Database of ionospheric rate of TEC change index (ROTI) map derived from Indonesian GNSS receiver network

Introduction

Indonesia, located near the magnetic equator in Southeast and East Asia, is essential for studying ionospheric phenomena, particularly equatorial plasma bubbles (EPBs). The Indonesian Geospatial Information Agency (BIG) has deployed a network of Global Navigation Satellite System (GNSS) receivers as part of the Indonesia Continuously Operating Reference Stations (Ina-CORS) across this country. This network has enabled the creation of detailed ionospheric irregularities maps based on the Rate of Total Electron Content (TEC) Change Index (ROTI). These maps are crucial for understanding EPBs in Southeast and East Asia.

GNSS network and ROTI map generation

The Ina-CORS consists of over 300 GNSS receivers strategically placed across Indonesia (see attached figure "geographic map_receivers.jpg"), spanning from 95°E to 140°E and from 5°N to 10°S. These receivers continuously gather GNSS observable data with a time resolution of 30 seconds in a Receiver Independent Exchange (RINEX) file. This data is then processed to generate the ROTI maps from the magnetic equator to the southern low-latitude region in Southeast/East Asia.

The GNSS data in the RINEX file is processed to calculate the Total Electron Content (TEC) using the open software developed by Seemala (2023). The software can be found at https://seemala.blogspot.com/2020/12/gps-tec-program-version-3-for-rinex-3.html. ROTI is derived by measuring the standard deviation of the rate of change of TEC over a 5-minute interval (Pi et al., 1997). This index is a critical indicator of ionospheric irregularities with kilometers of spatial scales inside the EPBs.
Using ROTI data plotted at the Ionospheric Pierce Point (IPP) altitude of 350 km, 2-dimensional (2D) latitude-longitude ROTI maps are generated. The grid size of the ROTI map is 0.25° × 0.25°. The ROTI map is smoothed by a boxcar average of 5 × 5 grid data regarding geographic latitude and longitude. In the map, sunset and sunrise terminators at altitudes of 110 km (red curve), 350 km (green curve), and 650 km (black curve) are plotted. The ROTI map is generated at each interval of 10 minutes from 9:00 to 23:50 UT. The name file of the zipped map in one day indicates the year and day of the year. For example, s_2024122_map.rar indicates the maps on day 122 in 2024. 

Purpose

Sharing GNSS data in RINEX files from the CORS could be strictly limited. Sharing the ROTI map derived from the CORS of Southeast Asian countries can be an alternative solution. This database aims to store the ROTI maps over Indonesia derived from GNSS data of the Ina-CORS network. The ROTI map database is also freely accessible and can be used for educational and scientific purposes. It is an academic/scientific resource and promotes a deeper understanding of EPB phenomena and their impact on navigation and communication systems. This database enables continuous monitoring and analysis of ionospheric conditions, particularly EPB occurrence. The database supports scientific research, enhances GNSS applications, and contributes to space weather forecasting by providing a high-resolution ROTI map. This ROTI map database has been developed to encourage research collaboration between researchers globally and in Indonesia.

Attribution

Users must appropriately credit the data source in this database in any publications, presentations, or products derived from it. When using the ROTI maps in this database, please cite the database. Users are also encouraged to collaborate with the ionospheric researchers in Indonesia. If the users need the numeric data for the ROTI maps, please get in touch with the email correspondence for this database.

References

Gopi K. Seemala (2023), Chapter 4 - Estimation of ionospheric total electron content (TEC) from GNSS observations, Editor(s): A.K. Singh, S. Tiwari, In Earth Observation, Atmospheric Remote Sensing, Elsevier, 2023, Pages 63 - 84, doi.org/10.1016/B978-0-323-99262-6.00022-5.

Pi, X., Mannucci, A. J., Lindqwister, U. J., and Ho, C. M. (1997), Monitoring of global ionospheric irregularities using the worldwide GPS network, Geophys. Res. Lett., 24, 2283–2286.

More Information
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Correspondence: P. Abadi, Dr.; Researcher at Research Center for Climate and Atmosphere, BRIN; email: pray001[at]brin.go.id (replace "[at]" with "@").