Pitching frequency scanning SAR satellite attitude deviation correction method and system

Abstract

The present application provides a kind of pitch frequency scanning SAR satellite attitude deviation correction method and system, comprising: step S1: input SAR system operating parameter, with the same distance information data accumulation to the same unit, carry out distance compression;Step S2: calculate and obtain Doppler center in each distance unit and Doppler center estimation accuracy in each distance unit;Step S3: solve radar center frequency of each distance unit;Step S4: solve each distance unit radar center beam pointing deviation;Step S5: solve attitude deviation by weighted least squares method, output pitch frequency scanning SAR satellite attitude correction result.The present application can obtain the deviation and correction constant of each direction of satellite attitude by changing beam pointing, effectively ensure SAR image quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of signal and information processing, in particular to a pitch direction frequency scanning SAR satellite attitude deviation correction method and system. BACKGROUND

[0002] Synthetic Aperture Radar (SAR) has been widely used in disaster prevention and reduction, ocean monitoring, and topographic mapping due to its all-weather, all-day, and high-resolution observation capabilities. However, during satellite transportation and launch, the SAR raw echoes received on the ground may exhibit varying degrees of pointing deviation due to factors such as vibration. This deviation needs to be corrected during the on-orbit commissioning phase. If the pointing deviation is not corrected, it will cause image azimuth deviation, reduced imaging quality, and other problems, which will further affect the subsequent application of SAR images.

[0003] Currently, to address the satellite attitude deviation correction technology problem, the patent CN113063435B discloses a satellite attitude stability and pointing accuracy evaluation method and system, which uses an inertial orientation attitude control method for star observation to obtain star observation information. Based on the star observation information, the satellite platform attitude stability information is obtained on the detector. The patent CN113361163B discloses a satellite attitude estimation method for earth reflection light correction. This method divides the earth's surface into multiple surface elements according to the latitude and longitude grid. The satellite's radiation intensity on the detector is calculated using the Lambertian reflection principle with only the sun as the light source. The satellite's attitude is estimated using the unscented Kalman filter method. The patent CN114413883B discloses a method for improving satellite attitude determination accuracy, a storage medium, and an electronic device. The satellite's control period and the star sensor's data update period are used to determine the attitude data sampling period, and the star sensor's attitude is calculated using the target sampling data. The patent CN106553770B discloses an imaging test method for remote sensing satellite attitude motion compensation. The satellite attitude compensation amount is obtained by comparing the zero attitude reference image with the image with attitude motion. The paper "External Calibration Results of the SAOCOM-1A Commissioning Phase" proposes a variable viewing angle Doppler center estimation method to estimate and correct pitch and yaw deviations. However, this method is not suitable for pitch direction frequency scanning SAR satellites, and it does not consider the impact of sample quality on estimation accuracy.

[0004] The above methods are all for the attitude correction of the SAR satellite working in the traditional imaging mode with constant radar center frequency, and the radar center frequency and the beam center pointing direction of the pitch frequency scanning SAR satellite are different when the satellite is illuminating different distance targets, so the above methods are not applicable to the attitude correction of the pitch frequency scanning SAR satellite. Currently, there is no public pitch frequency scanning SAR satellite attitude deviation correction method at home and abroad. SUMMARY

[0005] In view of the defects in the prior art, the application provides a pitch frequency scanning SAR satellite attitude deviation correction method and system.

[0006] According to the pitch frequency scanning SAR satellite attitude deviation correction method and system provided by the application, the scheme is as follows:

[0007] In a first aspect, a pitch frequency scanning SAR satellite attitude deviation correction method is provided, and the method comprises:

[0008] Step S1: input the SAR system working parameters, accumulate the data with the same distance information to the same unit, and perform distance compression;

[0009] Step S2: calculate and obtain the Doppler center in each distance unit and the Doppler center estimation accuracy in each distance unit;

[0010] Step S3: solve the radar center frequency of each distance unit;

[0011] Step S4: solve the radar center beam pointing deviation of each distance unit;

[0012] Step S5: solve the attitude deviation by the weighted least square method, and output the pitch frequency scanning SAR satellite attitude correction result.

[0013] Preferably, the step S2 is calculated by the coherence coefficient between the adjacent two signals in the azimuth direction, comprising:

[0014] Step S2.1: input the pulse repetition frequency PRF;

[0015] Step S2.2: calculate the coherence coefficient theoretical value γ between the adjacent echo signals s

[0016]

[0017] In the formula, s(t a ) is the received echo signal at the azimuth time t a , PRF is the pulse repetition frequency, E(·) is the expectation operator, and SNR is the signal-to-noise ratio;

[0018] Step S2.3: Calculate the coherence coefficient between echo signals in the frequency domain, and determine the theoretical value as the minimum theoretical value γ of sample selection min

[0019]

[0020] where PRF is the pulse repetition frequency, E(·) is the expectation operator, S(·) is the frequency domain expression after Fourier transform, f a is the Doppler frequency, j is the imaginary unit, and SNR is the signal-to-noise ratio.

