SR
XR
[72] Inventor
39633239721?
7 [Law/115
["1 3,633,212
"Iartary
Guy F.
484 Ra
Q. Baxter Warner and
[211 App]. No. 80,866
[22] Filed
[45] Patented
l'lUWaH-l J. l'lulla,, .Il.
Oct. 15, 1970
Jan. 4, 1972»
[54] SYSTEM FOR DETERMINING THE ORIENTATION
OF AN OBJECT BY EMPLOYING PLANE
POLARIZED LIGHT
ABSTRACT: A system for ascertaining the positional charac
teristics of a moving object from a given viewing point. In one
embodiment, the invention is employed to determine the at
9 Claims, 8 Drawing Figs.
titude of a missile subsequent to its being launched from an
[52]
U.S. Cl ...................................................... ..
346/107,
[51]
[50]
Int. Cl ....................................................... .. G01p 13/00
Field of Search .......................................... ..
346/107,
aircraft. A plurality of specially oriented light-polarizing
350/153, 356/118
re?ectors are attached to the missile surface, and observed by
a viewing camera on the aircraft. A source of plane-polarized
light on the aircraft illuminates the re?ectors on the missile.
The attitude of the latter with respect to this source deter
38,2; 356/114, 118, 119, 138; 352/39, 131, 132;
350/153, 159; 250/225, 231 SE; 95/1 .1
3,269,254
8/1966
Cooper etal. .............. ..
356/138 X
mines the amount of illumination picked up by the camera
from each re?ector. Such data is then coordinated to yield the
positional information desired. In another embodiment, the
invention time-correlates a plurality of viewing cameras by
causing a time-coded re?ection of light to be visible on the
3,306,159
2/1967
Beall et al. .................. ..
356/114 X
missile regardless of view angle.
[56]
References Cited
UNITED STATES PATENTS
SOURCE 14 OF PLANE
POLARIZED LIGHT
WING OF
AIRCRAFT
l2
STORES
SEPARATING
MISSILE
IO
cows 20 OF PLANE \ \
POLARIZED LIGHT
\
ARRAYZGOF
POLARIZED 4
\\
REFLECTORS
\
i
VIEW 24
2
CAMERA
\\
\
7/
\
\
PATENTEDJIW mm
31333212
SHEET 1 OF 3
REFLECTOR
SOURCE
FILTER
A
‘i1
A
MAXIMUM REFLECTRR
ILLUMINATION
A
I 8k
j—TH8Ik'TH
-
WHEN A-P2=I
POLARIZED
A
SOURCE
A
NI FILTERS
\\
A
REFLECTOR
FILTER
MINIMUM REFLECTOR
ILLUMINAATIION
WHENA-P2=O
“ 2
’
j-TH8k-TH8
POLARIZED 2;
REFLECTORS
R
‘
GUYF COUPE/C?
INVENTOR
4/2
I,
8W
A
S
Q/
Q
'
A%0RNEY
GENT
'
1
3,633,212
2
SYSTEM FOR DETERMINING THE ORIENTATION OF
AN OBJECT BY EMPLOYIN G PLANE-POLARIZED
LIGHT
Another object of the invention is to supplement, but not in
terfere with, present photogrammetric techniques of deter
mining body kinematics wherein several points on the body
are tracked.
