rus
Issue #6/2023
M. P. Ivanov, S. G. Dolgikh
Calculation of the Field Data Conversion Coefficient of a Laser Meter for Hydrosphere Pressure Variations
Calculation of the Field Data Conversion Coefficient of a Laser Meter for Hydrosphere Pressure Variations
DOI: 10.22184/1993-7296.FRos.2023.17.6.462.472
Calculation of the Field Data Conversion Coefficient of a Laser Meter for Hydrosphere Pressure Variations
M. P. Ivanov, S. G. Dolgikh
V. I. Il’ichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia
The paper presents a determination method for the field data conversion coefficient of the laser-interferential instruments developed on the basis of equal-arm and unequal-arm Michelson interferometers, into the values of hydrospheric pressure variations during the sea wave registration. Based on a comparison of experimental data obtained in the bays of the Primorsky Territory in various wave period ranges and at different depths, it is shown that there is a strong dependence of the dimension conversion coefficient on the depth of immersion.
Key words: laser meter for hydrosphere pressure variations, sound velocimeter with pressure and temperature sensor, sea disturbance
Article received: 30.05 2023
Article accepted: 15.07. 2023
INTRODUCTION
Earlier, in the early 2000s, the staff of the laboratory for geosphere physics, V. I. Il’ichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences, developed the hydrophysical laser-interferential receiving systems for recording pressure variations in the hydrosphere. These are the unique laser-interferential devices based on the equal-arm and unequal-arm Michelson interferometers [1]. With the expansion of the list of tasks to be solved, the design of devices has undergone many changes, some modifications have appeared: a laser meter for hydrosphere pressure variations [2], laser hydrophones [3, 4], and an autonomous laser meter for pressure fluctuations [5].
Two types of lasers are used as the light sources in all indicated modifications of hydrosphere pressure recording devices: a frequency-stabilized helium-neon laser and a diode laser. Application of a diode laser made it possible to significantly reduce the weight and dimensions of the devices. All laser-interferential receiving systems were tested in various water areas: at the marine experimental station, V. I. Il’ichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences “cape Schultz” in the south of the Primorsky Territory, at “cape Svobodniy” (Sakhalin Island) and in the waters of other bays. A wide frequency range (from 0 (conditionally) to 1,000 Hz) and high accuracy (about 1 mPa) make it possible to record the hydrospheric pressure variations by direct methods that significantly increases the values of field data obtained.
Application of the hydrophysical laser-interferential receiving systems made it possible to study the own oscillation period of the bays in the Posyet Bay of the Sea of Japan [6], interaction of the low-frequency hydroacoustic waves with wind-induced sea waves [7], the dynamics of wind-induced waves when moving along the shelf of decreasing depth [8], features of the occurrence of sea infragravitational waves [9], interaction of the sea internal waves and atmospheric depressions [10] and some other natural phenomena. When solving such scientific problems, primary attention was paid to the sea disturbance period values increase in the amplitudes. To obtain the height of sea waves, the theoretical calculations and laboratory benches were used.
The sensitive element of laser-interferential receiving systems is a round membrane rigidly fixed around the perimeter. Depending on the pressure changes at the bottom, the membrane center deflection is changed that is determined by the laser interference method. To determine the pressure variations, it is necessary to recalculate the displacement values determined by the laser-interferential devices in the length units and recorded in volts, voltage units, by the membrane piezo-pushers into pascals, the pressure units. The parameter linking the dimensions is called the conversion factor, and it is calculated experimentally for each device. The conversion factor determination procedure is rather conventional; for this purpose, the laser meter for hydrosphere pressure variations (LMHPV) are immersed in a basin where the water is initially rising, while increasing the pressure, and then lowering, while reducing the pressure.
Over the past years, new issues have appeared, the solution of which has required another sensitivity level of the tools used. To expand the application boundaries of the laser-interferential devices in the field of hydrospheric pressure recording, it is necessary to calculate the field data conversion coefficient of the LMHPV. For this purpose, as well as for determination of the dependence of field data conversion factor on the measurement conditions, a series of experiments and tests were performed in various bays of the Primorsky Territory. The experimental design assumed the LMHPV installation together with a Valeport Mini SVP sound velocimeter with a pressure and temperature sensor (Mini SVP) [11]. The measurements were performed at different depths. The results obtained from both devices were compared and grouped by the waves with various periods. For each group of waves, the field data conversion coefficient of the LMHPV was calculated depending on the depth of immersion.
