CN114354844B - Long-term real-time sediment oxygen consumption rate in-situ measurement device and method - Google Patents

Long-term real-time sediment oxygen consumption rate in-situ measurement device and method Download PDF

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CN114354844B
CN114354844B CN202111486695.5A CN202111486695A CN114354844B CN 114354844 B CN114354844 B CN 114354844B CN 202111486695 A CN202111486695 A CN 202111486695A CN 114354844 B CN114354844 B CN 114354844B
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consumption rate
oxygen consumption
sediment
current meter
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CN114354844A (en
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张袁宁
孙博闻
宗庆志
高学平
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Tianjin University
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Tianjin University
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Abstract

The invention discloses a long-term real-time sediment oxygen consumption rate in-situ measurement device and a long-term real-time sediment oxygen consumption rate in-situ measurement method, wherein the long-term real-time sediment oxygen consumption rate in-situ measurement device comprises a buoy arranged on the water surface and a measurement frame arranged under water, a lifting platform capable of moving vertically is arranged on the measurement frame, a rotating motor is installed on the lifting platform, an acoustic Doppler current meter and a dissolved oxygen gradient acquisition instrument are arranged at the output end of the rotating motor, and a self-adaptive guide plate is also fixedly arranged on the surface of the acoustic Doppler current meter; the invention can effectively adjust the observation height and the observation angle of the acoustic Doppler current meter in the measurement process, and realizes the long-term in-situ observation of the sediment oxygen consumption rate.

Description

Long-term real-time sediment oxygen consumption rate in-situ measurement device and method
Technical Field
The invention relates to the technical field of water environment monitoring, in particular to a long-term real-time sediment oxygen consumption rate in-situ measurement device and method.
Background
The sediment is a main place for substance metabolism and energy circulation in the water body, the oxygen consumption rate of the sediment is widely used for the research on the aspects of primary productivity, mineralization rate of organic matters, conversion direction of pollutants and the like of benthos, and the sediment has important significance for evaluating benthos environment of the water body, controlling endogenous pollution of the water body and researching geochemical cycle process of water environment organisms.
At present, methods for measuring the sediment oxygen consumption rate at home and abroad mainly comprise a laboratory observation method, a benthic culture room method and a microelectrode section method. The laboratory observation method needs operations such as titration and the like in a laboratory after sampling the sediment, belongs to an ex-situ method, and therefore, the interference of the sediment structure and the change of the physicochemical property of the sample in the collection process are avoided. The benthic culture room method tracks the dissolved oxygen concentration of the closed overlying water body through a sensor to calculate the oxygen consumption of the sediment, belongs to an in-situ observation method, but breaks the connection between an observation point and the surrounding environment, and cannot be developed for a long time because the dissolved oxygen in the closed water body is gradually consumed. The microelectrode sectioning method is used for gradually penetrating dissolved oxygen microelectrodes into sediments so as to detect the dissolved oxygen concentrations at different depths of the microelectrodes and calculate the oxygen consumption rate of the sediments, inevitably interferes with the structure of the sediments, and is difficult to carry out in situ for a long time due to the weak probe.
Swirl related techniques, originally intended for observing turbulent flux of the atmosphere and its underlying surface, have also been used in recent years in succession to measure the oxygen consumption rate of deposits in aqueous environments. The technology is a non-invasive in-situ observation technology for calculating the oxygen consumption rate of the sediment by synchronously measuring the turbulence of the vertical water flow and the turbulence of the dissolved oxygen concentration in an open mode. The technology has the advantages of wide measurement range, high time precision, good adaptability to different substrates and the like, but also puts higher requirements on links such as measurement environment conditions, data processing methods and the like. At present, the water environment whirl related technology is mostly used for measuring the short-term change of the sediment oxygen consumption rate in a self-contained mode, the observation capability of the technology is not fully utilized, but no related patent provides a solution for measuring the sediment oxygen consumption rate in a long-term and online mode.
The theory of the water environment vortex motion correlation indicates that when a certain observation point in an logarithmic layer in a water bottom boundary layer is synchronously observed with the vertical flow velocity and the dissolved oxygen concentration, the sediment oxygen consumption rate can be calculated as the covariance of an observation sequence of the vertical flow velocity and the dissolved oxygen concentration. In order to meet the application condition of the theory, the following two key points should be noticed in the long-term online observation process: (1) the acoustic Doppler current meter and the dissolved oxygen gradiometer are used for observing the same space point. However, the flow meter measures the flow velocity in a cylindrical sampling region (i.e., sampling point) having a diameter and a height of about 1cm located 15 cm below its central sensor, and the dissolved oxygen gradiometer measures the dissolved oxygen in contact with the water body with its probe; in order to avoid interference of a water flow structure and sound wave signals, the probe of the dissolved oxygen gradiometer and the flow velocity sampling point cannot be completely coincided, and the dissolved oxygen gradiometer and the flow velocity sampling point are equal in height but are arranged at a distance of 1-2 cm. The arrangement of the instruments determines that the observation direction of a connecting line of the gradiometer probe and the flow velocity sampling point in the observation process is parallel to the water flow direction, so that the two instruments measure the same vortex structure (Taylor freezing turbulence) in sequence, otherwise, the sediment oxygen consumption rate cannot be calculated according to the observation data of the two instruments. However, the water flow direction in the actual observation environment is variable, so that the observation angle needs to be continuously adjusted in the long-term measurement process. (2) An observation area consisting of a flow velocity sampling point and a dissolved oxygen gradiometer probe is required to be positioned in a logarithmic layer of a water bottom boundary layer. The logarithmic layer is an area where the flow velocity above the sediment is logarithmically changed along with the water depth, and only when the observation area is in the logarithmic layer, the diffusion flux does not change along with the observation height from the observation area to the sediment, so that the theory related to the vortex motion of the water environment can be applied.