[0021] Step S2.4: Calculate the maximum theoretical value γ of the coherence coefficient of adjacent echo signals in sample selection when the signal-to-noise ratio is infinite max

[0022]

[0023] where P a is the signal power spectrum, PRF is the pulse repetition frequency, f a is the Doppler frequency, and E(·) is the expectation operator.

[0024] Step S2.5: Output the Doppler center estimation sample selection interval [γ min , γ max ] according to the calculation results of step S2.3 and step S2.4.

[0025] Step S2.6: Calculate the Doppler center f dc,i

[0026]

[0027] where arg{·} is an angle calculation factor, PRF is the pulse repetition frequency, is the coherence coefficient between echo signals in the i-th range cell,

[0028] Step S2.7: Calculate the estimation accuracy of the Doppler center in the i-th range cell

[0029]

[0030] where N is the number of sample points in the sample interval, PRF is the pulse repetition frequency, is the coherence coefficient between echo signals in the i-th range cell.

[0031] Preferably, the step S3 comprises:

[0032] Step S3.1: Input the delay time τ of the elevation frequency scanning array, the fixed phase shift amount and the inter-element distance d;

[0033] Step S3.2: assuming the earth radius R g and the orbit height H, calculate the beam pointing angle θ i

[0034]

[0035] where R i is the distance of the i-th range cell;

[0036] Step S3.3: calculate the radar center frequency f i

[0037]

[0038] where τ is the delay line time of the frequency scanning array, is the phase shift amount obtained by the phased array, d is the inter-element distance, and c is the speed of light.

[0039] Preferably, the step S4 comprises:

[0040] Step S4.1: calculate the Doppler center frequency difference Δf dc,i

[0041] Δf dc,i = f dce,i - f dc,i

[0042] where f dce,i is the Doppler center estimated by the satellite attitude measurement data of the i-th range cell, f dc,i is the Doppler center of the i-th range cell.

[0043] Step S4.2: calculate the beam pointing deviation Δθ i

[0044]

[0045] where f i is the radar center frequency in the i-th range cell, V s is the satellite flight speed, Δf dc,i is the Doppler center frequency difference of the i-th range cell, and c is the speed of light.

[0046] Preferably, the step S5 comprises:

[0047] Step S5.1: construct the beam pointing deviation Δθ i caused by the pitch deviation δp and the yaw deviation δy in each range cell;

[0048]

[0049] wherein η i is the pitch angle in the i-th range cell, δy i is the yaw deviation in the i-th range cell, δp i is the pitch deviation in the i-th range cell;

[0050] Step S5.2: Constructing the pitch deviation δp and yaw deviation δy solution matrix;

[0051]

[0052] wherein, Δθ i is the pointing deviation in the i-th range cell, η i is the pitch angle in the i-th range cell; Step S5.3: Calculating the weighting matrix W

[0053]

[0054] wherein, is the Doppler center estimation accuracy in the i-th range cell;

[0055] Step S5.4: Calculating the least square solution x

[0056]

[0057] wherein, A T is the matrix A transpose matrix, δy is the yaw deviation, δp is the pitch deviation, η i is the pitch angle in the i-th range cell, Δθ i is the pointing deviation in the i-th range cell;

[0058] Step S5.5: Outputting the pitch deviation δp and yaw deviation δy results in the beam pointing correction.

[0059] In a second aspect, a pitch direction frequency scanning SAR satellite attitude deviation correction system is provided, and the system comprises:

[0060] Module M1: Inputting the SAR system working parameters, accumulating data with the same distance information to the same cell, and performing distance compression;

[0061] Module M2: Calculating and obtaining the Doppler center in each range cell and the Doppler center estimation accuracy in each range cell;

[0062] Module M3: Solving the radar center frequency in each range cell;

[0063] Module M4: solve the deviation of each range unit radar center beam pointing;

[0064] Module M5: solve the attitude deviation by weighted least squares method, and output the attitude correction result of the elevation frequency scanning SAR satellite.

[0065] Preferably, the module M2 calculates by the coherence coefficient between the adjacent two signals in the azimuth direction, including:

[0066] Module M2.1: input the pulse repetition frequency PRF;

[0067] Module M2.2: calculate the theoretical value of the coherence coefficient γ between adjacent echo signals s

[0068]

[0069] In the formula, s(t a ) is the echo signal received at the azimuth time t a , PRF is the pulse repetition frequency, E(·) is the expectation operator, and SNR is the signal-to-noise ratio;

[0070] Module M2.3: calculate the coherence coefficient between the echo signals in the frequency domain, and determine the theoretical value as the minimum theoretical value γ min

[0071]