Experiment
The laser meter for hydrosphere pressure variations and a Mini SVP sound velocimeter by Valeport were used as the receiving measurement systems in the experimental studies (Fig. 1). For synchronization, the Mini SVP (2) was attached to the measuring module of the laser-interferential device (1) and installed on the bottom. Prior to installation, the devices were synchronized using an exact time clock. The LMHPV optical circuit was based on a modernized unequal-arm Michelson interferometer using a Melles Griot frequency-stabilized helium-neon laser as a light source that ensured the radiation frequency stability of 10–9. As in all laser-interferential devices, the digital registration system (5) in this setup measured the difference between the interferometer reference arm and the active arm. The radiation in the interferometer reference arm passes along the optical path from the dividing plate to the mirrors installed on the piezoceramic bases (4) and back. The radiation in the interferometer active arm passes along the optical path from the dividing plate to the “cat’s eye” system, consisting of a lens (6) and a mirror rigidly fixed in the center of the flexible membrane (7). After returning to the dividing plate, both beams are combined and become incident to the photodetector while generating an interference pattern.
The LMHPV detecting element is a round membrane fixed along the edge. It is set to the neutral position when the device is placed on the bottom. Such position is ensured due to the compensation system consisting of a balance chamber, a valve (8) and an air tank (1). During the device immersion, the valve is opened and, under the influence of water pressure, air from the tank begins to flow into the balance chamber, while equalizing the pressure in the chamber with the pressure acting on the membrane from the other side. After reaching the working depth, the valve is closed, and the device begins to register the hydrosphere pressure variation on the membrane. Under the water pressure, the membrane is bent while changing the optical length of the active arm. The registration system installed in the measuring module compensates for any length changes of the active arm by changing the length of the reference arm. For this purpose, a piezoceramic cylinder is used, to which voltage is applied. The change in the voltage values is recorded by a digital registration system and transmitted to a recording computer installed in the autonomization module. The experimental data are received from the registration system through an automatic digital converter and are generated in the form of data files with a duration of 1 hour and a sampling frequency of 800 Hz.
The joint measurement results of a laser meter for hydrosphere pressure variations and a Valeport Mini SVP sound velocimeter attached to it were obtained in three bays of the Primorsky Territory at various depths. In the Alekseev Bay (Popov Island), the instruments were installed on June 24, 2021 at a depth of 8 m (Fig. 2a). In the Uliss Bay (Vladivostok), the experiment was performed during the period from July 06, 2021 to July 13, 2021. The depth at the installation site was 7 m (Fig. 2b). In the Vityaz Bay of the Posyet Bay, the instruments were located at a depth of 5 m during the period from June 30, 2022 to July 1, 2022 (Fig. 2c).
The Mini SVP installed on the measuring module has a lower autonomy; at a recording frequency of 8 Hz, it is a little more than one day. The data of pressure variations in the hydrosphere were recorded in a continuous form on the internal bulk storage of the device at a frequency of 8 Hz. To compare the experimental data, the pressure sensor data only will be used.
Processing and analysis of the obtained experimental data
Prior to comparing the experimental data, the records of hydrospheric pressure variations will be reduced to the unified form. For this purpose, the LMHPV data will be filtered by a low-pass filter with a Hamming window with the length of 3000 to a frequency of 8 Hz and then prodecimated by a factor of 100. The resulting one-hour files will be combined into a continuous data series. As a result, we obtain the LMHPV and Mini SVP experimental data of the same duration with a sampling rate of 8 Hz. When analyzing the experimental data spectra, the harmonics with periods from several seconds to several minutes were identified. The periods with the duration from 4 to 6 s correspond to the surface wind-induced waves at the instrument installation site, and the periods with the duration from 8 to 20 s correspond to the swell waves. Moreover, the device records demonstrate oscillations with the periods relevant to the natural disturbances of the bays where they have been installed. The synchronous sections of instrument records with the maximum correlations for various periods of sea disturbances for each of the bays will be selected (Fig. 3).
