CN113702933A - Synthetic aperture radar radiation calibration method and device - Google Patents

Synthetic aperture radar radiation calibration method and device Download PDF

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CN113702933A
CN113702933A CN202110671440.XA CN202110671440A CN113702933A CN 113702933 A CN113702933 A CN 113702933A CN 202110671440 A CN202110671440 A CN 202110671440A CN 113702933 A CN113702933 A CN 113702933A
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reference image
synthetic aperture
aperture radar
image
calibrated
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易明宽
周勇胜
马灵玲
王新鸿
庄丽
王宁
赵永光
汪琪
黎荆梅
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Beijing University of Chemical Technology
Aerospace Information Research Institute of CAS
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Beijing University of Chemical Technology
Aerospace Information Research Institute of CAS
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
    • G01S13/9021—SAR image post-processing techniques

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  • Radar Systems Or Details Thereof (AREA)

Abstract

The invention provides a synthetic aperture radar radiometric calibration method and a synthetic aperture radar radiometric calibration device, which relate to the technical field of radar calibration, and the method comprises the following steps: selecting a corresponding reference image of a synthetic aperture radar load image to be calibrated; verifying whether the reference image meets a first imaging scene, and if so, obtaining a verified reference image; registering the verified reference image with a synthetic aperture radar load image to be calibrated; according to the verified reference image, obtaining surface parameters through inversion, and according to the surface parameters and the synthetic aperture radar load image to be calibrated, obtaining a backscattering coefficient of the synthetic aperture radar load image to be calibrated; according to the backscattering coefficient, the absolute radiation calibration coefficient is obtained, and the radiation calibration is completed.

Description

Synthetic aperture radar radiation calibration method and device
Technical Field
The invention relates to the technical field of radar calibration, in particular to a synthetic aperture radar radiation calibration method and a synthetic aperture radar radiation calibration device.
Background
Synthetic Aperture Radars (SAR) are widely used in important fields such as exploration, environmental monitoring, water and soil monitoring, and the like. Compared with other sensors such as optical, infrared and far infrared sensors, the SAR technology has a unique imaging mode, and can be used for disregarding the influence of atmosphere and illumination, so that all-weather and multi-angle ground shooting and detection tasks are realized. Therefore, by means of the characteristics of the SAR image, the interference of various terrain, illumination and weather conditions can be overcome. Even if the ground trees are shielded from each other, the shielding can be relieved to a certain extent, so that the shielding device has wide utilization value in various fields such as ground exploration and the like. However, the SAR data cannot directly obtain the ground feature parameters, and data conversion processing needs to be performed through radiometric calibration.
SAR radiometric calibration is an indispensable step in quantitative acquisition of surface physical parameters (such as soil humidity and biomass), establishes a relation between an SAR image digital quantization value and a surface feature backscattering coefficient value, and has important significance for quantitative extraction and accurate interpretation of surface feature target characteristics and electromagnetic information contained in SAR data. SAR radiometric calibration is important front-end processing for observing physical characteristics of a target, is processing of end-to-end system performance, and simultaneously establishes an accurate relation between an image and a ground object backscattering coefficient. The absolute radiometric calibration coefficient is a key parameter for linking the gray value of the image pixel of the synthetic aperture radar with the actual backscattering area or coefficient of the target, and accurate calculation of the parameter is an important step in the calibration of the synthetic aperture radar.
Referring to fig. 1, the conventional SAR absolute radiometric calibration method generally uses a single-point stable point target (a manual scaler with a limited number of calibration fields) with a known true value of the backscatter area or a uniform tropical rainforest target with the backscatter coefficient not changing with the incident angle of the radar. The methods are limited by the satellite revisiting period to a great extent, and have great defects in the calibration timeliness; absolute radiometric calibration by the point target method requires a large number of manual calibrators to be laid. The manpower and material resources of the development, transportation, installation, long-term field operation maintenance and other work of the artificial scaler are greatly consumed, and the revisit period is long; the method for calibrating by the uniform tropical rainforest is limited by the limited number of natural scenes and the limitation of geographic space of the tropical rainforest, and can only calibrate once at intervals. Both of these factors greatly limit the timeliness of the calibration.
Therefore, the need for SAR calibration that can reduce the manpower and material resources consumed in the experimental process while ensuring timeliness is an important issue to be solved in the industry at present.
Disclosure of Invention
The invention provides a synthetic aperture radar radiometric calibration method and a synthetic aperture radar radiometric calibration device, which are used for overcoming the defects that manpower and material resources are greatly consumed and timeliness cannot be guaranteed in the calibration process in the prior art, omitting an external calibration test flow for placing reference equipment, expanding a distributed target standard reference range, realizing normalized monitoring of a calibration coefficient and guaranteeing normalized monitoring of the calibration coefficient.
The invention provides a synthetic aperture radar radiation calibration method, which comprises the following steps:
selecting a corresponding reference image of a synthetic aperture radar load image to be calibrated; wherein the spatial resolution ratio of the reference image to the synthetic aperture radar payload image is within a first selected threshold;
verifying whether the reference image meets a first imaging scene, and if the reference image meets the first imaging scene condition, obtaining a verified reference image;
registering the verified reference image with a synthetic aperture radar load image to be calibrated, and converting the geometric relation and the resolution of the verified reference image into the geometric relation and the resolution consistent with the synthetic aperture radar load image to be calibrated;
according to the verified reference image, obtaining surface parameters through inversion, and according to the surface parameters and the synthetic aperture radar load image to be calibrated, obtaining a backscattering coefficient of the synthetic aperture radar load image to be calibrated;
and obtaining an absolute radiometric calibration coefficient according to the backscattering coefficient to finish radiometric calibration.
According to the synthetic aperture radar radiation calibration method provided by the invention, whether a reference image meets a first imaging scene is verified, and if the reference image meets the first imaging scene condition, a verified reference image is obtained; the method specifically comprises the following steps:
acquiring the root mean square height of the ground surface of the imaging scene of the reference image, and judging whether the imaging scene of the reference image meets a first imaging scene condition or not according to scene parameters; the scene parameters comprise radar carrier wave number, radar incidence angle and incidence frequency of the synthetic aperture radar for generating a load image of the synthetic aperture radar to be calibrated, and soil water content;
if the imaging scene of the reference image meets the first imaging scene condition, the reference image is reserved to obtain a verified reference image;
and if the imaging scene of the reference image does not meet the first imaging scene condition, deleting the reference image and reselecting the reference image.
