CN114283128B - Ocean mesoscale vortex edge detection method and system based on multi-parameter threshold - Google Patents
Ocean mesoscale vortex edge detection method and system based on multi-parameter threshold Download PDFInfo
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Abstract
The invention discloses a marine mesoscale vortex edge detection method and system based on a multi-parameter threshold, comprising the following steps: collecting SAR data containing a mesoscale vortex phenomenon, and obtaining a mesoscale vortex SAR image with high geometric resolution through radiation calibration, distance direction correction and geocoding; detecting a mesoscale vortex characteristic region of the mesoscale vortex SAR image by adopting a multiparameter threshold method, extracting a mesoscale vortex edge of the mesoscale vortex characteristic region, and acquiring edge position parameters; based on the mesoscale vortex characteristic region and the edge position parameter, extracting a scroll center of the vortex region as a mesoscale vortex center, and acquiring a mesoscale vortex center position parameter; the method effectively solves the problem that the mesoscale vortex phenomenon is difficult to effectively detect under the condition of unobvious and unclear view of the mesoscale vortex phenomenon in the SAR image, and has important theoretical value and practical significance for improving the comprehensive application benefit of multi-source high-resolution SAR data and the development of novel SAR detection satellite data.
Description
Technical Field
The invention relates to the technical field of ocean remote sensing information processing, in particular to a method and a system for detecting ocean mesoscale vortex edges based on multi-parameter threshold values.
Background
With the rapid development of aerospace technology, the method has the advantages of all-day, all-weather, high-resolution and wide-breadth Synthetic Aperture Radar (SAR) satellites, and provides abundant data resources for marine phenomenon research. However, in a complex ocean background, ocean mesoscale vortex is expressed as a weak scattering signal on an SAR image, a local backward scattering coefficient is interfered by radar observation incident angle, imaging information loss, multi-scale factors such as sea surface wind fields and flow fields, and the like, and the problems of unobvious texture features, invisible and invisible texture and the like exist, so that the complete ocean mesoscale vortex edge is difficult to effectively obtain by adopting the existing gradient threshold method.
Disclosure of Invention
In order to solve the technical problems, the invention aims to effectively detect the ocean mesoscale vortex edge by adjusting the multi-parameter threshold through man-machine interaction.
In order to achieve the technical aim, the invention provides a marine mesoscale vortex edge detection method based on a multi-parameter threshold, which comprises the following steps:
Collecting SAR data containing a mesoscale vortex phenomenon, and obtaining a mesoscale vortex SAR image with high geometric resolution through radiation calibration, distance direction correction and geocoding;
Detecting a mesoscale vortex characteristic region of the mesoscale vortex SAR image by adopting a multiparameter threshold method, extracting a mesoscale vortex edge of the mesoscale vortex characteristic region, and obtaining edge position parameters, wherein the multiparameter threshold method is used for representing adjustment of the mesoscale vortex SAR image according to a radiation resolution improving parameter, a backscattering coefficient gradient threshold parameter, a small area scattered point eliminating parameter, an expansion processing parameter and a corrosion processing parameter and is used for detecting the mesoscale vortex characteristic region;
And extracting the scroll center of the scroll area as a mesoscale vortex center based on the mesoscale vortex characteristic area and the edge position parameter, and acquiring the mesoscale vortex center position parameter.
Preferably, in the process of acquiring the mesoscale vortex SAR image, the expression of the radiation scaling is:
Wherein, P d is the back scattering intensity received by the sensor, P t is the transmission power, P n is the additional power, G A is the transmission and receiving antenna gain, G E is the current gain of the radar receiver, G P is the processor constant, R is the distance propagation loss, θ el is the antenna elevation angle, θ az is the antenna azimuth angle, L is the loss of the atmosphere L a and the system L s, a is the scattering area, and σ 0 is the back scattering coefficient.
Preferably, in acquiring the mesoscale eddy SAR image, the range correction is used to eliminate the range-up luminance variation caused by the incident angle;
the distance correction expression is:
Where σ 0′ (i, j) is the back scattering coefficient result after distance correction and σ 0 (i, j) is the back scattering coefficient before correction.
Preferably, in acquiring the mesoscale vortex SAR image, geocoding is used to convert SAR data from a range or range projection to a geocoordinate projection using a doppler method.