Figure 3 presents the obtained experimental data on hydrospheric pressure variations by two instruments for each of the bays: the signals in Fig. 3a and Fig. 3b correspond to the data obtained by the Mini SVP and LMHPV in the Alekseev Bay (Popov Island), the signals in Fig. 3c and Fig. 3d were obtained during the installation of devices in the Uliss Bay (Vladivostok), the signals in Fig. 3e and Fig. 3d were obtained during the experiment in the Vityaz Bay (Posyet Bay). The blue color corresponds to the experimental data of the pressure sensor of the Mini SVP sound velocimeter, and the red color corresponds to the data of the laser meter for hydrosphere pressure variations.
When analyzing the spectra of instrument records for calculating the conversion coefficient, the sea disturbances were divided into the groups. Figure 4 shows the spectra of records of sea wave instruments with the periods from 5.5 to 30 s (left) and from 100 to 350 s (right). We divide the waves into the groups as follows: the first group with waves in the range from 5 to 10 s, the second group with the periods from 10 to 30 s and the third group with the periods of sea disturbances from 100 to 400 s. Variations in the sea disturbances with these periods were recorded in each experiment. The fourth group includes the natural disturbances of the bays where the devices have been installed. These fluctuations for various device installation points ranged from 600 to 1100 s.
We select several trains of waves for each group on the records of the laser-interferential device and the pressure sensor of the sound velocimeter with the maximum correlation. Figure 5 shows the synchronous segments of instrument records when they were installed in the Alekseev Bay (Popov Island). On the top record, the wind-induced waves with a period of about 6 s are emphasized, and on the bottom record, the natural disturbances of the bay with the periods of about 600 s are indicated [12].
For the sea disturbances with an oscillation period of 5 to 10 s, twenty such areas were selected for each of the three bays where the instruments were installed. As a result of comparing the experimental data of two devices for a given range of periods, when the device was immersed to 5 meters, the average coefficient was about 10 Pa / V, when the devices were immersed to a depth of 7 meters, it was 26 Pa/V, and when the devices were installed to a depth of 8 meters, the average coefficient value was approximately 39 Pa/V. Based on the data obtained, the dependence of the conversion coefficient on the depth of immersion for the sea disturbances with the periods from 5 to 10 s was plotted (Fig. 6a).
Let us analyze the pressure variations with the periods from 10 to 30 s. For this range of periods, twenty sites were selected for each of the bays. When comparing the experimental data of LMHPV and Mini SVP in the Vityaz Bay (Posyet Bay), the average coefficient value was 11.6 Pa/V. When installing the devices in the Uliss Bay (Vladivostok), the average coefficient was 29 Pa/V, and when comparing the data of pressure variations in the Alekseev Bay (Popov Island), it was 39 Pa/V. As a result, according to the experimental data obtained related to the hydrosphere pressure variations with the periods from 10 to 30 s, the dependence of this coefficient on the immersion depth was indicated (Fig. 6b).
We will consider the sea disturbances with the periods from 180 to 360 s. For such sea disturbances, the synchronous sections of instrument records with the maximum correlation were selected for each of the three bays. When comparing the amplitude values of pressure fluctuations, the average conversion coefficient value for a depth of 5 m was 12.5 Pa/V. When setting up the instruments at a depth of 7 m, the average coefficient value was 29 Pa/V. When the instruments were immersed to a depth of 8 m, this value turned out to be 36 Pa/V. According to the obtained calculated data, the dependence of the conversion coefficient on the depth of immersion for the sea disturbances with the periods from 180 to 360 s was plotted (Fig. 6c).
When analyzing the experimental data of devices during registration of natural oscillations in the bays with the periods from 600 to 1200 s, about 10 synchronous sites were selected for each of the bays. For this range of periods, when the meters were installed in the Vityaz Bay (Posyet Bay), the average coefficient value was 11.5 Pa/V. For a depth of 7 m, the average coefficient value was 28 Pa/V, and when analyzing the experimental data obtained in the Alekseev Bay (Popov Island), the coefficient was equal to 38 Pa/V. As a result of the experimental data analysis on the hydrosphere pressure variations during the registration of natural oscillations in the bays, the dependence of the average conversion coefficient value on the immersion depth of the devices was noted (Fig. 6d).
As a result of calculations, the dependence of the data conversion coefficient of the laser meter for hydrosphere pressure variations on the depth of immersion was found. For all ranges of sea disturbance periods under study, the calculated conversion coefficients for each device installation site demonstrated approximately equal values. There is a strong dependence of the dimension conversion coefficient on the depth of immersion. As a result, the average value of the conversion coefficient for the Vityaz Bay when the devices were installed at a depth of 5 m was 11.6 Pa/V, for the Uliss Bay at a depth of 7 m the average conversion coefficient value was 28.1 Pa/V, and for the Alekseev Bay when the instruments were installed at a depth of 8 m it was equal to 38 Pa/V.
