International Journal of Advancements in Research & Technology, Volume 1, Issue 4, September-2012
ISSN 2278-7763
Design and development of CCD Optical Sight for tracking real
time objects
R. Sudhakar Rao1, Prof. S. Chandra Lingam2
_____________________________________________________________________________________________________________________________________
1
Senior Manager, Optics Lab, Design & Engineering Division, Bharat Dynamics Limited, Kanchanbagh, Hyderabad – 500 058, AP, India; Email:rsrbdl@yahoo.com;
2
Dept. of Physics, College of Engg., JNTU, Kukatpally, Hyderabad–500 085, AP,India;E-mail:chandra_lingam@yahoo.com
ABSTRACT
Charge Coupled Devices enable instant imaging. Basing on this principle, novel CCD Optical Sight was developed. The
necessity, design principles with the help of theory and development details with the help of system data, diagrams and
photographs are provided in this paper. Application of the device is explained.
Keywords: Aberrations, Airy Disc, CCD imaging, Film based Imaging, Optical Design, Optical Device, Solid State Technology,
Weapon Simulator.
1 INTRODUCTION
S
cientific imaging applications are expanding in to
different domains [1]. Image observation through
eyepiece based instruments is cumbersome and strenuous. The
observation cannot be made for longer periods. Later, the
imaging units were clubbed with a film for recording the
image. These delivered sharp, clear pictures with plenty of
details and good contrast. The hard copy print was a result of
the photographic’s efforts. Nevertheless, there were many
drawbacks in the use of the film. The wait to see a picture was
a lengthy process. It was difficult to get a film image into a
computer. Storage of film based pictures consumed a lot of
space, the files were difficult and time consuming to retrieve,
and they degraded over time. Finally, some of the
characteristics of film, such as its dynamic range, linearity at
different light levels and consistency left a lot to be improved
upon. Solid State Technology helped to overcome the difficulty
experienced in using the film based imaging. This technology
has given, Charge Coupled Devices (CCDs). These devices
have become the image-capturing platform of choice for
scientific imaging, because of their ability to image in real time
and ensured the accuracy of focus and exposure. This type of
imaging is called CCD Imaging. Solid-state technology enabled
the image on a screen as soon as it is exposed. This screen is
either a Television Monitor or Computer Monitor. Storing
images on standard computer media is highly efficient and
there is no danger of degradation. There is no chemical
processing. Solid-state imaging delivers consistent and
repeatable results. Notable improvements in CCD image over a
photographic image are: a) Low noise, b) Large dynamic range,
c) High resolution and d) Higher quantum efficiency. Taking
advantage of the better characteristics of the CCD sensors and
contemporary Optical software and hardware tools, a novel
Copyright © 2012 SciResPub.
CCD Optical Sight was conceived and it was developed to
function as real time video capturing unit. Following
paragraphs provides the design, development, integration,
evaluation and application stages of the equipment.
2
DESIRABLE
SIMULATOR
FEATURES
OF
WEAPON
A second generation Anti Tank Guided Weapon (ATGW)
system consists of a Weapon and a Launcher. A pilot is
required to swivel the Launcher Optical Device manually for
surveillance and aiming purposes. Once a specified target is
in the vicinity of detection range, pilot is expected to acquire
the target, aim at it and then fire the weapon and continue to
track the target until the weapon reaches it. This is a difficult
task for a pilot considering the technology, accuracy, short
flight duration of 12 to 13 s for its range, cost of the weapon
and expensive drills in outdoor environments.
Therefore, a pilot needs training on a Simulator with the
following desirable features:





Actual Launcher or close to it used in battlefield
conditions on actual targets in real terrain
Immersion effect to the pilot in the battlefield
environment.
Instant feedback during and after the exercise on
aiming, tracking, launching, guiding the weapon, lead,
lag, hit and miss information
Measurement of improvements made from drills and
Equipment which is easy to install, operate and
rugged.
3 DESIGN ASPECTS OF CCD IMAGER
International journal of advancements in research & technology, volume 1, issue 4, september-2012
ISSN 2278-7763
While developing a weapon simulator, necessity arose to
capture the target movements in real time to enable the
instructor to assess and improve the performance of the pilot.
