CN108489916A - A kind of lake algae chlorophyll-a concentration quick monitoring method - Google Patents

Abstract

The invention discloses a method for quickly monitoring the concentration of algae chlorophyll a in a lake. A non-contact measuring device is used to measure and obtain the downlink irradiance E _d of the four bands of 665nm, 681nm, 709nm and 753nm of the water body to be tested, and the sky radiance L _sky , Water surface radiance L _sw ; use the difference between water surface radiance L _sw and sky radiance L _sky to obtain water surface radiance L _w , and calculate water remote sensing reflectance based on water surface radiance L _w and downlink irradiance E _d ; Finally, calculate the pigment concentration based on the two-band algorithm, FLH algorithm, and MCI algorithm, and take the average value of the three as the pigment concentration value. The rapid monitoring method of lake algae pigment concentration based on four pigment sensitive bands of the present invention avoids the numerical saturation problem that may occur in existing measurements, and the pigment concentration obtained by calculating the average value based on the four sensitive bands is more accurate, and can quickly obtain lake water Based on the change dynamics of pigment concentration, a single-factor early warning model of lake water quality is constructed, including different stages such as algal bloom occurrence and outbreak.

Description

A rapid monitoring method for the concentration of chlorophyll-a in lake algae

technical field

The invention relates to a method for quickly monitoring the concentration of algal chlorophyll a in lakes, which relates to monitoring the concentration of algae pigments in lakes, and provides a method for quickly obtaining the concentration of pigments for the problem of frequent outbreaks of algal blooms in eutrophic lakes, which can be applied to eutrophication Prediction and early warning of lake algal bloom outbreak and supervision of lake eutrophication.

Background technique

The concentration of algae pigments in lakes is an important indicator of lake eutrophication status and prediction and early warning, and plays a decisive role in the growth and development, yield and quality of crops. At present, the methods for measuring the concentration of algal pigments include: counting method, black and white bottle method, 14C method, spectrophotometry, laboratory fluorescence measurement method, etc. The monochromatic spectrophotometry proposed by Lorenzen (1966) is mostly used in spectrophotometry. Spectrophotometric measurement requires procedures such as sampling, extraction, and centrifugation of chlorophyll and phycocyanin, which are cumbersome in operation. When using this method, the collected samples must be pretreated, and the detection limit is 1 μg/L. The principle of measuring algae pigments in water by fluorescence photometry is: irradiate phytoplankton in water with light of 430nm wavelength, the chlorophyll or phycocyanin in phytoplankton will produce fluorescence with a wavelength of about 677nm or 620nm, and measure the intensity of this fluorescence by The corresponding relationship with the concentration of chlorophyll and the concentration of phycocyanin can obtain the content of algae pigment in water. The excitation light source and emitted light will be affected by the scattering effect of suspended particles in the water body to reduce the light intensity, and when the water body is illuminated, in addition to the fluorescent substance emitting light, there are also liquid molecular scattering that is the same as the incident light, particle scattering of inorganic suspended matter, etc. . The disadvantages of the above two methods are: the spectrum or fluorescence characteristics of algae pigments are affected by light, temperature, etc. during the extraction process, and there are cases where the extraction is incomplete or the pigments deteriorate. At this time, the measured pigment concentration has a large error; The randomness and unevenness of the sampling process also affect the distribution of pigment concentration when collected indoors for analysis; in the laboratory measurement process, it also consumes a lot of manpower and material resources, and the pigment concentration cannot be quickly determined.

When the existing chlorophyll measuring instruments (YSI, water quality meter, etc.) are used in turbid and eutrophic lake water, the numerical saturation will occur. The main reason is that the content of inorganic suspended matter in turbid water is too high, which affects the chlorophyll. the fluorescent signal. Therefore, it is necessary to develop a method that can quickly and accurately monitor the concentration of algal pigments in turbid, eutrophic lakes.