According to the synthetic aperture radar radiometric calibration method provided by the invention, the verified reference image and the synthetic aperture radar load image to be calibrated are registered, and the geometric relation and the resolution of the verified reference image are converted to be consistent with the synthetic aperture radar load image to be calibrated, and the method specifically comprises the following steps:
taking a synthetic aperture radar load image to be calibrated as a reference image;
performing first translation registration on pixel positions corresponding to the synthetic aperture radar load image to be calibrated and the verified reference image by taking the edge equal points in the reference image as control points;
and performing second translation registration on the pixel positions corresponding to the synthetic aperture radar load image to be calibrated after the first registration and the verified reference image through a maximum correlation function method, and converting the geometric relation and the resolution of the verified reference image to be consistent with the synthetic aperture radar load image to be calibrated.
According to the synthetic aperture radar radiometric calibration method provided by the invention, the earth surface parameters are obtained through inversion according to the verified reference image, and the backscattering coefficient of the synthetic aperture radar load image to be calibrated is obtained according to the earth surface parameters and the synthetic aperture radar load image to be calibrated, and the synthetic aperture radar radiometric calibration method specifically comprises the following steps:
according to the length of a grid of a synthetic aperture radar load image to be calibrated, carrying out grid division on a verified reference image and the synthetic aperture radar load image to be calibrated, and dividing the verified reference image and the synthetic aperture radar load image to be calibrated into grids with the side length of l multiplied by l; wherein, the l is the correlation length;
obtaining a backscattering coefficient of the verified reference image according to the divided verified reference image; the backscatter coefficients of the verified reference image comprise a backscatter coefficient of the verified reference image in a horizontal transmitting and receiving polarization direction and a backscatter coefficient of the verified reference image in a vertical transmitting and receiving polarization direction;
inverting the earth surface parameters according to the backscattering coefficient of the verified reference image; the surface parameters comprise a real surface dielectric constant part and a root-mean-square height of the surface;
obtaining a backscattering coefficient of the synthetic aperture radar load image to be calibrated according to the earth surface parameters and the self attitude data of the synthetic aperture radar load image to be calibrated; the self attitude data comprises an incidence angle and a wave number, and the backscattering coefficient of the synthetic aperture radar load image to be calibrated comprises a backscattering coefficient of the synthetic aperture radar load image to be calibrated in a horizontal transmitting and receiving polarization direction and a backscattering coefficient of the synthetic aperture radar load image to be calibrated in a vertical transmitting and receiving polarization direction.
According to the synthetic aperture radar radiometric calibration method provided by the invention, an absolute radiometric calibration coefficient is obtained according to the backscattering coefficient, and the radiometric calibration is completed, and the method specifically comprises the following steps:
acquiring an absolute radiometric calibration coefficient of each grid of the synthetic aperture radar load image to be calibrated by taking the grid as a unit according to the backscattering coefficient of the synthetic aperture radar load image to be calibrated;
and taking the mean value of the absolute radiometric calibration coefficients of all the grids to obtain the absolute radiometric calibration coefficient of the synthetic aperture radar load image to be calibrated, and finishing radiometric calibration.
According to the synthetic aperture radar radiation calibration method provided by the invention, whether a reference image meets a first imaging scene is verified, and if the reference image meets the first imaging scene condition, a verified reference image is obtained; the method also comprises the following steps:
and preprocessing the synthetic aperture radar load image to be calibrated and the reference image.
According to the synthetic aperture radar radiometric calibration method provided by the invention, the synthetic aperture radar load image to be calibrated and the reference image are preprocessed, and the method specifically comprises the following steps:
determining a target scene area, and selecting data of a synthetic aperture radar load image to be calibrated and data of a reference image in the target scene area to obtain a cutting data set;
performing track correction on the cutting data set to obtain a first correction data set;
carrying out coherent speckle filtering on the first correction data set to obtain a filtering data set;
and performing relative radiation correction on the filtering data set to obtain a second correction data set, namely the preprocessed synthetic aperture radar load image to be calibrated and the reference image.
The invention also provides a synthetic aperture radar radiation calibration device, which comprises the following steps:
the reference image selecting module is used for selecting a corresponding reference image of the synthetic aperture radar load image to be calibrated; wherein the spatial resolution ratio of the reference image to the synthetic aperture radar payload image is within a first selected threshold;
the uniform bare ground checking module is used for verifying whether the reference image meets a first imaging scene or not, and if the reference image meets the first imaging scene condition, obtaining a verified reference image;
the registration module is used for registering the verified reference image and the synthetic aperture radar load image to be calibrated and converting the geometric relation and the resolution of the verified reference image into the geometric relation and the resolution which are consistent with the synthetic aperture radar load image to be calibrated;
the backscattering coefficient acquisition module is used for obtaining surface parameters through inversion according to the verified reference image and obtaining backscattering coefficients of the synthetic aperture radar load image to be calibrated according to the surface parameters and the synthetic aperture radar load image to be calibrated;
and the radiation calibration module is used for obtaining an absolute radiation calibration coefficient according to the backscattering coefficient to finish radiation calibration.
The invention also provides an electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the steps of the synthetic aperture radar radiometric calibration method according to any of the above.
The invention also provides a non-transitory computer readable storage medium having stored thereon a computer program which, when executed by a processor, performs the steps of the synthetic aperture radar radiometric calibration method according to any of the above-mentioned methods.
The invention provides a synthetic aperture Radar radiometric calibration method and a device, which are the absolute radiometric calibration method and the device aiming at SAR real data under the actual condition, different from the traditional absolute radiometric calibration method, the image data after calibration processing of a calibrated satellite-borne or airborne load is taken as the reference data of Radar scattering Cross section (RCS) to calculate the absolute radiometric calibration coefficient of the synthetic aperture Radar load image to be calibrated, and whether the reference image meets a first imaging scene is verified, the verified reference image is obtained, a reference area can be effectively screened, the influence on the subsequent radiometric calibration caused by the data not meeting the bare ground requirement is reduced, the geometric relation and the resolution of the verified reference image are converted to be consistent with the synthetic aperture Radar load image to be calibrated by registering the reference image and the synthetic aperture Radar load image to be calibrated, the load image of the synthetic aperture radar to be calibrated is used as a reference image during registration, the reference image is registered, so that the registration precision reaches the pixel level, the matching between the images is more accurate, the traditional absolute radiometric calibration method is avoided through inversion, so that the acquired backscattering parameters are more accurate and reliable, then more accurate and reliable absolute radiometric calibration coefficients are obtained according to the acquired backscattering parameters, the calculation of the needed backscattering coefficient is carried out on the basis of inversion, an external calibration test flow for placing reference equipment is omitted, the standard reference range of the distributed targets is expanded, the normalized monitoring of the calibration coefficient can be realized, meanwhile, manpower and material resources consumed in the experimental process can be reduced, the time consumed for laying single external calibration experimental equipment is reduced, multiple times of calibration can be realized in a short time, and the normalized monitoring of the calibration coefficient is ensured.
