CN109900724B - Crop water in-situ monitoring device and method based on microwave ground radar - Google Patents
Crop water in-situ monitoring device and method based on microwave ground radar Download PDFInfo
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Abstract
The invention discloses a crop moisture in-situ monitoring device and method based on a microwave ground radar, which belong to the technical field of microwave application. The measuring device can carry out rapid and in-situ nondestructive measurement on the water content of the crop plants, so that the measuring result is not influenced by factors such as crop growth vigor, planting density, surface water content, fluctuation and the like, and is particularly suitable for a field accurate management scene of modern agriculture.
Description
Technical Field
The invention belongs to the technical field of microwave application, and particularly relates to a crop moisture in-situ monitoring device and method based on a microwave ground radar.
Background
The water content is important crop growth information, and the plants in the state of water deficiency for a long time can slow down the photosynthesis rate and the transpiration rate, so that the plants grow slowly, the plant height is reduced, and the yield is reduced. The traditional unified irrigation mode can not accurately control different conditions of water content of specific crop plants, and the water resource utilization rate is low. Therefore, the method realizes the rapid and effective monitoring of the moisture state of crops in the growth process, and has important significance for drought prevention, irrigation management and yield prediction.
At present, the real-time measurement method of the water content of the crop plants mainly comprises a thermal equilibrium method, a small liquid flow method, a thermocouple method, a Peng Manmeng Tess method, a spectrum method, a dielectric constant method and the like. In general, the state monitoring speed of crop moisture based on morphology is high, but the error is large, and the response to short-term moisture change in a critical period of crops is not timely enough; the measurement method based on the physiological index is high in precision, but most of the measurement methods are destructive sampling random measurement, continuous crop growth results cannot be obtained, and the measurement method is difficult to popularize and apply in a field automation device.
The microwave detection technology utilizes the difference between the high-frequency dielectric property of the water-containing substance and the dry substance to realize the measurement of the water content of the substance. The measurement results represent the overall distribution of the regional moisture due to the strong penetration of microwaves. Based on the characteristics, the microwave space wave technology is widely applied to remote sensing and ground monitoring in crop measurement, and the remote sensing technology is applied to regional measurement, so that the monitoring of the growth state of local specific crops is difficult to realize; the ground radar remote sensing is to erect a transmitting and receiving device in the field, measure the energy attenuation, phase change and other parameters of reflected or transmitted microwaves, and invert to obtain vegetation and soil information.
Although vegetation remote sensing technology is widely applied, the effective method of in-situ measurement of the moisture state of the crop plants in a specific area is few, and the reason is that the currently commonly adopted radar crop measurement model has a plurality of interference factors during target inversion, the microwave reflection is influenced by factors such as the form density degree of the crops, the moisture content of the soil, the fluctuation degree of the earth surface layer and the like, and under the combined action of the factors, the effective information of the moisture content change in the interior of the crop plants is difficult to accurately extract.
Disclosure of Invention
Aiming at the defects existing in the prior art, in order to improve the effective precision of in-situ measurement of crop plant moisture and reduce the interference of external factors, the invention aims to provide a device and a method for in-situ measurement of crop moisture based on a microwave ground radar.
The invention is realized by the following technical scheme:
the crop moisture in-situ measurement device based on the microwave ground radar comprises a sensor bracket 1, a power supply unit 2, a temperature monitoring unit 3, a servo motor unit 4, a lead screw guide rail unit 5, a sliding platform 6, a microwave probe 7, a signal control unit 8 and a crop 9 to be measured; the sensor support 1 is vertically fixed on the ground, the power supply unit 2 is fixedly arranged on the sensor support 1, and the power supply unit is used for supplying required direct-current voltage signals to all units of the system through internal voltage transformation output; the temperature monitoring unit 3 and the signal control unit 8 are fixedly arranged on the sensor bracket 1, and a temperature signal wire of the temperature monitoring unit 3 is connected with the signal control unit 8; the servo motor unit 4 and the screw guide rail unit 5 are transversely arranged on the sensor bracket 1 and keep horizontal with the ground, a motor signal wire of the servo motor unit 4 is connected with the signal control unit 8, and when a control signal is input, the electric energy is converted into kinetic energy by a motor of the servo motor unit 4 to pull the ball screw of the screw guide rail unit 5 to rotate; the sliding platform 6 is arranged above the screw guide rail unit 5, and the sliding platform 6 can move horizontally and freely along the linear guide rail along with the rotation of the ball screw; the microwave probe 7 is fixedly arranged above the sliding platform 6, radiates microwave signals towards the direction of the crops 9 to be measured, does not directly contact the crops during measurement, and outputs measurement signals output by the microwave probe 7 to the signal control unit 8; the signal control unit 8 controls the servo motor unit 4, acquires measurement output signals of the microwave probe 7 and the temperature monitoring unit 3, performs corresponding operation processing to convert the measurement output signals into water content values, and transmits the data back to the control center through the wireless module.