Contents of the invention

The purpose of the present invention is to solve the problem that the existing lake algae pigment concentration monitoring cannot meet the daily monitoring requirements, and to provide a method for quickly detecting the concentration of lake algae chlorophyll a by using the pigment-sensitive band, which can realize portable, low-cost, and low-power consumption. Measure optical and water quality parameters such as photosynthetically active radiation, remote sensing reflectance, algae chlorophyll a concentration, and phycocyanin concentration of lake water.

In order to achieve the above-mentioned technical purpose, the present invention adopts the following technical solutions,

A method for quickly monitoring the concentration of chlorophyll-a in lake algae, comprising the steps of:

1) The downlink irradiance E _d , the sky radiance L _sky , and the water surface radiance L _sw are obtained by using a non-contact measuring device to measure and obtain the downlink irradiance E d in four bands of 665nm, 681nm, 709nm, and 753nm of the water body to be tested;

2) Use the difference between the water surface radiance L _sw and the sky radiance L _sky to obtain the water surface radiance L _w , and calculate the water remote sensing reflectance Rrs based on the water surface radiance L _w and the downlink irradiance E _d :

L _w (λ _i )＝L _sw (λ _i )-0.028L _sky (λ _i ) (1)

Rrs(λ _i )＝L _w (λ _i )/E _d (λ _i ) (2)

Among them, λ _i is the wavelength value under the band i, i=1, 2, 3, 4;

3) Calculate the chlorophyll a concentration based on the two-band algorithm, FLH algorithm, and MCI algorithm respectively, and take the average value of the three as the chlorophyll a concentration value.

In the method of the present invention, the non-contact measuring device in the step 1) includes a support rod, on which an algae pigment concentration sensor is provided, and the algae pigment concentration sensor includes a downlink irradiance sensor, and the water surface radiation A brightness sensor and a sky radiance sensor are respectively used to measure the downlink irradiance E _d , the sky radiance L _sky and the water surface radiance L _sw ;

The sensor structure includes a light pipe and a photodetector array arranged at intervals in the light pipe, a filter, and a cleaning glass, and a filter ring is fixed at one end of the light pipe near the photodetector array; The surface of the filter circle in the illuminance sensor is attached with a uniform light plate.

According to the method of the present invention, the viewing angle of the light pipe is 25°, the hole depth is 36mm, and the aperture is 24mm.

In the method of the present invention, the photodetector array is formed by four photodiodes arranged at intervals; the central wavelength bands of the optical filters are 665nm, 681nm, 709nm, 753nm, and the bandwidth is 9nm-10nm.

In the method of the present invention, the surface of the filter circle in the water surface radiance sensor and the sky radiance sensor is provided with protective glass.

In the method of the present invention, the downward irradiance sensor is connected to the upper surface of the support rod perpendicular to the support rod; the water surface irradiance sensor is fixedly connected to the front end of the support rod, and the inclination angle between the support rod and the support rod is -40°; The sky radiance sensor and the water surface radiance sensor are perpendicular to each other, the inclination angle with the support rod is 50°, and the water surface radiance sensor and the support rod are in the same plane. Further, the non-contact measuring device measures against the direction of the sun, and the azimuth angle between the observation plane and the sun incident plane is 135°.

In the method of the present invention, the downlink irradiance sensor, the water surface radiance sensor and the sky radiance sensor are detachably connected to the support rod. Easy to replace and adjust the sensor.

In the method of the present invention, the non-contact measuring device also includes a low-pass filter module, an AD conversion module and a data processing module, and the data processing module includes a microprocessor and a control keyboard; the downlink irradiance sensor, The water surface radiance sensor and the sky radiance sensor are connected to a low-pass filter circuit through a three-core cable, and the output signal is converted into a discrete signal by an AD conversion circuit and sent to a microprocessor data processing module; the microprocessor selects an AVR single-chip microcomputer; The control keyboard controls the working mode of the microprocessor. Further, a display device is also included, and the display device is connected to the microprocessor for outputting measurement parameters.

