CN111337553A - Contact type soil humidity measuring method based on navigation satellite signals - Google Patents
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Abstract
The invention discloses a contact type soil humidity measuring method based on navigation satellite signals, which belongs to the technical field of soil humidity measurement. The method not only utilizes the refraction information of the navigation signal on the soil-air interface when measuring the soil humidity, but also utilizes the information attenuated by the soil when the navigation signal is transmitted in the soil, thereby having the characteristics of a remote sensing means and a contact type measuring means, further enriching the existing soil humidity measuring means, and simultaneously providing a reliable ground verification means for satellite soil humidity remote sensing. The problems in the prior art are solved.
Description
Technical Field
The invention relates to a contact type soil humidity measuring method based on navigation satellite signals, and belongs to the technical field of soil humidity measurement.
Background
Soil moisture is a description of the moisture content of soil. In agriculture, the fertilizer is an important element for growth of crops and is also an important element for researching agricultural natural disasters; it is a key variable in global water circulation and energy exchange studies. Since soil humidity is largely coupled to climate systems and hydrologic processes, global and regional climate prediction imposes high demands on the knowledge of this variable, and it is desirable to improve the accuracy of drought disaster prediction by studying soil humidity measurements to improve the simulation of climate systems.
At present, the most common soil humidity measurement method in agricultural production and life is contact soil humidity measurement, and is based on time domain reflection in a plurality of contact measurement methods, such as the following published numbers: CN105181715A, discloses a time domain reflective soil moisture sensor and frequency domain reflection, as patent publication No.: CN102788823A discloses a frequency domain reflection type soil moisture sensor, and the methods of the two technical scheme principles have the advantages of high measurement accuracy, good stability and wide application. Sensors made by such techniques typically take the form of multiple probes that are buried in the soil and emit electromagnetic waves into the soil while receiving soil echoes, and soil moisture can be measured by measuring the difference between the emitted and received electromagnetic waves. However, the contact method has the disadvantage that the measuring range is very limited, and the method is limited to the soil of a few centimeters around the probe and cannot be used for large-area measurement.
Later, with the development of satellite technology, active and passive microwave remote sensing technologies are developed and successfully applied to medium and large-scale soil humidity monitoring. In 2009, the european space launched Soil Moisture and Ocean Salinity (SMOS) satellites; in 1 month 2015, the united states space agency launched soil moisture passive active (SMAP) satellites. The two satellite remote sensing tasks are carried out in a microwave L wave band which is most sensitive to soil. With the development of global navigation system in recent years, a method for measuring soil humidity by using Global Navigation Satellite System (GNSS) reflection signals appears, and patent publications are as follows: CN104698150A discloses a surface soil humidity measuring device and a measuring method based on GNSS-R, which utilize the change of reflection signal parameters along with soil humidity, and the principle is very similar to active microwave remote sensing. Virtually all of these remote sensing methods measure the overall moisture of a few centimeters of soil on the surface. The ground verification of satellite soil humidity data products mostly takes the measurement result of the contact type measurement means as a reference, however, the contact type measurement means can only obtain the information caused by the interaction between the electromagnetic wave and the soil, and can not obtain the information of the soil-air interface, so that the high dynamic change information of the soil-air interface captured by the remote sensing satellite can not be fully represented by the information obtained by the contact type means.
Therefore, a soil humidity measurement means and a satellite remote sensing ground verification means for acquiring information of a soil-air interface become technical problems which need to be solved urgently at present.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a contact type soil humidity measuring method based on navigation satellite signals, which utilizes the refraction of the satellite signals on a soil-air interface and the attenuation of the satellite signals in soil to measure the soil humidity and solves the problems in the prior art.