[0072] In the formula, PRF is the pulse repetition frequency, E(·) is the expectation operator, S(·) is the frequency domain expression after Fourier transform, f a is the Doppler frequency, j is the imaginary unit, and SNR is the signal-to-noise ratio;

[0073] Module M2.4: calculate the maximum theoretical value γ max

[0074]

[0075] In the formula, P a is the signal power spectrum, PRF is the pulse repetition frequency, f a is the Doppler frequency, and E(·) is the expectation operator;

[0076] Module M2.5: output the Doppler center estimation sample selection interval [γ min , γ max ] according to the calculation results of module M2.3 and module M2.4;

[0077] Module M2.6: calculate the Doppler center fdc,i

[0078]

[0079] where arg{•} is the angle calculation factor, PRF is the pulse repetition frequency, is the inter-echo signal coherence factor of the ith range cell,

[0080] Module M2.7: Calculate the Doppler center estimation accuracy of the ith range cell

[0081]

[0082] where N is the number of sample points in the sample interval, PRF is the pulse repetition frequency, is the inter-echo signal coherence factor of the ith range cell.

[0083] Preferably, the module M3 comprises:

[0084] Module M3.1: Input the frequency scanning array delay time τ, the fixed phase shift amount and the inter-element spacing d;

[0085] Module M3.2: Assuming the Earth radius is R g and the orbital height is H, calculate the beam pointing angle θ of the ith range cell within the same pulse i

[0086]

[0087] where R i is the distance of the ith range cell;

[0088] Module M3.3: Calculate the radar center frequency f of the ith range cell i

[0089]

[0090] where τ is the frequency scanning array delay line time, is the phase shift amount obtained by the phased array, d is the inter-element spacing, and c is the speed of light.

[0091] Preferably, the module M4 comprises:

[0092] Module M4.1: Calculate the Doppler center frequency difference Δf of the ith range cell dc,i

[0093] Δf dc,i = f dce,i - f dc,i

[0094] In the formula, f dce,i f is the Doppler center estimated using satellite attitude measurement data for the i-th range cell. dc,i The center of the i-th distance unit is the Doppler center.

[0095] Module M4.2: Calculate the beam pointing deviation Δθ within the i-th range cell. i

[0096]

[0097] In the formula, f i V is the radar center frequency within the i-th range cell. s Let Δf be the satellite's flight speed. dc,i Let be the Doppler center frequency difference of the i-th distance unit, and c be the speed of light.

[0098] Preferably, the module M5 includes:

[0099] Module M5.1: Constructs the beam pointing deviation Δθ caused by pitch deviation δp and yaw deviation δy within each range cell. i System of equations;

[0100]

[0101] In the formula, η i Let δy be the pitch angle within the i-th distance cell. i Let δp be the yaw deviation within the i-th distance cell. i The pitch deviation is within the i-th distance cell;

[0102] Module M5.2: Construct the solution matrices for pitch deviation δp and yaw deviation δy;

[0103]

[0104] In the formula, Δθ i η represents the pointing deviation within the i-th distance cell. i The pitch angle within the i-th distance cell;

[0105] Module M5.3: Calculate the weighted matrix W based on the Doppler center estimation accuracy.

[0106]

[0107] In the formula, The accuracy of Doppler center estimation within the i-th distance cell;

[0108] Module M5.4: Calculate the least squares solution x

[0109]

[0110] In the formula, A T is the matrix A transpose matrix, δy is the yaw deviation, δp is the pitch deviation, η i is the pitch angle in the i-th range cell, Δθ i is the pointing deviation in the i-th range cell.

[0111] Module M5.5: output the pitch deviation δp and yaw deviation δy results in the beam pointing correction.

[0112] Compared with the prior art, the present application has the following beneficial effects:

[0113] 1. The present application can obtain high-precision satellite attitude deviation through echo data without increasing any hardware, can reduce the complexity of the system design of the SAR satellite when considering attitude correction, and can improve the accuracy of data interpretation during imaging processing, thereby ensuring the high quality of the image during the observation of the SAR system to the earth.

[0114] 2. The present application has no additional design requirements for the SAR system design, the processing method is simple, the center frequency of each range cell can be obtained by using the geometric model to effectively judge the pitch deviation and yaw deviation affecting the beam pointing, and has strong reliability and high realizability.

[0115] Other beneficial effects of the present application will be described in the specific embodiments through the introduction of specific technical features and technical solutions, and those skilled in the art should be able to understand the beneficial technical effects brought by the technical features and technical solutions through the introduction of the technical features and technical solutions. BRIEF DESCRIPTION OF DRAWINGS

[0116] Other features, objects and advantages of the present application will become more apparent through the following detailed description of the non-limiting embodiments with reference to the accompanying drawings:

[0117] Figure 1 is the pitch angle in the i-th range cell, Δθ DETAILED DESCRIPTION

[0118] The present application will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present application. These all belong to the protection scope of the present application.

