A method and system for calculating wave spectrum of a spaceborne ocean spectrometer

Abstract

The present invention belongs to the technical field of wave spectrum estimation of spaceborne ocean spectrometers, and discloses a wave spectrum calculation method and system for spaceborne ocean spectrometers, comprising: performing k range gate averaging on a received power signal #imgabs0# to obtain a received power signal #imgabs1# after the range gate averaging; calculating the Fourier transform #imgabs3# of the received power signal #imgabs2# to calculate the wave spectrum P of the received power signal #imgabs4#; k (ω); Based on the time-shift property of Fourier transform, the wave spectrum P k (ω) is expanded to obtain the fluctuation spectrum P(ω) and the fluctuation spectrum P k (ω) to realize the fluctuation spectrum calculation; wherein P(ω) is the fluctuation spectrum of the received power signal #imgabs5#. The present invention is based on the fluctuation spectrum P after the range gate average k (ω) is used to derive the wave spectrum P(ω) without range gate averaging. The calculation method is simple, and the subsequent estimation of the wave directional spectrum based on P(ω) can also improve the accuracy of the wave directional spectrum estimation.

Description

Technical Field

[0001] The present invention belongs to the technical field of wave spectrum estimation of a space-borne ocean spectrometer, and more specifically, relates to a wave spectrum calculation method and system for a space-borne ocean spectrometer. Background Art

[0002] The study of many dynamic processes in the ocean requires precise information about ocean waves. A spaceborne ocean spectrometer is a microwave sensor specifically designed to detect the directional spectrum of ocean waves. It can obtain a wave spectrum that includes both the directional spectrum and the speckle noise spectrum. After removing the speckle noise spectrum from the wave spectrum, the directional spectrum can be obtained. The SWIM (Surface Wave Investigation and Monitoring) satellite-borne spectrometer aboard the Sino-French ocean satellite is the world's first spaceborne microwave radar focused on detecting ocean wave spectra. SWIM emits short pulse beams at six smaller incident angles of 0°, 2°, 4°, 6°, 8°, and 10° to illuminate the sea surface in turn, and receives scattered field signals modulated by the long waves of the sea surface, i.e., echo signals. The echo signals then pass through a square-law detector, normalization operation, slow-time filter, and fast spectrum analyzer to obtain the wave spectrum.

[0003] To reduce the data rate, the received power signal is typically range-gate averaged before entering the fast spectrum analyzer. For example, the received power signal at 6°, 8°, and 10° in SWIM is averaged over two, three, and three range gates, respectively, before performing the wave spectrum estimation. However, because range-gate averaging reduces the amount of data, using the received power signal after range-gate averaging for wave spectrum estimation reduces the accuracy of the wave spectrum, which in turn results in inaccurate wave directional spectra. Summary of the Invention

[0004] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides a method and system for calculating the wave spectrum of a space-borne ocean spectrometer, the purpose of which is to improve the accuracy of wave spectrum calculation.

[0005] To achieve the above object, according to a first aspect of the present invention, a method for calculating a wave spectrum of a spaceborne ocean spectrometer is provided, comprising:

[0006] Receive power signal Perform k range gate averages to obtain the received power signal after range gate average

[0007]

[0008] Among them, the received power signal is the power signal corresponding to the echo signal of the spaceborne ocean spectrometer; β p It represents the bandwidth of the pulses transmitted by the spaceborne ocean spectrometer;

[0009] Calculate the received power signal Fourier transform of To calculate the received power signal The fluctuation spectrum P k (ω);

[0010] Based on the time-shift property of Fourier transform, the wave spectrum P k (ω) is expanded to obtain the fluctuation spectrum P(ω) and the fluctuation spectrum P k (ω) to realize the fluctuation spectrum calculation; where P(ω) is the received power signal The fluctuation spectrum.

[0011] Furthermore, the fluctuation spectrum P(ω) and the fluctuation spectrum P k The relationship between (ω) is:

[0012]

[0013] in, β p It represents the bandwidth of the pulses transmitted by the spaceborne ocean spectrometer.