The invention relates to a contact type soil humidity measuring method based on navigation satellite signals, which comprises the following steps:
step 1: the antenna is installed on the base plate,
horizontally fixing two antennas with the same type on the soil surface, and marking as A1The other is horizontally buried under the soil surface, the actual depth is recorded as d, and the antenna is recorded as A2Leading out the feeder lines of the two antennas;
step 2: the signal is received and processed, and then the signal is processed,
connecting the feeder lines of the two antennas with a receiver respectively, and measuring and recording the power or signal-to-noise ratio of signals received by the two antennas and satellite ephemeris data at synchronous and fixed sampling time intervals;
and step 3: the satellite elevation and azimuth calculations are performed,
by an antenna A1The precise position of the satellite is taken as a reference, and satellite ephemeris data and sampling time n are combined to calculate the satellite relative to the antenna A1Elevation angle θ (n) and azimuth angle;
and 4, step 4: the data is screened out, and the data is filtered out,
selecting data of the satellite consistent with the azimuth of the measurement area according to the azimuth of the satellite;
and 5: the ratio of the signal powers is calculated,
calculating antenna A at each sampling instant2And an antenna A1The power ratio of (a) is denoted as K (n) and is expressed by the following formula:
step 6: the attenuation coefficient is calculated and the calculated value,
calculating an attenuation coefficient α (n) according to the signal power ratio calculated in the step 5:
wherein: dsIn order to obtain the propagation path length of the navigation signal in the soil, gamma (n) is a soil reflection coefficient, and n is sampling time;
and 7: the inversion of the soil moisture is carried out,
calculating the soil humidity according to the soil attenuation coefficient model and the microwave band soil dielectric model, wherein the soil attenuation coefficient model is described by the following formula:
wherein: f is the navigation signal carrier frequency, ε0，μ0Is air dielectric constant and magnetic permeability, epsilon's，ε′sThe real part and the imaginary part of the complex relative dielectric constant of the soil are respectively; and finally, combining the formula (2) and the formula (3), and solving the soil humidity by using the technology of iterative equation solving.
Further, the receiver in step 2 is a GNSS satellite signal receiver, and the connection mode between the feeder lines of the two antennas and the GNSS satellite signal receiver includes: the feeder lines of the two antennas are respectively connected with the two GNSS satellite signal receivers or connected with two antenna interfaces of a double-channel GNSS satellite signal receiver.
Further, step 6 dsThe length of the propagation path of the navigation signal in the soil is calculated by the following formula:
wherein: thetat(n) is the angle of refraction, calculated from Snell's law:
wherein: epsilon'sIs the real part of the complex relative dielectric constant of the soil.
Further, Γ (n) in step 6 is the soil reflection coefficient, calculated by the following formula:
wherein: gamma-shaped⊥And gamma||The reflection coefficients for vertical and parallel polarizations, respectively.
Γ⊥And gamma||The reflection coefficients of the vertical polarization and the parallel polarization, respectively, are calculated by the following formula
Wherein: zs，ZaThe impedance of the soil and the air wave, respectively, is represented by the following formula:
wherein: epsilon0，μ0Air dielectric constant and magnetic permeability; epsilon's，ε′sThe real part and the imaginary part of the complex relative dielectric constant of the soil are respectively;
further, the microwave band soil dielectric model in step 7 is used for describing the relationship between the real part and the imaginary part of the complex relative dielectric constant of the soil and the soil humidity, and comprises the following steps: dielectric hybrid models, semi-empirical models, and empirical models.
Further, the microwave band soil dielectric model is described by the following formula:
wherein: s is the weight percentage of sand in the soil, C is the weight percentage of clay in the soil, and the clay is regarded as a known amount; m isVIs volume soil humidity in cm3/cm3。
Compared with the prior art, the invention has the following beneficial effects:
according to the contact type soil humidity measuring method based on the navigation satellite signals, a GNSS receiving antenna is buried in soil, and soil humidity measurement is carried out by utilizing refraction of the GNSS satellite signals on a soil-air interface and attenuation of the GNSS satellite signals in the soil. The method not only utilizes the refraction information of the navigation signal on the soil-air interface when measuring the soil humidity, but also utilizes the information attenuated by the soil when the navigation signal is transmitted in the soil, thereby having the characteristics of a remote sensing means and a contact type measuring means, further enriching the existing soil humidity measuring means, and simultaneously providing a reliable ground verification means for satellite soil humidity remote sensing. The problems in the prior art are solved.
Drawings
FIG. 1 is a diagram illustrating an application scenario of a contact soil moisture measurement method based on a navigation satellite signal according to an embodiment of the present invention;
FIG. 2 is a graph comparing signal strengths of two antennas according to an embodiment of the present invention;
FIG. 3 is a flow chart of soil moisture inversion in an embodiment of the present invention;
FIG. 4 is a graph of soil moisture inversion results in an embodiment of the present invention.