Therefore, a novel CCD Optical Sight was conceived and
developed. Design of CCD Optical Sight started with an
assessment of: a) Target Acquisition; b) Lens System; c) Image
Sensor and d) Display Device parameters. Application
constraints, requirements and desired results are discussed in
the beginning. Later, the selection of the lens system, image
sensor and display devices are studied.
3.1Target Acquisition Constraints, Requirements and
Desired Results
The criteria of target acquisition [2] is dependent on how
much field of view supported by the optical sensor, its
magnification and its ability to provide data that is
meaningful for visual discrimination task. Target acquisition
generally deals with Detection, Recognition and Identification
of the target of interest. For a weapon simulator application,
targets could be military vehicles, soldiers and static
installations.
The human eye has a resolving power of about one-minute of
arc, which is equivalent to 291 µrad. Comparing this
resolution with the required sensor’s field of view can
provide an estimation of the magnification necessary for the
required visual task. As per the Johnson’s criterion, there
exists a relationship between observer’s ability to resolve bar
targets through an imaging device and their ability to Detect,
Recognize and Identify targets. It was found that observers
coul
Target
Detection Recognition Identifid
(cycles)
(cycles)
cation
dete
(cycles)
ct a
Truck
0.9
4.5
8
targ
Jeep
1.2
4.5
5.5
et
Commando
1.2
4.3
5.5
whe
Car
n
M-48 Tank
0.7
3.5
7
pres
Soldier
1.5
3.8
8
ente
105
1
4.8
6
d
Howitzer
wit
Average
1.0
4.0
6.4
h
[+0.5, -0.3]
[+0.8, -0.5]
[+2, -0.5]
‚on
e cycle‛ of information, which in the case of a bar target is one
black and one white bar. Table 1, provides the information
about the ‚number of cycles‛ that is just resolvable across a
target’s critical dimension for various discrimination tasks.
Johnson’s criterion thus helped to calculate the sensor
resolution necessary for any visual acquisition task at any
range. With this criterion and other data shown in Table 2, it
was possible to arrive at an appropriate sensor size, its field
Copyright © 2012 SciResPub.
of view, resolution and other parameters. The design criteria
mainly centered on capturing a target of 1.5 m x 1.5 m located
at a distance of 1000 m to 1500 m with clarity and its image
must be displayed on a computer monitor and it should
provide not less than 10 x 10 pixels out of 220 x 144 pixels.
Once this condition is fulfilled, then the dedicated software
programs written such that the targets could be recognized
and process the image, analyze & provide useful data. These
conditions were taken care at the design stage.
3.2 Lens System, Image Sensor and Display Devices
Selection
Lens System is the important subsystem of an imaging
device. It collects light from a target and refracts/reflects that
light to form a usable image of the target. Basic lens system
properties are: Effective Focal Length (EFL), Aperture, Field
of View (FOV) and Image Format. FOV is often determined
by the size of a detector. To suit the design conditions, the
required field of view was one degree. Clear Aperture of the
Optical System selected was 80 mm, so that this size caters to
the light gathering power in the day environment from dawn
to dusk.
The relation between FOV, image size and EFL is:
FOV = 2 tan-1 {image height / EFL}
(1)
Since FOV value decided was one degree to suit the picture
format on the computer, a CCD sensor of 8.0 mm (diagonal
size of ½ inch CCD camera) was selected. Lens System speed
is a useful indicator of the brightness conditions under which
it functions. Lens system speed (F-No) is related to EFL and
Entrance Pupil Diameter with the following relation:
F-No. = EFL  Entrance Pupil Dia. (2)
Using the Eq. (2), EFL of the optical system was calculated
and its value was 458 mm. Practically, Lens System’s F-No
varies from F-1, which is very fast, to a slow F-22.