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and
used by or for the Government of the United States of Amer
ica for governmental purposes without the payment of any
royalties thereon or therefor.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, advantages and novel features of the inven
tion will become apparent from the following detailed descrip
tion of the invention when considered in conjunction with the
BACKGROUND OF THE INVENTION
At the present time, devices such as accelerometers and ex
accompanying drawings wherein:
FIG. 1 is a vector diagram useful in understanding the
mathematical model upon which the present invention is
tensometers are frequently utilized to instrument kinematic
based;
events. In addition, moving-picture cameras ?nd particular 15
FIGS. 2a and b illustrate the relative orientations of the
application for such operations as the launch of a missile from
source and re?ector ?lters of the invention and the plane of
an aircraft. In such cases, efforts are made to place the respec
polarization of the light beam for maximum and minimum
re?ector illumination, respectively;
tive camera centerlines perpendicular to the plane of motion
FIG. 3 is a schematic view of a system designed in ac
(as with cameras in chase planes directly abeam of the missile
cordance with the principles of the present invention and in
launching aircraft). However, onboard launch-viewing
stalled upon a missile-launching aircraft;
cameras rarely have good view angles, so that several are
FIG. 4 is a vector diagram of a particular relationship of the
required to triangulate the missile’s position. Kinematic data is
source and re?ector ?lters of the present invention;
extracted from these ?lms, using semiautomatic “viewers with
FIG. 5 is a schematic diagram of a preferred system for
crosshairs manually positioned on a tracking point. The opera
tor then records the crosshair positions in arbitrary units (of 25 generating three colored rotating beams of plane-polarized
light used in one embodiment of the invention;
ten punched on cards after being scaled). If dif?cult angles
FIG. 6 is one arrangement of re?ectors to be carried on the
require trigonometric correction or triangulation to be made,
the data is fed to a computer that generates the true kinematic
surface of the object the kinematics of which are to be ascer
tained; and
trajectory of the missile in coordinate systems related to the
FIG. 7 is a sectional view of one of the re?ectors of FIG. 6 as
launching aircraft. This entire data system is subject to limita 30 attached
to such object.
tions in “resolving power" because of camera misalignment,
calibration tolerances and operator error. Time correlation
may be achieved by a coded signal on the border of each ?lm'
DESCRIPTION OF THE PREFERRED EMBODIMENT
from some central secondary time standard. Alternatively, the 35 Before considering the manner in which the invention
results are achieved, it will be helpful to recall that when
plane-polarized light is re?ected from a mirror, its major plane
frame rates are calibrated and the event itself (or possibly '
several ?ash bulbs) can serve to time-synchronize the camera
?lms. Cameras without provision for a coded time track on the
of vibration is rotated by an amount which is a function of
both the angle of incidence and the relative orientation of the
?lm border often experience changes in frame speed due to
environmental conditions. Greater expense and, need for 40 plane of vibration. A diffuse re?ecting surface (which can be
considered to be composed of many small randomly oriented
telemetering a time signal follow from the use of a time code
mirror elements) will, by de?nition, scatter the incident beam
on each ?lm.
in all directions. If the incident beam is polarized, the diffuse
re?ected beams will also have all possible planes of vibration.
SUMMARY OF THE INVENTION
Thus, a diffuse re?ecting surface illuminated by a beam of
The purpose of the present disclosure is to supplementthe 45 plane-polarized light will appear equally luminous to an ob
present moving-picture instrumentation of kinematic events
server positioned at any point from which the illuminated sur
insofar as the derivation of time and position data is con
face can be seen. Further, the emitted rays will have a
cerned by employing one or more sources of polarized light
uniformly random orientation of planes of polarization re
and a plurality of unique re?ecting members so as to
gardless of observer position.
50
a. Correlate each of several viewing camera ?lms with an
If a polarizing ?lter (such as Polaroid) is now placed over
optical time signal on the moving object independent of: dif
the diffuse re?ecting surface so that both the incident beam
fering camera view stations, rotational attitude of the object,
and all re?ected beams must pass through it, the re?ector will
differing and unsteady ?lm speeds, and intensive ?ow ?elds
again appear equally luminous to an observer at any position
_( as with missiles launched from aircraft);
55 (neglecting the factor of greater absorption at more oblique
b. Provide each of several viewing cameras with an optical
angles through the Polaroid ?lm). However, the observed
signal on the moving object which indicates that object's rota
tional position independent of differing camera view stations
and intensive flow ?elds. No modi?cation whatsoever is
required to conventional high-speed cameras, ?lms, or
camera-operating techniques.
STATEMENT OF THE OBJECTS OF THE INVENTION
magnitude of surface luminosity will be a function of the angle
between the polarization axis of the ?lter and the plane‘ of
vibration of the incident beam. Also, and of particular im
portance to this invention, is the fact that the condition of light _
extinction (when the plane of vibration of the incident beam is
so rotated) is observable simultaneously at all positions from
which the diffuse re?ecting surface can be seen. This behavior
is the basis for the hereinafter-disclosed techniques for instru~
One object of the present invention, therefore, is to provide
menting dynamic events, particularly the separation of mis
means for ascertaining the orientation of a moving object by 65 siles
from aircraft.
employing plane-polarized light.
