Methods and Systems of Optical and Physical Measurements (in Conditions of a priori Uncertainty)
The review presents optical and electronic methods and systems of various functional purpose developed by the authors on the basis of the “a priori-free” concept, which make it possible to exclude a priori information or assumptions about the object under study in the interpretation of measurement information, as well as “non-calibration” measuring systems that are resistant to changes in the instrumentation constants of reception radiating, recording blocks, environment, pollution of optical elements.
Accepted on: 28.08.2020
Currently, optical and physical measuring systems are widely used in various fields of science, technology, and the national economy. When carrying out optical and physical measurements, information about the measured object or medium is obtained based on the analysis of the reflected, scattered, refracted or absorbed electromagnetic radiation in the optical wavelength range.
The existing optical and physical systems have the following disadvantages:
The influence of noise and measurement errors leads to the incorrectness of the inverse problem when interpreting the measurement information;
There are no methods and algorithms for solving incorrect inverse problems of recovering the determined parameters operating in real time;
The need to use a large amount of a priori information about the research object;
Difficulties in metrological certification of systems.
In this regard, in the task of processing optical and physical measurements, it is necessary to develop such methods of information processing that would maximally exclude a priori information or assumptions about the object under study, the need to make corrections for the background and drift of instrument readings, environmental influences, or otherwise, methods information processing based on the concept of “a priori-free” [1–3]. The essence of this concept regarding the problem of interpreting the data of optical and physical measurements is the minimum use of a priori information or assumptions about the investigated medium, obtaining the reference (calibration) values of the determined parameters without additional independent measurements, solving the problem of calibration measurements (maximally eliminating the influence of instrumental parameters on the measurement results).
CALIBRATION MEASUREMENT PROBLEM
Calibration issues for measuring systems arise in most cases of experimental measurements. In practical terms, they result in the problem of metrological certification of the system. In some cases, the solution to the issue of metrological certification is even more difficult than the creation of the measuring system itself.
Typically, a measuring system contains a source of energy radiation and a receiver part that converts the received energy into a measured signal. Conversion of energy into a measured signal and its output in a form convenient for perception is carried out in the form of an unknown dependence on many parameters. The purpose of calibration is to establish the type of this dependence. Mathematically, this is expressed in the fact that the magnitude of the output signal includes both the constants of sources, receivers, and the constants of the entire information conversion path, the values of which must be set. All these constants can change over time and changes in experimental conditions, which further complicates the calibration problem.
These drawbacks are eliminated by excluding dependence on the influence of the environment, instrumental constants, pollution, etc. The urgency of creating “non-calibration” measuring systems (maximally eliminating dependence on the influences just noted) is obvious from this . The measuring system, in its turn, can be “non-calibration” only if it is maximally resistant to changes in the hardware constants.
In laser-location measurements, the task of information processing implies not only the establishment of functional links between the received information and the characteristic being determined, including the hardware constants of the system, but also the interpretation of the obtained indirect information about the object under study (i. e., the solution of the inverse problem. In almost all cases, the problem of interpretation obtained indirect information is a multi-parameter and often incorrect inverse problem .
To solve it, knowledge of the reference (calibration) values of the determined optical characteristics is required by additional measurements or from the backscattered signals themselves (without additional independent measurements). In particular, it is proposed to use backscattered signals from intervals overlapping at least by the width of the recording channel. Methods for establishing reference (integral and local) calibration values are discussed in detail in .
In connection with the above, the essence of the concept of “a priori-free” with respect to the problem of interpreting the data of laser-ranging sounding is the minimum use of a priori information or assumptions about the studied medium, the maximum elimination of the influence of the equipment and the physical processes used on the measurement results, the exclusion of reference (calibration) values of the determined parameters [1,5].
Thus, the effective use of optical and physical measurements in diagnostics, control, in technical processes, in scientific research, etc. requires the development of methods and systems based on the concept of “a priori-free”, solving problems that allow the creation of “non-calibration” measuring systems.
