A millimetre wave ‘camera’ is bigger than a normal
camera. Since the wavelength is typically 6000 times larger than
the light your eyes see, the imager needs to focus the light with
a much larger lens or mirror.
Millimetre wave cameras typically only have a few detecting elements
which are very expensive. these must be scanned back and forth across
the scene to build up a full picture. This is difficult to do quickly
- imagine that your digital camera could only record one pixel at
a time: how long would it take you to take a photo?
In order to record millimetre wave video less time can be spent
looking at each pixel in the image and the temperature reading is
less accurate. This is why the video images don’t look as
‘clean’ as the still images.
TYPES OF IMAGING
almost entirely reflected light
(unless observing light source directly)
mostly emitted heat + some reflected heat
some emitted heat + mostly reflected heat
recording naturally occurring signals from the scene
illuminating the scene artificially and comparing the reflected
signal with a copy of the illuminating signal