ROV-based pressure-maintained depth-keeping seawater in-situ measuring device and application thereof

Abstract

The application relates to a ROV-based pressure-maintaining fixed-depth seawater in-situ measuring device and application thereof, and belongs to the technical field of seawater in-situ measurement. The pressure-maintaining fixed-depth seawater in-situ measuring device comprises a measuring cylinder, a gas sensor, an upper end cover driving assembly and a lower end cover driving assembly. The measuring cylinder comprises a cylinder body, an upper end cover and a lower end cover. The cylinder body is installed on an ROV, and the top end and the bottom end of the cylinder body are both provided in an open manner. The upper end cover is used for opening or closing the top end opening of the cylinder body, and the lower end cover is used for opening or closing the bottom end opening of the cylinder body. The gas sensor is arranged in a measuring cavity surrounded by the upper end cover, the lower end cover and the cylinder body. The upper end cover driving assembly and the lower end cover driving assembly are both connected to the control system of the ROV, so as to drive the upper end cover and the lower end cover to be synchronously opened or synchronously closed. The ROV-based pressure-maintaining fixed-depth seawater in-situ measuring device can realize in-situ measurement of seawater samples at different water depths, and can be used for measuring the balance time of the gas sensor under different water pressure environments.

Description

Technical Field

[0001] This invention belongs to the field of in-situ seawater measurement technology, and particularly relates to an ROV-based pressure-maintaining, constant-depth seawater in-situ measurement device and its application. Background Technology

[0002] Dissolved gases in the ocean mainly include oxygen, carbon dioxide, nitrogen, methane, hydrogen sulfide, and inert gases. They are the core research objects of marine environment, biology, geochemistry, and climate system. The content of dissolved gases is affected by environmental factors such as seawater pressure, temperature, and salinity. Therefore, to obtain accurate dissolved gas concentrations, in-situ seawater measurements must be conducted.

[0003] Vertical seawater stratification typically includes the upper and middle layers, the middle layer, the far-bottom overlying water, the near-bottom overlying water (water area a few centimeters to several meters above seabed sediments), and the sediment-water interface (water area centimeters above seabed sediments). Currently, in-situ measurements of the upper and middle layers, the middle layer, and the far-bottom overlying water are usually achieved using profiling floats. These floats integrate gas sensors and utilize the float's hovering capability to measure gas concentrations at a fixed depth. However, to avoid touching the bottom, profiling floats typically stop descending at depths of tens to hundreds of meters, thus preventing in-situ measurements of the near-bottom overlying water and the sediment-water interface. In-situ measurements of the near-bottom overlying water and the sediment-water interface are usually achieved using gas sensors mounted on a seabed lander. Therefore, it is currently impossible to use a single in-situ measurement method to achieve in-situ measurements of all different seawater layers from the upper and middle layers to the sediment-water interface, making it difficult to conduct accurate analysis of all different seawater layers under the same conditions.

[0004] Currently, gas sensors used for in-situ seawater measurements typically employ membrane degassing. First, dissolved gases are separated from the seawater through a degassing membrane. The separated dissolved gases then enter the measuring chamber of the gas sensor in gaseous form for measurement, and finally, the concentration of dissolved gases in the seawater is calculated. For gas sensors using membrane degassing, the gas concentration equilibrium time directly affects the measurement efficiency and accuracy. Gas concentration equilibrium time refers to how quickly a gas system reaches a new steady-state equilibrium after a disturbance. It is a core parameter for judging measurement timeliness, data error, and observation scheme design. The equilibrium time is generally considered to be the time it takes for the reading to reach 63.2% of the concentration step difference. Currently, the existing method for measuring the equilibrium time of gas sensors involves dividing a water tank into two zones. The first zone contains water with a relatively low concentration of dissolved gas, while the second zone contains water with a relatively high concentration. The gas sensor is initially placed in the water in the first zone. Once the sensor reaches equilibrium, it is immediately switched to the water in the second zone. The equilibrium time is then calculated by observing the time required for the gas concentration to reach a concentration difference of 63.2%. However, this existing method is performed under normal laboratory pressure. In actual in-situ seawater measurements, the degassing membrane undergoes structural changes under water pressure, affecting the equilibrium time. Currently, there is no suitable device or method for measuring the equilibrium time of gas sensors under different water pressure conditions.

[0005] Existing pressure-holding sampling devices are typically used for deep-sea sampling. Each immersion in the water allows for the collection of seawater samples from a single sampling point at a fixed depth. The collected samples are then pressurized and extracted for measurement in a laboratory. These devices cannot be repeatedly activated at multiple sampling points at different depths. Therefore, they can only achieve in-situ seawater sampling and cannot be used for in-situ seawater measurement. Furthermore, they cannot enable rapid switching between seawater samples with different dissolved gas concentrations under different water pressure environments, and cannot be used for measuring the equilibration time of gas sensors. Summary of the Invention

[0006] This invention provides a pressure-maintaining, depth-controlled in-situ seawater measurement device based on ROV. Utilizing ROV diving, surfacing, and seabed operations, it enables the collection of seawater samples at different depths. Simultaneously, it maintains pressure on the sample between sampling operations and measures dissolved gas concentration. This allows for in-situ measurement of seawater samples at different depths in the upper and middle layers, the middle layer, the far-bottom overlying water, the near-bottom overlying water, and the sediment-water interface. Furthermore, it enables rapid replacement of samples with different dissolved gas concentrations during sampling, thus facilitating the measurement of the equilibration time of gas sensors under varying water pressure environments.

[0007] This invention provides a pressure-holding, constant-depth seawater in-situ measurement device based on an ROV. The device is mounted on an ROV, which is used to submerge and surface in seawater to remain at sampling points at different depths. The pressure-holding, constant-depth seawater in-situ measurement device includes: The measuring cylinder, used for collecting seawater samples, includes a cylinder body, an upper end cap, and a lower end cap. The cylinder body is installed on the ROV, with its axis set vertically. Both the top and bottom ends of the cylinder body are open. The upper end cap is used to open or close the top opening of the cylinder body, and the lower end cap is used to open or close the bottom opening of the cylinder body. When the upper and lower end caps close their respective openings, a closed and pressure-maintaining measuring cavity is formed between the upper end cap, the lower end cap, and the cylinder body to store the collected seawater samples. A gas sensor, installed inside the measuring chamber, is used to measure the dissolved gas concentration of the collected seawater sample; The upper cover drive assembly is used to drive the upper cover to open or close the top opening; The lower end cover drive assembly is used to drive the lower end cover to open or close the bottom opening; The upper and lower end cap drive components are both connected to the ROV's control system. The ROV's control system controls the upper and lower end cap drive components to open and close the upper and lower end caps synchronously multiple times at different water depth sampling points. This allows for the collection of seawater samples at different water depth sampling points and the rapid replacement of seawater samples. This is used to measure the dissolved gas concentration in seawater at different water depths and to measure the equilibrium time of the gas sensor under the corresponding water pressure at different water depths.