The multi-parameter threshold method is used for detecting the mesoscale vortex characteristic region, and comprises the following steps:
s201, performing radiation resolution improvement treatment on the mesoscale eddy SAR image;
S202, performing backward scattering coefficient gradient threshold segmentation on a mesoscale vortex SAR image;
s203, carrying out small-area scattered point processing on the mesoscale vortex SAR image, and removing an interference block;
s204, performing characteristic image expansion processing on the mesoscale vortex SAR image;
S205, performing characteristic image corrosion treatment on the mesoscale vortex SAR image;
s206, judging whether to adjust by a multi-parameter threshold method according to the initial mesoscale eddy characteristic area obtained in the steps;
S207, if the parameters are adjusted through a multi-parameter threshold method, adjusting the parameters from S201 to S205 until a final mesoscale eddy characteristic area is obtained.
Preferably, in the process of detecting the mesoscale eddy characteristic region by adopting a multiparameter threshold method, setting a radiation resolution improvement parameter, and carrying out radiation resolution improvement treatment on the mesoscale eddy SAR image;
the radiation resolution improvement process includes: the frequency domain radiation resolution and the airspace radiation resolution are improved; the formula for improving the frequency domain radiation resolution is as follows:
Wherein, I M is an image processed according to M, M represents a radiation resolution improvement parameter, and I i is a neighborhood pixel sub-view;
the improvement of the airspace radiation resolution is realized by enhancing Lee filtering, and the formula for improving the airspace radiation resolution is as follows:
Wherein w=exp (-k (C y-Cu)/Cmax-Cy), Sigma y is the standard deviation of the sample,/>Is the average of the pixels in the filter window.
Preferably, in the process of detecting the mesoscale eddy characteristic region by adopting a multiparameter threshold method, setting a backscattering coefficient gradient threshold parameter, and carrying out backscattering coefficient gradient threshold segmentation on the mesoscale eddy SAR image;
Distinguishing a mesoscale vortex characteristic region from a marine background region according to a backscattering coefficient gradient threshold parameter by acquiring a backscattering coefficient gradient, and acquiring a mesoscale vortex backscattering coefficient gradient binary image, wherein when the backscattering coefficient gradient is greater than the backscattering coefficient gradient threshold parameter, the mesoscale vortex characteristic region is determined; when the backscattering coefficient gradient is smaller than the backscattering coefficient gradient threshold parameter, determining that the ocean background area is formed;
the expression of the backscatter coefficient gradient is:
Preferably, in the process of detecting the mesoscale eddy characteristic area by adopting the multi-parameter threshold method, a small-area scattered point eliminating parameter is set, and a block smaller than the small-area scattered point eliminating parameter in the mesoscale eddy backward scattering coefficient gradient binary image is deleted, so that a typical mesoscale eddy block binary image is obtained.
Preferably, in the process of detecting the mesoscale eddy characteristic region by adopting a multiparameter threshold method, the typical mesoscale eddy block binary image is subjected to expansion processing by setting expansion processing parameters to obtain the typical coherent mesoscale eddy characteristic block binary image, wherein the expansion processing is used for realizing hole filling or intermittent ravines connection of the mesoscale eddy block; the expansion treatment process comprises the following steps:
wherein A represents a typical mesoscale turboprop binary map, B is a structural element of an expansion processing parameter, Indicating the expansion operation.
Preferably, in the process of detecting the mesoscale eddy characteristic region by adopting a multiparameter threshold method, setting corrosion treatment parameters, and carrying out corrosion treatment on a typical consecutive mesoscale eddy block binary image to obtain a preliminary mesoscale eddy characteristic region, wherein the corrosion treatment is used for realizing shrinkage and smoothness of the mesoscale eddy block; the expression of the etching treatment is:
Wherein C represents a typical coherent mesoscale eddy current block binary map, D is a structural element of the corrosion treatment parameters, and Θ represents the corrosion operation.
