An aperture synthesis telescope, like the GMRT, consists of a
number of antennas located on the ground and the resolution of
such a telescope is proportional to the maximum projected
separation between the antennas. The locations of the antennas
are usually specified in the Earth-centred co-ordinate system.
The Earth centred frame is related to the location of the
antennas on the ground by However, for the purpose of imaging,
only the relative separation between the antennas is important.
This separation between the antennas is usually referred to as
the baseline and is measured in units of the wavelength of the
incident radiation. For the purpose of the theory of synthesis
imaging, the antenna positions are specified in the so called
frame. The geometric relationship between this frame and the
frame is shown in Fig. 2.1 and the co-ordinate transformation is
given by The geometric relation between the observing plane
represented by the -plane and the sky plane represented by the
-plane is shown in Fig. 2.2. T