KEYWORDS: LIDAR, Photodetectors, Signal attenuation, Temperature metrology, Pulse signals, Photon counting, Laser sintering, Signal intensity, Air temperature, Rectangular pulse
A lidar response simulator has been created that makes it possible to generate an optical signal close in shape and intensity to a real lidar signal in the temperature measurement channels at the main lidar of the Siberian Lidar Station. An experimental evaluation of the linearity range of the photodetection system has been carried out. The paper shows a block diagram of a stand for experimental evaluation of the linearity range of a lidar photodetection system with the ability to synthesize a pulsed optical signal. It is shown that when a signal is recorded in the photon counting mode, nonlinear distortions are observed at an average counting pulse arrival frequency of 2.5 MHz.
The paper considers the problem of solving the inverse problem of retrieval of the vertical distribution of atmospheric temperature from a Rayleigh scattering lidar signal in a high spectral resolution lidar. It is shown that the lidar signal, filtered from the aerosol scattering signal using a molecular filter, acquires a parasitic dependence on the atmospheric temperature due to a change in the width and shape of the Rayleigh scattering line contour. Signal distortions have a significant effect on the result of retrieval of the vertical temperature distribution and do not allow using the standard signal processing technique. To eliminate the influence of the signal filtering effect, the advanced temperature retrieval algorithms should be applied.
The winter of 2022-2023 was characterized by intense dynamic processes associated with the formation of blocks in the middle troposphere and the occurrence of sudden stratospheric warmings (SSW) in the stratosphere. The SSW event in January-February 2023 is likely related to prolonged blocking over the Urals and Europe in the second half of January. Lidar measurements of atmospheric temperature based on the use of pure rotational raman spectra on nitrogen and oxygen molecules at altitudes up to 70 km in the Akademgorodok area of Tomsk during the SSW period, and their comparison with WACCM model data and satellite Aura data showed a number of characteristic features associated with changes in the structure of the stratopause due to SSW.
The paper considers a block diagram of a photodetection system based on a new version of the four-channel photon counter "PHCOUNT-4" used for precision lidar measurements of atmospheric temperature. The results of using the new capabilities of the analog part of the photon counting system, which makes it possible to automatically record the amplitude distribution of single-electron pulses of each of the photodetectors installed in the channels and determine the optimal discrimination threshold, are described. It is shown that setting the optimal discrimination thresholds makes it possible to achieve a small spread in the end-to-end quantum efficiency of each of the channels
The paper discusses the problem of ensuring the linearity of photo registration of the lidar signal of molecular scattering on the main lidar of the Siberian lidar station (SLS) based on a unique mirror with a diameter of 2.2 m. To reduce the dynamic range of signal changes, it is proposed to use a mechanical shutter based on a disk obturator to cut off the near zone of the lidar signal in the altitude range of 0÷30 km. A high-speed brushless motor was used as an obturator driver. The synchronization signal was generated by a Hall sensor. Bench and full-scale tests of the obturator were carried out. It is shown that the error of the Hall sensor does not affect the delay and duration of the shutter opening.
The paper considers the problems of optimization of the molecular scattering signal registration system at the Siberian lidar station for the photon counting mode. The modern element base makes it possible to design recorders with a gigahertz counting rate that allow to implement hardware methods for evaluating and accounting for the effect of dead time. Modified photon counting systems allow more efficient use of algorithms of the nonlinear distortion correction. Simulation of operation of a photon counter with various methods of recording events and methods of processing the recorded signals is performed. A method is proposed for determining the value of the dead time and evaluating the limits of applicability of the photon counting mode of the modified counter. A quantitative assessment of the advantage when using various correction formulas is carried out in comparison with the classical photon counting.
The paper considers the equipment and methodology for remote determination of the vertical distribution of atmospheric temperature up to altitudes of 90 km. The technique is based on the lidar measurements of the vertical profile of the molecular density of the atmosphere using the Rayleigh scattering effect. The results obtained on the modernized Rayleigh scattering channel of the lidar based on the main mirror of the Siberian lidar station with a diameter of 2.2 m are demonstrated. The atmospheric temperature profile obtained from the lidar data is compared with the temperature profile of a satellite radiometer in the altitude range of 40-90 km.
