by considering the latitude (left figure) the highest standard derivation values are related to the low latitude stations. It has pointed out that the effects, in the pressure error, are inversely proportional to the latitude. By considering the height dependency (right figure), the worse standard derivation values are related with the height of the station, showing that height effects in the pressure error, represent a continental effect. 2 2 HD TD WD Z Z Z 2 2 3 - 2 2 3 - ) 00028 , 0 ) 2 cos( 00026 , 0 1 ( 10 27683157 , 2 ) 00028 , 0 ) 2 cos( 00026 , 0 1 ( 10 27683157 , 2 00028 , 0 h Ps s Z h x h P x HD 2 4 2 2 3 2 2 2 2 2 2 2 2 2 2 2 3 ' 2 Y T K Y T Y R Z Z W M T M K K W R WD Z WD IWV M W WD Tm k k R Z IWV w WD 3 ' 2 6 10 . ) 00028 , 0 - 2 cos 0026 , 0 - 1 ( ) 10 27683157 , 2 ( 3 - h Ps x Z HD WD HD TD Z Z Z ) , ' , , , , , ( 3 2 K K R Tm Z Z Z f IWV W WD HD TD Acknowledgements: AGU 2010 THE MEETING OF THE AMERICAS , 8–12 AUGUST, FOZ DO IGUAÇU, BRAZIL Fig. 1 – Brazilian Meteorological stations Fig. 2 – RBMC : Brazilian GNSS stations Fig. 6 – Meteorological and GNSS stations location Fig. 4 – Experiment localization: Alcântara-MA, Brazil Fig. 5 – Meteorological stations localization Fig. 3 – GNSS signal propagation Fig. 7 – Stations location of future experiment