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temperature data. 
The majority of high performance TVFS systems 
operating in the 8 to 13 pm band have been developed 
for avionic and military applications. Development of 
the current range of UK military imagers began in 
1976 and at that time the decision was made to adopt 
a modular design philosophy. This is known as the 
Thermal Imaging Common Module (TICM) programme. The 
GEC V1010 TICM 11 is representative of this design. 
Instruments of this type can be mounted in either a 
fixed wing aircraft or a helicopter, in the latter 
case the scanner is mounted in a pod to allow a 
forward looking image to be obtained. 
The Rank Pull in Controls (RPC) SS600 thermal imager 
differs from the conventional TICM scanning design 
which uses a flapping mirror to scan the.field in 
elevation and a rotating polygon to provide the line 
scan. In contrast, the RPC design uses two coaxially 
mounted rotating polygons to form the two dimensional 
scan pattern. This unique design (Figure 1) is 
claimed to result in a lighter, more robust and more 
compact imager suitable for use where severe 
vibration may be experienced. 
DETECTOR 
10Omm 
Figure 1. Rank Pullin Controls SS600-scanning system 
(Lettington, 1985) 
The Barr and Stroud IR18 is another TVFS system based 
on a modular design approach. A narrower scanner 
field of view is used compared with several other 
equivalent systems. In this case also a novel 
optical-mechanical scanning design is used which is 
discussed in the following section of the paper. 
3.3 The Barr and Stroud IR18 Mk II Thermal Video 
Frame Scanner 
The scanner used in these tests was developed 
initially for military use, but it is now available 
for commercial remote sensing applications. Table 2 
outlines some of the technical specifications of the 
sensor and Figure 2 illustrates the principle of 
operation of the scanner. 
To achieve a video compatible image, two main 
criteria have to be met: firstly, the resultant image 
must be rectilinear and, secondly, it should have a 
625 line CCTV output (525 lines in the USA). In order 
to achieve this, banded scanning is carried out using 
a high speed rotor, turning at 39,000 rpm, to give 
Figure 2. Barr and Stroud IR18 Mk 11 thermal video 
frame scanner - principle of operation (Berry and 
Runciman, 1981) 
the line format, and a slower galvanometer driven 
rotor to achieve the frame transfer at 50Hz. Petrie 
(1983) has estimated, that the system has a data 
collection rate equivalent to 19 X 10^ pixels/second. 
The optics of the IR18 are used to collimate the 
incoming radiation and, by using afocal telescopes, 
enable a variety of magnification ratios to be used, 
so producing various object field of views (Table 
3). Such an arrangement ensures that the 
incident radiation forms a bundle of parallel rays 
which can then be focussed onto the frame scanning 
rotor. A concave mirror then re-collimates the image 
onto the rotating hexagonal rotor and subsequently 
onto the detector. 
Table 3: Barr and Stroud IR18 - object field of view 
with various auxiliary telescopes 
Magnification 
Ratio 
Object Field 
of View 
(H° XV 0 ) 
1 
38.0 25.5 
1.5 
25.3 17.0 
6 
6.30 4.25 
9 
4.22 2.8 
14 
2.7 1.8 
The detector used is an eight-element Mu Hard 
’SPRITE’, although four elements are normally 
preselected for use. The scanning sequence is such 
that on each successive frame scan a different 
element (of the four active elements) scans the same 
part of the scene. A consequence of this is that if 
the imager output is integrated over a number of 
frames, detector non-uniformity errors can be 
eliminated. Complex microprocessor controlled 
circuitry controls the synchronisation of the rotor 
speeds and signal outputs and the transfer of the 
data onto video tape. A conventional U-Matic video 
tape recorder is used to store the imagery.