The submissions received and submitted can be summarized as follows:
METHODS AND SYSTEMS OF OPTICAL AND PHYSICAL MEASUREMENTS IN CONDITIONS OF A PRIORI UNCERTAINTY
In [1, 2, 6–14], regression methods for solving inverse problems of optical sensing of light scattering media are proposed, which consist in determining the parameters of the medium under study on the basis of analytical expressions approximating the relationship of the required parameters of the medium with the optical signals measured in the experiment. These expressions are obtained by regression analysis of the results of statistical modeling of optical signals with a wide variation of the environmental parameters. An important advantage of this approach to the interpretation of optical sounding data is the ability to reconstruct the parameters of the medium in real time without using a priori information for this (if the real values of the parameters of the medium do not go beyond the sample used to obtain the statistical operator for solving the inverse problem). The obtained regression relations, moreover, are not affected by the hardware constants connecting the calculated signals with the parameters of the scattering media.
The effectiveness of the regression approach to solving inverse problems was demonstrated in [1, 2], where by numerical modeling of the optical parameters of aerosol with a wide variation of its microphysical parameters, numerous regression relationships were established between the optical, as well as between the optical and microphysical characteristics of multicomponent aerosols of natural and anthropogenic origin.
The obtained regression relations between the optical and optical and microphysical characteristics of atmospheric aerosol are in good agreement with the calculated and experimental data of the global aerosol monitoring network based on the AERONET scanning solar photometers and the known experimental optical-microstructural correlations for stratospheric and surface aerosols [8, 13].
Based on this, a number of methods and techniques have been developed for determining the microphysical characteristics of an aerosol from the data of laser-ranging, satellite, photometric and nephelometric measurements. In particular:
a method for reconstructing the profiles of aerosol backscattering coefficients on horizontal and inclined paths in the atmosphere from the results of sounding by laser-ranging systems based on the YAG : Nd3+ laser, using the regression relationship between the spectral values of the backscattering coefficients established on the basis of a statistical-microphysical model of urban and background aerosols at wavelengths 355; 532 and 1 064 nm . The developed method can be effectively used to monitor aerosol air pollution and to control the visibility range along the glide path at airports;
a method for reconstructing the altitude profiles of optical and microphysical parameters of postvolcanic stratospheric aerosol from the results of sounding at wavelengths of 355, 532 and 1064 nm . The method uses the stable multiple regressions between the optical characteristics of the aerosol established on the basis of a statistical optical-microphysical model of the stratospheric aerosol and an algorithm for reconstructing the profiles of the aerosol backscattering coefficient at the indicated wavelengths. The inverse problem is solved using polynomial multiple regressions between the integral microphysical parameters of the aerosol and the spectral values of the backscattering coefficients;
methods for determining the concentration of background atmospheric aerosol, based on measuring the spectral values of the attenuation coefficients or backscattering coefficients (Patent BY10845 C1, 2008), as well as scattering coefficients at angles (Patent BY10844 C1, 2008) and establishing regression relations between the determined and measured parameters;
a method of online monitoring of the mass concentration and effective size of dust particles in aspiration air and exhaust gases at cement plants, based on the measurement of directional scattering by dust particles at angles of 3, 5 and 15° at wavelengths of 0.40 and 0.87 μm . The method is resistant to the instability of the chemical and dispersed composition of dust, which makes it possible to eliminate the need for recalibration of the device when it is used to control dust emitted during various technological operations;
a method for determining the mass concentration of respirable aerosol particles in the atmosphere from the results of lidar sounding at wavelengths of the YAG : Nd3+ laser, using the established polynomial regressions between the coefficients of aerosol attenuation and backscattering at wavelengths 355; 532 and 1 064 nm (Patent BY14094 C1, 2008);
a method for remote determination of mass concentrations of atmospheric aerosol fractions (PM1,.0, PM2,.5 and PM10) based on data from joint measurements of lidar signals at wavelengths of 355; 532, 1 064 and 2 130 nm, processing of measurement information using regression relationships with linearly independent components of spectral measurement data (Eurasian patent 026024 B1, 2014);
a method for determining the mass concentration of aerosol (Eurasian patent 026528 B1, 2014). It uses the sending of light radiation at wavelengths of 532 and 1 064 nm, the measurement of directional scatter coefficients for angles of 5 and 20° and regression relations that relate concentrations to the recorded directional scatter coefficients;
a method for reconstructing the height profile of the volumetric concentration of a finely dispersed aerosol fraction directly from lidar signals at elastic and Raman scattering wavelengths without using additional data for calibrating the lidar and for completing the determination of the inverse problem . Allows, with an error of a few percent, to reconstruct the altitude profile of the volume concentration of fine aerosol particles and the parameters of their size distribution from lidar signals at wavelengths of the Nd : YAG3+ laser, and with the use of channels for registering Raman scattering by atmospheric nitrogen – also the complex refractive index (CRI) of aerosol matter. It is shown that the information obtained is sufficient for calculating the optical parameters of aerosol that affect the transfer of solar radiation in the atmosphere.
