CN115616006A - Method for inverting soil humidity by utilizing QZSS system satellite L5 reflection signal - Google Patents
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Abstract
The invention discloses a method for inverting soil humidity by utilizing L5 reflection signals of a QZSS system satellite in the field of soil humidity detection, which comprises the following steps: s101, receiving direct intermediate frequency signals of the QZSS satellite by using an upward right-handed circularly polarized antenna, and receiving ground reflected intermediate frequency signals of the QZSS satellite by using a downward left-handed circularly polarized antenna; s102, inputting the two signals into a software receiver for processing, outputting power ratio observation data of the reflected signal and the direct signal, and then calculating soil humidity through a formula to obtain a final soil humidity inversion result. The GNSS reflected signal technology can utilize the GNSS signals provided at present for free to carry out land remote sensing, has the advantages of low cost, extremely abundant signal sources, capability of realizing high space-time resolution observation and the like, and compared with the traditional microwave remote sensing, the GNSS L-band signals can penetrate through cloud layers, thereby realizing all-weather and all-time observation and having better development prospect in the field of microwave remote sensing.
Description
Technical Field
The invention relates to the field of soil humidity detection, in particular to a method for inverting soil humidity by utilizing a QZSS system satellite L5 reflection signal.
Background
The soil humidity, also called soil moisture content, is a reference quantity for characterizing the water-containing condition of soil, is a key physical quantity for connecting land-gas interaction, is a key parameter for researching land water resources, surface land-gas energy and water exchange, and plays a very important role in the aspects of climatic environment (such as global climate change), human productive life (such as agricultural environment drought monitoring and weather forecast) and the like.
The means of measuring the soil humidity can be divided into in-situ observation and remote sensing. Typical in situ observations include both direct and indirect measurements. The direct measurement method is also called a drying and weighing method, the measurement result is accurate, but the physical structure of the soil can be damaged due to the fact that soil needs to be collected in situ, single-point soil collection cannot replace the whole measurement area, the sampling process is complex, time consumption is long, and the method has certain limitations. Indirect measurement methods include the ray method and the time domain/frequency domain reflection method, wherein various ray methods also have certain limitations, such as low spatial resolution of neutron scattering method, dangerous operation of radiation method, expensive instruments of pulse nuclear magnetic resonance method, and the like. The time domain/frequency domain reflection method is rapid and accurate in measurement and high in automation degree, but belongs to point location measurement, and large-range measurement cannot be achieved. The microwave remote sensing technology can realize large-range and long-term continuous non-contact soil humidity detection, but the prior passive microwave remote sensing technology utilizes the self thermal radiation of ground objects, the active microwave remote sensing technology mostly adopts X-waveband signals, and the weather such as cloud, rain and the like can shield the signals to cause the technology to be unavailable. Active microwave remote sensing requires the fabrication of transmitting and monitoring equipment, is costly, and has limited temporal and spatial resolution.
Accordingly, those skilled in the art have provided a method for inverting soil moisture using a QZSS system satellite L5 reflection signal to solve the above-mentioned problems occurring in the background art.
Disclosure of Invention
The invention aims to provide a method for inverting soil humidity by utilizing a QZSS system satellite L5 reflection signal, so as to solve the problems in the background technology.
In order to achieve the purpose, the invention provides the following technical scheme:
the method for inverting the soil humidity by utilizing the L5 reflection signal of the QZSS system satellite comprises the following steps:
s101, receiving direct intermediate frequency signals of the QZSS satellite by using an upward right-handed circularly polarized antenna, and receiving ground reflected intermediate frequency signals of the QZSS satellite by using a downward left-handed circularly polarized antenna;
s102, inputting the two signals into a software receiver for processing, outputting power ratio observation data of a reflected signal and a direct signal, and then calculating soil humidity through a formula to obtain a final soil humidity inversion result.
As a further scheme of the invention: in a software receiver, to realize tracking and processing of a direct signal and a reflected signal respectively, coherent integration of 1ms is performed on the received signal and a local replica signal respectively, and then noncoherent accumulation of 200ms is performed to obtain an effective delay-doppler correlation integration result, so that the power of the direct signal and the reflected signal is determined.
As a further scheme of the invention: the relative powers of the direct and reflected signals obtained in the software receiver can be represented by the following equations, respectively:
in the formula: t is i Denotes the integration time, A d (. Cndot.) is the signal amplitude, D (-) is the signal data bit, Y d,q And Y r,q The amplitudes of the direct and reflected signals, respectively.
As a further scheme of the invention: the surface reflectivity is the power ratio of the reflected signal to the direct signal, and the power ratio of the reflected signal to the direct signal can be expressed as:
in the formula: and <. Represents the averaging operation, and R is the surface reflectivity.
