Articles | Volume 18, issue 22
https://doi.org/10.5194/amt-18-6997-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-18-6997-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
24 Nov 2025
Research article |
| 24 Nov 2025
| 24 Nov 2025
Evaluation of biases and uncertainties in ROMEX radio occultation observations
University Corporation for Atmospheric Research Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Program, Boulder, USA
Jeremiah Sjoberg
University Corporation for Atmospheric Research Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Program, Boulder, USA
Jon Starr
University Corporation for Atmospheric Research Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Program, Boulder, USA
Zhen Zeng
University Corporation for Atmospheric Research Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Program, Boulder, USA
Related authors
Randhir Singh, Satya P. Ojha, K.F. Muhammed, and Richard Anthes
EGUsphere, https://doi.org/10.5194/egusphere-2026-2304, https://doi.org/10.5194/egusphere-2026-2304, 2026
This preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).
Short summary
Short summary
This study investigated whether short-range weather forecasting over India could be improved by incorporating GNSS radio occultation (RO) data from ROMEX. Data assimilation experiments using the WRF model were conducted for September 2022. The findings demonstrate how GNSS-RO measurements improved predictions for temperature, humidity, wind, and precipitation. The biggest gains came from better initial water vapour fields, which reduced forecast error and improved rainfall skill.
Randhir Singh, Satya P. Ojha, K.F. Muhammed, and Richard Anthes
EGUsphere, https://doi.org/10.5194/egusphere-2026-2304, https://doi.org/10.5194/egusphere-2026-2304, 2026
This preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).
Short summary
Short summary
This study investigated whether short-range weather forecasting over India could be improved by incorporating GNSS radio occultation (RO) data from ROMEX. Data assimilation experiments using the WRF model were conducted for September 2022. The findings demonstrate how GNSS-RO measurements improved predictions for temperature, humidity, wind, and precipitation. The biggest gains came from better initial water vapour fields, which reduced forecast error and improved rainfall skill.
Matthias Aichinger-Rosenberger and Jeremiah Sjoberg
EGUsphere, https://doi.org/10.5194/egusphere-2025-2767, https://doi.org/10.5194/egusphere-2025-2767, 2025
Short summary
Short summary
This paper presents a data-driven framework for retrieving atmospheric profiles from Global Navigation Satellite Systems (GNSS) radio occultation (RO). The benefit compared to standard products is its independence of external information. Profiles are validated using reanalysis and radiosonde data, with results showing accuracy comparable to standard methods. This represents a promising investigation on the applicability of such models in RO, which could advance the quality of RO products.
Cited articles
Anthes, R. and Rieckh, T.: Estimating observation and model error variances using multiple data sets, Atmos. Meas. Tech., 11, 4239–4260, https://doi.org/10.5194/amt-11-4239-2018, 2018.
Anthes, R. A., Rocken, C., and Kuo Y.-H.: Applications of COSMIC to meteorology and climate. Special issue of Terrestrial, Atmospheric and Oceanic Sciences (TAO), 11, 115–156, https://n2t.org/ark:/85065/d7fn16ch, 2000.
Anthes, R., Sjoberg, J., Feng, X., and Syndergaard, S.: Comparison of COSMIC and COSMIC-2 Radio Occultation Refractivity and Bending Angle Uncertainties with Latitude in August 2006 and 2021, Atmosphere 13, 5, https://doi.org/10.3390/atmos13050790, 2022.
Anthes, R. A., Marquardt, C., Ruston, B., and Shao, H.: Radio Occultation Modeling Experiment (ROMEX)-Determining the impact of radio occultation observations on numerical weather prediction. Bull. Am. Meteorol. Soc., 105, https://doi.org/10.1175/BAMS-D-23-0326.1, 2024.
Ao, C. O., Waliser, D. E., Chan, S. K., Li, J.-L., Tian, B., Xie, F., and Mannucci, A. J.: Planetary boundary layer heights from GPS radio occultation refractivity and humidity profiles, J. Geophys. Res., 117, D16117, https://doi.org/10.1029/2012JD017598, 2012.
Aparicio, J. M. and Deblonde, S.: Estimation of the added value of the absolute calibration of GPS radio occultation data for numerical weather prediction, Mon. Wea. Rev., 143, 1259–1274, https://doi.org/10.1175/2007MWR1951.1, 2015.
Bonnedal, M., Christensen, J., Carlström, A., and Berg, A.: Metop-GRAS in-orbit instrument performance, GPS Solut., 14, 109–120, https://doi.org/10.1007/s10291-009-0142-3, 2010.