Another object of the invention is to determine the attitude
of a missile following its launch from an aircraft.
A further object of the invention is to provide each of a plu
rality of cameras viewing a moving object with an optical indi—
cation on such object which indicates the latter’s attitude in
dependently of di?ering view stations and ?ow ?elds.
A still further object of the invention is to achieve the
foregoing results regardless of variations in camera ?lm speed.
TABLE OF SYMBOLS
A= Intersection of plane of vibration and plane of mirror.
E, = Direction of electric vector of the incident beam of
pla e-polarized light, (FIG. 1 ).
E: = Direction of electric vector of the re?ected beam of
plaPe-polarized light, (FIG. 1).
H, = Direction of magnetic vector of the incident beam of
plane-polarized light, (FIG. 1).
I
3,633,212
3
4
A, = Direction of magnetic vector of the re?ected beam of
in order that $2 also falls within the plane of vibration of the
re?ected ray; i.e., maximum light is re?ected from the ?lter
mirror combination:
plane-polarized light, (FIG. 1).
1i1= Unit normal to the plane of a source ?lter, (FIG. 4).
'62 = Unit normal to the plane of a re?ector ?lter, (FIG. 4).
(?.-1A1,..)(15lnl2fh.>=0
i),,,= Unit normal to a ?at mirror element, (FIG. 1).
(3)
If the ?rst term, Hriim, is zero, then the special case arises in
which the planes of vibration of both the incident and the
IA’, = Polarization direction of a source ?lter, (FIG. 2).
F; = Polarization direction of a re?ector ?lter, (FIG. 2).
re?ected rays are the same and are normal to the plane of the
mirror. In the most genAeikalAcase, the second term is zero:
S, = Incident beam direction (direction of Poynting vector),
and Iine-of-sight direction from source to re?ector, (FIGS. 1,
2, and 4).
S, = Re?ected beam direction, (FIG. 1).
(Hlnlnm
10 From (4), if the ?lter plane is parallel to the mirror plane ('i/izX
,,,=0), then any orientation of H, is permissible. From (3), if
HwiLf-O, then any orientation of the ?lter is permissible. In the
vectors, (FIG. 4).
most likely case, if 162 is not parallel to 4),“, then H, must be per
02 = Angle between jth and [cth re?ector ?lter polarization is pendicular to the line formed by 1% X ‘6",. Geometrically, this
0, = Angle between jth and kth source ?lter polarization
- vectors, (FIG. 4).
means that the incident magnetic vector must be perpendicu—
lar to the line of intersection of the mirror and ?lter planes for
111,= Angle between normal to source ?lter plane and line
of-sight vector, 5,, (FIG. 4).
maximum re?ected light intensity. From (4), the electric,
1112 = Angle between normal to re?ector ?lter plane and line
Poynting, and the two rkormalAvactorAs must be related by:
of-sight vector, S,_ (FIG. 4).
0, = Angle between a source ?lter polarization vector and 20
the line-of-sight vector, S,-, (F IG. 4).
62 = Angle between a re?ector ?lter polarization vector and
the line-of-sight vector, 3,, (FIG 4)_
subscripts:
Any rotation of the polarized ?lter about its normal by an
angle a away from that orientation in which 2 lies within the
plane of vibration of the incident ray will cause attenuation of
the transmitted ray’s intensity by the factor:
"Tm-A"
25
l = source polarization ?lter.
2 = re?ector polarization ?lter.
Attenuation Factor = COS‘ a
(6)
This is because the observed intensity of a light ray depends
upon its power, which in turn varies as the square of the elec
i = incident.
tric vector magnitude. The intensity of the re?ected ray after
j, k = identi?cation of different polarized beams; if beams
retransmission through the ?lter is multiplied by the same at
are color coded, these would identify parameters as
30 tenuation factor, (6), whether or not the conditions of equa
sociated with the jth and kth colors respectively.
tion (4) are complied with. Noncompliance with equation (4)
m = mirror element.
simply introduces an additional attenuation that is unrelated
to a. (Note: In tracing a ray from source, through the ?lter,
Note: All of the above vectors are of unit length only for the
re?ecting off the mirror, and back through the ?lter, the inten
purpose of showing direction.
sity of the ray at any point for 0z=0 is multiplied by the attenua
The essential elements of plane-polarizedlight re?ecting 35 tion factor in (6) only once to obtain the effects of a; (6) is the
from a mirror can, for the purposes of this invention, be
law of Malus.)
