Rainy-day Tropospheric Refractive Index Profile Inversion Method Based on Buoy Platform

Abstract

The present invention discloses a method for inverting the refractive index profile of the troposphere on rainy days based on a buoy platform, which relates to the technical field of offshore atmospheric detection, including obtaining a priori knowledge base based on statistical learning of sounding data, setting a threshold, searching in the priori knowledge base, and constructing an initial parameter profile; decomposing a population into a number of sub-populations, and distributing each sub-population to different CPU / GPU nodes, and calculating an objective function for each individual; obtaining sea surface temperature and sea surface humidity from the buoy platform as boundary constraints, and performing inversion using a multi-objective genetic immune algorithm, and obtaining an inversion result when the objective function value is less than or equal to the threshold; and calculating the atmospheric refractive index profile based on the inversion result. The present invention takes into account the attitude sway of the offshore floating platform and corrects it; effectively improves the accuracy of the inversion of the refractive index profile of the troposphere on rainy days, realizes real-time detection of the refractive index profile of the offshore troposphere, and effectively improves the calculation efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of marine atmospheric sounding, in particular to a method for retrieving the tropospheric refractive index profile on rainy days based on a buoy platform. Background Art

[0002] The tropospheric refractive index is a core parameter for evaluating the propagation of space radio waves and plays a key role in fields such as aviation navigation, space vehicle tracking and control, over-the-horizon propagation, radar blind area detection, and satellite remote sensing calibration. The abnormal tropospheric refractive index over the sea, which causes electromagnetic signal loss of lock, transmission delay, and even changes in the signal propagation path (atmospheric duct propagation), has always been a major safety hazard for maritime activities. In areas where ships enter and leave ports or where the navigation density is high, signal loss of lock easily causes chaos in the navigation order; signal transmission delay brings difficulties to the maritime tracking and control of spacecraft; changes in the signal propagation path expand the radar detection blind area and pose a serious threat to maritime safety activities. At the same time, the abnormal tropospheric refractive index over the sea can also increase the errors in radar ranging, angle measurement, and speed measurement, enhance radar clutter, and have a greater impact on radio communication.

[0003] The phenomenon of abnormal tropospheric refractive index over the sea occurs frequently, especially the interference of precipitation under rainy conditions. Raindrops themselves change the electromagnetic wave propagation path, resulting in the need to additionally consider the correction of the liquid water path (LWP) for the inversion of the refractive index profile. The existing methods for retrieving the tropospheric refractive index over the sea have low accuracy in the inversion results for rainy days and low computational efficiency, and cannot meet the real-time requirements for computational speed in engineering applications. Summary of the Invention

[0004] In order to overcome the above problems existing in the prior art, the present invention proposes a method for retrieving the tropospheric refractive index profile on rainy days based on a buoy platform.

[0005] The technical solution adopted by the present invention to solve its technical problems is: A method for retrieving the tropospheric refractive index profile on rainy days based on a buoy platform, comprising the following steps:

[0006] Step 1, constructing a temperature and humidity stratification knowledge base Q using the archived data of the nearshore sounding station, and setting a threshold group , searching in the knowledge base, randomly taking m groups in Q, and calculating the pressure profile using the pressure-height empirical formula with the sea surface pressure obtained by the buoy platform as the initial value to obtain m groups ;

[0007] Step 2, calculating the zenith angle, constructing m groups , decomposing the population m into s subpopulations, and distributing each subpopulation to different CPU / GPU nodes, and calculating the objective function for each individual ;

[0008] Step 3: Obtain the sea surface temperature from the buoy platform , the sea surface humidity As boundary constraint conditions, use the designed multi-objective genetic immune algorithm for inversion. When the condition is satisfied , the retrieved atmospheric temperature profile is , the relative humidity profile , the calculated pressure profile , where is the number of atmospheric layers;

[0009] Step 4: Calculate the partial pressure of water vapor profile , from the atmospheric temperature profile , the partial pressure of water vapor profile , the pressure profile , calculate the atmospheric refractive index profile.

[0010] For the above method for retrieving the rainy-day tropospheric refractive index profile based on a buoy platform, the method for calculating the objective function value in step 2 is: Calculate the zenith atmospheric absorption coefficient and the zenith atmospheric absorption . The slant path atmospheric absorption satisfies the relationship. Use the slant path atmospheric microwave equation to calculate the atmospheric brightness temperature . Given the observed brightness temperature , and then obtain the objective function value .

