18 Jul 2023
 | 18 Jul 2023
Status: this preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).

Estimating the refractivity bias of Formosat-7/COSMIC-II GNSS Radio Occultation in the planetary boundary layer

Gia Huan Pham, Shu-Chih Yang, Chih-Chien Chang, Shu-Ya Chen, and Cheng-Yung Huang

Abstract. FORMOSAT-7/COSMIC-2 radio occultation (RO) measurements are promising for observing the deep troposphere and providing critical information on the Earth's planetary boundary layer (PBL). However, refractivity retrieved in the low troposphere can have severe bias under certain thermodynamic conditions. This research examines the characteristics of bias in the low troposphere and presents methods for estimating the region-dependent bias using regression models. The results show that the bias has characteristics that vary with land and oceans. With substantial correlation between local spectral width (LSW) and bias, the LSW-based bias estimation model can explain the general pattern of the refractivity bias but with deficiencies in measuring the bias in the ducting regions and certain areas over land. The estimation model involving the relationship with temperature and specific humidity can capture the bias of large amplitude associated with ducting. Finally, a minimum variance estimation that combines the benefits of the individual estimation provides the most accurate estimation of the refractivity bias.

Gia Huan Pham et al.

Status: open (until 22 Oct 2023)

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Gia Huan Pham et al.

Gia Huan Pham et al.


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Short summary
This research examines the characteristics of low-level GNSS radio occultation (RO) refractivity bias over ocean and land and their dependency on the RO retrieval uncertainty, atmospheric temperature, and moisture. We proposed methods for estimating the region-dependent refractivity bias. Our methods can be applied to calibrate the bias under different atmospheric conditions and thus improves the applications of the GNSS RO data in the planetary boundary layer.