The method for quickly monitoring the concentration of chlorophyll a in lake algae of the present invention is based on the acquisition of four pigment-sensitive bands 665nm, 681nm, 709nm, and 753nm, which avoids the numerical saturation problem that may occur in existing measurements, and uses the two-band algorithm, FLH based on the four sensitive bands The pigment concentration obtained by calculating the average value of the algorithm and the MCI algorithm is more accurate, and the method of the present invention can be used to quickly obtain the change dynamics of the pigment concentration of the lake water body, and construct a single-factor early warning model of the lake water quality, including different stages such as algal bloom occurrence and outbreak. In addition, the device selected in the method of the present invention is a hand-held device, which is small in size and adopts non-contact measurement, so that the algae pigment concentration can be obtained quickly without destroying the distribution of algal blooms floating on the water surface. And for highly turbid water bodies, sensors that measure continuous spectrum have poor anti-interference ability; while the measurement of a single sensitive band has a higher signal-to-noise ratio, it is not easy to reach saturation in highly reflective water bodies such as turbid or eutrophic water bodies. The invention selects sensitive bands to better extract pigment information, avoid numerical saturation, realize more accurate monitoring of pigment concentration in eutrophic lakes, and can be used for real-time and rapid early warning of cyanobacteria blooms.

Description of drawings

The structural representation of the measuring device of the inventive method of Fig. 1;

Figure 2 is a schematic diagram of the top view structure of the sensor;

Figure 3 is a cross-sectional view of the downlink irradiance sensor;

Fig. 4 is a sectional view of water body and sky radiance sensor;

Figure 5 is a schematic diagram of the use of the measuring device;

Figure 6 is the comparison between the actual measurement results of different sampling points and the measurement results of the three methods;

Fig. 7 is the method of the present invention and measured result contrast;

In the figure: 12. Downlink irradiance sensor, 13. Water surface radiance sensor, 14. Sky radiance sensor, 15. Support rod, 16. Integrated module, 17. Three-core cable, 18. Light pipe, 19. Photoelectric Detector array, 20, optical filter, 21, cleaning glass, 22, filter ring, 23, uniform light plate, 24, protective glass.

Detailed ways

Example 1

This embodiment illustrates the specific technical solution of the method of the present invention.

Method of the present invention comprises the steps:

1) Measure and obtain the downlink irradiance E _d , the sky radiance L _sky , the water surface radiance L _sw , and calculate the remote sensing reflectance of the water body;

L _w (λ _i )＝L _sw (λ _i )-0.028L _sky (λ _i ) (1)

Rrs(λ _i )＝L _w (λ _i )/E _d (λ _i ) (2)

Wherein, λ _i is the wavelength value in band i, λ ₁ =665nm, λ ₂ =681nm, λ ₃ =709nm, λ ₄ =753nm;

2) Calculate the pigment concentration based on the remote sensing reflectance of the water body.

The two-band algorithm, MCI algorithm, and FLH algorithm were used to calculate the concentration of chlorophyll a, as follows:

Two-band algorithm:

index=Rrs(λ ₃ )/Rrs(λ ₁ )

Chla＝-45.5×index ² +220.1×index-137.6 (3)

MCI algorithm:

Chla=7.97×exp ^167.79×MCI (4)

FLH algorithm:

Chla=-13929×FLH+19.1 (5)

Calculate and obtain the chlorophyll a concentration value, and take the average value as the final chlorophyll a concentration value. Fig. 6 is that the actual measurement result of different sampling points is compared with two-band algorithm, MCI algorithm, FLH algorithm independent measurement result, and average relative error is respectively 27.6%, 35.8%, 32.7%; Fig. 7 is the average Chla and actual measurement of the inventive method measurement Compared with Chla (true value), the average relative error is 25.3%, R ² is 0.76, and the accuracy is high, which can meet the needs of actual measurement.

The above method is used to obtain the chlorophyll a concentration value in real time to realize the rapid monitoring of the chromaticity concentration of lake algae.

In this embodiment, the structure of the non-contact measuring device is as shown in Figure 1, including a support rod 15, on which an algae pigment concentration sensor is provided, and the algae pigment concentration sensor includes a downlink irradiance sensor 12 , the water surface radiance sensor 13 and the sky radiance sensor 14; the uniform light plate 23 can realize the integration of the solar incident radiation at different angles.

