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  1. Description: Absolute Radiometry: Electrically Calibrated Thermal Detectors of Optical Radiation considers the application of absolute radiometry, a technique employed in optical radiation metrology for the absolute measurement of radiant power. This book is composed of eight chapters and begins with the principles of the absolute measurement of radiant power.
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CN102338664A
CN102338664ACN201010238090XACN201010238090ACN102338664ACN 102338664 ACN102338664 ACN 102338664ACN 201010238090X ACN201010238090X ACN 201010238090XACN 201010238090 ACN201010238090 ACN 201010238090ACN 102338664 ACN102338664 ACN 102338664A
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上海闻泰电子科技有限公司
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Abstract

The invention discloses a real-time background deduction method for target radiometry. A target, a background, an optical system, a scanning vibration lens, a first photoelectric detector, a second photoelectric detector, a signal processing system and a computer are used for achieving the real-time deduction method, wherein the optical system is used for imaging the target; when the scanning vibration lens vibrates, the target is imaged on the first photoelectric detector and the second photoelectric detector in turn; when the target is imaged on the first photoelectric detector, the background is imaged on the second photoelectric detector; when the target is imaged on the second photoelectric detector, the background is imaged on the first photoelectric detector; and the signal processing system is used for subtracting the signals of the first photoelectric detector and the second photoelectric detector in real time, thereby efficiently eliminating the influence of the background on the target radiometry in real time and acquiring an accurate target radiometry value. Compared with an afterward background deduction method, the real-time background deduction method for the target radiometry provided by the invention has the advantages that the instantaneity is better and the change of target radiation intensity can be reflected in real time.

Description

Translated from Chinese

一种目标辐射测量背景实时扣除的方法 A Target real-time radiometric background subtraction method

技术领域 FIELD

[0001] 本发明涉及一种测量技术,特别是涉及一种目标辐射测量背景实时扣除的方法。 [0001] The present invention relates to a measuring technique, particularly to a method for measuring a target background radiation subtraction real time.背景技术 Background technique

[0002] 目标的辐射特性是表征目标的重要数据,对其进行精确测量具有重要意义。 [0002] The radiation characteristics of the target data are important characteristics of the target, its is important for accurate measurement.目标辐射特性测量的困难之一是背景辐射的存在。 One of the difficulties target radiation characteristic measurement is the presence of background radiation.背景辐射的存在会影响目标辐射测量的准确度。 The presence of background radiation can affect the accuracy of target radiation measurements.尤其是对低信噪比目标,背景辐射的强度甚至远远大于目标本身的信号强度,将使目标的辐射测量几乎成为不可能。 Especially for low SNR target, background radiation intensity is far greater than even the goal itself signal strength, will radiometric target is almost impossible.因此,背景辐射的扣除,便成了目标辐射测量必须解决的关键技术之一。 Therefore, the background radiation is deducted, it has become the target radiation measurement must be solved one of the key technologies.

Rom yoshi island espanol zsnes. [0003] 对于背景辐射的扣除,以往解决的途径是事后扣除的方法,但如果背景的变化很大就会影响目标辐射测量的精度。 [0003] For background radiation deduction way in the past to solve is after the deduction method, but if the changes will affect the background of a large target radiation measurement accuracy.尤其在大背景小目标情况下,背景的细微变化或不稳定, 都会对测量结果造成较大影响,而且造成目标辐射测量的不准确。 In particular, in the context of small target, the background of subtle changes or instability, will lead to a greater impact on the measurement results and cause inaccurate radiation measurement target.目标辐射测量采用的事后背景扣除方法的另一个缺陷是实时性差,不能及时将背景辐射的扣除掉,因而不能实时反映目标辐射强度的变化。 Another drawback afterwards target background radiation measured by the subtraction method is poor real-time and can not be deducted background radiation, and therefore can not reflect real-time changes in radiation intensity target.

发明内容 SUMMARY

[0004] 本发明要解决的技术问题是为了克服现有技术的缺陷,提供一种标辐射测量背景实时扣除的方法,其在目标辐射测量中,即使背景变化很大,采用背景实时扣除方法仍能将背景辐射扣除,提取出目标辐射的数值,而且具有较高精度。 [0004] The present invention is to solve the technical problem to overcome the drawbacks of the prior art, to provide a standard method for real-time measurement of the background radiation subtraction, in which the target radiation measurement, even if a large change in the background, using the background subtraction method is still real background radiation can be deducted, the value of the extracted target radiation, and with high accuracy.

[0005] 本发明是通过下述技术方案来解决上述技术问题的:一种目标辐射测量背景实时扣除的方法,其特征在于,该方法通过目标、背景、光学系统、扫描振镜、第一光电探测器、 第二光电探测器、信号处理系统和计算机来完成,光学系统对目标成像,当扫描振镜作振动时,目标依次在第一光电探测器和第二光电探测器上成像,目标在第一光电探测器上成像时,第二光电探测器上对背景成像,目标在第二光电探测器上时,第一光电探测器上对背景成像,通过信号处理系统将第一光电探测器和第二光电探测器的信号实时相减,实时有效地扣除背景对目标辐射测量的影响,获得精确的目标辐射的量值。 [0005] The present invention is to solve the above problems by the following technical solution: A method for objective measurement of the background radiation subtraction real time, wherein the method through the target, a background, an optical system, a scanning galvanometer, a first photo detector, the second photo detector, and a signal processing system to complete a computer, an optical system for imaging target, when scanning galvanometer for oscillation, a first target sequentially imaged on the photodetector and the second photodetector, the target when imaged on the first photo detector, the background image, when the target on the second photodetector, the background image, the signal processing system by the first photodetector and the second photodetector on the first photodetector second photodetector signals in real time subtraction, effectively discounting the effect of real-time target background radiation measurements, to obtain an accurate value of the radiation target.

[0006] 优选地,所述第一光电探测器和第二光电探测器分别连接第一前置放大器和第二前置放大器,第一光电探测器和第二光电探测器分别测量目标和单独背景的模拟信号,模拟信号经过第一前置放大器和第二前置放大器放大后达到所需的电平,第一前置放大器和第二前置放大器与一差分放大器连接,差分放大器将两路模拟信号相减,将背景辐射信号扣除后获得目标信号,差分放大器与一整流电路连接,经整流电路将目标信号电压转换成单极性的目标信号电压,整流电路与一滤波电路连接,再通过滤波电路使目标信号电压直接表征目标辐射量的数值,目标信号电压表征的目标辐射量的数值经一数据采集系统输入到计算机进行分析处理。 [0006] Preferably, the first photodetector and the second photodetector are respectively connected to a first preamplifier and the second preamplifier, a first photodetector and a second photodetector and a measurement target are separately BACKGROUND an analog signal, an analog signal after the first preamplifier and the second preamplifier reaches the desired level, first preamplifier and the second preamplifier is connected to a differential amplifier, a differential amplifier the two analog subtracting the signals to obtain a target signal after deduction of background radiation signal, and a differential amplifier connected to a rectifier circuit, the rectified circuit converts the target voltage signal to a unipolar signal of a target voltage, a rectifying circuit and a filter circuit is connected, through the filter characterizing the target signal circuit voltage value of the target amount of radiation directly, the target value of the target amount of radiation characterized by a signal voltage of the data acquisition system to a computer for analysis.

