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Single frequency processing of Ørsted GPS radio occultation measurements

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Abstract

The Global Positioning System (GPS) radio occultation measurements obtained using the TurboRogue GPS receiver on the Danish satellite Ørsted have been processed using the single frequency method. Atmospheric profiles of refractivity and temperature are derived and validated against numerical weather prediction data from the European Centre for Medium-Range Weather Forecast (ECMWF). Results from the Ørsted GPS measurement campaign in February 2000 indicate that the single frequency method can provide retrievals with accuracy comparable to that of using two frequencies. From comparisons between measured dry temperature profiles and corresponding dry temperature profiles derived from ECMWF analysis fields, we find a mean difference of less than 0.5 K and a standard deviation of 2–4 K between 500 and 30 hPa in height. Above 30 hPa the impact of the ionosphere becomes more dominant and more difficult to eliminate using the single frequency method, and the results show degraded accuracy when compared to previous analysis results of occultation data from other missions using the dual frequency method. At latitudes less than 40° (denoted low latitudes), the standard deviation is generally smaller than at latitudes higher than 40° (denoted high latitudes). A small temperature bias is observed centered at 200 hPa for low latitudes and at 300 hPa for high latitudes. This indicates that the ECMWF analyses do not adequately resolve the tropopause temperature minimum. In the lowest part of the troposphere an observed warm bias is thought to be due to erroneous tracking of the GPS signal in cases of atmospheric multipath propagation.

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Acknowledgements

We are grateful to Bjarne Amstrup, DMI, for extracting ECMWF data for all occultation events used in this work. The Ørsted Data Center at DMI provided the raw data packages down-linked from the TurboRogue receiver onboard the Ørsted satellite. This work was sponsored by the Danish Natural Science Research Council and in part by the EUMETSAT GRAS SAF project.

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Author notes

  1. Stig Syndergaard

    Present address: COSMIC Project Office, University Corporation for Atmospheric Research, P.O. Box 3000, Boulder, CO, 80307-3000

Authors and Affiliations

  1. Danish Meteorological Institute, Lyngbyvej 100, DK-2100, Copenhagen, Denmark

    Georg Bergeton Larsen & Martin Bjært Sørensen

  2. Institute of Atmospheric Physics, The University of Arizona, P.O. Box 210081, Tucson, AZ, 85721-0081

    Stig Syndergaard

  3. Aalborg University, Niels Jernes Vej 14, DK-9220, Aalborg, Denmark

    Per Høeg

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  1. Georg Bergeton Larsen
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  2. Stig Syndergaard
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  3. Per Høeg
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  4. Martin Bjært Sørensen
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Correspondence to Georg Bergeton Larsen.

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Larsen, G.B., Syndergaard, S., Høeg, P. et al. Single frequency processing of Ørsted GPS radio occultation measurements. GPS Solut 9, 144–155 (2005). https://doi.org/10.1007/s10291-005-0142-x

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  • DOI: https://doi.org/10.1007/s10291-005-0142-x

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