[0008] In some embodiments, the upper end cap drive assembly includes a first hydraulic cylinder and an upper end cap connecting rod. The first hydraulic cylinder is connected to the hydraulic system of the ROV and includes a first cylinder body and a first piston rod. The first cylinder body is mounted on the ROV, and the first piston rod extends vertically from the top of the first cylinder body. The free end of the first piston rod is connected to the upper end cap via the upper end cap connecting rod. The lower end cap drive assembly includes a second hydraulic cylinder and a lower end cap connecting rod. The second hydraulic cylinder is connected to the hydraulic system of the ROV and includes a second cylinder body and a second piston rod. The second cylinder body is mounted on the ROV, and the second piston rod extends vertically from the top of the second cylinder body. The free end of the second piston rod is connected to the lower end cap via the lower end cap connecting rod. The ROV's control system controls the hydraulic system to simultaneously inject or retract hydraulic oil into the first and second hydraulic cylinders to control the synchronous extension and retraction of the first and second piston rods.

[0009] In some embodiments, there are two first hydraulic cylinders, which are symmetrically arranged with respect to the axis of the cylinder. The upper end cover connecting rod extends radially along the cylinder and is located above the upper end cover. The middle part of the upper end cover connecting rod is connected to the upper end cover, and the two ends of the upper end cover connecting rod are respectively connected to the first piston rods of the two first hydraulic cylinders. There are two second hydraulic cylinders, which are symmetrically arranged with respect to the axis of the cylinder. The lower end cover connecting rod extends radially along the cylinder and is located below the lower end cover. The middle part of the lower end cover connecting rod is connected to the lower end cover, and the two ends of the lower end cover connecting rod are respectively connected to the second piston rods of the two second hydraulic cylinders.

[0010] In some embodiments, the measuring cylinder further includes a first guide flare and a second guide flare. The first guide flare is located above the cylinder body, and its small end is connected to the outer periphery of the top end of the cylinder body and communicates with the top opening. The second guide flare is located below the cylinder body, and its small end is connected to the outer periphery of the bottom end of the cylinder body and communicates with the bottom opening.

[0011] The present invention also provides the application of the ROV-based pressure-maintaining, constant-depth seawater in-situ measurement device described in any of the above technical solutions in obtaining the relationship between dissolved gas concentration in seawater and water depth, including the following steps: S11. Determine the sampling interval time. Multiply the sampling interval time by the set movement speed of the ROV to obtain the water depth between sampling points. Set multiple sampling points from the sea surface to the seabed according to the water depth between sampling points, with the seabed as one sampling point. S12. Install the pressure-holding and constant-depth seawater in-situ measurement device on the ROV. In an air environment, use the ROV to control the upper and lower end caps to close synchronously, so that the measurement chamber is filled with air, and use air as the initial sample to be tested. S13. The ROV, carrying a pressure-maintaining and constant-depth seawater in-situ measurement device, descends from the sea surface to the seabed at a set moving speed, and then rises from the seabed back to the sea surface. During the descent and ascent, the ROV stops at each sampling point in sequence to collect samples. The specific sampling steps are as follows: control the upper and lower end caps to open synchronously, so that the seawater at the current sampling point replaces the sample to be tested in the measurement chamber; control the upper and lower end caps to close synchronously to reform the measurement chamber and complete the sampling. During the process of the ROV moving from the current sampling point to the next sampling point, the gas sensor collects and records the gas concentration of the sample to be tested in the measurement chamber in real time. The gas concentration collected by the gas sensor at the moment when the ROV reaches the next sampling point but has not yet been sampled is taken as the dissolved gas concentration at the corresponding water depth of the current sampling point. S14. Based on the dissolved gas concentration at each sampling point at the corresponding water depth during the descent or ascent process, draw a graph showing the change of seawater dissolved gas concentration with water depth.

[0012] In some embodiments, the step of determining the sampling interval time in step S11 is as follows: the equilibrium time of the gas sensor under atmospheric pressure is taken as the minimum equilibrium time, and the product of the minimum equilibrium time and the set amplification factor is taken as the sampling interval time.

[0013] Furthermore, the present invention also provides the application of the ROV-based pressure-maintaining deep-sea in-situ measurement device described in any of the above technical solutions in obtaining the relationship between the equilibrium time of a gas sensor and water pressure, including the following steps: S21. Determine the sampling interval time. Multiply the sampling interval time by the set movement speed of the ROV to obtain the water depth between sampling points. Set multiple sampling points from the sea surface to the seabed according to the water depth between sampling points, with the seabed as one sampling point. S22. Install the pressure-holding and constant-depth seawater in-situ measurement device on the ROV. In an air environment, use the ROV to control the upper and lower end caps to close synchronously, so that the measurement chamber is filled with air, and use air as the initial sample to be tested. S23. The ROV, carrying a pressure-maintaining, constant-depth seawater in-situ measurement device, descends from the sea surface to the seabed at a set moving speed, and then rises from the seabed back to the sea surface. During the descent and ascent, the ROV stops at each sampling point in sequence to collect samples. The specific sampling steps are as follows: control the upper and lower end caps to open synchronously, so that the seawater at the current sampling point replaces the sample to be tested in the measurement chamber; control the upper and lower end caps to close synchronously to reform the measurement chamber and complete the sampling. The timing starts when the ROV begins to descend from the sea surface. As the ROV moves from the current sampling point to the next sampling point, the gas sensor collects and records the gas concentration of the sample to be tested in the measurement chamber and the corresponding time in real time. The gas concentration collected by the gas sensor at the moment when the ROV reaches the next sampling point but has not yet been sampled is taken as the dissolved gas concentration at the corresponding water depth of the current sampling point. S24. The concentration step at the current sampling point is taken as the concentration step when the gas concentration changes from the dissolved gas concentration at the previous sampling point to the dissolved gas concentration at the current sampling point. The gas concentration at which the gas concentration reaches 63.2% of the concentration step difference is taken as the equilibrium gas concentration. The equilibrium gas concentration and the gas concentration and time data recorded by the gas sensor from the current sampling point to the next sampling point are used to calculate the equilibrium time of the gas sensor under the water pressure at the current sampling point. S25. Calculate the corresponding water pressure based on the water depth at each sampling point, and combine the equilibrium time of the gas sensor at each sampling point with the water pressure to plot the equilibrium time of the gas sensor as a function of water pressure.

[0014] In some embodiments, the step of determining the sampling interval time in step S21 is as follows: the equilibrium time of the gas sensor under atmospheric pressure is taken as the minimum equilibrium time, and the product of the minimum equilibrium time and the set amplification factor is taken as the sampling interval time.