[0007] 优选地,所述第一光电探测器和第二光电探测器采用的是Si-Pin光电二极管平面和防反射增透工艺的十元阵列探测器。 [0007] Preferably, the first photodetector and the second photodetector uses a Si-Pin photodiode and the planar process antireflection AR $ 10 detector array.[0008] 优选地,所述第一前置放大器和第二前置放大器采用两级放大电路,第一级放大电路采用高输入阻抗、高共模抑制比的BiMOS工艺的仪器放大器构成电流一电压变换器, 将电流信号变换为电压信号;第二级放大电路采用低噪声精密仪用放大器将前级送入的电压信号进行再次放大。 [0008] Preferably, the first preamplifier and the second preamplifier two-stage amplifier, a first stage amplifier circuit with high input impedance, high common mode rejection ratio BiMOS process instrumentation amplifier constituting the current-voltage a converter that converts the current signal into a voltage signal; a second stage amplifier circuit uses a voltage signal from the low noise precision instrument amplifier stage is fed to the front again amplified.

[0009] 优选地,所述差分放大器是精密仪用AD620型差分放大器。 [0009] Preferably, the differential amplifier is a precision instrument with AD620 differential amplifier.

[0010] 优选地,所述整流电路是全波精密整流电路。 [0010] Preferably, the rectifier circuit is a full wave precision rectifier circuit.

[0011] 优选地,所述滤波电路为是二阶压控电压源低通滤波器。 [0011] Preferably, the filter circuit is a voltage-controlled voltage source is a second order low pass filter.

[0012] 本发明的积极进步效果在于:本发明背景实时扣除方法所扣除的是同一时刻的背景,与背景的变化量大小无关。 [0012] The positive effect of the present invention is that the progress of: background subtraction method of the present invention, real-time background is deducted the same time, regardless of the amount of change in the size of the background.本发明目标辐射测量采用的实时背景扣除方法与事后背景扣除方法相比具有较好的实时性,可以实时扣除背景辐射的影响,实时反映目标辐射强度的变化。 BACKGROUND Real-time measurement of target radiation employed in the present invention compared to the background subtraction method and post subtraction method has better real-time, real-time discounting the effect of background radiation, the radiation intensity reflect changes in real target.

附图说明 BRIEF DESCRIPTION

[0013] 图1为本发明目标辐射测量背景实时扣除方法的工作原理示意图。 Be deducted schematic radiometric method works certain background [0013] FIG. 1 of the present invention.

[0014] 图2为本发明目标辐射测量背景实时扣除方法的实验方案示意图。 [0014] FIG. 2 is a schematic diagram of the method of real-time deduction of experimental measurement of the background radiation targets invention.

[0015] 图3为信号处理流程图。 [0015] FIG. 3 is a flowchart showing a signal processing.

[0016] 图4为前置放大器的电路原理图。 [0016] FIG. 4 is a circuit diagram of the preamplifier.

[0017] 图5为差分放大器的电路原理图。 [0017] FIG. 5 is a schematic circuit diagram of the differential amplifier.

[0018] 图6为全波精密整流电路原理图。 [0018] FIG. 6 is a full-wave precision rectifier circuit diagram.

[0019] 图7为二阶压控电压源低通滤波电路的原理图。 [0019] FIG. 7 is a second order low-pass filter a voltage controlled voltage source circuit diagram.

具体实施方式 Detailed ways

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[0020] 下面结合附图给出本发明较佳实施例,以详细说明本发明的技术方案。 [0020] The following drawings are given preferred embodiments of the present invention, to be described in detail in conjunction with the technical solutions of the present invention.

[0021] 如图1所示,一种目标辐射测量背景实时扣除的方法,其通过目标、背景、光学系统、扫描振镜、第一光电探测器、第二光电探测器、信号处理系统和计算机来完成。 [0021] As shown, a method for real-time measurement of the background radiation target subtracted, which is the target, a background, an optical system, a scanning galvanometer, a first photodetector, a second photodetector, a signal processing system and a computer To be done.光学系统对目标成像,在光学系统和第一光电探测器、第二光电探测器之间加入一个扫描振镜,在光学系统焦面上放置两个单元光电探测器。 Target imaging optical system, the optical system and the first photodetector, a second photodetector is added between a scanning galvanometer, two units placed at the focal plane photodetectors of the optical system.当扫描振镜作振动时,目标依次在第一光电探测器和第二光电探测器上成像。 When scanning galvanometer for oscillation, a first target sequentially imaged on the photodetector and the second photodetector.若目标在第一光电探测器上成像时,第二光电探测器上对背景成像,反之,目标在第二光电探测器上时,背景就在第一光电探测器上。 If the target when imaged on a first photodetector, a second photodetector of the background image, and vice versa, the second photodetector on the target, on the background in a first photodetector.由于两个光电探测器靠得很近(间距只有40 μ m),而目标是近似无限远,故可以认为背景在这两个光电探测器上是相同的。 As the two photodetectors in close proximity (spacing of only 40 μ m), and the target is to approximate infinity, it can be considered in this context are the same two photodetectors.通过信号处理系统将两个光电探测器信号实时相减,可以实时有效地扣除背景对目标辐射测量的影响,获得精确的目标辐射的量值。 The signal processing system by the two photodetectors subtraction signals in real time, real time effectively discounting the effect on the target background radiation measurements, to obtain an accurate value of the radiation target.

[0022] 如图2所示,目标光源发出的光经直径为0. 2mm的针孔后形成点目标,点目标发出的光经光学准直系统后变为平行光束,接着由扫描振镜反射给成像光学系统,经成像光学系统会聚,最后在第一光电探测器和第二光电探测器上形成目标像点。 [0022] As shown, the target 2 is formed by light from the source pinhole having a diameter of 0. 2mm after the point target, the collimating optical system optically emanating from an object point becomes a parallel beam, and then reflected by the scanning mirror to the imaging optical system, an imaging optical system converges, the final target image point formed on the first photodetector and the second photodetector.背景光源经毛玻璃在光电探测器上形成均勻的背景辐射,背景和目标的辐射光功率都能够分别控制。 BACKGROUND ground glass to form a uniform light source by background radiation on the photodetector, the light power radiated object from the background can be separately controlled.在实验光路中的扫描振镜,以一定周期调制目标信号,使点目标的像分别落在两个光电探测器上。 Scanning mirror in the optical path of the experiment, a constant cycle modulation target signal to the target point of the image falls on the two photodetectors respectively.扫描振镜由计算机控制,计算机通过波形发生器产生要求波形的电压,此电压再送给扫描振镜伺服驱动电路,实现扫描振镜的精确振动。 Scanning galvanometer generate a voltage waveform required by the waveform generator controlled by the computer, the computer, and then sent to the voltage driving scanning mirror servo circuit, accurate vibration of the scanning mirror.第一光电探测器和第二光电探测器接收目标和背景信号,经信号处理电路进行信号处理,实时扣除背景辐射的影响,提取出目标辐射量的数值,再输入计算机进行分析处理。 First photodetector and the second photodetector receives the target and a background signal, the signal processing by the signal processing circuit, discounting the effect of background radiation in real time, extract the value of the target radiation, and then entered into a computer for analysis.

