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Introduction to Infrared and Electro-Optical Systems
Answers to RF Cafe Quiz #48

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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.

Return to RF Cafe Quiz #48

Introduction to Infrared and Electro-Optical Systems - RF CafeThis quiz is based on the information presented in "Introduction to Infrared and Electro-Optical Systems," by Ronald G. Driggers and Melvin H. Friedman.

1.  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?

d)  Coherence

Coherence 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?"

c)  Diffraction

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)?

a)  Snow & graphite

See Table 5.3 on page 131.

Optical Lens Ray Tracing - RF Cafe5.  Match the lens ray tracing diagram with its application type.

a)  Magnifying glass _D_
b)  Telescope          _A_
c)  Camera             _B_
d)  Search light       _C_

See Figure 7.14 on page 201.

6.  What is a 'Cold Shield' as used in electro-optical systems?

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 page 253)

7.  What are the two general classes of electro-photonic detectors?

b)  Photon (quantum) and thermal

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.

Bolometer detection 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)?

b)  Night Vision & Electronic Sensors Directorate (NVESD)

The [infrared] 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)

Note: 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.

10.  What is Persistent Surveillance?

a)  The use of wide-area coverage airborne sensors

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)