  Intensity mapping with the redshifted 21-cm line is an emerging tool in
cosmology. Drift scan observations, where the antennas are fixed to the ground
and the telescope's pointing center (PC) changes continuously on the sky due to
earth's rotation, provide broad sky coverage and sustained instrumental
stability needed for 21-cm intensity mapping. Here we present the Tracking
Tapered Grided Estimator (TTGE) to quantify the power spectrum of the sky
signal estimated directly from the visibilities measured in drift scan radio
interferometric observations. The TTGE uses the data from the different PC to
estimate the power spectrum of the signal from a small angular region located
around a fixed tracking center (TC). The size of this angular region is decided
by a suitably chosen tapering window function which serves to reduce the
foreground contamination from bright sources located at large angles from the
TC. It is possible to cover the angular footprint of the drift scan
observations using multiple TC, and combine the estimated power spectra to
increase the signal to noise ratio. Here we have validated the TTGE using
simulations of $154 \, {\rm MHz}$ MWA drift scan observations. We show that the
TTGE can recover the input model angular power spectrum $C_{\ell}$ within $20
\%$ accuracy over the $\ell$ range $40 < \ell < 700$.