[0015] In some embodiments, in step S24, the first i The formula for calculating the equilibrium gas concentration corresponding to each sampling point is as follows: , in, i =1, 2, ..., n , n The total number of sampling points. For the first i The equilibrium gas concentration corresponding to each sampling point For the first i Dissolved gas concentration corresponding to each sampling point For the first i -1 sampling point corresponding to the dissolved gas concentration; when i When =1, The initial concentration of the dissolved gas to be measured in the air is taken as the concentration collected by the gas sensor at the moment when the ROV arrives at the first sampling point but before sampling is performed. During calculation, and All data recorded during the descent are taken, or all data recorded during the ascent are taken.

[0016] In some embodiments, in step S24, the first i The specific calculation steps for the equilibrium time of the gas sensor under water pressure corresponding to each sampling point are as follows: From the gas sensor since the first... i From the sampling point to the... i Search for the gas concentration and corresponding time data recorded during the +1 sampling process to find the first time the concentration reaches the specified value. i The time corresponding to the equilibrium gas concentration at each sampling point Combined with ROV to reach the first i Time of each sampling point ,according to Calculate to obtain the first i Each sampling point corresponds to the balancing time of the gas sensor under water pressure. .

[0017] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. The ROV-based pressure-maintaining, constant-depth seawater in-situ measurement device provided by this invention comprises a measuring cylinder consisting of an open-top and open-bottom cylinder, which, in conjunction with an upper end cap and a lower end cap, forms a measuring cylinder. The measuring cylinder is carried by an ROV, which, by diving or surfacing, can transport the measuring cylinder to sampling points at different depths, including the upper and middle layers, the middle layer, the far-bottom overlying water, the near-bottom overlying water, and the sediment-water interface. At the sampling point, the ROV's control system controls the upper and lower end cap drive components to synchronously open the upper and lower end caps, enabling the sampling... Seawater at the sampling point enters the cylinder rapidly through the top and bottom openings. By controlling the simultaneous closing of the upper and lower end caps, a closed and pressure-maintaining measurement chamber can be formed. Before the measurement chamber is opened for the next sampling, the gas sensor installed in the measurement chamber can be used to achieve in-situ measurement of the dissolved gas concentration in the sample to be tested. Thus, by opening and sampling the upper and lower end caps multiple times, in-situ measurement of dissolved gas concentration in seawater samples at different depths, including the upper and middle layers, the middle layer, the far bottom overlying water, the near bottom overlying water, and the sediment-water interface, can be achieved. 2. The ROV-based pressure-holding in-situ measurement device for deep seawater provided by the present invention can maintain pressure on the sample to be tested between two samplings, thereby enabling rapid replacement of the sample to be tested with different dissolved gas concentrations under different water pressure environments corresponding to two different water depths at the moment of sampling when the upper and lower end caps are opened. It can be used to measure the equilibrium time of gas sensors under different water pressure environments. 3. When the ROV-based pressure-holding and depth-fixed seawater in-situ measurement device provided by the present invention is used for sampling, when sampling points are set at fixed water depth intervals, when the ROV carries the pressure-holding and depth-fixed seawater in-situ measurement device to any sampling point, since the seawater sample collected at the previous sampling point is inside the measuring cylinder, that is, the pressure inside the measuring cylinder is the same as the water pressure at the previous sampling point, the pressure difference inside and outside the measuring cylinder is always equal to the water pressure difference between two adjacent sampling points, which greatly reduces the pressure requirements of the measuring cylinder and reduces the manufacturing cost; 4. In the application of obtaining the relationship between dissolved gas concentration and water depth in seawater, the ROV-based pressure-holding and depth-fixed in-situ seawater measurement device provided by this invention sets multiple sampling points sequentially from the sea surface to the seabed according to the sampling point intervals at different water depths. The ROV carries the pressure-holding and depth-fixed in-situ seawater measurement device from the sea surface to the seabed, and then rises from the seabed back to the sea surface. During the descent and ascent, at each set sampling point, the in-situ seawater is pressurized and collected into the measurement chamber by synchronously opening and closing the upper and lower end caps. The gas sensor in the measurement chamber is used to measure the dissolved gas concentration of the in-situ seawater, thereby realizing the in-situ measurement of seawater samples at different depths in the upper and middle layers, the middle layer, the far bottom overlying water, the near bottom overlying water, and the sediment-water interface. Based on the dissolved gas concentration at the corresponding water depth of each sampling point during the descent or ascent, a seawater dissolved gas concentration variation diagram with water depth can be drawn. This seawater dissolved gas concentration variation diagram with water depth completely covers all water layers from the surface to the seabed sediment-water interface, providing a comprehensive data foundation for research. 5. In the application of the ROV-based pressure-holding, constant-depth seawater in-situ measurement device provided by this invention to obtain the relationship between the equilibrium time of a gas sensor and water pressure, the device is carried by an ROV from the sea surface to the seabed and then back to the surface. During the descent and ascent, at each set sampling point, the in-situ seawater is pressurized and collected into the measurement chamber by simultaneously opening and closing the upper and lower end caps. This allows for the rapid replacement of test samples with different dissolved gas concentrations under different water pressure environments corresponding to two different water depths. Simultaneously, because the measurement chamber maintains the in-situ pressure of the sampling point after the upper and lower end caps are closed, This allows the gas sensor to continuously collect and record the gas concentration and corresponding time of the sample in the chamber under the same in-situ pressure as the ROV moves from the current sampling point to the next sampling point. Thus, the concentration step corresponding to the current sampling point is taken as the gas concentration difference from the previous sampling point. The gas concentration at 63.2% of this concentration step difference is taken as the equilibrium gas concentration. By combining the recorded time and concentration data, the equilibrium time of the gas sensor under the corresponding water pressure at each sampling point can be calculated, thereby obtaining the relationship between the equilibrium time of the gas sensor and the water pressure, and realizing the quantification of the equilibrium time of the gas sensor. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 A perspective view of the ROV-based pressure-maintaining and deep-sea in-situ measurement device provided in Embodiment 1 of the present invention, with the upper and lower end caps in the closed state; Figure 2This is a perspective view of the ROV-based pressure-maintaining and deep-sea in-situ measurement device provided in Embodiment 1 of the present invention, with the upper and lower end caps in the closed state. Figure 3 The front view of the ROV-based pressure-maintaining and constant-depth seawater in-situ measurement device provided in Embodiment 1 of the present invention with the upper and lower end caps closed and the measuring cylinder in a cut-open state. Figure 4 The front view of the ROV-based pressure-holding and constant-depth seawater in-situ measurement device provided in Embodiment 1 of the present invention with the upper and lower end caps in the open state and the measuring cylinder in the cut-open state. Figure 5 The control block diagram of the ROV control system, hydraulic system, and control block diagram of the first hydraulic cylinder and the second hydraulic cylinder in the ROV-based pressure-holding and constant-depth seawater in-situ measurement device provided in Embodiment 1 of the present invention; Figure 6 A flowchart illustrating the application of the ROV-based pressure-holding and depth-controlled in-situ seawater measurement device in obtaining the relationship between dissolved gas concentration and water depth in seawater, as provided in Embodiment 2 of the present invention. Figure 7 This is a flowchart of the sampling process during the descent of the ROV-based pressure-holding and depth-controlled in-situ seawater measurement device provided in Embodiment 2 of the present invention for obtaining the relationship between dissolved gas concentration in seawater and water depth. Figure 8 This is a flowchart illustrating the application of the ROV-based pressure-holding, constant-depth seawater in-situ measurement device in obtaining the relationship between the equilibrium time of the gas sensor and water pressure, as provided in Embodiment 3 of the present invention.