[0119] The embodiment of the present application provides a pitch frequency scanning SAR satellite attitude deviation correction method, aiming at the pitch frequency scanning SAR satellite attitude deviation correction problem, can utilize distance-frequency-beam pointing coupling characteristics, separates the received echo distance compression into different distances, estimates the Doppler center frequency in each distance unit and differentiates with the theoretical value, finally, the Doppler frequency difference of different distance units is weighted to invert the global antenna pointing offset angle to obtain the satellite attitude deviation. Figure 1 As shown in the figure, the method specifically includes the following contents:

[0120] Step S1: input the SAR system working parameters, accumulate the data with the same distance information to the same unit, and perform distance compression.

[0121] Step S2: calculate the Doppler center in each distance unit and the Doppler center estimation accuracy in each distance unit.

[0122] The step S2 is calculated by the coherence coefficient between the adjacent signals in the azimuth direction, including:

[0123] Step S2.1: input the pulse repetition frequency PRF;

[0124] Step S2.2: calculate the coherence coefficient theoretical value γ between the adjacent echo signals s

[0125]

[0126] In the formula, s(t a ) is the received echo signal at the azimuth time t a , PRF is the pulse repetition frequency, E(·) is the expectation operator, and SNR is the signal-to-noise ratio;

[0127] Step S2.3: calculate the coherence coefficient between the echo signals in the frequency domain, and determine the minimum theoretical value γ min

[0128]

[0129] In the formula, PRF is the pulse repetition frequency, E(·) is the expectation operator, S(·) is the frequency domain expression after Fourier transform, f a is the Doppler frequency, j is the imaginary unit, and SNR is the signal-to-noise ratio;

[0130] Step S2.4: calculate the maximum theoretical value γ max

[0131]

[0132] In the formula, P a The signal power spectrum is given by f, where PRF is the pulse repetition frequency. a Let E(·) be the Doppler frequency, and E(·) be the expectation operator.

[0133] Step S2.5: Based on the calculation results of steps S2.3 and S2.4, output the Doppler center estimation sample selection interval [γ]. min ,γ max );

[0134] Step S2.6: Calculate the Doppler center f of the i-th distance cell. dc,i

[0135]

[0136] In the formula, arg{·} is the angle calculation factor, and PRF is the pulse repetition frequency. Let be the coherence coefficient between the echo signals of the i-th distance cell.

[0137] Step S2.7: Calculate the Doppler center estimation accuracy of the i-th distance cell.

[0138]

[0139] In the formula, N is the number of sample points in the sample interval, and PRF is the pulse repetition frequency. Let be the coherence coefficient between the echo signals of the i-th distance unit.

[0140] Step S3: Calculate the radar center frequency of each range cell.

[0141] Step S3 includes:

[0142] Step S3.1: Input the pitch direction frequency scanning array delay time τ and the fixed phase shift. And the element spacing d;

[0143] Step S3.2: Assume the Earth's radius is R. g Given an orbital altitude of H, calculate the beam pointing angle θ of the i-th range cell within the same pulse. i

[0144]

[0145] In the formula, R i The distance is the distance to the i-th distance unit;

[0146] Step S3.3: Calculate the radar center frequency f of the i-th range element. i

[0147]

[0148] where τ is the frequency scanning array delay line time, is the phase shift obtained by the phased array, d is the array element spacing, and c is the speed of light.

[0149] Step S4: Solve the pointing deviation of each range cell radar center beam.

[0150] This step S4 includes:

[0151] Step S4.1: Calculate the Doppler center frequency difference Δf dc,i

[0152] Δf dc,i = f dce,i -f dc,i

[0153] where f dce,i is the Doppler center estimated by the satellite attitude measurement data of the ith range cell, f dc,i is the Doppler center of the ith range cell.

[0154] Step S4.2: Calculate the beam pointing deviation Δθ i

[0155]

[0156] where f i is the radar center frequency in the ith range cell, V s is the satellite flight speed, Δf dc,i is the Doppler center frequency difference of the ith range cell, and c is the speed of light.

[0157] Step S5: Solve the attitude deviation by weighted least squares method, and output the pitch direction frequency scanning SAR satellite attitude correction result.

[0158] This step S5 includes:

[0159] Step S5.1: Construct the beam pointing deviation Δθ i caused by the pitch deviation δp and the yaw deviation δy in each range cell.

[0160]

[0161] where η i is the pitch angle in the ith range cell, δy i is the yaw deviation in the ith range cell, δp i is the pitch deviation in the ith range cell.