Disclosure of Invention
The invention aims to provide a long-term real-time sediment oxygen consumption rate in-situ measuring device which can effectively adjust the observation height and the observation angle of an acoustic Doppler current meter in the measuring process and realize long-term in-situ observation of the sediment oxygen consumption rate.
In order to achieve the purpose, the invention provides the following technical scheme: the utility model provides a long-term real-time deposit oxygen consumption rate normal position measuring device, is including the buoy of locating the surface of water and locating underwater measurement frame, but be equipped with vertical removal's lift platform on the measurement frame, the last rotating electrical machines that installs of lift platform, the rotating electrical machines output is equipped with acoustics Doppler current meter and dissolved oxygen gradient collection appearance, acoustics Doppler current meter surface still fixes and is equipped with the self-adaptation guide plate.
Preferably, the lifting platform is provided with a heave motor in a vertical fixed mounting mode, the output end of the heave motor is provided with a first gear, the first gear is meshed with a second gear, a rotating shaft at the bottom of the second gear is mounted on the upper surface of the lifting platform through a bearing, the center of the top of the second gear is fixedly connected with the bottom of a threaded rod through a joint, the surface of the threaded rod is in threaded fit with a fixing nut, and the fixing nut is fixed to the top of the measuring frame through an installation frame.
Preferably, the lifting platform is fixedly provided with sliding chutes at two ends, the sliding chutes are in sliding fit with vertically arranged sliding rails, and the sliding rails are fixed on the side parts of the measuring frame.
Preferably, the rotating electrical machines is vertically fixed on the lifting platform, the output end of the rotating electrical machines is provided with a third gear, the third gear is meshed with a fourth gear, a rotating shaft at the top of the fourth gear is mounted on the lower surface of the lifting platform through a bearing, the center of the bottom of the fourth gear is fixedly connected with the top of the acoustic Doppler current meter through a joint, and the acoustic Doppler current meter is fixedly connected with the dissolved oxygen gradient acquisition instrument through a first support.
Preferably, the acoustic doppler velocimeter is connected to the CO via a second holder 2 The partial pressure sensor is connected.
Preferably, the buoy top is equipped with solar panel and sealed cabin, be equipped with battery, electrical source controller, serial servers and data transmission equipment in the sealed cabin, the measuring frame top is equipped with the watertight cabin, be equipped with data collection station and serial servers in the watertight cabin, and pass through watertight cable connection with the sealed cabin, be connected through the rope between measuring frame top and the buoy bottom, the measuring frame bottom is equipped with the supporting leg.
In addition, the invention also discloses a measuring method of the long-term real-time sediment oxygen consumption rate in-situ measuring device, which comprises the following steps:
s1: coarse adjustment of the observation height: after the heave motor works, the lifting platform vertically moves, so that the heights of observation equipment, namely the acoustic Doppler current meter and the dissolved oxygen gradient acquisition instrument, are adjustable, sufficient observation heights are reserved, and acoustic signals received by the acoustic Doppler current meter are analyzed after the equipment is settled stably to determine the distance between a sampling point and a sediment-water interface;
s2: fine adjustment of observation height: after the rough adjustment of the observation height is finished, the fine adjustment is continuously carried out under the condition that the hydrodynamic condition of the bottom boundary layer is stable, the equipment is driven to rise for a certain distance by a heave motor at intervals, the oxygen consumption rate of the sediment is synchronously measured by an acoustic Doppler current meter and a dissolved oxygen gradient acquisition instrument, a change curve of the oxygen consumption rate along with the observation height is further obtained, and the observation height is finally adjusted to a proper position according to the curve;
s3: and (3) checking fine adjustment conditions: and (5) checking the stability of the hydrodynamic condition in the fine adjustment process of S2, and repeating the step S2 if the hydrodynamic condition is unstable.
Preferably, the S1 is specifically: when the acoustic Doppler current meter works, a sound wave signal is transmitted through a central sensor of the acoustic Doppler current meter, two obvious signal peak values appear at a pulse transmitting position and a sampling point, then the position of the observation equipment is gradually reduced through a heaving motor, the sound wave suddenly changes due to reflection properties when encountering a medium interaction interface, a third peak appears, the distance between the sampling point and a sediment-water interface can be calculated, the position of the observation equipment is continuously reduced through the heaving motor until the distance between the sampling point and the sediment-water interface is 10 cm, and coarse adjustment is completed;
the S2 specifically includes: after the rough adjustment of the observation height is finished, the fine adjustment is continuously carried out under the condition that the hydrodynamic force condition of the bottom boundary layer is stable, namely from the observation period of a certain vortex related measurement, the observation equipment is driven to rise by 1cm through a lifting and sinking motor every 30 s until the distance between a sampling point and a sediment-water interface is 20-35cm, the sediment oxygen consumption rate is calculated once for the observation data of the vertical flow speed and the dissolved oxygen concentration in every 30 s, so that a change curve of the oxygen consumption rate along with the observation height is obtained, and an area where the oxygen consumption rate is basically kept unchanged along with the observation height is selected as a proper observation height range;
the method for checking whether the hydrodynamic condition is stable in S3 includes: and calculating the average flow direction and the turbulence dissipation rate of the three-way flow velocity observation data every 30 s, and if the average flow direction is always kept stable along with the observation height and the turbulence dissipation rate is kept stable in a selected proper observation range, the hydrodynamic condition of the water bottom boundary layer in the fine adjustment process is stable, and the fine adjustment result of the observation height is effective.
