Method and device for extracting positive and negative slope chirp transmit signals of spaceborne scatterometer

Abstract

The present invention belongs to the technical fields of active microwave remote sensing, extraction of linear frequency modulation transmitted signals of scatterometers, and ocean data processing. Specifically, it relates to a method and device for extracting positive and negative slope linear frequency modulation transmitted signals of a spaceborne scatterometer. The method includes: using a spaceborne microwave scatterometer to perform conical scanning on an area to be observed within a swath through a fan beam, and obtaining in real time the scanning azimuth angle for this observed area; based on the scanning azimuth angle for this observed area obtained in real time, determining whether the antenna transmits a linear frequency modulation pulse signal with a negative slope or a linear frequency modulation pulse signal with a positive slope.

Description

Technical Field

[0001] The present invention belongs to the technical fields of active microwave remote sensing, extraction of linear frequency modulation transmitted signals of scatterometers, and ocean data processing. Specifically, it relates to a method and device for extracting positive and negative slope linear frequency modulation transmitted signals of spaceborne scatterometers. Background Art

[0002] The sea surface wind field is an important physical parameter in the research and application of ocean and atmospheric sciences. As the most important remote sensing instrument for obtaining global sea surface wind field data at present, the sensing results of spaceborne microwave scatterometers play an important role in numerical weather forecasting, marine disaster monitoring, numerical ocean environmental forecasting, meteorological forecasting, and climate research.

[0003] The ground footprint of a fan-beam conical scanning scatterometer is about several hundred kilometers in the pitch direction. At the same time, the fan-beam antenna performs conical scanning at a certain rotation speed. While obtaining multi-azimuth angle observations of the target, it achieves complete coverage of the observation area. Due to the large pitch angle range of the fan beam, the Doppler frequency of the echo fluctuates greatly, and the Doppler bandwidth increases accordingly, increasing the difficulty of calculating the backscattering coefficient and increasing the complexity of the system.

[0004] In summary, the existing spaceborne fan-beam conical scanning scatterometer has the defects of large echo Doppler frequency fluctuation range and high processing difficulty. Summary of the Invention

[0005] To solve the above-mentioned defects existing in the prior art, the present invention proposes a method for extracting positive and negative slope linear frequency modulation transmitted signals of a spaceborne scatterometer, and the method includes:

[0006] Using a spaceborne microwave scatterometer to perform conical scanning on the area to be observed within the swath through a fan beam, and obtaining the scanning azimuth angle for this observation area in real time;

[0007] Judging whether the antenna transmits a linear frequency modulation pulse signal with a negative slope or a linear frequency modulation pulse signal with a positive slope according to the scanning azimuth angle for this observation area obtained in real time.

[0008] As an improvement of the above technical solution, the spaceborne microwave scatterometer is a fan-beam conical scanning microwave scatterometer.

[0009] As an improvement of the above technical solution, the use of a spaceborne microwave scatterometer to perform conical scanning detection on multiple targets within the swath through a fan beam to obtain the scanning azimuth and beam pointing of the antenna fan beam for a certain target; the specific process is as follows:

[0010] Using a spaceborne microwave scatterometer to perform conical scanning on the area to be observed within the swath through a fan beam, and obtaining the azimuth angle of the antenna fan beam for this observation area;

[0011] When the antenna beam looks forward, determine the corresponding range of the antenna beam azimuth angle as 0 - 90° and 270° - 360°;

[0012] When the antenna beam looks backward, determine the corresponding range of the antenna beam azimuth angle as 90° - 270°.

[0013] As one of the improvements of the above technical solution, it is determined whether the antenna emits a linear frequency modulation pulse signal with a negative slope or a positive slope according to the scanning azimuth angle of the observation area obtained in real time; the specific process is as follows:

[0014] According to the antenna fan beam azimuth angle of the observation area obtained in real time, determine whether the antenna beam is looking forward, and then determine whether the antenna emits a linear frequency modulation pulse signal with a negative slope or a positive slope;

[0015] If the antenna fan beam azimuth angle of the observation area obtained is in the range of 0 - 90° or 270° - 360°, the antenna beam looks forward, the antenna emits a linear frequency modulation pulse signal with a negative slope, and it is used as the final transmitted signal;

[0016] If the antenna fan beam azimuth angle of the observation area obtained is in the range of 90 - 270°, the antenna beam looks backward, the antenna emits a linear frequency modulation pulse signal with a positive slope, and it is used as the final transmitted signal.

