RU2753651C1 - Autonomous underwater fluorimeter probe - Google Patents

Abstract

FIELD: measuring.

SUBSTANCE: invention relates to the field of research of the parameters of seawater and pertains to an autonomous underwater fluorimeter probe for measuring the bio-optical parameters of seawater. The probe is comprised of a hermetic body with an upper and a lower covers, a power supply unit, a data processing system based on a microcontroller, connected with an ADC unit, temperature and pressure sensors for the outboard water, installed in the upper cover, as well as sensors hermetically installed in the lower cover of the body. The sensors comprise, connected with the data processing system, a coherent fluorescence excitation source in the form of a semiconductor laser emitting at a wavelength of 447 nm with an optical focusing system and a sealed port hole, and highly sensitive photodiodes with peak sensitivity at a wavelength of 690 nm and corresponding optical filters and focusing lenses, recording the intensity of laser emission, chlorophyll "A" fluorescence emission, Raman scattering of water, and fluorescence of dissolved organic substances.

EFFECT: increasing the accuracy of recording of fluorescence emission, reducing the power consumption, reducing the dimensions, increasing the autonomy and reliability of the apparatus.

1 cl, 3 dwg

Description

The invention relates to instrumentation for studying the parameters of seawater by spectrofluorometry and can be used in ecology, limnology, oceanology as a device for in situ studies of the functioning of phytoplankton communities and the processes of distribution of dissolved organic substances, as well as for monitoring anthropogenic pollution of marine and freshwater areas.

Known fluorimeter designed for installation on controlled underwater vehicles (p. US No. 8017928 B2). The device is a sealed case of two blocks, one of which contains a source of exciting radiation based on a powerful LED with an optical system for focusing this radiation into the water column, and the second contains a highly sensitive photodiode fluorescence sensor. The device records the fluorescence of pollutants dissolved in water directly in the water column, without using a flow cell.

Also known is a fluorometer probe for measuring the concentration of chlorophyll A, which uses a powerful light-emitting diode emitting at a wavelength of 350 nm as a fluorescence excitation source (China No. 101403695 A). The device is a sealed stainless steel body immersed in water, in which a data processing system based on a microcontroller is installed, to which a signal from a highly sensitive photodiode is supplied. The device has no built-in memory for recording measurement results and requires a permanent connection to a PC.

The main disadvantages of the known solutions is the use of an incoherent LED radiation source for fluorescence excitation, which reduces the measurement accuracy and increases power consumption. In addition, the known solutions do not register such auxiliary optical parameters as Raman scattering (RS) of water, fluorescence of dissolved organic substances (DOM), which are necessary for normalizing and correcting the measured values of chlorophyll A fluorescence, which reduces the measurement accuracy.

Known two-channel fluorometer for recording and measuring the dynamics of the differential fluorescent signal of nano- and micro-objects, which is technically the closest to the proposed one. The fluorimeter is made in the form of a sealed case with top and bottom covers, contains a sealed cuvette with a measuring chamber with a lid, batteries, highly sensitive photodiodes in combination with interference filters with sealed windows, a powerful LED radiation source with a focusing system and a sealed window, an ADC unit, a processing system data on the basis of a microcontroller, and also equipped with sensors for measuring temperature and pressure (p. RF №2375701 C1).

The main disadvantage of this solution is also the use of an incoherent LED source as a source of fluorescence excitation, which generates both radiation in a given wavelength range and "spurious" radiation in a wide spectral range and requires a complex optical focusing system and expensive narrow-band interference filters, which reduces the intensity exciting radiation and deteriorates the energy efficiency of the device, increases the dimensions of the device and reduces its reliability. In addition, LED sources have a dependence of the excitation radiation wavelength on the device temperature, which further reduces the measurement accuracy due to the fact that variations in the excitation radiation wavelength lead to variations in the recorded fluorescence signals and thus enter into the error of the resulting measurements.

The device registers the fluorescence of various nano and micro-objects, as well as the temperature and pressure of the medium, but does not register auxiliary optical parameters, for example, such as Raman scattering of water, fluorescence of dissolved organic substances (DOM) and others necessary for normalizing and correcting the measured fluorescence values. In addition, the prototype uses a measuring chamber through which water is pumped through a pump, which increases energy consumption and reduces autonomy.

The problem being solved is the expansion of the range of autonomous underwater "probes-fluorimeters.

