阅读说明：本技术 一种适用于小雨量级的gnss极化信号正演方法及系统 (GNSS polarized signal forward modeling method and system suitable for small rainfall magnitude ) 是由 白伟华 孙越强 苏豆豆 杜起飞 刘黎军 李伟 王先毅 蔡跃荣 曹光伟 夏俊明 孟 于 2021-07-06 设计创作，主要内容包括：本发明公开了一种适用于小雨量级的GNSS极化信号正演方法及系统,所述小雨的降雨率小于等于2.5毫米/小时,所述方法包括：获取待测小雨雨区内的降雨信息；所述小雨雨区有GNSS极化无线电掩星事件发生,并且掩星的射线路径穿过雨区；分别建立雨滴形状模型和雨滴谱分布模型；计算雨滴的相对复介电常数；结合雨滴形状模型计算单一雨滴水平极化前向散射幅度和垂直极化前向散射幅度；根据雨滴谱分布模型和单一雨滴水平极化前向散射幅度及垂直极化前向散射幅度,计算差分相位延迟；根据差分相位延迟对整个雨区内射线总路径长度进行积分,得到正演后的极化相移。(The invention discloses a GNSS polarized signal forward modeling method and system suitable for light rain magnitude, wherein the rainfall rate of the light rain is less than or equal to 2.5 mm/h, and the method comprises the following steps: acquiring rainfall information in a small rain area to be detected; the small rain area has a GNSS polarized radio occultation event, and a ray path of occultation passes through the rain area; respectively establishing a raindrop shape model and a raindrop spectrum distribution model; calculating the relative complex dielectric constant of the raindrops; calculating the horizontal polarization forward scattering amplitude and the vertical polarization forward scattering amplitude of the single raindrop by combining the raindrop shape model; calculating differential phase delay according to a raindrop spectrum distribution model and the single raindrop horizontal polarization forward scattering amplitude and the single raindrop vertical polarization forward scattering amplitude; and integrating the total path length of rays in the whole rain area according to the differential phase delay to obtain the forward polarization phase shift.)

1. A GNSS polarized signal forward modeling method suitable for small rain magnitude, wherein the rainfall rate of the small rain is less than or equal to 2.5 mm/h, the method comprises the following steps:

acquiring rainfall information in a small rain area to be detected; the small rain area has a GNSS polarized radio occultation event, and a ray path of occultation passes through the rain area;

respectively establishing a raindrop shape model and a raindrop spectrum distribution model according to rainfall information;

calculating the relative complex dielectric constant of raindrops according to rainfall information;

calculating the horizontal polarization forward scattering amplitude and the vertical polarization forward scattering amplitude of the single raindrop by combining the raindrop shape model;

calculating differential phase delay according to a raindrop spectrum distribution model and the single raindrop horizontal polarization forward scattering amplitude and the single raindrop vertical polarization forward scattering amplitude;

and integrating the total path length of rays in the whole rain area according to the differential phase delay to obtain the forward polarization phase shift.

2. The GNSS polarized signal forward modeling method applicable to small rainfall magnitude according to claim 1, wherein the rainfall information in the small rainfall area to be tested comprises: rain range, rain rate information along the ray path, frequency, equivalent volume diameter, total path length, air temperature, and raindrop inclination angle.

3. The GNSS polarized signal forward modeling method applicable to small rainfall magnitude according to claim 1, wherein the raindrop shape model is SC raindrop shape model; the method specifically comprises the following steps:

the raindrop is shaped as an oblate ellipsoid with axial ratioAnd the equivalent volume diameter D satisfies the following formula:

wherein b is the short radius, a is the long radius, and D is the diameter of the same volume.