Preferably, it further comprises the step of adjusting the observation direction to be parallel to the flow direction during the rest period of the whirl related measurement, specifically:
step 1: after entering a resting period of vortex related measurement each time, carrying out vector synthesis on the horizontal flow velocity in the previous observation period to obtain an average flow direction angle; if the average flow direction angle is smaller than 5 degrees, the water flow direction is not obviously changed after a vortex motion related observation period, and the rotating motor enters a locking mode at the moment; if the average flow direction angle is larger than 5 degrees, the rotating motor enters a free mode, the rotating motor is not powered at the moment, an output shaft of the rotating motor can rotate freely under the pushing of external force, and the flow of water flow can drive the self-adaptive guide plate to rotate, so that the acoustic Doppler current meter is also driven to adjust the observation angle;
step 2: awakening the acoustic Doppler current meter 30 s before the wake-up of the resting period of the vortex-related measurement, taking the difference between the geographic azimuth angle read at the moment and the geographic azimuth angle in the last observation period as the rotating angle of the acoustic Doppler current meter in the resting period, and if the difference between the rotating angle and the average flow direction angle calculated in Step1 is less than 5 degrees, indicating that the adaptive guide plate effectively adjusts the observation angle of the acoustic Doppler current meter, and enabling the rotating motor to enter a locking mode at the moment; if the difference between the rotation angle and the average flow direction angle calculated in Step1 is larger than 5 degrees, then Step3 is entered;
step 3: the rotating motor enters a working mode, the rotating motor is called, an output shaft of the rotating motor drives the third gear to rotate after rotating, and then the fourth gear drives the acoustic Doppler current meter to adjust the observation angle, so that the included angle between the observation direction of the acoustic Doppler current meter and the average water flow direction is finally smaller than 5 degrees.
Compared with the prior art, the invention has the beneficial effects that:
1. the measuring end of the in-situ sediment oxygen consumption rate observation method adopted by the invention does not invade the sediment structure, is suitable for various types of sediment underlying surfaces, has wide representative range of the measuring result and high time precision, and can fully reflect the response relation of the sediment oxygen consumption rate to the environmental factors. By effectively adjusting the observation height and the observation angle of the acoustic Doppler current meter in the measurement process, the long-term in-situ observation of the sediment oxygen consumption rate is realized; meanwhile, the invention solves the problems of storage and transmission of huge observation data, can monitor the working state of equipment in real time and provides data for water environment risk prediction.
2. The invention adopts a method of matching sound wave signal ranging with heave motor adjustment, and adjusts the observation height of the acoustic Doppler current meter through three steps of rough adjustment, fine adjustment and inspection, thereby ensuring that the observation process meets the theoretical requirements of the water environment whirl related technology; the invention determines the distance between the flow velocity sampling point and the sediment by analyzing the acoustic wave signal of the acoustic Doppler current meter, has dual purposes, does not need to add equipment such as laser ranging and the like to judge the distance between the observation point and the sediment-water interface, avoids the interference on various biogeochemical reactions at the interface to the maximum extent, and can obtain more real sediment oxygen consumption rate data.
3. The invention adopts the method that the adjustment of the rotating motor is matched with the adjustment of the self-adaptive guide plate, the measurement direction is consistent with the water flow direction through three times of rotating adjustment in the dormant period of each section of vortex related measurement, and the same vortex structure measured by the acoustic Doppler current meter and the dissolved oxygen gradient acquisition instrument in each observation period is ensured.
Drawings
FIG. 1 is a flow chart of the operation of an in situ measurement device for long-term real-time oxygen consumption rate of a deposit;
FIG. 2 is a logic diagram of an in situ measurement apparatus for long term real time oxygen consumption rate of deposits;
FIG. 3 is a schematic view of a water surface structure of an in-situ sediment oxygen consumption rate measuring device for long-term real-time measurement;
FIG. 4 is a schematic perspective view of an underwater structure of an in situ measuring device for oxygen consumption rate of sediment in long-term real-time;
FIG. 5 is an enlarged schematic structural view of the region where the lifting platform of FIG. 4 is located;
FIG. 6 is an enlarged schematic view of the acoustic Doppler velocimeter of FIG. 4 in the region of the Doppler velocimeter;
FIG. 7 is a schematic diagram of a method for determining the distance between a flow rate sampling point and a sediment by analyzing an acoustic signal;
FIG. 8 is a schematic view of a method of fine adjustment of observed height and inspection thereof;
FIG. 9 is a schematic diagram of a method of determining the length of a sliding window;
FIG. 10 is a schematic diagram of a method of determining a skew correction value;
FIG. 11 is a graph of the results of calculation of cumulative oxygen consumption of deposits;
FIG. 12 is a schematic diagram of a method for high frequency correction of the oxygen consumption rate of a deposit;
FIG. 13 is a graph showing the variation trend of the horizontal velocity in the boundary layer of the measured water bottom;
FIG. 14 is a graph showing the trend of vertical velocity variation in the boundary layer of the measured water bottom;
FIG. 15 is a graph showing the trend of the concentration of dissolved oxygen in the boundary layer of the actually measured water bottom;
FIG. 16 is CO of measured sediment oxygen consumption products 2 A partial pressure change trend graph;
FIG. 17 is a graph of a trend of measured deposit oxygen consumption rates;
FIG. 18 is a flow chart of data computation according to the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and specific embodiments.
As shown in fig. 1-6: the utility model provides a long-term real-time deposit oxygen consumption rate in situ measurement device, is including the buoy 1 of locating the surface of water and locating underwater measuring frame 2, but be equipped with vertical removal's lift platform 3 on the measuring frame 2, install rotating electrical machines 4 on the lift platform 3, 4 outputs of rotating electrical machines are equipped with acoustics Doppler current meter 5 and dissolved oxygen gradient collection appearance 6, 5 fixed self-adaptation guide plates 7 that are equipped with in surface of acoustics Doppler current meter.
