Insect orientation estimation method based on minimum polarization phase

Abstract

The application discloses an insect orientation estimation method based on minimum polarization phase. First, the polarization phase characteristics of insects are studied based on the PSM of insects measured in a microwave darkroom, and the corresponding relationship between the insect orientation and the polarization phase is found, that is, the minimum value of the polarization phase always appears when the polarization direction is parallel to the body axis of the insect, and the relationship is established for all body types of insects. Then, a new insect orientation estimation method is proposed based on the newly found polarization phase characteristics. The insect orientation estimated by the method theoretically does not have 90-degree error, and the estimation accuracy is higher under low signal-to-noise ratio. The application provides an effective means for measuring the insect orientation, helps to improve the observation ability of the insect radar, and promotes the research on the insect migration behavior.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of insect radar, and particularly relates to an insect orientation estimation method based on minimum polarization phase. BACKGROUND

[0002] Seasonal migration behavior widely exists in aquatic, terrestrial and aerial animals. However, how do migratory animals know where they are going is still a scientific mystery. In order to study the navigation mechanism of animals, it is necessary to effectively monitor migratory animals. Among migratory animals, migratory insects are small in size, high in flight height, 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. The ability of insect radar to measure insect orientation makes it possible to study the migration strategy of insects.

[0003] Insect radar has undergone three generations of development, including scanning insect radar, vertical insect radar and full polarization insect radar. The earliest insect radar is a scanning radar. Based on the scattering characteristics that the side surface radar cross-section (RCS) of an insect body is larger than that of the head-tail surface, for a migratory insect group with a common orientation, the measured echo P of the scanning insect radar shows a "dumbbell" shape. 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 the migratory insect group. The second generation of insect radar is a vertical radar. The RCS of the abdomen of an insect in 360 polarization directions is measured by a beam vertically pointing to the sky and a high-speed rotating linear polarization beam. Based on the assumption that the maximum RCS of an insect appears when the polarization direction is parallel to the body axis, the vertical insect radar can measure the head orientation of an individual insect. However, this assumption is only valid for small insects. For some large insects, the maximum RCS of the insect appears when the polarization direction is perpendicular to the body axis. In this case, the extracted head orientation will have a 90° error. The first two generations of insect radar are non-coherent radars, which cannot measure the complete echo phase of the target. The third generation of insect radar is a full polarization insect radar. This type of radar is full polarization, high resolution and coherent system, which can directly measure the polarization scattering matrix (PSM) of an individual insect and obtain the echo phase information of the target. The ability to obtain more dimensions makes it possible for the full polarization radar to identify 90° orientation error and improve the accuracy of orientation measurement. SUMMARY

[0004] Therefore, the present application provides an insect orientation estimation method based on minimum polarization phase, which can solve the 90° orientation error problem in measuring insect orientation and improve the accuracy of orientation measurement. This helps to improve the observation ability of insect radar and promote the study of insect migration behavior.

[0005] To achieve the above object, the technical scheme of the present application comprises the following steps:

[0006] Step one, obtaining insect polarization scattering matrix PSM by radar measurement, establishing insect polarization phase pattern model, and analyzing insect polarization phase characteristics;

[0007] Step two, based on the insect polarization phase characteristics, establishing insect orientation estimation basic assumption; the insect orientation estimation basic assumption is that when the polarization direction is parallel to the insect body axis, the insect polarization phase is minimum, and the minimum polarization phase is obtained;

[0008] Step three, based on the minimum polarization phase, constructing insect orientation estimation expression based on PSM, and using the insect orientation estimation expression based on PSM for insect orientation estimation.

