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The GPS data provides an effective way to estimate the total electroncontent (TEC) from the differential time delay of L1 and L2 transmissionsfrom the GPS. The spacing of the constellation of GPS satellites in orbits aresuch that a minimum of four GPS satellites are observed at any given pointin time from any location on the ground. Since these satellites are indifferent parts of the sky and the electron content in the ionosphere variesboth spatially and temporally, the ionospheric pierce point (IPP) altitudeor the assumed altitude of the centroid of mass of the ionosphere plays animportant role in converting the vertical TEC from the measured slant TECand vice versa. In this paper efforts are made to examine the validity ofthe IPP altitude of 350 km in the Indian zone comprising of theever-changing and dynamic ionosphere from the equator to the ionization anomalycrest region and beyond, using the simultaneous ionosonde data from fourdifferent locations in India. From this data it is found that the peakelectron density height (hpF2) varies from about 275 to 575 km atthe equatorial region, and varies marginally from 300 to 350 km at andbeyond the anomaly crest regions. Determination of the effective altitude ofthe IPP employing the inverse method suggested by Birch et al. (2002) didnot yield any consistent altitude in particular for low elevation angles, butvaried from a few hundred to one thousand kilometers and beyond in the Indianregion. However, the vertical TEC computed from the measured GPS slant TECfor different IPP altitudes ranging from 250 to 750 km in the Indian regionhas revealed that the TEC does not change significantly with the IPPaltitude, as long as the elevation angle of the satellite is greater than 50degrees. However, in the case of satellites with lower elevation angles(<50°), there is a significant departure in the TEC computed usingdifferent IPP altitudes from both methods. Therefore, the IPP altitudeof 350 km may be taken as valid even in the Indian sector but only in thecases of satellite passes with elevation angles greater than 50°

On the validity of the ionospheric pierce point (IPP) altitude of 350 km in the Indian equatorial and low-latitude sector