A multi-parameter threshold based marine mesoscale vortex edge detection system comprising:
The SAR image generation module is used for acquiring SAR data containing a mesoscale vortex phenomenon and acquiring a mesoscale vortex SAR image with high geometric resolution through radiation calibration, distance direction correction and geocoding processing;
The data processing module is used for detecting a mesoscale vortex characteristic region of the mesoscale vortex SAR image by adopting a multiparameter threshold method, extracting a mesoscale vortex edge of the mesoscale vortex characteristic region and obtaining edge position parameters, wherein the multiparameter threshold method is used for representing adjustment of the mesoscale vortex SAR image according to a radiation resolution lifting parameter, a backscattering coefficient gradient threshold parameter, a small area scattered point eliminating parameter, an expansion processing parameter and a corrosion processing parameter and is used for detecting the mesoscale vortex characteristic region;
The mesoscale vortex center recognition module is used for extracting the centroid of the vortex area as a mesoscale vortex center based on the mesoscale vortex characteristic area and the edge position parameter, and acquiring the mesoscale vortex center position parameter.
The invention discloses the following technical effects:
The invention applies all-day and all-weather SAR data to research on the marine mesoscale phenomenon, and provides a marine mesoscale vortex edge detection method and system based on a multi-parameter threshold value, which effectively solve the problem that the mesoscale vortex edge is difficult to effectively detect under the condition that the mesoscale vortex phenomenon is unobvious and invisible in SAR images, and have important theoretical value and practical significance for improving comprehensive application benefit of multi-source high-resolution SAR data and developing novel SAR detection satellite data.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method according to an embodiment of the invention;
FIG. 2 is a high-resolution third-order SAR satellite data comprising mesoscale eddy current according to an embodiment of the present disclosure;
FIG. 3 is radiometric, range-corrected and geocoded high-resolution SAR satellite data in accordance with an embodiment of the present subject matter;
FIG. 4 is a mesoscale vortex SAR image according to an embodiment of the present disclosure;
Fig. 5 is a mesoscale eddy SAR image result obtained after the parameter m=4 threshold radiation resolution improvement processing according to the embodiment of the present invention;
fig. 6 is a graph of a mesoscale eddy back scattering coefficient gradient threshold obtained after a segmentation process of a parameter t=0.5 threshold gradient according to an embodiment of the present invention;
Fig. 7 is a typical mesoscale eddy block binary diagram obtained after the parameter p=200 threshold small area scatter removal processing according to an embodiment of the present invention;
Fig. 8 is a binary image of a typical coherent mesoscale eddy feature block obtained after a threshold expansion process for parameters n1=2 according to an embodiment of the present invention;
fig. 9 is a diagram of a preliminary mesoscale eddy current feature area detection result obtained after a parameter n2=1 threshold etching treatment according to an embodiment of the present invention;
fig. 10 is a mesoscale eddy SAR image result obtained after the parameter m=5 threshold radiation resolution improvement processing according to the embodiment of the present invention;
Fig. 11 is a mesoscale eddy current backscattering coefficient gradient threshold diagram obtained after a threshold gradient segmentation process for the parameter t=0.8 according to an embodiment of the present invention;
Fig. 12 is a typical mesoscale eddy block binary diagram obtained after the parameter p=170 threshold small-area scatter removal processing according to an embodiment of the present invention;
Fig. 13 is a binary image of a typical coherent mesoscale eddy feature block obtained after a threshold expansion process for parameters n1=2 according to an embodiment of the present invention;
Fig. 14 is a diagram of a preliminary mesoscale eddy current feature area detection result obtained after a parameter n2=2 threshold etching treatment according to an embodiment of the present invention;
FIG. 15 is a graph of mesoscale vortex edge results in accordance with an embodiment of the present invention;
FIG. 16 is a graph of vortex center results according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. The components of the embodiments of the present application generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the application, as presented in the figures, is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, which can be made by a person skilled in the art without making any inventive effort, are intended to be within the scope of the present application.
As shown in fig. 1-16, the invention provides a marine mesoscale vortex edge detection method based on a multi-parameter threshold, which comprises the following steps:
S1, performing radiation calibration, distance direction correction and geocoding on SAR data containing a mesoscale vortex phenomenon to obtain a mesoscale vortex SAR image with high geometric resolution;
s2, detecting a mesoscale eddy characteristic area by adopting a multi-parameter threshold (M, T, P, N, N2) method;
s3, extracting a mesoscale vortex edge based on the mesoscale vortex feature area to obtain edge position parameters;
And S4, extracting a mesoscale vortex center based on the mesoscale vortex characteristic region and the edge to obtain a center position parameter.
