Note: Descriptions are shown in the official language in which they were submitted.
CA 02804006 2015-03-03
Attorney Docket No. 22182-73402
DEVICE AND METHOD FOR QUANTIFICATION OF GASES IN
PLUMES BY REMOTE SENSING
This application is being filed as PCT International Patent application in the
name
of Hager Environmental And Atmospheric Technologies, LLC, a U.S. national
corporation, Applicant for all countries except the U.S., and J. Stewart
Hager, a U.S.
residents, Applicant for the designation of the U.S. only, on 16 September
2010.
CROSS-REFERENCE TO RELATED PATENT APPLICATION
This application claims priority to PCT Inaternational Application Serial No.
PCT/U52010/040330, filed June 29, 2010, entitled "DEVICE FOR REMOTE SENSING
OF VEHICLE EMISSION," by J. Stewart Hager.
This application relates to and claims benefit of U.S.
patent application Serial No. 12/493,634, filed June 29, 2009, entitled
"DEVICE FOR
REMOTE SENSING OF VEHICLE EMISSION," by J. Stewart Hager.
Some references, which may include patents, patent applications and various
publications, are cited and discussed in the description of this invention.
The citation
and/or discussion of such references is provided merely to clarify the
description of the
present invention and is not an admission that any such reference is "prior
art" to the
invention described herein.
FIELD OF THE INVENTION
The present invention generally relates to remote detection of emission, and
more
particularly to an apparatus and method that utilize optical masses for
quantifying
absolute amounts of ingredients of a plume using remotely acquired infrared
and
ultraviolet images of the plume.
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BACKGROUND OF THE INVENTION
It is known that vehicle emissions are a major contributor to air pollution.
In
order to identify vehicles that are releasing excessive polluting emissions,
many countries
mandate annual vehicle emission inspections. To this purpose various vehicle
emission
inspection systems have been developed. Generally, these systems can be very
expensive, and their operation can require a vast amount of labor and skill.
Additionally,
emission inspection systems have traditionally been operated in testing
stations where the
emissions are measured when the test vehicle is idling or running under
artificially loaded
conditions. Although such measurements provide general baseline information
regarding
a vehicle's emissions and state of repair, it is not necessarily
representative of "real
world" driving conditions.
Recently, remote emission sensing systems have been developed for detecting
emissions of vehicles as they are driving on the road. For example, U.S.
Patent Nos.
5,319,199 and 5,498,872 to Stedman et al. discloses a remote sensing system in
which the
light source 1110 and detector 1130 are oppositely located on both sides of
the road 1101,
respectively, as shown in Fig. 11(a). For such an arrangement, a beam of light
1115
generated from the source 1110 passes through an exhaust plume 1140 emitted
from a
vehicle 1105 driven on the road 1101, thereby carrying an absorption signal
associated
with components and concentrations of the exhaust plume 1140. The beam 1115 is
collected by the detector 1130 for analyzing the components and concentrations
of
exhaust plume 1140. Alternatively, as shown in Fig. 11(b), the light source
1110 and
detector 1130 are located on the same side of the road 1101. And two
reflectors 1150
located on the opposite side of the road 1101 are used to reflect the beam
1115 generated
from the source 1110 to the detector 1130 with two passes through the vehicle
exhaust
plume 1140, which increases the absorption signal. This system measures only
part of
the plume and has to ratio the CO2 measurements to all other pollutants to get
relative
values. It does not measure the amount left behind or absolute values.
However, for such remote emission sensing systems, the source, detector and
reflectors are set up on both sides of the road, and much care needs to be
taken during
their installation and maintenance. Additionally, such a system is difficult
to operate
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with more than one lane of traffic particularly when more than one vehicle
passes through
the detector simultaneously. In other words, if multiple vehicles are present
at the
sensing location, each vehicle's exhaust plume may contribute equally to the
emission
measurement. Thus, on a single lane road, such as entrance and exit ramps, the
existing
remote sensing systems are not able to detect more than one exhaust plume at a
time.
Furthermore, with current remote sensing systems the precision of the
measurement can also depend on the position of the beam of light going across
the road
since the location of the vehicle's one or more exhaust pipes can vary from
vehicle to
vehicle. The precision of the emissions measured will vary depending on
whether the
beam is at the height of the tail pipe, or lower or higher where the exhaust
has time to
dilute before detection. With such an arrangement is also possible to miss the
exhaust
plume altogether.
Ultimately, the main drawback to current remote emission sensing is that since
it
only measures a portion of an exhaust plume it can only determine a plume's
constituent
gases and their relative concentrations. While such results can indicate if a
vehicle is in
need of repair, existing systems are not able to measure absolute amounts of
emission
components. Measuring absolute amounts of components is important since a
surfeit can
lead to severe air pollution. It is for this reason that many countries
statutorily limit the
amount of gas pollutants allowed in emissions. In fact, state and federal
vehicle
emissions standards and control requirements are stated in "grams per mile."
With
existing systems this value must be extrapolated from the ratios reported by
identifying
the vehicle make and model and making assumptions about whether the vehicle is
running rich or lean, the load on the vehicle, etc.
Quantitative imaging of gas emissions techniques has been patented. For
example, U.S. Patent No. 5,319,199 describes an elaborate system which uses
gas self-
emission radiation and gas filled cells. Unfortunately, the complexity of this
method is
unnecessary and cost prohibitive.
Therefore, a heretofore unaddressed need exists in the art to address the
aforementioned deficiencies and inadequacies.
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SUMMARY OF THE INVENTION
The objectives of the present invention are to measure absolute values of
ingredients in an exhaust plume using infrared and/or ultraviolet images of
the plume.
By measuring the percent absorption of individual pixels in the images and
their
projected area, one can calculate the total amount of a constituent in the
plume.
In one aspect, the present invention relates to a device quantifying absolute
amounts of ingredients of a plume. In one embodiment, the device comprises a
source
for emitting a beam of light and transmitting the emitted light through the
plume to a
surface on which the transmitted light is scattered and reflected; a detector
for acquiring
an image of the plume, where the acquired image contains information of
absorption of
the light scattered and reflected from the surface; and a processor for
processing the
acquired image to determine an absolute amount of at least one of components
of the
visible plume.
The processor is configured to perform the steps of choosing a plurality of
pixels
from the acquired image along a section crossing the plume, each pixel having
a pixel
area; characterizing an absorption rate of light of each chosen pixel from the
acquired
image; calculating the optical mass of each pixel from the characterized
absorption rate
of the pixel; multiplying the optical mass of a pixel and the corresponding
projected pixel
area to obtain the number of molecules in the pixel; and summing the number of
molecules of each pixel to obtain the total number of molecules in the visible
plume.
In one embodiment, Beer's Law determines the optical mass IA of each pixel:
iti = ¨ ln(/// )/K(v)
0 ,
where (Ho) is associated with the absorption rate, and K(v) is a monochromatic
absorption coefficient.
Light detection and ranging (LIDAR) is a broad term that includes scattering,
fluorescence, absorption, and differential absorption and scattering (DAS).