[0017] The present invention also provides a device for extracting positive and negative slope linear frequency modulation transmitted signals of a spaceborne scatterometer, and the device includes:

[0018] An azimuth angle acquisition module, which is used to perform conical scanning on the to-be-observed area within the swath range through a fan beam by using a spaceborne microwave scatterometer, and acquire the scanning azimuth angle of the observation area in real time; and

[0019] A signal transmission module, which is used to determine whether the antenna emits a linear frequency modulation pulse signal with a negative slope or a positive slope according to the scanning azimuth angle of the observation area obtained in real time.

[0020] As one of the improvements of the above technical solution, the specific implementation process of the azimuth angle acquisition module is as follows;

[0021] Perform conical scanning on the to-be-observed area within the swath range through a fan beam by using a spaceborne microwave scatterometer, and acquire the antenna fan beam azimuth angle of the observation area;

[0022] When the antenna beam looks forward, determine the corresponding range of the antenna beam azimuth angle as 0 - 90° and 270° - 360°;

[0023] When the antenna beam looks backward, the corresponding antenna beam azimuth angle is determined to be in the range of 90° - 270°.

[0024] As one of the improvements of the above technical solution, the specific implementation process of the signal transmitting module is as follows;

[0025] According to the antenna fan beam azimuth angle obtained in real time for the observation area, it is judged whether the antenna beam is looking forward, and then it is judged whether the antenna transmits a linear frequency modulation pulse signal with a negative slope or a linear frequency modulation pulse signal with a positive slope;

[0026] If the antenna fan beam azimuth angle obtained for the observation area is in the range of 0 - 90° or 270° - 360°, the antenna beam is looking forward, and the antenna transmits a linear frequency modulation pulse signal with a negative slope, which is used as the final transmitted signal;

[0027] If the antenna fan beam azimuth angle obtained for the observation area is in the range of 90 - 270°, the antenna beam is looking backward, and the antenna transmits a linear frequency modulation pulse signal with a positive slope, which is used as the final transmitted signal.

[0028] The beneficial effects of the present invention compared with the prior art are as follows:

[0029] 1. The method of the present invention reduces the Doppler frequency bandwidth of the echo of the spaceborne scatterometer and restricts non-target signals such as clutter and noise from entering the antenna;

[0030] 2. The method of the present invention reduces the possibility of range ambiguity caused by the Doppler frequency bandwidth;

[0031] 3. The method of the present invention makes the total bandwidth of the backscattering signal have good symmetry, which provides convenience for the subsequent processing of the scatterometer. Description of the Drawings

[0032] Figure 1 is the observation geometry schematic diagram of the spaceborne scatterometer of the present invention performing conical scanning through a fan beam;

[0033] Figure 2 is the schematic diagram of the working principle of the spaceborne scatterometer of the present invention;

[0034] Figure 3 is the principle flow chart of synthesizing the transmitted signal of the positive and negative frequency modulation slope linear frequency modulation signals in the method for extracting the positive and negative slope linear frequency modulation transmitted signals of the spaceborne scatterometer provided by the present invention;

[0035] Figure 4 is the schematic diagram of the frequency modulation slopes of the positive and negative frequency modulation slope linear frequency modulation signals in an embodiment of the method of the present invention;

[0036] Figure 5It is a schematic diagram of the curve of the Doppler frequency varying with the azimuth angle within the echo frequency range when the forward and backward viewing of the spaceborne scatterometer provided by the present invention have the same FM slope.

[0037] Figure 6 It is a schematic diagram of the curve of the Doppler frequency varying with the azimuth angle within the echo frequency range when the forward and backward viewing of the spaceborne scatterometer provided by the present invention have different FM slopes. Detailed implementation manners

[0038] The present invention will be further described below in conjunction with the accompanying drawings and examples.