If the above mirror (or that shown in FIG. 1) is replaced by
a diffuse re?ecting surface consisting, by de?nition, of many
represented by the vectors shown inAFIG. 1 of the drawings. "9],,
is the normal to the mirror surface, H is the magnetic vector, é
is the electric vector, and
is the Poynting vector (where
randomly oriented mirror elements, each with its own 4),", then
S = E X H). (Note: In this discussion certain_aspects of plane; 40 'from equations (1) and (2) random orientations of E and Sr
ptllaiizgilght reflection from metallic or dielectric surfaces
will result from a single incident ray of polarized light having
have been neglected; the physical phenomena of the com
specific values of F1, and S,. If, further, a single polarized ?lter
ponent of the electric veptor parallel to the plane of incidence
is placed over the diffuse re?ector, as in FIGS. 6 and 7, then it
(described by vectors S and 17,") experiencing a different 45 is seen that many of the mirror elements of the re?ector will
phase shift and attenuation than the component perpendicular
comply with, or nearly comply with, the condition of max
to the plane of incidence are not considered. From experimen
tation, it appears that the dominant electric vectors of the
imum re?ected ray intensity speci?ed by equation (4). Thus,
the diffuse re?ector will appear illuminated from any view
re?ected light obey the above relationships. Therefore, while
angle subject only to the limitations imposed by equation (6).
FIG. 1 of the drawings is physically over-simpli?ed, it does 50 Further, for a completely diffuse re?ector, the randomness of
allow development of formulae which are correct for the spe
cial cases of polarized light re?ection to be set forth below.
4)," and hence of E, and S, is also complete, so the re?ector ap
pears equally illuminated regardless of view angle. The feature
Subscript i denotes vectors of the incident beam, while sub
of being able to view from any angle (with camera or eye) the
script r denotes vectors of the re?ected beam. The electric
results of changes in the angle a of a ?lter~diffuse-re?ector
vector of an electromagnetic wave, which is responsible for 55 sandwich is of key importance in the present concept.
A
optical phenomena, is used to determine the plane of vibration
Two polarized ?lters can be arranged as shown in FIG. 2. A
of polarized light in the development of the following formu
and P2 are unit vectors representing, respectively, the
direction of the intersection line between ?lter plane and
plane of vibration and the direction of ?lter polarization. Sub
FIG. I, which represents the most general Acase of plane 60 scripts I and 2 refer, respectively, to the ?lter over the light
las. Since the vector direction rather than magnitude is of pri
mary importance, all vectors shown will be unit vectors. From
polarized light re?ection, it is seen that both E, a/pd‘E, and S,
and Sr are symmetrical about @(while
source and the ?lter over the diffuse re?ector. The two ex
I and H, are not).
tremes of re?ector illumination, maximum and minimum (or
extin/ption), are shown with the associated relationships of A
and P2. From the condition for extinction, the following must
Therefore, the followin relationships result:
65
Placement of a polarized ?lteTa‘bove the mirror so that its
intercepts both the re?ected and the incident ray will cause
maximum or minumum attenuation of the ?nal re?ected ray
depending upon its orientation relative to the mirror and the
plane of vibration of the incident beam. If it is assumed that
the direction of polarization of the ?lter, represented by X32‘
(subscript 2 for re?ector, subscript 1 being used for light
source), falls within the plane of vibration of the incident
hold:
’
(7) i
Lln FIG. 2, the direction of the ray from the source to thef.
I re?ector can be represented by the Poyntingvector of the in-%
lcident polarized light, 3‘.- since (I51XS‘J sin 0, is _a_l_1_ni~t_normal_t_o
j the plane of vibration as well as to S‘, and since (pzXgirin 02
iis‘a unit vector normal to S‘, then when extinction occurs,
these two unit vectors are also perpendicular to each other
beam; then the following vector relationship de?nes the possi
ble orientations of the unit normal of the plane of the ?lter ‘$2, 75
‘and CaEIEILdEEiPE Se
3,633,212
6
polarized light 20 within the aircraft coordinate system will
sin 01 sin 02
reduce this uncertainty.