Drawings
In order to more clearly illustrate the technical solutions of the present invention or the prior art, the drawings needed for the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.
FIG. 1 is a schematic flow diagram of a prior art synthetic aperture radar radiometric calibration method;
FIG. 2 is a schematic flow chart of a SAR radiometric calibration method provided by the present invention;
fig. 3 is a flowchart illustrating a step S200 in the method for calibrating radiation of a synthetic aperture radar according to the present invention;
fig. 4 is a flowchart illustrating a step S300 in the method for calibrating radiation of a synthetic aperture radar according to the present invention;
fig. 5 is a flowchart illustrating a step S400 in the method for calibrating radiation of a synthetic aperture radar according to the present invention;
fig. 6 is a flowchart illustrating a step S500 in the method for calibrating radiation of a synthetic aperture radar according to the present invention;
FIG. 7 is a second schematic flow chart of a SAR radiometric calibration method provided by the present invention;
fig. 8 is a flowchart illustrating a step a200 in the method for calibrating radiation of a synthetic aperture radar according to the present invention;
FIG. 9 is a logic diagram of a synthetic aperture radar radiometric calibration method provided by the present invention;
FIG. 10 is a schematic structural diagram of a SAR radiometric calibration device provided by the present invention;
FIG. 11 is a schematic diagram of a detailed structure of a uniform bare ground calibration module in the SAR radiometric calibration apparatus provided by the present invention;
fig. 12 is a schematic structural diagram of a specific registration module in the synthetic aperture radar radiometric calibration apparatus provided by the present invention;
fig. 13 is a schematic structural diagram of a backscatter coefficient obtaining module in the synthetic aperture radar radiometric calibration apparatus provided by the present invention;
fig. 14 is a schematic structural diagram of a radiometric calibration module in the synthetic aperture radar radiometric calibration device provided by the present invention;
FIG. 15 is a second schematic structural diagram of a SAR radiometric calibration device provided by the present invention;
FIG. 16 is a schematic diagram of a specific structure of a preprocessing module in the SAR radiometric calibration device provided by the present invention;
fig. 17 is a schematic structural diagram of an electronic device provided by the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The synthetic aperture radar radiometric calibration method of the present invention is described below with reference to fig. 2 and 9, the method comprising the steps of:
s100, selecting a corresponding reference image of the SAR load image to be calibrated; and the spatial resolution ratio of the reference image to the SAR load image is within a first selected threshold value.
In step S100, the purpose is to select a high-precision SAR load image with similar spatial resolution, illuminating the same imaging scene, and having a small transit time difference from the SAR load image to be calibrated as a reference image. The set of reference images and the SAR load image to be calibrated need to be corrected and calibrated to the backscattering coefficient.
In one alternative, the reference image is selected as a Radarsat-2 satellite image. Radarsat-2 is a C-band satellite and has a variety of polarization options available. The satellite data resolution can reach 1m at most, the calibration precision is high, and the experimental requirements of the invention are met. The synthetic aperture radar radiometric calibration method selects the complete polarization data of the uniform rough bare ground target irradiated by the Radarsat-2 satellite and coincided with the satellite of the SAR load image to be calibrated, and the selected Radarsat-2 image and the SAR load image to be calibrated have close spatial resolution, irradiate the same scene and have little transit time difference.
It should be noted that, preferably, the reference image is image data after calibration processing of a calibrated satellite-borne or airborne load.
In this embodiment, the value range of the first selected threshold is 0.5 to 2, that is, the spatial resolution ratio of the reference image to the SAR load image to be calibrated is 0.5 to 2 times.
S200, verifying whether the reference image meets a first imaging scene or not, and if the reference image meets the first imaging scene condition, obtaining a verified reference image;
the synthetic aperture radar radiometric calibration method of the invention can use Dubois formula to obtain each parameter, and simultaneously, the Dubois formula has the application conditions that: the product ks of the radar carrier wave number k and the root mean square height s of the earth surface is less than 2.5, the radar incidence angle theta is more than or equal to 30 degrees, the incidence frequency f is between 1.5 and 11GHz, and the soil water content mvLess than 35%. The purpose of step S200 is to verify whether the imaging scene of the image to be referenced, i.e. the selected surface parameters of the uniform bare area and the wave number of the reference image, are within the application conditions of the Dubois formula, so as to determine whether the reference image can be applied in the subsequent steps.
S300, registering the verified reference image and the SAR load image to be calibrated, and converting the geometric relation and the resolution of the verified reference image into the geometric relation and the resolution which are consistent with the SAR load image to be calibrated.
The purpose of the step S300 is to make the horizontal and vertical coordinates of the pixel images of the reference image and the SAR load image to be calibrated correspond to each other one by one, so as to ensure that the image numerical value Ian of the reference image and the SAR load image to be calibrated can be directly calculated and compared.
S400, obtaining surface parameters through inversion according to the verified reference image, and obtaining a backscattering coefficient of the SAR load image to be calibrated according to the surface parameters and the SAR load image to be calibrated.
After the data preparation of step S100, the uniform bare ground condition check of step S200 and the image registration of step S300 are performed, the formal calculation of the backscattering coefficient of the SAR load image to be calibrated is started in step S400.
S500, obtaining an absolute radiometric calibration coefficient according to the backscattering coefficient, and finishing radiometric calibration.
The invention relates to a synthetic aperture radar radiation calibration method, which is an absolute radiation calibration method aiming at SAR real data under the real condition, and is different from the traditional absolute radiation calibration method, image data after calibration satellite-borne or airborne load correction processing is used as reference data of RCS to calculate the absolute radiation calibration coefficient of an SAR load image to be calibrated, whether the reference image meets a first imaging scene is verified, the verified reference image is obtained, a reference area can be effectively screened, the influence on the subsequent radiation calibration caused by the data not meeting the bare ground requirement is reduced, the geometric relation and the resolution of the verified reference image are converted to be consistent with the SAR load image to be calibrated by registering the reference image and the SAR load image to be calibrated, the SAR load image to be calibrated is used as a reference image during the registration, the registration of the reference image is carried out, so that the registration precision reaches the pixel level, the matching between the images is more accurate, the traditional absolute radiometric calibration method is avoided through inversion, the acquired backscattering parameters are more accurate and reliable, then more accurate and reliable absolute radiometric calibration coefficients are obtained according to the acquired backscattering parameters, the needed backscattering coefficients are calculated on the basis of inversion, an external calibration test flow for placing reference equipment is omitted, the standard reference range of a distributed target is enlarged, the normalization monitoring of the calibration coefficients can be realized, meanwhile, the manpower and material resources consumed in the experimental process can be reduced, the time consumed for laying single external calibration experimental equipment is reduced, multiple times of calibration can be realized in a short time, and the normalization monitoring of the calibration coefficients is guaranteed.
