  Foreground removal is the most important step in detecting the large-scale
redshifted HI 21-cm signal. Modelling foreground spectra is challenging and is
further complicated by the chromatic response of the telescope. We present a
multi-frequency angular power spectrum (MAPS) estimator for use in a survey for
redshifted HI 21-cm emission from z~3.35, and demonstrate its ability to
accurately characterize the foregrounds. This survey will be carried out with
the two wide-field interferometer modes of the upgraded Ooty Radio Telescope,
called the Ooty Wide Field Array (OWFA), at 326.5 MHz. We have tailored the
two-visibility correlation for OWFA to estimate the MAPS and test it with
simulated foregrounds. In the process, we describe a software model that
encodes the geometry and the details of the telescope, and simulates a
realistic model for the bright radio sky. This article presents simulations
which include the full chromatic response of the telescope, in addition to the
frequency dependence intrinsic to the foregrounds. We find that the visibility
correlation MAPS estimator recovers the input angular power spectrum
accurately, and that the instrument response to the foregrounds dominates the
systematic errors in the recovered foreground power spectra.
