A method for extracting background temperature field from remote sensing images of thermal discharge from coastal nuclear power plants

Abstract

The present invention discloses a method for extracting the background temperature field of coastal nuclear power plant warm discharge remote sensing imagery, belonging to the technical field of seawater temperature field construction. The method comprises inverting remote sensing image data to obtain an absolute temperature field data matrix; calculating the spatial gradient of the remote sensing inverted temperature field; determining the critical spatial gradient and drawing a contour map of the critical spatial gradient; calculating the divergence value of the critical spatial gradient and drawing a contour line with a divergence value of zero; obtaining an envelope line containing the outermost portion of the warm discharge outlet, and using this envelope line as a reference line for calculating the background temperature; and calculating the background temperature based on the inverted temperatures of all pixels within a set range on both sides of the background temperature reference line. The method calculates the background temperature field of remote sensing inversion data without the use of additional historical remote sensing data and is applicable to semi-enclosed bays and open seas. The operation steps have clear physical meanings and provide good calculation results, thus solving the current problem of difficulty in obtaining the background temperature field of warm discharge.

Description

Technical Field

[0001] The present invention relates to the field of seawater temperature field construction, and in particular to a method for extracting background temperature fields from remote sensing images of coastal nuclear power plant thermal discharge. Background Art

[0002] Nuclear power generation uses the sea for high-demand purposes, with diverse sea use methods and complex impacts on the marine ecosystem. Among these, the use of warm water discharge is the most critical of coastal nuclear power generation, with the most profound impact on marine ecological and environmental safety. Warm water discharge is water with a higher temperature than that of natural water bodies, discharged by nuclear power units when they utilize seawater circulation for cooling. Under the influence of ocean dynamics, warm water diffuses into the surrounding seas, diluting heat with seawater and ocean dynamics, and dissipating heat to the atmosphere through the sea surface. High-temperature rise areas of warm water discharge have a significant impact on marine ecology. Areas with temperature rises above 4°C serve as the basis for determining the scope of warm water discharge use, with sea areas above 1°C in summer and 2°C in winter primarily impacting the resource and environmental impacts of warm water discharge.

[0003] Given the importance of the temperature rise zone of thermal discharge, accurate and effective calculation of this zone is crucial. Background temperature refers to the seawater temperature unaffected by thermal discharge. Accurately extracting this background temperature field is crucial for calculating the temperature rise zone. Currently, the "Technical Specifications for Satellite Remote Sensing Monitoring of Thermal Discharge from Coastal Nuclear Power Plants (Trial)" (HJ 1213-2021) provides three methods for extracting the background temperature field (also known as the reference temperature): the "Discrete Multi-Point Averaging Method," the "Adjacent Area Substitution Method," and the "Bay Average Temperature Method."

[0004] In daily practice, the inventors found that the existing technical solutions have the following problems:

[0005] The adjacent area substitution method requires a large amount of historical remote sensing inversion data. The discrete multi-point averaging method requires the calculation of the submerged drainage zone, which has large errors in determining the boundary of the submerged drainage zone. The bay average temperature method is only applicable to semi-enclosed seas and has limited applicability. This leads to problems such as the high requirement for historical remote sensing image data, poor calculation accuracy, and limited applicability of existing background temperature field extraction methods.

[0006] Chinese invention patent application number 201510607456.9 discloses a method for extracting offshore industrial warm discharge water based on aerial remote sensing. This method can obtain the temperature rise value of the temperature rise area. However, this method requires many parameters and relies on a large amount of remote sensing inversion data. It still cannot solve the problem that the background temperature field of warm discharge water is difficult to obtain.

[0007] In view of this, it is necessary to provide a new technical solution to solve the above problems. Summary of the Invention

[0008] In order to solve the above technical problems, this application provides a method for extracting the background temperature field of coastal nuclear power plant warm discharge remote sensing images, which does not require historical remote sensing image data, can be applied to various bay types, and the operation steps have clear physical meanings and good calculation results, solving the current problem that the background temperature field of warm discharge water is difficult to obtain.

[0009] A method for extracting background temperature fields from remote sensing images of thermal drainage from coastal nuclear power plants, comprising:

[0010] Invert remote sensing image data to obtain absolute temperature field data matrix;

[0011] Calculate the spatial gradient of the temperature field retrieved from remote sensing;

[0012] Determine the critical spatial gradient and draw the contour map of the critical spatial gradient;

[0013] Calculate the divergence value of the critical spatial gradient and draw the contour line with zero divergence value;

[0014] Optimize the contour line of the critical spatial gradient divergence value of zero, and draw the contour line of the optimized critical spatial gradient divergence value of zero;

[0015] Obtain an envelope line including the outermost side of the warm water discharge outlet, and use this envelope line as a reference line for calculating the background temperature;

[0016] The background temperature is calculated based on the inverted temperature of all pixels within the set range on both sides of the background temperature reference line.