The synthetic aperture radar radiometric calibration method of the present invention is described below with reference to fig. 3, where step S200 specifically includes the following steps:
s210, acquiring the root-mean-square height of the ground surface of the imaging scene of the reference image, and judging whether the imaging scene of the reference image meets a first imaging scene condition or not according to scene parameters; the scene parameters comprise radar carrier wave number, radar incidence angle and incidence frequency of the SAR used for generating the SAR load image to be calibrated, and soil water content.
In step S210, surface parameter estimation is performed on the reference load image imaging scene to verify whether the imaging area meets the application condition of the Dubois formula. Specifically, whether an imaging area meets application conditions of a Dubois formula is verified through an oh bare soil empirical model, and the root mean square height s of the earth surface is estimated through the oh empirical model, wherein an expression of the oh empirical model is shown as a formula (1), and the formula (1) is as follows:
σvh＝0.11mv 0.7(cosθ)2.2[1-exp(-0.32(ks))1.8] (1)
therefore, the root mean square height s of the earth surface can be derived through an oh empirical model, and the calculation formula is shown as formula (2), and formula (2) is:
Figure BDA0003119443820000111
wherein σvhIs the backscattering coefficient m in the vertical transmission and horizontal reception polarization direction of the reference imagevIs the soil moisture content of the imaged scene, and theta is the incident angle of the reference image on the uniform rough bare soil target, namely the radar incident angle. In this embodiment, the soil moisture content m for the imaged scenevThe Information is obtained by querying a World Soil Information base (HWSD) and a Soil Information System (SIS).
S220, if the imaging scene of the reference image meets the first imaging scene condition, the reference image is reserved to obtain a verified reference image;
and S230, if the imaging scene of the reference image does not meet the first imaging scene condition, deleting the reference image, and reselecting the reference image, namely executing the steps S100 and the following steps.
If the calculated ks is less than 2.5, the water content m of the soilvIf the average value is less than 35%, the target is regarded as an effective uniform rough bare target, otherwise, the step S100 is returned again, and the reference image is picked again.
It should be noted that the root mean square height calculated by the selected uniform rough bare land in the synthetic aperture radar radiometric calibration method of the present invention is centimeter level, the water content of the selected uniform rough bare soil target soil is about 15%, and all parameters satisfy the application conditions of the Dubois formula.
The synthetic aperture radar radiometric calibration method of the present invention is described below with reference to fig. 4, where step S300 specifically includes the following steps:
s310, firstly, the SAR load image to be calibrated is used as a reference image.
And S320, performing first translation registration on pixel positions corresponding to the SAR load image to be calibrated and the verified reference image by taking the edge angle equal points in the reference image as control points, wherein the first translation registration is subjective registration on the two images of the verified reference image and the SAR load image to be calibrated.
S330, performing second translation registration on the pixel positions corresponding to the SAR load image to be calibrated after the first registration and the verified reference image through a maximum correlation function method, and converting the geometric relation and the resolution of the verified reference image to be consistent with the SAR load image to be calibrated. For example, after the processing in step S200, the size of the SAR load image to be calibrated is 100 × 100, and in step S320, the size of the reference image is subjectively reduced by using the edge equal point in the SAR load image to be calibrated as a control point. And adjusting the size of the verified reference image to 110 × 110, and reserving a10 × 10 size pre-selection frame for registration by the maximum correlation function method in the subsequent step S330.
The step S330 uses a maximum correlation function method to perform formal image registration, and the correlation function method is a basic method for image registration and is the basis of many matching algorithms. The maximum correlation function method calculates the cross-correlation coefficient R of two images at different azimuth and distance offsets, and in this embodiment, the image position at which R is maximized is taken for image cropping, the expression of the maximum correlation function method is shown in formula (3), and formula (3) is:
Figure BDA0003119443820000121
where u 'is the frequency shift in the range direction and v' is the offset in the azimuth direction. The amplitudes of the SAR load image to be calibrated and the reference image after verification are respectively M1(i,j)、M2(i, j). And selecting u 'and v' with the maximum R as a registration result, and finishing pixel-level registration between the verified reference image and the SAR load image to be calibrated.
After the processing of step S300, the verified reference image data is also cropped to a size of 100 × 100.
The synthetic aperture radar radiometric calibration method of the present invention is described below with reference to fig. 5, where step S400 specifically includes the following steps:
s410, according to the grid length of the verified SAR load image, grid division is carried out on the reference image and the verified SAR load image, and the reference image and the verified SAR load image are divided into grids with side length of l multiplied by l; l is the correlation length.
In step S410, in order to reduce errors caused by uneven ground surface, poor registration effect, influence of incident angles, and influence of system parameters, it is necessary to perform mesh division on the verified reference image and the SAR load image to be calibrated, the length of the mesh is determined according to the SAR load image to be calibrated, first, a distance-to-mean value of a selected bare area is calculated, a spatial correlation function of a discrete point target is calculated by using the distance-to-mean value, a spatial correlation function calculation formula is shown in formula (4), and formula (4) is:
Figure BDA0003119443820000131
wherein z isiTaking the maximum integral value when rho (l) is less than or equal to 1/e as the statistical correlation length between the backscattering coefficient values of the image pixels, and dividing the reference image and the verified SAR load image into grids with the side length of l multiplied by l.
For example, the correlation length l is calculated to be 10, and thus the image is divided into a grid having a side length of 10 × 10. And taking the mean value of the backscattering coefficient values under various polarization modes in the grid, and compressing the selected verified reference image and the data of the SAR load image to be calibrated to 10 multiplied by 10.
S420, obtaining a backscattering coefficient of the reference image according to the divided reference image; wherein, the backscattering coefficient of the reference image comprises the backscattering coefficient of the horizontal emission and horizontal receiving polarization direction and the backscattering coefficient of the vertical emission and vertical receiving polarization direction of the reference image.