[0009] Further, the insect polarization phase pattern model in step one is:

[0010]

[0011] Wherein, Φ(α) represents the phase value in the direction of α, α represents the polarization direction, s 11 , s 12 , s 21 and s 22 are the amplitudes of HH, HV, VH and VV polarization channels in PSM, β, β' and γ are the phases of HV, VH and VV polarization channels in PSM, H represents horizontal polarization, V represents vertical polarization, HV represents that the transmission polarization mode is V and the receiving polarization mode is H; VH represents that the transmission polarization mode is H and the receiving polarization mode is V; VV represents that the transmission polarization mode is V and the receiving polarization mode is V; a and b are both parameters for indicating the following contents:

[0012]

[0013] Further, in step three, based on the minimum polarization phase, the insect orientation estimation expression based on PSM is constructed as:

[0014]

[0015] Wherein, α min is the polarization direction corresponding to the minimum phase; α1 and α2 are two solutions when the derivative of formula (1) is zero, and are specifically represented as:

[0016]

[0017] Wherein, θ represents:

[0018]

[0019] c0, c1 and c2 are all parameters, respectively used for referring to the following contents:

[0020]

[0021] The present application has the following beneficial effects:

[0022] The present application is an insect orientation estimation method based on minimum polarization phase, which provides an effective means for measuring insect orientation. The present application first studies the polarization phase characteristics of insects based on the measured insect PSM in a microwave darkroom, and finds the corresponding relationship between insect orientation and polarization phase, that is, the minimum value of polarization phase always appears when the polarization direction is parallel to the insect body axis, and this is true for all body size insects. Then, based on the newly found polarization phase characteristics, a new insect orientation estimation method is proposed. The insect orientation estimated by this method theoretically does not have 90° error, and the estimation accuracy is higher under low signal-to-noise ratio. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The present application provides a flow chart of the insect orientation estimation method based on minimum polarization phase.

[0024] Figure 2a The mean comparison of the orientation error of 159 insects extracted based on the existing method and the new method under different signal-to-noise ratios, Figure 2b The standard deviation comparison of the orientation error of 159 insects extracted based on the existing method and the new method under different signal-to-noise ratios. DETAILED DESCRIPTION

[0025] The present application provides an insect orientation estimation method based on minimum polarization phase, and the flow is as shown in Figure 1 The present application provides an insect orientation estimation method based on minimum polarization phase, and the flow is as shown in

[0026] Step one, obtain the insect polarization scattering matrix PSM by radar measurement, establish the insect polarization phase direction pattern model, and analyze the polarization phase characteristics of the insect;

[0027] Step two, based on the polarization phase characteristics of the insect, establish the basic assumption of insect orientation estimation; the basic assumption of insect orientation estimation is that when the polarization direction is parallel to the insect body axis, the polarization phase of the insect is minimum, and the minimum polarization phase is obtained;

[0028] Step three, based on the minimum polarization phase, construct the insect orientation estimation expression based on PSM, and use the insect orientation estimation expression based on PSM for insect orientation estimation.

[0029] The present application will be described in detail below in conjunction with the drawings and examples.

[0030] Assume that the insect PSM is

[0031]

[0032] where s 11 , s 12 , s 21 and s 22 are the amplitudes of HH, HV, VH and VV polarized channels, and β, β' and γ are the phases of HV, VH and VV polarized channels, respectively. For monostatic radar, s 12 = s 21 and β = β'.

[0033] The radar return of an insect in different polarization directions can be expressed as

[0034]

[0035] where α denotes the polarization direction.

[0036] Let

[0037]

[0038] Then

[0039] e(α) = b + ja (4)

[0040] The polarization phase pattern of an insect is defined as

[0041]

[0042] Based on the PSMs of 159 insects measured in a microwave anechoic chamber using a full-polarimetric radar, the polarization phase characteristics of insects were studied. During the measurement, the 0° and 180° polarization directions were parallel to the insect heading. Since the two polarization directions with a phase difference of 180° have the same relationship with the insect heading, they are equivalent, and thus the period of the polarization phase pattern is 180°. For all insects, the maximum phase occurs when the polarization direction is perpendicular to the insect heading (90° and 270°), and the minimum phase occurs when the polarization direction is parallel to the insect heading (0° and 180°).

[0043] Based on this characteristic, a new heading extraction hypothesis can be proposed: the polarization phase of an insect is minimum when the polarization direction is parallel to the insect body axis. Based on this hypothesis, the polarization direction corresponding to the minimum polarization phase can be used to estimate the insect heading. In the following, the insect heading expression will be derived by means of derivation.