Should the light source 14 be a laser w?éh éiiiits P0167223
(8)
This, when developed, becomes:
A
A _ A_
A
A
A _ A
A.
(9)
given zyz
‘
light directly, rather than a conventional noncoherent source
behind a ?lter, the aboye equations are still valid, with P,
becoming identical with E,.
A _
(P1SZS’L)PZ— (P1S'LP2)S'L
sin 01 smr?z
a: :81
While the system shown in FIG. 3 increases the overall data
accuracy for relatively simply missile trajectories where rota
(A ,?2)=:isin 6, sin 02
A
A00) 10 tion is about one axis only, anomalies in angular data can arise
if the missile experiences combinations of roll, pitch, and yaw.
a.
.‘where 6, and 02 are the angles between S1 and P1 and P3 re
For this situation, two polarized light beams with nonparallel
spectivelyq The i sign arises because polarization Infection
of a ?lter has no positive. or negative sense; therefore equa
tion (llDagcgnmodates vectors of either sign‘ in representing
lpolarizatiohl
'
W-
Q
'1
m‘
‘
wwm?wi
‘m _
m
T
i
'
15
Application of the Invention Concept to Determine the At
1ltitude of a Missile Following Separation from an Aircraft
In FIG. 3 of the drawings is shown a missile 10 immediately
lfollowing its launch from an aircraft 12. A source 14 of plane
ipolarized light is carried on a pod 16 supported from the air
craft wing 12 by a pylon 18. Such source 14 may, for example,
:be a laser having both polarization and monochromaticity, but
‘in any event incorporates a lens developing a cone of illumina
tion 20 directed toward missile 10, as illustrated in the draw
,mg.
planes of vibration may be used. These two beams are color
coded by placing color ?lters 32 over both source and re?ec
tor polarized ?lters, as shown in FIG. 7. The analysis below
demonstrates the validity of this multibeam method.
The two polarized light beams (whose planes of vibration
are not parallel) are color coded with colors j and k. It is as
sumed that the two sources and the two sets of re?ectors are
so close together that, for analytical urposes, they share a
common line of sight represented by ,. The unit vectors for
this situation are shown in FIG. 4. For each colored beam, the
same development as used for equations (7) and (10) gives,
for extinction:
(it) are”
25
i A high-speed motion-picture camera 22 of standard design
1is also carried on pod 16, such camera having a ?eld of view
Since, as shown in FIG. 4, the j and k source ?lters are as
sumed at one point, and the j and k re?ector ?lters are as
i24, encompassing the separating missile 10.
An array 26 of re?ectors is attached to the surface or skin of
sumed at another point, so that g, is common to both polarized
rays; then the angle between j and k planes of vibration is con
stant along the line of sight between source point and re?ector
point. Another way of representing this is to state that the
lmissile 10. These re?ectors are impinged by the light from
:source 14, and lie within the ?eld of view 24 of camera 22.
‘Each re?ector of the array 26 may be in the form shown in
%FIG. 7 of the drawings, consisting of a polarizing ?lter 28 in
angle between theAunit normals to the, planes of vibration at
the source point, (P,, X ,)/sin 0,, and (P,kXS,)/sin 0",, is equal
‘front of a diffuse re?ector 30, the assembly being bonded
together into a thin ?exible “package” that can be pasted,
to the ngleAbetween the u it n rmals to S, at the re?ector
ftaped, or otherwise attached to the surface of missile 10. The
point,_( HXSJ/sin 62, and ( 2k>< .-)/sin 62k. (Note: Where P2]
'polarization direction of each of the re?ectors A, B, C, and D
i of array 26 in FIG. 3 is rotated a predetermined amount from
jthe preceding member so that the full 360° rotation is evenly
and 2k are for those re?ectors observed to experience extinc
tion.)Thus:
A
A
’
A
__g__
A
_
A
A
A
A
(P1,><Si) (Pik><Si)_i (P2,><Si) (P2,,XSi)
jdivided over the total number of re?ectors (although four are
fshown, any number can be used). The angular relationship
sin 01].
between the plane of polarization and the polarization of a
sin 01k
h
sin 02,.