4. The GNSS polarized signal forward modeling method suitable for small rainfall magnitude according to claim 1, wherein the raindrop spectrum distribution model adopts an MP distribution raindrop spectrum distribution model or a JD raindrop spectrum distribution model; when the MP distribution raindrop spectrum distribution model is adopted, the raindrop spectrum distribution n (d) satisfies the following formula:

N(D)＝N₀e^-AD N₀＝8000，Λ＝4.1R^-0.21

when the JD raindrop spectrum distribution model is used, the raindrop spectrum distribution n (d) satisfies the following equation:

N(D)＝N₀e^-AD N₀＝30000，Λ＝5.7R^-0.21；

wherein N is₀Is a constant, Λ is a parameter related to rainfall rate, R is rainfall rate in mm/h, and D is the equivalent volume diameter of raindrops in the rain zone.

5. The GNSS polarized signal forward modeling method applicable to small rainfall magnitude according to claim 1, wherein the computation of the relative complex dielectric constant ε of the raindrops satisfies the following equation:

ε＝(ε₀-ε₁)/[1-i(f/f₁)]+(ε₁-ε₂)/[1-i(f/f₂)]+ε₂

wherein the real part ε 'of ε, the imaginary part ε' satisfies the following equation:

wherein the content of the first and second substances,

ε₀＝77.66-103.3·T₁

ε₁＝0.0671·ε₀

ε₂＝3.52

f₁＝20.20+146.4·T₁+316·T₁ ²

f₂＝39.8·f₁

T₁＝1-300/T

wherein f is frequency, f₁To relaxation frequency, f₂Is a coefficient related to the relaxation frequency, ε₀Is the static dielectric constant,. epsilon₁Is a coefficient related to the static dielectric constant, ε₂Is constant, T is the atmospheric temperature, T₁Is a coefficient related to the atmospheric temperature.

6. The GNSS polarized signal forward modeling method suitable for small rainfall levels according to claim 1, wherein the differential phase delay is calculated according to a raindrop spectrum distribution model and a single raindrop horizontal polarization forward scattering amplitude and a single raindrop vertical polarization forward scattering amplitude; the method specifically comprises the following steps:

according to the selected raindrop spectrum distribution model and the calculated horizontal polarization forward scattering amplitude f_h(D) And the amplitude f of the vertically polarized forward scattering_v(D) Calculating the differential phase delay K using the following equation_dpComprises the following steps:

wherein the content of the first and second substances,is expressed by taking f_h(D)-f_v(D) The real number part of (1), N (D) is raindrop spectrum distribution, lambda is the wave band wavelength of a GNSS polarization signal, sigma is the standard deviation of the distribution of the inclination angle, D is the equal volume diameter of raindrops in a rain zone, and theta is the inclination angle of the raindrops.

7. The GNSS polarized signal forward modeling method applicable to small rainfall magnitude according to claim 1, characterized in that the forward modeling polarization phase shift is obtained by integrating the total path length of rays in the whole rain zone according to the differential phase delay; the method specifically comprises the following steps:

integrating the differential phase delay of each point along the RO ray path in the rain zone on the total length L of the ray path in the whole rain zone to obtain the forward polarization phase shift delta phi as follows:

ΔΦ＝∫_LK_dp(l)dl

wherein, K_dp(l) The unit of Δ Φ is mm for the differential phase delay of a single point l.

8. A GNSS polarized signal forward-acting system suitable for small rainfall levels, the rainfall rate of which is less than or equal to 2.5 mm/h, the system comprising: the device comprises a data acquisition module, a model establishing module, a relative complex dielectric constant calculation module, a forward scattering amplitude calculation module, a differential phase delay calculation module and a polarization phase shift calculation module; wherein the content of the first and second substances,

the data acquisition module is used for acquiring rainfall information in a to-be-detected light rain area; the small rain area has a GNSS polarized radio occultation event, and a ray path of occultation passes through the rain area;

the model establishing module is used for respectively establishing a raindrop shape model and a raindrop spectrum distribution model according to rainfall information;

the relative complex dielectric constant calculation module is used for calculating the relative complex dielectric constant of raindrops according to rainfall information;

the forward scattering amplitude calculation module is used for calculating the horizontal polarization forward scattering amplitude and the vertical polarization forward scattering amplitude of the single raindrop by combining the raindrop shape model;

the differential phase delay calculation module is used for calculating differential phase delay according to the raindrop spectrum distribution model and the single raindrop horizontal polarization forward scattering amplitude and the single raindrop vertical polarization forward scattering amplitude;

and the polarization phase shift calculation module is used for integrating the total path length of rays in the whole rain zone according to the differential phase delay to obtain the forward polarization phase shift.

