CN115236625A - Typhoon wind field inversion method in SAR remote sensing image with rainfall rate removed - Google Patents

Abstract

The invention provides a typhoon wind field inversion method in SAR remote sensing images for removing rainfall rate, which comprises the following steps: acquiring an original satellite-borne SAR image and wind field and rainfall rate data observed by an SFMR; calculating the wind speed of VH of the SAR through a formula, and calculating the NRCS value influenced by the rainfall rate; according to the difference value of NRCS observed by the NRCS and SAR images influenced by the rainfall rate, the relation between the NRCS difference value and the rainfall rate is explored; identifying the typhoon wind field and the rainfall rate based on the relation between the NRCS difference value and the rainfall rate, eliminating the influence of the rainfall rate on the typhoon wind field, and reconstructing the typhoon wind field; verifying the result of the wind field to form a typhoon wind field inversion algorithm for removing the rainfall rate. The method solves the problem that the rainfall rate interferes with the inversion result of the typhoon wind field with high wind speed.

Description

An inversion method of typhoon wind field in SAR remote sensing images without rainfall rate

technical field

The invention relates to the technical field of synthetic aperture radar signal processing, in particular to a method for typhoon wind field inversion in a SAR remote sensing image from which rainfall rate is removed.

Background technique

The global ocean area accounts for 71% of the earth's surface area and is an important part of global climate change. The wind speed and direction of the sea surface is one of the important elements of the ocean and the atmosphere, and is the main dynamic factor for the movement of the upper ocean. For marine environmental dynamics, the surface wind field is not only the direct driving force of sea surface waves, but also the driving force of regional and global ocean circulation. At the same time, the surface wind field regulates the air-sea interaction and plays an important role in global climate change. In addition, surface wind farms also directly affect marine operations such as marine engineering, marine fisheries and marine shipping.

Hurricane disasters are generally accompanied by strong winds and rainstorms, which seriously threaten people's lives and property, and have a great impact on people's livelihood, agriculture, and economy. From the perspective of grading, typhoons with winds above 12 are divided into three grades, while hurricanes have more grades and higher upper limits. Category 1 hurricanes are equivalent to typhoons or strong typhoons, Category 2 hurricanes are equivalent to strong typhoons, Category 3 hurricanes are equivalent to strong typhoons or super typhoons, and Category 4 and 5 hurricanes are equivalent to super typhoons. From ancient times to the present, hurricanes have brought countless devastating blows to human production and life. Human beings lack effective means of observing hurricanes, unable to identify rainstorm areas and reconstruct wind speed, and correct the wind recovery methods for rainwater-contaminated areas in the hurricane core. Not good enough. Synthetic Aperture Radar (SAR) is an active microwave imaging radar. By emitting microwaves of a certain frequency and measuring the amplitude and phase information of the backscattered signal, an image of the sea surface backscattering intensity can be obtained. High resolution, can reach the order of several meters, and SAR is very sensitive to changes in sea surface roughness, and can provide more marine dynamic information, such as sea surface wind field, sea surface waves, Internal waves, currents, sea ice, wakes of ships on the sea surface, and oil slicks on the sea surface. At the same time, SAR, as a microwave imaging radar, can observe the sea surface at any time and under any weather conditions. Therefore, SAR is an imaging radar that observes the ocean in all-day, all-weather and high-resolution.

In the prior art, SAR can continuously obtain high-resolution images of a large area of the ocean surface in its orbit around the clock, which is very beneficial for monitoring the wind field on the sea surface. And C-band SAR co-polarization, namely VV polarization and HH polarization, the sea surface wind field inversion technology CMODs has been fully mature, and the geophysical models of CMODs have been widely used in the past few decades, such as CMOD4, CMOD- IFR2, CMOD5, neutral wind retrieval algorithm CMOD5N and the new GMF C-SARMOD, etc. So far, CMODs, which describe the complex relationship between the SAR normalized backscatter cross section (NRCS value) and the wind speed at 10 meters above the sea surface, have been successfully applied to the sea surface wind field retrieval from C-band SAR remote sensing images. . However, the existing typhoon wind speed inversion algorithms do not take into account the influence of rainfall rate on the wind speed inversion results, and the obtained high wind speed inversion results are usually interfered by the rainfall rate, resulting in errors in the inversion results.