Further, the microwave probe 7 is composed of a microwave cavity oscillator, a mixer and a horn antenna, microwave signals are generated by the microwave cavity oscillator and are subjected to radiation measurement towards crops through the horn antenna, meanwhile, the horn antenna receives reflected echo signals and carries out detection through the mixer to output direct-current voltage signals, the frequency of the microwave cavity oscillator is 3-26 GHz, the power range is 5-30 mw, and the direct-current excitation voltage is 5-24V; the horn antenna adopts a pyramid shape or a conical shape, and the effective gain is not less than 15dB.
Further, the screw guide rail unit 5 is composed of a ball screw in the middle and linear guide rails on two sides.
Further, the effective sliding distance of the sliding platform 6 on the lead screw guide rail unit 5 should be greater than 1 microwave working wavelength, so as to ensure that the microwave probe 7 can obtain a measurement signal with a complete period.
Further, the vertical installation height of the horn antenna of the microwave probe 7 is 1/2 of the height Hc of the crop to be measured, the horn antenna is positioned in the middle area of the crop to measure, and when the microwave probe 7 horizontally slides to be close to one end of the crop, the horizontal distance between the horn antenna port and the crop is 1/2 of the height Hc of the crop.
Further, the power supply unit 2 is composed of a solar panel, a storage battery and a voltage control module, and can automatically control and switch solar power supply and battery power supply, so that the system can work continuously day and night.
Further, the signal control unit 8 comprises an A/D converter, a singlechip operation control unit, a motor driving module and a wireless transmission module; the A/D converter converts analog signals measured by the sensor into digital signals, and the single chip microcomputer operation control unit realizes the functions of digital signal acquisition, internal operation processing, control of the motor driving module and control of the wireless transmission module.
Further, the crops 9 to be tested are field crops artificially planted such as corns, sorghum, beans and the like, and have uniform planting density and uniform growth vigor.
The invention relates to a crop water content measuring principle of a crop water content in-situ measuring device based on a microwave ground radar, which is described as follows:
the microwave and crop interact to generate a reflected signal, the emitted wave and the reflected wave are overlapped in space to form a space standing wave, the energy is distributed periodically, and related researches show that the standing wave ratio and the phase change are related to the moisture content and the growth morphology of the crop, so that the microwave probe of the device is utilized to continuously measure the microwave space standing wave, and an inversion formula is established to realize the real-time measurement of the moisture content of the crop.