The structure of described sensor comprises light pipe 18 and the photodetector array 19, optical filter 20, cleaning glass 21 that are arranged at intervals in the light pipe successively, and described light pipe 18 is fixed with one end nozzle near photodetector array 19 Filter ring 22 ; the filter ring 22 in the downlink irradiance sensor 12 has a uniform light plate 23 attached to its surface. A protective glass 24 is provided on the surface of the filter ring 22 in the water surface radiance sensor 13 and the sky radiance sensor 14 .

The downlink irradiance sensor 12 measures the incident solar radiation in the entire upper hemisphere space, and is connected to the upper surface of the support rod 15 perpendicular to the support rod 15; It is -45°; the sky radiance sensor 14 and the water surface radiance sensor 13 are symmetrically connected with the support rod 15 as a symmetrical axis, and the inclination angle with the support rod 15 is 45°, and the water surface radiance sensor 13 and the support rod 15 are on the same plane Inside. The downlink irradiance sensor 12 , the water surface radiance sensor 13 and the sky irradiance sensor 14 are connected to the support rod 15 in a detachable manner.

The device also includes a low-pass filter module, an AD conversion module, a data processing module and a display device, and the data processing module includes a microprocessor and a control keyboard; the downlink irradiance sensor 12, the water surface radiance sensor 13 and the sky The radiance sensor 14 is connected to the low-pass filter circuit by the three-core cable 17, and the output signal is converted into a discrete signal by the AD conversion circuit and then sent to the microprocessor data processing module; the microprocessor selects an AVR single-chip microcomputer; the control keyboard controls Microprocessor working mode; the display device is used to output measurement parameters. For easy portability, the low-pass filter module, AD conversion module, data processing module and display device are integrated together as an integrated module 16, which is fixed on the support rod 15.

In this embodiment, the viewing angle of the light pipe 18 is 25°, the hole depth is 36 mm, and the hole diameter is 24 mm. The photodetector array 19 is formed by four photodiodes arranged at intervals; the filter 20 selects the central wavelength bands of 665nm, 681nm, 709nm, 753nm, and the bandwidth is 9nm-10nm.

The operating mode of the microprocessor can be set as required. In this embodiment, three modes of "measurement", "monitoring" and "reset" are set, and the control keyboard includes three modes of "measurement", "monitoring" and "reset". When the control keyboard is switched to the "measurement" mode, the single-chip microprocessor collects the spectral information of the water body in real time and processes the collected information, and displays the results on the display device in real time; when switched to the "monitoring" mode , the microprocessor interrupts the current real-time measurement, captures the current value, and the display device displays photosynthetically active radiation and pigment concentration, including chlorophyll a concentration, phycocyanin concentration, etc.; when switching to "reset" mode, the system and screen return to the initialization state .

When monitoring the lake algae pigment concentration, hold or fix one end of the support rod 15 so that the fixed support rod 15 is in a horizontal position, the plane where the support rod 15 and the surveyor are located is perpendicular to the plane where the sun and the surveyor are located, the support rod is placed horizontally, and the water surface The radiance sensor 13 is 0.5m-1m higher than the water surface. Simultaneously, support bar 15 stretches out beyond the hull 1m, to avoid the influence of hull itself.

As shown in Fig. 5, when the above-mentioned device of the present invention is in use, since the light reflected by the water body is strong, the optical signal entering the sensor carries water surface reflection information and sky light information, which directly affects the measurement accuracy of the sensor. When the device is in use, the azimuth angle of the incident plane of the sun is 135°, so as to minimize the influence of reflected light from the sun.

Since the measurement angle of the instrument has a great influence on the spectrum, when measuring on a field survey ship, after the survey ship is stable, avoid the influence of foam in the water and the shadow of the hull. When the wind speed is greater than 3m/s, it needs to be measured several times. In the process of data post-processing, the one with the lowest spectrum is selected as the best value of the measurement point.