SUMMARY OF THE INVENTION

In order to solve the above problems, the purpose of the present invention is to provide a typhoon wind field inversion method in a SAR remote sensing image that removes the rainfall rate, which solves the interference problem of rainfall on the typhoon wind field inversion algorithm of the SAR remote sensing image in the prior art.

For solving the above problems, the technical scheme of the present invention is:

A typhoon wind field inversion method in a SAR remote sensing image with a rainfall rate removed, comprising the following steps:

Obtain the original spaceborne SAR images and the wind field and rainfall rate data observed by SFMR;

Calculate the VH wind speed of the SAR by the formula, and calculate the NRCS value affected by the rainfall rate;

According to the difference between the NRCS affected by the rainfall rate and the NRCS observed in the SAR image, the relationship between the NRCS difference and the rainfall rate was explored;

Identify the typhoon wind field and the rainfall rate based on the relationship between the NRCS difference and the rainfall rate, eliminate the influence of the rainfall rate on the typhoon wind field, and reconstruct the typhoon wind field;

Verify the wind field results and form a typhoon wind field inversion algorithm that removes the rainfall rate.

Optionally, the step of acquiring the original spaceborne SAR image and the wind field and rainfall rate data observed by the SFMR specifically includes: collecting four SAR remote sensing images, and simultaneously collecting the four SAR images temporally from the SFMR observed rainfall rate and wind speed data.

Optionally, the step of calculating the VH wind speed of the SAR by the formula, and calculating the NRCS value affected by the rainfall rate specifically includes: after the to-be-inverted SAR remote sensing image is subjected to radiometric calibration, inverting the cross-polarized A quick view of the wind field, the VH wind speed of the SAR is calculated by the formula, and the co-polar NRCS value affected by the rainfall rate is calculated by using the co-polar GMF formula CMOD5.N.

Optionally, the step of exploring the relationship between the NRCS difference and the rainfall rate according to the difference between the NRCS and the NRCS observed in the NRCS affected by the rainfall rate specifically includes: calculating the observed difference between the NRCS and the SAR image affected by the rainfall rate. The relationship between NRCS, rainfall rate, and typhoon eye distance was analyzed.

Optionally, the analyzing the relationship between the NRCS, the rainfall rate, and the distance to the eye of the typhoon specifically includes the following steps:

Perform difference processing between the observed co-polar NRCS on the SAR image obtained by radiometric calibration and the simulated co-polar NRCS with rainfall rate interference;

Calculate the relationship between each point in the SAR and the center of the typhoon eye;

Find the location points where the rainfall rate exists in SFMR and match with the difference result;

Construct the relationship between distance, co-polarized NRCS difference, and rainfall rate.

Optionally, the typhoon wind field and the rainfall rate are identified based on the relationship between the NRCS difference and the rainfall rate, the influence of the rainfall rate on the typhoon wind field is excluded, and the steps of reconstructing the typhoon wind field include: analyzing the same The relationship between polarization NRCS difference and rainfall rate, identify the rainfall rate area, fix the area affected by the rainfall rate from the SAR image, use the Holland model to simulate the wind field in the area with the rainfall rate, and use the model to simulate the rainfall rate area. The wind speed obtained from the SAR image is combined with the inversion wind field obtained by the empirical formula from the SAR image to form the inversion result of the typhoon wind field without the rainfall rate.

其中Vg表示在距离中心眼的距离r上的风速值，pc表示中心气压，pn表示标准大气压，f表示纬向科氏力，ρ表示大气密度，A、B表示模型设置固定参数。Optionally, the specific formula of the Holland model is:

Among them, Vg represents the wind speed value at the distance r from the central eye, pc represents the central pressure, pn represents the standard atmospheric pressure, f represents the zonal Coriolis force, ρ represents the atmospheric density, and A and B represent the model setting fixed parameters.

Optionally, the step of verifying the wind field results and forming the typhoon wind field inversion algorithm with the rainfall rate removed specifically includes: comparing the wind speed inversion results with the rainfall rate interference with the wind speed inversion results with the rainfall rate removed, and using To verify the accuracy of the typhoon wind field inversion algorithm for wind field reconstruction.

