A method and device for extracting a local oscillator signal with a pre-offset center frequency

Abstract

The present application belongs to the field of active microwave remote sensing and ocean data processing technology, and particularly relates to a center frequency pre-biased local oscillator signal extraction method and extraction device, which comprises: a satellite-borne scatterometer performs fan beam conical scanning, and according to the relative motion between the satellite ground footprint coverage and the earth, a three-dimensional distribution of Doppler frequency offset with latitude, azimuth and elevation angle is obtained; according to the obtained three-dimensional distribution of Doppler frequency offset with latitude, azimuth and elevation angle, a Doppler frequency offset lookup table is generated according to the division interval of the azimuth angle; the center frequency of the local oscillator signal is pre-biased using the Doppler frequency offset lookup table according to the division interval of the azimuth angle, and a pre-biased local oscillator signal is obtained.

Description

Technical Field

[0001] This invention belongs to the field of active microwave remote sensing and marine data processing technology. Specifically, it relates to a method and device for extracting local oscillator signals with pre-biased center frequency. Background Technology

[0002] Sea surface wind field is an important physical parameter in marine and atmospheric science research and applications. As the most important remote sensing instrument for acquiring global sea surface wind field data, spaceborne microwave scatterometers play a vital role in numerical weather prediction, marine disaster monitoring, marine environmental numerical forecasting, meteorological forecasting, and climate research.

[0003] The ground footprint of the fan-beam conical scanning scatterometer extends over an area of ​​approximately several hundred kilometers in elevation. Simultaneously, the fan-beam antenna performs a conical scan at a certain rotational speed, obtaining multi-azimuth observations of the target while achieving complete coverage of the observation area. However, due to the large elevation range of the fan-beam, the Doppler frequency of the echo fluctuates significantly, resulting in a corresponding increase in Doppler bandwidth and the appearance of Doppler ambiguity. This leads to reduced accuracy in backscattering coefficient calculation and increased wind field inversion error.

[0004] Therefore, existing spaceborne fan-beam conical scanning scatterometers suffer from the problem of large echo Doppler bandwidth and high difficulty in Doppler blur processing. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, this invention proposes a method for extracting local oscillator signals with a pre-biased center frequency. This method includes:

[0006] The spaceborne scatterometer performs a fan-beam conical scan and obtains the three-dimensional distribution of Doppler frequency shift with latitude, azimuth, and elevation angle based on the relative motion between the satellite's ground footprint coverage and the Earth.

[0007] Based on the three-dimensional distribution of the obtained Doppler frequency offset with latitude, azimuth, and elevation angle, a Doppler frequency offset lookup table is generated according to the azimuth interval.

[0008] The intervals are divided according to the azimuth angle. The center frequency of the local oscillator signal is pre-biased using a Doppler frequency offset lookup table to obtain the pre-biased local oscillator signal.

[0009] As one improvement to the above technical solution, the spaceborne scatterometer performs a fan-beam conical scan and obtains the three-dimensional distribution of Doppler frequency shift with latitude, azimuth, and elevation angle based on the relative motion between the satellite's ground footprint coverage and the Earth; the specific implementation process is as follows:

[0010] The spaceborne microwave scatterometer performs conical scanning of targets within the sweep range using a fan-shaped beam;

[0011] The latitude (lat), azimuth (azi), and elevation (ele) are divided into equal intervals according to their respective preset intervals to obtain N. lat A range divided by latitude, N azi The intervals divided according to the azimuth angle and N ele An interval divided according to the pitch angle;

[0012] Based on the relative motion between the satellite's ground footprint coverage and the Earth, the following parameters are calculated: latitude (lat), azimuth (θ). azi and pitch angle θ ele The three-dimensional distribution of Doppler frequency shift f lat，azi，ele ;

[0013]

[0014] Where λ is the wavelength of the transmitted signal; r is the relative distance between the scatterometer and the footprint on the ground, which is affected by the Earth's radius r, which varies with latitude. lat The effect, v is the relative velocity between the scatterometer and the ground footprint; it is related to the satellite velocity V. sat Azimuth θ azi and pitch angle θ ele The function.