Detailed Description
The invention is further illustrated by the following figures and examples:
example 1:
the typical application scenario of the contact type soil humidity measuring method based on the navigation satellite signal is shown in fig. 1:
two general GNSS antennas a in fig. 11、A2The device is horizontally placed on the soil surface and about 10cm below the soil (the actual depth is denoted by d), and is connected with a signal receiving and processing unit through a feeder line, the signal processing unit can be two identical GNSS receivers made by the prior art or a dual-channel GNSS receiver, the signal processing unit is mainly used for measuring and recording the power or signal-to-noise ratio of signals received by two antennas, and meanwhile, the ephemeris data of the navigation satellite is demodulated from the navigation signals so as to calculate the elevation angle and the azimuth angle of the satellite. Antenna A1Receiving a direct navigation signal with signal power S1The grazing angle is θ, which is equal to the satellite elevation angle. Antenna A2The received signal is attenuated twice and the final power is set to S2: the first attenuation is caused by the fact that the direct signal is reflected when reaching the air-soil interface, a part of energy is returned to the air after reflection, and the rest energy is refracted at an angle thetatInto the soil, according to Snell's law, the power decay of the refracted signal at this time relative to the power of the incident signal can be described by the refractive index, which is related to the angle of refraction θtAll are real part epsilon of complex phase relative permittivity of soil'sAnd (6) determining. According to the law of conservation of energy, the sum of the refractive index and the reflection coefficient is 1, so that the refractive index can be calculated from the reflection coefficient:
T＝1-Γ (13)
wherein Γ reflection coefficient, Γ, may be calculated by:
wherein gamma is⊥And gamma||The vertical polarization reflection coefficient and the parallel polarization reflection coefficient are respectively calculated by the following formula:
wherein Zs，ZaThe impedance of the soil and the air wave, respectively, is represented by the following formula:
wherein: epsilon0，μ0Air dielectric constant and magnetic permeability; epsilon's，ε′sThe real part and the imaginary part of the complex relative dielectric constant of the soil are respectively;
θtthe angle of refraction can be expressed by the following formula:
the second attenuation is the attenuation of the refracted signal as it propagates through the soil, affected by soil moisture (primarily conductivity), and can be expressed as an attenuation coefficient:
where f is the navigation signal carrier frequency.
Final antenna A2Received signal power S2Can be described by the following formula:
wherein d issFor the propagation path length of the refracted signal in the soil, it can be described by the following equation according to the geometrical relationship:
fig. 2 is a signal strength comparison graph of two antennas, which is an example of actual soil moisture attenuation, and it can be seen that the antenna under the soil has a weak signal strength.
Humidity m of soilVBy influencing the real and imaginary parts of the complex relative permittivity of the soil, i.e. epsilon'sAnd epsilon's', which in turn affects the antenna A by the physical process described above2Received signal strength, mVThe relationship with the complex relative permittivity of the soil can be described by a microwave band soil permittivity model, and various mature models can be used, including theoretical models such as a dielectric mixture model, semi-empirical models such as Wang model and Dobson model, empirical models such as Topp model and Hallikainen model, wherein the Hallikainen model can be described by the following formula, which is simple and convenient to apply:
wherein S is the weight percentage of sand in the soil, C is the weight percentage of clay in the soil, and the weight percentage can be measured by the prior art and is regarded as a known quantity; m isVIs volume soil humidity in cm3/cm3。
Example 2:
on the basis of embodiment 1, the contact type soil humidity measuring method based on the navigation satellite signal comprises the following steps:
step 1: antenna mounting
Horizontally fixing one of two GNSS antennas with the same model on the soil surface, and recording as A1The other one is horizontally buried about 10cm below the soil surface (actual depth is denoted as d) and is denoted as A2The horizontal distance between the two antennas is slightly larger than 1 meter, and the feeder lines of the two antennas are led out;
step 2: signal reception processing
The feeder lines of the two antennas are respectively connected with two GNSS receivers with the same model manufactured by the prior art or two antenna interfaces of a dual-channel GNSS receiver, and the power or the signal-to-noise ratio (respectively recorded as S) of signals received by the two antennas is measured and recorded at synchronous and fixed sampling time intervals1(n) and S2(n)) and satellite ephemeris data, where n is a sample time;
and step 3: satellite elevation and azimuth calculation
By an antenna A1Calculates the satellite relative to the antenna A by combining the satellite ephemeris data and the sampling time n1Elevation angle θ (n) and azimuth angle;
and 4, step 4: data screening
And selecting the data of the satellite consistent with the position of the measurement area according to the azimuth angle of the satellite.