Compared with the prior art, the present invention removes the typhoon wind field inversion method in the SAR remote sensing image of the rainfall rate, uses the spaceborne SAR to obtain the cross-polarized remote sensing image, calculates the VH wind speed of the SAR through the formula, and calculates the influence of the rainfall rate. According to the difference between the NRCS and the NRCS observed in the SAR images affected by the rainfall rate, explore the relationship between the NRCS difference and the rainfall rate, and fully analyze the difference between the NRCS difference and the rainfall rate and the distance from the typhoon eye. Therefore, a typhoon wind field inversion algorithm based on SAR remote sensing images without rainfall rate was constructed.

Description of drawings

Other features, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings:

FIG. 1 is a flowchart of a method for typhoon wind field inversion from a SAR remote sensing image with a rainfall rate removed according to an embodiment of the present invention.

2 is a cross-polarized Sentinel-1SAR remote sensing image provided by an embodiment of the present invention;

Fig. 3 is the Sentinel-1SAR IW mode remote sensing image cross-polarization wind field inversion result diagram provided by the embodiment of the present invention;

FIG. 4 is a relationship diagram between the difference of NRCS and the rainfall rate provided by an embodiment of the present invention;

5 is a result diagram of wind field reconstruction of a Sentinel-1SAR IW mode remote sensing image provided by an embodiment of the present invention;

Fig. 6a is a comparison result diagram of a typhoon wind field and SFMR data provided by an embodiment of the present invention that is affected by a rainfall rate;

FIG. 6b is a comparison result of the typhoon wind field and the SFMR data provided by the embodiment of the present invention without the influence of the rainfall rate.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, and will make the technical solutions and beneficial effects of the present invention obvious.

Fig. 1 is the flow chart of the typhoon wind field inversion method of the synthetic aperture radar remote sensing image of removing rainfall rate provided by the embodiment of the present invention, the present invention is the development of the typhoon wind field inversion algorithm of removing rainfall rate based on Sentinel-1SAR, as shown in Fig. 1, the method includes the following steps:

S1: Obtain the original spaceborne SAR image and the wind field and rainfall rate data observed by SFMR;

Specifically, a total of 4 Sentinel-1GRD IW mode SAR remote sensing images were collected, each image with a single pixel width of 10 meters and a resolution of 0.125°×0.125°, ECMWF reanalysis wind field data of about 12.5km×12.5km , image distortion caused by other marine phenomena such as upwelling, rainfall or oil slicks is rarely present in the collected SAR remote sensing images. In the remote sensing images of hurricanes on the east and west coasts of the United States, there is at least one obvious typhoon eye in each image. At the same time, the observed rainfall rate and wind speed data from SFMR were collected in four SAR images.

S2: Calculate the wind speed of the VH of the SAR by the formula, and calculate the NRCS value affected by the rainfall rate;

Specifically, we first used the existing empirical typhoon wind speed inversion algorithm in Sentinel-1IW mode, and the NRCS and incident angles obtained by radiometric calibration were 31° to 35.9°, 35.9° to 41.3°, 41.3° to 46° ° is divided into three intervals, and the cross-polarization wind field inversion results on the SAR image are calculated. And using the co-polar GMF formula CMOD5.N, based on the cross-polar typhoon wind speed (hereinafter referred to as the VH wind speed) retrieved from the SAR, the co-polar NRCS with the influence of the rainfall rate is simulated, and it is used as a quality index and SAR. The NRCS data observed on the images are compared.

Figure 2 shows the VH polarization fast-view images of the 2 Sentinel-1 SAR images, from which the obvious typhoon eye position can be found. Figure 3 shows the wind field inversion results obtained on the cross-polarized Sentinel-1SAR image. From the image, we can find that the inversion results have obvious banding phenomenon and the interference of the rainfall belt.