[0015] in,

[0016] v = V sat ·sinθ ele ·cosθ azi

[0017] Among them, V sat For satellite velocity; θ azi θ is the azimuth angle. ele The pitch angle.

[0018] As one improvement to the above technical solution, the process of generating a Doppler frequency offset lookup table based on azimuth angle intervals is as follows:

[0019] Based on the three-dimensional distribution of the obtained Doppler frequency offset with latitude, azimuth and pitch angle, the Doppler frequency offset under the maximum pitch angle and the Doppler frequency offset under the minimum pitch angle are obtained.

[0020] Based on the division of pitch angle intervals, select the corresponding maximum and minimum pitch angles;

[0021] The Doppler frequency offset f at the maximum pitch angle lat，azi，elemax Doppler frequency offset f at the minimum pitch angle lat，azi，elemin On average, we get N. lat ×N azi The Doppler frequency shift f varies with latitude and azimuth. lat，azi ;

[0022]

[0023] Based on the division of latitude, f lat，azi The Doppler frequency shift f, which varies with azimuth angle, is obtained by averaging across intervals defined by that latitude. azi ;

[0024]

[0025] Where, N lat The number of latitude intervals;

[0026] Based on the division of azimuth angle intervals, f azi The Doppler frequency shift f, which varies with the azimuth angle, is obtained by averaging across the intervals defined by the azimuth angle. i ;

[0027]

[0028] Where, N azi This represents the number of azimuth intervals.

[0029] Divide the intervals according to the azimuth angle, repeat the above process, and obtain the Doppler frequency shift lookup table.

[0030] As an improvement to the above technical solution, the process of dividing the signal into intervals according to azimuth angle and using a Doppler frequency offset lookup table to pre-bias the center frequency of the local oscillator signal to obtain the pre-biased local oscillator signal is as follows:

[0031] The antenna collects azimuth angle data in real time, dividing the data into intervals based on azimuth angle. A Doppler frequency offset lookup table is then used to obtain the corresponding Doppler frequency offset f that varies with the azimuth angle. i ;

[0032] Using the Doppler frequency shift f that varies with azimuth angle i By biasing the center frequency f0 of the local oscillator signal, the pre-biased local oscillator signal f0+f is obtained. i .

[0033] The present invention also provides a local oscillator signal extraction device with center frequency pre-biased, the device comprising:

[0034] The three-dimensional distribution acquisition module is used by the spaceborne scatterometer to perform fan-beam conical scanning and obtain the three-dimensional distribution of Doppler frequency offset with latitude, azimuth and elevation angle based on the relative motion between the satellite ground footprint coverage and the Earth.

[0035] The lookup table acquisition module is used to generate a Doppler frequency shift lookup table based on the obtained three-dimensional distribution of Doppler frequency shift with latitude, azimuth, and elevation angle, divided into intervals according to azimuth angle; and

[0036] The bias module is used to divide the interval according to the azimuth angle and use the Doppler frequency offset lookup table to pre-bias the center frequency of the local oscillator signal to obtain the pre-biased local oscillator signal.

[0037] As an improvement to the above technical solution, the three-dimensional distribution acquisition module includes:

[0038] The scanning unit is used by the spaceborne microwave scatterometer to perform conical scanning of targets within a swath area using a fan-shaped beam; and

[0039] A three-dimensional distribution unit is used to divide the latitude (lat), azimuth (azi), and elevation (ele) at equal intervals according to their respective preset intervals, resulting in N. lat A range divided by latitude, N azi The intervals divided according to the azimuth angle and N ele An interval divided according to the pitch angle;

[0040] Based on the relative motion between the satellite's ground footprint coverage and the Earth, the following parameters are calculated: latitude (lat), azimuth (θ). azi and pitch angle θ ele The three-dimensional distribution of Doppler frequency shift f lat，azi，ele ;

[0041]

[0042] Where λ is the wavelength of the transmitted signal; r is the relative distance between the scatterometer and the ground footprint; and v is the relative velocity between the scatterometer and the ground footprint.

