But only with the advent of the techniques called radio interferometry and
aperture synthesis in the 1960s did astronomers succeed in obtaining detailed "images" of the radio sky.
Modern radar systems like Synthetic Aperture Radar (SAR) and Associative
Aperture Synthesis Radar (AASR) can employ inexpensive means to locate low observable targets.
Johnson switched on the "Torus" - a doughnut-shaped apparatus made from miles of wound copper wire hooked up to a machine - an "
aperture synthesis controller" - and then a kaleidoscope of coloured shapes formed in the centre of the Torus, and focused into the image of a girl in a short, fuchsia-coloured skirt.
Down-looking array SAR is an innovative imaging mode, which obtains range resolution by pulse compression, azimuth resolution by virtual
aperture synthesis with platform movement, and cross-track resolution by a linear array antenna [5-7].
Taylor, "First video rate imagery from a 32-channel 22-GHz
aperture synthesis passive millimetre wave imager," Proc.
Interferometric
aperture synthesis imaging technology, initially developed for radio astronomy in the 1980s [4,5], can well solve the contradiction between the antenna aperture and spatial resolution.
Torres, "Radiometric sensitivity computation in
aperture synthesis interferometric radiometry," IEEE Trans.
Here, the
aperture synthesis with a cosecant pattern was realized in the E-plane.
Baldwin of the University of Cambridge and his colleagues used the combination telescope, known as COAST (Cambridge Optical
Aperture Synthesis Telescope), to examine Capella, a double star system 40 light-years away.
Interferometric
aperture synthesis, initially developed for radio astronomy [4], can be an effective alternative to real aperture radiometers for the Earth observation.
This effort was continued by experimenting coherent radar with non-focused
aperture synthesis methods and produced the first SAR image in July 1953 [5].