S3: Explore the relationship between the NRCS difference and the rainfall rate based on the difference between the NRCS affected by the rainfall rate and the NRCS observed in the SAR image;

Specifically, calculate the difference between the NRCS affected by the rainfall rate and the NRCS observed in the SAR image, analyze the relationship between the NRCS, the rainfall rate, and the distance from the typhoon eye, and follow the following steps to explore the difference between the rainfall and the NRCS and the typhoon Eye distance relationship:

Step 1: Perform difference processing between the observed co-polar NRCS on the SAR image obtained by radiometric calibration and the simulated co-polar NRCS with rainfall rate interference;

Step 2: Calculate the relationship between each point in the SAR and the center of the typhoon eye;

Step 3: Find the location points where the rainfall rate exists in the SFMR and match it with the difference result;

Step 4: Construct the relationship between distance, co-polarized NRCS difference, and rainfall rate.

From Figure 4, it is found that the difference of satisfying NRCS is 1-2(db) and the distance is less than 100km; the difference of NRCS is 3.5-4.5(db) and the distance is less than 200km, and the distance is more than 100km, we think that this area is affected by rainfall area.

S4: Identify the typhoon wind field and the rainfall rate based on the relationship between the NRCS difference and the rainfall rate, eliminate the influence of the rainfall rate on the typhoon wind field, and reconstruct the typhoon wind field;

Specifically, the area considered to be affected by the rainfall rate in step S3 is fixed from the SAR image, and according to the central pressure of the typhoon, the maximum wind speed radius, the zonal Coriolis force parameter, and the atmospheric density, etc. The typhoon wind speed in the rainfall area was simulated, and the wind speed in the rainfall rate area simulated by the model was combined with the inversion wind field obtained from the SAR image through the empirical formula to form the typhoon wind field inversion result without rainfall rate. The specific formula of the Holland model is as follows:

其中Vg表示在距离中心眼的距离r上的风速值，pc表示中心气压，pn表示标准大气压，f表示纬向科氏力，ρ表示大气密度，A、B表示模型设置固定参数。

Among them, Vg represents the wind speed value at the distance r from the central eye, pc represents the central pressure, pn represents the standard atmospheric pressure, f represents the zonal Coriolis force, ρ represents the atmospheric density, and A and B represent the model setting fixed parameters.

Figure 5 shows the inversion results of the typhoon wind field obtained by using the above inversion algorithm. It can be clearly seen from the figure that the banding phenomenon in Figure 3 has been removed, and the inversion results are more continuous.

S5: Verify the wind field results, and form a typhoon wind field inversion algorithm that removes the rainfall rate.

Specifically, a comparison was made between the wind speed observed in SFMR and the SAR inversion wind speed results accompanying rainfall and the wind speed of the reconstructed wind field. From the comparison chart, we can clearly see that the reconstructed wind field has a better correlation. The accuracy of our algorithm is verified, as shown in Figure 6a and Figure 6b, in which Figure 6a describes the comparison result of the typhoon wind field affected by the rainfall rate and the SFMR data, and the root mean square error of the wind speed inversion result is 5.99 m/s, Figure 6b depicts the comparison results of the typhoon wind field and SFMR data without the influence of the rainfall rate. The root mean square error of the wind speed inversion results is 3.79m/s. Therefore, the inversion results show the feasibility of reconstructing the typhoon wind field by removing the influence of rainfall rate, and solve the deficiency in the cross-polarization sea surface wind field inversion of the hurricane wind field in the rainfall rate.

Compared with the prior art, the present invention removes the typhoon wind field inversion method in the SAR remote sensing image of the rainfall rate, uses the spaceborne SAR to obtain the cross-polarized remote sensing image, calculates the VH wind speed of the SAR through the formula, and calculates the influence of the rainfall rate. According to the difference between the NRCS and the NRCS observed in the SAR images affected by the rainfall rate, explore the relationship between the NRCS difference and the rainfall rate, and fully analyze the difference between the NRCS difference and the rainfall rate and the distance from the typhoon eye. Therefore, a typhoon wind field inversion algorithm based on SAR remote sensing images without rainfall rate was constructed.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above-mentioned specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essential content of the present invention. The embodiments of the present application and features in the embodiments may be combined with each other arbitrarily, provided that there is no conflict.