As a further scheme of the invention: during reception of the signal, adoptThe left-hand circularly polarized antenna is used for receiving reflected signals, the right-hand circularly polarized antenna is used for receiving direct signals, and the surface reflectivity can be expressed as Fresnel cross polarization reflection coefficient gamma rl Function of (c):
wherein epsilon is the soil dielectric constant, theta is the satellite height angle, and can be calculated by satellite orbit data and the receiver position.
As a further scheme of the invention: the dielectric constant epsilon of the soil can be reversely deduced through the power ratio data obtained by the receiver;
ε＝3.1+17.36m v +63.12m v 2 +j(0.031+4.65m v +20.42m v 2 )
wherein epsilon is the dielectric constant of the soil, and the water content m of the soil can be calculated by the above formula v 。
Compared with the prior art, the invention has the beneficial effects that:
the GNSS reflected signal technology can utilize the GNSS signals provided at present for free to carry out land remote sensing, has the advantages of low cost, extremely abundant signal sources, capability of realizing high-space-time resolution observation and the like, and compared with the traditional microwave remote sensing, the GNSS L-band signals can penetrate through a cloud layer, thereby realizing all-weather and all-day observation, and having better development prospect in the field of microwave remote sensing.
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FIG. 1 is a diagram of the locus of points under the QZSS 4 satellites relative to the position of a survey station on the summer day of the experiment of the invention;
FIG. 2 is a schematic diagram of the apparatus setup and signal reception during the experiment of the present invention;
FIG. 3 is a satellite diagram of the experimental field of the present invention;
FIG. 4 is a graph comparing the soil moisture meter results with the GNSS-R soil moisture inversion results for two days of the experiment.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1 to 4, in the embodiment of the present invention, in order to implement tracking and processing of a direct signal and a reflected signal in a software receiver, respectively, a method for inverting soil humidity by using a QZSS system satellite L5 reflected signal performs coherent integration on a received signal and a local replica signal for 1ms, and then performs incoherent accumulation for 200ms to obtain an effective delay-doppler coherent integration result, thereby determining powers of the direct signal and the reflected signal.
In this embodiment, the powers related to the direct signal and the reflected signal obtained in the software receiver can be respectively expressed by the following formulas:
in the formula: t is i Denotes the integration time, A d (. Cndot.) is the signal amplitude, D (-) is the signal data bit, Y d,q And Y r,q The amplitudes of the direct and reflected signals, respectively.
In this embodiment, the surface reflectivity is a power ratio of the surface reflection signal to the direct signal, and the power ratio of the reflection signal to the direct signal can be expressed as:
in the formula: and < > represents the averaging operation, and R is the surface reflectivity.
This implementationIn the example, in the process of receiving signals, a left-hand circularly polarized antenna is adopted to receive reflected signals, a right-hand circularly polarized antenna is adopted to receive direct signals, and the surface reflectivity can be expressed as a Fresnel cross polarization reflection coefficient gamma rl Function of (c):
wherein epsilon is the soil dielectric constant, theta is the satellite height angle, and can be calculated by satellite orbit data and the receiver position.
In the embodiment, the dielectric constant epsilon of the soil can be reversely deduced through the power ratio data obtained by the receiver;
ε＝3.1+17.36m v +63.12m v 2 +j(0.031+4.65m v +20.42m v 2 )
wherein epsilon is the dielectric constant of the soil, and the water content m of the soil can be calculated by the above formula v 。
In this example, to further verify the performance of the QZSS system L5 signal in soil moisture inversion, we performed nearly one day experiments in taian city, shandong province (35.58 ° N,117.15 ° E) in summer and winter, respectively, with the experimental dates 2021, 6-27 pm, 16 pm, 26, 00, and 2021, 11, 16, 18, 00 to 11, 17, 13, 00. GNSS intermediate frequency data with the sampling rate of 62MHz, the center frequency of 1176.45MHz and the bandwidth of 20.46MHz are obtained, then data processing is carried out through a software receiver which is spontaneously developed by people, power ratio data of a reflected signal and a direct signal are finally obtained through 1ms coherent integration and 200ms incoherent accumulation, then a soil humidity inversion result can be obtained through the inversion theory, meanwhile, soil humidity in-situ data with the precision of +/-3% is obtained locally through a soil humidity probe, the soil humidity in-situ data can be compared with the inversion result of GNSS-R, and the inversion result of the text is verified.
As can be seen from fig. 1, 4 satellites are in the southeast direction of the survey station, the altitude angle of the J07 satellite is about 47 °, and the satellite is a GEO satellite, thus providing long-term stable altitude angle observation.
As can be seen from fig. 2, in which the direct and reflected antennas are respectively positioned upward and downward, the direct and reflected signals from the satellite are respectively received, and the two antennas and the stand assume an equilateral triangle, so that the influence of the gains of the direct and reflected antennas on the received signals can be attenuated.
As can be seen from fig. 3, the experimental field is located in the southeast direction of the erected instrument, which is the same as the direction in which the QZSS satellite is located, and the QZSS signal can be maximally received.