And 5: calculating the signal power ratio
Calculating antenna A at each sampling instant2And an antenna A1The power ratio of (a) and (b), denoted as k (n), can be expressed by the following formula:
step 6: calculating attenuation coefficient
Calculating an attenuation coefficient α (n) according to the signal power ratio calculated in the step 5:
wherein: dsThe propagation path length of the navigation signal in the soil can be calculated by the following formula:
wherein theta ist(n) is the angle of refraction, which can be calculated from Snell's law:
wherein epsilon'sIs the real part of the complex relative dielectric constant of the soil.
In equation (26), Γ (n) is the soil reflection coefficient, which can be calculated by the following equation:
wherein gamma is⊥And gamma||The reflection coefficients of the vertical polarization and the parallel polarization, respectively, can be calculated by the following formula
Wherein Zs，ZaThe impedance of the soil and the air wave, respectively, can be expressed by the following formula:
wherein epsilon0，μ0Is the dielectric constant and permeability of air；ε′s，ε′sThe real part and the imaginary part of the complex relative dielectric constant of the soil are respectively;
and 7: soil moisture inversion
And calculating the soil humidity according to the soil attenuation coefficient model and the microwave band soil dielectric model. The soil attenuation coefficient model is described by the following equation:
where f is the navigation signal carrier frequency.
The microwave band soil dielectric model describes the relationship between the real part and imaginary part of the complex relative dielectric constant of soil and the soil humidity, and various mature models can be used, including theoretical models such as dielectric hybrid model, semi-empirical models such as Wang model and Dobson model, empirical models such as Topp model and Hallikainen model, wherein the Hallikainen model is described by the following formula simply and conveniently applied:
wherein S is the weight percentage of sand in the soil, C is the weight percentage of clay in the soil, and the weight percentage can be measured by the prior art and is regarded as a known quantity; m isVIs volume soil humidity in cm3/cm3。
Finally, combining the formula (2) and the formula (3), solving the soil humidity by using the technology of iteratively solving the equation, namely m in the formulaVVolumetric soil moisture.
As shown in fig. 4, in the soil humidity inversion result in the embodiment of the present invention, in the graph, the inverted soil humidity represents a soil humidity value inverted by the method of the present invention, and the actually measured soil humidity represents an actually measured soil humidity value, as can be seen from the graph, the correlation coefficient (R) between the inversion result and the actually measured soil humidity is as high as 0.94, and the inverted Root Mean Square Error (RMSE) is less than 0.05, which proves the feasibility of the method of the present invention, the method of the present invention not only utilizes the refraction information of the navigation signal at the soil-air interface when measuring the soil humidity, but also utilizes the information attenuated by the soil when the navigation signal propagates in the soil, therefore, the method has the characteristics of a remote sensing means and a contact type measuring means, further enriches the existing soil humidity measuring means, and provides a reliable ground verification means for satellite soil humidity remote sensing.
By adopting the contact type soil humidity measuring method based on the navigation satellite signal of the embodiment of the invention described in the attached drawings, the receiving antenna is buried in the soil, and the soil humidity measurement is carried out by utilizing the refraction of the satellite signal at the soil-air interface and the attenuation of the satellite signal in the soil. The problems in the prior art are solved. The present invention is not limited to the embodiments described, but rather, variations, modifications, substitutions and alterations are possible without departing from the spirit and scope of the present invention.