Step S420 is to take the mean value of the backscattering coefficient values in various polarization modes in the grid, and use the mean value as the backscattering coefficient value used when performing the inversion by the Dubois formula.
S430, inverting the earth surface parameters according to the backscattering coefficient of the reference image; the surface parameters comprise a real part of the surface dielectric constant and a root-mean-square height of the surface.
In step S430, the real part of the surface dielectric constant ∈' and the root-mean-square height S of the surface are calculated back using the Dubois formula, and the specific calculation formula is shown in formula (5) and formula (6), where formula (5) and formula (6) are respectively:
Figure BDA0003119443820000132
Figure BDA0003119443820000141
wherein σHHBackscatter coefficients, σ, for horizontal transmit horizontal receive polarization directions of the verified reference imageVVAnd vertically transmitting the backscatter coefficients perpendicular to the receiving polarization direction for the verified reference image. And k is the verified reference image carrier wave number, and the expression is k-2 pi/lambda. λ is carrier wavelength, θ0Indicating the radar incidence angle of the verified reference image.
In this embodiment, the second inspection may be performed on the real part epsilon 'of the surface dielectric constant and the root-mean-square height s of the surface obtained by inversion, the real part epsilon' of the surface dielectric constant is calculated by fitting a Topp empirical model, the expression of the Topp empirical model is formula (7), and the formula (7) is:
mv＝-5.3×10-2+2.92×10-2ε'-5.5×10-4(ε')2+4.3×10-6(ε')3 (7)
and comparing the real part epsilon 'of the surface dielectric constant and the root mean square height s of the surface obtained by the Dubois formula inversion with the real part epsilon' of the surface dielectric constant estimated by the Topp empirical formula and the root mean square height s of the surface calculated by the oh model (calculated by the formula (1)), judging the accuracy of the surface parameters obtained by the Dubois inversion again, and re-selecting the data set if the accuracy error is large. In this embodiment, the threshold of the error is set to 10%, and when the accuracy error exceeds 10%, the data set is reselected, that is, the reference image is reselected, and the corresponding steps are continuously performed afterwards.
S440, obtaining a backscattering coefficient of the verified SAR load image according to the earth surface parameters and the self attitude data of the verified SAR load image; the self-attitude data comprises an incidence angle and a wave number, and the backscatter coefficients of the verified SAR load image comprise the backscatter coefficients of the verified SAR load image in a horizontal transmitting and receiving polarization direction and the backscatter coefficients of the verified SAR load image in a vertical transmitting and receiving polarization direction.
In step S440, the real part of the surface dielectric constant ∈ obtained by inversion of the Duboi formula, the root-mean-square height S of the surface, and the incidence angle θ and the wave number k of the posture data of the load image to be calibrated are substituted into the Dubois model for calculation. Calculating the backscattering coefficient of the SAR load image to be calibrated
Figure BDA0003119443820000142
Figure BDA0003119443820000143
Receiving the backscattering coefficient in the polarization direction for the horizontal transmission level of the SAR load image to be calibrated,
Figure BDA0003119443820000144
specifically, the calculation formula of the Dubois model is shown in formula (8) and formula (9), and formula (8) and formula (9) are respectively as follows:
Figure BDA0003119443820000151
Figure BDA0003119443820000152
the synthetic aperture radar radiometric calibration method of the present invention is described below with reference to fig. 6, where step S500 specifically includes the following steps:
s510, obtaining an absolute radiation calibration coefficient of each grid of the AR load image to be calibrated by taking the grid as a unit, namely the grid with the size of 10 multiplied by 10 as a unit in the embodiment, according to the backscattering coefficient of the SAR load image to be calibrated;
s520, taking the mean value of the absolute radiometric calibration coefficients of all grids to obtain the absolute radiometric calibration coefficient of the SAR load image to be calibrated, and finishing radiometric calibration. The absolute radiometric calibration coefficient calculation formula is shown as formula (10), and formula (10) is:
Figure BDA0003119443820000153
wherein CF is the absolute radiometric calibration coefficient,
Figure BDA0003119443820000154
for horizontally transmitting and horizontally receiving remote sensing image pixel brightness (DN) values in the polarization direction of the SAR load image to be calibrated,
Figure BDA0003119443820000155
receiving the backscatter coefficient value in the polarization direction for the horizontal transmission level of the SAR payload image to be calibrated calculated by the Dubois formula.
After that, the absolute emissivity calculated in step S520 may also be used. And comparing the calculation result with the real absolute radiation coefficient, calculating the error rate, and judging the accuracy of the synthetic aperture radar radiometric calibration method.
The synthetic aperture radar radiometric calibration method of the present invention is described below in connection with fig. 7, and in another embodiment, the method comprises the steps of:
a100, selecting a corresponding reference image of a synthetic aperture radar load image to be calibrated; wherein the spatial resolution ratio of the reference image to the synthetic aperture radar payload image is within a first selected threshold.
And A200, preprocessing the SAR load image to be calibrated and the reference image.
And A300, verifying whether the reference image meets a first imaging scene, and if the reference image meets the first imaging scene condition, obtaining a verified reference image.
And A400, registering the verified reference image with the synthetic aperture radar load image to be calibrated, and converting the geometric relation and the resolution of the verified reference image into the geometric relation consistent with the synthetic aperture radar load image to be calibrated.
And A500, obtaining surface parameters through inversion according to the verified reference image, and obtaining a backscattering coefficient of the synthetic aperture radar load image to be calibrated according to the surface parameters and the synthetic aperture radar load image to be calibrated.
And A600, obtaining an absolute radiometric calibration coefficient according to the backscattering coefficient, and finishing radiometric calibration.
Different from the previous embodiment, in the present embodiment, a step a200 is added between the step a100 and the step a300, and the purpose of the step a200 is to perform a series of processing procedures on the image, so as to improve the precision of satellite orbit state information, reduce system noise, and eliminate systematic errors caused by external factors.
The synthetic aperture radar radiometric calibration method of the present invention is described below with reference to fig. 8, where step a200 specifically includes the following steps:
and A210, determining a target scene area, and selecting data of the SAR load image to be calibrated and the data of the reference image in the target scene area to obtain a cutting data set.
In step a210, the uniform coarse bare soil area is different due to different widths of different SAR satellite images. The reference image and the SAR load image to be calibrated need to be roughly cut, and data in a target scene area is cut to be used as a cutting data set.