Differential
Absorption LIDAR (DIAL) is a commonly used technique to measure column
abundances of gases in the atmosphere. The method uses two different
wavelengths of
light to make the measurement. One wavelength is centered on to an absorption
feature
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of the target gas and a second wavelength closes to the first wavelength but
away from
the absorption feature. The two different absorptions are compared and the
column
abundance is calculated using the DIAL equation.
Detecting vehicle exhaust serendipitously allows one to use the DIAL equation
with just one wavelength. The second wavelength can be substituted with the
measurement using the first wavelength just before the vehicle arrives.
In one embodiment, the source comprises a black-body light source such as a
halogen light bulb or a "glowbar" gas igniter. Accordingly, the device further
has a
collimating or spreading optics for the emitted light and transmitting the
light through the
plume to the surface. The collimating or spreading optics comprise a first
concave mirror
and a second concave mirror positioned in relation to the source such that the
first
concave mirror receives the beam of light emitted from the source and reflects
the
received light to the second concave mirror, the second concave mirror, in
turn,
collimates or spreads the reflected light and transmits the light through the
plume to the
surface of the lane. The first concave mirror and the second concave mirror
define a
focus therebetween, and a chopper is placed on the focus.
In another embodiment, the source comprises one or more narrowband source like
LED devices or filtered broadband sources. In yet another embodiment, the
source
comprises one or more coherent sources or lasers.
In yet another embodiment, the source is the natural sunlight. As long as the
entire plume along with its "shadow" is imaged, all molecules are double-
passed by the
light. One can then retrieve the total amount of targeted molecules in the
plume using
double pass retrieval methods.
Additionally, the source can be modulated which enables the measurement of
light transmitted through hot exhaust since hot exhaust itself radiates
infrared light
relative to the colder background. When the active source is blocked by a
chopper or
turned off, a measurement of the emission of the exhaust is made. The emission
of the
exhaust plume can then be subtracted from the measurement when the active
source is
unblocked or turned on to obtain only the transmission of the hot exhaust.
Other well
known modulation/demodulation techniques can be used as well.
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Alternatively, a modulated source can be used such as LEDs and lasers to
achieve
the same effect.
The reflective surface can be the road itself or some form of retroreflective
material.
In one embodiment, the detector comprises at least one of an infrared camera
and/or an ultraviolet camera with narrow bandpass filters, wherein the filters
incorporate
the absorption bands of specific gases. In another embodiment, the detector
comprises a
detector array capable of capturing images of the plume and the surface. In
yet another
embodiment, the detector comprises a plurality of photosensors, each
photosensor
generating an electrical signal responsive of the received light, wherein the
electrical
signal is indicative of the absorption of the received light by the plume. In
one
embodiment, the detector comprises a spectrometer, a focal plane array, a
linear array, a
single element or any combination of them.
In a further embodiment, the detector comprises a detector array capable of
capturing images of the plume and the surface.
In one embodiment, the source comprises a halogen light source. Accordingly,
the device further has a collimating optics for collimating the emitted light
and
transmitting the collimated light through the plume to the surface. The
collimating optics
comprises a first concave mirror and a second concave mirror positioned in
relation to the
source such that the first concave mirror receives the beam of light emitted
from the
source and reflects the received light to the second concave mirror, the
second concave
mirror, in turn, collimates the reflected light and transmits the collimated
light through
the plume to the surface of the lane. The first concave mirror and the second
concave
mirror define a focus therebetween, and a chopper is placed on the focus.
In another embodiment, the source comprises a laser or modulated laser.
In another aspect, the present invention relates to a method for quantifying
absolute amounts of ingredients of a plume. In one embodiment, the method
includes the
steps of directing a beam of light through the plume to a surface on which the
beam of
light is scattered; acquiring an image of the plume, the acquired image
containing
information of absorption of the scattered light scattered from the surface;
and processing
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the acquired image to determine an absolute amount of at least one of
components of the
plume.
The processing step comprises the steps of choosing a plurality of pixels from
the
acquired image along a section crossing the plume, each pixel having a pixel
area;
characterizing an absorption rate of light of each chosen pixel from the
acquired image;
calculating optical mass of each pixel from the characterized absorption rate
of the pixel;
multiplying the optical mass of a pixel and the corresponding pixel area to
obtain the
number of molecules in the pixel; and summing the number of molecules of each
pixel to
obtain the total number of molecules in the plume.
In one embodiment, the image of the plume is acquired by an infrared camera
and/or an ultraviolet camera with narrow bandpass filters, wherein the filters
incorporate
the absorption bands of specific gases. In another embodiment, the image of
the plume is
acquired by a plurality of photosensors.
These and other aspects of the present invention will become apparent from the
following description of the preferred embodiment taken in conjunction with
the
following drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate one or more embodiments of the invention
and, together with the written description, serve to explain the principles of
the invention.
Wherever possible, the same reference numbers are used throughout the drawings
to refer
to the same or like elements of an embodiment, wherein:
Figs. 1(a)-1(e) illustrate a method of using the optical mass for quantifying
absolute amounts of ingredients of a plume according to one embodiment of the
present
invention;
Fig. l(f) shows an example for calculating absolute amounts of a plume from
its
image at chosen pixels, where each box represents a pixel in an image of the
plume, and
the percentages are the absorption in each pixel due to the target gas;
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Fig. 2(a) shows schematically a device for remote sensing of vehicle emission
according to one embodiment of the present invention;
Fig. 2(b) shows schematically an optical diagram of the remote sensing device
according to one embodiment of the present invention;
Fig. 3(a) shows schematically the device for imaging a first state of the lane
when
no detected vehicle arrives according to one embodiment of the present
invention;
Fig. 3(b) shows schematically the device for imaging a second state of the
lane
when the detected vehicle arrives leaving behind the exhaust plume according
to one
embodiment of the present invention;
Fig. 3(c) shows schematically the transmitted path of the beam of light;
Fig. 3(d) shows schematically the device, illustrating that the light source
and the
detector do not have to be in the same optical axis in order to double-pass
the whole
section of the plume;
Fig. 4 shows schematically a device for imaging the state of the lane
according to
another embodiment of the present invention;
Fig. 5 shows schematically a collimating and speading optics utilized in the
remote sensing device according to one embodiment of the present invention;
Fig. 6 shows the absorption lines at higher rotational energies follow the
Boltzmann Factor;
Fig. 7 shows schematically a collecting optics utilized in the remote sensing
device according to another embodiment of the present invention;
Fig. 8(a) shows schematically a device for scanning a laser across the roadway
according to one embodiment of the present invention;
Fig. 8(b) shows two possible wavelengths on a transmission spectrum which may
be used for DIAL according to one embodiment of the present invention;
Fig. 9(a) shows schematically a device scanning a single laser line across the
road
according to one embodiment of the present invention;
Fig. 9(b) shows schematically a device scanning multiple laser lines across
the
road according to one embodiment of the present invention;
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Fig. 10 shows schematically a device for imaging a plume emitted from a
factory
according to another embodiment of the present invention; and
Fig. 11 shows schematically a conventional device for remote sensing of
vehicle
emission.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is more particularly described in the following examples
that are intended as illustrative only since numerous modifications and
variations therein
will be apparent to those skilled in the art. Various embodiments of the
invention are
now described in detail. Referring to the drawings, like numbers indicate like
components throughout the views. As used in the description herein and
throughout the
claims that follow, the meaning of "a", "an", and "the" includes plural
reference unless
the context clearly dictates otherwise. Also, as used in the description
herein and
throughout the claims that follow, the meaning of "in" includes "in" and "on"
unless the
context clearly dictates otherwise. Additionally, some terms used in this
specification are
more specifically defined below.