The above method was used to obtain the chlorophyll a concentration value in real time, and then the time series data of the water body chlorophyll a concentration of the virtual stations of Chaohu Lake and Taihu Lake from 2016 to 2017 were obtained. Without the need for laboratory measurement, it can reflect the change of chlorophyll a at the monitoring point in real time to analyze the reason for the change of Chla in a short period of time, and make a quick and timely response, that is, to realize the rapid monitoring of the chromaticity concentration of algae in the lake.

Claims (10)

1. a kind of lake algae chlorophyll-a concentration quick monitoring method, which is characterized in that include the following steps：

1) it uses non-contact measurement apparatus to measure to obtain under tetra- wave bands of water body 665nm, 681nm, 709nm, 753nm to be measured Row irradiation level E_d, sky spoke brightness L_sky, water surface spoke brightness L_sw；

2) water surface spoke brightness L is utilized_swWith sky spoke brightness L_skyDifference obtain the water surface from water spoke brightness L_w, based on the water surface from water Spoke brightness L_wWith downlink irradiation level E_dCalculate water body remote sensing reflectance Rrs：

L_w(λ_i)=L_sw(λ_i)-0.028L_sky(λ_i) (1)

Rrs(λ_i)=L_w(λ_i)/E_d(λ_i) (2)

Wherein, λ_iFor the wavelength value under wave band i, i=1,2,3,4；

3) two wave band algorithms, FLH algorithms, MCI algorithms are based respectively on and calculates chlorophyll-a concentration, takes three's average value green as leaf Plain a concentration values.

2. according to the method described in claim 1, it is characterized in that, in the step 1), non-contact measurement apparatus includes branch Strut, the supporting rod are equipped with algal pigment concentration sensor, and the algal pigment concentration sensor includes downlink irradiation level Sensor, water surface spoke luminance sensor and sky spoke luminance sensor are respectively used to measure the downlink irradiation level E_d, sky spoke Brightness L_skyWith water surface spoke brightness L_sw；

The sensor structure includes light pipe and the photodetector array being sequentially arranged at intervals in light pipe, optical filter, cleaning Glass, the light pipe are fixed with filtering circle close to one end nozzle of photodetector array；In the downlink irradiance sensor Filtering circle surface post equal tabula rasa.

3. according to the method described in claim 2, it is characterized in that, the light pipe field angle be 25 °, hole depth 36mm, aperture 24mm。

4. according to the method described in claim 2, it is characterized in that, the photodetector array is by between four photodiodes Every arranging；It is 665nm, 681nm, 709nm, 753nm, bandwidth 9nm-10nm that optical filter, which selects center wave band,.

5. according to the method described in claim 2, it is characterized in that, the water surface spoke luminance sensor, sky spoke brightness sensing Filtering circle surface in device is equipped with protective glass.

6. according to the method described in claim 2, it is characterized in that, the downlink irradiance sensor is connected perpendicular to supporting rod In supporting rod upper surface；The water surface spoke luminance sensor is fixedly connected on supporting rod front end, and inclination angle is -40 ° between supporting rod； The sky spoke luminance sensor is mutually perpendicular to water surface spoke luminance sensor, between supporting rod inclination angle be 50 °, and with water surface spoke Luminance sensor, supporting rod are in a plane.

7. according to the method described in claim 6, it is characterized in that, the non-contact measurement apparatus is surveyed backwards to solar direction The cut angle of azimuths of amount, plane of vision and sun plane of incidence is in 135 °.

8. according to the method described in claim 2, it is characterized in that, the downlink irradiance sensor, water surface spoke brightness sensing Device and sky spoke luminance sensor are removably connect with supporting rod.

9. according to the method described in claim 2, it is characterized in that, further including low-pass filtering module, AD conversion module and data Processing module, the data processing module include microprocessor and control keyboard；The downlink irradiance sensor, water surface spoke are bright Degree sensor connects low-pass filter circuit with sky spoke luminance sensor by triple core cable, and output signal is through A/D converter circuit It is sent to microprocessor data processing module after being converted to discrete signal；The microprocessor selects AVR single chip；The control Keyboard Control microprocessor work pattern.

10. according to the method described in claim 9, it is characterized in that, further including display device, the display device connects micro- place Device is managed, for exporting measurement parameter.