Technical Field

The invention relates to the field of rainfall remote sensing detection research, in particular to a forward modeling method and a system of a GNSS polarized signal suitable for a small rainfall-magnitude rainfall event.

Background

Rainfall is one of basic variables for researching climate change, and plays an important role in agricultural production, ecological environment and daily life of people. At present, the rainfall is detected internationally in various ways, and a sky-based rainfall radar system comprises a tropical rainfall measurement task TRMM with a rainfall radar, a global rainfall measurement task GPM with a dual-frequency rainfall radar, a hyperspectral infrared detector, a microwave detector, a foundation rainfall radar and the like. However, these methods cannot directly or indirectly extract factors affecting water vapor or precipitation from the observed values, and are not suitable for observing the internal structure of strong precipitation clouds. The Radio Occultation (RO) technology of a Global Navigation Satellite System (GNSS) obtains atmospheric physical parameter profiles such as refractive index, temperature, density and the like by inversion according to additional time delay and bending information during radio link propagation, and is an important means for planetary ionosphere and atmosphere detection. Compared with a sonde or a meteorological satellite, the technology has the advantages of all weather, high precision, high vertical resolution, low system error and the like, and research shows that the GNSS RO technology can jointly detect and quantify the atmospheric thermodynamic profile and rainfall information in a heavy rainfall event by utilizing the potential capability of a Polar Radio Occultation (PRO).

In order to effectively utilize GNSS RO which is a rich and reliable data source and improve the accuracy of rainfall event forecasting, polarization differential phase delay is caused by large-size non-spherical water condensate based on the fact that signals pass through the non-spherical water condensate, the meteorological service is not developed in China at present, the theory and method for GNSS polarized radio occultation detection and rainfall quantification are explored, and the theory and method for the GNSS polarized radio occultation detection and rainfall inversion are not developed and matured.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a GNSS polarized signal forward modeling method and system suitable for small rainfall magnitude.

In order to achieve the above object, the present invention provides a GNSS polarized signal forward modeling method suitable for light rain magnitude, wherein the rainfall rate of the light rain is less than or equal to 2.5 mm/h, the method comprising:

acquiring rainfall information in a small rain area to be detected; the small rain area has a GNSS polarized radio occultation event, and a ray path of occultation passes through the rain area;

respectively establishing a raindrop shape model and a raindrop spectrum distribution model according to rainfall information;

calculating the relative complex dielectric constant of raindrops according to rainfall information;

calculating the horizontal polarization forward scattering amplitude and the vertical polarization forward scattering amplitude of the single raindrop by combining the raindrop shape model;

calculating differential phase delay according to a raindrop spectrum distribution model and the single raindrop horizontal polarization forward scattering amplitude and the single raindrop vertical polarization forward scattering amplitude;

and integrating the total path length of rays in the whole rain area according to the differential phase delay to obtain the forward polarization phase shift.

As an improvement of the above method, the rainfall information in the rainstorm area to be measured includes: rain range, rain rate information along the ray path, frequency, equivalent volume diameter, total path length, air temperature, and raindrop inclination angle.

As an improvement of the above method, the raindrop shape model adopts an SC raindrop shape model; the method specifically comprises the following steps:

set the raindrop shape asOblate ellipsoid, axial ratioAnd the equivalent volume diameter D satisfies the following formula:

wherein b is the short radius, a is the long radius, and D is the diameter of the same volume.

As an improvement of the above method, the raindrop spectrum distribution model adopts an MP distribution raindrop spectrum distribution model or a JD raindrop spectrum distribution model; when the MP distribution raindrop spectrum distribution model is adopted, the raindrop spectrum distribution n (d) satisfies the following formula:

N(D)＝N₀e^-ΛD N₀＝8000,Λ＝4.1R^-0.21

when the JD raindrop spectrum distribution model is used, the raindrop spectrum distribution n (d) satisfies the following equation:

N(D)＝N₀e^-ΛD N₀＝30000,Λ＝5.7R^-0.21；

wherein N is₀Is a constant, Λ is a parameter related to rainfall rate, R is rainfall rate in mm/h, and D is the equivalent volume diameter of raindrops in the rain zone.