[0162] Step S5.2: Constructing the pitch deviation δp and the yaw deviation δy solution matrix;

[0163]

[0164] In the formula, Δθ i is the pointing deviation in the i-th range cell, η i is the pitch angle in the i-th range cell;

[0165] Step S5.3: Calculating the weighting matrix W according to the Doppler center estimation accuracy

[0166]

[0167] In the formula, is the Doppler center estimation accuracy in the i-th range cell;

[0168] Step S5.4: Calculating the least square solution x

[0169]

[0170] In the formula, A T is the matrix A transpose matrix, δy is the yaw deviation, δp is the pitch deviation, η i is the pitch angle in the i-th range cell, Δθ i is the pointing deviation in the i-th range cell;

[0171] Step S5.5: Outputting the pitch deviation δp and the yaw deviation δy results in the beam pointing correction.

[0172] The present application also provides a pitch frequency scanning SAR satellite attitude deviation correction system, which can be realized by executing the flow steps of the pitch frequency scanning SAR satellite attitude deviation correction method, i.e. the pitch frequency scanning SAR satellite attitude deviation correction method can be understood by those skilled in the art as the preferred embodiment of the pitch frequency scanning SAR satellite attitude deviation correction system. The system specifically includes the following contents:

[0173] Module M1: Inputting the SAR system working parameters, accumulating data with the same distance information to the same unit, and performing distance compression.

[0174] Module M2: Calculating and obtaining the Doppler center in each range cell and the Doppler center estimation accuracy in each range cell.

[0175] This module M2 calculates through the coherence coefficient between the adjacent two signals in the azimuth direction, including:

[0176] Module M2.1: input pulse repetition frequency PRF;

[0177] Module M2.2: calculate theoretical value of coherence coefficient γ between adjacent echo signals s

[0178]

[0179] wherein s(t a ) is echo signal received at azimuth time t a , PRF is pulse repetition frequency, E(·) is expectation operator, and SNR is signal-to-noise ratio;

[0180] Module M2.3: calculate coherence coefficient between echo signals in frequency domain, and determine theoretical value as minimum theoretical value γ of sample selection min

[0181]

[0182] wherein PRF is pulse repetition frequency, E(·) is expectation operator, S(·) is expression in frequency domain after Fourier transform, f a is Doppler frequency, j is imaginary unit, and SNR is signal-to-noise ratio;

[0183] Module M2.4: calculate maximum theoretical value γ of sample selection of adjacent echo signal coherence coefficient when signal-to-noise ratio is infinite max

[0184]

[0185] wherein P a is signal power spectrum, PRF is pulse repetition frequency, f a is Doppler frequency, and E(·) is expectation operator;

[0186] Module M2.5: output Doppler center estimation sample selection interval [γ min , γ max ) according to calculation results of module M2.3 and module M2.4;

[0187] Module M2.6: calculate Doppler center f dc,i

[0188]

[0189] wherein arg{·} is angle calculation factor, PRF is pulse repetition frequency, is coherence coefficient between echo signals of i-th range cell, γ si ∈ [γ min , γ max ].

[0190] Module M2.7: Calculate the estimation accuracy of the Doppler center of the i-th range cell

[0191]

[0192] where N is the number of sample points in the sample interval, PRF is the pulse repetition frequency, is the coherence coefficient between the echo signals of the i-th range cell.

[0193] Module M3: Solve the radar center frequency of each range cell.

[0194] This module M3 includes:

[0195] Module M3.1: Input the frequency scanning array delay time τ, the fixed phase shift amount and the inter-element spacing d;

[0196] Module M3.2: Assuming the Earth's radius is R g and the orbital height is H, calculate the beam pointing angle θ i

[0197]

[0198] where R i is the distance of the i-th range cell;

[0199] Module M3.3: Calculate the radar center frequency f i

[0200]

[0201] where τ is the frequency scanning array delay line time, is the phase shift amount obtained by the phased array, d is the inter-element spacing, and c is the speed of light.

[0202] Module M4: Solve the radar center beam pointing deviation of each range cell.

[0203] This module M4 includes:

[0204] Module M4.1: Calculate the Doppler center frequency difference Δf dc,i

[0205] Δf dc,i = f dce,i - f dc,i

[0206] where f dce,iThe Doppler center estimated by using satellite attitude measurement data for the i-th range cell, f dc,i The Doppler center for the i-th range cell;

[0207] Module M4.2: Calculate the beam pointing deviation Δθ in the i-th range cell i

[0208]

[0209] Wherein, f i The radar center frequency in the i-th range cell, V s The satellite flight speed, Δf dc,i The Doppler center frequency difference of the i-th range cell, c is the speed of light.

[0210] Module M5: Solve the attitude deviation by weighted least squares method, and output the attitude correction result of the pitch frequency scanning SAR satellite.