[0043] in,

[0044] v = V sat ·sinθ ele ·cosθ azi

[0045] Among them, V sat For satellite velocity; θ azi θ is the azimuth angle. ele The pitch angle.

[0046] As one of the improvements to the above technical solution, the specific implementation process of the lookup table acquisition module is as follows:

[0047] Based on the three-dimensional distribution of Doppler frequency shift with latitude, azimuth, and pitch angle, the Doppler frequency shift under the maximum pitch angle and the Doppler frequency shift under the minimum pitch angle are obtained.

[0048] Based on the division of pitch angle intervals, select the corresponding maximum and minimum pitch angles;

[0049] The Doppler frequency offset f at the maximum pitch angle lat，azi，elemax Doppler frequency offset f at the minimum pitch angle lat，azi，elemin On average, we get N. lat ×N azi The Doppler frequency shift f varies with latitude and azimuth. lat，azi ;

[0050]

[0051] Based on the division of latitude, f lat，azi The Doppler frequency shift f, which varies with azimuth angle, is obtained by averaging across intervals defined by that latitude. azi ;

[0052]

[0053] Where, N lat The number of latitude intervals;

[0054] Based on the division of azimuth angle intervals, f azi The Doppler frequency shift f, which varies with the azimuth angle, is obtained by averaging across the intervals defined by the azimuth angle. i ;

[0055]

[0056] Where, N azi This represents the number of azimuth intervals.

[0057] Divide the intervals according to the azimuth angle, repeat the above process, and obtain the Doppler frequency shift lookup table.

[0058] As an improvement to the above technical solution, the bias module includes:

[0059] The offset acquisition unit is used to divide the range according to the azimuth angle. The antenna acquires the azimuth angle in real time and uses a Doppler frequency offset lookup table to obtain the corresponding Doppler frequency offset f that varies with the azimuth angle. i ;and

[0060] Offset element, used to utilize the Doppler frequency offset f that varies with azimuth angle i By biasing the center frequency f0 of the local oscillator signal, the pre-biased local oscillator signal f0+f is obtained. i .

[0061] The beneficial effects of this invention compared to the prior art are:

[0062] 1. The method of the present invention corrects the Doppler frequency shift caused by the relative motion between the satellite and the Earth, reduces the Doppler bandwidth, and reduces the echo Doppler frequency ambiguity;

[0063] 2. The method of the present invention corrects the Doppler frequency shift by pre-biasing the center frequency of the local oscillator signal, thereby reducing the software burden and lowering the implementation complexity. Attached Figure Description

[0064] Figure 1 This is a schematic diagram of the observation geometry of the spaceborne scatterometer of the present invention performing conical scanning using a fan-shaped beam;

[0065] Figure 2 This is a schematic diagram illustrating the principle of generating three-dimensional Doppler frequency shifts using the method of the present invention.

[0066] Figure 3 This is a schematic diagram illustrating the generation principle of the Doppler frequency offset lookup table generated by dividing intervals according to azimuth angle in the method of the present invention.

[0067] Figure 4 This is a schematic diagram of the pre-biasing of the local oscillator signal in the method of the present invention.

[0068] Figure 5 This is a schematic diagram of the scatterometer antenna scanning geometry. Detailed Implementation

[0069] The present invention will now be further described in conjunction with the accompanying drawings and examples.

[0070] like Figure 1 As shown, the present invention provides a method for extracting a local oscillator signal with a pre-biased center frequency, the method comprising:

[0071] The spaceborne scatterometer performs a fan-beam conical scan and obtains the three-dimensional distribution of Doppler frequency shift with latitude, azimuth, and elevation angle based on the relative motion between the satellite's ground footprint coverage and the Earth.

[0072] Specifically, the spaceborne microwave scatterometer performs a conical scan of the target within the sweep range using a fan-shaped beam;

[0073] The latitude (lat), azimuth (azi), and elevation (ele) are divided into equal intervals according to their respective preset intervals to obtain N. lat A range divided by latitude, N azi The intervals divided according to the azimuth angle and N ele The intervals are divided according to the pitch angle; the purpose is to make the subsequent Doppler compensation simple and fast. According to the accuracy requirements of Doppler frequency offset, the latitude, azimuth angle and pitch angle are divided at equal intervals, and the Doppler frequency offsets within the divided intervals are averaged.