Preferably, vertical fixed mounting has a heave motor 8 on lift platform 3, the output of heave motor 8 is equipped with first gear 9, first gear 9 meshes with second gear 10, the axis of rotation of second gear 10 bottom passes through the bearing and installs in lift platform 3 upper surface, and second gear 10 top central point puts through joint and 11 bottom fixed connection of threaded rod, 11 surface and the 12 screw-thread fit of fixation nut of threaded rod, fixation nut 12 is fixed in measuring frame 2 top through mounting bracket 13.
Preferably, fixed spout 14 that is equipped with in lift platform 3 both ends, spout 14 and the slide rail 15 sliding fit of vertical setting, slide rail 15 is fixed in the lateral part of measuring frame 2.
In the above technical scheme, when the heave motor 8 during operation, can drive first gear 9 rotatory, and then drive second gear 10 and rotate to make threaded rod 11 take place to rotate, because 11 surfaces of threaded rod and 12 screw-thread fit of fixation nut, so vertical removal can take place for lift platform 3, realize the purpose of effective adjustment acoustics Doppler current meter's observation height.
Preferably, the rotating electrical machine 4 is vertically fixed on the lifting platform 3, and the output end thereof is provided with a third gear 16, the third gear 16 is meshed with a fourth gear 17, a rotating shaft at the top of the fourth gear 17 is mounted on the lower surface of the lifting platform 3 through a bearing, the center position of the bottom of the fourth gear 17 is fixedly connected with the top of the acoustic doppler flow velocity meter 5 through a joint, and the acoustic doppler flow velocity meter 5 is fixedly connected with the dissolved oxygen gradient acquisition instrument 6 through a first support 18.
In the above technical solution, when the rotating electrical machine 4 works, the third gear 16 can be driven to rotate, and then the fourth gear 17 is driven to rotate, so that the observation angle of the acoustic doppler current meter 5 can be adjusted.
Preferably, the acoustic doppler velocimeter 5 is connected to the CO via a second holder 19 2 The partial pressure sensor 20 is connected. CO 2 2 The partial pressure sensor 20 can measure the CO generated by the sediment oxygen consumption process 2 CO produced by oxygen consuming processes of the deposit 2 Is significantly inversely related to the change in dissolved oxygen concentration, and therefore the reliability of the sediment oxygen consumption rate measurement can be verified by measurement comparison.
Preferably, 1 top of buoy is equipped with solar panel 21 and sealed cabin 22, be equipped with battery, electrical source controller, serial servers and data transmission equipment in the sealed cabin 22, 2 tops of measuring frame are equipped with watertight cabin 23, be equipped with data collection station and serial servers in the watertight cabin 23, and pass through watertight cable connection with sealed cabin 22, be connected through the rope between 2 tops of measuring frame and the 1 bottom of buoy, and 2 bottoms of measuring frame are equipped with supporting leg 25. In the present example, wherein CO 2 The partial pressure sensor is connected with a data acquisition unit in the watertight cabin through a cable, and the data acquisition unit supplies power and controls the work; then the data acquisition unit is connected to a serial server in the watertight cabin to realize CO 2 And outputting the partial pressure observation data. The dissolved oxygen gradiometer can be firstly connected with the acoustic Doppler current meter by a cable, and the acoustic Doppler current meter supplies power and controls the dissolved oxygen gradiometerMaking it carry on the same frequency sampling; and then, connecting the acoustic Doppler current meter with a serial server in the watertight cabin, and synchronously outputting the observation data (including the concentration of dissolved oxygen and the water temperature) of the dissolved oxygen gradiometer and the observation data (including three-way flow velocity, sound wave signals, water depth and the like) of the current meter. In this embodiment, after the device is put in, the measuring frame 2 can be fixed on the water bottom through the supporting legs 25, so that the measuring frame 2 always keeps the same position during the measuring process.
The device of the invention needs to go through four stages of equipment release, system configuration, initial debugging and long-term operation when working, as shown in figure 1. The equipment throwing refers to throwing and anchoring a buoy, installing and throwing underwater equipment and debugging a power supply management module. The system configuration comprises network configuration, a current meter, a dissolved oxygen gradiometer and CO 2 The configuration of the partial pressure sensor, wherein a flow velocity meter and a dissolved oxygen gradiometer used for carrying out vortex related observation are both intermittently carried out, namely, after a period of observation period, the flow velocity meter enters a period of dormancy period, and then enters the observation period again, so that measurement is carried out in a circulating reciprocating manner, and 32 Hz high-frequency measurement is carried out in each observation period. The working method of the initial debugging stage and the long-term operation stage is a measuring method of the long-term real-time sediment oxygen consumption rate in-situ measuring device, and comprises the following steps:
s1: coarse adjustment of the observation height: after the heave motor 8 works, the lifting platform 3 vertically moves, so that the heights of observation devices, namely the acoustic Doppler current velocity meter 5 and the dissolved oxygen gradient acquisition instrument 6, are adjustable, a sufficient observation height is reserved, and after the devices are settled stably, acoustic signals received by the acoustic Doppler current velocity meter 5 are analyzed to determine the distance between a sampling point 24 and a sediment-water interface;
s2: fine adjustment of observation height: after the rough adjustment of the observation height is finished, the fine adjustment is continuously carried out under the condition that the hydrodynamic condition of the bottom boundary layer is stable, the equipment is driven to rise for a certain distance by a heave motor 8 at intervals, the oxygen consumption rate of the sediment is synchronously measured by an acoustic Doppler current meter 5 and a dissolved oxygen gradient acquisition instrument 6, a change curve of the oxygen consumption rate along with the observation height is further obtained, and the observation height is finally adjusted to a proper position according to the curve; in this embodiment, specifically, the vertical flow velocity at the corresponding observation height is measured by the acoustic doppler flow velocity meter 5, the dissolved oxygen concentration at the corresponding observation height is measured by the dissolved oxygen gradient collector 6, and then the sediment oxygen consumption rate can be calculated as the covariance of the vertical flow velocity and the dissolved oxygen concentration observation sequence.
