Insect Orientation Estimation Method Based on Polarization Phase Characteristics

Abstract

The present invention discloses an insect orientation estimation method based on polarization phase characteristics. First, based on the insect PSM measured in a microwave anechoic chamber, the polarization phase characteristics of insects are studied, and the corresponding relationship between insect orientation and polarization phase is found, that is, the maximum value of polarization phase always appears when the polarization direction is perpendicular to the insect body axis, while the minimum value of polarization phase always appears when the polarization direction is parallel to the insect body axis, and this holds for all sized insects. Then, based on the newly discovered polarization phase characteristics, a new insect orientation estimation method is proposed. The insect orientation estimated by this method theoretically has no 90° error and has higher estimation accuracy under low signal-to-noise ratio. The present invention provides an effective means for measuring insect orientation, helps to improve the observation ability of insect radars, and promotes the research on insect migration behavior.

Description

Technical Field

[0001] The present invention belongs to the technical field of insect radar, and particularly relates to a method for estimating insect orientation based on polarization phase characteristics. Background Art

[0002] Seasonal migration behaviors widely exist in aquatic, terrestrial, and aerial animals. However, "how migratory animals know where they are going" remains an unsolved scientific mystery. To study the navigation mechanism of animals, it is necessary to effectively monitor migratory animals. Among migratory animals, migratory insects are small in size, fly at high altitudes, and usually migrate at night, which makes it difficult to monitor migratory insects. The emergence of insect radar makes it possible to monitor migratory insects. Its ability to measure the orientation of insects makes it possible to study the orientation strategy of insect migration.

[0003] Insect radar has gone through three generations of development, including scanning insect radar, vertical insect radar, and full-polarization insect radar. The earliest insect radar was the scanning radar. Based on the scattering characteristic that the radar cross-section (RCS) of the side of the insect body is larger than that of the head and tail surfaces, for a group of migratory insects with a common orientation, the P display of the echo measured by the scanning insect radar shows a "dumbbell" shape, and the direction perpendicular to the dumbbell is the common orientation direction of the insects. Therefore, the scanning insect radar can measure the common orientation of migratory insect groups. The second-generation insect radar is the vertical radar, which measures the RCS of the insect abdomen in 360° polarization directions through a beam vertically facing the sky and a high-speed rotating linearly polarized beam. Based on the assumption that the maximum RCS of the insect appears when the polarization direction is parallel to the body axis, the vertical insect radar can measure the head orientation of individual insects. However, this assumption is only valid for small insects. For some large insects, there is a situation where the maximum RCS of the insect appears when the polarization direction is perpendicular to the body axis. At this time, the extracted head orientation will have a 90° error. The first two generations of insect radar are non-coherent radars and cannot measure the complete echo phase of the target. The third-generation insect radar is the full-polarization insect radar, which is a full-polarization, high-resolution, coherent system and can directly measure the polarization scattering matrix (PSM) of individual insects to obtain the echo phase information of the target. The ability to obtain more-dimensional information provides the possibility for the full-polarization radar to distinguish 90° orientation errors and improve the orientation measurement accuracy. Summary of the Invention

[0004] In view of this, the present invention provides a method for estimating insect orientation based on polarization phase characteristics, which can solve the 90° orientation error problem when measuring insect orientation and improve the orientation measurement accuracy. This helps to improve the observation ability of insect radar and promote the research on insect migration behavior.

[0005] To achieve the above object, the technical solution of the present invention is as follows: 1. An insect orientation estimation method based on polarization phase characteristics, characterized by including the following steps:

[0006] Step 1: Use radar measurement to obtain the insect polarization scattering matrix (PSM), establish an insect polarization phase pattern model, and analyze the insect polarization phase characteristics;

[0007] Step 2: Based on the insect polarization phase characteristics, establish basic assumptions for insect orientation estimation, including: when the polarization direction is perpendicular to the insect body axis, the insect polarization phase is the largest; when the polarization direction is parallel to the insect body axis, the insect polarization phase is the smallest. Thus, the maximum polarization phase and the minimum polarization phase are obtained respectively;

[0008] Step 3: Based on the obtained maximum polarization phase and minimum polarization phase, establish an insect orientation estimation expression based on the PSM, and use the insect orientation estimation expression based on the PSM to estimate the insect orientation.