The terms used in this specification generally have their ordinary meanings in
the
art, within the context of the invention, and in the specific context where
each term is
used. Certain terms that are used to describe the invention are discussed
below, or
elsewhere in the specification, to provide additional guidance to the
practitioner regarding
the description of the invention. The use of examples anywhere in this
specification,
including examples of any terms discussed herein, is illustrative only, and in
no way
limits the scope and meaning of the invention or of any exemplified term.
Likewise, the
invention is not limited to various embodiments given in this specification.
As used herein, "around", "about" or "approximately" shall generally mean
within 20 percent, preferably within 10 percent, and more preferably within 5
percent of a
given value or range. Numerical quantities given herein are approximate,
meaning that
the term "around", "about" or "approximately" can be inferred if not expressly
stated.
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As used herein, the term "LIDAR" is an acronym or abbreviation of "light
detection and ranging", and is an optical remote sensing technology that
measures
properties of scattered light to find range and/or other information of a
distant target.
Differential Absorption LIDAR (DIAL) is a commonly used technique to measure
column abundances of gases in the atmosphere.
As used herein, the term "optical mass" is a measure of the total number of
absorbing molecules per unit area occurring along the direction of propagation
of the
radiation in a gas sample.
As used herein, the terms "comprising," "including," "having," "containing,"
"involving," and the like are to be understood to be open-ended, i.e., to mean
including
but not limited to.
The description will be made as to the embodiments of the present invention in
conjunction with the accompanying drawings in Figs. 1-10. In accordance with
the
purposes of this invention, as embodied and broadly described herein, this
invention, in
one aspect, relates to an apparatus that utilizes the LIDAR technology to
detect emissions
of a vehicle as well as the amount of at least one of the pollutants emitted
from the
vehicle. The invented device is a portable or permanent roadside system for
detection of
exhaust emissions of a vehicle having internal combustion engines and driven
on a lane
of a road. While the conventional emission detection devices use mirrors or
retro
reflectors to return a beam of light emitted from a source and transmitted
through an
exhaust plume of the vehicle to a detector, the invented device uses the LIDAR
technology. The beam of light emitted from a source is directed downwards,
passing
through the exhaust plume, toward the surface of a traffic lane of a road on
which the
vehicle is driven. The transmitted light is then scattered at the surface of
the traffic lane.
The invented device collects the scattered light from the surface of the
traffic lane for the
detector to receive. Further, a detector array can be utilized to acquire
images of the
exhaust plume and the surface of the road for determining the intensity of the
received
light absorbed by the exhaust plume.
Specifically, the device utilizes the optical masses for quantifying absolute
amounts of ingredients of a plume using remotely acquired infrared and
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images of the plume. The optical mass is a measure of the total number of
absorbing
molecules per unit area occurring along the direction of propagation of the
radiation in a
gas sample such as a plume or vapor, i.e., ,u = D
molecules = 1 ¨ N molecules I , where P molecules is
the number density of molecules, 1 is the length of the cylinder, Nmoiecuies
is the number of
molecules in a unit area and A is the unit area. Accordingly, the amount of a
gas in a
plume is equal to the optical mass multiplied by the projected area of the
plume, that is,
Ncell ¨ * Atotalz the optical mass is multiplied by the area of the gas cell
perpendicular to
the direction of propagation of the radiation to acquire the total number of
molecules of
the specific gas in the cell. The total number of molecules can then be
divided by
Avogadro's number to get moles. Then the total mass of a specific gas in the
cell is just
the molar mass or atomic weight of the molecule multiplied by the number of
moles.
This technique is utilized with in situ devices to measure the concentrations
of pollutants
coming from an exhaust pipe. The in situ device draws the exhaust into a gas
cell
through a hose attached to the tailpipe, for the absorption to be measured.
Figs. 1(a)-1(e) illustrate the method/principle of using the optical mass for
quantifying absolute amounts of ingredients of a plume according to one
embodiment of
the present invention. Usually, the plume is observed from the top or side for
remote
sensing purposes. For the illustration of the present invention, the gas cell
is looked at
from the top and assumed as a cylindrical plume, as shown in Fig. 1(a). As
shown in
Figs. 1(b) and 1(c), a small disc is cut and divided into smaller individual
gas cells. Now
the light is propagating perpendicular to the length of the cell. As the light
propagates
through the top of the disc it will have different path lengths. Looking
through the top of
the disc one will see different absorptions due to the different path lengths,
as shown in
Fig. 1(d). Each small cell will approximately have a constant absorption over
the width
of the cell, shown in Fig. 1(e). Then, the area of the ends of the smaller
absorption cells is
calculated and multiplied by the optical mass of each cell to get the number
of molecules
in each cell. The N molecules are added in each small cell to get the total
number of
molecules in the disc, i.e., Ndzsc= E,U, = . The total number of molecules or
mass of a
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specific species in the disc is known. If the concentration of the chosen gas
is uniformly
mixed in the cell and the disc width is unit length, then the total number of
molecules is
Nmolecules ¨ Ndisc * 1. This number is the same as the first calculated number
along the
length of the cell.
As a vehicle travels down a road, it leaves a plume of exhaust behind. If one
can
take a section of the exhaust plume and count the molecules in the section,
one could
estimate the amounts of pollutants the vehicle is leaving behind. According to
the
present invention, images of the plume are acquired using infrared and/or
ultraviolet
cameras with narrow bandpass filters. These filters incorporate the absorption
bands of
specific gases. The images would show a plume coming out of the exhaust pipe
for a
specific gas.
Each pixel in the images can be considered of as detecting an individual light
beam with a gas cell in the path. The size and shape of these beams can be
calculated
using simple geometric techniques. The image of the road without a vehicle is
used to
measure the baseline intensity and then the absorption of a section of pixels
across the
plume is calculated, and thus, the change in optical mass of each pixel [Li is
calculated.
Then the each change in optical mass [Li is multiplied by the area Ai
perpendicular to
direction of propagation to get the number of molecules per pixel and those
quantities are
added together to get the total number of molecules of a specific gas in the
section of the
plume. Then, the number of molecules is multiplied by the atomic weight to get
the mass
of the targeted molecule in the section of the plume i.e., Nsection * AMU
(g/molecule) =
Ng.. The width of the section can be utilized to calculate grams per distance
the
vehicle is spewing out. Likewise with a fixed source, the speed of the flow
can be
utilized to calculate grams per time the source is spewing out.