[0019] In the picture: 1. Measuring cylinder; 2. Upper end cap drive assembly; 3. Lower end cap drive assembly; 4. Mounting bracket; 5. Gas sensor; 6. ROV; 11. Upper end cap; 111. First plug; 112. First stepped surface; 12. First guide bell mouth; 13. Cylinder; 14. Second guide bell mouth; 15. Lower end cap; 151. Second plug; 152. Second stepped surface; 21. First hydraulic cylinder; 211. First cylinder body; 212. First piston rod; 22. Upper end cover connecting rod; 31. Second hydraulic cylinder; 311. Second cylinder body; 312. Second piston rod; 32. Lower end cover connecting rod; 61. Control system; 62. Hydraulic system; a. Measuring cavity. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be understood that the terms "upper", "lower", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0023] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] Example 1 As attached Figures 1-5As shown, this embodiment provides a pressure-holding, constant-depth seawater in-situ measurement device based on an ROV6. The ROV6 is used to dive and surface in seawater to stop at sampling points at different depths. The pressure-holding, constant-depth seawater in-situ measurement device includes a measuring cylinder 1, a gas sensor 5, an upper end cap drive assembly 2, and a lower end cap drive assembly 3. The measuring cylinder 1 is used to collect seawater samples and includes a cylinder body 13, an upper end cap 11, and a lower end cap 15. The cylinder body 13 is installed on the ROV6, with its axis vertically aligned. Both the top and bottom ends of the cylinder body 13 are open. The upper end cap 11 is used to open or close the top opening of the cylinder body 13, and the lower end cap 15 is used to open or close the bottom opening of the cylinder body 13. When the upper end cap 11 and the lower end cap 15 close their respective openings, a closed system is formed between the upper end cap 11, the lower end cap 15, and the cylinder body 13. The pressure measurement chamber a stores the collected seawater samples; the gas sensor 5 is installed in the measurement chamber a to measure the dissolved gas concentration of the collected seawater samples; the upper end cover drive assembly 2 is used to drive the upper end cover 11 to open or close the top opening; the lower end cover drive assembly 3 is used to drive the lower end cover 15 to open or close the bottom opening; wherein, the upper end cover drive assembly 2 and the lower end cover drive assembly 3 are both connected to the control system 61 of the ROV6, so that at different water depth sampling points, the control system 61 of the ROV6 controls the upper end cover drive assembly 2 and the lower end cover drive assembly 3 to drive the upper end cover 11 and the lower end cover 15 to open and close synchronously multiple times, so as to collect seawater samples at different water depth sampling points and complete the rapid replacement of seawater samples, which is used to measure the dissolved gas concentration of seawater at different water depths and measure the equilibration time of the gas sensor 5 under the corresponding water pressure at different water depths.

[0025] The aforementioned ROV6-based pressure-maintaining, constant-depth seawater in-situ measurement device comprises a measuring cylinder 1, consisting of an open-top and open-bottom cylinder 13, and an upper end cap 11 and a lower end cap 15. The measuring cylinder 1 is carried by an ROV6, which, through its descent or ascent, can reach sampling points at different depths, including the upper and middle layers, the middle layer, the far-bottom overlying water, the near-bottom overlying water, and the sediment-water interface. At the sampling points, the ROV6's control system 61 controls the upper end cap drive assembly 2 and the lower end cap drive assembly 3 to simultaneously open the upper end cap 11 and the lower end cap 15, enabling sampling... Seawater at the sampling point rapidly enters the cylinder 13 through the top and bottom openings. By controlling the simultaneous closing of the upper cover 11 and the lower cover 15, a closed and pressure-maintaining measurement chamber a can be formed. Before the measurement chamber a is opened for the next sampling, the dissolved gas concentration in the sample to be tested can be measured in situ using the gas sensor 5 installed in the measurement chamber a. Thus, by opening and sampling the upper cover 11 and the lower cover 15 multiple times, in-situ measurements of dissolved gas concentrations in seawater samples at different depths, including the upper and middle layers, the middle layer, the far bottom overlying water, the near bottom overlying water, and the sediment-water interface, can be achieved. Simultaneously, the aforementioned pressure-maintaining and depth-fixed seawater in-situ measurement device based on ROV6 can maintain pressure on the sample to be tested between two sampling sessions. This allows for rapid replacement of the sample to be tested with different dissolved gas concentrations under different water pressure environments corresponding to two different water depths at the moment the upper cover 11 and the lower cover 15 are opened for sampling. This can be used to measure the equilibration time of the gas sensor 5 under different water pressure environments. Furthermore, when the aforementioned pressure-holding, constant-depth seawater in-situ measurement device based on ROV6 is used for sampling, and sampling points are set at fixed water depth intervals, when the ROV6 carries the pressure-holding, constant-depth seawater in-situ measurement device to any sampling point, since the seawater sample collected at the previous sampling point is inside the measuring cylinder 1, the pressure inside the measuring cylinder 1 is consistent with the water pressure at the previous sampling point. Therefore, the pressure difference inside and outside the measuring cylinder 1 is always equal to the water pressure difference between two adjacent sampling points, which greatly reduces the pressure requirements on the measuring cylinder 1 and reduces manufacturing costs.

[0026] Preferably, the measuring cylinder 1 is made of titanium alloy to ensure that the measuring cylinder 1 has good pressure resistance.

