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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/amtd-7-12719-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
18 Dec 2014
Review status
This discussion paper has been under review for the journal Atmospheric Measurement Techniques (AMT). A final paper in AMT is not foreseen.
GPS radio occultation with TerraSAR-X and TanDEM-X: sensitivity of lower troposphere sounding to the Open-Loop Doppler model
F. Zus, G. Beyerle, S. Heise, T. Schmidt, and J. Wickert Helmholtz Centre Potsdam, GFZ German Research Centre for Geoscience Potsdam, Potsdam, Germany
Abstract. The Global Positioning System (GPS) radio occultation (RO) technique provides valuable input for numerical weather prediction and is considered as a data source for climate related research. Numerous studies outline the high precision and accuracy of RO atmospheric soundings in the upper troposphere and lower stratosphere. In this altitude region (8–25 km) RO atmospheric soundings are considered to be free of any systematic error. In the tropical (30° S–30° N) Lower (<8 km) Troposphere (LT), this is not the case; systematic differences with respect to independent data sources exist and are still not completely understood. To date only little attention has been paid to the Open Loop (OL) Doppler model. Here we report on a RO experiment carried out on-board of the twin satellite configuration TerraSAR-X and TanDEM-X which possibly explains to some extent biases in the tropical LT. In two sessions we altered the OL Doppler model aboard TanDEM-X by not more than ±5 Hz with respect to TerraSAR-X and compare collocated atmospheric refractivity profiles. We find a systematic difference in the retrieved refractivity. The bias mainly stems from the tropical LT; there the bias reaches up to ±1%. Hence, we conclude that the negative bias (several Hz) of the OL Doppler model aboard TerraSAR-X introduces a negative bias (in addition to the negative bias which is primarily caused by critical refraction) in our retrieved refractivity in the tropical LT.

Citation: Zus, F., Beyerle, G., Heise, S., Schmidt, T., and Wickert, J.: GPS radio occultation with TerraSAR-X and TanDEM-X: sensitivity of lower troposphere sounding to the Open-Loop Doppler model, Atmos. Meas. Tech. Discuss., 7, 12719-12733, https://doi.org/10.5194/amtd-7-12719-2014, 2014.
F. Zus et al.
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
 
RC C4576: 'review', Anonymous Referee #2, 15 Jan 2015 Printer-friendly Version Supplement 
AC C5138: 'reply#1', Florian Zus, 13 Mar 2015 Printer-friendly Version 
 
RC C4590: 'Referee comment to updated paper', Magnus Bonnedal, 15 Jan 2015 Printer-friendly Version Supplement 
AC C5140: 'reply#2', Florian Zus, 13 Mar 2015 Printer-friendly Version 
F. Zus et al.
F. Zus et al.

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