According to the present invention, by examining a picture/image of an exhaust
plume, the amount of a substance in the plume can be determined. Fig. l(f)
shows an
example of the calculations needed to retrieve absolute amounts. Each box in
Fig. l(f)
represents a pixel in an image of the exhaust plume. The distance away from
the plume
is considered large enough so that each pixel has approximately the same area
from the
top to the bottom of the plume. The percentages are the absorption in each
pixel due to
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the target gas. These percentages can be found two ways. One way is by
comparing the
image of the road just before the car arrives to the image of the exhaust
plume. The
ratios of the reflected light from a source next to the camera will give the
percentages.
These percentages can also be found by DIAL (Differential Absorption LIDAR)
methods
using two different wavelengths of light, one at resonance and the other off
resonance.
Using Beer's law, the optical mass of each pixel is obtained. Then the area of
that pixel is
used to calculate the total number of molecules in that pixel.
For example, the band strength of a chosen band of Carbon Dioxide is:
K(Band)c02 = 0.9 cm-2 atm-1 at STP.
The units are converted into cm-1 [cm2 moll:
K(Band)c02 = (0.9 * 2.2414 * 104) cm-1 [cm2 mon
= 20173.0 cm-1 [cm2 moll.
Using the equivalent width method and for simplicity assuming the weak line
limit, we
know the equivalent width is equal to 413 and) = ,u . The equivalent width is:
W = f(_ exp(-413 and) = ,u)sl v or the total area of the absorption band.
The area of each pixel is about 20 cm * 20 cm = 400.0 cm2:
IA= - ln (Ho) /x(Band), and Number of Moles = IA *Area
Chosen [t= - ln (Ho) /x(Band) No. of Moles = IA *Area
Pixel No. (mol cm-2) (mol)
1 4.6751x10-6 1.8700 x 10-3
2 1.0446 x 10-5 4.1784x10-3
3 2.3697x10-5 9.4788x10-3
4 1.9118x10-5 7.6472x10
5 1.1685x10-5 4.6740 x 10-3
6 2.0236x10-6 8.0944x10-4
Total Mole Number 2.8658x10-2
Therefore, the absolute amount of CO2 in the chosen pixels is 2.8658x10-2 mol
or
2.8658x10-2 mol * 44.01 (g/mol) = 1.2612 g.
EPA, though, uses units such as (g/mi). To convert to (g/mi), (cm/mi) is
needed,
which is 1.6093x105 (cm/mi). The vehicle leaves behind 1.2612 g of CO2 every
20 cm, it
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is about 1.0148 x104 g of CO2 per mile.
Referring to Figs. 2(a) and 2(b), and particularly to Fig. 2(b), a device 100
for
remote sensing of vehicle emission is shown schematically according to one
embodiment
of the present invention. The device 100 includes a source 110, a detector 130
and an
optical collecting optics 150. The source 110 and the detector 130 define an
optical path
along which a beam of light travels from the source 110 to the detector 130,
and the
collecting optics 150 is positioned in the optical path. Further, the source
110, the
detector 130 and the collecting means 150 are located in the same side of the
road.
While in operation, a beam of light 112 emitted from the source 110 is
scattered,
in a 2n steradian hemisphere, at a surface 102 of the lane 101 of the road on
which a
vehicle 105 is driven. A received light 122, portion of the scattered light
120 along the
optical path, is collected by the concave mirror (the collecting optics) 150.
The collecting
optics 150, in turn, delivers the received light 122 of the scattered light
120 to the
detector 130 that is located at the focus of the collecting optics 150.
According to one embodiment of the present invention, the detector 130
comprises a camera with a focal plane array. The emitting light source
comprises a
halogen bulb and/or a glowbar such as natural gas igniter. In another
embodiment, the
detector 130 comprises a plurality of photosensors, thereby corresponding to a
plurality
of pixels. A pixel can be corresponding to one or more photosensors. To
clarify the
embodiments described as below, the case that one pixel corresponds to one
photosensor
is established therein the embodiments are based on. Nevertheless,
illustrations and
description are not intended to be exhaustive or be limited to the scope of
the invention
disclosed. Alternative pixel relatively to a plurality of photosensors is
possible as well.
The camera 130 for receiving the received light 122 shall be set next to the
source
110 and thus used to picture the state of the lane 101 as an imaging camera
for obtaining
the optical intensity of the received light 122. Since the detector 130 can be
used to
transfer the optical signals into electrical signals, the device 100
furthermore comprises a
processor 132 in communication to the detector 130 so as to process the
electrical signals.
For instance, referring to Fig. 3(a), when at least one part of the beam of
light 112
can be incident to one pixel 170 the detector 130 is characterized by, the
detector 130 in
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the first place can be used to picture the state of the lane 101 and to detect
a first optical
intensity of the received light 122 while no detected vehicle is passing
through.
Moreover referring to Fig. 3(b), after the vehicle 105 passes through the
surface
102 of the lane 101 and leaves behind the exhaust plume 140, the detector 130
further
images the state of the lane 101 and detects a second optical intensity of the
received light
122 transmitted through the exhaust plume 140. Under such circumstances, the
distance
away from the exhaust plume 140 is considered large enough so that the pixel
170 has
approximately the same area from the top to the bottom of the exhaust plume
140.
By comparing the former to the latter image, the processor 132 in
communication
with the detector 130 can not only process the electrical signals transferred
from the
optical signals of the received light 122 therein to provide one or more
spectra of the
received light 122 but also accordingly give the difference between the first
optical
intensity and the second optical intensity of the received light 122. Hence,
as shown in
Fig. 3(b), an attenuated ratio of the second optical intensity to the first
optical intensity of
the spectrum is obtained.
Besides, following by the detector 130, the processor 132 processing the
electrical
signals transferred from the optical signals of the received light 122 therein
measures a
detected area Am which is a cross sectional area of the exhaust plume 140 by
which the
received light 122 is absorbed. Referring to Fig. 3(c), when the beam of light
112 is
emitted from the vehicle 105, scattered, and collected by the detector 130, on
its
transmitted path exposed to the exhaust plume 140, a first area A1, a second
area A2, a
third area A3, and a fourth area A4 are formed. Hereby given the optimization,
the first
area A1, the second area A2, the third area A3, and the fourth area A4 are
about equal to
one another. The detected area Am, any of the four areas A1-A4, is measured.
On the account of Beer's law:
la = - ln(I/I0)/K(v).
The processor 132 can be used to obtain an optical mass independent of the
concentration
or the path length of the exhaust plume 140, wherein IA is the optical mass,
(Ho) is the
attenuated ratio and K(v) is a monochromatic absorption cross-section
corresponding to
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the spectrum. Multiplying the optical mass by the detected area Am, the
processor 132
can be utilized to give an amount of the determined component of the exhaust
plume 140.
In another embodiment of the present invention, the detector 130 may
furthermore
include a plurality of pixels 170 corresponding to a plurality of photosensors
160,
wherein one pixel 170 corresponds to one photosensor 160. The photosensor 160
can be
used to transfer the optical signals the detector 130 detects into electrical
signals thereby
the processor 132 comprised by the device 100 in communication to the detector
130 can
accordingly process with.
