System for measuring an estimated degree of linear polarization of an electromagnetic radiation reflected by a scene
View Patent ↗A system for determining an estimated degree of polarization of a radiation reflected) by a scene, including a first light source of a first electromagnetic radiation at a first frequency and rectilinearly polarized according to a first direction, a second light source of a second electromagnetic radiation at a second frequency greater than the first frequency and rectilinearly polarized according to a second direction non-parallel to the first direction, and a device of acquisition of an image of the radiation reflected by the scene including first pixels configured to capture the reflected radiation, each first pixel being covered with a rectilinear polarizer according to a third direction non-perpendicular to the first direction.
1 . System for determining an estimated degree of polarization of a radiation reflected by a scene, comprising:
a first light source of a first electromagnetic radiation modulated at a first frequency and rectilinearly polarized according to a first direction;
a second light source of a second electromagnetic radiation modulated at a second frequency greater than the first frequency and rectilinearly polarized according to a second direction non-parallel to the first direction; and
a device of acquisition of an image of the radiation reflected by the scene comprising first pixels configured to capture the reflected radiation, each first pixel being covered with a linear polarizer according to a third direction non-perpendicular to the first direction;
wherein the second frequency is equal to twice the first frequency, the method further comprising the following steps:
the acquisition by the first pixels of N tap samples I k of charges photogenerated by detection of the reflected radiation during shifted time periods T int , N tap being an integer number greater than or equal to five;
the determination of coefficients a n and b n , n being an integer number varying from 1 to 2, according to the following relations:
{
a
n
=
2
N
tap
1
sin
c
(
1
2
n
ω
T
i
n
t
)
∑
k
=
0
N
tap
-
1
I
k
cos
(
n
ω
kT
e
)
b
n
=
2
N
tap
1
sin
c
(
1
2
n
ω
T
i
n
t
)
∑
k
=
0
N
tap
-
1
I
k
sin
(
n
ω
kT
e
)
where ω is the pulse associated with the first frequency and where Te is the time period separating the beginnings of acquisitions of two successive samples;
the determination of coefficients c n according to the following relation:
c
n
=
a
n
2
+
b
n
2
the determination of the estimated degree of polarization DOP′ according to the following relation:
D
O
P
′
=
c
1
-
c
2
c
1
+
c
2
.
2 . System according to claim 1 , wherein the third direction is identical to the first direction.
3 . System according to claim 1 , wherein the second frequency is a multiple of the first frequency.
4 . System according to claim 3 , wherein the second frequency is twice the first frequency.
5 . System according to claim 1 , wherein the first frequency is the range from 25 MHz to 100 MHz.
6 . System according to claim 1 , wherein the second direction is perpendicular to the first direction.
7 . System according to claim 1 , wherein the acquisition device comprises no other rectilinear polarizers than the rectilinear polarizers according to the third direction.
8 . System according to claim 1 , wherein the acquisition device is further configured to deliver a depth image of the scene.
9 . System according to claim 1 , wherein the acquisition device is further configured for the acquisition of a 2D image of the scene and comprises second 2D image pixels.
10 . System according to claim 9 , wherein the acquisition device comprises a stack of a first sensor comprising the second pixels and of a second sensor comprising the first pixels.
11 . Method of determining an estimated degree of polarization of a radiation reflected by a scene, comprising the following steps:
emission by a first light source of a first electromagnetic radiation modulated at a first frequency and rectilinearly polarized according to a first direction;
emission by a second light source of a second electromagnetic radiation modulated at a second frequency greater than the first frequency and rectilinearly polarized according to a second direction non-parallel to the first direction; and
acquisition by an acquisition device of an image of the radiation reflected by the scene, the acquisition device comprising first pixels configured to capture the reflected radiation, each first pixel being covered with a rectilinear polarizer according to a third direction non-perpendicular to the first direction;
wherein the second frequency is equal to twice the first frequency, the method further comprising the following steps:
the acquisition by the first pixels of N tap samples I k of charges photogenerated by detection of the reflected radiation during shifted time periods T int , N tap being an integer number greater than or equal to five;
the determination of coefficients a n and b n , n being an integer number varying from 1 to 2, according to the following relations:
{
a
n
=
2
N
tap
1
sin
c
(
1
2
n
ω
T
int
)
∑
k
=
0
N
tap
-
1
I
k
cos
(
n
ω
kT
e
)
b
n
=
2
N
tap
1
sin
c
(
1
2
n
ω
T
int
)
∑
k
=
0
N
tap
-
1
I
k
sin
(
n
ω
kT
e
)
[
Math
24
]
where ω is the pulse associated with the first frequency and where Te is the time period separating the beginnings of acquisitions of two successive samples;
the determination of coefficients c n according to the following relation:
c
n
=
a
n
2
+
b
n
2
the determination of the estimated degree of polarization DOP′ according to the following relation:
D
O
P
′
=
c
1
-
c
2
c
1
+
c
2
.
[
Math
26
]