I sin 02k
(13)
,i‘particular re?ector determines whether or not that re?ector
‘appears illuminated to the viewing camera 22. This condition 45
;of illumination as seen by the camera 22 is independent of the
i‘camera’s angular relationship to the re?ector, as long as it can.
1-'“see" any of the re?ector’s surface. The pattern of illumina
jtion or darkness in the array 26 of progressively arranged
ipolarized re?ectors then indicates the angular relationship
l'between the plane of polarization of illuminating light and the
(14)
missile on which the array is mounted.
'
or, since the dot products of unit vectors give the co!
sines of the angles between them:
The camera 22 thus views the array 26 of polarized-?lter
‘diffuse-re?ector “sandwiches” af?xed to the skin of missile
':10, and which are in turn illuminated with polarized light from
(source 14. The polarization direction of each re?ector A, B,
vcos ¢1—cos elj-cos 01k
sin 015-sin 61k
_
1" (15, is the angle tbet'ween the polarization vectors of the
‘C, and D of the array 26 (shown by a double-headed arrow in,
: periencing extinction, If; and Pzk. The angles ¢and (1:2 are
f
3
,
,
j‘shown the primary rotation would be about the pitching axis)
relative to the plane of vibration of the polarized light, succes
:‘?xed relative to the aircraft, and since the condition of re?ec
5
alone. Noting which of re?ectors A, B, C, and D extinguishes,E
and knowing the orientation of the plane of vibration of the,
known when the source‘?lters are installed on the aircraft and
the re?ector arrays (for colors j and k) are af?xed to the sur
face of the missile to be launched. A ground optical calibra
tion may be made before ?ight to measure all angles.
The unknown angles in equation ( l5) are 492i and 02,‘. These
I two angles are used to relate the polarization vectors of the
, extinguished re?ectors, P2j and P2,‘, to the line of sight
f represented by §,. Since, from ground calibration, P2 i and Pzk
I
l
70
conventional arrangements, only one camera station has an
‘
oblique view of a missile, then true pitch or yaw attitude rela
tive to the launching aircraft is very uncertain from this source
‘tion as to missile attitude is available. If, as often happens with
two 7
polarization vectors of; the twoA re?ector ?lters that are ex
ire?ector, so that a full revolution is divided into a number of
;'equal divisions. As the missile 10 rotates (in the example
ltor extinction (as well as the observability of the extinction) is
independent of pure translation of the missile (as long as equa
tions (7) and (10) are complied with), then angular informa
(15)
5 source ?lters, P,i and PH‘. ¢, is the angle between the
.‘FIG. 3) is, as above stated, rotated relative to the preceding
‘f‘sive re?ectors will show extinction according to equations (7)
for (10). Since the plane of vibration of the polarized light is
cos ¢2—cos 02, cos 02k
sin 02j-sin 02k
are known relative to the body axis system of the missile, then .
02,- and 021‘ will indicate the orientation of the missile to the
line of sight. However, since there are two unknowns, an addi
tional equation besides (15) is needed. To obtain the addi
tional equation, the condition of equal angles between normal
unit vector pairs at source and re?ector points is stated in a
75 manner similar to that in equation ( l3 ):
3,633,212
8
frame rate. Assuming the rotation rate of the plane of vibra
tion is at a constant predetermined value, the accuracy of this
clock depends upon the number of pasted-on re?ectors 26
and the ratio of vibration plane rotation to missile pitch or yaw
rate. The higher the vibration plane rotation rate (while not
approaching the movie frame rate) the less error the missile
rotation rate will introduce. However, if the rotation rate of
the plane of vibration is high, a time anomaly might occur in
that there could be an uncertainty between the time
references of two or more cameras of one or more revolutions.
For the above reason, several polarized beams of different
colors are rotated at different rates and in opposite directions
for greater precision and to eliminate the time anomaly with
the slowest rotating beam in the same manner as the hour
15 hand does on a conventional clock.
A
A
_
A
(PiiPikS'l')
.