The step S1 specifically comprises the steps of performing radiation calibration, distance direction correction and geocoding on SAR data containing the mesoscale eddy phenomenon to obtain a mesoscale eddy SAR image with high geometric resolution.
(1) The SAR data radiometric scaling process proceeds as follows:
Wherein, P d is the back scattering intensity received by the sensor, P t is the transmission power, P n is the additional power, G A is the transmission and receiving antenna gain, G E is the current gain of the radar receiver, G P is the processor constant, R is the distance propagation loss, θ el is the antenna elevation angle, θ az is the antenna azimuth angle, L is the loss of the atmosphere (L a) and the system (L s), a is the scattering area, and σ 0 is the back scattering coefficient.
(2) The distance correction is to eliminate the change in brightness in the distance direction caused by the incident angle, and is calculated as follows:
Where σ 0′ (i, j) is the back scattering coefficient result after distance correction and σ 0 (i, j) is the back scattering coefficient before correction.
(3) Geocoding is the conversion of SAR data from a range or range projection to a geocoordinate projection using doppler methods.
The step S2 specifically comprises the following steps:
s21, performing radiation resolution improvement treatment on the mesoscale eddy SAR image;
s22, segmenting a backscattering coefficient gradient threshold of the mesoscale vortex SAR image;
S23, eliminating interference blocks by small-area scattered points;
s24, feature image expansion processing;
s25, characteristic image corrosion treatment;
s26, judging whether to perform multi-parameter threshold adjustment according to the preliminary mesoscale eddy characteristic area obtained in the step;
And S27, if the multi-parameter adjustment is carried out, adjusting the parameters from S21 to S25 until a final mesoscale eddy characteristic area detection result is obtained.
(1) The frequency domain radiation resolution is improved by carrying out weighted average on pixels in a plurality of sub-images, and the specific formula is as follows:
wherein, I M is the image processed according to M, and I i is the neighborhood pixel sub-view.
(2) The spatial radiation resolution is improved by enhancing Lee filtering, and the specific formula is as follows:
the coefficient of variation based on the multiplicative noise model is expressed as: Sigma y is the standard deviation of the sample,/> Is the average of the pixels in the filter window. Where w=exp (-k (C y-Cu)/Cmax-Cy),M is a radiation resolution improvement parameter.
Step S22 specifically includes firstly calculating a backscattering coefficient gradient of a mesoscale vortex SAR image, then setting a backscattering coefficient gradient threshold value parameter T, and finally distinguishing a mesoscale vortex characteristic and a marine background area according to the threshold value parameter T to obtain a mesoscale vortex backscattering coefficient gradient binary image, wherein the criterion of gradient threshold value segmentation is that the backscattering coefficient gradient is larger than the threshold value T, and is determined as a marine mesoscale vortex characteristic area, and is smaller than the threshold value T, and is determined as a background area.
(1) Back scattering coefficient gradient calculation:
(2) And setting a backscattering coefficient gradient threshold parameter T.
(3) And distinguishing the mesoscale vortex characteristics from the ocean background area by using T. The backscattering coefficient gradient is larger than the threshold value T, and the backscattering coefficient gradient is smaller than the threshold value T, and is larger than the threshold value T.
Step S23 specifically includes setting a small-area scatter point eliminating parameter P, deleting a block smaller than an area threshold parameter P in a mesoscale vortex backscattering coefficient gradient binary image, and obtaining a typical mesoscale vortex block binary image.
Step S24 specifically includes setting an expansion parameter N1, and performing expansion processing on a typical mesoscale eddy block binary image, so as to implement hole filling or intermittent ravine connection of the mesoscale eddy block, thereby obtaining a typical consecutive mesoscale eddy feature block binary image.
The expansion operation can be usedThe formula is as follows:
wherein A represents a typical mesoscale vortex block binary image, and B is a structural element with a parameter of N1.
The step S25 specifically includes setting a corrosion treatment parameter N2, and performing corrosion treatment on a typical consecutive mesoscale eddy block binary image, so as to achieve shrinkage and smoothness of the mesoscale eddy block, and obtain a preliminary mesoscale eddy feature region detection result.