[0027] To ensure a tight seal between the upper end cap 11, the lower end cap 15, and the cylinder 13, and to ensure that the volume of the measurement cavity a formed during each sampling remains constant, preferably, as follows: Figure 3 and Figure 4As shown, the bottom surface of the upper end cover 11 protrudes downward to form a first plug 111, so that the portion of the bottom surface of the upper end cover 11 located on the outer periphery of the first plug 111 forms a first stepped surface 112. When the top opening of the upper end cover 11 is closed, the first plug 111 is inserted into the top opening, and the first stepped surface 112 contacts and seals with the top end face of the cylinder 13, thus limiting the upper end cover 11. The bottom surface of the lower end cover 15 protrudes upward to form a second plug 151, so that the portion of the bottom surface of the lower end cover 15 located on the outer periphery of the second plug 151 forms a second stepped surface 152. When the bottom opening of the lower end cover 15 is closed, the second plug 151 is inserted into the bottom opening, and the second stepped surface 152 contacts and seals with the bottom end face of the cylinder 13, thus limiting the lower end cover 15.

[0028] For ease of installation and maintenance of gas sensor 5, preferably, as follows: Figure 3 and Figure 4 As shown, the gas sensor 5 is suspended below the upper end cover 11. It can be understood that the gas sensor 5 can also be fixedly installed on the inner wall of the cylinder 13. It should be noted that when measuring various dissolved gases, multiple different gas sensors 5 can be correspondingly set.

[0029] like Figures 1-5 As shown, the upper end cap drive assembly 2 includes a first hydraulic cylinder 21 and an upper end cap connecting rod 22. The first hydraulic cylinder 21 is connected to the hydraulic system 62 of the ROV6. The first hydraulic cylinder 21 includes a first cylinder body 211 and a first piston rod 212. The first cylinder body 211 is mounted on the ROV6, and the first piston rod 212 extends vertically from the top of the first cylinder body 211. The free end of the first piston rod 212 is connected to the upper end cap 11 via the upper end cap connecting rod 22. The lower end cap drive assembly 3 includes a second hydraulic cylinder 31 and a lower end cap connecting rod 32. The second hydraulic cylinder 31 is connected to... In the hydraulic system 62 of the ROV6, the second hydraulic cylinder 31 includes a second cylinder body 311 and a second piston rod 312. The second cylinder body 311 is installed on the ROV6, and the second piston rod 312 extends vertically from the top of the second cylinder body 311. The free end of the second piston rod 312 is connected to the lower end cover 15 via the lower end cover connecting rod 32. The control system 61 of the ROV6 controls the hydraulic system 62 to simultaneously inject or retract hydraulic oil into the first hydraulic cylinder 21 and the second hydraulic cylinder 31, so as to control the synchronous extension and retraction of the first piston rod 212 and the second piston rod 312. The first hydraulic cylinder 21 and the upper end cover connecting rod 22 are used as the upper end cover drive assembly 2, and the second hydraulic cylinder 31 and the lower end cover connecting rod 32 are used as the lower end cover drive assembly 3. The ROV6's built-in hydraulic system 62 can be used directly as a power source to drive the upper end cover 11 and the lower end cover 15 to open or close synchronously through synchronous hydraulic control, without the need for additional independent drive energy.

[0030] Preferred, such as Figure 1 and Figure 2 As shown, there are two first hydraulic cylinders 21, symmetrically arranged with respect to the axis of the cylinder 13. The upper end cap connecting rod 22 extends radially along the cylinder 13 and is located above the upper end cap 11. The middle part of the upper end cap connecting rod 22 is connected to the upper end cap 11, and both ends of the upper end cap connecting rod 22 are respectively connected to the first piston rods 212 of the two first hydraulic cylinders 21. Similarly, there are two second hydraulic cylinders 31, symmetrically arranged with respect to the axis of the cylinder 13. The lower end cap connecting rod 32 extends radially along the cylinder 13 and is located below the lower end cap 15. The middle part of the lower end cap connecting rod 32 is connected to the lower end cap 15, and both ends of the lower end cap connecting rod 32 are respectively connected to the second piston rods 312 of the two second hydraulic cylinders 31. It should be noted that the ROV6 control system 61 needs to control the hydraulic system 62 to simultaneously inject or simultaneously retract hydraulic oil into the two first hydraulic cylinders 21 and the two second hydraulic cylinders 31. By synchronously driving two first hydraulic cylinders 21 symmetrically arranged relative to the cylinder 13, the upper end cover 11 can be smoothly raised or lowered relative to the cylinder 13, avoiding the problem of poor sealing caused by the tilting of the upper end cover 11. Similarly, by synchronously driving two second hydraulic cylinders 31 symmetrically arranged relative to the cylinder 13, the lower end cover 15 can be smoothly raised or lowered relative to the cylinder 13, avoiding the problem of poor sealing caused by the tilting of the lower end cover 15.

[0031] like Figure 2 As shown, the cylinder 13, the first hydraulic cylinder 21, and the second hydraulic cylinder 31 are mounted on the ROV6 via the mounting bracket 4.

[0032] like Figures 1-4 As shown, the measuring cylinder 1 also includes a first guide flare 12 and a second guide flare 14. The first guide flare 12 is located above the cylinder body 13, and its small end is connected to the outer periphery of the top of the cylinder body 13 and communicates with the top opening. The second guide flare 14 is located below the cylinder body 13, and its small end is connected to the outer periphery of the bottom of the cylinder body 13 and communicates with the bottom opening. The first guide flare 12 and the second guide flare 14 allow external seawater to flow smoothly into the cylinder body 13, replacing the previously collected sample.

[0033] Example 2 The ROV6-based in-situ pressure-holding, constant-depth seawater measurement device provided in Example 1 was applied to obtain the relationship between seawater dissolved gas concentration and water depth, as shown in the attached figure. Figure 6 and Figure 7 As shown, the method for obtaining the relationship between seawater dissolved gas concentration and water depth includes the following steps: S11. Determine the sampling interval time. Multiply the sampling interval time by the set movement speed of ROV6 to obtain the water depth between sampling points. Set multiple sampling points from the sea surface to the seabed according to the water depth between sampling points, with the seabed as one sampling point. S12. Install the pressure-maintaining and constant-depth seawater in-situ measurement device on ROV6. In an air environment, use ROV6 to control the upper end cover 11 and the lower end cover 15 to close synchronously, so that the measurement chamber a is filled with air, and use air as the initial sample to be tested. S13 and ROV6, carrying a pressure-maintaining, constant-depth seawater in-situ measurement device, descend from the sea surface to the seabed at a set moving speed, and then rise from the seabed back to the sea surface. During the descent and ascent, ROV6 stops at each sampling point in sequence to collect samples. The specific steps of sampling are as follows: control the upper end cover 11 and the lower end cover 15 to open synchronously, so that the seawater at the current sampling point replaces the sample to be tested in the measurement chamber a; control the upper end cover 11 and the lower end cover 15 to close synchronously to reform the measurement chamber a, and complete the sampling. During the process of ROV6 moving from the current sampling point to the next sampling point, gas sensor 5 collects and records the gas concentration of the sample to be tested in the measurement chamber a in real time. The gas concentration collected by gas sensor 5 at the moment when ROV6 reaches the next sampling point but has not yet been sampled is taken as the dissolved gas concentration at the corresponding water depth of the current sampling point. S14. Based on the dissolved gas concentration at each sampling point at the corresponding water depth during the descent or ascent process, draw a graph showing the change of seawater dissolved gas concentration with water depth.