In operation, the detector 130 comprising a plurality of pixels 170 is located
next
to the source 110 so as to retrieve the state of the lane 101 as an imaging
camera. When
the vehicle 105 being detected arrives in the surface 102 of the lane 101, the
exhaust
plume 140 emitted from the vehicle 105 can also be pictured by the detector
130. Under
such circumstances, the distance away from the exhaust plume 140 is considered
large
enough so that each pixel has approximately the same area from the top to the
bottom of
the exhaust plume140.
The detector 130 is initially operated to acquire images of the surface 102 of
the
lane 101 when the vehicle 105 being detected has not arrived and therein the
exhaust
plume 140 is not formed yet so as to obtain the first intensity of the
received light 122.
After the vehicle 105 arrives and spews out the exhaust plume 140 which the
received
light 122 is transmitted through, the detector 130 again is utilized to
picture the exhaust
plume 140 so as to obtain the second intensity of the received light 122.
Alternately, in Fig. 3(d) the source 110 can be natural sunlight. As long as
the
entire plume 140 along with its' "shadow" is imaged, all molecules are double-
passed by
the light. One can then retrieve the total amount of targeted molecules in the
plume 140
using double-pass retrieval methods.
Practically, as shown in Fig. 4, each of the plurality of pixels 160 can be
corresponding to a portion of the received light 122 and a portion of the
total area A.
Thus, involving with the detector 130, the processor 132 accordingly measures
the pixel
area Ai, wherein the number i is a positive integer. In one embodiment, the
number i can
be number of six, and Ai comprises At, A2, A3, A4, As, and A6. The pixel area
Ai is the
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portion of the total area A. More accurately, the pixel area Ai is a cross
sectional area of
the exhaust plume 140 by which the portion of the received light 122 is
absorbed as
shown as A15 A25 A35 A45 A55 and A6.
Since each photosensor 170 can be used to generate an electrical signal
responsive
of the portion of the received light 122 in each pixel area Ai and each
electrical signal is
indicative of each optical difference in each pixel area Ai, representing each
absorption
percentage of the portion of the received light 122 absorbed by the exhaust
plume 140,
the processor 132 can be used to compare the image of the surface 102 of the
lane 101
just before the vehicle 105 arrives to the image of the exhaust plume 140.
More specifically, the processor 132 can be used to process the electrical
signals
transferred from the optical signals of the received light 122 to have the
absorption
percentage and accordingly to obtain a plurality of pixel ratios (I'/I0') as
numbers shown
in Fig. 4.
Each of the pixel ratios (I'/I0') is corresponding to each pixel area Ai,
wherein
the pixel ratio (I'/I0') is an attenuated ratio of the second optical
intensity to the first
optical intensity of the portion of the received light 122 in each pixel area
A.
In practice, the detector 130 comprising the plurality of pixels is utilized
along
with narrow band-pass filters. These filters incorporate the absorption bands
of specific
gases with a predetermined bandwidth thereof.
Hence, the processor 132 in communication of the detector 130 can be carried
out
to process the electrical signals transferred from the optical signals of the
received light
122 therein so as to determine one or more spectra of the received light 122
and further to
retrieve a plurality of sub optical masses p. Each of the sub optical masses
[Li is
corresponding to the pixel area Ai, and the pixel ratios (I'/I0') based on
Beer's law:
= - ln(F/I0')/K(v),
where [it is the sub optical mass, (I'/I0') is the pixel ratio is and K(v) is
a monochromatic
absorption coefficient corresponding to the spectrum of the portion of the
received light
122. Thereby the amount of the determined component can be summed up in the
numbers of the plurality of pixels 160 with each product of the sub optical
mass [it and
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the pixel area Ai, as E x Ai wherein the number N is a positive integer and
according
to one embodiment, the number N is six.
In another embodiment of the present invention, the detector 130 may
furthermore
comprise a detector array capable of capturing images of the exhaust plume 140
and the
surface 102 of the road.
In one embodiment, the processor 132 may have a computer and/or spectrometer.
The processor 132 can also demodulate the detected beam of light.
Alternatively, what is described above in the specification while the second
intensity and the first intensity of the received light 122 respectively
refers to the point of
time after and before the received light 122 passes through the exhaust plume
140 is not
limited. One can easily substitute the two point of time as a late occurring
point of time
and an early occurring point of time for the foregoing definition even though
both the
point of time happens after the exhaust plume 140 is formed and therein the
received
light 122 has passed through the exhaust plume 140. In such application, the
device 100
can still be applied to retrieve an amount of at least one of components of
the exhaust
plume 140 changed within a time period.
Additionally, the focal plane of the concave mirror 150 can be used to
position
several different detectors that image different sections of the road. One can
image a
strip of the road surface by using a parallel array detector.
Another embodiment involves using measurements using two filters imaging
bands which contain different cross-sections of the same gas and using the
DIAL
equation to retrieve absolute amounts.
Different light sources are utilized requiring different configurations and
detector
technologies. The light sources are pulsed or chopped in accord with lock-in
amplifiers
to increase sensitivity and to differentiate light sources.
A Broadband Source - Halogen Light Bulb: In one embodiment, a halogen light
bulb such as a car headlight is used as the source. For such a broadband
source, a
collimating optics can be utilized to collimate the beam of light emitted from
the halogen
light bulb and to transmit the collimated light through the exhaust plume to
the surface of
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the lane. As shown in Fig. 5, the collimating optics includes a first concave
mirror 361
and a second concave mirror 362 positioned in relation to the broadband source
310 such
that the first concave mirror 361 receives the beam of light 312 emitted from
the source
310 and reflects the received light 312 to the second concave mirror 362. The
second
concave mirror 362, in turn, collimates the reflected light 363 and transmits
the
collimated light 370 through the exhaust plume to the surface of the lane. The
first
concave mirror 361 and the second concave mirror 362 define a focus 365. At
the focus
365, the reflected light 363 is chopped with a wheel or bell chopper 366. The
chopper
signal is fed in to a dual-phase lock-in amplifier. The lock-in amplifier then
amplifies the
signal without adding noise.
This broadband source radiates from ultraviolet to infrared light out to 5pm.
This
covers strong fundamental absorption bands of CO and CO2 as well as strong
violet and
ultraviolet bands of NO2, NO and SO2. Filters can be used to isolate specific
bands of
these molecules, along with water vapor, hydrocarbons, ammonia and others.
A modulated halogen light source is strong in intensity and can be scattered
over
the complete lane. The modulation can be synchronized with the detector in
order to
eliminate the need for phase locking. This allows one to subtract the
background
radiation due to the hot car exhaust to only get the absorption due to the
exhaust. Mirrors
can be used to collect the light anywhere it is shining. Depending on the
focal length and
distance, these mirrors can image specific illuminated positions on to a
detector. This
allows different paths or position to be used to target different tailpipe
positions.
Narrow Band Sources: By filtering a broadband source or using LEDs, the need
for filtering the detector can be eliminated.