[0009] Further, the insect polarization phase pattern model in Step 1 is:

[0010]

[0011] where Φ(α) represents the phase value in the α direction, α represents the polarization direction, s 11 、s 12 、s 21 and s 22 are the amplitudes of the HH, HV, VH, and VV polarization channels in the PSM respectively, β, β′, γ are the phases of the HV, VH, and VV polarization channels in the PSM respectively, H represents horizontal polarization, V represents vertical polarization, HV represents the transmission polarization mode is V and the reception polarization mode is H; VH represents the transmission polarization mode is H and the reception polarization mode is V; VV represents the transmission polarization mode is V and the reception polarization mode is V; a and b are both reference parameters respectively used to refer to the following content:

[0012]

[0013] Further, in Step 3, the insect orientation estimation expression is:

[0014]

[0015] where, is the insect orientation, and θ is expressed as:

[0016]

[0017] c 0 、c 1 and c 2They are all reference parameters, respectively used to refer to the following contents:

[0018]

[0019] The present invention has the following beneficial effects:

[0020] The present invention is an insect orientation estimation method based on polarization phase characteristics, providing an effective means for measuring the orientation of insects. First, based on the insect PSM measured in a microwave anechoic chamber, the polarization phase characteristics of insects are studied, and the corresponding relationship between insect orientation and polarization phase is found, that is, the maximum value of polarization phase always appears when the polarization direction is perpendicular to the insect body axis, while the minimum value of polarization phase always appears when the polarization direction is parallel to the insect body axis, and it holds for all insects of different sizes; then, based on the newly discovered polarization phase characteristics, a new insect orientation estimation method is proposed. The insect orientation estimated by this method theoretically has no 90° error, and the estimation accuracy is higher under low signal-to-noise ratio. Description of the Drawings

[0021] Figure 1 It is a flow chart of the insect orientation estimation method based on polarization phase characteristics provided by the present invention;

[0022] Figure 2a It is a distribution diagram of the offset δ values of all insects when the orientation is 0°; Figure 2b It is a distribution diagram of the offset δ values of all insects when the orientation is 30°; Figure 2c It is a distribution diagram of the offset δ values of all insects when the orientation is 90°;

[0023] Figure 2d It is a distribution diagram of the offset δ values of all insects when the orientation is 140°;

[0024] Figure 3a It is a comparison of the mean values of the orientation errors of 159 insects extracted based on the existing method and the new method under different signal-to-noise ratios, Figure 3b It is a comparison of the standard deviations of the orientation errors of 159 insects extracted based on the existing method and the new method under different signal-to-noise ratios. Detailed Embodiments

[0025] The present invention provides an insect orientation estimation method based on polarization phase characteristics. Its basic idea is that first, based on the insect PSM measured in a microwave anechoic chamber, the polarization phase characteristics of insects are studied, and the mapping relationship between insect orientation and polarization phase is established; then, based on the established mapping relationship between insect orientation and polarization phase, the basic assumptions for orientation extraction are set; finally, based on the insect PSM, a polarization phase model is established, and the insect orientation estimation expression is derived.

[0026] The following takes the drawings and gives embodiments to describe the present invention in detail.

[0027] Assume the insect PSM is

[0028]

[0029] where s 11 、s 12 、s 21 and s 22 are the amplitudes of the HH, HV, VH, and VV polarization channels respectively, and β, β′, γ are the phases of the HV, VH, and VV polarization channels respectively. For a monostatic radar, s 12 = s 21 , β = β′.

[0030] The radar echo of the insect in different polarization directions can be expressed as

[0031]

[0032] where α represents the polarization direction.

[0033] Let

[0034]

[0035] Then

[0036] e(α) = b + ja (4)

[0037] The insect polarization phase pattern is defined as

[0038]

[0039] Based on the PSM of 159 insects measured by a full-polarization radar in a microwave anechoic chamber, the polarization phase characteristics of the insects were studied. During the measurement, the 0° and 180° polarization directions were parallel to the insect orientation. Since the relationship between the two polarization directions with a 180° difference and the insect orientation is the same and they are equivalent, the period of the polarization phase pattern is 180°. For all insects, the maximum phase appears when perpendicular to the insect orientation (90° and 270°), and the minimum phase appears when parallel to the insect orientation (0° and 180°).

[0040] Based on this characteristic, a new hypothesis for orientation extraction can be proposed: when the polarization direction is perpendicular to the insect body axis, the insect polarization phase is the maximum; when the polarization direction is parallel to the insect body axis, the insect polarization phase is the minimum. Based on this hypothesis, the polarization direction corresponding to the maximum or minimum polarization phase can be obtained to estimate the insect orientation. Below, the insect orientation expression will be derived by taking the derivative.