[0039] As Figure 3 shown, the present invention provides a method for extracting the positive and negative slope linear frequency modulation transmitted signals of a spaceborne scatterometer. The method of the present invention not only restricts non-target signals such as clutter and noise from entering the antenna, reducing the possibility of range ambiguity, but also makes the total bandwidth of the backscattering signal have good symmetry, providing convenience for subsequent processing.

[0040] The method includes:

[0041] Using a spaceborne microwave scatterometer to perform conical scanning on the area to be observed within the swath through a fan beam, and obtaining the scanning azimuth angle for this observation area in real time;

[0042] Among them, the spaceborne microwave scatterometer is a fan beam conical scanning microwave scatterometer.

[0043] Specifically, using a spaceborne microwave scatterometer to perform conical scanning on the area to be observed within the swath through a fan beam, and obtaining the azimuth angle of the antenna fan beam for this observation area;

[0044] When the antenna beam is forward viewing, determining the corresponding range of the antenna beam azimuth angle as 0 - 90° and 270° - 360°;

[0045] When the antenna beam is backward viewing, determining the corresponding range of the antenna beam azimuth angle as 90° - 270°.

[0046] Judging whether the antenna emits a linear frequency modulation pulse signal with a negative slope or a positive slope according to the scanning azimuth angle for this observation area obtained in real time.

[0047] Specifically, judging whether the antenna emits a linear frequency modulation pulse signal with a negative slope or a positive slope according to the scanning azimuth angle for this observation area obtained in real time; the specific process is as follows:

[0048] Judging whether the antenna beam is forward viewing according to the azimuth angle of the antenna fan beam for this observation area obtained in real time, and further judging whether the antenna emits a linear frequency modulation pulse signal with a negative slope or a positive slope.

[0049] If the azimuth range of the antenna fan beam for the observation area is in the range of 0 - 90° or 270° - 360°, the antenna beam looks forward, and the antenna emits a linear frequency modulated pulse signal with a negative slope, which is used as the final transmitted signal;

[0050] If the azimuth range of the antenna fan beam for the observation area is in the range of 90 - 270°, the antenna beam looks backward, and the antenna emits a linear frequency modulated pulse signal with a positive slope, which is used as the final transmitted signal.

[0051] The present invention also provides a device for extracting positive and negative slope linear frequency modulated transmitted signals of a spaceborne scatterometer, and the device includes: an azimuth acquisition module and a signal transmission module;

[0052] The azimuth acquisition module is used to perform conical scanning on the area to be observed within the swath range through a fan beam by using a spaceborne microwave scatterometer, and to acquire the scanning azimuth angle for the observation area in real time;

[0053] Specifically, a spaceborne microwave scatterometer is used to perform conical scanning on the area to be observed within the swath range through a fan beam to acquire the azimuth angle of the antenna fan beam for the observation area;

[0054] When the antenna beam looks forward, the corresponding azimuth range of the antenna beam is determined to be in the range of 0 - 90° and 270° - 360°;

[0055] When the antenna beam looks backward, the corresponding azimuth range of the antenna beam is determined to be in the range of 90° - 270°.

[0056] The signal transmission module is used to determine whether the antenna emits a linear frequency modulated pulse signal with a negative slope or a positive slope according to the scanning azimuth angle for the observation area acquired in real time.

[0057] Specifically, determining whether the antenna emits a linear frequency modulated pulse signal with a negative slope or a positive slope according to the scanning azimuth angle for the observation area acquired in real time; the specific process is as follows:

[0058] According to the azimuth angle of the antenna fan beam for the observation area acquired in real time, it is determined whether the antenna beam is looking forward, and further, it is determined whether the antenna emits a linear frequency modulated pulse signal with a negative slope or a positive slope;

[0059] If the azimuth range of the antenna fan beam for the observation area is in the range of 0 - 90° or 270° - 360°, the antenna beam looks forward, and the antenna emits a linear frequency modulated pulse signal with a negative slope, which is used as the final transmitted signal;

[0060] Obtain the range of the azimuth angle of the antenna fan beam for the observation area, which is 90° - 270°. Then, with the antenna beam looking backward, the antenna transmits a linear frequency modulation pulse signal with a positive slope, and this is used as the final transmitted signal.

