IMPROVEMENT OF THE METHODOLOGY AND TIME SERIES EVALUATION OF NEUTROSPHERIC ZENITAL DELAY AND PWV IN BRAZILIAN REGIONS

• Grant number: 25/04942-8
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: May 01, 2025
• End date: April 30, 2026
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geodesy
• Principal Investigator: Tayná Aparecida Ferreira Gouveia
• Grantee: Izabele Lima Peres
• Host Institution: Faculdade de Ciências e Tecnologia (FCT). Universidade Estadual Paulista (UNESP). Campus de Presidente Prudente. Presidente Prudente , SP, Brazil

Abstract

GNSS (Global Navigation Satellite Systems) has been increasingly used in activities that require position estimates. However, something that significantly influences the quality of GNSS positioning is the propagation of the signal in the atmosphere. In this sense, considering accurate GNSS applications, adequate ionospheric and neutrospheric modeling is necessary, especially under the effect of the atmospheric peculiarities existing in Brazil. Regarding the neutrosphere, research in this area is essential, as the country has very adverse conditions, very humid regions due to the Amazon rainforest and very dry regions, such as in the interior of the country, in addition to coastal regions. The Neutrosphere (also called Troposphere) is one of the most investigated sources in the modeling of errors that affect GNSS positioning, considering applications that require accurate positions, such as: precision agriculture, autonomous vehicles, aviation applications, among others. One of the most relevant effects caused by this atmospheric layer is called neutrospheric (or tropospheric) delay, which in the vertical (or zenith) direction is known as ZTD (Zenith Total Delay) (for a given time and place - latitude, longitude and altitude). This effect depends on the refractive index of the gases and water vapor present at the time and the portion of the neutrosphere that the GNSS signal passes through. The ZTD is the sum of two components, the hydrostatic (dry) component, whose delay is called ZHD (Zenith Hydrostatic Delay), and the wet component, called ZWD (Zenith Wet Delay). From ZWD measurements, it is possible to obtain the amount of precipitable water vapor (PWV - Precipitable Water Vapor) in the zenith direction, a measurement that is difficult to determine. Empirical models are often applied as a way to simplify the modeling of the GNSS signal propagation delay, presenting satisfactory results under normal atmospheric conditions and according to the application and region to be investigated. In Brazil, research conducted by the project supervisors found that, especially in the Amazon region, Numerical Weather Prediction (NWP) models are much more efficient than the empirical models widely used in modeling zenithal delay, especially the humid component. Furthermore, the more accurate the ZTD modeling, as well as the ZWD modeling, the more accurate the PWV will be. When calculating this delay from GNSS measurements, accurate ZHD modeling will provide more accurate ZWD/GNSS and consequently PWV/GNSS estimates. In GNSS positioning, the neutral atmosphere represents a source of error (ZTD, ZHD and ZWD), but for other sciences, such as Meteorology, it can represent a source of information (PWV), and this measurement has a high correlation with precipitation measurements. Research of this nature, as proposed in this scientific initiation project, is very important and presents interdisciplinarity. Therefore, the main objective of this project is to investigate and make improvements in the calculation of the neutrosphere delay over Brazilian territory, considering greater sensitivity in the modeling of the zenithal delay and the PWV, using direct measurements of the atmosphere, such as meteorological data sources (automatic surface and altitude stations - radiosonde). To achieve this objective, we intend to use data from different climatological regions of the country and time series that contemplate the seasons of the year, aiming to analyze the zenith delay and PWV according to seasonality and under different atmospheric conditions, such as periods of extreme precipitation. Finally, this scientific initiation project is linked to the Post-Doctorate project of the advisor and to the Research Productivity (PQ) project of the co-advisor. (AU)