As an improvement of the above method, the calculating of the relative complex dielectric constant ∈ of the raindrop satisfies the following expression:

ε＝(ε₀-ε₁)/[1-i(f/f₁)]+(ε₁-ε₂)/[1-i(f/f₂)]+ε₂

wherein the real part ε 'of ε, the imaginary part ε' satisfies the following equation:

wherein the content of the first and second substances,

ε₀＝77.66-103.3·T₁

ε₁＝0.0671·ε₀

ε₂＝3.52

f₁＝20.20+146.4·T₁+316·T₁ ²

f₂＝39.8·f₁

T₁＝1-300/T

wherein f is frequency, f₁To relaxation frequency, f₂Is a coefficient related to the relaxation frequency, ε₀Is the static dielectric constant,. epsilon₁Is a coefficient related to the static dielectric constant, ε₂Is constant, T is the atmospheric temperature, T₁Is a coefficient related to the atmospheric temperature.

As an improvement of the above method, the differential phase delay is calculated according to a raindrop spectrum distribution model and a single raindrop horizontal polarization forward scattering amplitude and a single raindrop vertical polarization forward scattering amplitude; the method specifically comprises the following steps:

according to the selected raindrop spectrum distribution model and the calculated horizontal polarization forward scattering amplitude f_h(D) And the amplitude f of the vertically polarized forward scattering_v(D) Calculating the differential phase delay K using the following equation_dpComprises the following steps:

wherein the content of the first and second substances,is expressed by taking f_h(D)-f_v(D) The real number part of (1), N (D) is raindrop spectrum distribution, lambda is the wave band wavelength of a GNSS polarization signal, sigma is the standard deviation of the distribution of the inclination angle, D is the equal volume diameter of raindrops in a rain zone, and theta is the inclination angle of the raindrops.

As an improvement of the above method, the total path length of the radiation in the whole rain zone is integrated according to the differential phase delay, so as to obtain a forward polarization phase shift; the method specifically comprises the following steps:

integrating the differential phase delay of each point along the RO ray path in the rain zone on the total length L of the ray path in the whole rain zone to obtain the forward polarization phase shift delta phi as follows:

ΔΦ＝∫_LK_dp(l)dl

wherein, K_dp(l) The unit of Δ Φ is mm for the differential phase delay of a single point l.

A GNSS polarized signal forward-acting system for small rainfall levels having a rainfall rate of 2.5 mm/hour or less, the system comprising: the device comprises a data acquisition module, a model establishing module, a relative complex dielectric constant calculation module, a forward scattering amplitude calculation module, a differential phase delay calculation module and a polarization phase shift calculation module; wherein the content of the first and second substances,

the data acquisition module is used for acquiring rainfall information in a to-be-detected light rain area; the small rain area has a GNSS polarized radio occultation event, and a ray path of occultation passes through the rain area;

the model establishing module is used for respectively establishing a raindrop shape model and a raindrop spectrum distribution model according to rainfall information;

the relative complex dielectric constant calculation module is used for calculating the relative complex dielectric constant of raindrops according to rainfall information;

the forward scattering amplitude calculation module is used for calculating the horizontal polarization forward scattering amplitude and the vertical polarization forward scattering amplitude of the single raindrop by combining the raindrop shape model;

the differential phase delay calculation module is used for calculating differential phase delay according to the raindrop spectrum distribution model and the single raindrop horizontal polarization forward scattering amplitude and the single raindrop vertical polarization forward scattering amplitude;

and the polarization phase shift calculation module is used for integrating the total path length of rays in the whole rain zone according to the differential phase delay to obtain the forward polarization phase shift.