In fig. 4, the upper graph is the inversion result of a day in summer, and the lower graph is the inversion result in winter, and compared with the data of the soil hygrometer, it is found that the GNSS-R inversion result and the data of the soil hygrometer have constant deviations in summer and winter, which are caused by the spatial difference of the soil humidity, the gain difference of the two antennas, the roughness of the ground, and the crosstalk between the direct and reflected signals. The standard deviation of soil moisture for GEO satellite inversion was 0.013m compared to the hygrometer data 3 /m 3 (summer) 0.007m 3 /m 3 (in winter), the standard deviation of the soil humidity of the IGSO satellite inversion is 0.033-0.071m 3 /m 3 . The inversion precision is high, and the correctness of the method is verified.
In this embodiment, the QZSS system is a local satellite system in japan, and a regional satellite augmentation system currently composed of 1 GEO satellite and 3 IGSO satellites has a special orbit, so that it is ensured that 4 satellites are visible in 24 hours per day in the asia-pacific region, and at least 1 satellite is always located above the east asia region at a higher elevation angle, and all weather services are provided for the region, which provides more possibilities for soil moisture inversion by using GNSS-R, and therefore, the method is characterized in that the QZSS satellite reflected signals are used for soil moisture inversion, the QZSS satellite broadcasts signals of 3 frequencies, L1, L2, and L5, and compared with the frequencies of L1 and L2, the carrier frequency of L5 is 1176.45MHz, the wavelength is longer, the diffraction capability is better, the free space attenuation is smaller, the power is higher when the signals reach the ground, and the pseudo random code rates of L5 are all 10.23Mcps, and compared with C/a code, the code rate is increased by 10 times, and the multipath resistance is increased. The L5 pilot signal has no 180-degree ambiguity, so that the carrier recovery capability is strong, and the instantaneous carrier ambiguity solution can be realized, therefore, the invention aims to realize soil humidity inversion by utilizing the L5 reflection signal of the QZSS system satellite, and in 2023 years, the QZSS satellite can realize a navigation system consisting of 7 satellites, and the addition of the QZSS satellite can provide more signals and higher spatial resolution observation for soil humidity inversion by utilizing the GNSS reflection signal.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (6)
1. The method for inverting the soil humidity by using the L5 reflection signal of the QZSS system satellite is characterized by comprising the following steps: the method comprises the following steps:
s101, receiving direct intermediate frequency signals of the QZSS satellite by using an upward right-handed circularly polarized antenna, and receiving ground reflected intermediate frequency signals of the QZSS satellite by using a downward left-handed circularly polarized antenna;
s102, inputting the two signals into a software receiver for processing, outputting power ratio observation data of a reflected signal and a direct signal, and then calculating soil humidity through a formula to obtain a final soil humidity inversion result.
2. The method for inversion of soil moisture using QZSS system satellite L5 reflection signals as claimed in claim 1, wherein: in a software receiver, to realize tracking and processing of a direct signal and a reflected signal respectively, coherent integration of 1ms is performed on the received signal and a local replica signal respectively, and then noncoherent accumulation of 200ms is performed to obtain an effective delay-doppler correlation integration result, so that the power of the direct signal and the reflected signal is determined.
3. The method for inversion of soil moisture using QZSS system satellite L5 reflection signals as claimed in claim 2, wherein: the relative powers of the direct and reflected signals obtained in the software receiver can be represented by the following equations, respectively:
in the formula: t is i Denotes the integration time, A d (. Cndot.) is the signal amplitude, D (-) is the signal data bit, Y d,q And Y r,q The amplitudes of the direct and reflected signals, respectively.
4. The method for soil moisture inversion using QZSS system satellite L5 reflection signal as claimed in claim 3, wherein: the surface reflectivity is the power ratio of the reflected signal to the direct signal, and the power ratio of the reflected signal to the direct signal can be expressed as:
in the formula: and < > represents the averaging operation, and R is the surface reflectivity.
5. The method for soil moisture inversion using QZSS system satellite L5 reflection signal as claimed in claim 4, wherein: in the process of receiving signals, a left-hand circularly polarized antenna is adopted to receive reflected signals, and a right-hand circularly polarized antenna is adopted to receive direct radiationThe signal, surface reflectivity, in turn, can be expressed as the Fresnel cross-polarization reflection coefficient Γ rl Function of (c):
wherein epsilon is the soil dielectric constant, theta is the satellite height angle, and can be calculated by satellite orbit data and the receiver position.
6. The method for soil moisture inversion using QZSS system satellite L5 reflection signal as claimed in claim 5, wherein: the dielectric constant epsilon of the soil can be reversely deduced through the power ratio data obtained by the receiver;
ε＝3.1+17.36m v +63.12m v 2 +j(0.031+4.65m v +20.42m v 2 )
wherein epsilon is the dielectric constant of the soil, and the water content m of the soil can be calculated by the formula v 。
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