Image Processing Reference
Figure3.7 Visible (top) and mmW (bottom) images of a runway in zero-visibility fog.
Airport in Bakersfield, California. The visible-light image shows nothing but white
fog, common early in the morning at this particular airport. The mmW image
(3-mm waveband) reveals the runway and control tower at a resolution on the
order of 60 by 60 pixels. This resolution is limited by the size of the imaging
system, which is set by the space available in the nose of a typical aircraft. This
imaging system uses a 46-cm-diameter plastic lens that focuses mmW light onto a
focal plane array of miniature mmW receivers. These convert the mmW image into
electrical signals that are processed into video that drives a visual display in front
of the pilot's face. 6 Figure 3.8 shows a mmW camera developed by TRW mounted
on the nose of an aircraft with the aerodynamic nose shroud removed. The white
plastic lens is visible in the front.
For thousands of years, astronomers were limited to visible-light bands of the
EM spectrum by the physiology of the human eye. The20 th century brought
the development of instruments that could view planets, stars, galaxies and other
more exotic celestial objects over much larger regions of the electromagnetic
spectrum than the visible band. Today, astronomers have observed the heavens
over a spectrum that is 20 powers of 10 wide in wavelength of the electromagnetic
spectrum, from radio waves to gamma rays—an amazing achievement that is
largely unknown outside of astronomy circles. One important branch of “invisible-
light” astronomy is radio astronomy, the observation of celestial objects in the 1-cm
to 10-m region of the electromagnetic spectrum. 7
Our ability to image celestial objects with light from the radio portion of the
electromagnetic spectrum has its roots in the 1932 discovery of radio waves of
6 Yujiri et al., “Passive millimeter-wave camera,”SPIEProc.,3064, p. 15, 21-22 April 1997 [doi: 10.
7 John Krause,RadioAstronomy, Cygnus-Quasar Books, Powell, Ohio (1986).