[0034] The method described above for obtaining the relationship between dissolved gas concentration in seawater and water depth involves setting multiple sampling points sequentially from the sea surface to the seabed at intervals of water depth. An ROV6 carrying a pressure-maintaining, depth-controlled in-situ seawater measurement device is used to descend from the sea surface to the seabed and then rise back to the surface. During the descent and ascent, at each designated sampling point, the in-situ seawater is pressurized and collected into measurement chamber a by simultaneously opening and closing the upper end cap 11 and the lower end cap 15. The gas sensor 5 within measurement chamber a is used to measure the dissolved gas concentration in the in-situ seawater. This allows for in-situ measurement of seawater samples at different depths in the upper and middle layers, the middle layer, the far-bottom overlying water, the near-bottom overlying water, and the sediment-water interface. Based on the dissolved gas concentration at each sampling point at the corresponding water depth during the descent or ascent, a map showing the change in dissolved gas concentration with water depth can be plotted. This map completely covers all water layers from the surface to the sediment-water interface, providing a comprehensive data foundation for research. Meanwhile, in the aforementioned method for obtaining the relationship between dissolved gas concentration in seawater and water depth, the gas sensor 5 performs measurements as the ROV6 moves from the current sampling point to the next, fully utilizing the ROV6's movement time to allow the gas concentration measured by the gas sensor 5 to reach equilibrium, eliminating the need for the ROV6 to hover at the sampling point for an extended period. Furthermore, this method involves sampling during both the ROV6's descent and ascent, allowing the data obtained during these processes to be cross-validated, thereby improving measurement accuracy.

[0035] Preferably, in step S11, the step of determining the sampling interval time is as follows: the equilibrium time of the gas sensor 5 under atmospheric pressure is taken as the minimum equilibrium time, and the product of the minimum equilibrium time and the set amplification factor is taken as the sampling interval time. It should be noted that the equilibrium time of the gas sensor 5 under atmospheric pressure is usually a known parameter of the gas sensor 5. Even if it is unknown, it can be calculated according to equation (1). As the pressure increases, the equilibrium time of the gas sensor 5 will increase. Therefore, the equilibrium time of the gas sensor 5 under atmospheric pressure is taken as the minimum equilibrium time, and then multiplied by the set amplification factor to amplify it. The sampling interval time obtained in this way can ensure that the gas sensor 5 has enough time to reach equilibrium between two adjacent sampling intervals. The expression of equation (1) is as follows: Equation (1), In equation (1), This is the equilibrium time of gas sensor 5 under atmospheric pressure; V This refers to the volume of the gas chamber inside the gas sensor 5; The effective mass transfer coefficient of the membrane can be obtained from the OMD database (OpenMembrance Database, https: / / openmembranedatabase.org / ) based on the membrane material selected for gas sensor 5; A The membrane area of ​​gas sensor 5; R The gas constant is taken as 8.314 J·mol⁻¹. 1 ·K 1 ; T It is the thermodynamic temperature.

[0036] Preferably, the magnification factor is set to 5 to 10.

[0037] In this embodiment, the equilibrium time of the gas sensor 5 under atmospheric pressure The sampling interval was set to 5 minutes, with a magnification factor of 10. The ROV6's set moving speed was 60 m / min, and the calculated sampling point interval was 300 m.

[0038] Preferably, in step S13, the ROV6 stays at the sampling point for 1-4 seconds to ensure sufficient replacement of the sample. (This embodiment is attached.) Figure 7 The sampling time shown is 2 seconds.

[0039] Example 3 The ROV6-based in-situ deep-sea water measurement device provided in Example 1 was applied to obtain the relationship between the equilibrium time of gas sensor 5 and water pressure, as shown in the attached figure. Figure 8 As shown, the method for obtaining the relationship between the equilibrium time of gas sensor 5 and water pressure includes the following steps: S21. Determine the sampling interval time. Multiply the sampling interval time by the set movement speed of ROV6 to obtain the water depth between sampling points. Set multiple sampling points from the sea surface to the seabed according to the water depth between sampling points, with the seabed as one sampling point.

[0040] It should be noted that the steps for determining the sampling interval are the same as in Example 2, and will not be repeated here.

[0041] S22. Install the pressure-maintaining, fixed-depth seawater in-situ measurement device on ROV6. In an air environment, use ROV6 to control the upper end cover 11 and the lower end cover 15 to close synchronously, so that the measurement chamber a is filled with air, and use air as the initial sample to be measured.

[0042] S23 and ROV6, carrying a pressure-maintaining, constant-depth seawater in-situ measurement device, descend from the sea surface to the seabed at a set moving speed, and then rise from the seabed back to the sea surface. During the descent and ascent, ROV6 stops at each sampling point in sequence to collect samples. The specific steps of sampling are as follows: control the upper end cover 11 and the lower end cover 15 to open synchronously, so that the seawater at the current sampling point replaces the sample to be tested in the measurement chamber a; control the upper end cover 11 and the lower end cover 15 to close synchronously to reform the measurement chamber a, and complete the sampling. The timing begins when the ROV6 begins its descent from the sea surface. As the ROV6 moves from the current sampling point to the next sampling point, the gas sensor 5 collects and records the gas concentration of the sample to be tested in the measurement chamber a and the corresponding time in real time. The gas concentration collected by the gas sensor 5 at the moment when the ROV6 reaches the next sampling point but has not yet taken a sample is taken as the dissolved gas concentration at the corresponding water depth of the current sampling point.

[0043] In this step, it should be noted that the sampling process of this embodiment is basically the same as that of embodiment 2. The difference between this step and S13 in embodiment 2 is that in this step, the timing starts when the ROV6 begins to descend from the sea surface, and the time corresponding to the collected gas concentration data is recorded synchronously by the gas sensor 5, which is used to calculate the equilibrium time of the gas sensor 5 later.

[0044] S24. The concentration step at the current sampling point is taken as the concentration step when the gas concentration changes from the dissolved gas concentration at the previous sampling point to the dissolved gas concentration at the current sampling point. The gas concentration at which the gas concentration reaches 63.2% of the concentration step difference is taken as the equilibrium gas concentration. Based on the equilibrium gas concentration and the gas concentration and time data recorded by the gas sensor 5 from the current sampling point to the next sampling point, the equilibrium time of the gas sensor 5 under the water pressure at the current sampling point is calculated. In this step, it should be noted that the first... i The formula for calculating the equilibrium gas concentration corresponding to each sampling point is as follows: Equation (2), In equation (2), i =1, 2, ..., n , n The total number of sampling points. For the first i The equilibrium gas concentration corresponding to each sampling point For the first i Dissolved gas concentration corresponding to each sampling point For the first i -1 sampling point corresponding to the dissolved gas concentration; when i When =1, The initial concentration of the dissolved gas to be measured in the air was taken as the concentration collected by gas sensor 5 at the moment when ROV6 reached the first sampling point but before sampling was performed. During calculation, and All data recorded during the descent are taken, or all data recorded during the ascent are taken.