Diode Lasers: The telecommunication industry through mass production has
significantly lowered the cost of diode lasers. The telecommunication industry
uses fiber
optics and diode lasers to transmit large amounts of data, long distances.
Because of the
material of the fiber optics the average wavelength of these lasers is
approximately
1.5[Lm. There are infrared absorption bands of CO2, CO, H20, NH2 and others in
this
region. The laser diodes and InGaAs detectors are extremely inexpensive and
extremely
high quality because of the mass production and cost affectedness of
sensitivity of the
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products. This allows for detection of these bands even though some are
extremely weak.
Diode lasers can be used to remotely sense the temperature of exhaust, because
of
the Boltzmann factor and the extreme narrowness of a laser line. The thermal
distribution of rotational levels is not simply given by the Boltzmann factor
eT . The
number of molecules N, in the rotational level J of the lowest vibrational
state at the
temperature T is proportional to (G. Herzberg. Spectra of Diatomic Molecules,
2nd ed. D.
Van Nostrand Co. 1950):
¨BJ(J+1)hc I kT
AT j -- (2,1 +1)e
This infers the higher the J value or rotational energy the more the
exponential
term dominates. One can then back out the temperature of the exhaust using
this
relationship. Fig. 6 shows the spectra of CO2 in the 1.5 m region. The
Boltzmann factor
can be seen in the higher rotational energies. The absorption lines at higher
rotational
energies follow the Boltzmann Factor and therefore can be used to calculate
the
temperature of the exhaust.
Since the mixing ratio of molecules in the exhaust changes as a vehicle warms
up,
a cold car pollutes more than a hot one. One can detect the temperature along
with the
amount of gases in an exhaust plume using two or three different wavelength
lasers. One
can then adjust amount expectations due to the temperature of the engine and
tailpipe.
Diode lasers have an FWHM (Full Width at Half Maximum) in the range of about
6-10 MHz. This means it can sit on top of one absorption line. Different
wavelength
lasers can be selected to give the slope or shape of the Boltzmann factor.
Then the
temperature of the exhaust can be calculated. These lasers can be modulated at
different
frequencies. This allows the different detectors with lock-in amplifiers to be
used to
differentiate between the lasers illuminating the same spot.
According to the present invention, the detectors are positioned at the focus
of the
collecting optics.
Different sources need different detector systems. For a broadband light
source,
one or more filters are positioned in front of the detectors. Array detectors
can be used to
image strips of the road. This allows one to capture the entire exhaust plume
and then to
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get absolute amounts of the exhaust of a vehicle, irrelevant to the position
or height of the
tailpipe.
For a diode laser source, the source 610 and the detector 630 are placed on
the
same optical axis 655, as shown in Fig. 7. The spherical mirror 650 serves as
the
collecting optics for collecting the scattered light scattered from the
surface of the lane
and focusing the collected light onto the detector 630. The laser source is
brought into
the mirror housing with optical fiber. The laser can be outside of the
housing.
Referring to Fig. 8 and 9, one embodiment of the apparatus 818 uses coherent
light sources 803 or lasers and a broadband, single-element detector 812. One
or more
coherent light sources 803 emitting at different selected wavelengths are time-
modulated
802 by a controller 801. In the case of tunable diode lasers, the wavelengths
can be
selected by setting the temperature of each laser 803 with a corresponding
cooling device
804. The resulting time-modulated light beams are optically combined 805, and
sent
through positioning optics 807. The positioned light beam 806 passes through a
gaseous
plume 810, reflecting off of some substantially reflective material 809. The
reflected
light beam 806 passes through detection optics 811 and is focused into an opto-
electronic
detector 812. The electric signal from the detector 812 passes into a low-
noise amplifier
813. The detector 812 as well as the amplifier 813 can be placed in a cooling
mechanism
814 to increase the sensitivity and stability of the detection. The resulting
signal is then
passed through a demodulation circuit 815 and into an analog-to-digital
converter 816.
Ultimately the measurement is digitized and processed by the controller 801.
The results
can be locally displayed or recorded as well as transmitted to a remote
location by some
communication mechanism 817.
The controller 801 can be a computing device such as an embedded computer in
conjunction with application specific digital electronics such as a Field
Programmable
Gate Array (FPGA).
Each coherent source 803 emits at a specified wavelength, which is chosen to
detect the presence or absence of an absorption peak. When placed on an
absorption
peak 821, or "on line", a light source 803 can be used to measure the
concentration or
alternatively absolute amounts of gas in the light path 806. When placed on an
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absorption trough 822, or "off line" measurements with a coherent source 803
can be
used to eliminate the properties of the environment. In other words, it is
desirable to
know how much light returns to the detector over the path with a lower
sensitivity, but at
approximately the same wavelength. This is preferably done in the wings of the
in
between the lines. A differential absorption cross-section is calculated and
put in to the
DIAL (Differential Absorption LIDAR) equation.
For remote vehicle exhaust measurements, some gases of interest are CO, CO2,
02, NO, various hydrocarbons, etc. Since the absorption peaks 821 for such
gases exist
over a wide range of wavelengths including visible, ultraviolet and infrared,
it is
advantageous to pick measurement wavelengths which maximize signal-to-noise
while
using practical and cost-effective sources 803 and detectors 809.
The coherent sources 803 are typically cooled by a cooling mechanism 804. The
cooling mechanism 804 is typically a thermo-electric cooler in conjunction
with a
temperature measurement device such as a thermistor, which allows the
temperature of
the source 803 to be precisely controlled electronically with a feedback
control system,
for example. Adjusting the temperature allows some lasers to be tuned for
wavelength.
Controlling the temperature has the added benefit of avoiding temperature
drift, which
can inadvertently modulate the source 803. If the source 803 is substantially
stable at a
desired wavelength, the cooling mechanism 804 can be omitted simplifying the
design as
well as lowering its cost.
Since wavelengths of tunable lasers can be swept over many absorption peaks,
the
controller 801 can pick a peak which maximizes the signal-to-noise ratio.
Usually, it will
be a wavelength with the largest absorption and the lowest temperature
sensitivity for the
measured gas while not coinciding with any other present gases. Also, the
system can
pick a different wavelength in case it detects is some form of interference at
the existing
wavelength.
The output power of each coherent source 803 can be regulated as well. This
can
be done with a current feedback system or a photo-diode feedback system or a
combination of the two.
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The sources can be modulated by direct electrical stimulation 802 or
mechanically
using an electrically controlled shutter such as a chopper wheel or a liquid
crystal shutter.
One method of modulating the light source 803 in the time domain is using a
constant
frequency waveform such as a sine wave or square wave as well as other more
complex,
orthogonal patterns. Other time-domain modulation techniques, such as shifting
the
phase between two sources by 90 degrees, are possible as well.