The in-situ crop water content measuring method based on microwave ground radar includes the following specific steps:
s1, initializing a measuring device;
the sliding platform 6 is moved to one end of the lead screw guide rail by the rotation of the servo motor unit 4, and the microwave probe 7 approaches the crop 9 to be measured at the moment to prepare for measurement; the vertical height of the microwave probe 7 is 1/2 of the height Hc of the crop to be measured, the microwave probe 7 is positioned in the middle area of the crop to measure, and the horizontal distance between the microwave probe 7 and the crop is 1/2 of the height Hc of the crop;
s2, continuous measurement of microwave space wave signals
The signal control unit 8 controls the servo motor unit 4 to rotate, so that the microwave probe 7 gradually moves away from crops, meanwhile, the signal control unit 8 continuously collects the moving distance Z of the microwave probe 7 and the output voltage signal V, the signal output of the microwave probe changes periodically, the signal control unit 8 compares the maximum value Vmax, the minimum value Vmin and the moving distance Zm of the microwave probe corresponding to the minimum value of the record voltage, and the voltage standing wave ratio Sc=Vmax/Vmin is calculated;
s3, synchronous acquisition of environment temperature
The signal control unit 8 controls the temperature monitoring unit 3 to collect the ambient temperature T while the microwave probe 7 measures;
s4, calculating the water content of crop plants
The single chip microcomputer control unit in the signal control unit 8 calculates the water content Mc of the crop plants according to the following formula:
wherein: ρc is the planting density of the crop 9 to be measured, and represents the number of plants per unit area of the planted crop, H C For the average plant height of the crops to be tested, D C The diameter of an effective space growth area of a single plant of the crop to be detected is defined, sc is the voltage standing wave ratio of the microwave probe, zm is the moving distance of the microwave probe corresponding to the minimum value, and T is the ambient temperature; K. a0 and b0 are fitting coefficients, and when the crop 9 to be measured is specifically determined, the fitting coefficients are constant and can be obtained by measuring the signal output of the microwave probe of the crop with known water content in advance and reversely pushing the signal output.
Compared with the prior art, the invention has the following advantages:
the measuring device can carry out rapid and in-situ nondestructive measurement on the water content of the crop plants, so that the measuring result is not influenced by factors such as crop growth vigor, planting density, surface water content, fluctuation and the like.
Drawings
FIG. 1 is a schematic structural diagram of a crop moisture in-situ measurement device based on a microwave ground radar;
FIG. 2 is a graph showing the relationship between signal output and position change of the microwave probe according to the present invention;
fig. 3 is a schematic diagram of the structure of a signal control unit of the device of the present invention.
In the figure: the device comprises a sensor bracket 1, a power supply unit 2, a temperature monitoring unit 3, a servo motor unit 4, a screw guide rail unit 5, a sliding platform 6, a microwave probe 7, a signal control unit 8 and crops 9 to be tested.
Detailed Description
The invention is further illustrated by the following examples.
Example 1:
as shown in fig. 1, the crop moisture in-situ measurement device based on the ground radar comprises a sensor bracket 1, a power supply unit 2, a temperature monitoring unit 3, a servo motor unit 4, a lead screw guide rail unit 5, a sliding platform 6, a microwave probe 7, a signal control unit 8 and a crop 9 to be measured; the sensor support 1 is vertically fixed on the ground, the power supply unit 2 is fixedly arranged on the sensor support 1, and direct-current voltage signals required by each unit of the system are output through internal voltage transformation; the temperature monitoring unit 3 and the signal control unit 8 are respectively and fixedly arranged on the sensor bracket 1, and a temperature signal wire of the temperature monitoring unit 3 is connected with the signal control unit 8; the servo motor unit 4 and the screw guide rail unit 5 are transversely arranged on the sensor bracket 1 and keep horizontal with the ground, a motor signal wire of the servo motor unit 4 is connected with the signal control unit 8, and when a control signal is input, the electric energy is converted into kinetic energy by a motor of the servo motor unit 4 to pull the ball screw of the screw guide rail unit 5 to rotate; the sliding platform 6 is arranged above the screw guide rail unit 5, and the sliding platform 6 can move horizontally and freely along the linear guide rail along with the rotation of the ball screw; the microwave probe 7 is fixedly arranged above the sliding platform 6, radiates microwave signals towards the direction of the crops 9 to be measured, does not directly contact the crops during measurement, and outputs measurement signals output by the microwave probe 7 to the signal control unit 8; the signal control unit 8 controls the servo motor unit 4, acquires measurement output signals of the microwave probe 7 and the temperature monitoring unit 3, performs corresponding operation processing to convert the measurement output signals into water content values, and transmits the data back to the control center through the wireless module.
The power supply unit 2 consists of a solar panel, a storage battery and a voltage control module, and can automatically control and switch solar power supply and battery power supply, wherein the power of the solar panel is 18 watts, 24 volts of voltage is output, and the capacity of the storage battery is 7 amperes, and when sunlight is insufficient or the storage battery supplies power for the system at night.