Bowler, N.: Revised GNSS-RO observation uncertainties in the Met Office NWP system, Q. J. R. Meteorol. Soc., 146, 2274–2296, https://doi.org/10.1002/qj.3791, 2020.
Caldeira, M. C. O., Caldeira, C. R. T., Cereja, S. S. A., Alves, D. B. M., and Aguiar, C. R.: Evaluation of the GNSS positioning performance under influence of the ionospheric scintillation, Bulletin of Geodetic Sciences, 26, e2020014, https://doi.org/10.1590/s1982-21702020000300014,2020.
Chang, L. C., Liu, H., Miyoshi, Y., Chen, C.-H., Chang, F.-Y., Lin, C.-H., Liu, J. Y., and Sun, Y.-Y.: Structure and origins of the Weddell Sea Anomaly from tidal and planetary wave signatures in FORMOSAT-3/COSMIC observations and GAIA GCM simulations, J. Geophys. Res.-Space, 120, 1325–1340, https://doi.org/10.1002/2014JA020752, 2015.
Chen, Y.-J., Hong, J.-S., and Chen, W.-J.: Impact of Assimilating FORMOSAT 7/COSMIC-2 Radio Occultation Data on Typhoon Prediction Using a Regional Model, Atmosphere, 13, 1879, https://doi.org/10.3390/atmos13111879, 2022.
Cheng, Y.: The improvement of Yunyao RO data. Quality and Development of Yunyao Constellations, Presentation at the 2nd ROMEX Workshop 27 February 2025 at EUMETSAT, Darmstadt, Germany, https://www.eventsforce.net/romex2025, 2025.
Cheng, Y., Fernhui, L., Naifeng, F., and Peng, G.: Yunyao meteorological constellation and products introduction, Presentation at the 1st ROMEX Workshop 17 April 2024 at EUMETSAT, Darmstadt, Germany, https://irowg.org/romex-1/ (last access: 22 November 2025), 2024.
Cucurull, L., Anthes, R. A., and Tsao, L.-L.: Radio occultation observations as anchor observations in numerical weather prediction models and associated reduction of bias corrections in microwave and infrared satellite observations, J. Atmos. Oceanic Technol., 31, 20–32, https://doi.org/10.1175/JTECH-D-13-00059.1, 2014.
Desroziers, G., Berre, L., Chapnik, B. and Poli, P.: Diagnosis of observation, background and analysis-error statistics in observation space, Q. J. Roy. Meteor. Soc., 131, 3385–3396, https://doi.org/10.1256/qj.05.108, 2005.
EUMETSAT: Sentinel-6A GNSS-RO NTC Cal/Val Report, EUM/LEO-JASC/REP/21/1243117, 71 pp., https://user.eumetsat.int/s3/eup-strapi-media/Sentinel_6_A_GNSS_RO_NTC_Cal_Val_Report_v1_E_3c966498f1.pdf (last access: 22 November 2025), 2022.
Eyre, J.: An introduction to GPS radio occultation and its use in numerical weather prediction. GRAS SAF Workshop on Applications of GPS radio occultation measurements, ECMWF, 16–18 June 2008, https://www.ecmwf.int/sites/default/files/elibrary/2008/9342-introduction-gps-radio-occultation-and-its-use-numerical-weather-prediction.pdf (last access: 22 November 2025), 2008.
Feng, X., Xie, F., Ao, C., and Anthes, R.: Ducting and biases of GPS radio occultation bending angle and refractivity in the moist lower troposphere. J. Atmos. Ocean. Technol., 37, 1013-01025, https://doi.org/10.1175/JTECH-D-19-0206.1, 2020.
Gilpin, S., Rieckh, T., and Anthes, R.: Reducing representativeness and sampling errors in radio occultation–radiosonde comparisons, Atmos. Meas. Tech., 11, 2567–2582, https://doi.org/10.5194/amt-11-2567-2018, 2018.
Gilpin, S., Anthes, R., and Sokolovskiy, S.: Sensitivity of forward-modeled bending angles to vertical interpolation of refractivity for radio occultation data assimilation, Mon. Wea. Rev., 147, 269–289, https://doi.org/10.1175/MWR-D-18-0223.1, 2019.
Gorbunov, M. E., Vorob'ev, V. V., and Lauritsen, K. B.: Fluctuations of refractivity as a systematic error source in radio occultations, Radio Sci., 50, 656–669, https://doi.org/10.1002/2014RS005639, 2015.