[0041] Due to the 180° ambiguity of the orientation, only considering the polarization direction α within the 180° period, the insect polarization phase pattern can be expressed as

[0042]

[0043] Derivation gives

[0044]

[0045] where

[0046]

[0047] Let obtain

[0048]

[0049] Substituting into Equation (8) gives

[0050]

[0051] where

[0052]

[0053]

[0054] From Equation (10), we get

[0055]

[0056] Thus, two solutions for α are obtained:

[0057]

[0058]

[0059] Among these two solutions, one is the polarization direction corresponding to the maximum phase, and the other is the polarization direction corresponding to the minimum phase. According to the discovered insect polarization phase, α 1 and α 2 should differ by 90°. However, as can be seen from Equations (14) and (15), the difference between the two has an additional term. Define this additional offset δ as

[0060]

[0061] Figure 2 analyzes the distribution of the offset δ under different orientations. It can be seen that when the insect orientation is 0° and 90°, δ = 0°; when the orientation is not 0°, δ is on the order of 10 -14 °, which is very small and can be ignored. Therefore, Equations (14) and (15) can be simplified to

[0062]

[0063]

[0064] Obviously, both the phase maximum and minimum are related to θ. Therefore, by obtaining θ, the insect orientation can be obtained. Thus, according to the basic assumption of orientation estimation, the orientation expression can be obtained:

[0065]

[0066] Therefore, the present invention provides an insect orientation estimation method based on polarization phase characteristics. The implementation steps will be described below with specific embodiments:

[0067] In order to verify the previous insect body axis orientation extraction method, based on the data of 159 insects measured in a microwave anechoic chamber, the proposed insect orientation extraction method was verified and compared with the existing orientation extraction methods (\"A high-precision insect body axis orientation extraction method based on polarization scattering matrix estimation\", patent number: ZL201710137290.8; \"A method for distinguishing parallel and perpendicular insects based on characteristic phases\", patent number: ZL201911203473.0). The steps are as follows:

[0068] Step 1, set a series of SNR (5dB, 10dB,..., 30dB). Taking the measured PSM of 159 insects as the true value and the power of the first element in the PSM (i.e., ) as the signal power, according to the set SNR, 4 complex Gaussian white noises are respectively simulated and added to the 4 values of the PSM.

[0069] Step 2, respectively use the insect orientation estimation method based on polarization phase characteristics of the present invention and the existing orientation extraction methods (\"A high-precision insect body axis orientation extraction method based on polarization scattering matrix estimation\", patent number: ZL201710137290.8; \"A method for distinguishing parallel and perpendicular insects based on characteristic phases\", patent number: ZL201911203473.0) to estimate the insect orientation and calculate the orientation error.

[0070] Step 3, repeat Steps 1 to 2 500 times, and statistically calculate the mean and standard deviation of the orientation errors estimated by the two methods.

[0071] The comparison results are shown in Figure 2. It can be seen that when the signal-to-noise ratio is lower than 23dB, the error of the new method is much smaller than that of the existing method. When the signal-to-noise ratio is higher than 23dB, the error of the new method is slightly larger than that of the existing method. Therefore, the insect orientation estimation method based on polarization phase characteristics of the present invention can realize insect orientation estimation and has better performance than the existing method at low signal-to-noise ratios.

[0072] In summary, the above is only an embodiment of the present invention based on the data of 159 insects, and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Insect orientation estimation method based on polarization phase characteristics, characterized in that, it includes the following steps: Step 1: Use radar measurement to obtain the polarization scattering matrix (PSM) of the insect, establish an insect polarization phase pattern model, and analyze the insect polarization phase characteristics; Step 2: Based on the insect polarization phase characteristics, establish basic assumptions for insect orientation estimation, including: when the polarization direction is perpendicular to the insect body axis, the insect polarization phase is the largest; when the polarization direction is parallel to the insect body axis, the insect polarization phase is the smallest, thereby obtaining the maximum polarization phase and the minimum polarization phase respectively; Step 3: Based on the obtained maximum polarization phase and minimum polarization phase, establish an insect orientation estimation expression based on the PSM, and use the insect orientation estimation expression based on the PSM to estimate the insect orientation; The insect polarization phase pattern model in Step 1 is: Among them, Φ(α) represents the phase value in the α direction, α represents the polarization direction, s 11 , s 12 , s 21 and s 22 are respectively the amplitudes of the HH, HV, VH, and VV polarization channels in the PSM, β and γ are respectively the phases of the HV and VV polarization channels in the PSM, H represents horizontal polarization, V represents vertical polarization, HV means the transmission polarization mode is V and the reception polarization mode is H; VH means the transmission polarization mode is H and the reception polarization mode is V; VV means the transmission polarization mode is V and the reception polarization mode is V; both a and b are reference parameters respectively used to refer to the following contents:

2. The method according to claim 1, characterized in that: in Step 3, the insect orientation estimation expression is: Among them, is the insect orientation, and θ is expressed as: c 0 、c 1 and c 2 are all reference parameters, respectively used to refer to the following contents:

Images