[0023] 本发明实施例中信号处理流程如图3所示,根据信号处理的需要第一光电探测器和第二光电探测器分别连接有第一前置放大器和第二前置放大器,分别测量目标(含背景)和单独背景的模拟信号。 [0023] Examples of the signal processing in the embodiment of the present invention is shown in Figure 3, the signal processing required in accordance with the first photodetector and the second photodetector are respectively connected to a first preamplifier and the second preamplifier, were measured a target analog signal (including the background) and a separate context.来自目标通道和背景通道的模拟信号,经过第一前置放大器和第二前置放大器放大后达到所需的电平。 Analog channel signals from the target and background channels, after the first preamplifier and the second preamplifier reaches the desired level.第一前置放大器和第二前置放大器与一差分放大器连接,差分放大器将两路模拟信号相减,将很强的背景辐射信号扣除,获得单纯的目标信号。 First preamplifier and the second preamplifier is connected to a differential amplifier, a differential amplifier the two analog signals are subtracted, the strong background radiation signal is deducted to give pure target signal.差分放大器与一整流电路连接,经整流电路把正、负交变的目标信号电压转换成单极性的目标信号电压,整流电路与一低通有源滤波电路连接,再通过低通有源滤波电路使目标信号电压可直接表征目标辐射量的数值。 The differential amplifier is connected to a rectifier circuit, the rectifier circuit via the positive, negative alternating voltage target signal is converted into a unipolar signal of a target voltage, a rectifying circuit connected to a low-pass active filter circuit, and then through the low-pass active filter circuit the target value of the target signal voltage can be characterized by the amount of radiation directly.最后,目标信号电压表征的目标辐射量的数值经数据采集系统输入到计算机进行分析处理。 Finally, the amount of radiation a target value of the target signal voltage is characterized by the data acquisition system to a computer for analysis.

[0024] 本发明信号处理系统中的第一光电探测器和第二光电探测器采用的是Si-Pin光电二极管平面和防反射增透工艺的十元阵列探测器,实施例中只用了其中两个相邻探测单元,由于探测器是将接收到的光信号变成与之成比例的电流信号,但输出的电流信号极其微小,因此需要串接一个前置放大电路将微小的电流信号变换成电压信号,并且前置放大电路须增益可调。 [0024] The signal processing system of the present invention the first photodetector and the second photodetector uses a Si-Pin photodiode plane and antireflection AR process ten cell array detector, in the embodiment wherein only a two adjacent detection units, since the probe is received optical signal into a current signal proportional thereto, but the extremely small signal output current, it is necessary to connect a preamplifier converting small current signals into a voltage signal, and to be adjustable gain preamplifier circuit.第一和第二前置放大器的电路如图4所示,第一前置放大器和第二前置放大器采用两级放大电路,第一级放大电路采用高输入阻抗、高共模抑制比的BiMOS工艺的仪器CA3140型放大器构成电流一电压变换器,将微弱的电流信号变换为电压信号;第二级放大电路采用低噪声精密仪用0P-07型放大器将前级送入的电压信号进行再次放大。 A first circuit and a second preamplifier 4, the first preamplifier and the second preamplifier two-stage amplifier, a first stage amplifier circuit with high input impedance, high common mode rejection ratio BiMOS CA3140 process instrumentation amplifier constituting a current-voltage converter, the weak current signal into a voltage signal; a second stage amplifier circuit uses a voltage signal with low noise precision instrument amplifier 0P-07 into the preceding stage is amplified again .其中R2为调零电位器,用于调节电路的零位;R5为增益调节电位器,用于调节电路的增益。 Wherein R2 is zero potentiometer, for adjusting circuit zero; R5 is the gain adjustment potentiometer, a gain adjusting circuit.

[0025] 本发明信号处理系统中采用的差分放大器是精密仪用AD620型差分放大器,其电路如图5所示。 [0025] The signal processing system of the present invention is employed in a differential amplifier with a precision instrument AD620 differential amplifier, the circuit shown in FIG.与三运放差分放大电路相比较,三运放差分放大电路中,电阻的误差及温漂会造成增益不准和共模抑制比的降低;此外,集成运放的输入失调电压会造成整个差分放大电路的失调,并降低放大器的参数对称性和共模抑制比。 With three op amp differential amplifier circuit comparing three op amp differential amplifier circuit, the resistance drift may cause errors and allowed gain and common mode rejection ratio is reduced; In addition, integrated operational amplifier input offset voltage difference can cause the entire offset amplifier circuit, and reduces the amplifier parameters symmetry and CMRR.AD620型差分放大器采用高精度内置电阻,具有体积小、功耗低、精度高、噪声低和输入偏置电流低的特点。 AD620 differential amplifier built-in resistor with high precision, small volume, low power consumption, high precision, low noise and low input bias current characteristics.AD620型差分放大器在外接电阻可实现1〜1000范围内的任意增益。 AD620 differential amplifier may be implemented in any external resistor gain within the range of 1~1000.因此,背景实时扣除系统中采用AD620型差分放大器实现差分放大。 Thus, real-time deduction system uses a background differential amplifier AD620 differential amplifier implemented.

[0026] 本发明信号处理系统中整流电路采用的是全波精密整流电路,其电路如图6所示。 [0026] The signal processing system of the present invention, the rectifying circuit uses a full-wave precision rectifier circuit, the circuit shown in Figure 6.具有单向导电性的二极管是常用的整流元件,但二极管的非线性将产生相当大的误差, 特别当信号幅度小于二极管的死区电压时,问题尤为严重,因此由二极管构成的整流电路精度低。 A diode having unidirectional conductivity are common rectifying elements, the diode will produce a non-linear considerable error, especially when the signal amplitude is less than a diode voltage of the dead zone, a particularly serious problem, and therefore low precision rectifier circuit composed of a diode .为了提高精度,本发明的全波精密整流电路利用集成运放的放大作用和深度负反馈克服二极管非线性和正向导通压降造成的误差。 To improve the accuracy, precision full-wave rectifier circuit of the present invention utilize amplification of the integrated operational amplifier of the negative feedback and depth to overcome errors and nonlinear diode forward voltage drop caused.

[0027] 本发明信号处理系统中采用的滤波电路是二阶压控电压源低通滤波器,其电路如图7所示。 [0027] The filter circuit according to the present invention, the signal processing system employed in a second order low-pass filter a voltage controlled voltage source, the circuit shown in Figure 7.有源滤波器相对无源滤波器具有不用电感、体积小、重量轻等优点。 Active filter having a passive filter without relative inductance, small size, light weight and so on.集成运放的开环电压增益和输入阻抗均很高,输出电阻小,构成有源滤波电路后还具有一定的电压放大和缓冲作用。 Integrated operational amplifier open-loop voltage gain and input impedance are very high output resistance is small, also has a certain voltage amplification and buffer constitute the active filter circuit.