The corrosion operation may be represented by "Θ" as follows:
Wherein C represents a typical coherent mesoscale eddy characteristic block binary image, and D is a structural element with a parameter of N2.
Step S26 specifically includes checking whether a non-mesoscale vortex block exists in the preliminary mesoscale vortex feature region detection result, whether a complete mesoscale vortex phenomenon is not detected, and the like. If the situation exists, carrying out multi-parameter threshold adjustment; otherwise, multi-parameter threshold adjustment is not required.
Step S27 specifically includes resetting the parameters M, T, P, N and N2 in steps S21 to S25, and detecting the mesoscale eddy using the new multiparameter threshold until a single, complete mesoscale eddy feature area detection result is obtained.
Step S3 specifically comprises the steps of extracting a mesoscale vortex edge based on a mesoscale vortex feature region detection result, and obtaining mesoscale vortex edge position parameters;
the step S4 specifically includes extracting a scroll centroid as a mesoscale vortex center based on the mesoscale vortex characteristic region and the edge position, and obtaining a mesoscale vortex center position parameter.
Example 1: a marine mesoscale vortex edge detection method and system based on a scene including marine mesoscale vortex phenomenon is implemented on the basis of high-third SAR satellite data, and the specific flow is as follows:
(1) Gao Jihe resolution mesoscale vortex SAR image
And (3) performing radiation calibration, distance direction correction and geocoding treatment on the high-resolution third-order SAR satellite data with the scene containing the mesoscale vortex phenomenon shown in fig. 2, and intercepting the area where the mesoscale vortex is positioned as shown in fig. 3 to obtain a mesoscale vortex SAR image with high geometric resolution as shown in fig. 4.
1) The SAR data radiometric scaling process proceeds as follows:
Wherein, P d is the back scattering intensity received by the sensor, P t is the transmission power, P n is the additional power, G A is the transmission and receiving antenna gain, G E is the current gain of the radar receiver, G P is the processor constant, R is the distance propagation loss, θ el is the antenna elevation angle, θ az is the antenna azimuth angle, L is the loss of the atmosphere (L a) and the system (L s), a is the scattering area, and σ 0 is the back scattering coefficient.
2) The distance correction is to eliminate the change in brightness in the distance direction caused by the incident angle, and is calculated as follows:
Where σ 0′ (i, j) is the back scattering coefficient result after distance correction and σ 0 (i, j) is the back scattering coefficient before correction.
3) Geocoding is the conversion of SAR data from a range or range projection to a geocoordinate projection using doppler methods.
(2) Method for detecting mesoscale eddy characteristic area by utilizing multiparameter threshold (M, T, P, N, N2)
The flow of detecting the mesoscale eddy current feature area by the multi-parameter threshold (M, T, P, N, N2) method is as follows:
Firstly, setting a parameter M to improve the radiation resolution of the mesoscale vortex SAR image, including frequency domain radiation resolution improvement and airspace radiation resolution improvement through enhancing Lee filtering. The result of the mid-scale vortex SAR image after the radiation resolution improvement is shown in fig. 5.
1) The frequency domain radiation resolution is improved by carrying out weighted average on pixels in a plurality of sub-images, and the specific formula is as follows:
wherein, I M is the image processed according to M, and I i is the neighborhood pixel sub-view.
2) The spatial radiation resolution is improved by enhancing Lee filtering, and the specific formula is as follows:
the coefficient of variation based on the multiplicative noise model is expressed as: Sigma y is the standard deviation of the sample,/> Is the average of the pixels in the filter window. Where w=exp (-k (C y-Cu)/Cmax-Cy),M is a radiation resolution improvement parameter.
Secondly, setting a parameter T, and carrying out backscattering coefficient gradient threshold segmentation to obtain a mesoscale vortex backscattering coefficient gradient threshold diagram (figure 6).
1) The backscattering coefficient gradient of the mesoscale vortex SAR image is calculated, and the formula is as follows:
2) Setting a backscattering coefficient gradient threshold parameter T
3) Gradient threshold segmentation, i.e., using T to distinguish between mesoscale vortex features and marine background regions. The backscattering coefficient gradient is larger than the threshold value T, and the backscattering coefficient gradient is smaller than the threshold value T, and is larger than the threshold value T.