Harnisch, F., Healy, S. B., Bauer, P., and English, S. J.: Scaling of GNSS Radio Occultation impact with observation number using an Ensemble of Data Assimilations, Mon. Wea. Rev., 141, 4395–4413, https://doi.org/10.1175/MWR-D-13-00098.1, 2013.
Healy, S. B.: Forecast impact experiment with a constellation of GPS radio occultation receivers, Atmos. Sci. Lett., 9, 111–118, https://doi.org/10.1002/asl.169, 2008.
Hersbach, H., Bell, B., Berrisford, P., Hirahara, S., Horányi, A., Muñoz-Sabater, J., Nicolas, J., Peubey, C., Radu, R., Schepers, D., Simmons, A., Soci, C., Abdalla, S., Abellan, X., Balsamo, G., Bechtold, P., Biavati, G., Bidlot, J., Bonavita, M., De Chiara, G., Dahlgren, P., Dee, D., Diamantakis, M., Dragani, R., Flemming, J., Forbes, R., Fuentes, M., Geer, A., Haimberger, L., Healy, S., Hogan, R. J., Hólm, E., Janisková, M., Keeley, S., Laloyaux, P., Lopez, P., Lupu, C., Radnoti, G., de Rosnay, P., Rozum, I., Vamborg, F., Villaume, S., and Thépaut, J.-N.: The ERA5 global reanalysis, Q. J. Roy. Meteor. Soc., 146, 1999–2049, https://doi.org/10.1002/qj.3803, 2020.
Ho, S.-P., Zhou, X., Shao, X., Chen, Y., Jing, X., and Miller, W.: Using the Commercial GNSS RO Spire Data in the Neutral Atmosphere for Climate and Weather Prediction Studies, Remote Sens., 15, 4836, https://doi.org/10.3390/rs15194836, 2023.
Ho, S.-P., Xi, S., Chen, Y., Zhou, J., Gu, G., Miller, W., and Jing, X.: Lessons Learned from the Preparation and Evaluation of Multiple GNSS RO Data for the ROMEX from NOAA/STAR, Presentation at the COSMIC/JCSDA Workshop and IROWG-10, Boulder, Colorado, 12–18 September 2024, https://www.cosmic.ucar.edu/events/cosmic-jcsda-workshop-irowg-10/agenda (last access: 22 November 2025), 2024.
Ho, S.-P., Xi, S., Chen, Y., Zhou, J., and Miller, W.: Advances in ROMEX data processing and evaluation: Lessons from NOAA STAR. Presentation at the 2nd ROMEX Workshop, 27 February 2025 at EUMETSAT, Darmstadt, Germany, https://www.eventsforce.net/romex2025 (last access: 22 November 2025), 2025.
Kosaka, Y., Kobayashi, S., Harada, Y., Kobayashi, C., Naoe, H., Yoshimoto, K., Harada, M., Goto, N., Chiba, J., Miyaoka, K., Sekiguchi, R., Deushi, M., Kamahori, H., Nakaegawa, T., Tanaka, T. Y., Tokuhiro, T., Sato, Y., Matsushita, Y., and Onogi, K: The JRA-3Q reanalysis. J. Meteor. Soc. Japan, 102, 49–109, https://doi.org/10.2151/jmsj.2024-004, 2024.
Kuo, Y.-H., Wee, T.-K. Sokolovskiy, S., Rocken, C., Schreiner, W., Hunt, D., and Anthes, R. A.: Inversion and error estimation of GPS radio occultation data, J. Meteor. Soc. Japan, 84, 507–531, https://doi.org/10.2151/jmsj.2004.507, 2004.
Kursinski, E. R., Hajj, G. A., Hardy, K. R., Schofield, J. T., and Linfield, R.: Observing Earth's atmosphere with radio occultation measurements, J. Geophys. Res., 102, 23429–23465, https://doi.org/10.1029/97JD01569, 1997.
Leroy, S. S., Anderson, J. G., and Dykema, J. A.: Climate benchmarking using GNSS occultation, in: Atmosphere and Climate: Studies by Occultation Methods, edited by: Foelsche, U., Kirchengast, G., and Steiner, A., 287–301, Springer-Verlag Berlin Heidelberg, https://doi.org/10.1007/3-540-34121-8_24, 2006.
McNally, A. P.: On the sensitivity of a 4D-Var analysis system to satellite observations located at different times within the assimilation window, Q. J. Roy. Meteor. Soc., 145, 2806–2816, https://doi.org/10.1002/qj.3596, 2019.