For example, the size of the reference image after cropping is 200 × 200, the size of the SAR load image to be calibrated is 100 × 100, and a larger area of the reference image is intercepted so as to reserve a certain range for subsequent image registration.
And A220, performing track correction on the cropping data set to obtain a first correction data set.
Step a220 aims at low precision of satellite orbit state information in a satellite raw data file, and accurate orbit information data is needed in subsequent image registration and other processes, so that the trimmed data set needs to be corrected for the first time through an orbit.
And A230, carrying out speckle filtering on the first correction data set to obtain a filtering data set.
Speckle noise is one of the system noises, and the speckle can reduce the signal-to-noise ratio of an image, blur the image, or even eliminate the characteristics of the image. Speckle is an inherent defect of polarized SAR. Coherent spots exist in any polarization mode, and therefore, the coherent spots need to be filtered through step a 230.
And A240, performing relative radiation correction on the filtering data set, particularly performing relative radiation correction on the SAR load image to be calibrated, and processing the SAR load image to be calibrated through the steps A210 to A240 to obtain a second correction data set, namely the preprocessed SAR load image to be calibrated and the reference image.
Step a240 performs relative radiation correction on the SAR load image to be calibrated, so as to eliminate systematic and random radiation distortion or distortion generated by the system in the process of external factors, data acquisition and transmission. In the present embodiment, the relative radiation correction is performed by a method including, but not limited to, a series of processing flows of antenna pattern correction, distance correction, in-device calibration, and the like. The error of the satellite device itself is compensated for by the relative correction in step a 240.
In the synthetic aperture radar radiation calibration method, a series of processing flows of track correction, coherent spot filtering, antenna directional diagram correction, distance correction, in-device calibration and the like are carried out on an image in steps A210 to A240 through SNAP software, so that the satellite track state information precision is improved, the system noise is reduced, and systematic errors caused by external factors are eliminated.
The synthetic aperture radar radiometric calibration device provided by the present invention is described below, and the synthetic aperture radar radiometric calibration device described below and the synthetic aperture radar radiometric calibration method described above may be referred to correspondingly.
The synthetic aperture radar radiometric calibration arrangement of the present invention is described below in connection with fig. 10, the arrangement comprising:
a reference image selection module 100, configured to select a reference image corresponding to an SAR load image to be calibrated; and the spatial resolution ratio of the reference image to the SAR load image is within a first selected threshold value.
A uniform bare ground verifying module 200, configured to verify whether the reference image meets a first imaging scene, and if the reference image meets the first imaging scene condition, obtain a verified reference image;
and the registration module 300 is configured to register the verified reference image with the SAR load image to be calibrated, and convert the geometric relationship and the resolution of the verified reference image into the geometric relationship and the resolution consistent with the SAR load image to be calibrated.
And the backscattering coefficient acquisition module 400 is configured to obtain a surface parameter through inversion according to the verified reference image, and obtain a backscattering coefficient of the SAR load image to be calibrated according to the surface parameter and the SAR load image to be calibrated.
And the radiometric calibration module 500 is configured to obtain an absolute radiometric calibration coefficient according to the backscatter coefficient, and complete radiometric calibration.
In the following, the synthetic aperture radar radiometric calibration apparatus of the present invention is described with reference to fig. 11, where the uniform bare ground verification module 200 specifically includes:
the first checking unit 210 is configured to obtain a root mean square height of a ground surface of an imaging scene of the reference image, and determine whether the imaging scene of the reference image meets a first imaging scene condition according to a scene parameter; the scene parameters comprise radar carrier wave number, radar incidence angle and incidence frequency of the SAR used for generating the SAR load image to be calibrated, and soil water content.
In the first verification unit 210, the surface parameters of the reference load image imaging scene are estimated, and whether the imaging area meets the application condition of the Dubois formula is verified.
A second checking unit 220, configured to, if an imaging scene of the reference image meets the first imaging scene condition, reserve the reference image to obtain a verified reference image;
the third verifying unit 230 is configured to delete the reference image and re-select the reference image if the imaging scene of the reference image does not satisfy the first imaging scene condition, and then execute the reference image selecting module 100 and subsequent steps.
In the following, the synthetic aperture radar radiometric calibration apparatus of the present invention is described with reference to fig. 12, and the registration module 300 specifically includes:
a first registration unit 310, configured to use the SAR load image to be calibrated as a reference image.
And the second registration unit 320 is configured to perform first translation registration on pixel positions corresponding to the to-be-calibrated SAR load image and the verified reference image, with the edge equal point in the reference image as a control point.
And the third registration unit 330 is configured to perform second translation registration on the pixel positions corresponding to the to-be-calibrated SAR load image after the first registration and the verified reference image by using a maximum correlation function method, and convert the geometric relationship and the resolution of the verified reference image into the to-be-calibrated SAR load image, which is consistent.
In the following, the synthetic aperture radar radiometric calibration apparatus of the present invention is described with reference to fig. 13, and the backscatter coefficient obtaining module 400 specifically includes:
the first obtaining unit 410 is configured to perform mesh division on the reference image and the verified SAR load image according to the mesh length of the verified SAR load image, and divide both the reference image and the verified SAR load image into meshes with side lengths of l × l; l is the correlation length.
A second obtaining unit 420, configured to obtain a backscattering coefficient of the reference image according to the divided reference image; wherein, the backscattering coefficient of the reference image comprises the backscattering coefficient of the horizontal emission and horizontal receiving polarization direction and the backscattering coefficient of the vertical emission and vertical receiving polarization direction of the reference image.
The second obtaining unit 420 uses the mean value of the backscattering coefficient values in various polarization modes in the grid as the backscattering coefficient value used when the Dubois formula is used for inversion.
A third obtaining unit 430, configured to invert the surface parameters according to the backscattering coefficient of the reference image; the surface parameters comprise a real part of the surface dielectric constant and a root-mean-square height of the surface.
The fourth obtaining unit 440 is configured to obtain a backscattering coefficient of the verified SAR load image according to the surface parameter and the self-posture data of the verified SAR load image; the self-attitude data comprises an incidence angle and a wave number, and the backscatter coefficients of the verified SAR load image comprise the backscatter coefficients of the verified SAR load image in a horizontal transmitting and receiving polarization direction and the backscatter coefficients of the verified SAR load image in a vertical transmitting and receiving polarization direction.