The microwave probe 7 consists of a microwave cavity oscillator, a mixer and a horn antenna, wherein the center frequency is 10GHz, the power is 30mW, the direct current excitation voltage is 12V, the waveguide cavity adopts BJ100 standard length of 22.9mm and the width of 10.2mm, the horn antenna adopts a conical structure and is made of alloy materials, the radiation angle is plus or minus 6 degrees, the effective gain at the center frequency of 10GHz is about 15dB, the corresponding microwave working wavelength is 3cm, an oscillation diode and a mixing diode are arranged in the waveguide cavity, the microwave local oscillation signal is generated by the oscillation diode, the microwave local oscillation signal is emitted through the horn antenna, the echo signal reflected after the action of the microwave local oscillation signal and the material are mixed on the mixing diode, and the output mixing signal is in the form that:
in the formula, the mixing conductance g1 is constant, U S Is the amplitude of the reflected echo,is the relative value of the phase of the reflected echo, and each time the microwave probe detectsShift by 1/2 wavelength distance,/o>The value varies by one cycle. FIG. 2 shows the relationship between the moving distance of the microwave probe 7 and the output of the probe signal when the microwave radiation frequency is 10GHz in the actual measurement process of corn crops, the signal has a periodic variation within 15mm moving distance, the signal control unit 8 converts the output signal of the microwave probe 7 into a digital quantity through an A/D converter, and the single-chip microcomputer operation control unit compares the minimum value V in the recording period min =0.887 volts, maximum V max =1.612 v, the minimum point corresponds to the microwave probe movement distance Z m Subsequent operations were performed =2.12 mm.
The basic composition structure of the signal control unit 8 is shown in fig. 3, and the signal control unit comprises an A/D converter, a singlechip operation control unit, a motor driving module and a wireless module, wherein the singlechip operation control unit adopts a 32-bit ARM core STM32F103 series processor, 3.6V is adopted for power supply, the working frequency of a chip is set to 72MHz, the A/D converter is an STM32 processor internal integrated analog-digital converter, and the measurement requirement is met by 12-bit conversion precision and 1 mu s single conversion acquisition time. The motor driving module adopts MA860H series motor driver, adopts 24V DC voltage to supply power, rated current 4A, controls and drives the servo motor unit 4 motor to rotate through PWM pulse output of STM32 processor, the motor adopts 86 type stepping motor design, the output torque range is 4-10NM, and the effective sliding distance of the sliding platform 6 in the lead screw guide rail unit 5 is controlled to be more than 3cm. The wireless module adopts a 4G transparent transmission module design, and the singlechip operation control unit transmits data to the 4G transparent transmission module through a serial port, and the data is uploaded to the server for bidirectional communication by utilizing a 4G network.
Example 2
The in-situ crop water content measuring method based on microwave ground radar includes the following specific steps:
in the embodiment, corn in the small bell mouth period is taken as a measuring object, the crop planting density ρc is 7.3 plants per square meter, and the average plant height H of a measuring area is measured C 1 meter, single plantDiameter D of effective space growth area of corn C For 0.5 meter, the measurement was taken in the early morning with clear weather.