Melbourne, W. G., Davis, E. S., Duncan, C. B., Hajj, G. A., Hardy, K. R., Kursinski, E. R., Meehan, T. K.,, Young, L. E., and Yunck, T. P.: The application of spaceborne GPS to atmospheric limb sounding and global change monitoring. JPL Publ. Tech. Rep. 94-18, 159 pp., https://ntrs.nasa.gov/citations/19960008694 (last access: 22 November 2025), 1994.
Nielsen, J. K., Gleisner, H., Syndergaard, S., and Lauritsen, K. B.: Estimation of refractivity uncertainties and vertical error correlations in collocated radio occultations, radiosondes, and model forecasts, Atmos. Meas. Tech., 15, 6243–6256, https://doi.org/10.5194/amt-15-6243-2022, 2022.
Numerical Prediction Division, Information Infrastructure Department: The Japanese Reanalysis for Three Quarters of a Century, Data Integration and Analysis System (DIAS) [data set], https://doi.org/10.20783/DIAS.645, 2022.
O'Carroll, A. G., Eyre, J. R., and Saunders, R. S.: Three-way error analysis between AATSR, AMSR-E, and in situ sea surface temperature observations, J. Atmos. Ocean. Tech., 25, 1197–1207, https://doi.org/10.1175/2007JTECHO542.1, 2008.
Padovan, S., von Engeln, A., Paolella, S., Andres, Y., Galley, C. R., Notarpietro, R., Rivas Boscan, V., Sancho, F., Martin Alemany, F., Morew, N., and Marquardt, C.: Observed impact of the GNSS clock data rate on radio occultation bending angles for Sentinel-6A and COSMIC-2, Atmos. Meas. Tech., 18, 3217–3228, https://doi.org/10.5194/amt-18-3217-2025, 2025.
Privé, N. C., Errico, R. M., and El Akkraoui, A.: Investigation of the potential saturation of information for the Global Navigation Satellite System radio occultation observations with an observing system simulation experiment, Mon. Wea. Rev., 150, 1293–1316, https://doi.org/10.1175/MWR-D-21-0230.1, 2022.
Rieckh, T., Sjoberg, J., and Anthes, R.: The three-cornered hat method for estimating error variances if three or more atmospheric data sets-Part II: Evaluating recent radio occultation and radiosonde observations, global model forecasts, and reanalyses, J. Atmos. Ocean. Technol., 35, https://doi.org/10.1175/JTECH-D-20-0209.1, 2021.
Ruston, B. and Healy, S.: Forecast Impact of FORMOSAT-7/COSMIC-2 GNSS Radio Occultation Measurements, Atmospheric Science Letters, 22, https://doi.org/10.1002/asl.1019, 2020.
Semane, N., Anthes, R., Sjoberg, J., Healy, S., and Ruston, B: Comparison of Desroziers and Three-Cornered Hat Methods for Estimating COSMIC-2 Bending Angle Uncertainties, J. Atmos. Ocean Tech., 39, 929–939, https://doi.org/10.1175/JTECH-D-21-0175.1, 2022.
Schreiner, W., Sokolovskiy, S., Weiss, J., Braun, J., Anthes, R., Kuo, Y.-H., Hunt, D., Zeng, Z., Wee, T.-K., VanHove, T., Sjoberg, J., and Huelsing, H.: Performance Assessment and Requirement Verification of COSMIC-2 Neutral Atmospheric Radio Occultation Data, Presentation at IROWG-7, 19 September 2019, Helsingør, Denmark, https://irowg.org/workshops/irowg-7/ (last access: 22 November 2025), 2019.
Schreiner, W. S., Weiss, J. P., Anthes, R. A., Braun, J., Chu, V., Fong, J., Hunt, D., Kuo, Y.-H., Meehan, T., Serafino, W., Sjoberg, J., Sokolovskiy, S., Talaat, E., Wee, T.-K., and Zeng, Z.: COSMIC-2 Radio Occultation Constellation-First Results. Geophys. Res. Lett., 47, e2019GL086841, https://doi.org/10.1029/2019GL086841, 2020.
Shao, H., Foelsche, U., Mannucci, A., Azeem, I., Bowler, N., Braun, J., Lonitz, K., Marquardt, C., Steiner, A., Ruston, B., and Panagiotis, V.: Advances in GNSS-Based Remote Sensing for Weather, Climate, and Space Weather: Missions, Applications, and Emerging Techniques, Bull. Amer. Meteor. Soc., 106, E1471–E1477 https://doi.org/10.1175/BAMS-D-25-0138.1, 2025.
Sjoberg, J. P., Anthes, R. A., and Rieckh, T.: The three-cornered hat method for estimating error variances of three or more data sets-Part I: Overview and Evaluation. J. Atmos. Ocean. Technol., 38, 555–572, https://doi.org/10.1175/JTECH-D-19-0217.1, 2021.