EFFECT: proposed design of the probe allows to obtain high accuracy of registration of fluorescence radiation (sensitivity to fluorescence radiation), provides low power consumption, increased autonomy, has small overall dimensions and high reliability.

The problem is solved by an autonomous underwater probe - a fluorimeter for measuring the bio-optical parameters of seawater, including a pressurized housing with upper and lower covers, containing a data processing system based on a microcontroller, an ADC unit, batteries, seawater temperature and pressure sensors installed in the upper cover, as well as, containing satellites hermetically installed in the bottom cover of the housing, including a coherent excitation source connected to the data processing system in the form of a semiconductor laser emitting at a wavelength of 447 nm with an optical focusing system and a sealed window, high-sensitivity photodiodes with a peak sensitivity at a wavelength of 690 nm, and appropriate optical filters and focusing lenses, recording the intensity of laser radiation, fluorescence emission of chlorophyll "A", Raman scattering of water and fluorescence of dissolved organic substances.

FIG. 1 shows the location of the windows of the excitation source and satellite sensors, where 1 is the receiving window of the chlorophyll A fluorescence sensor; 2 - a satellite-emitter containing a powerful semiconductor laser; 3 - satellite sensor designed to register the intensity of laser radiation; 4 - satellite sensor registering the intensity of the Raman scattering (RR) peak of water; 5 - satellite sensor registering the intensity of fluorescence of dissolved organic substances (DOM).

FIG. 2 shows a schematic diagram of the proposed fluorometer probe, where 1.1 is a photodiode of a chlorophyll fluorescence sensor, 1.2 is an optical filter of a fluorescence sensor, 2.1 is a semiconductor laser with an optical focusing system; 3.1 - photodiode of the laser radiation intensity sensor; 3.2 - optical filter of the laser radiation intensity sensor; 4.1- photodiode of the KR sensor; 4.2 - optical filter of the KR sensor; 5.1 - photodiode of the DOM fluorescence sensor; 4.2 - optical filter of the DOM fluorescence sensor; 6 - data processing system based on a microcontroller; 7 - ADC; 8 - seawater temperature sensor; 9 - pressure sensor; 10 - nonvolatile memory; 11 - power supply unit.

FIG. 3 shows a photograph of the bottom cover of the fluorimeter probe.

An autonomous underwater fluorometer probe is a sealed metal case with top and bottom covers. Inside the case there are large-capacity batteries, for example, lithium, as well as a data processing system based on a microcontroller (6). On the top cover of the device there are sensors that measure temperature (8) and seawater pressure (9). In the central part of the bottom cover of the device there is a receiving window (1) of a sensor that records the intensity of chlorophyll A fluorescence, a satellite-emitter (2.1) containing a powerful semiconductor laser emitting at a wavelength of 447 nm, interlocked with an optical focusing system, and satellite sensors designed to register the intensity of laser radiation (3), the peak of Raman scattering (RS) of water (4) and the intensity of fluorescence of dissolved organic substances (DOM) (5). All sensors are located at right angles to each other along the axes of the Cartesian coordinate system.

A semiconductor laser with high efficiency and generating coherent radiation at a strictly specified wavelength of 447 nm, for example, of the PL-TB450 V type, is used as a source of fluorescence excitation (2.1).

The probe is capable of autonomously operating at depths of up to 100 meters for four days and measuring bio-optical parameters in the water column, without using a pump pumping water through the measuring cuvette.

The additionally installed satellite sensors (3-5) make it possible to expand information on the state of phytoplankton communities and their functioning and to increase the accuracy of measuring the fluorescence of chlorophyll-A.

The device works as follows. Before immersing the fluorimeter probe in water, the top cover is removed from it, under which are located the "work / sleep" switch and the MicroUSb connector of the microcontroller for connection to a working computer installed on the data processing system board (6). The probe is connected to a computer via a data cable, with the help of which the basic measurement parameters are set, after which the "work / sleep" switch is set to the "work" position, the lid is hermetically closed and the probe is immersed in water.

In the "work" mode, the microcontroller of the data processing system (6) (Fig. 2), at specified time intervals, gives a signal to turn on the semiconductor laser (2.1) installed in the satellite and operating at a wavelength of 447 nm, which is optimal for simultaneous recording fluorescence of chlorophyll A, fluorescence of DOM at a wavelength of 500 nm and Raman scattering of water at a wavelength of 532 nm (Popik A.Yu. Dynamics of spectra of laser-induced fluorescence of phytoplankton chlorophyll-a in conditions of changing environmental parameters Thesis for the degree of candidate of physical and mathematical Sciences Vladivostok 2015 p. 17. Figure 1.2).

