Positioning accuracy analyses on GPS single point positioning determination with GAGAN correction services in Thailand

At present, Global Positioning System (GPS) is applied in various applications such as surveying, mapping, navigation, aviation, etc. However, GPS positioning accuracy and precision are not sufficient for some applications. Satellite Based Augmentation Systems (SBAS) are developed by several developed countries and each SBAS is named differently, with an intention to further improve GPS positioning systems accuracy and precision, especially for aircraft navigation. Currently SBAS covering Thailand is geostationary Earth orbit (GEO) Augmented Navigation (GAGAN) developed by India. GAGAN provides im-proved positioning accuracies and reliabilities in aviation in India and nearby areas. This study focuses on analysis of positioning accuracy using GAGAN correction services for GPS single point positioning determination in Thailand. The results are compared with reference coordinates by using GNSS observations of 11 GNSS CORSs operated by the Department of Lands (DOL) and 11 GNSS CORSs from Department of Public Works and Town & Country Planning (DPT). This study had been carried out with GPS observation data starting from 1 January 2017 until 31 March 2017. According to the obtained results, the performance of GAGAN could not provide a good service in any part of Thailand due to GAGANs ionosphere correction is not suitable for Thailand, as shown in the positioning accuracy from GPS aided by GAGAN which is lower than the results obtained from GAGAN combined with Klobuchar model and GPS by applying ionosphere-free combination in some parts of Thailand.