POSTER ID: G23B-10

The impact of interpolation of meteorological measurements in the quality of IWV-GNSS valuesMariana Dias Chaves*, Luiz Fernando Sapucci**, João Francisco Galera Monico*

mariana.unesp@hotmail.com; luiz.sapucci@cptec.inpe.br; galera@fct.unesp.br

*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.

ObjectivesThe 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.

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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