[0014] Furthermore, it also includes the fluctuation spectrum P(ω) and the fluctuation spectrum P k (ω) is converted into the wavenumber domain:

[0015]

[0016] Among them, P k (K,Φ) is P k (ω) is expressed in the wavenumber domain, K represents the current wavenumber, Φ is the azimuth angle of the target detected by the spaceborne ocean spectrometer relative to the ground of the satellite orbit; P(K,Φ) is the wavenumber domain expression of P(ω); c represents the speed of light, and θ is the incident angle of the current beam.

[0017] Furthermore, the received power signal Fourier transform of for:

[0018]

[0019] in, Indicates the received power signal The Fourier transform of .

[0020] Furthermore, the corresponding k values ​​of the satellite-borne ocean spectrometer under 6°, 8° and 10° beams are 2, 3 and 3 respectively.

[0021] According to a second aspect of the present invention, a spaceborne ocean spectrometer wave spectrum calculation system is provided, which is used to execute the spaceborne ocean spectrometer wave spectrum calculation method according to any one of the first aspects, comprising:

[0022] The received power signal calculation module after the range gate average is used to calculate the received power signal Perform k range gate averages to obtain the received power signal after range gate average

[0023]

[0024] Among them, the received power signal is the power signal corresponding to the echo signal of the spaceborne ocean spectrometer; β p It represents the bandwidth of the pulses transmitted by the spaceborne ocean spectrometer;

[0025] The first wave spectrum calculation module is used to calculate the received power signal Fourier transform of To calculate the received power signal The fluctuation spectrum P k (ω);

[0026] The second wave spectrum calculation module is used to convert the wave spectrum P k (ω) is expanded to obtain the fluctuation spectrum P(ω) and the fluctuation spectrum P k (ω) to realize the fluctuation spectrum calculation; where P(ω) is the received power signal The fluctuation spectrum.

[0027] According to a third aspect of the present invention, there is provided an electronic device comprising a computer-readable storage medium and a processor;

[0028] The computer-readable storage medium is used to store executable instructions;

[0029] The processor is used to read the executable instructions stored in the computer-readable storage medium to execute the wave spectrum calculation method of the space-borne ocean spectrometer described in any one of the first aspects.

[0030] According to a fourth aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored. When the program is executed by a processor, the method for calculating the wave spectrum of a space-borne ocean spectrometer as described in any one of the first aspects is implemented.

[0031] According to a fifth aspect of the present invention, a computer program product is provided. When the computer program product is run on a computer, the computer is enabled to execute the method for calculating the wave spectrum of a space-borne ocean spectrometer as described in any one of the first aspects.

[0032] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0033] (1) The present invention takes into account that in order to reduce the data rate, the received power signal of the satellite-borne ocean spectrometer needs to be averaged by the range gate. However, the calculation of the fluctuation spectrum by using the received power signal after the range gate averaging will reduce the accuracy of the fluctuation spectrum calculation. Therefore, in order to be able to infer the accurate fluctuation spectrum without the range gate averaging based on the fluctuation spectrum after the range gate averaging under the premise of performing the range gate averaging, the present invention is different from the existing method of averaging the power signal of each k range gates. Use the power signals of any k adjacent range gates The corresponding Fourier transform and fluctuation spectrum model P are calculated based on the received power signal after the range gate average. k (ω), we only need to use the time-shift property of Fourier transform to obtain the fluctuation spectrum P after averaging over k range gates. k The relationship between (ω) and the wave spectrum P(ω) without range gate averaging, P(ω) is the precise wave spectrum to be solved. The wave spectrum calculation method of the present invention is simple, and the subsequent estimation of the wave direction spectrum based on the wave spectrum P(ω) without range gate averaging can also improve the accuracy of the wave direction spectrum estimation.

[0034] (2) Furthermore, the present invention also provides the fluctuation spectrum P after averaging k range gates. k The specific analytical relationship between (ω) and the fluctuation spectrum P(ω) without range gate averaging is based on the analytical relationship. k (ω)Quickly calculate the accurate fluctuation spectrum P(ω). BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of a wave spectrum calculation method for a spaceborne ocean spectrometer in an embodiment of the present invention.

[0036] Figure 2 This is the fluctuation spectrum of SWIM under a 6° beam in an embodiment of the present invention.

[0037] Figure 3 This is the fluctuation spectrum of SWIM under 8° beam in an embodiment of the present invention.

