Precise Tropospheric Delay Map of Thailand using GNSS Precise Point Positioning Technique

Abstract

It is well known that the atmospheric effects are the most dominant spatially correlated errors in GNSS observations. The atmosphere causing the delay in GNSS observations consists of two main layers i.e. ionosphere and troposphere. The ionospheric delay can be mitigated using a linear combination of the two-frequency data. Unlike the ionospheric delay, the tropospheric delay cannot be removed using the same methodology. Compensation for the tropospheric delay is usually carried out using a standard tropospheric model. However, a standard tropospheric model cannot be used to completely remove the tropospheric delay in GNSS observations. With the use of GNSS Precise Point Positioning (PPP) technique, the tropospheric delay can be precisely obtained in a data processing step. Therefore, this paper focuses on an estimation of precise tropospheric delay using the GNSS PPP technique with the Positioning and Navigation Data Analyst (PANDA) software. Results obtained from the PPP technique are then compared with IGS tropospheric products and standard tropospheric models e.g. Saastamonien, modified Hopfield and simplified Hopfield. The obtained tropospheric delay shows a good agreement with the IGS product at millimeter level. It is found that the standard tropospheric models can only provide tropospheric corrections which are accurate at decimeter level in Thailand region. Finally, the same processing procedure is applied to produce precise tropospheric delays for all GNSS Continuously Operating Reference Stations (CORS) in Thailand and initial tropospheric delay results are presented in this paper.