The developed methods are resistant to variations in the disperse and chemical composition of the investigated aerosols, to errors in optical measurements and allow real-time local and remote monitoring of aerosol microphysical parameters with the accuracy required for practice.
“Non-calibration” basic and nephelometric methods
In the theory of measurements, it is customary to distinguish between direct and indirect, as well as joint and aggregate measurements, which differ in the way of processing experimental data . Joint and cumulative measurements by the methods of finding the desired values of the determined quantities are close: in both cases they are found by solving a system of equations, the coefficients in which and individual terms are obtained from experimental data. The main difference is that with aggregate measurements, several values of the same name are simultaneously determined, and with joint measurements, dissimilar ones.
It is shown in [3–5] that when using aggregate measurements, due to the use of combinations of the same receiving-emitting and measuring units and their different locations, dependences on changes in their instrumental constants are excluded. The use of this property is the basis for the synthesis of structures of new “non-calibration” measuring and diagnostic systems that most fully satisfy the task of metrological certification and automation of the measurement process. So, in particular, developed:
two-beam nephelometric method for measuring the optical thickness of scattering media (Patents BY6450 C1, 2004; BY3670 C1, 2000);
basic “non-calibration” methods for changing the optical characteristics of scattering media, their component composition (Patent BY4655 C1, 2002);
a method for measuring scattering indicatrices of the underlying surface (Patent BY4120 C1, 2001);
a method for measuring the backscattering coefficient .
The developed basic nephelometric methods for measuring optical characteristics make it possible to exclude the influence (spread) of instrumental constants on the measurement result and weaken the requirements for carrying out calibration measurements. These critical benefits improve both accuracy and performance. The exclusion of calibration measurements, which are the most difficult part concerning the optical component, and the resistance to the spread of the instrumental constants makes it possible to replace any of the blocks of the measuring system and not pay particular attention to the protection of optics from contamination.
Measuring and diagnostic methods based on two-wave semiconductor lasers
In spectral systems, e. g., gas analysis, a combination of radiation paths at the wavelengths used is required, which is easily achieved in two- and multi-wavelength semiconductor radiation sources. Within the framework of the concept of “a priori-free”, methods have been developed for constructing nephelometric and basic meters for various functional purposes using a two-wave semiconductor laser, which have advanced capabilities . These systems include:
a laser distance meter, in which an increase in accuracy is achieved by taking into account the propagation speed of radiation along the path in given meteorological conditions, based on determining the difference in frequencies of simultaneous recirculation at two optical wavelengths outside the bands of anomalous dispersion of atmospheric gas components, which ensures a decrease in the error in measuring the range up to 10–6–10–7] (Patents of the Republic of Belarus No. 8172, No. 3994);
a gas analyzer, the measurement principle of which is based on converting the amplitude of the probe pulse into the difference in frequencies of simultaneous recirculation at two optical wavelengths, one of which is in the absorption band of the monitored gas, which provides a sensitivity of 10–3 to 10–4 ppb and measuring the length of the monitored path (Patent RB. No. 7676, RF patent No. 2480737);
precision laser range finders based on automatic tuning of the repetition rate of probe pulses at two optical wavelengths; application as a recirculating chirp and processing of a remote signal with matched filters; using two parallel beams of probing radiation at two optical wavelengths; use of two channels of synchronous detection with clock signals shifted by π / 2; using an optical attenuator and measuring the phase at different amplitudes of the optical signal (Patents RB No. 17091, 6490, 13549, 8914);
Doppler two-frequency meters of motion parameters with a high spatial-temporal resolution, based on the use of various laws of modulation of sounding signals and allowing to simultaneously measure the range and speed of several objects in one sounding pulse (Patent RB No. 12740);
Doppler speed meter on a two-wavelength laser, which provides measurement of both the exact value of the speed and the angle of direction of the object movement. Doppler meter for the frequency and amplitude of vibrations with a measurement accuracy less than λ / 2 (Patent RB No. 10018);
a meter for the chromatic dispersion of fiber-optic fibers, based on the conversion of dispersion into the difference in frequencies of simultaneous recirculation at two optical wavelengths, providing an accuracy of measuring the dispersion of ~2–5 · 10–2 ps · km / nm, and a short optical pulse generator using a fiber light guide (Patents of RB No. 8171, 10703, 11002).