Claims (7)
1. A contact type soil humidity measuring method based on navigation satellite signals is characterized in that: the method comprises the following steps:
step 1: the antenna is installed on the base plate,
horizontally fixing two antennas with the same type on the soil surface, and marking as A1The other is horizontally buried under the soil surface, the actual depth is recorded as d, and the antenna is recorded as A2Leading out the feeder lines of the two antennas;
step 2: the signal is received and processed, and then the signal is processed,
connecting the feeder lines of the two antennas with a receiver respectively, and measuring and recording the power or signal-to-noise ratio of signals received by the two antennas and satellite ephemeris data at synchronous and fixed sampling time intervals;
and step 3: the satellite elevation and azimuth calculations are performed,
by an antenna A1The precise position of the satellite is taken as a reference, and satellite ephemeris data and sampling time n are combined to calculate the satellite relative to the antenna A1Elevation angle θ (n) and azimuth angle;
and 4, step 4: the data is screened out, and the data is filtered out,
selecting data of the satellite consistent with the azimuth of the measurement area according to the azimuth of the satellite;
and 5: the ratio of the signal powers is calculated,
calculating antenna A at each sampling instant2And an antenna A1The power ratio of (a) is denoted as K (n) and is expressed by the following formula:
step 6: the attenuation coefficient is calculated and the calculated value,
calculating an attenuation coefficient α (n) according to the signal power ratio calculated in the step 5:
wherein: dsIn order to obtain the propagation path length of the navigation signal in the soil, gamma (n) is a soil reflection coefficient, and n is sampling time;
and 7: the inversion of the soil moisture is carried out,
calculating the soil humidity according to the soil attenuation coefficient model and the microwave band soil dielectric model, wherein the soil attenuation coefficient model is described by the following formula:
wherein: f is the navigation signal carrier frequency, ε0，μ0Is air dielectric constant and magnetic permeability, epsilon's，ε″sRespectively a real part and an imaginary part of the complex relative dielectric constant of the soil; and finally, combining the formula (2) and the formula (3), and solving the soil humidity by using the technology of iterative equation solving.
2. The method according to claim 1, wherein the receiver in step 2 is a GNSS satellite signal receiver, and the connection between the feeder lines of the two antennas and the GNSS satellite signal receiver comprises: the feeder lines of the two antennas are respectively connected with the two GNSS satellite signal receivers or connected with two antenna interfaces of a double-channel GNSS satellite signal receiver.
3. The method of claim 1, wherein d in step 6 is a contact-type soil moisture measurement method based on the navigation satellite signalsThe length of the propagation path of the navigation signal in the soil is calculated by the following formula:
wherein: thetat(n) is the angle of refraction, calculated from Snell's law:
wherein: epsilon'sIs the real part of the complex relative dielectric constant of the soil.
4. The method of claim 1, wherein Γ (n) in step 6 is a soil reflection coefficient, and is calculated by the following equation:
wherein: gamma-shaped⊥And gamma||The reflection coefficients for vertical and parallel polarizations, respectively.
5. The method as claimed in claim 4, wherein Γ is the same as the original value of the soil moisture content measured by the contact type soil moisture content measuring method based on the navigation satellite signal⊥And gamma||The reflection coefficients of the vertical polarization and the parallel polarization, respectively, are calculated by the following formula
Wherein: zs，ZaThe impedance of the soil and the air wave, respectively, is represented by the following formula:
wherein: epsilon0，μ0Air dielectric constant and magnetic permeability; epsilon's，ε″sRespectively the real part and the imaginary part of the complex relative dielectric constant of the soil.
6. The method for contact-type soil moisture measurement based on navigational satellite signals as claimed in claim 1, wherein the microwave band soil dielectric model in step 7 is used for describing the relationship between the real part and the imaginary part of the complex relative dielectric constant of the soil and the soil moisture, and comprises: dielectric hybrid models, semi-empirical models, and empirical models.
7. The method for contact-type soil moisture measurement based on the navigation satellite signal as claimed in claim 1 or 6, wherein the microwave band soil dielectric model is described by the following formula:
wherein: s is the weight percentage of sand in the soil, C is the weight percentage of clay in the soil, and the clay is regarded as a known amount; m isVIs volume soil humidity in cm3/cm3。
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| CN115616006A (en) * | 2022-04-25 | 2023-01-17 | 山东大学 | Method for inverting soil humidity by utilizing QZSS system satellite L5 reflection signal |
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