Conclusion
As a result of the experimental data analysis of the laser meter for hydrosphere pressure variations and the pressure sensor of the Valeport Mini SVP sound velocimeter, the data conversion coefficient of the laser-interferential device was calculated depending on the immersion depth. The studies were performed in three bays of the Primorsky Territory at various depths, namely in the Vityaz Bay (Posyet Bay) at a depth of 5 m, in the Uliss Bay (Vladivostok) at a depth of 7 m and in the Alekseev Bay (Popov Island) at a depth of 8 m. For each of the bays, the synchronous sections of device records with the maximum correlation for various ranges of sea disturbances were selected. In total, four ranges of periods were selected from the wind-induced waves to the natural oscillations of the bays where the instruments were installed. Based on the data obtained, the LMHPV data conversion coefficient from the dimension of voltage, expressed in volts, to the dimension of pressure, expressed in pascals, was determined. Thus, at a depth of 5 m, it was approximately 11.6 Pa/V, at a depth of 7 m, the average conversion coefficient was 28.1 Pa/V, and when the instruments were located at a depth of 8 m, its value was 38 Pa/V.
The calculated conversion coefficient will expand the scope of application of laser meter for hydrosphere pressure variations with various modifications. For a more precise determination of the conversion coefficient of experimental data from the laser-interferential device, it is necessary to perform further studies at great depths. Such research is scheduled to be carried out in the Vityaz Bay (Posyet Bay) at the depths of 10 to 20 m in summer-autumn 2023.
Acknowledgement
The research was performed with the partial financial support of the Russian Science Foundation, project No. 22–27–00678 “Micro-deformations of the earth’s crust caused by marine infragravity waves according to laser interference devices”.
ABOUT AUTHORS
Ivanov M. P., V. I. Il’ichev Pacific Oceanological Institute Far Eastern Branch Russian Academy of Sciences, Vladivostok, Russia.
ORCID: 0000-0003-3178-2634
Dolgikh S. G., Doctor of Technical Sciences, V. I. Il’ichev Pacific Oceanological Institute Far Eastern Branch Russian Academy of Sciences, Vladivostok, Russia.
ORCID: 0000-0001-9828-5929
M. P. Ivanov, S. G. Dolgikh
V. I. Il’ichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia
The paper presents a determination method for the field data conversion coefficient of the laser-interferential instruments developed on the basis of equal-arm and unequal-arm Michelson interferometers, into the values of hydrospheric pressure variations during the sea wave registration. Based on a comparison of experimental data obtained in the bays of the Primorsky Territory in various wave period ranges and at different depths, it is shown that there is a strong dependence of the dimension conversion coefficient on the depth of immersion.
Key words: laser meter for hydrosphere pressure variations, sound velocimeter with pressure and temperature sensor, sea disturbance
Article received: 30.05 2023
Article accepted: 15.07. 2023
INTRODUCTION
Earlier, in the early 2000s, the staff of the laboratory for geosphere physics, V. I. Il’ichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences, developed the hydrophysical laser-interferential receiving systems for recording pressure variations in the hydrosphere. These are the unique laser-interferential devices based on the equal-arm and unequal-arm Michelson interferometers [1]. With the expansion of the list of tasks to be solved, the design of devices has undergone many changes, some modifications have appeared: a laser meter for hydrosphere pressure variations [2], laser hydrophones [3, 4], and an autonomous laser meter for pressure fluctuations [5].
Two types of lasers are used as the light sources in all indicated modifications of hydrosphere pressure recording devices: a frequency-stabilized helium-neon laser and a diode laser. Application of a diode laser made it possible to significantly reduce the weight and dimensions of the devices. All laser-interferential receiving systems were tested in various water areas: at the marine experimental station, V. I. Il’ichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences “cape Schultz” in the south of the Primorsky Territory, at “cape Svobodniy” (Sakhalin Island) and in the waters of other bays. A wide frequency range (from 0 (conditionally) to 1,000 Hz) and high accuracy (about 1 mPa) make it possible to record the hydrospheric pressure variations by direct methods that significantly increases the values of field data obtained.