S3: and (3) checking fine adjustment conditions: and (5) checking the stability of the hydrodynamic condition in the fine adjustment process of S2, and repeating the step S2 if the hydrodynamic condition is unstable.
Preferably, the S1 is specifically: when the acoustic Doppler current meter 5 works, a sound wave signal is transmitted through a central sensor of the acoustic Doppler current meter, two obvious signal peak values appear at a pulse transmitting position and a sampling point 24, then the position of the observation equipment is gradually reduced through the heave motor 8, when the sound wave meets a medium interaction interface, a third peak appears due to sudden change of reflection properties, at the moment, the distance between the sampling point 24 and a sediment-water interface can be calculated, the position of the observation equipment is continuously reduced through the heave motor 8, and rough adjustment is completed until the distance between the sampling point 24 and the sediment-water interface is 10 cm; in this example, only two peaks are observed at this time (fig. 7) since the observation height reserve is sufficient at the beginning of the coarse adjustment, and the interface is outside the monitoring limit of the acoustic wave. And then, gradually lowering the position of the observation equipment by using a heave motor until three sound wave signal peak values (figure 8) representing the position of the sediment-water interface are found, further calculating the distance between the sampling point and the interface, if the distance between the sampling point and the sediment-water interface is about 19 cm according to figure 8, continuing to lower the position of the observation equipment by using the heave motor until the distance between the sampling point and the interface is about 10 cm, and finishing coarse adjustment. According to the method, the position of the sediment-water interface is judged through the acoustic Doppler current meter, compared with other methods such as laser ranging, interference on various biochemical reaction processes at the sediment-water interface is avoided, and the accuracy of the measured sediment oxygen consumption rate is guaranteed.
The S2 specifically includes: after the rough adjustment of the observation height is finished, the fine adjustment is continuously carried out under the condition that the hydrodynamic force condition of the bottom boundary layer is stable, namely from the observation period of a certain vortex related measurement, the observation equipment is driven to rise by 1cm through a heave motor 8 every 30 s until the distance from a sampling point 24 to a sediment-water interface is 20-35cm, the sediment oxygen consumption rate is calculated once for the observation data of the vertical flow rate and the dissolved oxygen concentration in every 30 s, so that a change curve of the oxygen consumption rate along with the observation height is obtained, and an area where the oxygen consumption rate is basically kept unchanged along with the observation height is selected as a proper observation height range; the area where the curve is basically stable along with the height is the appropriate observation height range, and the larger observation height value in the range is selected as the final observation height in consideration of the fact that the observation equipment still generates settlement. As shown in FIG. 8, the observation height in this embodiment is suitably in the range of 20-35cm, and the observation height is finally selected to be 35cm
The method for checking whether the hydrodynamic condition is stable in S3 includes: and calculating the average flow direction and the turbulence dissipation rate of the three-way flow velocity observation data every 30 s, and if the average flow direction is always kept stable along with the observation height and the turbulence dissipation rate is kept stable in a selected proper observation range, the hydrodynamic condition of the water bottom boundary layer in the fine adjustment process is stable, and the fine adjustment result of the observation height is effective. The right graph of fig. 8 is a result of the hydrodynamic condition stability test in the fine adjustment process of the left graph of fig. 8, and it can be seen that the flow direction of the water flow is basically maintained at 25-45 degrees in the fine adjustment process, the flow direction is basically maintained stable relative to the variation range of 0-360 degrees, and meanwhile, the dissipation rate of the turbulent kinetic energy is basically maintained stable within the suitable observation range of 20-35cm, so the fine adjustment result in the left graph of fig. 8 is effective.
Preferably, it further comprises the step of adjusting the observation direction to be parallel to the flow direction during the rest period of the whirl related measurement, specifically:
step 1: after entering a resting period of vortex related measurement each time, carrying out vector synthesis on the horizontal flow velocity in the previous observation period to obtain an average flow direction angle; if the average flow direction angle is smaller than 5 degrees, the water flow direction is not obviously changed after a vortex motion related observation period, and the rotating motor 4 enters a locking mode at the moment; if the average flow direction angle is larger than 5 degrees, the rotating motor 4 enters a free mode, the rotating motor 4 is not powered at the moment, an output shaft of the rotating motor can rotate freely under the pushing of external force, and the flow of water flow can drive the self-adaptive guide plate 7 to rotate, so that the acoustic Doppler current meter 5 is also driven to adjust the observation angle; in this embodiment, the average flow direction angle is an included angle between the observation direction of the acoustic doppler flow velocity meter 5 and the water flow direction.
Step 2: awakening the acoustic Doppler current meter 5 30 s before the wake-up of the resting period of the vortex-related measurement, taking the difference between the geographic azimuth angle read at this time and the geographic azimuth angle in the last observation period as the rotating angle of the acoustic Doppler current meter 5 in the resting period, and if the difference between the rotating angle and the average flow direction angle calculated in Step1 is less than 5 degrees, indicating that the adaptive guide plate 7 effectively adjusts the observation angle of the acoustic Doppler current meter 5, and at this time, enabling the rotating motor 4 to enter a locking mode; if the difference between the rotation angle and the average flow direction angle calculated in Step1 is larger than 5 degrees, entering Step 3; in this embodiment, the geographic azimuth angle of the acoustic doppler velocimeter 5 is the angle between the observation direction and the north direction of the geography. In addition, after the rotating motor 4 enters the locking mode, the output shaft of the rotating motor cannot rotate, and the self-adaptive guide plate 7 cannot drive the observation equipment to rotate under the pushing of water flow.