The synthetic aperture radar radiometric calibration apparatus of the present invention is described below with reference to fig. 14, where the radiometric calibration module 500 specifically includes:
a first scaling unit 510, configured to obtain an absolute radiation scaling coefficient of each grid of the AR load image to be scaled, by using the grid as a unit, in this embodiment, that is, by using a grid with a size of 10 × 10 as a unit, according to a backscattering coefficient of the SAR load image to be scaled;
and a second scaling unit 520, configured to take an average of the absolute radiometric scaling coefficients of all the grids, obtain an absolute radiometric scaling coefficient of the SAR load image to be scaled, and complete radiometric scaling.
In another embodiment, which is different from the previous embodiment, a preprocessing module 600 is added between the reference image selecting module 100 and the uniform ground verifying module 200.
In the following, the synthetic aperture radar radiometric calibration apparatus of the present invention is described with reference to fig. 16, and the preprocessing module 600 specifically includes:
the first processing unit 610 is configured to determine a target scene area, select data of the SAR load image to be calibrated and the reference image located in the target scene area, and obtain a clipping data set.
And the second processing unit 620 is configured to perform track correction on the clipping data set to obtain a first correction data set.
The second processing unit 620 aims at that the precision of the satellite orbit state information in the satellite raw data file is not high, and the precise orbit information data is needed in the subsequent image registration and other processes, so that the first correction processing needs to be performed on the cutting data set through the orbit.
The third processing unit 630 is configured to perform speckle filtering on the first correction data set to obtain a filtered data set.
The fourth processing unit 640 is configured to perform relative radiation correction on the filtered data set, specifically, perform relative radiation correction on the SAR load image to be calibrated, and obtain a second corrected data set, that is, the preprocessed SAR load image to be calibrated and the reference image, after the processing by the first processing unit 610 to the fourth processing unit 640.
The fourth processing unit 640 performs relative radiation correction on the SAR load image to be calibrated, so as to eliminate systematic and random radiation distortion or distortion generated by the system in the external factors, data acquisition and transmission processes.
Fig. 17 illustrates a physical structure diagram of an electronic device, and as shown in fig. 17, the electronic device may include: a processor (processor)810, a communication Interface 820, a memory 830 and a communication bus 840, wherein the processor 810, the communication Interface 820 and the memory 830 communicate with each other via the communication bus 840. Processor 810 may invoke logic instructions in memory 830 to perform a synthetic aperture radar radiometric calibration method comprising:
s100, selecting a corresponding reference image of a synthetic aperture radar load image to be calibrated; wherein the spatial resolution ratio of the reference image to the synthetic aperture radar payload image is within a first selected threshold;
s200, verifying whether the reference image meets a first imaging scene or not, and if the reference image meets the first imaging scene condition, obtaining a verified reference image;
s300, registering the verified reference image with a synthetic aperture radar load image to be calibrated, and converting the geometric relation and the resolution of the verified reference image into the geometric relation and the resolution consistent with the synthetic aperture radar load image to be calibrated;
s400, obtaining surface parameters through inversion according to the verified reference image, and obtaining a backscattering coefficient of the synthetic aperture radar load image to be calibrated according to the surface parameters and the synthetic aperture radar load image to be calibrated;
s500, obtaining an absolute radiometric calibration coefficient according to the backscattering coefficient, and finishing radiometric calibration.
In addition, the logic instructions in the memory 830 may be implemented in software functional units and stored in a computer readable storage medium when the logic instructions are sold or used as independent products. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
In another aspect, the present invention also provides a computer program product comprising a computer program stored on a non-transitory computer readable storage medium, the computer program comprising program instructions which, when executed by a computer, enable the computer to perform the synthetic aperture radar radiometric calibration method provided by the above methods, the synthetic aperture radar radiometric calibration method comprising:
s100, selecting a corresponding reference image of a synthetic aperture radar load image to be calibrated; wherein the spatial resolution ratio of the reference image to the synthetic aperture radar payload image is within a first selected threshold;
s200, verifying whether the reference image meets a first imaging scene or not, and if the reference image meets the first imaging scene condition, obtaining a verified reference image;
s300, registering the verified reference image with a synthetic aperture radar load image to be calibrated, and converting the geometric relation and the resolution of the verified reference image into the geometric relation and the resolution consistent with the synthetic aperture radar load image to be calibrated;
s400, obtaining surface parameters through inversion according to the verified reference image, and obtaining a backscattering coefficient of the synthetic aperture radar load image to be calibrated according to the surface parameters and the synthetic aperture radar load image to be calibrated;
s500, obtaining an absolute radiometric calibration coefficient according to the backscattering coefficient, and finishing radiometric calibration.
In yet another aspect, the present invention also provides a non-transitory computer readable storage medium having stored thereon a computer program which, when executed by a processor, is implemented to perform the synthetic aperture radar radiometric calibration method provided above, the synthetic aperture radar radiometric calibration method comprising:
s100, selecting a corresponding reference image of a synthetic aperture radar load image to be calibrated; wherein the spatial resolution ratio of the reference image to the synthetic aperture radar payload image is within a first selected threshold;
s200, verifying whether the reference image meets a first imaging scene or not, and if the reference image meets the first imaging scene condition, obtaining a verified reference image;
s300, registering the verified reference image with a synthetic aperture radar load image to be calibrated, and converting the geometric relation and the resolution of the verified reference image into the geometric relation and the resolution consistent with the synthetic aperture radar load image to be calibrated;
s400, obtaining surface parameters through inversion according to the verified reference image, and obtaining a backscattering coefficient of the synthetic aperture radar load image to be calibrated according to the surface parameters and the synthetic aperture radar load image to be calibrated;
s500, obtaining an absolute radiometric calibration coefficient according to the backscattering coefficient, and finishing radiometric calibration.
The above-described embodiments of the apparatus are merely illustrative, and the units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (10)

1. A synthetic aperture radar radiometric calibration method is characterized by comprising the following steps:
selecting a corresponding reference image of a synthetic aperture radar load image to be calibrated; wherein the spatial resolution ratio of the reference image to the synthetic aperture radar payload image is within a first selected threshold;
verifying whether the reference image meets a first imaging scene, and if the reference image meets the first imaging scene condition, obtaining a verified reference image;
registering the verified reference image with a synthetic aperture radar load image to be calibrated, and converting the geometric relation and the resolution of the verified reference image into the geometric relation and the resolution consistent with the synthetic aperture radar load image to be calibrated;
according to the verified reference image, obtaining surface parameters through inversion, and according to the surface parameters and the synthetic aperture radar load image to be calibrated, obtaining a backscattering coefficient of the synthetic aperture radar load image to be calibrated;
and obtaining an absolute radiometric calibration coefficient according to the backscattering coefficient to finish radiometric calibration.