Compared with the prior art, the invention has the advantages that:

1. the method has the advantages of simplicity in operation, quickness in calculation, high accuracy, high precision and the like, and can meet the requirement of forward polarization phase shift of a small rainfall-magnitude rainfall event;

2. the rainfall particles in any shape can be calculated by adopting a T-matrix method, so that the method has higher universality;

3. the invention can conveniently calculate the forward modeling simulation of large-scale rainfall, and can meet the requirement of calculating the forward scattering characteristics of a large amount of raindrop particles with different shapes;

4. by the method, forward modeling can be performed by utilizing the existing rainfall product data set, forward modeling of the rainfall area is completed under the condition of not increasing any cost and observation, and important contribution is made to the field of rainfall weather research.

Drawings

FIG. 1 is a flowchart of a GNSS polarized signal forward modeling method applicable to small rainfall levels according to the present invention;

FIG. 2 is a diagram of information related to a light rain area prepared according to the present invention;

fig. 3 is a simulation diagram of 2018/12/19 light raining areas in an embodiment of the present invention, in which fig. 3(a) shows a distribution of rainfall rate of each raining Layer, a height of Layer2 is 4km, a height of Layer1 is 2km, Surface is a ground Surface, and fig. 3(b) shows a raining area where an RO event passes through each raining Layer;

fig. 4 is a graph of the change in the RO event ray tangent point trajectory that occurs at 2018/12/1916:54 in an embodiment of the present invention.

Detailed Description

The invention aims to provide a GNSS polarized signal forward modeling method suitable for small rainfall level, which has the advantages of simplicity, rapidness, suitability for large-scale calculation, good simulation effect, high precision, high universality and the like, and can meet the requirement of forward modeling on small rainfall level rainfall events by utilizing the GNSS polarized signal.

In order to improve the theory of GNSS polarized rainfall measurement and explore a method for quantifying rainfall by a GNSS PRO technology, the invention provides a GNSS polarized signal forward modeling method suitable for a rainfall event with small rainfall magnitude, and a model and an algorithm of the method are mainly used for the GNSS polarized signal forward modeling under the condition with small rainfall magnitude, and particularly the rainfall rate is less than or equal to 2.5 mm/h. The method is simple, rapid and high in accuracy, has high universality, is convenient for large-scale calculation, is beneficial to developing deep research on rainfall parameter mechanism quantitative detection of GNSS PRO technology and index error transfer quantitative analysis, guides subsequent load scheme design, test and research and lays a foundation for subsequent data inversion.

In order to achieve the above purpose, the present invention provides a GNSS polarized signal forward modeling method suitable for small rainfall level, which mainly includes the following 7 steps:

data preparation, raindrop shape model selection, raindrop spectrum model selection, raindrop relative complex dielectric constant calculation, forward scattering amplitude calculation, differential phase delay calculation and polarization phase shift calculation.

The data preparation refers to acquiring rainfall information in a small rain area to be researched, and the rainfall information comprises information such as rainfall rate information along a ray path, an equal volume diameter, a total path length, air temperature, a raindrop inclination angle and the like. It should be noted that the rainstorm to be studied requires a GNSS polarized radio occultation event, and the ray path of the occultation passes through the rain.

The raindrop shape model selection refers to the selection of a Steinert-Chandra (SC) raindrop shape model as a raindrop model in a small rain area. The raindrop shape is regarded as an oblate ellipsoid, the model of the raindrop shape is mainly described by the relation between the axial ratio and the equal volume diameter, and the expression is

Wherein b is the short radius, a is the long radius, and D is the diameter of the same volume.