A
The system shown in FIG. 5 of the drawings generates such
multiple beams of polarized light. All rotation rates and phase
_
(pzkpzilgzl
.
= 2.“.5
angles, as well as reference time marks for comparison with
sin 62i SID. 02k
(18)
Fig. 4 shows two unit normal vectors which are de 20 range time and synchronization of a strobe light source (op
‘ tional, if high intensity is needed), are controlled by a single
?ned as:
S111 0,5 sin 0,,
precision drive motor 34. FIG. 6 shows the re?ector arrays
which may be used in the system shown in FIG. 5. In principle,
A
sin ¢i
sin ¢2
,
_.
.
The angles between these unit normal vectors and the line of
sight are given by:
A A
A A
60-8 damn-91.605 IIIFnZ'St
these re?ector arrays are the same as those used in FIG. 3 for
(19)
.
(20)
w§ubst>ituting ( 19) and (20) into (18):
25
attitude determination.
As shown in FIG. 5, the plane of polarization of the illu
minating beam can be made to rotate by mechanically rotating
the polarizers 36, 38, and 40. The re?ectors constituting the
red, blue, and green arrays of FIG. 6 then illuminate or darken
30 in a cyclic pattern of the same frequency as that of the effec
tive rotation of the source ?lters 42, 44, and 46. This serves to
establish a “clock" on the missile (hence the term “clock ap
plique”). This “clock" functions as an optical time base re
there is now a second equation relating the unknown anglesl92k_
gardless of missile attitude or ?ow field as long as the re?ec
and 62J . However, two more angles have been introduced, ill,
and 1112. At the time of optical calibration, the two unit normal 35 tors of FIG. 6 can be seen by the camera and are impinged by
light from the system of FIG. 5.
vectors i7] and {)2, are known relative to the aircraft and mis- .
sin ¢1 cos r111 _ sin ¢>2 cos 11/2
sin 61,. sin 01k sin 02, sin 62k
(21)
sile coordinate systems respectively. From conventional photo
reduction techniques (i.e., not using any information available
from the polarized light phenomena), 3, can be determined in
the aircraft coordinate system by tracking the position in the
camera ?eld of view of the re?ector point. Thus, from (20), 1111
can be determined for each moment in time. (Note: A position
vector in the aircraft coordinate system relating the camera to
To achieve a “Vernier” effect, the polarizers 36, 38, and 40
can rotate at different speeds to simulate the hour, minute,
and second hands of a clock. The rotation of these polarizers
should be at a speed high enough so that the movement of the
missile l0 introduces a negligible error into the derived data.
The data derived and recorded on the ?lm of camera 22, as
well as on the respective ?lms of additional cameras if such
are used, is time-correlated by well-known techniques.
the polarized light source point is determined during pre?ight
45
Although the preceding description has been directed to the
optical and calibration.) 1112, the ?nal unknown, is determined
by trigonometry (see the lower portion of FIG. 4):
use of polarized light in obtaining kinematic data concerning
missile separation from aircraft, similar techniques can be
sin ‘112:: I 1
sin ¢2
2
/ cos 02k
_
2 cos 92’. cos 02, cos ¢2 _
used in a wide range of dynamic testing where conventional
+cos 262,. cos 4:2 +cos 262i SID 452
photoinstrumentation is presently employed. Digital compu
ters are ideally suited to converting the polarized light data
into a missile attitude history in any desired coordinate
The Clock Applique —Placing Time Marks on a Separating
system. In addition to the equations with which computers are
Missile for Time Synchronization of Viewing Cameras
presently programmed in order to convert moving-picture
The task of photo-instrumentation of missiles separating 55 data into trajectory data, additional programming to allow use
from aircraft is often made more difficult because of uncertain
of polarized-light data is possible by utilizing many of the
(22)
time calibration of events on the ?lm. This is because movie
frame rates can vary from their pre?ight measured values due
to such environmental factors as temperature changes (espe
cially units mounted in the free stream) and shock and vibra
tion (often caused by the launching impulse). A known ex
equations hereinabove developed.