[0028] 为了验证本发明实施例的效果,分别对以下两种情况进行了研究:一是背景变化, 目标不变的情况;二是目标变化,背景不变的情况。 [0028] In order to verify the effect of the embodiment of the present invention, the following two cases were studied: one background change, the target unchanged; second target change, where the same background.在背景变化,目标不变的情况下,在背景与目标信号之比从36. 61逐渐变化到208. 63的条件下,基于扫描振镜的目标辐射测量背景实时扣除的方法能将很强的背景辐射扣除掉,提取出精确的目标信号,而相对误差在士0. 5%之内。 In the context change, the same target, the target to background ratio in the signals is gradually changed from 36.61 to 208.63 condition, based on a target scanning galvanometer radiometric method can be deducted BACKGROUND strong background radiation is deducted, the precise target signal is extracted, and the relative error is within 0.5% of the persons.在目标变化,背景不变的情况下,背景与目标信号之比从170. 79逐渐变化到5. 53时,该实时背景扣除方法依然能将较强的背景辐射扣除掉,提取出湮没在背景中的目标信号,并实时反映目标信号的变化量,相对误差在士1 %之内。 In the case where the target change, the same background, and the target than the background signals is gradually changed from 170.79 to 5.53, the real-time background subtraction method can still strong background radiation is deducted, the background is extracted annihilation the target signal and the target signal in real time to reflect the amount of change, the relative error is within ± 1% of the.通过上述实验可见,该目标辐射测量背景实时扣除技术的方法,可以将湮没在强背景辐射中的微弱的目标信号实时提取出来,具有较高的可行性。 Through the above experiment can be seen, the target background radiation measurement method be deducted art, it may be buried in a strong target signal weak real-time background radiation extracted with high feasibility.

[0029] 虽然以上描述了本发明的具体实施方式,但是本领域的技术人员应当理解,这些仅是举例说明,在不背离本发明的原理和实质的前提下,可以对这些实施方式做出多种变更或修改。 [0029] While the above described specific embodiment of the present invention, those skilled in the art will appreciate that these are merely illustrative, of the present invention without departing from the principles and spirit of the may be made in these embodiments multiple kinds of changes or modifications.因此,本发明的保护范围由所附权利要求书限定。 Accordingly, the scope of the invention defined by the appended claims.

Claims (7)

Translated from Chinese
1. 一种目标辐射测量背景实时扣除的方法,其特征在于,该方法通过目标、背景、光学系统、扫描振镜、第一光电探测器、第二光电探测器、信号处理系统和计算机来完成,光学系统对目标成像,当扫描振镜作振动时,目标依次在第一光电探测器和第二光电探测器上成像,目标在第一光电探测器上成像时,第二光电探测器上对背景成像,目标在第二光电探测器上时,第一光电探测器上对背景成像,通过信号处理系统将第一光电探测器和第二光电探测器的信号实时相减,实时有效地扣除背景对目标辐射测量的影响,获得精确的目标辐射的量值。 An objective measurement of the background radiation subtraction method in real time, characterized in that the method through the target, a background, an optical system, a scanning galvanometer, a first photodetector, a second photodetector, the signal processing system and a computer to complete , target imaging optical system, when the scanning galvanometer for oscillation, a target sequence on the first photodetector and the second photodetector imaging target imaged on a first photodetector, the second photodetector pair background image, when the target on the second photodetector, the first photodetector of the background image, the signal processing system by a first photodetector signal and a second photodetector real time subtraction, effectively in real time background subtraction impact on the target radiation measurements to obtain precise target radiation values.
2.如权利要求1所述的目标辐射测量背景实时扣除的方法,其特征在于,所述第一光电探测器和第二光电探测器分别连接第一前置放大器和第二前置放大器,第一光电探测器和第二光电探测器分别测量目标和单独背景的模拟信号,模拟信号经过第一前置放大器和第二前置放大器放大后达到所需的电平,第一前置放大器和第二前置放大器与一差分放大器连接,差分放大器将两路模拟信号相减,将背景辐射信号扣除后获得目标信号,差分放大器与一整流电路连接,经整流电路将目标信号电压转换成单极性的目标信号电压,整流电路与一滤波电路连接,再通过滤波电路使目标信号电压直接表征目标辐射量的数值,目标信号电压表征的目标辐射量的数值经一数据采集系统输入到计算机进行分析处理。 2. The target as claimed in claim 1 radiometric background subtraction method of real time, characterized in that the first photodetector and the second photodetector are respectively connected to a first preamplifier and the second preamplifier, the first a photodetector and a second photodetector analog signal of the target were measured and the background of the individual, an analog signal after the first preamplifier and the second preamplifier reaches the desired level, first preamplifier and two preamplifier connected to a differential amplifier, a differential amplifier the two analog signals are subtracted to obtain a target signal after deducting the background radiation signal, the differential amplifier is connected to a rectifier circuit, the rectified circuit converts the voltage signal into a unipolar target target signal voltage, a rectifying circuit and a filter circuit, characterizing value of the target amount of radiation is directly and then the target signal voltage by the filter circuit, value of the target radiation target signal voltage is characterized by a data acquisition system to a computer for analysis and processing .
3.如权利要求2所述的目标辐射测量背景实时扣除的方法,其特征在于,所述第一光电探测器和第二光电探测器采用的是Si-Pin光电二极管平面和防反射增透工艺的十元阵列探测器。 Radiometric target as claimed in claim 2 in real time background subtraction method of claim, wherein said first photodetector and the second photodetector uses a Si-Pin photodiode and the planar process antireflection AR ten cell array detector.
4.如权利要求2所述的目标辐射测量背景实时扣除的方法,其特征在于,所述第一前置放大器和第二前置放大器采用两级放大电路,第一级放大电路采用高输入阻抗、高共模抑制比的BiMOS工艺的仪器放大器构成电流一电压变换器,将电流信号变换为电压信号; 第二级放大电路采用低噪声精密仪用放大器将前级送入的电压信号进行再次放大。 Radiometric target as claimed in claim 2 in real time background subtraction method of claim, wherein the first preamplifier and the second preamplifier two-stage amplifier, a first stage amplifier circuit with high input impedance , high common mode rejection ratio BiMOS process instrumentation amplifier constituting a current-voltage converter, the current signal into a voltage signal; a second stage amplifier circuit uses a voltage signal from the low noise precision instrumentation amplifier front stage amplifying fed again .
5.如权利要求2所述的目标辐射测量背景实时扣除的方法,其特征在于,所述差分放大器是精密仪用AD620型差分放大器。 Radiometric target as claimed in claim 2 in real time background subtraction method of claim, wherein the differential amplifier is a precision instrument with AD620 differential amplifier.
6.如权利要求2所述的目标辐射测量背景实时扣除的方法,其特征在于,所述整流电路是全波精密整流电路。 BACKGROUND target radiometric method of claim 2 in real time subtraction as claimed in claim, wherein the rectifier circuit is a full wave precision rectifier circuit.
7.如权利要求2所述的目标辐射测量背景实时扣除的方法,其特征在于,所述滤波电路为是二阶压控电压源低通滤波器。 7. The target background radiation measurement method according to the real-time deduction in claim 2, wherein said filter circuit is a voltage-controlled voltage source is a second order low pass filter.
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  • G01J3/08Beam switching arrangements
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  • G01N21/17Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/31Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01MEASURING; TESTING
  • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using infra-red, visible or ultra-violet light
  • G01N21/25Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/35Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infra-red light
  • G01N21/3518Devices using gas filter correlation techniques; Devices using gas pressure modulation techniques
  • Abstract

    A system and method are provided for detecting one or more substances. An optical path switch divides sample path radiation into a time of alternating first and second polarized components. The first polarized components are transmitted along a first optical path and the second polarized components along a second optical path. A first gasless optical filter train filters the first polarized components to isolate at least a first wavelength band thereby generating first filtered radiation. A second gasless optical filter train filters the second polarized components to isolate at least a second wavelength band thereby generating second filter radiation. Spectral absorption of a substance of interest is different at the first wavelength band as compared to the second wavelength band. A beam combiner combines the first and the second filtered radiation to form a combined beam of radiation. A detector is disposed to monitor magnitude of at least a portion of the combined beam alternately at the first wavelength band and the second wavelength band as an indication of the concentration of the substance in the sample path.