[0074] Based on the relative motion between the satellite's ground footprint coverage and the Earth, the following parameters are calculated: latitude (lat), azimuth (θ). azi and pitch angle θ ele The three-dimensional distribution of Doppler frequency shift f lat，azi，ele ;

[0075]

[0076] Where λ is the wavelength of the transmitted signal; r is the relative distance between the scatterometer and the footprint on the ground, which is affected by the Earth's radius r, which varies with latitude. lat The effect, v is the relative velocity between the scatterometer and the ground footprint; it is related to the satellite velocity V. sat Azimuth θ azi and pitch angle θ ele The function.

[0077] in,

[0078] v = V sat ·sinθ ele ·cosθ azi

[0079] Among them, V sat For satellite velocity; θ azi θ is the azimuth angle. ele The pitch angle.

[0080] like Figure 2 As shown, a geocentric inertial coordinate system, a geocentric-ground-fixed coordinate system, and a latitude-longitude-height coordinate system are established respectively. Based on the satellite orbit model and the scatterometer model, the relative distance between the satellite and the ground footprint and the relative distance between the satellite and the scatterometer are obtained. After transforming the two coordinate systems through the geocentric inertial coordinate system, the geocentric-ground-fixed coordinate system, and the latitude-longitude-height coordinate system, the relative distance r between the scatterometer and the ground footprint is obtained. The entire process is a prior art known in the art and can be obtained by those skilled in the art based on common knowledge in the art.

[0081] like Figure 2 As shown, the satellite velocity is obtained based on the satellite orbit model and the scatterometer model. After transformation through the geocentric inertial coordinate system, the geocentric-ground-fixed coordinate system, and the latitude-longitude-height coordinate system, the relative velocity v between the scatterometer and the ground footprint is obtained. The entire process is known prior art in the field and can be obtained by those skilled in the art based on common knowledge in the field.

[0082] The Doppler frequency shift is calculated based on the relative distance r between the scatterometer and the ground footprint, and the relative velocity v between them.

[0083] A Doppler frequency offset lookup table is generated based on the azimuth angle intervals.

[0084] Specifically, based on the three-dimensional distribution of the Doppler frequency shift with latitude, azimuth, and pitch angle, the Doppler frequency shift under the maximum pitch angle and the Doppler frequency shift under the minimum pitch angle are obtained.

[0085] Based on the division of pitch angle intervals, select the corresponding maximum and minimum pitch angles;

[0086] The Doppler frequency offset f at the maximum pitch angle lat，azi，elemax Doppler frequency offset f at the minimum pitch angle lat，azi，elemin On average, we get N. lat ×N azi The Doppler frequency shift f varies with latitude and azimuth. lat，azi ;

[0087]

[0088] Based on the division of latitude, f lat，azi The Doppler frequency shift f, which varies with azimuth angle, is obtained by averaging across intervals defined by that latitude. azi ;

[0089]

[0090] Where, N lat The number of latitude intervals;

[0091] Based on the division of azimuth angle intervals, f azi The Doppler frequency shift f, which varies with the azimuth angle, is obtained by averaging across the intervals defined by the azimuth angle. i ;

[0092]

[0093] Where, N azi This represents the number of azimuth intervals.

[0094] Divide the intervals according to the azimuth angle, repeat the above process, and obtain the Doppler frequency shift lookup table.

[0095] The intervals are divided according to the azimuth angle. The center frequency of the local oscillator signal is pre-biased using a Doppler frequency offset lookup table to obtain the pre-biased local oscillator signal.

[0096] Specifically, based on the azimuth angle division, the antenna collects the azimuth angle in real time, and uses a Doppler frequency offset lookup table to obtain the corresponding Doppler frequency offset f that varies with the azimuth angle. i ;

[0097] Using the Doppler frequency shift f that varies with azimuth angle iBy biasing the center frequency f0 of the local oscillator signal, the pre-biased local oscillator signal f0+f is obtained. i .