Step 3: the rotating motor 4 enters a working mode, the rotating motor 4 is called, an output shaft of the rotating motor rotates to drive the third gear 16 to rotate, the acoustic Doppler current meter 5 is driven by the fourth gear 17 to adjust an observation angle, and finally, an included angle between the observation direction of the acoustic Doppler current meter 5 and the average water flow direction is smaller than 5 degrees.
In addition, the embodiment also relates to a related data calculation method as follows:
the method is based on the water environment whirl related technology, the sediment oxygen consumption rate is obtained by calculating the covariance of the vertical flow velocity and the dissolved oxygen concentration, wherein the calculation of the flow velocity and the oxygen concentration turbulence sequence needs to be carried out through a series of steps (such as figure 18) of data inspection, coordinate rotation, turbulence calculation, time-lag correction, high-frequency correction and the like.
Step 1: and inputting a calculation parameter. And inputting calculation parameters independent of the vortex related measurement environment, including a frequency scaling factor, an instrument installation distance, an instrument response time difference, a water flow acceleration limit value, a flow meter signal-to-noise ratio and a correlation threshold value, a sliding average window for judging a dissolved oxygen field point, a standard deviation coefficient and the like.
Step 2: observation data is received. Immediately calculating the sediment oxygen consumption rate in the observation period based on the received data after the observation period of each section of whirl related measurement is finished, namely calculating from Step3 to Step 8.
Step 3: and (5) performing sequence optimization. The observation sequence optimization comprises frequency reduction and noise reduction, threshold filtering, outlier inspection, data interpolation, coordinate rotation and the like, and is calculated based on the input parameters in Step 1. The step of reducing the frequency and the noise refers to averaging original observation data to reduce the interference of environmental noise, the step of threshold filtering and the step of outlier detection are used for deleting abnormal observation data caused by various reasons, and the deleted data are subjected to linear interpolation. Coordinate rotation aims to force the vertical and longitudinal time-average flow velocity to approach zero, thereby avoiding cross interference between different components of turbulent flux; coordinate rotation by two rotations, i.e. first about a vertical axis: (zDirection) rotation to zero the mean time of the longitudinal flow velocity component, a second time about the longitudinal axis: (yAnd) is rotated such that the vertical flow velocity component has a mean value of zero.
Step 4: and (5) performing inclination removal correction. The observation data often have certain trend changes in the measurement period, so before calculating the turbulence sequence, a moving average method is adopted for inclination removal correction, wherein the selection of the length of a sliding window is highly dependent on the observation environment, and the measurement data of each section of the vortex related observation period needs to be determined independently. According to the invention, the length of the sliding window is equidistantly selected in the logarithmic interval of the length of the observation period to perform inclination removal correction and trial calculation of the sediment oxygen consumption rate, namely, Step 5-Step 6 is repeatedly performed, and finally, the trial calculation result of the oxygen consumption rate along with the length of the window is obtained (figure 9). And respectively performing linear fitting and logarithmic fitting on the trial calculation result, then translating the fitting straight line up and down until the fitting straight line is tangent to the logarithmic curve, and dividing a change area and a stable area by taking the tangent point as a boundary. And taking the window length corresponding to the scatter closest to the logarithmic curve in the stable region as the optimal sliding window length and performing inclination removal correction.
Step 5: and performing time lag correction. Because an installation space of 1-2 cm is reserved between the flow velocity sampling point 9 and the probe of the dissolved oxygen gradiometer 10, the measurement sequences of the two have time difference, time lag correction is needed to align the two measurement sequences, namely, the two measurement sequences are subjected to cross correlation analysis, and the relative movement time corresponding to the absolute value of the maximum cross correlation degree is selected as the time lag correction value. However, the cross-correlation analysis result is usually not monotonous, so that the selection of the time-lag correction value is often in a local optimum state, and the reliability of the oxygen consumption rate calculation result is influenced. When the sampling point of the current meter is positioned at the upstream of the dissolved oxygen gradiometer, the pre-judging time lag is recorded as the sum of the time of the water flow flowing through the space between the sensors and the response time difference of each sensor, otherwise, if the sampling point of the current meter is positioned at the downstream, the pre-judging time lag is the absolute value of the difference between the two. As shown in fig. 10, first, cross-correlation analysis of the vertical flow velocity and the dissolved oxygen concentration sequence is performed in a ten-fold interval of the predetermined time lag, and a relationship between the cross-correlation degree and the relative movement time is obtained. And then, taking the relative movement time corresponding to the sequence which is 10 percent of the absolute value of the cross correlation degree, performing time lag correction one by one, and calculating the time interval representativeness of the sediment oxygen consumption rate by trial, namely, repeating Step6 to obtain the relation between the time interval representativeness and the cross correlation degree. And finally, searching a first time interval representative maximum value from the maximum absolute cross correlation degree, taking the relative moving time corresponding to the cross correlation degree corresponding to the time interval representative as the optimal moving time, and performing time lag correction according to the optimal moving time.
Step 6: flux calculations were performed. Performing Reynolds decomposition on the inclination-removing observation sequence subjected to time-lag correction to obtain a turbulent motion sequence of vertical flow velocity and dissolved oxygen concentration; according to the water environment whirl correlation theory, the product of the two sequences is the time variation process of the sediment oxygen consumption rate. The time course is integrated to obtain a curve (figure 11) of the total oxygen consumption of the sediment in the observation period along with the time, the curve is linearly fitted, the fitting slope is the average sediment oxygen consumption rate in the observation period, and the fitting goodness is the period representativeness of the average oxygen consumption rate.