[0011] For the above method for retrieving the rainy-day tropospheric refractive index profile based on a buoy platform, the method for calculating the zenith atmospheric absorption coefficient under rainy conditions is:

[0012] ;

[0013] ;

[0014] ;

[0015] ;

[0016] where f represents the observed channel frequency; R represents the rainfall intensity ； k and α are coefficients. When the microwave radiometer operates in the horizontal polarization mode, , when the microwave radiometer operates in the vertical polarization mode, ; , , , , , , are all equation coefficients;

[0017] For all path geometries in linear polarization and circular polarization:

[0018] ;

[0019] ;

[0020] where is the path tilt angle, is the polarization tilt angle relative to the horizontal position, which can be obtained from the parameters of the microwave radiometer.

[0021] The above method for retrieving the rainy-day tropospheric refractive index profile based on a buoy platform, the specific process of the multi-objective genetic immune algorithm inversion in step 3 includes:

[0022] Step 3.1, sort the individuals in the population according to their non-dominated relationship in the objective function space, and divide the individuals into different levels;

[0023] Step 3.2, for each level of individuals, calculate their crowding degree in the objective function; identify the excellent individuals and poor individuals in the solution space, and record the excellent individuals that have appeared in history;

[0024] Step 3.3, use crossover and mutation operations, select parent individuals from the current population according to the selection strategy, and generate the corresponding number of offspring individuals, and merge the parent individuals and offspring individuals into a new population;

[0025] Step 3.4, select the next generation population according to non-dominated sorting and crowding degree. First, divide the individuals into different levels according to non-dominated sorting, and then select according to the crowding degree. Finally, retain the individuals with high levels and high crowding degrees;

[0026] Step 3.5, repeat steps 3.1 - 3.4 until is satisfied, and the inversion result is obtained.

[0027] The above method for retrieving the rainy-day tropospheric refractive index profile based on a buoy platform, the formula for calculating the atmospheric refractive index profile in step 4 is:

[0028] ;

[0029] where is the atmospheric temperature profile, is the partial pressure of water vapor profile, is the atmospheric pressure profile.

[0030] The above method for retrieving the rainy-day tropospheric refractive index profile based on a buoy platform, when the radio wave is transmitted over a long distance, introduce the atmospheric modified refractive index:

[0031] ;

[0032] where r0 is the mean radius of the Earth, is the height;

[0033] The slope of the refractive index profile is detected. or If there is an abnormal atmospheric refractive index, the altitude will be automatically given. , and issue an alarm prompt.

[0034] The beneficial effects of the present invention are that the present invention takes into account the attitude sway of the offshore floating platform and corrects it; effectively improves the accuracy of the inversion of the tropospheric refractive index profile on rainy days, realizes real-time detection of the offshore tropospheric refractive index profile, and effectively improves the calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the process of the present invention;

[0036] Figure 2 It is the inversion flow chart of the multi-objective genetic immune algorithm of the present invention. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0038] like Figure 1 As shown, this embodiment discloses a method for inverting the refractive index profile of the troposphere on rainy days based on a buoy platform, which specifically includes the following steps.

[0039] Step 1: Build a knowledge base of temperature and humidity stratification using archived data from nearshore sounding stations , and set a threshold group , search in the knowledge base and randomly construct m groups , m is the population size, such as m=80, the pressure profile uses the modified pressure-height empirical formula:

[0040] Calculated, that is, m groups .

[0041] Step 2: Obtain the motion attitude angle (roll angle and pitch angle) of the platform from the attitude sensor, and calculate the zenith angle from the attitude angle. The calculation formula is: , where is the zenith angle, is the pitch and roll attitude angle, construct m groups , decompose the population m into s small populations.

[0042] Step 3: Distribute the sub-population to different CPU / GPU nodes. For each individual, calculate the zenith atmospheric absorption coefficient and the zenith atmospheric absorption . The slant-path atmospheric absorption satisfies relationship. Use the slant-path atmospheric microwave equation to calculate the atmospheric brightness temperature , where is taken as 2.73 K, and calculate its objective function value .