[0038] Figure 4This is the fluctuation spectrum of SWIM under a 10° beam in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0040] In the present invention, the terms "first", "second", etc. in the present invention and the accompanying drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0041] Example 1

[0042] In an embodiment of the present invention, in order to reduce the data rate, the received power signal needs to be range-gate averaged before entering the fast spectrum analyzer. However, the power spectrum (fluctuation spectrum) calculated by inputting the received power signal after range gate averaging into the fast spectrum analyzer is not very accurate. How to obtain the accurate fluctuation spectrum corresponding to the received power signal without range gate averaging while performing range gate averaging is a technical problem that needs to be solved by the present invention.

[0043] In the embodiment of the present invention, a received power signal assumed not to be averaged by a range gate and its corresponding fluctuation spectrum are first analyzed.

[0044] Assume that the incident field signal at the center of the pulse beam emitted by the spaceborne ocean spectrometer is e0(τ). In the embodiment of the present invention, the spaceborne ocean spectrometer is SWIM; the echo signal received by the spectrometer is e s (τ, t); where τ represents fast time and t represents slow time;

[0045] The output of the square law detector is p(τ,t)=|e s (τ,t)| 2 . Let its Fourier transform be Then we have:

[0046]

[0047] The output of the square law detector is normalized, and the received power signal p after normalization is ′ (τ,t) is:

[0048]

[0049] Where <*> means taking the ensemble average of *.

[0050] The received power signal p after normalization is ′ (τ,t) input slow time filter, that is, in the integration time T int Internal pair p ′ (τ, t) is averaged to obtain the received power signal without range gate averaging

[0051]

[0052] Use a fast spectrum analyzer to calculate the power spectrum, that is, the fluctuation spectrum P(ω):

[0053]

[0054] in, express The Fourier transform of ; P(ω) is the precise wave spectrum required by the present invention.

[0055] After the above analysis, we can know that the following focus is how to obtain the received power signal without range gate averaging based on the fluctuation spectrum corresponding to the received power signal after range gate averaging. The corresponding fluctuation spectrum is also the precise fluctuation spectrum P(ω).

[0056] like Figure 1 As shown, in an embodiment of the present invention, a method for calculating a wave spectrum of a spaceborne ocean spectrometer is provided, comprising:

[0057] The received power signal output by the slow time filter Perform k range gate averages to obtain the received power signal after range gate average

[0058]

[0059] in, β p Indicates the bandwidth of the pulse transmitted by the satellite-borne ocean spectrometer; k is set according to actual needs. For example, in the embodiment of the present invention, the received power signals corresponding to 6°, 8° and 10° of SWIM are averaged for 2, 3 and 3 range gates respectively, that is, k is 2, 3 and 3 respectively; it should be noted that in other embodiments, the range gate average can also be placed after the output of the square law detector or after the normalization operation, and adjusted according to actual needs. That is, the received power signal It only represents the power signal corresponding to the echo signal of the space-borne ocean spectrometer, and is not necessarily the received power signal output by the slow-time filter.

[0060] Calculate the received power signal after range gate averaging Fourier transform of

[0061]

[0062] Then the fluctuation spectrum model P after range gate averaging is k (ω) is:

[0063]

[0064] because:

[0065]

[0066] The above Bring in In the above equation, we can get:

[0067]

[0068] Substitute the above formula into According to the time-shift property of Fourier transform, the fluctuation spectrum P after averaging over k range gates can be obtained: k The relationship between (ω) and the fluctuation spectrum P(ω) without range gate averaging is:

[0069]

[0070]

[0071] Converting this formula to the wavenumber domain yields:

[0072]

[0073] Among them, P k (K,Φ) is P k (ω) is expressed in the wavenumber domain, K represents the current wavenumber, Φ is the azimuth angle of the target detected by the spaceborne ocean spectrometer relative to the ground of the satellite orbit; P(K,Φ) is the wavenumber domain expression of P(ω); c represents the speed of light, and θ is the incident angle of the current beam.

[0074] Specifically, in the embodiment of the present invention, the received power signals corresponding to 6°, 8° and 10° of SWIM are averaged over 2, 3 and 3 range gates respectively, that is, k is 2, 3 and 3 respectively, as an example to further illustrate the above method.