[0061] Embodiment 1

[0062] As Figure 1 shown, the China-France Oceanographic Satellite Microwave Scatterometer (CSCAT) of the present invention is a fan beam conical scanning microwave scatterometer. Through the large pitch angle (26° - 46°) of the fan beam on a low-earth orbit remote sensing satellite (at an altitude of 450 km), it realizes the observation geometry for a large swath (swath > 2000 km). Through fan beam conical scanning, it realizes the observation of all targets within the swath range.

[0063] Figure 2 The schematic diagram of the scatterometer working principle is given. The transmitted signal is sent out by the antenna unit. This transmitted signal is a linear frequency modulation pulse signal with a negative slope or a positive slope transmitted by the method of the present invention, and it is used as the echo signal of the swath area. The echo signal of this swath area enters the receiving unit through the antenna unit. After the receiving unit receives the echo signal, it enters the digital signal processing unit after down-conversion and de-chirping processing. The digital signal processing unit processes the processed signal through analog-to-digital conversion, low-pass filtering, FFT, modulus calculation, etc., and then enters the preprocessing unit to calculate the backscattering coefficient. Finally, the sea surface wind field information is calculated in the inversion unit.

[0064] As Figure 4 shown, judge the azimuth angle of the CSCAT antenna beam. When the antenna beam is looking forward, that is, when the azimuth angle is in the range of 0 - 90° and 270° - 360°, transmit a linear frequency modulation signal with a negative slope of -3.7×10 8 Hz / s, and use this as the final transmitted signal;

[0065] When the antenna beam is looking backward, that is, when the azimuth angle is in the range of 90° - 270°, transmit a linear frequency modulation signal with a positive slope of 3.7×10 8 Hz / s, and use this as the final transmitted signal.

[0066] The known target echo frequency f r can be expressed as the result of the combined action of the echo delay frequency f k and the Doppler frequency f d together.

[0067] f r = f k + f d

[0068] Among them, the subscripts r, d, and k are all used to distinguish each frequency and have no actual meaning.

[0069] Echo delay frequency f k It is the frequency returned by targets at different positions within the footprint, and this frequency is the final transmitted signal extracted by using the method of the present invention:

[0070]

[0071] where K is the frequency modulation slope; t ele corresponds to the antenna elevation angle θ ele and is the echo time for illuminating different positions within the footprint, θ azi is the antenna azimuth angle;

[0072]

[0073] R ele is the echo distance corresponding to the elevation angle θ ele , and c is the speed of light.

[0074]

[0075] r e is the radius of the earth, H is the satellite altitude, α ele corresponds to the elevation angle θ ele and is the geocentric angle.

[0076]

[0077] Doppler frequency f d is generated by the relative motion between the scatterometer and the footprint and varies with different incident angles and azimuth angles when the antenna rotates.

[0078]

[0079] v = V sat ·sinθ ele ·cosθ azi

[0080] where λ is the wavelength of the transmitted signal, r is the relative distance between the scatterometer and the ground footprint, v is the relative velocity between the scatterometer and the ground footprint, and it is a function of the satellite velocity V sat , the azimuth angle θ azi and the elevation angle θ ele .

[0081] The following respectively gives the variation of the echo frequency in two cases where the frequency modulation slope of the transmitted signal is constant and the frequency modulation slope varies with the forward and backward views.

[0082] Simulation Figure 5It shows the variation range of the echo frequency with the antenna azimuth angle when the FM slope is a constant value. It can be seen that the frequency variation range is from -200 kHz to 700 kHz, and the Doppler bandwidth is about 900 kHz.

[0083] Simulation Figure 6 It shows the variation range of the echo frequency with the antenna azimuth angle when the FM slope changes with the forward and backward views. It can be seen that the frequency variation ranges are from 250 kHz to 700 kHz and from -250 kHz to -700 kHz, and the Doppler bandwidth is about 450 kHz.