Step 7: and performing frequency correction. To extract the turbulence scale contributing to the sediment oxygen consumption rate calculation and to exclude high frequency noise signals, a frequency correction of the oxygen consumption rate calculation results is required. First, the calculated sink is calculated by fast Fourier transformThe product oxygen consumption rate sequence is converted from the time domain to the frequency domain, then the spectral data in the water flow signal interval is multiplied by a correction function, and finally the corrected average sediment oxygen consumption rate is obtained by integrating the frequency through the corrected spectral data (figure 12). The invention determines the non-noise interval based on Kolmogorov turbulence statistical theory, namely the noise frequency is determined byf n =(L K 2 /ε) -1/3 Calculation in the formulaL K =2π(ν 3 /ε) 1/4 For the smallest spatial dimension at which turbulence exists,ε=u 0 3 /кhv is the kinetic energy dissipation rate of the turbulence, v is the kinematic viscosity of the water body obtained by looking up a table according to the water temperature,u 0 is the friction flow speed of the boundary layer of the water bottom,к=0.41 is von karman constant,his the observed altitude of the acoustic doppler velocimeter.
Step 8: and (6) evaluating the data quality. The method carries out quality evaluation on the vortex related observation data from four aspects of effective data ratio, turbulence sequence robustness, time lag correction robustness and turbulence development sufficiency. The effective data ratio refers to the ratio of the data volume after transmission loss, threshold filtering and outlier inspection to the expected data volume in the observation period. The turbulence sequence robustness refers to the robustness of the oxygen consumption rate calculation result to the selection of the sliding window value in the process of inclination removal correction, and is measured by a fitting quality meter of a logarithmic function in Step 4. The time lag correction robustness refers to the robustness of the oxygen consumption rate calculation result to the selection of the relative movement time value in the time lag correction process, and is calculated by the variation coefficient of the oxygen consumption rate trial value in Step 5. The sufficiency of the turbulent flow development refers to the development degree of the turbulent flow in the vortex related observation period, and the noise frequency calculated in Step7 is adoptedf n Measured as the ratio of the 90% flux contribution frequency integrated from the low frequency region.
The data calculation method automatically determines the optimal sliding window length and the optimal relative movement time required in the sediment oxygen consumption rate calculation process through multiple iterative optimization, introduces the Kolmogorov scale to cut off the environmental noise, and can timely process and evaluate the quality of the measurement data of each observation period. The data processing method adopted by the invention avoids the analysis and the reexamination of the measured data in each observation period by manpower, and reduces the data processing cost in the long-term sediment oxygen consumption rate observation.
The embodiment of the invention is carried out in the large-sized black ink reservoir in the West county of Tangshan City of Hebei province, and the actual measurement results shown in figures 13-17 show that under the driving of various environmental factors of a water bottom boundary layer, the sediment oxygen consumption rate is frequently and violently changed within a period of time, and CO generated in the sediment oxygen consumption process 2 Is significantly inversely related to the change in the dissolved oxygen concentration. The embodiment shows that the device and the method designed by the invention can be effectively suitable for long-term real-time in-situ observation of the sediment oxygen consumption rate, the oxygen consumption rate measurement result can respond to the change of the underwater boundary layer environmental factors such as the dissolved oxygen concentration, hydrodynamic force conditions and the like with high precision, and the change of sediment oxygen consumption products is supported to be further analyzed, so that the device and the method have important significance for monitoring the endogenous release risk of the water body and researching the geochemical cycle process of water environment biology.
The above-described embodiments are merely preferred embodiments of the present invention, and should not be construed as limiting the present invention, and features in the embodiments and examples in the present application may be arbitrarily combined with each other without conflict. The protection scope of the present invention is defined by the claims, and includes equivalents of technical features of the claims. I.e., equivalent alterations and modifications within the scope hereof, are also intended to be within the scope of the invention.

Claims (6)

1. A long-term real-time measurement method of a sediment oxygen consumption rate in-situ measurement device comprises a buoy (1) arranged on the water surface and a measurement frame (2) arranged under the water, wherein a lifting platform (3) capable of moving vertically is arranged on the measurement frame (2), a rotating motor (4) is installed on the lifting platform (3), an acoustic Doppler current meter (5) and a dissolved oxygen gradient acquisition instrument (6) are arranged at the output end of the rotating motor (4), and a self-adaptive guide plate (7) is fixedly arranged on the surface of the acoustic Doppler current meter (5); the method is characterized in that: it comprises the following steps:
s1: coarse adjustment of the observation height: after the heave motor (8) works, the lifting platform (3) vertically moves, so that the heights of observation devices, namely the acoustic Doppler current meter (5) and the dissolved oxygen gradient acquisition instrument (6), can be adjusted, a sufficient observation height is reserved, and after the devices settle stably, sound wave signals received by the acoustic Doppler current meter (5) are analyzed to determine the distance between a sampling point (24) and a sediment-water interface;
s2: fine adjustment of observation height: after the rough adjustment of the observation height is finished, the fine adjustment is continuously carried out under the condition that the hydrodynamic condition of the bottom boundary layer is stable, the equipment is driven to rise for a certain distance by a heave motor (8) at intervals, the sediment oxygen consumption rate is synchronously measured by an acoustic Doppler current meter (5) and a dissolved oxygen gradient acquisition instrument (6), a change curve of the oxygen consumption rate along with the observation height is further obtained, and the observation height is finally adjusted to a proper position according to the curve;
s3: and (3) checking fine adjustment conditions: checking the stability of the hydrodynamic condition in the S2 fine adjustment process, and repeating the S2 if the hydrodynamic condition is unstable;
the S1 specifically includes: the acoustic Doppler current meter (5) emits sound wave signals through a central sensor thereof when in work,