[0045] It should also be noted that the first i The specific calculation steps for the balancing time of gas sensor 5 under water pressure corresponding to each sampling point are as follows: starting from the gas sensor 5 from the first... i From the sampling point to the... i Search for the gas concentration and corresponding time data recorded during the +1 sampling process to find the first time the concentration reaches the specified value. i The time corresponding to the equilibrium gas concentration at each sampling point Combined with ROV6, it reached the first i Time of each sampling point The first one is obtained by calculating according to equation (3). i Each sampling point corresponds to the balancing time of gas sensor 5 under water pressure. The expression for equation (3) is as follows: Equation (3).

[0046] S25. Calculate the corresponding water pressure based on the water depth at each sampling point, and combine the equilibrium time of gas sensor 5 at each sampling point with the water pressure to draw a graph showing the change of equilibrium time of gas sensor 5 with water pressure.

[0047] The method described above for obtaining the relationship between the equilibrium time of gas sensor 5 and water pressure variation utilizes an ROV6 carrying a pressure-maintaining, depth-controlled in-situ seawater measurement device. The device descends from the sea surface to the seabed and then rises back to the surface. During the descent and ascent, at each designated sampling point, the upper end cover 11 and the lower end cover 15 are simultaneously opened and closed to maintain in-situ pressure and collect seawater samples into measurement chamber a. This allows for rapid replacement of samples with different dissolved gas concentrations under different water pressure environments corresponding to two different water depths. Simultaneously, because measurement chamber a maintains the in-situ pressure of the sampling point after the upper end cover 11 and the lower end cover 15 are closed, the ROV6 can achieve rapid pressure-maintaining measurement of seawater samples at different depths and water pressure environments. During the process of moving from the previous sampling point to the next sampling point, the gas sensor 5 continuously collects and records the gas concentration and corresponding time of the sample to be tested in the cavity under the same in-situ pressure. Thus, the concentration step corresponding to the current sampling point is taken as the gas concentration from the previous sampling point to the current sampling point, and the gas concentration at 63.2% of the difference of the concentration step is taken as the equilibrium gas concentration. By combining the recorded time and concentration data, the equilibrium time of the gas sensor 5 under the corresponding water pressure at each sampling point can be calculated, thereby obtaining the relationship between the equilibrium time of the gas sensor 5 and the water pressure, and realizing the quantification of the equilibrium time of the gas sensor 5.

[0048] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A pressure-maintaining, constant-depth seawater in-situ measurement device based on ROV, characterized in that, The pressure-holding, constant-depth seawater in-situ measurement device is mounted on an ROV (Return-to-Vehicle), which is used to dive and surface in seawater to remain at sampling points at different depths. The pressure-holding, constant-depth seawater in-situ measurement device includes: A measuring cylinder for collecting seawater samples includes a cylinder body, an upper end cap, and a lower end cap. The cylinder body is installed on an ROV, with its axis arranged vertically. Both the top and bottom ends of the cylinder body are open. The upper end cap is used to open or close the top opening of the cylinder body, and the lower end cap is used to open or close the bottom opening of the cylinder body. When the upper and lower end caps are closed, a closed and pressure-maintaining measuring cavity is formed between the upper end cap, the lower end cap, and the cylinder body to store the collected seawater samples. A gas sensor, which is installed inside the measuring chamber, is used to measure the dissolved gas concentration of the collected seawater sample; The upper cover driving assembly is used to drive the upper cover to open or close the top opening; The lower end cover driving assembly is used to drive the lower end cover to open or close the bottom opening; The upper end cap drive assembly and the lower end cap drive assembly are both connected to the ROV's control system. The ROV's control system controls the upper end cap drive assembly and the lower end cap drive assembly to open and close synchronously multiple times at different water depth sampling points. This is to collect seawater samples at different water depth sampling points and complete the rapid replacement of seawater samples. This is used to measure the dissolved gas concentration of seawater at different water depths and to measure the gas sensor equilibration time under the corresponding water pressure at different water depths.

2. The ROV-based pressure-maintaining, constant-depth seawater in-situ measurement device according to claim 1, characterized in that, The upper end cap drive assembly includes a first hydraulic cylinder and an upper end cap connecting rod. The first hydraulic cylinder is connected to the hydraulic system of the ROV. The first hydraulic cylinder includes a first cylinder body and a first piston rod. The first cylinder body is mounted on the ROV. The first piston rod extends vertically from the top of the first cylinder body and extends and retracts vertically. The free end of the first piston rod is connected to the upper end cap via the upper end cap connecting rod. The lower end cap drive assembly includes a second hydraulic cylinder and a lower end cap connecting rod. The second hydraulic cylinder is connected to the hydraulic system of the ROV. The second hydraulic cylinder includes a second cylinder body and a second piston rod. The second cylinder body is mounted on the ROV. The second piston rod extends vertically from the top of the second cylinder body and extends and retracts vertically. The free end of the second piston rod is connected to the lower end cap via the lower end cap connecting rod. The ROV's control system controls the hydraulic system to simultaneously inject or simultaneously retract hydraulic oil into the first hydraulic cylinder and the second hydraulic cylinder to control the synchronous extension and retraction of the first piston rod and the second piston rod.

3. The ROV-based pressure-maintaining, constant-depth seawater in-situ measurement device according to claim 2, characterized in that, There are two first hydraulic cylinders, which are symmetrically arranged with respect to the axis of the cylinder. The upper end cover connecting rod extends radially along the cylinder and is located above the upper end cover. The middle part of the upper end cover connecting rod is connected to the upper end cover, and the two ends of the upper end cover connecting rod are respectively connected to the first piston rods of the two first hydraulic cylinders. There are two second hydraulic cylinders, which are symmetrically arranged with respect to the axis of the cylinder. The lower end cover connecting rod extends radially along the cylinder and is located below the lower end cover. The middle part of the lower end cover connecting rod is connected to the lower end cover, and the two ends of the lower end cover connecting rod are respectively connected to the second piston rods of the two second hydraulic cylinders.