Time-modulating the sources allows the system to ignore background signals or
noise by picking a modulation which avoids external light sources. This not
only
includes any ambient light sources, but also any light emitted by the hot
gaseous plume
itself The transmission of light through a plume can be then be consistently
measured
regardless of the temperature of the plume. Time-modulation also allows the
invention to
use a single detector 812 by placing each light signal in its own frequency
band which
can be separated electronically by a demodulation mechanism 815. This reduces
the
physical complexity of the design as well as replacing high-cost exotic light
detection
materials with low-cost demodulation electronics or digital computation.
Additionally,
time-modulation increases the sensitivity of the detector 812 by operating in
a band
where 1/f noise is lower.
If the sources 803 are not modulated separately in the time domain, other
means
can be used to detect each source. For example, the system can use multiple
detectors,
each tuned to a specific optical wavelength, one for each coherent source. One
method is
to use an optical filter in conjunction with each detector or even use the
detector's natural
bandwidth to discriminate each light source. Another method involves changing
the
polarization of each source and using detectors in conjunction with
polarization filters.
The function of the optical combiner 805 is to form the separate coherent
beams
from the sources 803 into a single light beam 806. The optical combiner 805
can be a
fused set of fiber optics or a reversed beam splitter, for example. The
optical combiner
can be eliminated if only one measurement wavelength is desired or if the
sources happen
to already be in a single beam or if separate positioning optics 807 are used
for each
source 803.
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Typically the positioning optics 807 is a spinning mirror connected to a speed-
controlled motor. The rotational speed of the motor determines how fast the
light beam is
scanned over an area of interest. The scan can be a single line 831 or a
series of lines 841
in some pattern which can be used to remotely detect the properties of the
gaseous plume
of interest. By scanning the light beam 806, the position of the gaseous plume
810 can be
determined. Since the speed of the scanning apparatus 807 is controlled, the
controlling
device 801 can correlate the measurement of the detector 812 with the position
of the
beam 806.
If the position of the plume is not desired, a line-generating lens 601 can be
used,
for example, eliminating the need for moving parts. The scanning apparatus 807
can be
omitted altogether if a single beam is sufficient for the desired measurement.
The reflector 809 can be made of various materials. Retro-reflective tape or
paint
can be used, for example. Alternatively, an array of mirrored corner cubes can
be
attached to the roadway. Other aspects over the choice of material involve
whether or not
the installation is temporary or permanent. The additional reflector 809 can
be omitted if
the roadway 808 or other pre-existing background feature is substantially
reflective so
that a suitable signal-to-noise ratio is achieved with the plume 810 of
interest. The
reflective surface 809 can be omitted altogether if the source and detector
are separated
such that the plume 810 is between the two. This requires two separate
controllers 801
and possible a phase-lock loop or other means to synchronize the two devices.
Since the reflective surface 809 is on a roadway 808 or some other
uncontrolled
area given to environmental wear-and-tear, it is reasonable to assume that the
reflection
will not be uniform over the area of the surface. Because this invention
divides the
measured region into substantially small beams 806, the reflection over any
one beam
806 will be mostly constant. Also, since the measurements can be made relative
to a
baseline measurement 203, the constant sources of attenuation will divide out
of the
calculations.
Since this embodiment uses an external reflective surface 809, both the
modulated
sources 803 as well as the detector 809 can be physically together 818, and
controlled by
a single controller 801. One advantage of this scheme is that since the
modulated sources
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and the detector can be controlled centrally, the modulated sources can be
synchronized
with the detector electronics. This eliminates the need for a phase-lock-loop
or other
synchronizing mechanism in the detector electronics.
The detection section of this embodiment includes focusing optics 811 as well
as
an electro-optical detector 812 connected to a low-noise amplifier 813. The
focusing
optics 811 allows the embodiment to image a large area, preferable large
enough to see
the entire plume of interest 810. The detector 812 can be a semi-conductor
photodiode or
a thermopile or any such sensitive detection device. The detector is made of a
material
that can detect light in the desired wavelengths. The low-noise amplifier 813
can consist
of any appropriate analog signal processing electronics able to suitably
extract the signal
of interest from the detector 812.
Conventionally, parallel light sources are utilized to measure gaseous plumes,
which is disadvantageous because it requires the measurement system to be as
large as
the plume itself. This can be impractical if the plume is very large such as
one from a
smoke stack. This embodiment of the invention uses focused light which allows
the
entire system 818 to be substantially smaller than the plume 810 itself or the
region of
interest and fit in a compact and practical space. This potentially makes the
device
unobtrusive and portable.
The opto-electronic detector 812 as well as the low-noise amplifier 813, can
be
cooled 814 to increase the sensitivity of the detection. Controlling the
temperature has
the added benefit of making the detector 812 more stable, eliminating unwanted
drift in
the measured signal. Various cooling techniques are possible including thermo-
electric
coolers, a Dewar flask containing some cryogenic liquid, or a Stirling engine.
If the
existing detector element 812 and the low-noise amplifier 813 are
substantially sensitive
enough, the cooling mechanism 814 can be omitted altogether saving cost and
simplifying the design.
While using only single broadband detector 812 is desirable to keep the system
simple, a series of narrow-band or otherwise band-limited detectors can be
used if there
isn't any one practical detector with contiguous band which contains all of
the
wavelengths of interest.
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Another embodiment replaces the single-element detector 812 with an array of
detectors. The detectors are arranged such that the position of each detector
element
corresponds with a desired measurement location. In this case the arrangement
of the
detectors will form an image of the plume of interest. Additionally, with the
combination
of both a positioning optics 807 and an imaging array, 3D measurements can be
made of
the gaseous plume or the vehicle or any other objects in the field of view
using well-
known photogrammetry techniques.
Yet another embodiment uses a diffuse, time-modulated broadband source in
conjunction with a focal plane array. The array elements can have one or more
optical
filters masking different areas of the FPA. A FPA can have a motorized filter
wheel
before, after or in between focusing elements of an imaging lens.
Alternatively, the
filters can be placed in front of the broadband source. This can improve the
signal-to-
noise ratio of the gaseous measurement over that of a coherent source by
encompassing
multiple absorption peaks. Temperature insensitivity can be achieved by
encompassing
individual absorption bands of a target molecule. The broadband source can be
modulated electronically or mechanically to help distinguish it from
background
radiation. Differently filtered broadband sources can be modulated at
different
frequencies to differentiate each target gas. Also, the source's position can
be modulated
so that a single element detector can be used. For example, an optical 1D or
2D spatial-
modulator such as a liquid crystal shutter can provide a separate modulation
for each
desired measurement position.
A further embodiment uses a series of narrow band sources. This embodiment
uses light sources which each cover a narrow band of wavelengths. Certain
light emitting
diodes (LED) can fill this requirement. This method is similar to using a
broadband
source in conjunction with an optical filter and can similarly improve the
signal-to-noise
ratio of the gaseous measurement by encompassing multiple absorption peaks.
Each light
source can be time-modulated as before and detected with a single detector or
a detector
array. With this approach, filters are not needed for the detector.
While this invention focuses on measuring car exhaust, it can be seen that the
invention is not limited to car exhaust, but can measure any form of gaseous
phenomenon
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within some field of view against some reflective background. Alternatively,
if the light
source and detector element are in line, a reflective background isn't
necessary.