    Description

    OPTICAL PATH SWITCHING BASED DIFFERENTIAL ABSORPTION RADIOMETRY FOR SUBSTANCE DETECTION

    Origin of the Invention

    The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

    Background of the Invention

    L_ Field of the Invention

    This invention relates to substance detection using optical systems. More specifically, the invention is a method and system for detecting the presence and/or concentration of a substance in a sample path using polarization-modulated optical path switching and the principles of differential absorption radiometry.

    2, Description of the Related Art

    Gas filter correlation radiometers (GFCRs) infer the concentration of a gas species along some sample path either external or internal to the GFCR. In many GFCRs, gas sensing is accomplished by viewing alternately through two optical cells the emission/absorption of the gas molecules along the sample path. These two optical cells are called the correlation and vacuum cells. The correlation cell contains a high optical depth of gas species i that strongly absorbs radiation at specific molecular transition wavelengths of the particular gas while passing all other wavelengths. In effect, the correlation cell defines a plurality of spectral notches (i.e., strong attenuation) coincident with the band structure of gas species i. The vacuum cell generally encloses a vacuum or a gas or gas mixture exhibiting negligible or no optical depth, e.g., nitrogen, an inert gas, or even clean dry air. An optical filter (e.g., interference filter) placed in front of the instrument or in front of the detector limits the spectral information to a region coinciding with an absorption band of the gas of interest. The difference in signal strength between these two views of the emitting/absorbing gas species i can be related to the concentration of this gas along the sample path.

    A known GFCR for measuring concentration of a single gas is disclosed in U.S. Patent No. 5,128,797, issued to Sachse et al. and assigned to the National Aeronautics and Space Administration (NASA), the specification of which is hereby incorporated by reference. The GFCR includes a non-mechanical optical path switch that comprises a polarizer, polarization modulator and a polarization beamsplitter. The polarizer polarizes light (that has crossed a sample path after originating from a light source) into a single, e.g., vertically polarized, component which is then rapidly modulated into alternate vertically and horizontally polarized components by a polarization modulator. The polarization modulator may be used in conjunction with an optical waveplate. The polarization modulated beam is then incident on a polarization beamsplitter which transmits light of one component, e.g., horizontally polarized, and reflects light of a perpendicular component, e.g., vertically polarized. The transmitted horizontally polarized beam is reflected by a mirror, passes through a gas correlation cell and on to a beam combiner. The reflected vertically polarized beam passes through a vacuum cell, is reflected by a mirror and is passed on to the beam combiner. The beam combiner recombines the horizontal and vertical components into a single beam which passes through an optical interference filter that limits the spectral content of the incoming radiation to an absorption band of the gas species of interest. The single beam is then incident on a conventional detector. However, this system is limited in that it can only measure a single gas concentration.

    A GFCR for measuring multiple gases based on the same optical path switching technique is disclosed in U.S. Patent application, serial number 09/019,473, filed February 5, 1998, by Sachse et al. and assigned to the National Aeronautics and Space Administration (NASA). In this system, each optical path contains one or more cells with each cell having spectral features of one or more gases of interest. The two optical paths are then intersected to form a combined polarization modulated beam which contains the two orthogonal components in alternate order. The combined polarization modulated beam is partitioned into one or more smaller spectral regions of interest where one or more gases of interest has an absoφtion band. The difference in intensity between the two orthogonal polarization components in each partitioned spectral region of interest is then determined as an indication of the spectral emission/absorption of the light beam along the sample path. The spectral emission/absorption is indicative of the concentration of the one or more gases of interest in the sample path.

    Both of the afore-described systems require the use of gas correlation cells. However, there are instances where gas correlation cells are not practical. For example, some gases are too dangerous and/or require a gas correlation cell construction that is too expensive for a particular application. Further, some gases such as ozone are too reactive to contain in a gas cell. Still further, it may also be desirable to detect/measure a broad category of gases, e.g., hydrocarbons. However, to accomplish this with a GFCR system, many gases would have to be contained within one cell or the beam would have to be passed through multiple gas cells. This complicates construction and adds to overall system expense. Still further, gas correlation cells are not useful for measuring spectral absorption characteristics of solids or liquids because these substances have broad absorption features.

    Summary of the Invention

    Accordingly, it is an object of the present invention to detect/measure any type of substances (i.e., gas, liquid or solid) in a non-mechanical optical fashion without the need for gas correlation cells.

    Another object of the present invention is to provide a method and system for detecting/measuring broad categories of gases using optical path switching techniques.

    Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.

    In accordance with the present invention, a system and method are provided for detecting one or more substances. An optical path switch receives radiation passing along a measurement or sample path of interest. The switch divides the radiation into a time series of alternating first polarized components and second polarized components that are orthogonal to the first polarized components. The first polarized components are transmitted along a first optical path and the second polarized components along a second optical path. A first gasless optical filter train disposed in the first optical path filters the first polarized components to isolate at least a first wavelength band thereby generating first filtered radiation. A second gasless optical filter train disposed in the second optical path filters the second polarized components to isolate at least a second wavelength band thereby generating second filtered radiation. The first wavelength band and second wavelength band are unique. Further, spectral absorption of a substance of interest is different at the first wavelength band as compared to the second wavelength band. A beam combiner disposed to receive the first and second filtered radiation combines same to form a combined beam of radiation. A detector is disposed to monitor magnitude of at least a portion of the combined beam alternately at the first wavelength band and the second wavelength band as an indication of the concentration of the substance in the sample path.

    Brief Description of the Drawings

    FIG. 1 is a schematic representation of one embodiment of a substance detection system according to the present invention;

    FIG. 2 is a graphical illustration of the filter characteristics of the bandpass filters used in the FIG. 1 embodiment;

    FIG. 3 is a schematic representation of another embodiment of the present invention in which two substances can be detected/measured simultaneously;

    FIG. 4 is a graphical illustration of the filter characteristics of the bandpass filters used in the FIG. 3 embodiment;

    FIG. 5 is a schematic representation of another embodiment of the present invention in which bandpass filters are used in reflection;

    FIG. 6A is a graphical illustration of one filter's characteristics used in the FIG. 5 embodiment;

    FIG. 6B is a graphical illustration of the other filter's characteristics used in the FIG. 5 embodiment;

    FIG. 6C is a graphical illustration of a bracketing bandpass filter's characteristics used in the FIG. 5 embodiment;

    FIG. 6D is a graphical illustration of the spectral information reaching the detector in the FIG. 5 embodiment;

    FIG. 7 is a schematic representation of another embodiment of the present invention in which differential absorption measurements and gas filter correlation radiometry (GFCR) measurements are made simultaneously;

    FIG. 8 is a schematic representation of another embodiment in which two substances can be detected/measured simultaneously using bandpass filters in reflection;

    FIG. 9 is a schematic representation of another embodiment in which three substances can be detected/measured simultaneously; and

    FIG. 10 is a schematic representation of another embodiment of the present invention.