[0098] The present invention also provides a local oscillator signal extraction device with center frequency pre-biased, the device comprising: a three-dimensional distribution acquisition module, a lookup table acquisition module, and a bias module;

[0099] The three-dimensional distribution acquisition module is used for the spaceborne scatterometer to perform fan-beam conical scanning and obtain the three-dimensional distribution of Doppler frequency offset with latitude, azimuth and elevation angle based on the relative motion between the satellite ground footprint coverage and the Earth.

[0100] Specifically, the three-dimensional distribution acquisition module includes:

[0101] The scanning unit is used by the spaceborne microwave scatterometer to perform conical scanning of targets within a swath area using a fan-shaped beam; and

[0102] A three-dimensional distribution unit is used to divide the latitude (lat), azimuth (azi), and elevation (ele) at equal intervals according to their respective preset intervals, resulting in N. lat A range divided by latitude, N azi The intervals divided according to the azimuth angle and N ele An interval divided according to the pitch angle;

[0103] Based on the relative motion between the satellite's ground footprint coverage and the Earth, the following parameters are calculated: latitude (lat), azimuth (θ). azi and pitch angle θ ele The three-dimensional distribution of Doppler frequency shift f lat，azi，ele ;

[0104]

[0105] Where λ is the wavelength of the transmitted signal; r is the relative distance between the scatterometer and the ground footprint; and v is the relative velocity between the scatterometer and the ground footprint.

[0106] in,

[0107] v = V sat ·sinθ ele ·cosθ azi

[0108] Among them, V sat For satellite velocity; θ azi θ is the azimuth angle. ele The pitch angle.

[0109] The lookup table acquisition module is used to generate a Doppler frequency offset lookup table based on the obtained three-dimensional distribution of Doppler frequency offset with latitude, azimuth angle and elevation angle, according to the interval division of azimuth angle.

[0110] Specifically, based on the three-dimensional distribution of the Doppler frequency shift with latitude, azimuth, and pitch angle, the Doppler frequency shift under the maximum pitch angle and the Doppler frequency shift under the minimum pitch angle are obtained.

[0111] Based on the division of pitch angle intervals, select the corresponding maximum and minimum pitch angles;

[0112] The Doppler frequency offset f at the maximum pitch angle lat，azi，elemax Doppler frequency offset f at the minimum pitch angle lat，azi，elemin On average, we get N. lat ×N azi The Doppler frequency shift f varies with latitude and azimuth. lat，azi ;

[0113]

[0114] Based on the division of latitude, f lat，azi The Doppler frequency shift f, which varies with azimuth angle, is obtained by averaging across intervals defined by that latitude. azi ;

[0115]

[0116] Where, N lat The number of latitude intervals;

[0117] Based on the division of azimuth angle intervals, f azi The Doppler frequency shift f, which varies with the azimuth angle, is obtained by averaging across the intervals defined by the azimuth angle. i ;

[0118]

[0119] Where, N azi This represents the number of azimuth intervals.

[0120] Divide the intervals according to the azimuth angle, repeat the above process, and obtain the Doppler frequency shift lookup table.

[0121] The offset module is used to divide the interval according to the azimuth angle and use the Doppler frequency offset lookup table to pre-offset the center frequency of the local oscillator signal to obtain the pre-offset local oscillator signal.

[0122] Specifically, the bias module includes:

[0123] The offset acquisition unit is used to divide the range according to the azimuth angle. The antenna acquires the azimuth angle in real time and uses a Doppler frequency offset lookup table to obtain the corresponding Doppler frequency offset f that varies with the azimuth angle. i ;and

[0124] Offset element, used to utilize the Doppler frequency offset f that varies with azimuth angle i By biasing the center frequency f0 of the local oscillator signal, the pre-biased local oscillator signal f0+f is obtained. i .

[0125] Example 1

[0126] like Figure 1 As shown, the Sino-French Ocean Satellite Microwave Scatterometer (CSCAT) of this invention is a fan-beam conical scanning microwave scatterometer. It achieves observation geometry of a large swath (swath > 2000 km) by using a fan-beam (elevation angle 26°-46°) on a low-orbit remote sensing satellite (altitude 500 km). By using fan-beam conical scanning, it achieves observation of all targets within the swath range.