Application of the hydrophysical laser-interferential receiving systems made it possible to study the own oscillation period of the bays in the Posyet Bay of the Sea of Japan [6], interaction of the low-frequency hydroacoustic waves with wind-induced sea waves [7], the dynamics of wind-induced waves when moving along the shelf of decreasing depth [8], features of the occurrence of sea infragravitational waves [9], interaction of the sea internal waves and atmospheric depressions [10] and some other natural phenomena. When solving such scientific problems, primary attention was paid to the sea disturbance period values increase in the amplitudes. To obtain the height of sea waves, the theoretical calculations and laboratory benches were used.
The sensitive element of laser-interferential receiving systems is a round membrane rigidly fixed around the perimeter. Depending on the pressure changes at the bottom, the membrane center deflection is changed that is determined by the laser interference method. To determine the pressure variations, it is necessary to recalculate the displacement values determined by the laser-interferential devices in the length units and recorded in volts, voltage units, by the membrane piezo-pushers into pascals, the pressure units. The parameter linking the dimensions is called the conversion factor, and it is calculated experimentally for each device. The conversion factor determination procedure is rather conventional; for this purpose, the laser meter for hydrosphere pressure variations (LMHPV) are immersed in a basin where the water is initially rising, while increasing the pressure, and then lowering, while reducing the pressure.
Over the past years, new issues have appeared, the solution of which has required another sensitivity level of the tools used. To expand the application boundaries of the laser-interferential devices in the field of hydrospheric pressure recording, it is necessary to calculate the field data conversion coefficient of the LMHPV. For this purpose, as well as for determination of the dependence of field data conversion factor on the measurement conditions, a series of experiments and tests were performed in various bays of the Primorsky Territory. The experimental design assumed the LMHPV installation together with a Valeport Mini SVP sound velocimeter with a pressure and temperature sensor (Mini SVP) [11]. The measurements were performed at different depths. The results obtained from both devices were compared and grouped by the waves with various periods. For each group of waves, the field data conversion coefficient of the LMHPV was calculated depending on the depth of immersion.
Experiment
The laser meter for hydrosphere pressure variations and a Mini SVP sound velocimeter by Valeport were used as the receiving measurement systems in the experimental studies (Fig. 1). For synchronization, the Mini SVP (2) was attached to the measuring module of the laser-interferential device (1) and installed on the bottom. Prior to installation, the devices were synchronized using an exact time clock. The LMHPV optical circuit was based on a modernized unequal-arm Michelson interferometer using a Melles Griot frequency-stabilized helium-neon laser as a light source that ensured the radiation frequency stability of 10–9. As in all laser-interferential devices, the digital registration system (5) in this setup measured the difference between the interferometer reference arm and the active arm. The radiation in the interferometer reference arm passes along the optical path from the dividing plate to the mirrors installed on the piezoceramic bases (4) and back. The radiation in the interferometer active arm passes along the optical path from the dividing plate to the “cat’s eye” system, consisting of a lens (6) and a mirror rigidly fixed in the center of the flexible membrane (7). After returning to the dividing plate, both beams are combined and become incident to the photodetector while generating an interference pattern.
The LMHPV detecting element is a round membrane fixed along the edge. It is set to the neutral position when the device is placed on the bottom. Such position is ensured due to the compensation system consisting of a balance chamber, a valve (8) and an air tank (1). During the device immersion, the valve is opened and, under the influence of water pressure, air from the tank begins to flow into the balance chamber, while equalizing the pressure in the chamber with the pressure acting on the membrane from the other side. After reaching the working depth, the valve is closed, and the device begins to register the hydrosphere pressure variation on the membrane. Under the water pressure, the membrane is bent while changing the optical length of the active arm. The registration system installed in the measuring module compensates for any length changes of the active arm by changing the length of the reference arm. For this purpose, a piezoceramic cylinder is used, to which voltage is applied. The change in the voltage values is recorded by a digital registration system and transmitted to a recording computer installed in the autonomization module. The experimental data are received from the registration system through an automatic digital converter and are generated in the form of data files with a duration of 1 hour and a sampling frequency of 800 Hz.