    Detailed Description of the Invention

    Referring now to the drawings, and more particularly to FIG. 1, one embodiment of a substance detection system according to the present invention is shown and referenced generally by numeral 10. By way of example, the present invention will be described as it relates to the detection, measurement and/or characterization of substances in the gaseous state. However, the present invention can be used to detect, measure and/or characterize any substance, i.e., gas, liquid or solid, that exhibits spectrally varying absorption characteristics.

    System 10 includes an optics system 12, e.g., a telescope or other lens/mirror system, that collects light from a radiation source 11 such as the earth and atmosphere when system 10 is mounted on a satellite or aircraft, a blackbody when system 10 is used as a laboratory or in-situ instrument, the sun, a laser, etc. Radiation from source 11 generally comprises both vertically polarized components V and horizontally polarized components H. The radiation passes between source 11 and system 10 along a sample path SP. The presence of a substance or substances of interest along path SP may affect the radiation in a way that can be detected, measured and/or characterized by system 10. An optical path switch provided after optics system 12 includes an optical polarizer 14, an optical waveplate 16, a polarization modulator 18 and a polarization beamsplitter 20. Such an optical path switch is disclosed in detail in the afore-mentioned U.S. Patent No. 5,128,797 to Sachse et al., and will therefore only be described briefly herein.

    Optical polarizer 14 is provided after the optics system 12 and is aligned to polarize the incoming radiation in the desired fashion, e.g., vertically in the embodiment depicted in FIG. 1. Polarization modulator 18 (e.g., a photo-elastic modulator) then receives the incident vertically polarized beam and rapidly modulates the output beam between vertical and horizontal polarization. Depending on the measurement application and the type of polarization modulator utilized, the polarization modulation frequency may range from near DC to radio frequencies (RF). The polarization modulator may be used in conjunction with optical waveplate 16. The output of modulator 18 is a time series of alternating vertically polarized components V and horizontally polarized components H as illustrated in FIG. 1. The switching frequency between N and H is determined by the modulation frequency of modulator 18.

    Polarization beamsplitter 20 non-mechanically switches the polarization modulated output beam between two paths by, for example, transmitting the beam along path 101 when it is vertically polarized and reflecting it along path 102 when it is horizontally polarized. Alternatively, beamsplitter 20 may be oriented so as to reflect vertically polarized light and to transmit horizontally polarized light. Thus, beamsplitter 20 rapidly diverts the radiation beam alternately between optical paths 101 and 102 depending on the rapidly time-varying state of polarization which is controlled by modulator 18. Note that although paths 101 and 102 are illustrated as being perpendicular to one another, this need not be the case as will be apparent in other embodiments of the present invention described later below.

    The radiation beam transmitted along optical path 101 is incident on a gasless optical bandpass filter 22 configured to transmit only a wavelength band of radiation centered at λA while reflecting other wavelengths. The radiation beam transmitted along optical path 102 is incident on a second gasless optical bandpass filter 24 configured to transmit only a wavelength band of radiation centered at λB while reflecting other wavelengths. Filters 22 and 24 are selected/constructed such that the bands centered at λA and λB are unique as illustrated in FIG. 2. Further, the spectral absorption of the substance to be detected, measured and/or characterized must be different at the two bands. The greater the difference in spectral absorption characteristics between the two bands, the greater the measurement sensitivity of system 10. Accordingly, in an example of the ideal case, spectral absorption occurs only in the band centered at λA (i.e., spectral absoφtion in the band centered at λB would be zero). However, it is to be understood that the present invention will work as long as there is some difference in spectral absoφtion (of the substance of interest) between the two bands.

    The resulting filtered radiation beams passed along optical paths 1.01 and 102 are directed/reflected by mirrors 26 and 28, respectively, to a polarization beam combiner 30 (e.g., a polarization beamsplitter). Beam combiner 30 outputs a single beam along path 103 in which the beam's polarization state varies in time at the fundamental frequency (and harmonics thereof) of modulator 18. In other words, the output of beam combiner 30 is essentially a time series that alternates between the vertically polarized components V passed by filter 22 and the horizontally polarized components passed by filter 24. The combined radiation beam passes along optical path 103 and is focused by focusing optics 32 onto a detector 34 which is sensitive to the magnitude of the radiation. Because this radiation is in the form of an alternating time series, detector 34 is essentially viewing an amplitude modulated signal. This is because a gas (or other substance) present along sample path SP absorbs radiation from radiation source 11 differentially at the bands centered at λA and λB. Thus, the differential absoφtion experienced by the radiation traversing sample path SP is viewed by detector 34 as an amplitude modulated signal. The magnitude of the amplitude modulated signal at the polarization modulation frequency (or its harmonics) is related to the amount or concentration of the substance of interest in sample path SP. Note that if system 10 is subject to changes in the incident radiation due to variations in strength of radiation source 11, turbulence noise, scattering along the optical paths, etc., it may be desirable to normalize the amplitude modulated signal sensed by detector 34. If this is the case, the amplitude modulated signal can be divided by the DC component sensed by detector 34 as is well known in the art.

    By way of illustrative example, the present invention will be described briefly for its use in the measurement of hydrocarbons. In this case, filter 22 is chosen so that the band centered at λA coincides with the carbon-hydrogen bond absorption typical of hydrocarbons (i.e., λA is approximately 3.4 microns). Filter 24 is chosen so that the band centered at λB coincides with a wavelength band that is relatively free from hydrocarbon absorption (i.e., λB is approximately 3.0 microns). By monitoring the magnitude of the amplitude modulated signal sensed by detector 34, the absoφtion by hydrocarbons present in sample path SP can be detected and measured in a simple fashion, i.e., multiple GFCR devices with multiple gas filter correlation cells (e.g., one for each hydrocarbon of interest) are not required.

    Although described relative to the embodiment in FIG. 1, the present invention is not so limited. For example, another embodiment of a substance detection system in accordance with the teachings of the present invention is shown and referenced generally by numeral 200 in FIG. 3. Like reference numerals will be used for those elements that are the same as those used in the FIG. 1 embodiment. The embodiment in FIG. 3 is similar to that in FIG. 1 except that filters 22 and 24 are replaced with dual bandpass filters 220 and 224, respectively. Specifically, filter 220 passes unique wavelength bands centered at λA1 and λ^ to mirror 26 with other wavelengths being reflected. Filter 224 passes unique wavelength bands centered at λB] and λB2 to mirror 28 with other wavelengths being reflected. The bandpass characteristics of filters 220 and 224 are illustrated in FIG. 4. As in the previous embodiment, filter 220 can be configured so that the bands centered at λA1 and λ^ coincide with radiation bands at which first and second substances of interest are respectively absorbed. Filter 224 can then be configured so that bands centered at λB1 and λB2 coincide with radiation bands at which the first and second substances are relatively free from absoφtion.