The raindrop spectrum model selection means that a Marshall-palm (MP) distribution or Joss Drizzle (JD) raindrop spectrum distribution model is selected as the raindrop spectrum model of the rainstorm region, and the expression and empirical parameters of the raindrop spectrum model are shown in the following table:

the calculation of the relative complex dielectric constant of the raindrops refers to calculating the relative complex dielectric constant of the raindrops by approximating the raindrops to pure water. The invention adopts a Liebe1993 model formula to calculate the relative complex dielectric constant of raindrops, wherein the formula is as follows:

ε＝(ε₀-ε₁)/[1-i(f/f₁)]+(ε₁-ε₂)/[1-i(f/f₂)]+ε₂

in the formula (I), the compound is shown in the specification,

ε₀＝77.66-103.3·T₁

ε₁＝0.0671·ε₀

ε₂＝3.52

f₁＝20.20+146.4·T₁+316·T₁ ²

f₂＝39.8·f₁

T₁＝1-300/T

wherein f is frequency, f₁To relaxation frequency, f₂Is a coefficient related to the relaxation frequency, ε₀Is the static dielectric constant,. epsilon₁Is a coefficient related to the static dielectric constant, ε₂Is constant, T is the atmospheric temperature, T₁Is a coefficient related to the atmospheric temperature.

The forward scattering amplitude calculation refers to the calculation of the single raindrop horizontal polarization forward scattering amplitude f by combining a T-matrix method with the selected raindrop shape model_h(D) And the amplitude f of the vertically polarized forward scattering_v(D) In that respect The T-matrix method is fast in calculation and accurate in result, and is suitable for large-scale calculation of non-spherical raindrops in any shape. The T-matrix method is not in the scope of this patent and is not described in detail.

The differential phase delay calculation refers to the calculation of the horizontal polarization forward scattering amplitude f according to the selected raindrop spectrum distribution model and the calculated horizontal polarization forward scattering amplitude_h(D) Amplitude f of forward scattering with vertical polarization_v(D) The calculation was carried out using the following formula,

wherein the content of the first and second substances,is represented by f_h(D)-f_v(D) The real number part of (1), N (D) is raindrop spectrum distribution, lambda is the wave band wavelength of a GNSS polarization signal, D is the equal volume diameter of raindrops in a rain zone, and theta is the dip angle of the raindrops.

The calculation of the polarization phase shift mainly refers to the integral of the differential phase delay of each point along the RO ray path in the rain area on the total length L of the ray path in the whole rain area, and the formula is as follows:

ΔΦ＝∫_LK_dp(l)dl

wherein, K_dpBeing the differential phase delay of a single point, Δ Φ is the polarization phase shift in mm.

The polarization phase shift of the forward simulation of the research rainstorm area can be obtained through the steps.

The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and examples.

Example 1

As shown in fig. 1, a GNSS polarization signal forward modeling method suitable for a small rainfall level according to an embodiment of the present invention mainly includes seven steps of data preparation, raindrop shape model selection, raindrop spectrum model selection, raindrop relative complex dielectric constant calculation, forward scattering amplitude calculation, differential phase delay calculation, and polarization phase shift calculation.

The rainfall product used in this example was GPM DPR and the polarization occultation product used was PAZ PRO data. And after the two products are matched, screening to obtain a light rain area in which the RO event occurs. The GNSS polarized signal forward modeling method suitable for the small rain magnitude is implemented by taking 2018/12/1916 as an example of forward modeling of the small rain area penetrated by the 54-hour occultation event.

In this embodiment, step one, data preparation. And acquiring related information of the light rain area according to the graph 2, wherein the related information comprises information such as rainfall rate, air temperature, frequency, rain area range and the like. The rainfall rate and air temperature information is from a GPM DPR daily product, the equivalent volume diameter is from a DPR 2A-grade track product, the frequency is L1 waveband frequency and is about 1.57542GHz, the raindrop inclination angle is set to be 0 degree, the rain area range is determined by the starting tangent point position and the ending tangent point position of the occurence of the occultation event, and the tangent point position information is calculated by the GPS position, the LEO position and the time information in the PAZ PRO data product. The small rain area is wide in geographical range, 34-38 degrees of north latitude are covered, the vertical distribution can reach 4km in height, the highest rainfall rate of a rainfall unit in a rainfall zone and an extension range is 5.0298mm/h, the average rainfall rate of each rainfall layer in the whole area is 1.0070, 1.1456 and 0.8432mm/h, the average rainfall rate along a ray path is 1.4317mm/h, and the overall rainfall rate is small. The time of the GPM satellite in scanning the rain area is 16:16, and the time difference is less than one hour. After visualization, the simulation diagram of the light rain area and the simulation diagram of the RO event passing through the rain area are obtained (see fig. 3). Therefore, rainfall information of each layer is rich and is intersected with the RO events, and the rainfall rate of the RO rays passing through the rain area is below 3 mm/h. FIG. 4 is a graph of the variation of the tangent point trajectory of the RO event ray generated at 2018/12/1916:54 according to the embodiment of the present invention, in which the bold line segment represents the tangent point trajectory of the RO ray with a height of less than 20km, and it can be seen that the variation of the tangent point trajectory of each ray when the RO occurs can approximately present a curve.

