Tropospheric delay in microwave propagation for tropical atmosphere based on data from the Indian subcontinent

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The Global Positioning System (GPS) finds important application in satellite-based navigation. This application requires 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 vapor partial pressure as well as columnar water vapor for different locations over the Indian subcontinent using the upper air data for three years (1995–1997). Different forms of the empirical relation were examined to develop these models. Site-specific models are first generated for different locations selected for this study (eight Range and Integrity Monitoring Station). Taking all these models into account a unified model is developed, which is applicable for the entire subcontinent. 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.