S1, initializing a measuring device;
the sliding platform 6 is moved to one end of the lead screw guide rail by the rotation of the servo motor unit 4, and the microwave probe 7 approaches to the crop to be measured to prepare measurement; the vertical height of the microwave probe 7 is half of the plant height Hc of corn, in this example, 0.55 m, and the initial horizontal distance between the microwave probe 7 and the crop is 0.55 m;
s2, continuous measurement of microwave space wave signals
The signal control unit 8 controls the servo motor unit 4 to rotate, so that the microwave probe 7 gradually moves away from crops, the probe moving speed is smaller than 1.25 millimeters per second, stable and continuous data are ensured, meanwhile, the signal control unit 8 continuously collects the moving distance Z of the microwave probe 7 and the output voltage signal V, the collecting frequency is 10 times per second, the output of the microwave probe signal changes periodically, as shown in a result of fig. 2, the signal control unit 8 compares the maximum value Vmax=1.612 volts, the minimum value Vmin=0.887 volts, the moving distance Zm=2.12 mm of the microwave probe corresponding to the minimum value, and the voltage standing wave ratio Sc=Vmax/Vmin=1.82 is calculated;
s3, synchronous acquisition of environment temperature
While the microwave probe 7 measures, the signal control unit 8 controls the temperature monitoring unit 3 to collect the measured environmental temperature t=24 ℃;
s4, calculating the water content of crop plants
The single chip microcomputer control unit in the signal control unit 8 calculates the water content Mc of the crop plants according to the following formula:
wherein: ρc=7.3 plants per square meter is the planting density of the corn crop tested; h C =1 meter is the average plant height of the crop; d (D) C =0.5 meters is the diameter of the effective spatial growth area of the individual crop; sc=1.82 is the voltage standing wave ratio of the microwave probe; zm=2.12 mm is the moving distance of the microwave probe corresponding to the minimum value; t=24 degrees celsius is ambient temperature;
K. a0 and b0 are fitting coefficients, and after the crop 9 to be tested is specifically determined, the fitting coefficients are constant, and in the example, the fitting coefficients are obtained by measuring the microwave probe signal output reverse of the corn crop with known water content in advance, and the specific method is as follows: independently selecting three groups of corn crops in different states, and respectively determining ρc and H measured in each group through the steps S1-S4 C 、D C Sampling 3-5 complete plants of each group of crops after parameters such as Sc, zm and T, classifying according to rhizome and leaves, weighing fresh weight, performing constant-temperature fixation and drying treatment, weighing corn plants with constant mass, respectively calculating average water content Mc of each group of corn plants, substituting the parameters into three groups of equations of different plant water contents in a formula (1), obtaining fitting coefficients of K, a and b0 simultaneously, wherein the specific measurement parameters in the example are shown in a table 1,
substituting into the formula (1) results in the following equation set:
the simultaneous (3) equation set yields k= 43.86, a0= -0.19, b0= -0.03.
Fitting coefficients k= 43.86, a0= -0.19, b0= -0.03 and measurement parameters ρc=7.3 strain per square meter, H C =1 meter, D C Substituting 0.5 m, sc=1.82, zm=2.12 mm, and t=24 degrees celsius into equation (1) yields a corn plant moisture content of mc=89.4% in this example.
Table 1 is a table of specific measurement parameters in this example.
Claims (6)
1. The crop moisture in-situ monitoring device based on the microwave ground radar is characterized by comprising a sensor bracket (1), a power supply unit (2), a temperature monitoring unit (3), a servo motor unit (4), a screw guide rail unit (5), a sliding platform (6), a microwave probe (7), a signal control unit (8) and a crop (9) to be tested; the sensor bracket (1) is vertically fixed above the ground, the power supply unit (2) is fixedly arranged on the sensor bracket (1), and the power supply unit outputs required direct-current voltage signals for each unit of the system through internal voltage transformation; the temperature monitoring unit (3) and the signal control unit (8) are fixedly arranged on the sensor bracket (1), and a temperature signal wire of the temperature monitoring unit (3) is connected with the signal control unit (8); the servo motor unit (4) and the screw guide rail unit (5) are transversely arranged on the sensor bracket (1) and keep horizontal with the ground, a motor signal wire of the servo motor unit (4) is connected with the signal control unit (8), and when a control signal is input, the electric energy is converted into kinetic energy by a motor of the servo motor unit (4) to pull a ball screw of the screw guide rail unit (5) to rotate; the sliding platform (6) is arranged on the screw guide rail unit (5), and the sliding platform (6) can move horizontally and freely along the linear guide rail along with the rotation of the ball screw; the microwave probe (7) is fixedly arranged above the sliding platform (6), radiates microwave signals towards the direction of the crops (9) to be measured, does not directly contact the crops during measurement, and outputs measurement signals output by the microwave probe (7) to the signal control unit (8); the signal control unit (8) is used for controlling the servo motor unit (4), collecting measurement output signals of the microwave probe (7) and the temperature monitoring unit (3), performing corresponding operation treatment, converting the measurement output signals into a water content value, and transmitting the data back to the control center through the wireless module;