[0127] like Figure 5 As shown, the relative motion between the satellite and the ground target P varies with the satellite velocity V. sat Antenna scanning elevation angle θ ele Azimuth θ azi Earth's radius r varying with latitude lat The impact.

[0128] like Figure 2 As shown, based on the relative motion between the satellite ground footprint coverage and the Earth, the Doppler frequency shift is calculated in three dimensions with latitude, azimuth, and elevation. The division criteria are: 5° intervals for latitude, 64 intervals with equal azimuth intervals of 5.625° each, and 40 intervals with equal elevation intervals, generating a 3D Doppler frequency shift of size 36×64×40.

[0129] like Figure 3 As shown, the Doppler frequency offsets with the largest and smallest pitch angles are first averaged to generate a 3D Doppler frequency offset of size 36×64. Then, the Doppler frequency offsets of each latitude interval are averaged to obtain a Doppler frequency offset lookup table of size 64 that varies with azimuth angle.

[0130] like Figure 3 and 4 As shown, the antenna beam azimuth angle is determined when the scatterometer is working. Based on the azimuth angle, the corresponding Doppler frequency offset is extracted from the lookup table. This offset is then used to pre-bias the center frequency of the local oscillator signal, resulting in the pre-biased local oscillator signal, i.e., the pre-biased local oscillator signal f0+f. i The signal is then processed by combining it with the real-time intermediate frequency echo signal for deskewing and other subsequent processing.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for extracting a local oscillator signal with a pre-biased center frequency, the method comprising: The spaceborne scatterometer performs a fan-beam conical scan and obtains the three-dimensional distribution of Doppler frequency shift with latitude, azimuth, and elevation angle based on the relative motion between the satellite's ground footprint coverage and the Earth. Based on the three-dimensional distribution of the obtained Doppler frequency offset with latitude, azimuth, and elevation angle, a Doppler frequency offset lookup table is generated according to the azimuth interval. The intervals are divided according to the azimuth angle, and the center frequency of the local oscillator signal is pre-biased using the Doppler frequency offset lookup table to obtain the pre-biased local oscillator signal. The process of generating a Doppler frequency shift lookup table based on azimuth angle intervals is as follows: Based on the three-dimensional distribution of the obtained Doppler frequency offset with latitude, azimuth and pitch angle, the Doppler frequency offset under the maximum pitch angle and the Doppler frequency offset under the minimum pitch angle are obtained. Based on the division of pitch angle intervals, select the corresponding maximum and minimum pitch angles; Doppler frequency offset at maximum pitch angle Doppler frequency offset at minimum pitch angle On average, we get Doppler frequency shift that varies with latitude and azimuth. ; ； Based on the division of latitude, The Doppler frequency shift as a function of azimuth angle is obtained by averaging across intervals defined by that latitude. ; ； in, The number of latitude intervals; Based on the division of azimuth angles, The Doppler frequency shift as a function of the azimuth angle is obtained by averaging across the intervals defined by the azimuth angle. ; ； in, This represents the number of azimuth intervals. Divide the intervals according to the azimuth angle, repeat the above process, and obtain the Doppler frequency shift lookup table; The process of dividing the signal into intervals by azimuth angle and using a Doppler frequency offset lookup table to pre-bias the center frequency of the local oscillator signal to obtain the pre-biased local oscillator signal is as follows: The antenna collects azimuth angle data in real time, dividing the data into intervals based on azimuth angle. A Doppler frequency offset lookup table is then used to obtain the corresponding Doppler frequency offset that varies with azimuth angle. ; Using the Doppler frequency shift that varies with azimuth angle The center frequency of the local oscillator signal Biasing is applied to obtain the pre-biased local oscillator signal. .