As a result of exposure to optical radiation in water, the following optical effects arise: elastic scattering at the wavelength of laser radiation, Raman scattering by water molecules, proportional to the intensity of the exciting laser radiation, fluorescence of chlorophyll A contained in phytoplankton cells, fluorescence, dissolved organic matter (DOM), arising from the vital activity of phytoplankton, rising from the bottom, or terrigenous origin. To normalize and correct the recorded fluorescence signals of chlorophyll A and DOM, taking into account the optical properties of the analyzed volume of water, the intensity of the Raman scattering of water, as well as the temperature of the seawater, are used. The DOM fluorescence intensity is used to correct the chlorophyll A fluorescence signal in waters with a high DOM content, where these substances begin to affect the fluorescence in the 660-700 nm region. After switching on the laser (2.1), the microcontroller of the data processing system (6) sequentially polls the inputs of a multi-bit, for example, 18-bit, ADC (7), which are connected to integrated high-sensitivity photodiodes (1.1,3.1,4.1,5.1), for example, of the TSL2571f type. Highly sensitive photodiodes, each located in its own satellite sensor, are interlocked with appropriate optical filters and focusing lenses (1.2,3.2,4.2,5.2), which ensures registration of radiation in the spectral ranges corresponding to the effects described above: Raman scattering at a wavelength of 532 nm, fluorescence of chlorophyll "A" at a wavelength of 680 nm, fluorescence of DOM at a wavelength of 500 nm, as well as the intensity of laser radiation in order to check that the laser is operating in the normal mode. Also, the microcontroller of the data processing system (6) interrogates digital temperature sensors (8) and seawater pressure (9). All data received from the ADC channels (7) are written into the data processing system (6) and the nonvolatile memory of the device (10). After the specified experiment time has elapsed, the fluorimeter probe is removed from the water and, with the help of the switch, is switched to the "sleep" mode. Subsequently, using a working PC, the data of the measurements are retrieved from the fluorometer, the battery is charged and the device is prepared for the next series of measurements.

All elements of the device are commercially available, and the indicated wavelengths are known for recording these effects. (Popik A.Yu. Dynamics of the spectra of laser-induced fluorescence of chlorophyll-a of phytoplankton in the conditions of changing environmental parameters Dissertation for the degree of candidate of physical and mathematical sciences Vladivostok 2015 p. 17. Figure 1.2; Schmidt V. Optical spectroscopy for chemists and biologists. Moscow: Technosphere, 2007 p. 312; AN Drozdova Optical properties of the dissolved organic matter of the surface layer of the Laptev Sea water Optics and spectroscopy, 2019, volume 126, issue 3). The probe body can be made of either thermosetting plastic or metal.

Due to the proposed design of the probe, which uses a semiconductor laser as an excitation source, which has a high efficiency and generates coherent radiation at a strictly specified wavelength of 447 nm, and does not contain a flow cell and a pump required for forced pumping of liquid through the cell, it allows significant reduce power consumption, increase the autonomy and reliability of the device, as well as reduce its dimensions, while the use of satellite sensors measuring auxiliary optical parameters necessary for normalizing and adjusting the measured values of fluorescence: CR-water, DOM fluorescence, laser radiation intensity, the proposed probe -fluorimeter, allows you to increase the accuracy of measuring the fluorescence of chlorophyll "A".

Claims (1)

An autonomous underwater fluorimeter probe for measuring the bio-optical parameters of seawater, consisting of a pressurized housing with upper and lower covers and containing a power supply, a microcontroller-based data processing system connected to an ADC unit, seawater temperature and pressure sensors installed in the upper cover, and also hermetically installed in the lower housing cover - satellites, including a coherent source of fluorescence excitation connected to the data processing system in the form of a semiconductor laser emitting at a wavelength of 447 nm with an optical focusing system and a sealed window, and high-sensitivity photodiodes with a peak sensitivity at a wavelength of 690 nm and appropriate optical filters and focusing lenses, recording the intensity of laser radiation, fluorescence emission of chlorophyll "A", Raman scattering of water and fluorescence of dissolved organic substances.

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