An optimization of the tropospheric correction interpolation method for PPP-RTK technique in Thailand

Precise Point Positioning with Real-Time Kinematic (PPP-RTK) has emerged as a key technique for achieving rapid, centimeter-level positioning by enabling user-side ambiguity resolution through precise satellite products and regionally derived atmospheric corrections. In low-latitude regions such as Thailand, however, pronounced spatial and temporal variability of precipitable water vapor—driven by monsoon dynamics and severe convective weather—remains a major limiting factor for fast convergence and robust positioning performance. This study aims to optimize the interpolation of zenith wet delay (ZWD) and its associated horizontal gradients derived from a regional GNSS reference network for PPP-RTK applications using the GFZ in-house RTPPP software. The proposed strategy consists of two sequential interpolation stages. First, tropospheric parameters are interpolated from GNSS reference stations onto a predefined regional grid. Second, the gridded corrections are interpolated to the rover location. Ordinary Kriging and Universal Kriging are investigated for the reference-station-to-grid interpolation, while bilinear and nearest-neighbor methods are applied for the grid-to-rover interpolation. The performance of the proposed approaches is systematically evaluated with respect to ZWD and horizontal gradient estimates at selected GNSS reference stations, derived independently using a standard PPP solution. In addition, predefined grid sizes of 1 km, 5 km, and 10 km are assessed to determine the optimal grid resolution for ZWD and horizontal gradient interpolation.