Application of the polarized~light concepts described herein
requires consideration of the following to obtain maximum
data precision:
a. The number of progressive re?ectors in an array deter
pedient has been to impress a time mark on each ?lm border
from a precision time signal generator on the aircraft or
mines the angular difference between successive polarization
directions and hence the angular resolving power of the array.
received by radio (such as range time). However, this requires
b. The polarized light source must be of high enough inten
extra wires on the aircraft and more sophisticated movie 65 sity to overcome both light absorption in various ?lters and
cameras. Even then, the time signal is occasionally lost by one
background illumination in order that the contrast between an
or more cameras.
illuminated and an extinguished re?ector register on moving
One solution to the above problems is an application of
picture ?lm. A strobe light or high-power laser may provide
polarized light in a manner similar to that described above to
sufficient intensity provided the light pulse repetition rate
obtain missile attitude information. If, in FIG. 3, the plane of
equals that of the fastest moving picture frame rate used (for
vibration is made to rotate about the optical center line of the
missile separation studies this is normally up to 500 frames per
polarized light source 14, then the re?ectors A, B, C, and D
will experience extinction in cyclical succession. This action
c. It is desirable that the surface on which a re?ector is
second).
..
. .
.
recorded on the ?lm of camera 22 will provide the ?lm viewer
glued be as ?at as possible, since curvature would introduce
with a stepwise or digital “clock” independent of the camera 75
an uncertainty as to whether or not a re?ector had reached
9
3,633,212
10
“maximum extinction.
d. Operators of ?lm viewers will identify which re?ectors
covered by all of said {565mm equaling substantially
360°; and
experience extinction in each movie frame. Because of the
at least one light pickup means at said viewing location, said
above problems (i.e., a ?nite number of re?ectors in each ar
pickup means being arranged to intercept light returned
iray, washout of contrast due to absorption and background
lighting, and some surface curvature), it will be up to the
manent record of changes in the respective amounts
by each re?ector of said plurality and to make a per
thereof as said object undergoes motion with respect to
said viewing location.
I operator’s judgement as to when a particular array reaches
maximum extinction. This can be aided by interpolation
between neighboring re?ectors and over a sequence of several
2. The apparatus of claim 1 in which said light source is a
laser.
3. The apparatus of claim 1 in which said light pickup means
frames. It is possible to increase the angular sensitivity of each
re?ector over that of a single polarized ?lter (as given by the
law of Malus) by placing a second ?lter over the ?rst with its
polarization direction at a small angle to that of the ?rst one.
is a motion-picture camera.
as speci?cally described.
I claim:
polarized re?ectors are arranged in groups with the re?ectors
4. The apparatus of claim 1 in which each re?ector of said
Also, multiplicity of re?ector arrays and polarized beams will
plurality includes a polarizing ?lter and a planar diffusing
allow greater interpolation plus RMS averaging of several 15 member arranged in closely spaced parallel relationship.
readings to lessen any human error in judgement.
5. The apparatus of claim 1 in which said viewing location is
Obviously many modi?cations and variations of the present
an aircraft and said object is a missile launched therefrom.
invention are possible in the light of the above teachings. It is
6. The apparatus of claim 1 in which said light source is ar
therefore to be understood that within the scope of the ap
ranged to develop separate beams of light having different
20
pended claims the invention may be practiced otherwise than
chromatic characteristics, and in which said plurality of
of each group being responsive only to the impingement
1. Apparatus for ascertaining the positional characteristics
thereon of light having one of such chromatic characteristics.
‘,of an object undergoing motion with respect to a given view
7. The apparatus of claim 6 in which the chromatic charac
25
ing location, said apparatus comprising:
'
teristics of said light beams are those of the three primary
a source of plane-polarized light at said viewing location,
colors.
the light from said source being directed toward said ob
8. The combination of claim 7 in which the plane of
ject to illuminate the latter;
polarization of each of the separate beams of light developed
a plurality of polarized re?ectors carried by said object, the
by said source is caused to rotate in cyclic fashion.
polarization direction of each re?ector of said plurality
9. The combination of claim 8 in which the cyclic rotation
being rotated a given amount with respect to the remain
of each of the said separate beams of light is at a speed dif
ing re?ectors, and with the total polarization angle
ferent from that of the remaining beams.
35
45
50
55
60
65
70
75