Thirdly, the parameters P are set for small-area scattered point elimination, and a typical mesoscale vortex block binary image (figure 7) is obtained.
And setting a small-area scatter point eliminating parameter P, and deleting a block smaller than an area threshold parameter P in the mesoscale vortex backscattering coefficient gradient binary image.
Fourth, setting a parameter N1, and performing expansion processing on the typical mesoscale eddy block binary image A by using a structural element B with the parameter N1 to obtain a typical continuous mesoscale eddy characteristic block binary image (fig. 8).
The expansion operation can be usedThe formula is as follows:
wherein A represents a typical mesoscale vortex block binary image, and B is a structural element with a parameter of N1.
Fifthly, setting a parameter N2, and performing corrosion treatment on the binary image C of the typical continuous mesoscale eddy characteristic block by using a structural element D with the parameter N2 to obtain a preliminary mesoscale eddy characteristic region detection result (fig. 9).
The expansion operation may be represented by "Θ" as follows:
Wherein C represents a typical coherent mesoscale eddy characteristic block binary image, and D is a structural element with a parameter of N2.
And sixthly, checking whether a non-mesoscale vortex block exists in the detection result of the preliminary mesoscale vortex feature area, whether a complete mesoscale vortex phenomenon is not detected, and the like. As shown in fig. 9, non-mesoscale vortex blocks were found to be present and therefore multi-parameter threshold adjustment was required.
Seventhly, the parameters of M, T, P, N1 and N2 in the steps S21 to S25 are reset, and the mesoscale vortex is detected by using a group of new multi-parameter thresholds of M ' (fig. 10), T ' (fig. 11), P ' (fig. 12), N1' (fig. 13) and N2' (fig. 14), so that a single and complete mesoscale vortex characteristic region detection result is obtained.
(3) Mesoscale vortex edge extraction
And extracting a mesoscale vortex edge based on the mesoscale vortex feature region detection result (fig. 15), and acquiring a mesoscale vortex edge position parameter.
(4) Mesoscale vortex center extraction
The scroll centroid is extracted as a mesoscale vortex center based on the mesoscale vortex feature region and the edge position (fig. 16), and a mesoscale vortex center position parameter is obtained.
The method effectively solves the problem that the mesoscale vortex phenomenon is difficult to effectively detect under the condition of unobvious and unclear view of the mesoscale vortex phenomenon in the SAR image, and has important theoretical value and practical significance for improving the comprehensive application benefit of multi-source high-resolution SAR data and the development of novel SAR detection satellite data.
Claims (1)
1. The marine mesoscale vortex edge detection method based on the multi-parameter threshold is characterized by comprising the following steps of:
Collecting SAR data containing a mesoscale vortex phenomenon, and obtaining a mesoscale vortex SAR image with high geometric resolution through radiation calibration, distance direction correction and geocoding;
Detecting a mesoscale eddy characteristic region of the mesoscale eddy SAR image by adopting a multiparameter threshold method, extracting a mesoscale eddy edge of the mesoscale eddy characteristic region, and obtaining an edge position parameter, wherein the multiparameter threshold method is used for representing that the mesoscale eddy SAR image is adjusted according to a radiation resolution lifting parameter, a backscattering coefficient gradient threshold parameter, a small-area scattered point eliminating parameter, an expansion processing parameter and a corrosion processing parameter, and is used for detecting the mesoscale eddy characteristic region;
based on the mesoscale vortex characteristic region and the edge position parameter, extracting a vortex region centroid as a mesoscale vortex center, and acquiring a mesoscale vortex center position parameter;
In the process of acquiring the mesoscale vortex SAR image, the radiometric scaling expression is as follows:
Where P d is the back scatter intensity received by the sensor, P t is the transmission power, P n is the additional power, For transmission gain,/>For receiving antenna gain,/>The current gain of the radar receiver is represented by G P, the processor constant, R, the distance propagation loss, theta el, the antenna elevation angle, theta az, the antenna azimuth angle, la, the atmospheric loss, ls, the system loss, A, the scattering area and sigma 0 are the backscattering coefficients;
in the process of acquiring the mesoscale eddy SAR image, the distance direction correction is used for eliminating the distance upward brightness change caused by the incident angle;
The distance correction expression is:
Wherein σ 0' (i, j) is the back scattering coefficient result after distance correction, σ 0 (i, j) is the back scattering coefficient before correction;
In the process of acquiring a mesoscale vortex SAR image, the geocoding is used for converting SAR data from a slant range or ground range projection into a geographic coordinate projection by adopting a Doppler method;
the step of acquiring the mesoscale eddy current feature area comprises the following processes:
S201, performing radiation resolution improvement treatment on the mesoscale vortex SAR image;
S202, performing back scattering coefficient gradient threshold segmentation on the mesoscale vortex SAR image;
S203, carrying out small-area scattered point processing on the mesoscale vortex SAR image, and removing an interference block;
s204, performing characteristic image expansion processing on the mesoscale vortex SAR image;
S205, performing characteristic image corrosion treatment on the mesoscale vortex SAR image;
S206, judging whether to adjust by the multi-parameter threshold method according to the initial mesoscale eddy characteristic area obtained in the steps;
S207, if the multi-parameter threshold method is adopted for adjustment, adjusting parameters from S201 to S205 until the final mesoscale eddy characteristic area is obtained;
Setting the radiation resolution improvement parameter in the process of detecting the mesoscale eddy characteristic region by adopting a multiparameter threshold method, and carrying out radiation resolution improvement treatment on the mesoscale eddy SAR image;
The radiation resolution improvement process includes: the frequency domain radiation resolution and the airspace radiation resolution are improved; the formula for improving the frequency domain radiation resolution is as follows:
Wherein, I M is an image processed according to M, M represents a radiation resolution improvement parameter, and I i is a neighborhood pixel sub-view;
The airspace radiation resolution is improved by enhancing Lee filtering, and the formula for improving the airspace radiation resolution is as follows:
Wherein w=exp (-k (C y-Cu)/Cmax-Cy), Sigma y is the standard deviation of the sample,/>Is the mean value of the pixels in the filter window;
setting a backscattering coefficient gradient threshold parameter in the process of detecting a mesoscale eddy characteristic region by adopting a multiparameter threshold method, and carrying out backscattering coefficient gradient threshold segmentation on the mesoscale eddy SAR image;
Distinguishing a mesoscale vortex characteristic region from a marine background region according to the backscattering coefficient gradient threshold parameter by acquiring a backscattering coefficient gradient, and acquiring a mesoscale vortex backscattering coefficient gradient binary image, wherein when the backscattering coefficient gradient is greater than the backscattering coefficient gradient threshold parameter, the mesoscale vortex characteristic region is determined; when the backscattering coefficient gradient is smaller than the backscattering coefficient gradient threshold parameter, determining that the ocean background area is formed;
The expression of the backscattering coefficient gradient is:
In the process of detecting a mesoscale vortex characteristic region by adopting a multiparameter threshold method, deleting a block smaller than the small-area scatter point eliminating parameter in the mesoscale vortex backscattering coefficient gradient binary image by setting the small-area scatter point eliminating parameter to obtain a mesoscale vortex block binary image;
In the process of detecting a mesoscale eddy characteristic region by adopting a multiparameter threshold method, performing expansion processing on the mesoscale eddy block binary image by setting the expansion processing parameters to obtain a coherent mesoscale eddy characteristic block binary image, wherein the expansion processing is used for realizing hole filling or intermittent ravines connection of the mesoscale eddy block; the expansion treatment process comprises the following steps:
Wherein A represents a mesoscale vortex block binary diagram, B represents a structural element of an expansion processing parameter, Representing an expansion operation;
setting the corrosion treatment parameters in the process of detecting the mesoscale eddy characteristic region by adopting a multiparameter threshold method, and carrying out corrosion treatment on the coherent mesoscale eddy block binary image to obtain a preliminary mesoscale eddy characteristic region, wherein the corrosion treatment is used for realizing shrinkage and smoothness of the mesoscale eddy block; the expression of the corrosion treatment is as follows:
Wherein C represents a continuous mesoscale eddy characteristic block binary diagram, D is a structural element of corrosion treatment parameters, and Θ represents corrosion operation.
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