Passive measuring systems for various functional purposes
Original methods have been developed for the non-contact determination of the temperature of bodies with an unknown coefficient of their thermal radiation, based on the use of registration of thermal radiation in several parts of the spectrum, the use of limiting conditions and the solution of nonlinear equations. The developed methods have been introduced into the domestic high-temperature thermograph IT3-SM (see Figure), and its small-scale production by UE Unitehprom BSU has been mastered (www.auris.ru; www.unitehprom.by).
For difficult conditions for measuring high temperatures during laser processing of metals, original methods have been created based on recording the absolute spectral brightness of radiation in the area of contact of the laser beam with the surface being processed, which makes it possible to significantly reduce the uncertainty of temperature control in comparison with traditional spectral ratio pyrometry (Patents BY13990, 13991, 2010).
The principles of construction and functional structures of passive measuring systems for various functional purposes have been developed:
Hardware and software suit “BIZAN” . Designed to measure the parameters of the traces of rifling fields on fired bullets. Provides measurement of track depth, distance between points, linear dimensions with a resolution of ~ 10 microns and measurement of angles of inclination of grooves with a resolution of ~ 0.01’ (Eurasian patent No. 028418). The suit was tested in the State Committee for Forensic Expertise of the Republic of Belarus. The suit is approved for use in the production of forensic ballistic examinations;
Rangefinder on a digital 3D camera (Eurasian patent No. 028167, RF patent No. 2485443). The range finder does not require the presence of calibration objects in the frame for measurements. Provides measurement of range, distance between objects, linear dimensions of all objects in a digital image and slope angles of lines in the image. The relative measurement uncertainty is 0.1% at distances up to 30 m and 0.3% at distances up to 100 m, which is more than 10 times higher than the known analogs [20, 21];
System of correlation analysis of digital optical images for solving problems of forensic science. Allows you to solve forensic tasks:
analysis of the length and aging degree of seals and stamps (Eurasian patent No. 026460);
analysis of defects of imprints of seals on the basis of the construction of a correlation map (Patent RB No. 11573);
analysis of the dimensional parameters of the scene of the accident from a digital image from a quadrocopter (Patent RB No. 12181);
analysis of distortions of laser printers; identification of printers (Patent RB No. 12107).
The need to use a priori information, assumptions about the object under study, the complexity of carrying out calibration measurements at the present time, e. g., did not allow metrological certification of laser-location systems in the created global networks (world, European, CIS, RB) for monitoring environmental pollution (for interpreting measurement information additional radiometric measurements are used), systems for non-invasive optical diagnostics of biophysical parameters of biological objects, etc.
Thus, the effective use of optical and physical measurements in diagnostics, control, in technical processes, in scientific research, etc. requires the development of methods and systems based on the concept of “a priori-free”, solving problems that allow the creation of “non-calibration” measuring systems. The above review also considers the optoelectronic methods and systems of various functional purposes, developed by the authors based on a priori-free concept, which are resistant to changes in instrumental constants and the environment, allowing measurements with high accuracy under conditions of information uncertainty about the research object.
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Lysenko S. A. Methods of optical diagnostics of biological objects. Minsk: BSU. 2014: 250
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Kugeiko M. M. Theory and methods of optical and physical diagnostics of inhomogeneous scattering media. – Minsk: BSU. 2003: 188.
Kugeiko M. M. Laser diagnostics and spectroscopy. – Minsk: BSU. 2002: 276.
Lysenko S. A. Kugeiko M. M. Regression approach to the analysis of information content and interpretation of aerosol optical measurement data. ZhPS. 2009: 76 (6); 876–883.