Table 1: Target’s critical dimension data for
three discrimination tasks
Table 2: Relationship between Sensor Instant Field of View
(IFOV), Range and Resolution
International journal of advancements in research & technology, volume 1, issue 4, september-2012
ISSN 2278-7763
Ima
ge
brig
Range-km
4
3.8
2.5
htn
No. of
0.7
3
6
ess
cycles (N)
is
Att. Factor
2
2
2
inve
Sensor
0.38
0.1
0.07
rsel
IFOV
y
(mrad)
pro
Hor. Pixels640
640
640
port
visible
iona
Sensor
14
3.7
2.8
l to
FOV- Deg
the
square of F-No. In the present system, F-No varied from 5.7 to
305. An adjustable iris mechanism was used to work in varied
brightness conditions. Lens system collects light from a point
on the target and focuses to a corresponding point on the
sensor. Ideally, the image of a point source formed by a
perfect lens system would be an image of zero diameters. In
the real world, even a perfect lens system gets affected from
diffraction and the lens system aperture causes diffraction
pattern called the Airy pattern. The central spot in the pattern
is called the Airy Disc. The diameter of the Airy Disc is
directly proportional to the lens system F-No and the central
wavelength (λ) in the band of the light spectrum where the
optical system is desired to function. In this case, the
operating spectrum band is 400 to 700 nm and the central
wavelength is 550 nm. The relation between Airy Disc (Spot)
diameter, F-No., and λ is given by the equation:
Resolution
Capability
Detection
Recognition
Spot diameter = 2.44 * λ * F-No.
Identifi
cation
(3)
Using Eq. (3), value of the spot diameter calculated to be 8
µm. It is a well known fact that 85 % of the incident light
power is focused by the lens system in to this spot. This spot
size decides the individual pixel size of the sensor, as it is
Copyright © 2012 SciResPub.
reasonable to match the blur size with pixel size. Therefore,
the spot size assessment makes optical design calculations
more meaningful. The inability of a lens system to form a
perfect image is due to lens aberrations [3]. It is normal
practice to choose a lens system with a small blur circle to
give the required resolution. While choosing a lens system,
the monochromatic aberrations-Spherical, Coma, Field
curvature, Astigmatism, Distortion & polychromatic
aberrations-Axial color, Lateral color are optimized using
the optical design software. In order to arrive at an optimum
lens system, design was carried out from the first order
layout, optimized and finalized using computer aided
optical design software. The results of the optical design are
shown in the following graphs, which are a result of
optimization to arrive at aberrations within the tolerable
limits. Sensor was selected based on the required image size.
Display device is desirable to have good fidelity of the
image generated by the lens system and CCD sensor
combination. It must support the display activity for
visualizing the image by a batch of trainees, as well as to
help the instructor in assessing the pilot’s performance.
4 SYSTEM DATA
Calculations were carried out to derive the System Data
(given in the Table 3), basing on the design principles and
equations keeping the image quality as prime concern.
System data was used in fabricating the CCD Optical Sight
(shown in the Fig. 2) and it was mounted on a Weapon
Simulator Optical Sight. The mounting details are illustrated
in Figures 3 and 4.
International journal of advancements in research & technology, volume 1, issue 4, september-2012
ISSN 2278-7763
Copyright © 2012 SciResPub.
International journal of advancements in research & technology, volume 1, issue 4, september-2012
ISSN 2278-7763
Computer and Auxiliary Display Unit (ADU) are added to
make it a complete system. Computer works as a Command
& Control Station for the System and analysis tool to the
Instructor. ADU functions as demonstrative tool to the copilots. CCD Optical Sight tracks target situated in the range
between 25-2000 m, in real time; sends analogue video image
to Computer and ADU. Once the trigger is pressed, computer
starts acquiring target images and continues the process till
the end of weapon flight time. The analogue image from the
CCD Optical Sight is converted into digital image by a frame
grabber resident in the computer. The acquired image is
processed and analyzed for specific purpose using dedicated
motion analysis algorithms using computer hardware. The
resulting data, such as aiming, tracking, hit / miss indication
and error etc., in graphic and text form, are displayed on the
computer monitor. The instructor then provides a feedback to
the pilot and reviews the sequence of performance of the
pilot. Simultaneously, co-pilots are shown the video display
on ADU. Initially few prototypes were fabricated. Rigorous
field trials at different locations proved the robustness and
efficacy of the system. During the evaluation, some problems
surfaced and they were corrected (details given in the Table
4). Afterwards few numbers of these items were fabricated,
integrated in to the Weapon Simulators.
Copyright © 2012 SciResPub.
International journal of advancements in research & technology, volume 1, issue 4, september-2012
ISSN 2278-7763
5
CONCLUSION
Table 3: System Data
Optical
System Data
Focal length: 458 mm;
Clear Aperture: 80 mm dia.