The joint measurement results of a laser meter for hydrosphere pressure variations and a Valeport Mini SVP sound velocimeter attached to it were obtained in three bays of the Primorsky Territory at various depths. In the Alekseev Bay (Popov Island), the instruments were installed on June 24, 2021 at a depth of 8 m (Fig. 2a). In the Uliss Bay (Vladivostok), the experiment was performed during the period from July 06, 2021 to July 13, 2021. The depth at the installation site was 7 m (Fig. 2b). In the Vityaz Bay of the Posyet Bay, the instruments were located at a depth of 5 m during the period from June 30, 2022 to July 1, 2022 (Fig. 2c).
The Mini SVP installed on the measuring module has a lower autonomy; at a recording frequency of 8 Hz, it is a little more than one day. The data of pressure variations in the hydrosphere were recorded in a continuous form on the internal bulk storage of the device at a frequency of 8 Hz. To compare the experimental data, the pressure sensor data only will be used.
Processing and analysis of the obtained experimental data
Prior to comparing the experimental data, the records of hydrospheric pressure variations will be reduced to the unified form. For this purpose, the LMHPV data will be filtered by a low-pass filter with a Hamming window with the length of 3000 to a frequency of 8 Hz and then prodecimated by a factor of 100. The resulting one-hour files will be combined into a continuous data series. As a result, we obtain the LMHPV and Mini SVP experimental data of the same duration with a sampling rate of 8 Hz. When analyzing the experimental data spectra, the harmonics with periods from several seconds to several minutes were identified. The periods with the duration from 4 to 6 s correspond to the surface wind-induced waves at the instrument installation site, and the periods with the duration from 8 to 20 s correspond to the swell waves. Moreover, the device records demonstrate oscillations with the periods relevant to the natural disturbances of the bays where they have been installed. The synchronous sections of instrument records with the maximum correlations for various periods of sea disturbances for each of the bays will be selected (Fig. 3).
Figure 3 presents the obtained experimental data on hydrospheric pressure variations by two instruments for each of the bays: the signals in Fig. 3a and Fig. 3b correspond to the data obtained by the Mini SVP and LMHPV in the Alekseev Bay (Popov Island), the signals in Fig. 3c and Fig. 3d were obtained during the installation of devices in the Uliss Bay (Vladivostok), the signals in Fig. 3e and Fig. 3d were obtained during the experiment in the Vityaz Bay (Posyet Bay). The blue color corresponds to the experimental data of the pressure sensor of the Mini SVP sound velocimeter, and the red color corresponds to the data of the laser meter for hydrosphere pressure variations.
When analyzing the spectra of instrument records for calculating the conversion coefficient, the sea disturbances were divided into the groups. Figure 4 shows the spectra of records of sea wave instruments with the periods from 5.5 to 30 s (left) and from 100 to 350 s (right). We divide the waves into the groups as follows: the first group with waves in the range from 5 to 10 s, the second group with the periods from 10 to 30 s and the third group with the periods of sea disturbances from 100 to 400 s. Variations in the sea disturbances with these periods were recorded in each experiment. The fourth group includes the natural disturbances of the bays where the devices have been installed. These fluctuations for various device installation points ranged from 600 to 1100 s.
We select several trains of waves for each group on the records of the laser-interferential device and the pressure sensor of the sound velocimeter with the maximum correlation. Figure 5 shows the synchronous segments of instrument records when they were installed in the Alekseev Bay (Popov Island). On the top record, the wind-induced waves with a period of about 6 s are emphasized, and on the bottom record, the natural disturbances of the bay with the periods of about 600 s are indicated [12].
For the sea disturbances with an oscillation period of 5 to 10 s, twenty such areas were selected for each of the three bays where the instruments were installed. As a result of comparing the experimental data of two devices for a given range of periods, when the device was immersed to 5 meters, the average coefficient was about 10 Pa / V, when the devices were immersed to a depth of 7 meters, it was 26 Pa/V, and when the devices were installed to a depth of 8 meters, the average coefficient value was approximately 39 Pa/V. Based on the data obtained, the dependence of the conversion coefficient on the depth of immersion for the sea disturbances with the periods from 5 to 10 s was plotted (Fig. 6a).
Let us analyze the pressure variations with the periods from 10 to 30 s. For this range of periods, twenty sites were selected for each of the bays. When comparing the experimental data of LMHPV and Mini SVP in the Vityaz Bay (Posyet Bay), the average coefficient value was 11.6 Pa/V. When installing the devices in the Uliss Bay (Vladivostok), the average coefficient was 29 Pa/V, and when comparing the data of pressure variations in the Alekseev Bay (Popov Island), it was 39 Pa/V. As a result, according to the experimental data obtained related to the hydrosphere pressure variations with the periods from 10 to 30 s, the dependence of this coefficient on the immersion depth was indicated (Fig. 6b).