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Lysenko S. A. Kugeiko M. M.Method for determining the concentration of the respirable fraction of atmospheric aerosol according to the data of three-frequency lidar sounding. Atmospheric and Ocean Optics. 2010: 23 (2); 149–155.
Lysenko S. A., Kugeiko M. M. A technique for reconstructing the altitude distribution of the aerosol mass concentration in the atmosphere from the results of lidar sounding at Nd : YAG laser wavelengths. Optics and spectroscopy. 2010: 109 (6); 1212–12210.
Lysenko S. A., Kugeiko M. M. Recovery of optical and microphysical characteristics of postvolcanic stratospheric aerosol from the results of three-frequency lidar sounding. Atmospheric and Ocean Optics. 2011: 24 (4); 308–318.
Lysenko S. A., Kugeiko M. M. Recovery of mass concentration of dust in industrial emissions from the results of optical sensing. Atmospheric and Ocean Optics. 2011: 24 (11); 960–968.
Lysenko S. A., Kugeiko M. M. Recovery of microphysical parameters of post-volcanic stratospheric aerosol from the results of satellite and ground multi-frequency sounding. Exploration of the Earth from space. 2011: 5; 21–33.
Lysenko S. A., Kugeiko M. M. Determination of the concentration of aerosol particles in the vertical column of the atmosphere from satellite measurements of spectral optical thickness. ZhPS. 2011: 78 (5); 793–800.
Lysenko S. A., Kugeiko M. M. Spectronefelometric methods for determining the microphysical characteristics of dust in the suction air and exhaust gases from the cement plants of the fire protection department. ZhPS. 2012: 79 (1); 66–76.
Kugeiko M. M., Lysenko S. A. A technique for reconstructing the profiles of atmospheric backscattering aerosol coefficients from the results of multiwave lidar sounding. ZhPS. 2008: 75 (3); 347–353.
Lysenko S. A., Kugeiko M. M. Spectronefelometric determination methods microphysical characteristics of dust in the suction air and off-gas from the cement production facilities. ZHPS. 2012: 79 (1); 66–76.
Lysenko S. A., Kugeiko M. M., Khomich V. V. Multifrequency lidar sounding of atmospheric aerosol under conditions of information uncertainty. Atmospheric and Ocean Optics. 2016: 29 (5); 404–413.
Kozlov V. L., Kugeiko M. M. Measuring and diagnostic systems based on two-wave semiconductor lasers. – Minsk: BSU. 2010: 176.
Kozlov V. L., Rubis A. S., Lappo E. A., Vasilchuk A. S. The use of correlation processing of digital images to optimize the process of measuring parameters and the depth of traces of rifling bullets. Forensic expertise. 2015: 1; 31–38.
Kozlov V. L., Vasilchuk A. S. Rangefinder based on a 3D digital camera for forensic research. Sensors and systems. 2015: 9; 70–76.
Kozlov V., Wojcik W., Zgirovskaya N. About Improving the Measuring Distances Accuracy Based on Correlation Analysis of Stereo Images. Proc. of XIth ISPC Electronics and Information Technologies (ELIT). – IEEE. 2019: 11–14. ISBN978-1-7281-3561-8.
Kugeiko Mikhail Mikhailovich, e-mail: firstname.lastname@example.org, Doctor of Phys.-Math. Sci., Professor of the Department of Quantum Radiophysics and Optoelectronics, Faculty of Radiophysics and Computer Technologies, Belarusian State University, Minsk, Republic of Belarus.
Kozlov Vladimir Leonidovich, e-mail: kozlovVL@bsu.by, Doctor of Tech. Sci., Professor of the Department of Informatics and Computer Systems, Faculty of Radiophysics and Computer Technologies, Belarusian State University, Minsk, Republic of Belarus.
Firago Vladimir Aleksandrovich, e-mail: Firago@bsu.by, Associate Professor of the Department of Quantum Radiophysics and Optoelectronics of the Belarusian State University, Ph. D. Sci., Associate Professor, Minsk, Republic of Belarus.
Zgirovskaya Natalya Vladimirovna, e-mail: email@example.com, Junior Researcher, Department of Quantum Radiophysics and Optoelectronics, Belarusian State University, Minsk, Republic of Belarus.