FOV (H x V x D): 0.8⁰ x 0.6⁰ x 1⁰;
Resolution: ~ 0.1 mil;
Diff. Lim.: 8 µm
Iris & Focus: Manual Control;
Range: 25–2000m;
Day Time use
CCD Sensor
CCD format: ½ inch Color
Data
Sensing Area: 6.4 mm x 4.8 mm
Pixels (H x V): 9 µm x 9 μm;
Res.:480TVL;
Sensitivity: 1.5 Lux(min.)
Display
Computer: Display size: 14 inch;
Devices
Format: 320 x 200 pixels;
Data:
Power:230 VAC, 50 Hz
ADU: CRT diagonal size: 14‛;
Resolution:480 TVL(H);
Scanning: PAL 625 TVL;
Power:230 VAC, 50 Hz.
Fig. 2. Photograph of CCD Optical Sight
Fig. 1.
Compu
ter
Aided
Design
(CAD)
models
of CCD
Optical
Sight
Novel concept of
introducing
a
CCD
Optical
Sight
on
a
Weapon
Simulator was realized. The system was successfully put into
practice in capturing the video images of the remote target
moving in real terrain. The development of CCD Optical
Sight gave further impetus to create a Long Range Telescope
CCD System for Real Time Target & Weapon Tracking [4].
This knowledge helped us to develop, ‚An Outdoor
Simulator for Training in Missile Launching and Guidance‛
in real time [5].
Table4: Problems encountered &
Solutions provided
Problems
Fig.3.
Fig.4. Photograph of CCD Optical Sight mounted on the
Optical Device of the Outdoor Simulator
Copyright © 2012 SciResPub.
ACK
NO
WLE
DG
MEN
T
The
autho
rs are
grate
ful to
the
CMD
, the
Direc
tors,
GM
(P&A
), ED
(P&A), Head–D&E, BDL for permitting to present this paper
in ‚Frontiers of Optics and Photonics FOP-11‛ jointly
conducted by the ‘Optical Society of India - Kolkata’ and
‘Indian Institute of Technology, Delhi’ during Dec 3-5, 2011 at
Indian Institute of Technology, Delhi, India.
Solutions
Photograph of
CAD drawings of CCD Optical Sight and its mount on the
Optical Device
Long focal length lens system required
a long lens barrel and so the balancing
the unit on the Launcher.
Flares were observed in the image
Image degradation due to atmospheric
turbulence and mirage effects
Rugged mount helped to adjust the
centre of gravity to suit the launcher
length.
Arrangement of decreasing steps
inside the lens housing and
application of dull black paint reduced
the flares.
Implementation of image processing
algorithms helped to control the image
degradation due to changes in
atmospheric conditions, turbulence &
mirage effects.
International journal of advancements in research & technology, volume 1, issue 4, september-2012
ISSN 2278-7763
R. Sudhakar Rao is also thankful to the project team guides,
colleagues and manufacturers who have coordinated in the
design, development, integration, evaluation and application
of the system.
REFERENCES
[1] EG&G Optoelectronics - Reticon Product Data Book on
‚Image Sensing & Solid State Cameras‛, 1994-95
[2] R L Lombardo Jr, ‚Target Acquisition: It’s Not Just for
Military Imaging‛, Photonics Spectra, p123, July 1998
[3] R. Kingslake, ‚Lens Design Fundamentals‛, Chapters 3 –
6, Academic Press, London, 1978
[4]R. Sudhakar Rao, M. Sreedhar Rao, S. Shivashankar, T.
Srinivas, P. Srinivasa Rao, A. K. Krupal, R. Babu, K. J.
Copyright © 2012 SciResPub.
Dharma Reddy, A. Ramamani, Brig. (Retd.) Raghavendra
Rao, V. Narayana and Prof. G. Ramachandra Reddy,
‚Design and development of a Long Range Telescope
coupled with CCD Camera
for Remote Detection
Applications‛, Journal of Optics (Published by the Optical
Society of India, Kolkata), Vol. 31, No. 3, Pages 145-152,
2002
[5]Government of India Patent No. 228497 dated
5th Feb 2009.