    After the radiation beams are combined at beam combiner 30, the combined beam is directed along optical path 103 to a partitioning or edge filter 226 configured, for example, to reflect wavelength bands centered at λA1 and λB1 through focusing optics 232 to detector 234 and transmit wavelength bands centered at λ^ and λB2 through focusing optics 233 to detector 235. Thus, detector 234 is sensitive to the amplitude modulation caused by the differential absoφtion between the bands centered at λA1 and λB, (i.e., associated with the first substance) while detector 235 is sensitive to the amplitude modulation caused by the differential absoφtion between the bands centered at λ^ and λB2 (i.e., associated with the second substance). Note that the FIG. 3 embodiment can be expanded to measure three or more substances simultaneously by using the appropriate bandpass (e.g., triple bandpass filter) and beam partitioning filters.

    Further, as would be understood by one skilled in the art, other filter configurations are possible. For example, the band centered at λA, could coincide with a radiation band at which the first substance is absorbed; the band centered at λB1 could coincide with a radiation band at which the first substance is not absorbed; the band centered at λ^ could coincide with a radiation band at which the second substance is not absorbed; and the band centered at λB2 could coincide with a radiation band at which the second substance is absorbed.

    Still another embodiment of the present invention is illustrated in FIG. 5 and referenced generally by numeral 300. Once again, like reference numerals will be used for those elements that are the same as those used in the FIG. 1 embodiment. In FIG. 5, bandpass filters 320 and 324 are used in reflection instead of transmission. That is, as illustrated respectively in FIGs. 6 A and 6B, filter 320 reflects all wavelengths (to beam combiner 30) except for the wavelength band centered at λA and filter 324 reflects all wavelengths (to beam combiner 30) except the wavelength band centered at λB. As in the FIG. 1 embodiment, absoφtion at the bands centered at λA and λB is different for the substance of interest. The beams are combined by beam combiner 30 and transmitted along optical path 103 to a bracketing bandpass filter 326 having a band pass characteristic that spans the two wavelength bands isolated by filters 320 and 324. The transmission characteristics of bracketing bandpass filter 326 are illustrated in FIG. 6C. Note that bracketing filter 326 could be replaced with a dual bandpass filter. Either way, focusing optics 32 and detector 34 receive a signal magnitude affected by absoφtion in the two bands illustrated in FIG. 6D. Since each band is alternately received by detector 34, an amplitude modulated signal is monitored. The advantages of the FIG. 5 embodiment include fewer components and the preservation of the majority of the radiation for further processing as will now be described with the aid of FIG. 7. The present invention could also be practiced by using dual (or triple) bandpass filters (in place of filters 320 and 324) and wavelength partitioning optics/detectors to enable the measurement of several substances simultaneously.

    The embodiment illustrated in FIG. 7, and referenced generally by numeral 400, is used to make differential absoφtion and gas filter correlation measurements simultaneously. As before, like reference numerals are used for elements that are common with the FIG. 5 embodiment. System 400 is useful in measurement applications that require both high measurement specificity for certain gas species and measurement of a broad class of gases. An example is the remote measurement of car exhaust. In this measurement, high gas specificity is needed to accurately measure NO because of the overlap of a strong water vapor band at 5.2 microns. At the same time, a 'total hydrocarbon' measurement is desired in the 3.4 micron carbon-hydrogen absoφtion region. In other words, the measurement of a specific hydrocarbon is not desired. Rather, the measurement of the net differential absorption in this C-H stretch region is desired as some indication of 'total hydrocarbons'. Such conflicting types of simultaneous measurements are possible in the present invention. That is, the present invention makes it possible to use the GFCR technique for the NO measurement and the differential absoφtion technique for the 'total hydrocarbon' measurement.

    In FIG. 7, a gas correlation cell 440 is disposed in optical path 101 and a vacuum cell 444 is disposed in optical path 102. Cells 440 and 444 enable a GFCR measurement while filters 320 and 324 enable the differential absoφtion measurement as described above with reference to FIG. 5. More specifically, the radiation beams are combined at beam combiner 30. The combined beam is partitioned at edge filter 426 which, for example, transmits the wavelength region associated with the GFCR measurement to a GFCR bandpass filter 446, focusing optics 432 and detector 434 so that a standard GFCR measurement can be made as is well known in the art. Edge filter 426 reflects other wavelengths to bracketing or bandpass filter 326 which functions as in the previous embodiment of FIG. 5.

    Another way to detect or measure two substances simultaneously using bandpass filters in reflection is shown and referenced generally by numeral 500 in FIG. 8. That is, system 500 is an alternative construction that achieves the results described above with respect to FIG. 3. In optical path 101, a first bandpass filter 520 reflects all wavelengths except those in a first band centered at λA1 towards one side of a two- sided mirror 526. Mirror 526 reflects the radiation to a second bandpass filter 521 that reflects all wavelengths except those in a second band centered at λ^. In a similar fashion, bandpass filters 524/525 and mirror 526 cooperate to remove wavelength bands centered at λB1 and λB2 in optical path 102. The single beam output from beam combiner 30 can then be processed as described in the FIG. 3 embodiment. Detection optics may include bracketing filters 326 as needed.

    Still another embodiment of the present invention is shown in FIG. 9 and is referenced generally by numeral 600. System 600 is similar to system 500 except that mirror 526 is replaced with a two-sided bandpass absorber 626. Absorber 626 is configured on side 626A to absorb radiation in a third wavelength band centered on λA3 while reflecting all other wavelengths. This can be accomplished by designing a bandpass filter stack that transmits the band centered at λA3 which is then absorbed internally. For example, the substrate material could strongly absorb this wavelength band. On the other side 626B of absorber 626 is a second filter stack that selectively transmits/absorbs a wavelength band centered at λB3. After being combined at beam combiner 30, a system of partitioning filters/focusing optics/detectors 632, similar to the systems disclosed in the embodiments of FIGS. 3, 7 and 8, are used to partition the single beam so that the differential absorption between each wavelength band pair (i.e., wavelength band pairs centered at λA! and λB], λ^ and λB2, and λA3 and λB3) can be individually and simultaneously sensed.

    In still another embodiment of the present invention, system 700 illustrated in FIG. 10 is an alternative construction for the FIG. 5 embodiment. System 700 is a compact configuration of the present invention in which optical path 103 exits a combination beamsplitter/combiner 750 at an acute angle thereto. A single optical element can be used for beamsplitting and beam combining by, for example, configuring the device's wire grids (not shown) to transmit horizontal polarization in the beamsplitter portion and to transmit vertical polarization in the beam combiner portion.

    The advantages of the present invention are numerous. Substance detection and measurement can be achieved without using gas cells. However, the present invention can be configured to provide for simultaneous differential absoφtion and GFCR measurements. Further, multiple differential absoφtion measurements associated with multiple substances can be made simultaneously.

    Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described.