Claims (8)

1. A typhoon wind field inversion method in SAR remote sensing images for removing rainfall rate is characterized by comprising the following steps:

acquiring an original satellite-borne SAR image and wind field and rainfall rate data observed by an SFMR;

calculating the wind speed of VH of the SAR through a formula, and calculating the NRCS value influenced by the rainfall rate;

according to the difference value of NRCS observed by the NRCS and SAR images influenced by the rainfall rate, the relation between the NRCS difference value and the rainfall rate is explored;

identifying the typhoon wind field and the rainfall rate based on the relation between the NRCS difference value and the rainfall rate, eliminating the influence of the rainfall rate on the typhoon wind field, and reconstructing the typhoon wind field;

verifying the result of the wind field to form a typhoon wind field inversion algorithm for removing the rainfall rate.

2. The method for inverting the typhoon wind field in the SAR remote sensing image with the rainfall removed according to claim 1, wherein the step of acquiring the wind field and rainfall data observed by the original satellite-borne SAR image and the SFMR specifically comprises the following steps: and 4 SAR remote sensing images are collected, and the observed rainfall rate and wind speed data from the SFMR on the time of four SAR images are collected at the same time.

3. The method for inverting the typhoon wind field in the SAR remote sensing image with the rainfall rate removed according to claim 1, wherein the step of calculating the wind speed of the VH of the SAR and calculating the NRCS value affected by the rainfall rate through a formula specifically comprises the following steps: after the SAR remote sensing image to be inverted is subjected to radiometric calibration, a cross-polarized wind field fast view is inverted, the wind speed of VH of the SAR is calculated through a formula, and a homopolarity NRCS value influenced by rainfall rate is calculated by utilizing a homopolarity GMF formula CMOD5.N.

4. The method for inverting the typhoon wind field in the SAR remote sensing image with the rainfall removed according to claim 1, wherein the step of exploring the relation between the NRCS difference and the rainfall according to the difference between the NRCS affected by the rainfall and the NRCS observed in the SAR image specifically comprises the following steps: and calculating the difference value of NRCS influenced by the rainfall rate and NRCS observed by the SAR image, and analyzing the relation between the NRCS, the rainfall rate and the typhoon eye distance.

5. The method for inverting the typhoon wind field in the SAR remote sensing image with the rainfall removed according to claim 4, wherein the analysis of the relation between the NRCS and the rainfall as well as the typhoon eye distance specifically comprises the following steps:

carrying out difference value processing on the homopolarity NRCS observed on the SAR image obtained by radiometric calibration and the simulated homopolarity NRCS with rainfall interference;

calculating the distance relation between each point in the SAR and the center of the typhoon eye;

finding out a position point with rainfall rate in the SFMR and matching the position point with the difference result;

and constructing a relation among the distance, the homopolar NRCS difference value and the rainfall rate.

6. The method for inverting the typhoon wind field in the SAR remote sensing image with the rainfall removed according to claim 1, wherein the identification of the typhoon wind field and the rainfall is performed based on the relation between the NRCS difference value and the rainfall, the influence of the rainfall on the typhoon wind field is eliminated, and the step of reconstructing the typhoon wind field specifically comprises the following steps: analyzing the relation between the homopolar NRCS difference and the rainfall rate, identifying the rainfall rate area, fixing the area affected by the rainfall rate from the SAR image, simulating the wind field in the area with the rainfall rate by adopting a Holland model, and combining the wind speed of the rainfall rate area simulated by the model with the inversion wind field obtained from the SAR image through an empirical formula to form the typhoon wind field inversion result for removing the rainfall rate.

7. The method for inverting the typhoon wind field in the SAR remote sensing image with the rainfall removed according to claim 6, characterized in that the specific formula of the Holland model is as follows:

wherein Vg represents the wind speed value at a distance r from the central eye, pc represents the central air pressure, pn represents the standard atmospheric pressure, f represents the latitudinal Coriolis force, ρ represents the atmospheric density, and A, B represents the model setting fixed parameters.

8. The method for inverting the typhoon wind field in the SAR remote sensing image with the rainfall removed according to claim 1, wherein the step of verifying the wind field result and forming the typhoon wind field inversion algorithm with the rainfall removed specifically comprises the following steps: and comparing the wind speed inversion result with rainfall interference with the wind speed inversion result without rainfall interference for verifying the accuracy of the typhoon wind field inversion algorithm for wind field reconstruction.

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