Aerospace & Defense Technology - May 2021 - 26

Tech Briefs

rameters: S0, S1, S2, and S3. For imaging
applications these Stokes parameters are
determined on a pixel-by-pixel basis in
order to reconstruct a 2-D image. The
Stokes parameters are determined by
measuring the intensity of radiance that
is projected through a polarizer/waveplate pair that are oriented at various angles in order to measure the intensity of
a particular state..
The Stokes images S0, S1, S2, and S3
are defined by Eqs. 1-4:
S1 = I(0) - I(90) (w/sr-cm2),
(1)
S2 = I(+45) - I(-45) (w/sr-cm2), (2)
S3 = I(R) - I(L) (w/sr-cm2),
(3)
where I(0), I(90), I(+45), and I(-45) represent the measured radiant intensity of

the linear states (measured relative to
the vertical), at angles 0°, 90°, +45°, and
-45°, respectively, and I(R) and I(L) represent right- and left-handed circularly
polarized radiant states. The total radiance, S0, image (often thought of as just
the intensity image) is defined as,
S0 = S12 +S22 + S32 (w/sr-cm2),

(4)

and the degree-of-total-polarization
parameter/image is defined as,

where

DoP = S12 + S22 + S32 ,
S0
0  DoP  1.
(5)

However, for most applications that
involve remote passive polarimetric im-

Example of conventional LWIR thermal image (left) and resultant LWIR polarimetric image (right) in which
a vehicle at ambient temperature is parked on a hillside. Shown is a key aspect for using thermal polarimetric imaging for low-observable targets in which the vehicle is difficult to discern from the background
in the conventional thermal image (left) while the polarimetric image clearly shows the " manmade " object
(right).

aging in the thermal IR, S3 is very small
and rarely measurable and thus taken to
be approximately zero. As a result, Eq. 5
is reduced to the more common degreeof- linear-polarization (DoLP) parameter/image and is defined as,
DoLP= S12 + S22 .
(6)
S0
There are a variety of optical approaches/methods implemented in various polarimetric camera designs appropriate for polarization state filtering and
analysis in the thermal IR. Examples include division-of-time approach, which
uses a spinning-achromatic-retarder
(SAR) arrangement, a division-of-amplitude (DoA) in which a polarized beamsplitting-plate is used to project different
polarization states of the same scene
onto one, two, or more focal-plane-arrays (FPA), and the division-of-focalplane (DoFP) design in which micro-polarizers oriented at different angles are
attached to individual pixels that make
up the FPA. An example of an LWIR thermal image (left) and its corresponding
polarimetric DoLP image (right) are
shown in the accompnying image.
This work was done by Kristan P. Gurton
for the Army Research Laboratory. For
more information, download the Technical Support Package (free white
paper) at www.aerodefensetech.com/tsp
under the Unmanned Vehicles & Robotics category. ARL-0238

Cyber Risk Assessment and Scoring Model for Small
Unmanned Aerial Vehicles
Based on lessons learned from similar domains of aircraft operation, information technologies,
cyber-physical systems, and cyber insurance, a cyber risk assessment methodology tailored for small
UAVs is developed.
Air Force Institute of Technology, Wright-Patterson Air Force Base, Ohio

T

he desire of man to fly is almost as
old as time itself. Since the dawn of
flight, aircraft have evolved to meet
new demands and innovations,
through the 20th century and into the
21st. While UAVs have been around
since the earliest days of aircraft, technology in the last two decades has allowed an explosion of options that

allow for militaries and commercial organizations alike to consider the aerial
automation of missions like never before. In particular, small UAVs provide a
lower cost of entry and less overhead,
with much of the same aerial advantages as larger vehicles.
As with all computer devices, small
UAVs come with risks associated with

their missions, both physical and cyber
related. The physical risks of collisions
and damage to structures or people is reflected in United States government
regulations and licensing through the
Federal Aviation Administration (FAA).
In contrast, the cyber risks accepted by
organizations and individuals has received very little attention and over-

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Aerospace & Defense Technology, May 2021

26

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ToC


http://www.aerodefensetech.com/tsp http://www.aerodefensetech.com http://www.abpi.net/ntbpdfclicks/l.php?202105ADTNAV

Aerospace & Defense Technology - May 2021

Table of Contents for the Digital Edition of Aerospace & Defense Technology - May 2021

Aerospace & Defense Technology - May 2021 - Intro
Aerospace & Defense Technology - May 2021 - Sponsor
Aerospace & Defense Technology - May 2021 - Cov1
Aerospace & Defense Technology - May 2021 - Cov2
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Aerospace & Defense Technology - May 2021 - Cov3
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