Retrieval and analysis of precipitable water vapour based on GNSS, AIRS, and reanalysis models over Nigeria

ABSTRACT

Precipitable water vapour (PWV) retrieved from ground-based Global Navigation Satellite System (GNSS) stations over Nigeria from 2013 to 2014 is compared with PWV from a satellite remote-sensing technique (Atmospheric Infrared Sounder [AIRS]) and a global reanalysis model (ERA-Interim) over Nigeria. The PWV for AIRS and ERA-Interim was obtained from the respective data providers. PWV estimates from the different techniques were grouped into daily estimates and were matched and re-grouped into monthly and seasonal averages. The performance of the PWV techniques was evaluated using recommended indices by the World Meteorological Organization. All datasets gave a reasonable estimate of PWV when compared against GNSS at daily, monthly, and seasonal scales, the agreement between the various techniques was better at monthly and seasonal scales. In terms of bias, precision, accuracy, fitness, and reliability of measurement, ERA-Interim outperformed the other technique and could possibly be a complementary data source to GNSS PWV, although as a reanalysis, it cannot be used for meteorology. The AIRS night-time (or descending) retrieval was ranked next to the ERA-Interim; AIRS daytime (or ascending) retrieval agreed less with GNSS PWV when compared with ERA Interim and night-time AIRS. These results indicate that GNSS PWV as observed over the study area represents a remarkable dataset for further evaluation studies and serves as a useful source of humidity information to improve the water cycle in numerical weather models for varying applications in the region.

Acknowledgements

This study was supported and funded by the Tertiary Education Trust Fund of Nigeria, Surveyors Council of Nigeria, and University of Pretoria PhD Research Support grant to the first author. The authors would wish to express their profound gratitude to the numerous reviewers for their productive observations that helped to perk up the manuscript. The authors thank the Goddard Earth Sciences Data and Information Services Centre (GESDISC), and the European Centre for Medium-Range Weather Forecasts (ECMWF) for making AIRS PWV retrievals, ERA-interim data used in this study publicly available. GAMIT/GLOBK GNSS processing software was also made unreservedly accessible by MIT through licence granted to HartRAO. Finally, our appreciation goes the office of the Surveyor General of the federal republic of Nigeria (OSGOF) for making available the GNSS data used in this study.

Disclosure statement

The authors avow that they have no competing interest regarding the publication of this article.

Additional information

Funding

This study is funded and supported by the Tertiary Education Trust Fund of Nigeria (TETFUND), Surveyors Council of Nigeria (SURCON), and University of Pretoria’s PhD Research Support Grant.

Notes on contributors

Olalekan Adekunle Isioye

OAI collected and processed all the data required for the study, all statistical analysis that followed and drafting of the manuscript was done by OAI. Technical advice and guidance were provided by LC and JOB. The final manuscript was checked and accepted by all three authors.

Ludwig Combrinck

OAI collected and processed all the data required for the study, all statistical analysis that followed and drafting of the manuscript was done by OAI. Technical advice and guidance were provided by LC and JOB. The final manuscript was checked and accepted by all three authors.

Joel Ondego Botai

OAI collected and processed all the data required for the study, all statistical analysis that followed and drafting of the manuscript was done by OAI. Technical advice and guidance were provided by LC and JOB. The final manuscript was checked and accepted by all three authors.