4. The ROV-based pressure-maintaining, constant-depth seawater in-situ measurement device according to claim 1, characterized in that, The measuring cylinder further includes a first guide flare and a second guide flare. The first guide flare is located above the cylinder body, and the small end of the first guide flare is connected to the outer periphery of the top end of the cylinder body and communicates with the top opening. The second guide flare is located below the cylinder body, and the small end of the second guide flare is connected to the outer periphery of the bottom end of the cylinder body and communicates with the bottom opening.

5. The application of the ROV-based pressure-maintaining, constant-depth seawater in-situ measurement device according to any one of claims 1-4 in obtaining the relationship between dissolved gas concentration in seawater and water depth, characterized in that, Includes the following steps: S11. Determine the sampling interval time, and obtain the sampling point interval water depth by multiplying the sampling interval time by the set movement speed of the ROV. Set multiple sampling points from the sea surface to the seabed according to the sampling point interval water depth, wherein the seabed is a sampling point. S12. Install the pressure-maintaining and constant-depth seawater in-situ measurement device on the ROV. In an air environment, use the ROV to control the upper end cover and the lower end cover to close synchronously, so that the measurement chamber is filled with air, and use air as the initial sample to be tested. S13. The ROV carrying the pressure-maintaining, constant-depth seawater in-situ measurement device descends from the sea surface to the seabed at the set moving speed, and then rises from the seabed back to the sea surface. During the descent and ascent, the ROV stops at each sampling point in sequence to collect samples. The specific steps of the sampling are as follows: control the upper end cover and the lower end cover to open synchronously, so that the seawater at the current sampling point replaces the sample to be tested in the measuring chamber; control the upper end cover and the lower end cover to close synchronously to reform the measuring chamber and complete the sampling. During the process of the ROV moving from the current sampling point to the next sampling point, the gas sensor collects and records the gas concentration of the sample to be tested in the measurement chamber in real time. The gas concentration collected by the gas sensor at the moment when the ROV reaches the next sampling point but has not yet been sampled is taken as the dissolved gas concentration at the corresponding water depth of the current sampling point. S14. Based on the dissolved gas concentration at each sampling point at the corresponding water depth during the descent or ascent process, draw a graph showing the change of seawater dissolved gas concentration with water depth.

6. The application of the ROV-based pressure-maintaining, constant-depth seawater in-situ measurement device according to claim 5 in obtaining the relationship between dissolved gas concentration in seawater and water depth, characterized in that, In step S11, the step of determining the sampling interval time is as follows: taking the equilibrium time of the gas sensor under atmospheric pressure as the minimum equilibrium time, and taking the product of the minimum equilibrium time and the set amplification factor as the sampling interval time.

7. The application of the ROV-based pressure-maintaining in-situ deep-sea water measurement device according to any one of claims 1-4 in obtaining the relationship between the equilibrium time of a gas sensor and water pressure, characterized in that... Includes the following steps: S21. Determine the sampling interval time, and obtain the sampling point interval water depth by multiplying the sampling interval time by the set movement speed of the ROV. Set multiple sampling points from the sea surface to the seabed according to the sampling point interval water depth, wherein the seabed is a sampling point. S22. Install the pressure-maintaining and constant-depth seawater in-situ measurement device on the ROV. In an air environment, use the ROV to control the upper end cover and the lower end cover to close synchronously, so that the measurement chamber is filled with air, and use air as the initial sample to be tested. S23. The ROV carrying the pressure-maintaining, constant-depth seawater in-situ measurement device descends from the sea surface to the seabed at the set moving speed, and then rises from the seabed back to the sea surface. During the descent and ascent, the ROV stops at each sampling point in sequence to collect samples. The specific steps of the sampling are as follows: control the upper end cover and the lower end cover to open synchronously, so that the seawater at the current sampling point replaces the sample to be tested in the measuring chamber; control the upper end cover and the lower end cover to close synchronously to reform the measuring chamber and complete the sampling. The timing begins when the ROV begins to descend from the sea surface. During the process of the ROV moving from the current sampling point to the next sampling point, the gas sensor collects and records the gas concentration of the sample to be tested in the measurement chamber and the corresponding time in real time. The gas concentration collected by the gas sensor at the moment when the ROV reaches the next sampling point but has not yet been sampled is taken as the dissolved gas concentration at the corresponding water depth of the current sampling point. S24. The concentration step at the current sampling point is taken as the concentration step when the dissolved gas concentration at the previous sampling point reaches the dissolved gas concentration at the current sampling point. The gas concentration at which the concentration step difference reaches 63.2% is taken as the equilibrium gas concentration. The equilibrium gas concentration and the gas concentration and time data recorded by the gas sensor from the current sampling point to the next sampling point are used to calculate the equilibrium time of the gas sensor under the water pressure at the current sampling point. S25. Calculate the corresponding water pressure based on the water depth at each sampling point, and combine the equilibrium time of the gas sensor at each sampling point under the corresponding water pressure to draw a graph showing the change of equilibrium time of the gas sensor with water pressure.

8. The application of the ROV-based pressure-maintaining deep-sea in-situ measurement device according to claim 7 in obtaining the relationship between the equilibrium time of the gas sensor and water pressure, characterized in that, In step S21, the step of determining the sampling interval time is as follows: taking the equilibrium time of the gas sensor under atmospheric pressure as the minimum equilibrium time, and taking the product of the minimum equilibrium time and the set amplification factor as the sampling interval time.

9. The application of the ROV-based pressure-maintaining in-situ deep-sea water measurement device according to claim 7 in obtaining the relationship between the equilibrium time of the gas sensor and water pressure, characterized in that, In step S24, the first i The formula for calculating the equilibrium gas concentration corresponding to each sampling point is as follows: ， in, i =1, 2, ..., n , n The total number of sampling points. For the first i The equilibrium gas concentration corresponding to each sampling point For the first i Dissolved gas concentration corresponding to each sampling point For the first i -1 sampling point corresponding to the dissolved gas concentration; when i When =1, The initial concentration of the dissolved gas to be measured in the air is taken as the concentration of the gas collected by the gas sensor at the moment when the ROV reaches the first sampling point but has not yet taken a sample. During calculation, and All data recorded during the descent are taken, or all data recorded during the ascent are taken.

10. The application of the ROV-based pressure-maintaining deep-sea in-situ measurement device according to claim 7 in obtaining the relationship between the equilibrium time of the gas sensor and water pressure, characterized in that, In step S24, the first i The specific calculation steps for the equilibrium time of the gas sensor corresponding to each sampling point under water pressure are as follows: starting from the gas sensor from the first... i From the sampling point to the... i Search for the gas concentration and corresponding time data recorded during the +1 sampling process to find the first time the concentration reaches the specified value. i The time corresponding to the equilibrium gas concentration at each sampling point Combined with the ROV reaching the first i Time of each sampling point ,according to Calculate to obtain the first i Each sampling point corresponds to the balancing time of the gas sensor under water pressure. .

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