The paper considers the equipment and methodology for remote determination of the vertical distribution of atmospheric temperature up to altitudes of 90 km. The technique is based on the lidar measurements of the vertical profile of the molecular density of the atmosphere using the Rayleigh scattering effect. The results obtained on the modernized Rayleigh scattering channel of the lidar based on the main mirror of the Siberian lidar station with a diameter of 2.2 m are discussed. A two-stage procedure for the remote estimation of temperature by molecular backscattering is proposed, which makes it possible to estimate the temperature both in a free atmosphere and in a cuvette in which the relationship between the temperature and pressure does not fit into the barometric model. Calculations have shown that the accuracy of the temperature profile retrieval depends on the choice of the calibration point and its error. The calculation of the profile by formula, when the calibration point is chosen at the upper part of the sounding path, has greater stability and accuracy compared to calculations by formula with the calibration point chosen at the beginning of the path.
The efficiency of application of the combined photodetection technique for recording the lidar signals of the main mirror of the Siberian Lidar Station (SLS) is evaluated. It is shown that under the lidar signal recording in the photon counting mode, nonlinear distortion of the lidar response is observed in the altitude range from 1 to 26 km. It is shown in that the use of a combined method of the lidar signal recording can significantly expand the range of the detection linearity in the photon counting mode. Experimental testing of the lidar recording system was carried out under the detection of signals of various intensities.
The article describes the technique and equipment created on the basis of unique equipment of the Siberian Lidar Station (SLS) for regular measurements of the vertical temperature profile of the atmosphere based on the joint use of the methods of pure rotational Raman spectra (PRRS) and Rayleigh scattering. A block diagram of the lidar complex based on the main receiving mirror of the SLS with the diameter of 2.2 m is presented.
To assess the parameters of the control loop of the automatic tuning system of the SLS lidar complex, the transfer function of the precision mechanism for adjusting the transmitting mirror of the transceiver was studied. To assess the possibility of using a single polychromator to select areas of the Raman spectra when measuring the temperature of the stratosphere, the level of suppression of the unshifted scattering line in a modernized single polychromator has been measured.
The article deals with the problem of developing a technique and creating equipment for regular observations of stationary variations in the vertical distribution of the stratosphere temperature. As a methodical basis, it is proposed to use a method for measuring the temperature of the atmosphere from the ratio of intensities of the sections of the purely rotational spectrum of spontaneous Raman scattering on nitrogen and oxygen molecules. A block diagram of a lidar based on the use of a single diffraction polychromator in combination with the transmission of optical signals by optical fibers is given. An experimental estimation of the total quantum efficiency of the photon counting system is carried out. The obtained data made it possible to clarify the technical parameters of the lidar and to increase the reliability of the estimate.
We summarize and analyze the lidar measurements (Tomsk: 56.5°N; 85.0°E) of the optical characteristics of the
stratospheric aerosol layer (SAL) in the volcanic activity period 2006-2011. The background SAL state with minimal
aerosol content, which was observed since 1997 under the conditions of long-term volcanically quiescent period, was
interrupted in October 2006 by a series of explosive eruptions of volcanoes of the Pacific Ring of Fire: Rabaul (October
2006, New Guinea); Okmok and Kasatochi (July-August 2008, Aleutian Islands); Redoubt (March-April 2009, Alaska);
Sarychev Peak (June 2009, Kuril Islands), and Grimsvötn (May 2011, Iceland). A short-term and minor disturbance of
the lower stratosphere was also observed in April 2010 after eruption of the Icelandic volcano Eyjafjallajokull. The
developed regional empirical model of the vertical distribution of background SAL optical characteristics was used to
identify the periods of elevated stratospheric aerosol content after each of the volcanic eruptions.
In 2010 and first half of 2011, a background aerosol content was observed in the atmosphere of the Northern Hemisphere
midlatitudes. The report presents the observations of aerosol disturbances of the stratosphere in the second half of 2011,
which were performed at lidar network stations of CIS countries CIS-LiNet in Minsk (53.9°N; 27.6°E), Tomsk (56.5°N;
85.0°E), and Vladivostok (43.0°N; 131.9°E). Data of lidar measurements at the sensing wavelengths of 353, 355, and
532 nm indicate that increased aerosol content was observed since June – July almost until the end of 2011 in the lower
stratosphere up to the altitudes ~ 18 km. A well-defined, temporally stable aerosol layer was observed until October 2011
in the altitude interval ~ (13-17) km.
The trajectory analysis of air mass transport in the stratosphere according to NOAA HYSPLIT MODEL with
employment of CALIPSO satellite data shows that the increased aerosol content observed was most likely due to
transport of eruption products of Grimsvötn volcano (May 21, 2011, Iceland: 64.4°N; 17.3°W).
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