[0043] Calculation of the zenith atmospheric absorption coefficient under rainy conditions :

[0044] Under rainy conditions, atmospheric absorption mainly includes oxygen absorption, water vapor absorption, and raindrop absorption, i.e., , where The calculation method is detailed in ZL202410642276.3, The specific calculation method of

[0045] Raindrop attenuation (dB / km) can be calculated from the power-law relationship of the rainfall intensity (mm / h):

[0046] , (1);

[0047] Coefficient k and the value of α are determined by the following equations,

[0048] (2);

[0049] (3);

[0050] where f represents the observation channel frequency; R represents the rainfall intensity ； k and α are coefficients. When the microwave radiometer operates in the horizontal polarization mode, , when the microwave radiometer operates in the vertical polarization mode, ; , , , , , , are all equation coefficients, and the specific values are shown in Table 1 - Table 4.

[0051] Table 1 Coefficient

[0052]

[0053] Table 2 Coefficient

[0054]

[0055] Table 3 Coefficient

[0056]

[0057] Table 4 Coefficient

[0058]

[0059] Coefficients of horizontal polarization The constant values are given in Table 1, while the coefficients of vertical polarization The constant values are given in Table 2. Table 3 gives the coefficients of horizontal polarization The constant values, while Table 4 gives the coefficients of vertical polarization The constant values.

[0060] For all path geometries in linear and circular polarizations, they can be calculated by the following equations from the values given in equations (2) and (3):

[0061] (4);

[0062] (5);

[0063] Here is the path tilt angle, is the polarization tilt angle relative to the horizontal position, which can be obtained from the microwave radiometer parameters.

[0064] Combined with the rainfall sensor carried by the microwave radiometer, use the above method to calculate , and then calculate to obtain .

[0065] Zenith atmospheric absorption Calculation of:

[0066] Continuous integral form: ;

[0067] Converted to discrete summation form: ;

[0068] where z represents height.

[0069] Step 4: Obtain the sea surface temperature from the buoy platform and sea surface humidity as boundary constraint conditions, and use the designed multi-objective genetic immune algorithm for inversion to satisfy , and the retrieved atmospheric temperature profile is , relative humidity profile , calculated barometric pressure profile , where is the number of atmospheric layers.

[0070] The multi-objective genetic immune algorithm corresponds the objective function of the problem to be solved to the antigen (fitness) of the invading organism, and the solution of the problem is the antibody (temperature / humidity profile) produced by the immune system. The multi-objective genetic immune algorithm is an efficient, parallel, and global search method that can automatically acquire and accumulate knowledge about the search space during the search process and can adaptively control the search process to obtain the non-dominated solution set. The algorithm has a self-regulating function, which not only retains the characteristics of the standard genetic algorithm's random global parallel search but also largely avoids premature convergence, ensuring rapid convergence to local or global optimal solutions and effectively improving the calculation efficiency.

[0071] The specific process of the multi-objective genetic immune algorithm inversion is as Figure 2 shown, including:

[0072] Step 4.1: Sort the individuals in the population according to their non-dominated relationship in the objective function space and divide the individuals into different ranks;

[0073] Step 4.2: For the individuals in each rank, calculate their crowding degree in the objective function; identify the excellent individuals and poor individuals in the solution space and record the excellent individuals that have appeared in history;

[0074] Step 4.3: Use crossover and mutation operations, select parent individuals from the current population according to the selection strategy, and generate the corresponding number of offspring individuals. Combine the parent individuals and offspring individuals into a new population;

[0075] Step 4.4: Select the next generation population according to non-dominated sorting and crowding degree. First, divide the individuals into different ranks according to non-dominated sorting, and then select according to the crowding degree. Finally, retain the individuals in the high ranks and those with high crowding degrees;

[0076] Step 4.5: Repeat steps 4.1 - 4.4 until is satisfied, and the inversion result is obtained.

[0077] Step 5: Calculate the partial pressure of water vapor for each layer , and the calculation method of the partial pressure of water vapor is the prior art and will not be elaborated here.

[0078] In the radio wave band, the atmospheric refractive index can be expressed as:

[0079] ;

[0080] where represents the dry term of the refractive index, represents the wet term of the refractive index is the total atmospheric pressure is the partial pressure of dry air is the partial pressure of water vapor , is the Kelvin temperature

[0081] can be approximately expressed by the following equation:

[0082] ;

[0083] wherein is the absolute temperature is the wet partial pressure is the air pressure, with the unit of .

