All RF Cafe quizzes would make perfect fodder for employment interviews for technicians or engineers
- particularly those who are fresh out of school or are relatively new to the work world. Come to
think of it, they would make equally excellent study material for the same persons who are going to
be interviewed for a job.
Some of these books used in quizzes are available as prizes
in the monthly RF Cafe Giveaway.
Note: Many answers contain passages quoted in whole or in part from the text.
RF Cafe Quiz #48
quiz is based on the information presented in "Introduction
to Infrared and Electro-Optical Systems," by Ronald G. Driggers and Melvin
What is the term for light distribution on the image plane from a point source?
a) Point spread function
The light distribution on the image
plane from a point source is called the point spread function and is abbreviated
psf. The psf is never smaller than a sixe predicted by diffraction theory
and is a manifestation of the wave nature of the incident radiation.
(see page 73)
2. What is the term
for when there is a fixed phase relationship of an EM field between two points
in space or two points in time?
can be described as a fixed phase relationship of a field between two points
in space or two points in time. (see page 77)
3. What is the term describing "any deviation of light
rays from rectilinear paths which cannot be interpreted as reflection or refraction?"
Diffraction is defined by Sommerfield as "any
deviation of light rays from rectilinear paths which cannot be interpreted
as reflection or refraction." (see page 83)
4. Which material listed below has the highest total
emissivity (defined as total spectral signature wrt a blackbody)?
Snow & graphite
See Table 5.3 on page 131.
Match the lens ray tracing diagram with its application type.
Magnifying glass _D_
d) Search light
See Figure 7.14
on page 201.
6. What is a 'Cold Shield' as used in electro-optical
b) A cooled aperture adjacent to the detector plane
The detector is placed within a vacuum enclosure called a Dewar which
is usually the only part of the system that is cooled. Within the Dewar a
cooled aperture called a cold shield is placed adjacent to the detector plane
to limit the angle over which the detectors receive radiation. (see
7. What are the two general
classes of electro-photonic detectors?
b) Photon (quantum) and
There are two general classes of detectors: photon (or quantum)
and thermal detectors. Photon detector convert absorbed energy into released
electrons. Thermal detectors absorb energy over a broad band of wavelengths.
(see page 265)
8. What is a bolometer?
d) A device which varies its electrical resistance depending on
the total electromagnetic power incident upon it.
is derived from a change in the resistance of the detector material.
(see page 273)
9. What is the modern
name of the U.S. Army's former Night Vision Laboratory (NVL)?
Night Vision & Electronic Sensors Directorate (NVESD)
effort began approximately 50 years ago at the then U.S. Army Night Vision
Laboratory (NVL). Today NVL is known as the U.S. Army Communications &
Electronics Command (CECOM), but is still referred to as NVL in the community
and that acronym. (see page 373)
The reference to West Virginia Senator
Robert C. Byrd is in jest for the well-joked-about large number
of places in the state that are named after him.
What is Persistent Surveillance?
a) The use of wide-area coverage
A new type of military missions and corresponding
sensor has been developed and fielded in the past few years. The application
is called persistent surveillance (square kilometers) airborne sensor, that
provides constant surveillance of a designated region. (see page 489)