the measuring method of the monitoring device comprises the following specific steps:
s1, initializing a monitoring device;
the sliding platform (6) is moved to one end of the lead screw guide rail through the rotation of the servo motor unit (4), and the microwave probe (7) approaches to the crop (9) to be measured at the moment to be measured; the vertical height of the microwave probe (7) is 1/2 of the height Hc of the crop to be measured, the microwave probe is positioned in the middle area of the crop to be measured, and the horizontal distance between the microwave probe (7) and the crop is 1/2 of the height Hc of the crop;
s2, continuous measurement of microwave space wave signals
The signal control unit (8) controls the servo motor unit (4) to rotate, so that the microwave probe (7) gradually moves away from crops, meanwhile, the signal control unit (8) continuously collects the moving distance Z of the microwave probe (7) and the output voltage signal V, the signal output of the microwave probe changes periodically, the signal control unit (8) compares the moving distance Zm of the microwave probe corresponding to the maximum value Vmax, the minimum value Vmin and the minimum value of the record voltage, and the voltage standing wave ratio Sc=Vmax/Vmin is calculated;
s3, synchronous acquisition of environment temperature
The signal control unit (8) controls the temperature monitoring unit (3) to collect the ambient temperature T while the microwave probe (7) measures;
s4, calculating the water content of crop plants
The single chip microcomputer control unit in the signal control unit (8) calculates the water content Mc of the crop plants according to the following formula:
wherein: ρc is the planting density of the crop (9) to be measured, and represents the plant number of the planted crop per unit area, H C For the average plant height of the crops to be tested, D C The diameter of an effective space growth area of a single plant of the crop to be detected is defined, sc is the voltage standing wave ratio of the microwave probe, zm is the moving distance of the microwave probe corresponding to the minimum value, and T is the ambient temperature; K. a0 and b0 are fitting coefficients, and when the crop (9) to be measured is specifically determined, the fitting coefficients are constant and can be obtained by measuring the signal output of the microwave probe of the crop with known water content in advance and performing back-pushing;
the microwave probe (7) consists of a microwave cavity oscillator, a mixer and a horn antenna, microwave signals are generated by the microwave cavity oscillator and face crops to be subjected to radiation measurement through the horn antenna, meanwhile, the horn antenna receives reflected echo signals and detects the reflected echo signals through the mixer to output direct-current voltage signals, the frequency of the microwave cavity oscillator is 3-26 GHz, the power range is 5-30 mw, and the direct-current excitation voltage is 5-24V; the horn antenna adopts a pyramid shape or a conical shape, and the effective gain is not less than 15dB;
the vertical height of the horn antenna of the microwave probe (7) is 1/2 of the height Hc of the crop to be measured, the horn antenna is positioned in the middle area of the crop to measure, and when the microwave probe (7) horizontally slides to be close to one end of the crop, the horizontal distance between the horn antenna port and the crop is 1/2 of the height Hc of the crop.
2. The in-situ monitoring device for crop moisture based on the microwave ground radar according to claim 1, wherein the screw guide rail unit (5) consists of a ball screw positioned in the middle and linear guide rails positioned at two sides.
3. The in-situ monitoring device for crop moisture based on the microwave ground radar according to claim 1, wherein the effective sliding distance of the sliding platform (6) on the lead screw guide rail unit (5) is larger than 1 microwave working wavelength, so that the microwave probe (7) can obtain a measurement signal with a complete period.
4. The in-situ crop moisture monitoring device based on the microwave ground radar according to claim 1, wherein the power supply unit (2) consists of a solar panel, a storage battery and a voltage control module, and can automatically control and switch between solar power supply and battery power supply, so that the system can work continuously day and night.
5. The in-situ monitoring device for crop moisture based on the microwave ground radar according to claim 1, wherein the signal control unit (8) comprises an A/D converter, a singlechip operation control unit, a motor driving module and a wireless transmission module; the A/D converter converts analog signals measured by the sensor into digital signals, and the single chip microcomputer operation control unit realizes the functions of digital signal acquisition, internal operation processing, control of the motor driving module and control of the wireless transmission module.
6. The in-situ monitoring device for crop moisture based on the microwave ground radar according to claim 1, wherein the detected crop (9) is a field crop artificially planted by corn, sorghum or beans, and the planting density is uniform and the growth vigor is uniform.
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| CN114858825B (en) * | 2022-05-31 | 2024-05-10 | 吉林农业大学 | Material moisture content measuring device and method based on microwave cavity detection |
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