[0084] When the radio wave is transmitted over a long distance, the atmospheric modified refractive index is introduced, where r0 is the average radius of the earth, generally taking , is the height, and the modified refractive index is dimensionless

[0085] Step 6: Detect the slope of the refractive index profile. When it is detected that or occurs, it indicates that there is an abnormal situation of the atmospheric refractive index, and the height is automatically given, and an alarm prompt is issued

[0086] The above embodiments are only exemplary embodiments of the present invention and are not used to limit the present invention. Those skilled in the art can make various modifications or equivalent replacements to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent replacements should also be regarded as falling within the protection scope of the present invention

Claims

1. Rainy tropospheric refractive index profile inversion method based on a buoy platform, characterized in that, including the following steps: Step 1: Construct a temperature and humidity stratification knowledge base Q using the archived data of the nearshore sounding stations, and set a threshold group , search in the knowledge base, and randomly select m groups in Q , use the pressure-height empirical formula to calculate the pressure profile with the sea surface pressure obtained from the buoy platform as the initial value, and obtain m groups ; Step 2, calculate the zenith angle to obtain m groups , decompose the population m into s sub-populations, distribute each sub-population to different CPU / GPU nodes, and calculate the objective function for each individual ; Step 3, obtain the sea surface temperature from the buoy platform , the sea surface humidity As boundary constraint conditions, use the designed multi-objective genetic immune algorithm for inversion. When it satisfies , the retrieved atmospheric temperature profile is , the relative humidity profile , and the calculated pressure profile , where is the number of atmospheric layers; Step 4, calculate the wet partial pressure profile , from the atmospheric temperature profile , the wet partial pressure profile , the air pressure profile , calculate the atmospheric refractive index profile; The calculation method of the objective function value in step 2 is as follows: calculate the zenith atmospheric absorption coefficient under rainy conditions and the zenith atmospheric absorption . The slant-path atmospheric absorption satisfies relationship, and use the slant-path atmospheric microwave equation to calculate the atmospheric brightness temperature . Given the observed brightness temperature of the microwave radiometer , and then obtain the objective function value ; The zenith atmospheric absorption coefficient under rainy conditions The calculation method is as follows: Among them, f represents the observation channel frequency; R represents the rainfall intensity ； k and are coefficients. When the microwave radiometer operates in the horizontal polarization mode, ; when the microwave radiometer operates in the vertical polarization mode, ; 、 、 、 、 、 、 are all coefficients of the equation; For all path geometries in linear polarization and circular polarization: Among them, is the path bevel angle, is the polarization bevel angle relative to the horizontal position, which can be obtained from the parameters of the microwave radiometer.

2. The method for inverting the rainy-day tropospheric refractive index profile based on a buoy platform according to claim 1, wherein The specific process of the multi-objective genetic immune algorithm inversion in step 3 includes: Step 3.1: Sort the individuals in the population according to their non-dominated relationship in the objective function space and divide the individuals into different levels; Step 3.2: For the individuals in each level, calculate their crowding degree in the objective function; identify the excellent individuals and poor individuals in the solution space, and record the excellent individuals that have appeared in history; Step 3.3: Use crossover and mutation operations, select parent individuals from the current population according to the selection strategy, and generate the corresponding number of offspring individuals. Combine the parent individuals and offspring individuals into a new population; Step 3.4: Select the next generation population according to non-dominated sorting and crowding degree. First, divide the individuals into different levels according to non-dominated sorting, and then select according to crowding degree. Finally, retain the individuals in the high levels and those with high crowding degree; Step 3.5, repeat Steps 3.1 - 3.4 until is satisfied, and the inversion result is obtained.

3. The method for inverting the rainy-day tropospheric refractive index profile based on a buoy platform according to claim 1, wherein The calculation formula for the atmospheric refractive index profile in step 4 is: wherein, is the atmospheric temperature profile, is the partial pressure of water vapor profile, is the air pressure profile.

4. The method for inverting the tropospheric refractive index profile on rainy days based on a buoy platform according to claim 3, wherein When the radio wave is transmitted over a long distance, introduce the atmospheric modified refractive index: where r0 is the mean Earth radius, is the altitude; Detect the slope of the refractive index profile. When the situation of or is detected, it indicates that there is an abnormal atmospheric refractive index situation, and the altitude is automatically given, and an alarm prompt is issued.

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