[0044] Due to the 180° ambiguity of the heading, only the polarization directions α within the 180° period are considered, and thus the polarization phase pattern of an insect can be expressed as

[0045]

[0046] The derivation gives

[0047]

[0048] wherein

[0049]

[0050] Let Get

[0051]

[0052] Substitute equation (8) into equation (7) to get

[0053]

[0054] wherein

[0055]

[0056]

[0057] From equation (10), we get

[0058]

[0059] Thus, we get two solutions of a:

[0060]

[0061]

[0062] Substitute equation (14) and equation (15) into equation (6) to get the polarization direction corresponding to the minimum phase

[0063]

[0064] According to the basic assumption of orientation estimation, a min That is, the insect orientation expression.

[0065] Therefore, the present application provides an insect orientation estimation method based on the minimum polarization phase, and the following will illustrate the implementation steps with specific examples:

[0066] In order to verify the insect body axis orientation extraction method described above, based on the data of 159 insects measured in the microwave darkroom, the proposed insect orientation extraction method is verified, and compared with the existing orientation extraction method (a high-precision insect body axis orientation extraction method based on polarization scattering matrix estimation, patent number: ZL201710137290.8; a parallel and vertical insect discrimination method based on characteristic phase, patent number: ZL201911203473.0). The steps are as follows:

[0067] Step one, set a series of SNR (5dB, 10dB, …, 30dB), take the PSM of 159 insects as the true value, take the power of the first element in PSM as the signal power, and generate four complex Gaussian white noises according to the set SNR and add them to the four values of PSM.

[0068] Step two, estimate the orientation of insects by using the insect orientation estimation method based on the minimum polarization phase and the existing orientation extraction method (a high-precision insect body axis orientation extraction method based on polarization scattering matrix estimation, patent number: ZL201710137290.8; a parallel and vertical insect discrimination method based on feature phase, patent number: ZL201911203473.0), and calculate the orientation error.

[0069] Step three, repeat steps one to two 500 times, and calculate the mean and standard deviation of the error of the two methods.

[0070] The comparison results are shown in Figure 2. It can be seen that when the signal-to-noise ratio is lower than 17dB, the error of the new method is much smaller than that of the existing method, and when the signal-to-noise ratio is higher than 17dB, the error of the existing method is smaller than that of the new method. Therefore, the insect orientation estimation method based on the minimum polarization phase can realize the estimation of the orientation of insects, and the performance is better than that of the existing method under low signal-to-noise ratio.

[0071] In summary, the above is only an embodiment of the present application based on 159 insects, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.​

Claims

1. A method for estimating the direction of an insect based on the minimum polarization phase, characterized in that, The application is used for realizing insect orientation estimation when signal-to-noise ratio is lower than 17dB, and the method comprises the following steps: Step one, obtaining insect polarization scattering matrix PSM by radar measurement, establishing insect polarization phase pattern model, and analyzing insect polarization phase characteristics; the insect PSM is where s 11 , s 12 , s 21 and s 22 are the amplitudes of HH, HV, VH and VV polarized channels respectively, and β, β' and γ are the phases of HV, VH and VV polarized channels respectively; for monostatic radar, s 12 =s 21 , β=β'. The radar echo of the insect in different polarization directions can be expressed as Wherein, alpha represents the polarization direction; Let Then e(alpha)=b+ja (4) The insect polarization phase pattern is defined as The period of the polarization phase pattern is 180°; for all insects, the maximum phase appears at 90° and 270° when the polarization direction is perpendicular to the insect orientation, and the minimum value appears at 0° and 180° when the polarization direction is parallel to the insect orientation; Step two, establishing insect orientation estimation basic assumption based on insect polarization phase characteristics; the insect orientation estimation basic assumption is that when the polarization direction is parallel to the insect body axis, the insect polarization phase is minimum, and the minimum polarization phase is obtained; Step three, constructing insect orientation estimation expression based on PSM based on the minimum polarization phase, and using the insect orientation estimation expression based on PSM for insect orientation estimation; Due to the 180° ambiguity of the orientation, only the polarization direction alpha in the 180° period is considered, and then the insect polarization phase pattern is expressed as: Derivation is obtained Wherein Let obtained Substituting formula (8) into formula (7) obtains Wherein From formula (10), we obtain Therefore, two solutions of alpha are obtained: Substituting formula (14) and formula (15) into formula (6), the polarization direction corresponding to the minimum phase is obtained According to the heading estimation basic assumption, a min is the insect heading expression.

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