Estimation of tropospheric time delay at a north Indian latitude

When a radio wave travels from space to Earth it gets refracted near the surface of the earth due to the inherent property of the tropospheric refractive index. As a result the wave travels a longer path than it would have if it had come through vacuum. This excess path length leads to time delay. A good estimate of tropospheric time delay is essential in various studies like satellite ranging, altimetry, VLBI (very long base line interferometry), etc. The authors attempt to estimate the zenith time delay at latitude 28°38\´14" using three years of radio sonde data. Also a mapping function is applied to find out the corresponding time delays at various elevation angles