JED - March 2013 - 48

EW 101

Infrared Systems and Countermeasures – Part 4

Sensors
By Dave Adamy

W

e have been talking about heat seeking
missiles, and last month focused on various types of reticles. This month, we will
take a closer look at the actual infrared (IR)
sensors. The sensor generates a signal from
received IR energy. Each type of sensor
material responds to a spectral range, which determines the
target temperature against which it is most effective.

The Journal of Electronic Defense | March 2013

48

of wings, can be expected to be between 300°K and 500°K so
the energy from these areas will peak in the 8 to 13 µm range.
You may want to refer back to the October 2012 “EW 101” column for a discussion of the peak temperature vs. wavelength
relationship.

ATMOSPHERIC WINDOWS

Another important issue, which also follows from the October 2012 discussion, is the transmittance of the atmosphere.
Figure 2 shows the four major windows through which infraAIRCRAFT TEMPERATURE CHARACTERISTICS
red energy propagates well. The two lower windows are at 1.5Figure 1 shows the approximate temperature ranges of
1.8 µm and 2-2.5 µm. These are in the near infrared region.
the parts of a jet aircraft that can be targeted by heatThere is a middle infrared region, which has two windows in
seeking missiles.
the 3- to 5-µm region. The far infrared region has a large window
from 8-13 µm.
Internal Engine Parts
1000 to 2000 ºK
Hot targets like the tail pipe
or internal engine parts are
Plume
tracked in the near infrared region, the plume is tracked in the
700 to 1000 ºK
middle infrared region and heated skin targets are tracked in the
External Engine Parts
Aerodynamically Heated Surfaces
1000 to 2000 ºK
far infrared region. In general,
300 to 500 ºK
heat seeking missiles like to target on the hotter targets
Figure 1: A jet aircraft can be attacked by a heat seeking missile, which tracks the hot internal parts of the
engine, the tail pipe, the plume or aerodynamically heated skin surfaces.

The compressor blades inside the engine are the hottest areas, the external engine “tail pipe” parts are slightly cooler.
Both are in the range of 1000°K to 2000°K, which means that
their energy peaks in the 1 to 2.5 micron (µm) wavelength
range. The plume from the engine is in the 700°K to 1000°K
range, so it peaks in the 3 to 5 µm wavelength range. Aerodynamically heated aircraft skin, for example the leading edges

SENSOR MATERIALS

Table 1 shows the peak response wavelengths of various
important sensor materials and their typical applications.
All of the sensor materials except Lead Sulfide are cooled
to 77°K (which is the boiling point of Nitrogen at one atmosphere) to increase sensitivity and signal-to-noise ratio and to
discriminate against solar energy. Lead Sulfide was used in the
first heat seeking missiles, which homed on the hottest part

TABLE 1
Symbol

Material

PbS
PbSe
HgCdTe

Mercury Cadmium Telluride

InSb

Indium Antimonide

Peak Response Wavelength (µm)

Typical Application

At 300ºK

At 77ºK

Lead Sulfide

2.4

3.1

Used at room temperature against hot targets

Lead Selenide*

4.5

5

Tracking Plume

10

Must be cooled to 77ºK. Used in missile trackers and FLIRs
Useful in both mid and long wavelength windows

3

Tracking Plume

3.5

*Note that in the January 2012 column, this was incorrectly called Lead Selenium, but this mistake was pointed out by one of your sharp
eyed colleagues.


http://www.crows.org

JED - March 2013

Table of Contents for the Digital Edition of JED - March 2013

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
Washington Report
World Report
Enabling Global Strike: EW Updates to the USAF’s Bomber Fleet
Technology Survey
EW 101
AOC News
2013 AOC Industry Member Guide
Index of Advertisers
JED Quick Look
JED - March 2013 - cover1
JED - March 2013 - cover2
JED - March 2013 - 3
JED - March 2013 - 4
JED - March 2013 - 5
JED - March 2013 - The View From Here
JED - March 2013 - 7
JED - March 2013 - Conferences Calendar
JED - March 2013 - 9
JED - March 2013 - Courses Calendar
JED - March 2013 - 11
JED - March 2013 - From the President
JED - March 2013 - 13
JED - March 2013 - 14
JED - March 2013 - The Monitor
JED - March 2013 - 16
JED - March 2013 - 17
JED - March 2013 - 18
JED - March 2013 - 19
JED - March 2013 - 20
JED - March 2013 - 21
JED - March 2013 - 22
JED - March 2013 - 23
JED - March 2013 - Washington Report
JED - March 2013 - 25
JED - March 2013 - World Report
JED - March 2013 - 27
JED - March 2013 - Enabling Global Strike: EW Updates to the USAF’s Bomber Fleet
JED - March 2013 - 29
JED - March 2013 - 30
JED - March 2013 - 31
JED - March 2013 - 32
JED - March 2013 - 33
JED - March 2013 - 34
JED - March 2013 - 35
JED - March 2013 - 36
JED - March 2013 - 37
JED - March 2013 - 38
JED - March 2013 - Technology Survey
JED - March 2013 - 40
JED - March 2013 - 41
JED - March 2013 - 42
JED - March 2013 - 43
JED - March 2013 - 44
JED - March 2013 - 45
JED - March 2013 - 46
JED - March 2013 - 47
JED - March 2013 - EW 101
JED - March 2013 - 49
JED - March 2013 - AOC News
JED - March 2013 - 51
JED - March 2013 - 52
JED - March 2013 - 2013 AOC Industry Member Guide
JED - March 2013 - 54
JED - March 2013 - 55
JED - March 2013 - 56
JED - March 2013 - 57
JED - March 2013 - 58
JED - March 2013 - 59
JED - March 2013 - 60
JED - March 2013 - 61
JED - March 2013 - 62
JED - March 2013 - 63
JED - March 2013 - 64
JED - March 2013 - 65
JED - March 2013 - 66
JED - March 2013 - 67
JED - March 2013 - 68
JED - March 2013 - 69
JED - March 2013 - 70
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JED - March 2013 - 72
JED - March 2013 - 73
JED - March 2013 - 74
JED - March 2013 - 75
JED - March 2013 - 76
JED - March 2013 - 77
JED - March 2013 - 78
JED - March 2013 - 79
JED - March 2013 - Index of Advertisers
JED - March 2013 - 81
JED - March 2013 - JED Quick Look
JED - March 2013 - cover3
JED - March 2013 - cover4
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