[0084] It can be seen Figure 6 Relatively Figure 5 The Doppler bandwidth is reduced by half, which not only restricts non-target signals such as clutter and noise from entering the antenna, but also reduces the possibility of range ambiguity. Moreover, the echo bandwidths of the forward and backward views have good symmetry, which provides convenience for subsequent processing.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for extracting positive and negative slope linear frequency modulation transmission signals of a spaceborne scatterometer, the method comprising: Using a spaceborne microwave scatterometer to perform conical scanning on the area to be observed within the swath range through a fan beam, and obtaining the scanning azimuth angle for the area to be observed in real time; Judging whether the antenna transmits a linear frequency modulation pulse signal with a negative slope or a linear frequency modulation pulse signal with a positive slope according to the scanning azimuth angle for the area to be observed obtained in real time; Using a spaceborne microwave scatterometer to perform conical scanning on the area to be observed within the swath range through a fan beam, and obtaining the scanning azimuth angle for the area to be observed in real time; The specific process is as follows: Using a spaceborne microwave scatterometer to perform conical scanning on the area to be observed within the swath range through a fan beam, and obtaining the antenna fan beam azimuth angle for the area to be observed; When the antenna beam is looking forward, determining the corresponding antenna beam azimuth angle range as 0 - 90° and 270° - 360°; When the antenna beam is looking backward, determining the corresponding antenna beam azimuth angle range as 90° - 270°; Judging whether the antenna transmits a linear frequency modulation pulse signal with a negative slope or a linear frequency modulation pulse signal with a positive slope according to the scanning azimuth angle for the area to be observed obtained in real time; The specific process is as follows: Judging whether the antenna beam is looking forward according to the antenna fan beam azimuth angle for the area to be observed obtained in real time, and further judging whether the antenna transmits a linear frequency modulation pulse signal with a negative slope or a linear frequency modulation pulse signal with a positive slope; If the obtained antenna fan beam azimuth angle for the area to be observed is in the range of 0 - 90° or 270° - 360°, then the antenna beam is looking forward, and the antenna transmits a linear frequency modulation pulse signal with a negative slope, and uses it as the final transmission signal; If the obtained antenna fan beam azimuth angle for the area to be observed is in the range of 90 - 270°, then the antenna beam is looking backward, and the antenna transmits a linear frequency modulation pulse signal with a positive slope, and uses it as the final transmission signal.

2. The method for extracting the positive and negative slope linear frequency modulation transmitted signal of the spaceborne scatterometer according to claim 1, wherein The spaceborne microwave scatterometer is a fan beam conical scanning microwave scatterometer.

3. An extraction device for positive and negative slope linear frequency modulation transmitted signals of a spaceborne scatterometer, characterized in that, The device includes: An azimuth angle acquisition module, configured to use a spaceborne microwave scatterometer to perform conical scanning on the area to be observed within the swath range through a fan beam, and obtain the scanning azimuth angle for the area to be observed in real time; and A signal transmission module, configured to judge whether the antenna transmits a linear frequency modulation pulse signal with a negative slope or a linear frequency modulation pulse signal with a positive slope according to the scanning azimuth angle for the area to be observed obtained in real time; The specific implementation process of the azimuth angle acquisition module is; Using a spaceborne microwave scatterometer to perform conical scanning on the area to be observed within the swath range through a fan beam, and obtaining the antenna fan beam azimuth angle for the area to be observed; When the antenna beam is looking forward, determining the corresponding antenna beam azimuth angle range as 0 - 90° and 270° - 360°; When the antenna beam is looking backward, determining the corresponding antenna beam azimuth angle range as 90° - 270°; The specific implementation process of the signal transmission module is; According to the azimuth angle of the antenna sector beam obtained in real time for the area to be observed, it is judged whether the antenna beam is forward-looking, and then it is judged whether to transmit a linear frequency modulation pulse signal with a negative slope or a linear frequency modulation pulse signal with a positive slope; If the azimuth angle of the antenna sector beam obtained for the area to be observed is in the range of 0-90° or 270°-360°, the antenna beam is forward-looking, and the antenna transmits a linear frequency modulation pulse signal with a negative slope, which is used as the final transmitted signal; If the azimuth angle of the antenna sector beam obtained for the area to be observed is in the range of 90-270°, the antenna beam is rearward-looking, and the antenna transmits a linear frequency modulation pulse signal with a positive slope, which is used as the final transmitted signal.

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