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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
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