[0211] This module M5 includes:

[0212] Module M5.1: Construct the beam pointing deviation Δθ caused by the pitch deviation δp and the yaw deviation δy in each range cell i Equation group;

[0213]

[0214] Wherein, η i The pitch angle in the i-th range cell, δy i The yaw deviation in the i-th range cell, δp i The pitch deviation in the i-th range cell;

[0215] Module M5.2: Construct the pitch deviation δp and the yaw deviation δy solution matrix;

[0216]

[0217] Wherein, Δθ i The pointing deviation in the i-th range cell, η i The pitch angle in the i-th range cell;

[0218] Module M5.3: Calculate the weighting matrix W according to the Doppler center estimation accuracy

[0219]

[0220] Wherein, The Doppler center estimation accuracy in the i-th range cell;

[0221] Module M5.4: Calculate the least squares solution x

[0222]

[0223] wherein, A T is the matrix A transpose matrix, δy is the yaw deviation, δp is the pitch deviation, η i is the pitch angle in the i-th range cell, Δθ i is the pointing deviation in the i-th range cell;

[0224] Module M5.5: output the pitch deviation δp and the yaw deviation δy results in the beam pointing correction.

[0225] Next, the present application is described in more detail.

[0226] Step one, range compression.

[0227] The input SAR original echo data size is Na (azimuth direction) and Nr (range direction), i.e. the input image size; the input SAR system operating parameters will have the same distance information data accumulation to the same unit.

[0228] Step two, Doppler center estimation and accuracy evaluation of each range cell.

[0229] (1) Calculate the coherence coefficient between the echo signals in the frequency domain, and determine the theoretical value as the minimum limit γ min

[0230]

[0231] PRF is the pulse repetition frequency, f a is the Doppler frequency, E(·) is the expectation operator, S(·) is the frequency domain expression after Fourier transform, SNR is the signal-to-noise ratio, and j is the imaginary unit;

[0232] (2) Calculate the maximum theoretical value γ max

[0233]

[0234] wherein, P a is the signal power spectrum, PRF is the pulse repetition frequency, f a is the Doppler frequency, and E(·) is the expectation operator;

[0235] (3) Use the calculation results of (1) and (2) to output the Doppler center estimation sample selection interval [γ min , γ max ];

[0236] (4) Calculate the Doppler center f dc,i

[0237]

[0238] where arg{·} is the angle calculation factor, PRF is the pulse repetition frequency,

[0239] (5) Calculate the Doppler center estimation accuracy in the i-th range cell

[0240]

[0241] where N is the number of sample points in the sample interval, PRF is the pulse repetition frequency, is the coherence coefficient between the echo signals in the i-th range cell.

[0242] Step three, calculate the radar center frequency of each range cell.

[0243] The following processing is completed for each range cell:

[0244] (1) Input the frequency scanning array delay time τ, the frequency scanning array phase shift amount and the array element spacing d;

[0245] (2) Assuming that the Earth's radius is R g and the orbital height is H, calculate the beam pointing angle θ i

[0246]

[0247] where R i is the distance of the i-th range cell;

[0248] (3) Calculate the radar center frequency f i

[0249]

[0250] where τ is the frequency scanning array delay line time, is the phase shift amount obtained by the phased array, d is the array element spacing, and c is the speed of light.

[0251] Step four, calculate the radar center beam pointing deviation of each range cell. Specifically as follows:

[0252] (1) Calculate the Doppler center frequency difference Δf dc,i

[0253] Δf dc,i = fdce,i -f dc,i

[0254] where f dce,i is the Doppler center estimated by the satellite attitude measurement data for the i-th range cell, f dc,i is the Doppler center for the i-th range cell;

[0255] (2) Calculate the beam pointing deviation Δθ i

[0256]

[0257] where f i is the radar center frequency in the i-th range cell, V s is the satellite flight velocity, Δf dc,i is the Doppler center frequency difference for the i-th range cell, and c is the speed of light.

[0258] Step five, solve the attitude deviation by weighted least squares.

[0259] After all the range cells complete the deviation calculation, the following processing is performed:

[0260] (1) Construct the beam pointing deviation Δθ i caused by the pitch deviation δp and the yaw deviation δy in each range cell

[0261]

[0262] where η i is the pitch angle in the i-th range cell, δy i is the yaw deviation in the i-th range cell, and δp is the pitch deviation in the i-th range cell.

[0263] (2) Construct the pitch deviation δp and the yaw deviation δy solution matrix

[0264]

[0265] where Δθ = [Δθ1Δθ2…Δθ n ] T , η i is the pitch angle in the i-th range cell, Δθ i is the pointing deviation in the i-th range cell.

[0266] (3) Calculate the weighting matrix W according to the Doppler center estimation accuracy in step two (5)

[0267]

[0268] where σ fdc,iThe estimation precision of the Doppler center in the i-th range cell;

[0269] (4) calculating the least square solution x

[0270] x=(A T WA) -1 A T WΔθ

[0271] In the formula, x=[delta y delta p] T , Delta theta=[Delta theta 1 Delta theta 2 … Delta theta n ] T , A T is the transpose matrix of the matrix A, delta y is the yaw deviation, delta p is the pitch deviation, eta i is the pitch angle in the i-th range cell, Delta theta i is the pointing deviation in the i-th range cell.

