Analyzing precipitable water vapor with GNSS radio occultation wet profiles, radiosonde observations and ECMWF ERA5 reanalysis data over the Türkiye region

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Çelik Tunçer S., Tanır Kayıkçı E.

JOURNAL OF APPLIED GEODESY, cilt.1, sa.1, ss.1-15, 2026 (ESCI, Scopus)

Özet

Abstract: The Global Navigation Satellite System (GNSS)-

Radio Occultation (RO) is a satellite-based technique providing

significant advantages for improving weather forecasts

and investigating climatic variations. In this study,

precipitable water vapor (PWV) derived from FORMOSAT-

7/COSMIC-2 GNSS-RO wet profiles was compared with that

calculated from radiosonde (RS) observations and the fifthgeneration

global reanalysis dataset (ERA5). For this purpose,

RS stations situated in Samsun, Istanbul, Izmir, and

Adana over Türkiye were selected as reference locations.

Two horizontal collocation distances, 300 km and 150 km,

were applied to examine the sensitivity of the results to

spatial matching. The performance of COSMIC-2 RO PWV

was evaluated using root mean square error (RMSE), linear

regression, Pearson correlation, and the R-squared coefficient

(R2). For both collocation distances, RMSE values are

about 3 mm for RO-RS and about 2 mm for RO-ERA5, and

correlation coefficients are generally above 0.8. Regression

slopes are lower for RO-RS, ranging between 0.6 and 0.8, and

closer to unity for RO-ERA5, ranging between 0.8 and 1.0.

Reducing the collocation distance leads to a small increase

in correlation. However, it does not result in a consistent

improvement in RMSE, indicating the influence of vertical

sampling characteristics. Overall, GNSS-RO shows reasonable

consistency with RS observations. When used in combination

with reanalysis products, it can provide reliable

atmospheric moisture estimates over Türkiye.

Keywords: GNSS-RO; radiosonde; ECMWF ERA5; precipitable

water vapor