In the second step of this embodiment, a raindrop shape model is selected. The SC model is mainly selected as the raindrop shape model of the rain zone of the embodiment.

In this embodiment, step three, a raindrop spectrum model is selected. MP distribution and JD distribution are respectively selected as raindrop spectrum distribution models of the rain areas of the embodiment to carry out forward modeling.

In the fourth step of this embodiment, the relative complex dielectric constant of the raindrops is calculated. And calculating the relative complex dielectric constant of the raindrop by using a Liebe1993 model formula.

In this embodiment, step five, the forward scattering amplitude is calculated. And calculating the forward scattering amplitude of the horizontal polarization and the vertical polarization of the single raindrop by combining a T-matrix method with the SC raindrop shape.

In step six of this embodiment, differential phase delay is calculated. And (4) calculating the differential phase delay of the raindrops in the group by combining the MP raindrop spectrum distribution model and the horizontal polarization forward scattering amplitude and the vertical polarization forward scattering amplitude obtained by the calculation in the step five. And calculating the differential phase delay of the group raindrops by combining the JD raindrop spectrum distribution model and the horizontal polarization and vertical polarization forward scattering amplitudes calculated in the step five.

In step seven of this embodiment, the polarization phase shift is calculated. And integrating the total path length of rays in the whole rain area according to the obtained differential phase delay to obtain the forward polarization phase shift.

By adopting the method, the GNSS polarization signal in the small rain area is forward-evolved, the polarization phase shift obtained by forward-evolving the MP raindrop spectrum distribution is 5.6636mm, and the polarization phase shift obtained by forward-evolving the JD raindrop spectrum distribution is 5.8649. The antenna phase corrected polarization phase shift for the PAZ satellite measured data is 6.0154 mm. The difference between the two forward modeling results and the actually measured data is not large, namely 0.3518mm and 0.1505mm, which are relatively close, and the accuracy and the reliability of the GNSS polarized signal forward modeling method applicable to the small rainfall magnitude are demonstrated.

Example 2

A GNSS polarized signal forward-acting system for small rainfall levels having a rainfall rate of 2.5 mm/hour or less, the system comprising: the device comprises a data acquisition module, a model establishing module, a relative complex dielectric constant calculation module, a forward scattering amplitude calculation module, a differential phase delay calculation module and a polarization phase shift calculation module; wherein the content of the first and second substances,

the data acquisition module is used for acquiring rainfall information in a to-be-detected light rain area; the small rain area has a GNSS polarized radio occultation event, and a ray path of occultation passes through the rain area;

the model establishing module is used for respectively establishing a raindrop shape model and a raindrop spectrum distribution model according to rainfall information;

the relative complex dielectric constant calculation module is used for calculating the relative complex dielectric constant of raindrops according to rainfall information;

the forward scattering amplitude calculation module is used for calculating the horizontal polarization forward scattering amplitude and the vertical polarization forward scattering amplitude of the single raindrop by combining the raindrop shape model;

the differential phase delay calculation module is used for calculating differential phase delay according to the raindrop spectrum distribution model and the single raindrop horizontal polarization forward scattering amplitude and the single raindrop vertical polarization forward scattering amplitude;

and the polarization phase shift calculation module is used for integrating the total path length of rays in the whole rain zone according to the differential phase delay to obtain the forward polarization phase shift.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.