Modeling of tropospheric delay correction for GPS navigation
The Global Positioning System (GPS) finds important application in satellite-based navigation. This application requires a priori modeling of tropospheric refraction of GPS signal, which is in the microwave domain. The tropospheric delay for microwaves, estimated by ray tracing through the Earth’s atmosphere, is modeled in terms of measurable surface meteorological parameters such as atmospheric pressure, temperature, water vapour partial pressure as well as columnar water vapour for different locations over the Indian subcontinent using the upper air data. Different forms of the empirical relation were examined to develop these models. Site-specific models are first generated for different locations of selected climetological conditions over the Indian subcontinent. Taking all these models into account a unified model has been developed, which is applicable for the entire Indian region. Though the unified model is slightly inferior to site-specific models, the deviations are within the allowable limits for this specific application. The merit of unified model, however, lies in the fact that a single model can be used for any location over the subcontinent. The model predictions are compared with the tropospheric delay derived from ground-based GPS measurements to establish the model accuracy.