We will consider the sea disturbances with the periods from 180 to 360 s. For such sea disturbances, the synchronous sections of instrument records with the maximum correlation were selected for each of the three bays. When comparing the amplitude values of pressure fluctuations, the average conversion coefficient value for a depth of 5 m was 12.5 Pa/V. When setting up the instruments at a depth of 7 m, the average coefficient value was 29 Pa/V. When the instruments were immersed to a depth of 8 m, this value turned out to be 36 Pa/V. According to the obtained calculated data, the dependence of the conversion coefficient on the depth of immersion for the sea disturbances with the periods from 180 to 360 s was plotted (Fig. 6c).
When analyzing the experimental data of devices during registration of natural oscillations in the bays with the periods from 600 to 1200 s, about 10 synchronous sites were selected for each of the bays. For this range of periods, when the meters were installed in the Vityaz Bay (Posyet Bay), the average coefficient value was 11.5 Pa/V. For a depth of 7 m, the average coefficient value was 28 Pa/V, and when analyzing the experimental data obtained in the Alekseev Bay (Popov Island), the coefficient was equal to 38 Pa/V. As a result of the experimental data analysis on the hydrosphere pressure variations during the registration of natural oscillations in the bays, the dependence of the average conversion coefficient value on the immersion depth of the devices was noted (Fig. 6d).
As a result of calculations, the dependence of the data conversion coefficient of the laser meter for hydrosphere pressure variations on the depth of immersion was found. For all ranges of sea disturbance periods under study, the calculated conversion coefficients for each device installation site demonstrated approximately equal values. There is a strong dependence of the dimension conversion coefficient on the depth of immersion. As a result, the average value of the conversion coefficient for the Vityaz Bay when the devices were installed at a depth of 5 m was 11.6 Pa/V, for the Uliss Bay at a depth of 7 m the average conversion coefficient value was 28.1 Pa/V, and for the Alekseev Bay when the instruments were installed at a depth of 8 m it was equal to 38 Pa/V.
Conclusion
As a result of the experimental data analysis of the laser meter for hydrosphere pressure variations and the pressure sensor of the Valeport Mini SVP sound velocimeter, the data conversion coefficient of the laser-interferential device was calculated depending on the immersion depth. The studies were performed in three bays of the Primorsky Territory at various depths, namely in the Vityaz Bay (Posyet Bay) at a depth of 5 m, in the Uliss Bay (Vladivostok) at a depth of 7 m and in the Alekseev Bay (Popov Island) at a depth of 8 m. For each of the bays, the synchronous sections of device records with the maximum correlation for various ranges of sea disturbances were selected. In total, four ranges of periods were selected from the wind-induced waves to the natural oscillations of the bays where the instruments were installed. Based on the data obtained, the LMHPV data conversion coefficient from the dimension of voltage, expressed in volts, to the dimension of pressure, expressed in pascals, was determined. Thus, at a depth of 5 m, it was approximately 11.6 Pa/V, at a depth of 7 m, the average conversion coefficient was 28.1 Pa/V, and when the instruments were located at a depth of 8 m, its value was 38 Pa/V.
The calculated conversion coefficient will expand the scope of application of laser meter for hydrosphere pressure variations with various modifications. For a more precise determination of the conversion coefficient of experimental data from the laser-interferential device, it is necessary to perform further studies at great depths. Such research is scheduled to be carried out in the Vityaz Bay (Posyet Bay) at the depths of 10 to 20 m in summer-autumn 2023.
Acknowledgement
The research was performed with the partial financial support of the Russian Science Foundation, project No. 22–27–00678 “Micro-deformations of the earth’s crust caused by marine infragravity waves according to laser interference devices”.
ABOUT AUTHORS
Ivanov M. P., V. I. Il’ichev Pacific Oceanological Institute Far Eastern Branch Russian Academy of Sciences, Vladivostok, Russia.
ORCID: 0000-0003-3178-2634
Dolgikh S. G., Doctor of Technical Sciences, V. I. Il’ichev Pacific Oceanological Institute Far Eastern Branch Russian Academy of Sciences, Vladivostok, Russia.
ORCID: 0000-0001-9828-5929
Readers feedback
