JED - March 2013 - 49

E W101
plane arrays, which allow image
tracking as discussed last month.

ONE-COLOR VS. TWO-COLOR
SENSORS

WHAT’S NEXT

Figure 3: Black Body Radiation from any object varies with wavelength. The peak moves left as
the temperature increases. When objects at different temperatures are sensed at two wavelengths,
the ratio of the energy at each wavelength varies strongly with temperature.

Next month, we will discuss flares
for protection against heat-seeking missiles. For your comments and suggestions, Dave Adamy can be reached at
dave@lynxpub.com. a

The Journal of Electronic Defense | March 2013

One of the issues faced by heatseeking missiles is to discriminate among the target aircraft
and flares, the sun and other high
temperature distractions. Conventional distractors are much
hotter than the targeted parts
of the target aircraft. Magnesium
flares are 2200°K to 2400°K and
the sun is 5900°K. This causes the
Hot Metal Parts
distractor to emit much higher
energy than the target. Note that
Hot Metal Parts
Room Temperature Objects
the black-body emission curves
& Exhaust Gasses
in Figure 3 (as explained earlier
in the October column) show inFigure 2: Atmospheric Transmittance at IR wavelengths has transmission windows and drop-outs at well
defined wavelength ranges.
creased energy with increased
temperature at any wavelength.
Therefore, a very hot magnesium flare will capture a missile’s
of the aircraft, the tailpipe and the compressor blades. For eftracker and lead it away from the target.
fective tracking, it was necessary for the missiles to approach
However, if the missile seeker detects its target at two
the aircraft from the rear to achieve a clear view of the trackwavelengths, it can, in effect, calculate the temperature
ing point. These early sensors did not require cooling but were
of the targeted object. This allows the missile to track a
restricted in sensitivity.
target at a chosen temperature, or at least to discriminate
With cooled Lead Selenide or Indium Antimonide sensors,
against false targets that are much hotter than the real
it was possible to track on the aircraft’s plume. Because the
target. Figure 3 deals with two hot objects (a distractor) at
plume can be seen from the front or the side of the aircraft,
2000°K and the other (a target) at 1600°K at two separate
the missiles could track from any angle, making these “all
wavelengths (2 µm and 4 µm). Note that these temperatures
aspect” missiles.
and wavelengths are chosen to illustrate the effect rather
With Mercury Cadmium Telluride sensors, missiles can track
than to represent the values of specific friendly or enemy
on aerodynamically heated aircraft skin, which allows all assensors. The 2000°K flare emits 5.3 times the energy at 2
pect tracking. This material can also be used to make focal
µm that it does at 4 µm. Now, consider the 1600°K target. It emits only
3.1 times as much energy at 2 µm as
it does at 4 µm. If only the tracking
waveform for objects with the proper
energy ratio range are input to the
missile’s processor, the missile will
ignore the flare at the wrong temperature and track the target at the right
temperature.
The two selected wavelengths must
be within atmospheric windows, and
can be selected to create significant ratio differences between flares and the
targeted part of the target aircraft.

49


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
JED - March 2013 - 71
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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