two obvious signal peak values appear at a pulse emission position and a sampling point (24), then the position of the observation equipment is gradually reduced through a heave motor (8), when sound waves encounter an interface of medium interaction, a third peak appears due to sudden change of reflection properties, at the moment, the distance between the sampling point (24) and a sediment-water interface can be calculated, the position of the observation equipment is continuously reduced through the heave motor (8), and coarse adjustment is completed until the distance between the sampling point (24) and the sediment-water interface is 10 cm;
the S2 specifically includes: after the rough adjustment of the observation height is finished, the fine adjustment is continuously carried out under the condition that the hydrodynamic force condition of the bottom boundary layer is stable, namely from the observation period of a certain vortex related measurement, the observation equipment is driven to rise by 1cm through a lifting and sinking motor (8) every 30 s until the distance between a sampling point (24) and a sediment-water interface is 20-35cm, the sediment oxygen consumption rate is calculated once for the observation data of the vertical flow speed and the dissolved oxygen concentration in every 30 s, so that a change curve of the oxygen consumption rate along with the observation height is obtained, and an area where the oxygen consumption rate is basically kept unchanged along with the observation height is selected as a proper observation height range;
the method for checking whether the hydrodynamic condition is stable in S3 includes: calculating the average flow direction and the turbulence dissipation rate of the three-way flow velocity observation data every 30 s, and if the average flow direction is always kept stable along with the observation height and the turbulence dissipation rate is kept stable in a selected proper observation range, indicating that the hydrodynamic condition of the water bottom boundary layer in the fine adjustment process is stable and the fine adjustment result of the observation height is effective;
vertical fixed mounting has a heave motor (8) on lift platform (3), heave motor (8) output is equipped with first gear (9), first gear (9) and second gear (10) meshing, the axis of rotation of second gear (10) bottom is passed through the bearing and is installed in lift platform (3) upper surface, and second gear (10) top central point puts through connecting and threaded rod (11) bottom fixed connection, threaded rod (11) surface and fixation nut (12) screw-thread fit, fixation nut (12) are fixed in measuring frame (2) top through mounting bracket (13).
2. The method for measuring the in-situ measurement device of the oxygen consumption rate of the sediment in the long term and in real time according to claim 1, wherein the method comprises the following steps: fixed spout (14) that are equipped with in lift platform (3) both ends, spout (14) and vertical slide rail (15) sliding fit who sets up, slide rail (15) are fixed in and measure frame (2) lateral part.
3. The method for measuring the long-term real-time sediment oxygen consumption rate in-situ measuring device according to claim 1, characterized in that: on rotating electrical machines (4) are vertical to be fixed in lift platform (3), its output is equipped with third gear (16), third gear (16) and fourth gear (17) meshing, the axis of rotation at fourth gear (17) top is passed through the bearing and is installed in lift platform (3) lower surface, and fourth gear (17) bottom central point puts through joint and acoustics Doppler current meter (5) top fixed connection, and acoustics Doppler current meter (5) are through first support (18) and dissolved oxygen gradient acquisition appearance (6) fixed connection.
4. The method for measuring the long-term real-time sediment oxygen consumption rate in-situ measuring device according to claim 3, characterized in that: the acoustic Doppler current meter (5) is connected with the CO through a second bracket (19) 2 The partial pressure sensor (20) is connected.
5. The method for measuring the long-term real-time sediment oxygen consumption rate in-situ measuring device according to claim 1, characterized in that: buoy (1) top is equipped with solar panel (21) and sealed cabin (22), be equipped with battery, electrical source controller, serial port server and data transmission equipment in sealed cabin (22), measuring frame (2) top is equipped with watertight cabin (23), be equipped with data collection station and serial port server in watertight cabin (23), and pass through watertight cable junction with sealed cabin (22), be connected through the rope between measuring frame (2) top and buoy (1) bottom, measuring frame (2) bottom is equipped with supporting leg (25).
6. The method for measuring the long-term real-time sediment oxygen consumption rate in-situ measuring device according to claim 3, characterized in that: the method also comprises the step of adjusting the observation direction to be parallel to the flow direction in the dormancy stage of the vortex related measurement, which specifically comprises the following steps:
step 1: after entering a resting period of vortex related measurement each time, carrying out vector synthesis on the horizontal flow velocity in the previous observation period to obtain an average flow direction angle; if the average flow direction angle is smaller than 5 degrees, the water flow direction is not obviously changed after a vortex motion related observation period, and the rotating motor (4) enters a locking mode at the moment; if the average flow direction angle is larger than 5 degrees, the rotating motor (4) enters a free mode, power is not supplied to the rotating motor (4), an output shaft of the rotating motor can rotate freely under the pushing of external force, the flow of water flow can drive the self-adaptive guide plate (7) to rotate, and therefore the acoustic Doppler current meter (5) is also driven to adjust the observation angle;
step 2: awakening the acoustic Doppler current meter (5) 30 s before the wake-up of the resting period of the vortex-related measurement, taking the difference between the geographic azimuth angle read at the moment and the geographic azimuth angle in the last observation period as the rotating angle of the acoustic Doppler current meter (5) in the resting period, and if the difference between the rotating angle and the average flow direction angle calculated in Step1 is less than 5 degrees, indicating that the adaptive guide plate (7) effectively adjusts the observation angle of the acoustic Doppler current meter (5), and enabling the rotating motor (4) to enter a locking mode at the moment; if the difference between the rotation angle and the average flow direction angle calculated in Step1 is larger than 5 degrees, entering Step 3;
step 3: the rotating motor (4) enters a working mode, the rotating motor (4) is called, an output shaft of the rotating motor drives the third gear (16) to rotate after rotating, and then the fourth gear (17) drives the acoustic Doppler current meter (5) to adjust an observation angle, so that the included angle between the observation direction of the acoustic Doppler current meter (5) and the average water flow direction is finally smaller than 5 degrees.
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