Analysis of the bias between TOPEX and GPS vTEC determinations |
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Authors: | Francisco Azpilicueta Claudio Brunini |
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Institution: | (1) Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque, 1900 La Plata, Argentina;(2) Consejo Nacional de Investigaciones Científicas y Tecnológicas, Buenos Aires, Argentina |
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Abstract: | The TOPEX/Poseidon satellite was jointly developed and deployed by the National Aeronautics and Space Administration (NASA),
USA, and the Centre National d’Etudes Spatiales (CNES), France (for details see Chelton et al. In: Fu L-L, Cazenave A (eds)
International geophysics series, vol 69, ISBN 0-12-269545-3, Academic Press, CA, pp 1–131, 2001), with the main scientific
goal of sea surface height monitoring. The process that ends with the TOPEX main observable (the range between the satellite
and the sea surface) involves the measurement of several parameters of the radar pulses reflected by the sea surface and the
computation of several other corrections. After several calibration campaigns performed by the Calibration/Validation team
of the mission, it was found that TOPEX range determinations were systematically shorter than expected and it was decided
to add an empirical correction of +15 mm to the TOPEX range-computation algorithm. As a by-product, TOPEX provides vertical
total electron content (vTEC) determinations which have turned out to be a very important data source for the ionospheric
research community. Since TOPEX vTEC measurements became available, several comparison studies have detected a constant bias,
from +2 to +5 TECu, when TOPEX is compared to other vTEC sources, e.g., Global Positioning System (GPS), Doppler Orbitography
and Radio-positioning Integrated by Satellite (DORIS), (TOPEX always greater than the others). In this work, we show that
miscalibration of the corrections used in the TOPEX processing algorithm can cause the shortening effect of TOPEX ranges and
at the same time the constant bias on the TOPEX vTEC values. It is also shown that changes on TOPEX System Biases of less
than 10 mm for the Ku-band and between 40 and 70 mm for the C-band, can make both effects disappear. The analyzed hypothesis
is supported by theoretical considerations and data analysis available in the specialized literature.
On behalf of the authors of the contribution ‘Analysis of the bias between TOPEX and GPS vTEC determinations’, I declare that
the paper has not been, nor is in the process of being published in any other publication. |
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Keywords: | TOPEX total electron content (TEC) bias TOPEX system biases GPS TEC |
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