    What is claimed as new and desired to be secured by Letters Patent of the United States is:

    Claims

    Claims
    1. A method of detecting a substance, comprising the steps of: receiving radiation passing along a sample path of interest; dividing said radiation into a time series of alternating first polarized components and second polarized components orthogonal to said first polarized components; transmitting said first polarized components along a first optical path and said second polarized components along a second optical path; filtering said first polarized components to isolate at least a first wavelength band wherein first filtered radiation is generated; filtering said second polarized components to isolate at least a second wavelength band wherein second filtered radiation is generated, wherein said first wavelength band and said second wavelength band are unique and wherein spectral absoφtion of a substance of interest is different at said first wavelength band as compared to said second wavelength band; combining said first filtered radiation and said second filtered radiation to form a combined beam of radiation; and monitoring magnitude of said combined beam alternately at said first wavelength band and said second wavelength band as an indication of the concentration of said substance in said sample path.
    2. A method according to claim 1 wherein said step of filtering said first polarized components comprises the step of passing only said first wavelength band to form said first filtered radiation, and wherein said step of filtering said second polarized components comprises the step of passing only said second wavelength band to form said second filtered radiation.
    3. A method according to claim 1 wherein said step of filtering said first polarized components comprises the step of passing all wavelengths except said first wavelength band to form said first filtered radiation, and wherein said step of filtering said second polarized components comprises the step of passing all wavelengths except said second wavelength band to form said second filtered radiation.

    Radiometry And The Detection Of Optical Radiation Pdf Converter Free

    4. A method according to claim 3 further comprising the step of performing gas filter correlation radiometry using one of said first polarized components and said first filtered radiation, and using one of said second polarized components and said second filtered radiation.
    5. A method according to claim 1 wherein said step of filtering said first polarized components comprises the step of isolating a plurality of unique first wavelength bands, and wherein said step of filtering said second polarized components comprises the step of isolating a plurality of unique second wavelength bands, said method further comprising the step of: partitioning said combined beam into a plurality of partitioned beams, each of said plurality of partitioned beams including one of said plurality of unique first wavelength bands and one of said plurality of unique second wavelength bands, wherein spectral absoφtion of a substance of interest is different at one of said one of said plurality of unique first wavelength bands as compared to said one of said plurality of unique second wavelength bands, wherein said step of monitoring comprises the step of monitoring magnitude of each of said plurality of partitioned beams.
    6. A method according to claim 1 wherein a plurality of related substances of interest are spectrally absorbed more at said first wavelength band than at said second wavelength band.
    7. A method according to claim 6 wherein said plurality of related substances are hydrocarbons.
    8. A method according to claim 1 wherein said first polarized components are vertically polarized and said second polarized components are horizontally polarized.
    9. A method according to claim 1 wherein said step of monitoring is harmonically synchronized to a frequency at which said time series alternates between said first polarized components and said second polarized components.
    10. A system for detecting a substance comprising: an optical path switch for receiving radiation passing along a sample path of interest, said optical path switch dividing said radiation into a time series of alternating first polarized components and second polarized components orthogonal to said first polarized components, said optical path switch transmitting said first polarized components along a first optical path and said second polarized components along a second optical path; a first gasless optical filter train disposed in said first optical path for filtering said first polarized components to isolate at least a first wavelength band wherein first filtered radiation is generated; a second gasless optical filter train disposed in said second optical path for filtering said second polarized components to isolate at least a second wavelength band wherein second filtered radiation is generated, wherein said first wavelength band and said second wavelength band are unique and wherein spectral absoφtion of a substance of interest is different at said first wavelength band as compared to said second wavelength band; a beam combiner disposed to receive said first filtered radiation and said second filtered radiation for combining said first filtered radiation and said second filtered radiation to form a combined beam of radiation; and detector means disposed to monitor magnitude of at least a portion of said combined beam alternately at said first wavelength band and said second wavelength band as an indication of the concentration of said substance in said sample path.
    11. A system as in claim 10 wherein said first gasless optical filter includes a first optical filtering means for passing only said first wavelength band to form said first filtered radiation, and wherein said second gasless optical filter includes a second optical filtering means for passing only said second wavelength band to form said second filtered radiation.
    12. A system as in claim 10 wherein said first gasless optical filter includes a first optical filtering means for passing all wavelengths except said first wavelength band to form said first filtered radiation, and wherein said second gasless optical filter includes a second optical filter means for passing all wavelengths except said second wavelength band to form said second filtered radiation.
    13. A system as in claim 12 further comprising a gas filter correlation radiometer coupled to said optical path switch, said gas filter correlation radiometer using one of said first polarized components and said first filtered radiation and using one of said second polarized components and said second filtered radiation to measure the concentration of at least one gas species in said sample path.
    14. A system as in claim 10 wherein said first gasless optical filter includes first optical filtering means for isolating a plurality of unique first wavelength bands, and wherein said second gasless optical filter includes second optical filtering means for isolating a plurality of unique second wavelength bands, said system further comprising: a beam partitioner disposed to receive said combined beam and for partitioning said combined beam into a plurality of partitioned beams, each of said plurality of partitioned beams including one of said plurality of unique first wavelength bands and one of said plurality of unique second wavelength bands, wherein spectral absoφtion of a substance of interest is different at one of said one of said plurality of unique first wavelength bands as compared to said one of said plurality of unique second wavelength bands, wherein said detector means comprises a plurality of detectors, each of said plurality of detectors disposed to receive one of said plurality of partitioned beams.
    15. A system as in claim 10 wherein said first polarized components are vertically polarized and said second polarized components are horizontally polarized.
    16. A system as in claim 10 wherein said detector means is harmonically synchronized to a frequency at which said time series alternates between said first polarized components and said second polarized components.
    17. A substance detection system comprising: an optical path switch for receiving radiation passing along a sample path of interest, said optical path switch dividing said radiation into a time series of alternating first polarized components and second polarized components orthogonal to said first polarized components, said optical path switch transmitting said first polarized components along a first optical path and said second polarized components along a second optical path; a first gasless optical filter train disposed in said first optical path for filtering said first polarized components to pass all wavelengths except those in a first wavelength band wherein first filtered radiation is generated; at least one gas correlation cell disposed in said first optical path for filtering one of said first polarized components and said first filtered radiation at spectral regions different from that of said first wavelength band; a second gasless optical filter train disposed in said second optical path for filtering said second polarized components to pass all wavelengths except those in a second wavelength band wherein second filtered radiation is generated, wherein said first wavelength band and said second wavelength band are unique and wherein spectral absoφtion of a substance of interest is different at said first wavelength band as compared to said second wavelength band; a vacuum cell disposed in said second optical path; a beam combiner disposed to receive said first filtered radiation and said second filtered radiation for combining said first filtered radiation and said second filtered radiation to form a combined beam of radiation; first detecting means disposed to monitor magnitude of at least a portion of said combined beam alternately at said first wavelength band and said second wavelength band as an indication of the concentration of said substance in said sample path; and second detecting means disposed to sense a difference in intensity between said first filtered radiation and said second filtered radiation at said spectral regions to measure the concentration of at least one gas species in said sample path.
    18. A system as in claim 17 wherein said first polarized components are vertically polarized and said second polarized components are horizontally polarized.
    19. A system as in claim 17 wherein said first detecting means is harmonically synchronized to a frequency at which said time series alternates between said first polarized components and said second polarized components.
    PCT/US1999/0266561998-04-201999-11-10Optical path switching based differential absorption radiometry for substance detection WO2000062041A1 (en)

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        EP1166089A1 (en) 2002-01-02
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        US20040156050A1 (en) 2004-08-12

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