INFRARED IMAGING IN THE TACTICAL AIRBORNE ENVIRONMENT 
Ralph L. Nardone 
Section Head, Reconnaissance Systems 
Honeywell 
Lexington. MA 02173 
U.S.A. 
ABSTRACT 
a 
An increasing need for tactical airborne reconnaissance has come with the substantial increase in 
military force concentrations in eastern Europe over the past several years. As the gross number of 
military equipment has grown, so too has the sophistication and capabilities of anti-aircraft weaponry- 
This has resulted in a shift from medium and high altitude reconnaissance missions to very low 
altitude, high speed penetration mission profiles in order to underfly air defence systems and increase 
survivability. For the infrared reconnaissance system designer the implication is an imaging environ- 
ment which is considerably more severe and which, if not properly dealt with, can substantially reduce 
system performance and hence mission effectiveness. 
This paper deals with the internal and external environments which affect infrared imaging systems 
in the tactical mission. Topics developed include the effects of vibration, shock, and aerodynamic i 
loading on the sensor system, and atmospheric effects on image quality during low level flight in 
adverse weather. Guidelines and tradeoffs are presented for both the specification of system perfor- 
mance and the proper installation of the sensor system into the airframe. The basis of this paper is 
work performed at Honeywell Electro-Optics Operations for the AN/AAD-5 Infrared Reconnaissance System 
(IRRS) and the Passive Autonomous Terminal Homing Sensor (PATHS) systems. 
DESIGN CONSIDERATIONS 
Today's Infrared Linescan System is generally comprised of four basic elements: an optical assembly 
which collects the infrared energy; a detector which converts the collected energy into an electrical 
signal; electronic circuitry to process the signal for display or recording; and a display or 
recording set. The specification and performance of each of these elements is obviously a determining 
factor in the overall system performance. Each element can be specified in such a way as to optimize 
the system performance to the specific mission environment of interest. 
In order to perform this optimization, a performance measure of each element must be determined, as 
well as a measure of the overall system performance. For the optical assembly the appropriate measures 
are the size of the collecting aperture and the field-of-view. For the detector the appropriate —— 
measures are the spectral response and-the sensitivity. For the electronics,-amplification factor (0r——-—--—————— 
gain) and dynamic .range are-appropriate.  And,:the proper measures of.performance for the recording or E | il 
display set are the storage capacity or image size, respectively, and the available dynamic range. Eu 
The mission environment must next be characterized to evaluate its impact on the IRLS performance. 
For purposes of illustration, the tactical penetration mission will be discussed because it presents a 
comprehensive set of internal and external environments to the system designer. T It 
Internal environments, in this context, are defined as those which directly affect the sensor 
system. Examples of these are airframe vibration, landing shock, thermal shock due to rapid changes in | 
altitude, etc. External environments are defined as those which affect the imaging system performance, | ilo 
independent of the air vehicle carrying it. Examples of these are atmospheric transmission, weather, 
smoke and dust, range to target, topology of terrain, etc. 
Perhaps the best way to approach an infrared imaging system design is to start with a thorough 
understanding of the tactical mission requirements and to work from the target of interest to the air- 
craft, and finally to the sensor system. Because the particulars of the imaging system are of concern 
here, a mission profile will be hypothesized at the outset. 
The mission is to locate mobile armor, such as tanks and cannons being broughtup from deep in enemy 
territory to reinforce forces at the forward edge of battle (FEBA). The mission must be carried out in 
day or night and under adverse weather conditions. Because the reconnaissance mission must be flown 
deep into enemy territory it can be presumed that heavy anti-aircraft defenses will have to be penetra- 
ted on route. To further complicate matters, the mission is to be flown from an aircraft carrier. 
Based upon this mission then, what are the internal and external environments presented to the sensor 
system, and how do they dictate the necessary sensor performance? 
Let us deal with the external environments first. Because the targets of interest are mobile armor 
their general location, but not their exact position, will be known. The sensor must, therefore, have a 
relatively wide field-of-view in order to have a high probability of detection. Because substantial air 
defense would be anticipated in the area, the mission will be flown at very low altitude and high 
airspeed. The low altitude decreases the probability of detection because the across track coverage is D 
small even with a wide field-of-view sensor. The low altitude and high airspeed taken in combination | 
yield a high y value, which will necessitate either a very high scanning speed to obtain contiguous 
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