2. The method for extracting the local oscillator signal with pre-biased center frequency according to claim 1, characterized in that, The spaceborne scatterometer performs a fan-beam conical scan and obtains the three-dimensional distribution of Doppler frequency shift with latitude, azimuth, and elevation angle based on the relative motion between the satellite's ground footprint coverage and the Earth. The specific implementation process is as follows: The spaceborne microwave scatterometer performs conical scanning of targets within the sweep range using a fan-shaped beam; Latitude (lat), azimuth (azi), and elevation (ele) are divided into equal intervals according to their respective preset intervals to obtain... A range divided by latitude, The intervals divided according to the azimuth angle and the sum An interval divided according to the pitch angle; Based on the relative motion between the satellite's ground footprint coverage and the Earth, the following parameters are calculated: latitude (lat), azimuth (...) and pitch angle Doppler frequency shift of three-dimensional distribution ; ； in, The wavelength of the transmitted signal; The relative distance between the scatterometer and the ground footprint is subject to the Earth's radius, which varies with latitude. Influence, The relative velocity between the scatterometer and the ground footprint; it is related to the satellite velocity. Azimuth and pitch angle The function; in, ； in, For satellite speed; It is the azimuth angle; The pitch angle.

3. A local oscillator signal extraction device with pre-biased center frequency, characterized in that, The device includes: The three-dimensional distribution acquisition module is used by the spaceborne scatterometer to perform fan-beam conical scanning and obtain the three-dimensional distribution of Doppler frequency offset with latitude, azimuth and elevation angle based on the relative motion between the satellite ground footprint coverage and the Earth. The lookup table acquisition module is used to generate a Doppler frequency shift lookup table based on the obtained three-dimensional distribution of Doppler frequency shift with latitude, azimuth, and elevation angle, divided into intervals according to azimuth angle; and The bias module is used to divide the interval according to the azimuth angle and use the Doppler frequency offset lookup table to pre-bias the center frequency of the local oscillator signal to obtain the pre-biased local oscillator signal. The specific implementation process of the lookup table retrieval module is as follows: Based on the three-dimensional distribution of Doppler frequency shift with latitude, azimuth, and pitch angle, the Doppler frequency shift under the maximum pitch angle and the Doppler frequency shift under the minimum pitch angle are obtained. Based on the division of pitch angle intervals, select the corresponding maximum and minimum pitch angles; Doppler frequency offset at maximum pitch angle Doppler frequency offset at minimum pitch angle On average, we get Doppler frequency shift that varies with latitude and azimuth. ; ； Based on the division of latitude, The Doppler frequency shift as a function of azimuth angle is obtained by averaging across intervals defined by that latitude. ; ； in, The number of latitude intervals; Based on the division of azimuth angles, The Doppler frequency shift as a function of the azimuth angle is obtained by averaging across the intervals defined by the azimuth angle. ; ； in, This represents the number of azimuth intervals. Divide the intervals according to the azimuth angle, repeat the above process, and obtain the Doppler frequency shift lookup table; The bias module includes: The offset acquisition unit is used to divide the range according to the azimuth angle. The antenna acquires the azimuth angle in real time and uses a Doppler frequency offset lookup table to obtain the corresponding Doppler frequency offset that varies with the azimuth angle. ;and Offset unit, used to utilize Doppler frequency offset that varies with azimuth angle The center frequency of the local oscillator signal Biasing is applied to obtain the pre-biased local oscillator signal. .

4. The local oscillator signal extraction device with pre-biased center frequency according to claim 3, characterized in that, The three-dimensional distribution acquisition module includes: The scanning unit is used by the spaceborne microwave scatterometer to perform conical scanning of targets within a swath area using a fan-shaped beam; and Three-dimensional distribution cells are used to divide latitude (lat), azimuth (azi), and elevation (ele) at equal intervals according to their respective preset intervals, resulting in... A range divided by latitude, The intervals divided according to the azimuth angle and the sum An interval divided according to the pitch angle; Based on the relative motion between the satellite's ground footprint coverage and the Earth, the following parameters are calculated: latitude (lat), azimuth (...) and pitch angle Doppler frequency shift of three-dimensional distribution ; ； in, The wavelength of the transmitted signal; The relative distance between the scatterometer and the ground footprint; The relative velocity between the scatterometer and the ground footprint; in, ； in, For satellite speed; It is the azimuth angle; The pitch angle.

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