[0075] For the received power signal corresponding to 6° of SWIM, two range gates are averaged, that is,

[0076]

[0077]

[0078] The wave spectrum model at this time is:

[0079]

[0080] but:

[0081]

[0082]

[0083] Similarly, the relationship P(ω) between the fluctuation spectrum model P3(ω) and the precise fluctuation spectrum after averaging three range gates for the received power signal corresponding to 8° or 10° of SWIM is:

[0084]

[0085] Converted to the wavenumber domain, we can get:

[0086]

[0087]

[0088] The following simulations are performed using the data from the 4762nd macrocycle of the 6, 8, and 10 degree beams of the Sino-French ocean satellite SWIM.

[0089] Simulation 1: Directly calculate the fluctuation spectrum without range gate averaging, that is, the received power signal output by the slow time filter Directly calculate the corresponding fluctuation spectrum, such as Figure 2-Figure 4 As shown by the black solid line in .

[0090] Simulation 2: Based on the fluctuation spectrum calculated in Simulation 1, the fluctuation spectrum after range gate averaging is calculated based on the relationship between the fluctuation spectrum without range gate averaging and the fluctuation spectrum after range gate averaging provided in the embodiment of the present invention, as shown in FIG. Figure 2-Figure 4 This is shown in red in the implementation.

[0091] Simulation 3: Received power signal output by slow-time filter The corresponding fluctuation spectrum is calculated after performing range gate averaging directly; for 6°, 8°, and 10° beams, 2, 3, and 3 range gate averaging are used respectively, as shown in the following example: Figure 2-Figure 4 As shown by the blue dotted line in .

[0092] Comparing Simulations 1 and 2, or 1 and 3, reveals that the amplitude of the fluctuation spectrum after range-gate averaging has changed compared to the amplitude before range-gate averaging. Furthermore, the amplitude of this change varies at different locations in the wavenumber domain, indicating that directly using the fluctuation spectrum after range-gate averaging is inaccurate. The fluctuation spectra obtained in Simulations 2 and 3 are completely consistent, demonstrating the accuracy of the method of the present invention.

[0093] In the present invention, in order to be able to infer the accurate fluctuation spectrum without range gate averaging based on the fluctuation spectrum after range gate averaging under the premise of range gate averaging, the present invention performs the received power signal output by the slow time filter on the received power signal output by the slow time filter. Use the power signals of any k adjacent range gates The received power signal after the range gate is averaged, and its corresponding Fourier transform and fluctuation spectrum model P is calculated based on the received power signal after the range gate is averaged. k (ω), we only need to use the time-shift property of Fourier transform to obtain the fluctuation spectrum P after averaging over k range gates. k The relationship between (ω) and the wave spectrum P(ω) without range gate averaging, P(ω) is the precise wave spectrum to be solved. The wave spectrum calculation method of the present invention is simple, and the wave direction spectrum is estimated based on the wave spectrum P(ω) without range gate averaging, which can improve the accuracy of the wave direction spectrum estimation.

[0094] Example 2

[0095] An embodiment of the present invention provides a spaceborne ocean spectrometer wave spectrum calculation system, which is used to execute the spaceborne ocean spectrometer wave spectrum calculation method in the above-mentioned embodiment 1, including:

[0096] The received power signal calculation module after the range gate average is used to calculate the received power signal Perform k range gate averages to obtain the received power signal after range gate average

[0097]

[0098] Among them, the received power signal is the power signal corresponding to the echo signal of the spaceborne ocean spectrometer; β p It represents the bandwidth of the pulses transmitted by the spaceborne ocean spectrometer;

[0099] The first wave spectrum calculation module is used to calculate the received power signal Fourier transform of To calculate the received power signal The fluctuation spectrum P k(ω);

[0100] The second wave spectrum calculation module is used to convert the wave spectrum P k (ω) expansion, we get the fluctuation spectrum P(ω) and the fluctuation spectrum P k (ω) to realize the fluctuation spectrum calculation; where P(ω) is the received power signal The fluctuation spectrum.