Sokolovskiy, S.: Effect of superrefraction on inversions of radio occultation signals in the lower troposphere, Radio Sci., 38, 1058, https://doi.org/10.1029/2002RS002728, 2003.
Sokolovskiy, S.: Standard RO Inversions in the Neutral Atmosphere 2013–2020 (Processing Steps and Explanation of Data), https://www.cosmic.ucar.edu/what-we-do/data-processing-center/data (last access: 22 November 2025), 2021.
Sokolovskiy, S., Rocken, C., Schreiner, W., and Hunt, D.: On the uncertainty of radio occultation inversions in the lower troposphere, J. Geophys. Res., 115, D22111, https://doi.org/10.1029/2010JD014058, 2010.
Steiner, A. K., Ladstädter, F., Ao, C. O., Gleisner, H., Ho, S.-P., Hunt, D., Schmidt, T., Foelsche, U., Kirchengast, G., Kuo, Y.-H., Lauritsen, K. B., Mannucci, A. J., Nielsen, J. K., Schreiner, W., Schwärz, M., Sokolovskiy, S., Syndergaard, S., and Wickert, J.: Consistency and structural uncertainty of multi-mission GPS radio occultation records, Atmos. Meas. Tech., 13, 2547–2575, https://doi.org/10.5194/amt-13-2547-2020, 2020.
Syndergaard, S. and Lauritsen, K.: ROM SAF processing and new products. Presentation at the COSMIC/JCSDA Workshop and IROWG-10, Boulder, Colorado, 12–18 September 2024, https://www.cosmic.ucar.edu/events/cosmic-jcsda-workshop-irowg-10/agenda (last access: 22 November 2025), 2024.
Syndergaard, S., Kuo, Y.-H., and Lohmann, M. S.: Observation operators for the assimilation of occultation data into atmospheric models: A review, in: Atmosphere and Climate, edited by: Foelsche U., Kirchengast G., and Steiner, A., Springer, Berlin, Heidelberg, 205–224, https://doi.org/10.1007/3-540-34121-8_18, 2006.
Tang, Q.: Introduction to GNSS-RO and GNSS-R products of Tianmu-1 constellation. Presentation at the 2nd ROMEX Workshop 27 February 2025 at EUMETSAT, Darmstadt, Germany, https://www.eventsforce.net/romex2025 (last access: 22 November 2025), 2025.
Todling, R., Semane, N., Anthes, R., and Healy, S.: The Relationship between Desroziers and Three-Cornered Hat Methods, Q. J. Roy. Meteor. Soc., 148, 2942–2954, https://doi.org/10.1002/qj.4343, 2022.
Tradowsky, J., Burrows, C., Healy, S., and Eyre, J.: A new method to correct radiosonde temperature biases using radio occultation data, J. Appl. Meteor. Clim., 56, 1643–1661, https://doi.org/10.1175/JAMC-D-16-0136.1, 2017.
Weiss, J., Veitel, H., Sokolovskiy, S., Zeng, Z., Anthes, R., Hunt, D., Petroni, V., Sjoberg, J., Sleziak-Sallee, M. and VanHove, T.: Update on Processing and Analysis of ROMEX Data, Presentation at the 2nd ROMEX Workshop 25–27 February 2025 at EUMETSAT, Darmstadt, Germany, https://www.eventsforce.net/romex2025 (last access: 22 November 2025), 2025.
Xie, F., Syndergaard, S., Kursinski, E. R., and Herman, B.: An approach for retrieving marine boundary layer refractivity from GPS occultation data in the presence of superrefraction, J. Atmos. Oceanic Tech., 23, 1629–1644, https://doi.org/10.1175/JTECH1996.1, 2006.
Xu, X., Han, W., Wang, J., Gao, Z., Li, F., Cheng, Y., and Fu, N.: Quality assessment of YUNYAO radio occultation data in the neutral atmosphere, Atmos. Meas. Tech., 18, 1339–1353, https://doi.org/10.5194/amt-18-1339-2025, 2025.
Short summary
The Radio Occultation Modeling EXperiment (ROMEX) is an international collaboration to test the impact of varying numbers of radio occultation (RO) observations in numerical weather prediction (NWP) forecast models. An unprecedented 35 000 RO profiles per day from 13 different satellite missions are being used in different NWP forecast models. The quality (random and bias errors) of the ROMEX observations is evaluated in this paper.
The Radio Occultation Modeling EXperiment (ROMEX) is an international collaboration to test the...