Calculating optical mass from light intensity measurements can be generalized
by
the following equation:
At) = H(v)T(t) Odt)
where,
v is the wavelength of light.
t is the time of the measurement.
1(t) is a light intensity measurement at time, t.
H(v) = I 0(OH (OH f (01 d (u) is the system function.
10(v) is the intensity of the light source.
H (u) is the attenuation of the reflector.
H f (u) is the attenuation of the filter.
H d (1)) is the attenuation of the detector.
-1 ,,,(00,;(t)
4), t)= e -1 is the transmittance through the gaseous path, or
Beer's law.
(u) is a cross - section for molecule, i.
omi (v)is the optical - mass for molecule, i .
N is the number of molecules.
It is useful to divide an intensity measurement by a reference measurement at
some time, to to obtain a relative total transmittance.
fo 1/(077(1)10dt)
TTotal = co
Ato jo 1/(1477(1), to )th)
This way, if any part of H(v) is constant over the bandwidth, the constant
will
cancel out in the division. Usually one of the system terms in H(v) is
dominant for each
embodiment of the invention. For the embodiment with a broad-band source, 1-
/f(v) is the
dominant term and the other terms mostly cancel. For the embodiments of a
narrow-band
source and a coherent source, /0(v) is the dominant term, because of its
intensity
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overcomes low reflectance of the road surface. Any of these terms can change
over time
as a function of environmental conditions. As a result, with a good
characterization of
the dominant system term, accurate measurements can be made without needing to
characterize the other terms.
Also, if the optical mass terms at to are zero (such as in a vacuum) then,
T(v,to)=1,
and the equation simplifies to:
So H(U)T(U, OdU
/(to
fo H(OdU
Since all of the terms but omi(t) are measured or known or cancel, the
invention
can solve for omi(t). One way to calculate omi(t) is to perform a
computational numerical
solution using a well-known technique like Newton's Method or some similar
method.
Alternatively, a look-up table can be computed ahead of time for a range of
desirable
values, or an approximate curve can be fitted to TTotal(011) . If N=1, one
such curve is:
e¨cpom.
TTotal("Ii)
= 1
where a and b are the coefficients.
Once omi(t) is calculated we can in-turn determine absolute amounts or
concentrations.
If more than one cross-section exists in the measured band for the gases
present in
the path, there is no one-dimensional relationship between transmittance and
optical-mass
anymore. One way to use such a measurement is to take additional independent
measurements in other bands in order to form a system of equations. With a
sufficient
number of independent measurements the optical-masses can be found. For
example, if
the invention was configured to measure two bands, one band which contains CO
and
CO2, and another band which contains only CO, the measurement of the CO band
can be
removed from the measurement of the CO/CO2 band allowing the invention to in-
turn
calculate the optical mass of CO2. This method allows the invention to use
bands that are
cost-effective to measure due to the availability of sources, filters, and
detectors, but are
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WO 2012/002979 PCT/US2010/049151
heavily populated with cross-sections.
For a coherent source, the integrals are eliminated since we are mostly
measuring
a single wavelength and the responses H(v) cancel out if they are mostly
constant
between measurements to and t, plus the summation of optical depth is
eliminated if there
is only one element in the intersection of the set of non-zero cross-sections
at that
wavelength and the set of optical masses in the path.
e¨ici(vo)omi(t)
I( t) ¨Ki(vo)(0mi(t)-0mi(to))
_______________________________________ = e
I(t0) e¨ici(u0)0mi(to)
Again, if the optical mass at to is zero, the equation simplifies to:
____________________________________ = -K(v0) m(t)
I0 ,(t0)
As an alternative to taking measurements at two different times, the DIAL
method
can be used where measurements are taken using two coherent sources at
different
wavelengths, one on-line and the other off-line.
/, , ; t
(Ji 4 = ¨(K.1 = 1 (I)0 )) rni (t)
e
Iõ
,0 ,i
According to the present invention, by taking a picture of an exhaust plume
with
an infrared or ultraviolet camera, the total mass of a specific gas in that
plume is
calculated. In the case of vehicle exhaust left behind, one can remotely
measure specific
gases in the grams per distance. In the case of smoke stack plumes, one can
remotely
measure specific gases in grams per time the smoke stack is spewing out. All
these
measurements come directly from the pictures/images. The ability to remotely
measure
the number of molecules in a plume is made possible by optical mass. It does
not matter
whether the molecules reside in the path. It is like compressing all the
molecules in the
path into a 2-D flat surface. It is immaterial that the plume is not uniform
in
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WO 2012/002979 PCT/US2010/049151
concentration or path length. This technique simply counts the number of
molecules in a
beam of light.
In addition to the above applications, the device of the present invention can
find
applications in a wide spectrum of fields. For example, as shown in Fig. 10,
the device
can be used to detect and analyze the ingredients and its quantity of exhaust
emission/plume 1040 emitted from a factory 1001. The light source 1010 emits a
beam
of light and transmits the emitted light through an exhaust plume 1040 emitted
from the
factory to a surface 1002, where the transmitted light 1020 is scattered at
the surface
1002. The detector 1030 receives at least one portion of the scattered light
1020 scattered
from the surface 1002 and processes the received light therein so as to
determine an
amount of at least one of components of the exhaust plume 1040. The detector
1030 can
be a camera or a photosensor array for taking images of the exhaust plume
1040. Further,
the detector 1030 can be on a satellite for taking satellite images of the
exhaust plume
1040 for processing.
Other applications include, but not limited to, using the satellite images of
atmosphere of the earth to quantify ingredients of the atmosphere so as to
identify the
source of the global warming. Another application includes quantifying
ingredients and
amounts of an unknown plume/gas from its images/pictures taken remotely, which
may
gain a great deal of relevance in anti-terrorism.
In sum, the present invention, among other things, recites a remote sensing
device
that uses the LIDAR technology. The beam of light emitted from a source is
directed
downwards, transmitting through the exhaust plume, toward the surface of a
traffic lane
of a road on which the vehicle is driven. The transmitted light is then
scattered at the
surface of the traffic lane. A collecting optics is used to collect the
scattered light from
the surface of the traffic lane. The collected light is delivered to the
detector for
analyzing the components and providing an amount of the determined component
of the
exhaust plume. Additionally, according to the present invention, a detector
array can be
utilized to acquire images of the exhaust plume and the surface of the road,
which would
enable to unveil the whole picture of gas pollutants in the vehicle exhaust.
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CA 02804006 2015-03-03
The foregoing description of the exemplary embodiments of the invention has
been presented only for the purposes of illustration and description and is
not intended to
be exhaustive or to limit the invention to the precise forms disclosed. Many
modifications and variations are possible in light of the above teaching.
The embodiments were chosen and described in order to explain the principles
of
the invention and their practical application so as to activate others skilled
in the art to
utilize the invention and various embodiments and with various modifications
as are
suited to the particular use contemplated. Accordingly, the scope of the
present
invention is defined by the appended claims rather than the foregoing
description and the
exemplary embodiments described therein.
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