2. The synthetic aperture radar radiometric calibration method according to claim 1, characterized by verifying whether a reference image meets a first imaging scenario, and if the first imaging scenario condition is met, obtaining a verified reference image; the method specifically comprises the following steps:
acquiring the root mean square height of the ground surface of the imaging scene of the reference image, and judging whether the imaging scene of the reference image meets a first imaging scene condition or not according to scene parameters; the scene parameters comprise radar carrier wave number, radar incidence angle and incidence frequency of the synthetic aperture radar for generating a load image of the synthetic aperture radar to be calibrated, and soil water content;
if the imaging scene of the reference image meets the first imaging scene condition, the reference image is reserved to obtain a verified reference image;
and if the imaging scene of the reference image does not meet the first imaging scene condition, deleting the reference image and reselecting the reference image.
3. The synthetic aperture radar radiometric calibration method according to claim 1, characterized in that the verified reference image is registered with the synthetic aperture radar payload image to be calibrated, and the geometrical relationship and resolution of the verified reference image is converted to be consistent with the synthetic aperture radar payload image to be calibrated, comprising the following steps:
taking a synthetic aperture radar load image to be calibrated as a reference image;
performing first translation registration on pixel positions corresponding to the synthetic aperture radar load image to be calibrated and the verified reference image by taking the edge equal points in the reference image as control points;
and performing second translation registration on the pixel positions corresponding to the synthetic aperture radar load image to be calibrated after the first registration and the verified reference image through a maximum correlation function method, and converting the geometric relation and the resolution of the verified reference image to be consistent with the synthetic aperture radar load image to be calibrated.
4. The synthetic aperture radar radiometric calibration method according to claim 1, characterized in that surface parameters are obtained by inversion according to the verified reference image, and the backscattering coefficient of the synthetic aperture radar load image to be calibrated is obtained according to the surface parameters and the synthetic aperture radar load image to be calibrated, comprising the following steps:
according to the length of the grid of the synthetic aperture radar load image to be calibrated, grid division is carried out on the verified reference image and the synthetic aperture radar load image to be calibrated, and the verified reference image and the synthetic aperture radar load image to be calibrated are divided into grids with the side length of l multiplied by l; wherein, the l is the correlation length;
obtaining a backscattering coefficient of the verified reference image according to the divided verified reference image; the backscatter coefficients of the verified reference image comprise a backscatter coefficient of the verified reference image in a horizontal transmitting and receiving polarization direction and a backscatter coefficient of the verified reference image in a vertical transmitting and receiving polarization direction;
inverting the earth surface parameters according to the backscattering coefficient of the verified reference image; the surface parameters comprise a real surface dielectric constant part and a root-mean-square height of the surface;
obtaining a backscattering coefficient of the synthetic aperture radar load image to be calibrated according to the earth surface parameters and the self attitude data of the synthetic aperture radar load image to be calibrated; the self attitude data comprises an incidence angle and a wave number, and the backscattering coefficient of the synthetic aperture radar load image to be calibrated comprises a backscattering coefficient of the synthetic aperture radar load image to be calibrated in a horizontal transmitting and receiving polarization direction and a backscattering coefficient of the synthetic aperture radar load image to be calibrated in a vertical transmitting and receiving polarization direction.
5. The method according to claim 4, wherein an absolute radiometric calibration coefficient is obtained from the backscatter coefficients to perform radiometric calibration, comprising the steps of:
acquiring an absolute radiometric calibration coefficient of each grid of the synthetic aperture radar load image to be calibrated by taking the grid as a unit according to the backscattering coefficient of the synthetic aperture radar load image to be calibrated;
and taking the mean value of the absolute radiometric calibration coefficients of all the grids to obtain the absolute radiometric calibration coefficient of the synthetic aperture radar load image to be calibrated, and finishing radiometric calibration.
6. The synthetic aperture radar radiometric calibration method according to claim 1, characterized by verifying whether a reference image meets a first imaging scenario, and if the first imaging scenario condition is met, obtaining a verified reference image; the method also comprises the following steps:
and preprocessing the synthetic aperture radar load image to be calibrated and the reference image.
7. The synthetic aperture radar radiometric calibration method according to claim 6, characterized in that the preprocessing of the synthetic aperture radar payload image to be calibrated and the reference image comprises the following steps:
determining a target scene area, and selecting data of a synthetic aperture radar load image to be calibrated and data of a reference image in the target scene area to obtain a cutting data set;
performing track correction on the cutting data set to obtain a first correction data set;
carrying out coherent speckle filtering on the first correction data set to obtain a filtering data set;
and performing relative radiation correction on the filtering data set to obtain a second correction data set, namely the preprocessed synthetic aperture radar load image to be calibrated and the reference image.
8. A synthetic aperture radar radiometric calibration device, comprising the steps of:
the reference image selection module (100) is used for selecting a corresponding reference image of a synthetic aperture radar load image to be calibrated; wherein the spatial resolution ratio of the reference image to the synthetic aperture radar payload image is within a first selected threshold;
the uniform bare ground checking module (200) is used for verifying whether the reference image meets a first imaging scene or not, and if the reference image meets the first imaging scene condition, obtaining a verified reference image;
the registration module (300) is used for registering the verified reference image and the synthetic aperture radar load image to be calibrated, and converting the geometric relation and the resolution of the verified reference image into the geometric relation and the resolution which are consistent with the synthetic aperture radar load image to be calibrated;
the backscattering coefficient acquisition module (400) is used for obtaining surface parameters through inversion according to the verified reference image, and obtaining backscattering coefficients of the synthetic aperture radar load image to be calibrated according to the surface parameters and the synthetic aperture radar load image to be calibrated;
and the radiometric calibration module (500) is used for obtaining an absolute radiometric calibration coefficient according to the backscattering coefficient to finish radiometric calibration.
9. An electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the processor, when executing the program, carries out the steps of the synthetic aperture radar radiometric calibration method according to any one of claims 1 to 7.
10. A non-transitory computer readable storage medium having stored thereon a computer program for implementing the steps of the synthetic aperture radar radiometric calibration method according to any of claims 1 to 7, when being executed by a processor.
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Publication number Priority date Publication date Assignee Title
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116184341A (en) * 2023-04-27 2023-05-30 中科星图测控技术股份有限公司 SAR load cross radiation calibration method in constellation
CN116184341B (en) * 2023-04-27 2023-08-29 中科星图测控技术股份有限公司 SAR load cross radiation calibration method in constellation

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