[0272] (5) outputting the pitch deviation delta p and the yaw deviation delta y results in the beam pointing correction.

[0273] (7) outputting the pitch direction frequency scanning SAR satellite attitude correction result.

[0274] The embodiment of the present application provides a pitch direction frequency scanning SAR satellite attitude deviation correction method and system, which can obtain high-precision satellite attitude deviation through echo data without increasing any hardware, can reduce the complexity of the system design of the SAR satellite when considering the attitude correction, and can improve the accuracy of data interpretation when imaging processing, thereby ensuring the high quality of the image when the SAR system observes the earth.

[0275] Those skilled in the art know that, in addition to implementing the system provided by the present application and each device, module and unit thereof in a pure computer readable program code manner, the system provided by the present application and each device, module and unit thereof can also be implemented in the form of logic gates, switches, special integrated circuits, programmable logic controllers and embedded microcontrollers by logically programming the method steps to achieve the same functions. Therefore, the system provided by the present application and each device, module and unit thereof can be considered as a hardware component, and the devices, modules and units included therein for achieving various functions can also be considered as structures in the hardware component. The devices, modules and units for achieving various functions can also be considered as both software modules for implementing methods and structures in the hardware component.

[0276] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be combined with each other at will without conflict.

Claims

1. A method for correcting attitude deviation of a pitch-frequency scanning SAR satellite, characterized in that, include: Step S1: Input the SAR system operating parameters, accumulate data with the same range information into the same cell, and perform range compression; Step S2: Calculate and obtain the Doppler center within each range cell and the estimation accuracy of the Doppler center within each range cell; Step S3: Calculate the radar center frequency for each range cell; Step S4: Calculate the pointing deviation of the radar center beam for each range cell; Step S5: Solve for the attitude deviation using the weighted least squares method and output the pitch-frequency scanning SAR satellite attitude correction results; Step S2 calculates the coherence coefficient between two adjacent signals in the azimuth direction, including: Step S2.1: Input pulse repetition frequency ; Step S2.2: Calculate the theoretical value of the coherence coefficient between adjacent echo signals. In the formula, For the location and time, The received echo signal, The pulse repetition frequency, For expectation operator, Signal-to-noise ratio; Step S2.3: Calculate the coherence coefficient between echo signals in the frequency domain, and determine the theoretical value as the minimum theoretical value for sample selection. In the formula, The pulse repetition frequency, For expectation operator, This is the frequency domain expression after Fourier transform. For Doppler frequency, The imaginary unit, Signal-to-noise ratio; Step S2.4: Calculate the maximum theoretical value of the coherence coefficient of adjacent echo signals selected from the samples when the signal-to-noise ratio is infinite. In the formula, For the signal power spectrum, The pulse repetition frequency, For Doppler frequency, For expectation operators; Step S2.5: Output the Doppler center estimation sample selection interval based on the calculation results of Steps S2.3 and S2.

4. ; Step S2.6: Calculate the first... Doppler center of distance unit In the formula, Angle calculation factor, The pulse repetition frequency, For the first Coherence coefficient between echo signals of each distance cell ; Step S2.7: Calculate the first... Doppler center estimation accuracy per distance unit In the formula, The number of sample points within the sample interval. The pulse repetition frequency, For the first Coherence coefficient between echo signals of each distance unit.

2. The method for correcting attitude deviation of a SAR satellite in elevation frequency scanning according to claim 1, characterized in that, Step S3 includes: Step S3.1: Input the pitch direction frequency scan array delay time Fixed phase shift and the spacing between array elements ; Step S3.2: Assume the Earth's radius is... The orbital height is Calculate the first pulse within the same pulse. Beam pointing angle per range unit In the formula, For the first Distance of one distance unit; Step S3.3: Calculate the first... The center frequency of each range unit radar In the formula, For frequency scanning array delay line time, The phase shift amount obtained by the phased array For the spacing between array elements, It is the speed of light.

3. The method for correcting attitude deviation of a SAR satellite in elevation frequency scanning according to claim 1, characterized in that, Step S4 includes: Step S4.1: Calculate the first... Doppler center frequency difference between each distance unit In the formula, For the first The Doppler center of each distance cell is estimated using satellite attitude measurement data. For the first Each distance unit Doppler center; Step S4.2: Calculate the first... Beam pointing deviation within a range cell In the formula, For the first Radar center frequency within each range cell For the satellite's flight speed, For the first The difference in frequency between the center of the Doppler array and the distance to the unit. It is the speed of light.