[0101] Among them, the first wave spectrum is the received power signal The corresponding fluctuation spectrum P after range gate averaging k (ω), the second wave spectrum is the received power signal The specific implementation of each module is described in the corresponding steps of the above embodiment 1, and will not be repeated here.

[0102] Example 3

[0103] An embodiment of the present invention provides an electronic device, including a computer-readable storage medium and a processor;

[0104] Computer-readable storage media for storing executable instructions;

[0105] The processor is configured to read executable instructions stored in a computer-readable storage medium to execute the method for calculating the wave spectrum of a spaceborne ocean spectrometer in Example 1. For related technical solutions, see Example 1 and will not be described in detail here.

[0106] Example 4

[0107] An embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon. When executed by a processor, the program implements the method for calculating the wave spectrum of a spaceborne ocean spectrometer as described in Example 1. For related technical solutions, see Example 1 and will not be described in detail here.

[0108] Example 5

[0109] The present invention provides a computer program product that, when executed on a computer, causes the computer to execute the wave spectrum calculation method for a spaceborne ocean spectrometer according to any one of the embodiments 1. For related technical solutions, see embodiment 1 and will not be described in detail here.

[0110] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for calculating wave spectrum of a spaceborne ocean spectrometer, characterized in that: include: Receive power signal conduct The received power signal after the range gate average is obtained : Among them, the received power signal is the power signal corresponding to the echo signal of the spaceborne ocean spectrometer; , It represents the bandwidth of the pulses transmitted by the spaceborne ocean spectrometer; Calculate the received power signal Fourier transform of , to calculate the received power signal The fluctuation spectrum ; Based on the time-shift property of Fourier transform, the wave spectrum Expand to get the wave spectrum With the fluctuation spectrum The relationship between them is used to realize the wave spectrum calculation; among them, The received power signal The fluctuation spectrum of The fluctuation spectrum With the fluctuation spectrum The relationship between them is: in, , It represents the bandwidth of the pulses transmitted by the spaceborne ocean spectrometer.

2. The method for calculating the wave spectrum of a spaceborne ocean spectrometer according to claim 1, wherein: Also includes the fluctuation spectrum With the fluctuation spectrum The relationship between is converted into the wavenumber domain: in, for The wave number domain expression of Indicates the current wave number. Detect the azimuth of the target relative to the satellite orbit ground for the spaceborne ocean spectrometer; for The wave number domain expression of , represents the speed of light, is the incident angle of the current beam.

3. The method for calculating the wave spectrum of a spaceborne ocean spectrometer according to claim 1 or 2, characterized in that: The received power signal Fourier transform of for: in, , indicating the received power signal The Fourier transform of .

4. The method for calculating the wave spectrum of a spaceborne ocean spectrometer according to claim 3, wherein: The satellite-borne ocean spectrometer corresponds to the following conditions under 6°, 8° and 10° beams: The values ​​are 2, 3, and 3 respectively.

5. A spaceborne ocean spectrometer wave spectrum calculation system, characterized in that: The method for calculating the wave spectrum of a spaceborne ocean spectrometer according to any one of claims 1 to 4 comprises: The received power signal calculation module after the range gate average is used to calculate the received power signal conduct The received power signal after the range gate average is obtained : Among them, the received power signal is the power signal corresponding to the echo signal of the spaceborne ocean spectrometer; , It represents the bandwidth of the pulses transmitted by the spaceborne ocean spectrometer; The first wave spectrum calculation module is used to calculate the received power signal Fourier transform of , to calculate the received power signal The fluctuation spectrum ; The second wave spectrum calculation module is used to convert the wave spectrum into Expand to get the wave spectrum With the fluctuation spectrum The relationship between them is used to realize the wave spectrum calculation; among them, The received power signal The fluctuation spectrum.

6. An electronic device, characterized in that: comprising a computer-readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is used to read the executable instructions stored in the computer-readable storage medium to execute the wave spectrum calculation method of the space-borne ocean spectrometer according to any one of claims 1 to 4.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the method for calculating the wave spectrum of a space-borne ocean spectrometer according to any one of claims 1 to 4 is implemented.

8. A computer program product, characterized in that When the computer program product is run on a computer, the computer is enabled to execute the method for calculating the wave spectrum of a space-borne ocean spectrometer according to any one of claims 1 to 4.

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