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https://doi.org/10.5194/egusphere-2024-4127
https://doi.org/10.5194/egusphere-2024-4127
24 Jan 2025
 | 24 Jan 2025

The Impact of Differences in Retrieval Algorithms between Processing Centers on GNSS Radio Occultation Refractivity Retrievals in the Planetary Boundary Layer

Sara Vannah, Stephen S. Leroy, Chi O. Ao, E. Robert Kursinski, Kevin J. Nelson, Kuo-Nung Wang, and Feiqin Xie

Abstract. GNSS radio occultation (GNSS RO) performance in the planetary boundary layer is strongly dependent on retrieval algorithms. In this work, we explore how differences in retrieval methodology across three major processing centers of GNSS RO data — NASA JPL, ROM SAF, and UCAR — impact refractivity retrievals in the planetary boundary layer. Using a shared base of occultations from the FORMOSAT-3/COSMIC-1 GNSS RO mission, we identify key differences between the three processing centers that are especially strong in the regions of frequent super-refraction. We find that the minimum penetration height allowed by each processing center is correlated with the amount of super-refraction, resulting in poorer penetration and higher refractivity biases in the Tropics. We found JPL to have the most conservative minimum height in this region at 1 km, followed by ROM SAF (640 m), and UCAR (420 km). We identify two key geopotential heights — 0.8 km and 2.6 km — to sample the global distribution of inter-center refractivity bias, finding differences of 0.3–0.5 % in the Tropics. We also find negative refractivity biases of up to -4 % relative to ERA5 reanalysis in regions of persistent high stratocumulus coverage, and areas along the descending branch of the Hadley circulation, with negligible bias along the intertropical convergence zone. A comparison to ERA5 also reveals areas of weak (0.2–0.5 %) positive refractivity biases in polar regions. We hypothesize potential causes for these biases based on truncation schemes, radio-holographic filtering choices, and quality control, and identify findings deserving of further investigation.

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Journal article(s) based on this preprint

09 Sep 2025
The impact of differences in retrieval algorithms between processing centers on GNSS radio occultation refractivity retrievals in the planetary boundary layer
Sara Vannah, Stephen S. Leroy, Chi O. Ao, E. Robert Kursinski, Kevin J. Nelson, Kuo-Nung Wang, and Feiqin Xie
Atmos. Meas. Tech., 18, 4293–4310, https://doi.org/10.5194/amt-18-4293-2025,https://doi.org/10.5194/amt-18-4293-2025, 2025
Short summary
Sara Vannah, Stephen S. Leroy, Chi O. Ao, E. Robert Kursinski, Kevin J. Nelson, Kuo-Nung Wang, and Feiqin Xie

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-4127', Anonymous Referee #1, 20 Feb 2025
  • RC2: 'Comment on egusphere-2024-4127', Anonymous Referee #2, 05 Mar 2025

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-4127', Anonymous Referee #1, 20 Feb 2025
  • RC2: 'Comment on egusphere-2024-4127', Anonymous Referee #2, 05 Mar 2025

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Sara Vannah on behalf of the Authors (21 May 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (26 May 2025) by Peter Alexander
RR by Anonymous Referee #1 (27 May 2025)
RR by Anonymous Referee #2 (02 Jun 2025)
ED: Publish as is (02 Jun 2025) by Peter Alexander
AR by Sara Vannah on behalf of the Authors (11 Jun 2025)

Journal article(s) based on this preprint

09 Sep 2025
The impact of differences in retrieval algorithms between processing centers on GNSS radio occultation refractivity retrievals in the planetary boundary layer
Sara Vannah, Stephen S. Leroy, Chi O. Ao, E. Robert Kursinski, Kevin J. Nelson, Kuo-Nung Wang, and Feiqin Xie
Atmos. Meas. Tech., 18, 4293–4310, https://doi.org/10.5194/amt-18-4293-2025,https://doi.org/10.5194/amt-18-4293-2025, 2025
Short summary
Sara Vannah, Stephen S. Leroy, Chi O. Ao, E. Robert Kursinski, Kevin J. Nelson, Kuo-Nung Wang, and Feiqin Xie
Sara Vannah, Stephen S. Leroy, Chi O. Ao, E. Robert Kursinski, Kevin J. Nelson, Kuo-Nung Wang, and Feiqin Xie

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Latest update: 09 Sep 2025
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Short summary
Uncertainty estimation for GNSS radio occultation (RO) soundings in the planetary boundary layer (PBL) depends on the algorithms used to process the RO data. We compare the refractivity retrievals from three RO processing centers — each with their own retrieval algorithm — in the PBL, finding a strong underestimation of refractivity in regions with the strongest refractivity gradients, especially in JPL processing, as well as areas of weak overestimation of refractivity near the Poles.
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