4. The method for correcting attitude deviation of a SAR satellite in elevation frequency scanning according to claim 1, characterized in that, Step S5 includes: Step S5.1: Construct pitch deviation within each distance cell and yaw deviation Beam pointing deviation caused System of equations; In the formula, For the first Pitch angle within a distance unit, For the first Yaw deviation within a distance unit For the first Pitch deviation within a distance unit; Step S5.2: Construct pitch deviation and yaw deviation Solve the matrix; In the formula, , For the first Pointing deviation within a distance unit For the first Pitch angle within a distance unit; Step S5.3: Calculate the weighting matrix based on the Doppler center estimation accuracy. In the formula, For the first Doppler center estimation accuracy within a distance cell; Step S5.4: Calculate the least squares solution In the formula, , , , For matrix transpose matrix, For yaw deviation, For pitch deviation, For the first Pitch angle within a distance unit, For the first Pointing deviation within a distance unit; Step S5.5: Pitch deviation during output beam pointing correction and yaw deviation result.

5. A pitch-frequency scanning SAR satellite attitude deviation correction system, characterized in that, include: Module M1: Inputs SAR system operating parameters, accumulates data with the same range information into the same cell, and performs range compression; Module M2: Calculates and obtains the Doppler center within each range cell and the estimation accuracy of the Doppler center within each range cell; Module M3: Calculates the radar center frequency for each range cell; Module M4: Calculates the pointing deviation of the radar center beam for each range cell; Module M5: Solve for attitude deviations using the weighted least squares method and outputs the attitude correction results for pitch-frequency scanning SAR satellites; The module M2 calculates the coherence coefficient between two adjacent signals in the azimuth direction, including: Module M2.1: Input pulse repetition frequency ; Module M2.2: Calculates the theoretical value of the coherence coefficient between adjacent echo signals. In the formula, For the location and time, The received echo signal, The pulse repetition frequency, For expectation operator, Signal-to-noise ratio; Module M2.3: Calculates the coherence coefficients between echo signals in the frequency domain and determines the theoretical values ​​as the minimum theoretical values ​​for sample selection. In the formula, The pulse repetition frequency, For expectation operator, This is the frequency domain expression after Fourier transform. For Doppler frequency, The imaginary unit, Signal-to-noise ratio; Module M2.4: Calculates the maximum theoretical value of the coherence coefficient of adjacent echo signals selected from samples when the signal-to-noise ratio is infinite. In the formula, For the signal power spectrum, The pulse repetition frequency, For Doppler frequency, For expectation operators; Module M2.5: Outputs the Doppler center estimation sample selection interval based on the calculation results of Modules M2.3 and M2.

4. ; Module M2.6: Calculate the first Doppler center of distance unit In the formula, Angle calculation factor, The pulse repetition frequency, For the first Coherence coefficient between echo signals of each distance cell ; Module M2.7: Calculate the first Doppler center estimation accuracy per distance unit In the formula, This represents the number of sample points within the sample interval. The pulse repetition frequency, For the first Coherence coefficient between echo signals of each distance unit.

6. The pitch-frequency scanning SAR satellite attitude deviation correction system according to claim 5, characterized in that, The module M3 includes: Module M3.1: Input pitch direction frequency scan array delay time Fixed phase shift and the spacing between array elements ; Module M3.2: Assuming the Earth's radius is... The orbital height is Calculate the first pulse within the same pulse. Beam pointing angle per range unit In the formula, For the first Distance of one distance unit; Module M3.3: Calculate the first The center frequency of each range unit radar In the formula, For frequency scanning array delay line time, The phase shift amount obtained by the phased array For the spacing between array elements, It is the speed of light.

7. The pitch-frequency scanning SAR satellite attitude deviation correction system according to claim 5, characterized in that, The module M4 includes: Module M4.1: Calculate the first... Doppler center frequency difference between each distance unit In the formula, For the first The Doppler center of each distance cell is estimated using satellite attitude measurement data. For the first Each distance unit Doppler center; Module M4.2: Calculate the first Beam pointing deviation within a range cell In the formula, For the first Radar center frequency within each range cell For the satellite's flight speed, For the first The difference in frequency between the center of the Doppler array and the distance to the unit. It is the speed of light.

8. The pitch-frequency scanning SAR satellite attitude deviation correction system according to claim 5, characterized in that, The module M5 includes: Module M5.1: Construct pitch deviation within each distance cell and yaw deviation Beam pointing deviation caused System of equations; In the formula, For the first Pitch angle within a distance unit, For the first Yaw deviation within a distance unit For the first Pitch deviation within a distance unit; Module M5.2: Constructing Pitch Deviation and yaw deviation Solve the matrix; In the formula, , For the first Pointing deviation within a distance unit For the first Pitch angle within a distance unit; Module M5.3: Calculate the weighting matrix based on the accuracy of the Doppler center estimation. In the formula, For the first Doppler center estimation accuracy within a distance cell; Module M5.4: Calculate Least Squares Solution In the formula, , , , For matrix transpose matrix, For yaw deviation, For pitch deviation, For the first Pitch angle within a distance unit, For the first Pointing deviation within a distance unit; Module M5.5: Pitch deviation during output beam pointing correction and yaw deviation result.

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