[0017] Preferably, the method for calculating the spatial gradient in the calculation of the spatial gradient of the remote sensing inversion temperature field is:

[0018]

[0019] in, is the spatial gradient; A is the temperature field obtained by remote sensing inversion; x and y are the spatial plane coordinates, and i and j are the unit vectors of x and y coordinates respectively.

[0020] Preferably, determining the critical spatial gradient and drawing the contour map of the critical spatial gradient include: drawing the critical contour map of the absolute value of the spatial gradient based on the calculated value of the spatial gradient of the remote sensing inversion temperature field; the critical contour line of the absolute value of the spatial gradient is between.

[0021] Preferably, the divergence value of the critical spatial gradient is calculated, and the divergence value of the critical spatial gradient is calculated by drawing an isoline with a divergence value of zero:

[0022]

[0023] Where, 、 Gradient field exist and Directional component.

[0024] Preferably, after calculating the divergence value of the critical spatial gradient and drawing the contour line with the divergence value of zero, the method further includes: optimizing the contour line with the critical spatial gradient divergence value of zero and drawing the contour line with the optimized critical spatial gradient divergence value of zero.

[0025] Preferably, the method of obtaining the outermost envelope line including the warm drainage outlet and using the envelope line as a reference line for calculating the background temperature includes: superimposing the obtained contour map of the critical spatial gradient with the contour line with the optimized critical spatial gradient divergence value of zero to obtain the outermost envelope including the warm drainage outlet.

[0026] Preferably, in the calculation of the background temperature based on the inverted temperatures of all pixels within a set range on both sides of the background temperature reference line, the average inverted temperature of all pixels within 100m on both sides of the reference line is used as the background temperature.

[0027] Compared with the prior art, this application has at least the following beneficial effects:

[0028] The method for extracting the background temperature field of nuclear power plant warm discharge water remote sensing images in the present invention is applicable to semi-enclosed bays and open sea areas, does not require the additional use of historical remote sensing data, and can handle multiple heat sources at the same time. At the same time, the operation steps have clear physical meanings and good calculation results, which solves the current problem of the difficulty in obtaining the background temperature field of warm discharge water. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0030] Figure 1 Schematic diagram of the overall process of an embodiment of the present invention;

[0031] Figure 2 This is a graph of absolute temperature field data obtained by inverting remote sensing image data in an embodiment of the present invention;

[0032] Figure 3 A spatial gradient vector field diagram of the remote sensing inversion temperature field in an embodiment of the present invention;

[0033] Figure 4 is a contour map of the critical spatial gradient in an embodiment of the present invention;

[0034] Figure 5 is a contour map of a critical spatial gradient divergence value of zero in an embodiment of the present invention;

[0035] Figure 6 This is a contour map of the divergence value of the critical spatial gradient after optimization in an embodiment of the present invention where zero;

[0036] Figure 7 A background temperature reference line diagram in an embodiment of the present invention;

[0037] Figure 8 This is a diagram of the area within 100m from the reference line in an embodiment of the present invention;

[0038] Figure 9 This is a temperature rise distribution diagram calculated based on the temperature gradient method in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the specific embodiments of this application and the corresponding drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0040] The existing discrete multi-point averaging method, adjacent area substitution method, and bay average temperature method have great limitations.

[0041] The main principle of the discrete multi-point averaging method is to use the boundary of a 0.5°C subduction zone as a reference when one exists. Otherwise, the boundary of an area within at least 100 km² of the current image that is 0.5°C above the average temperature retrieved from remote sensing is used as a reference. Within a 200-500m buffer zone outside the reference boundary, reference positions are regularly spaced. The average temperature retrieved from remote sensing at these reference positions is used as the background temperature. This method, known as the discrete multi-point averaging method, lacks theoretical basis for selecting reference boundaries. The discrete multi-point averaging method requires first calculating the subduction zone, which can lead to large errors in determining the boundary. Furthermore, in practice, background temperatures can vary significantly depending on the image range selected.

[0042] The main scheme of the adjacent region substitution method is to select the closest stable area outside the 0.5°C subduction zone as a reference location based on the statistics of historical temperature data retrieved from remote sensing. The average temperature retrieved from remote sensing within this reference location is used as the background temperature. This method, called the adjacent region substitution method, requires a large amount of historical remote sensing data, but multiple historical remote sensing images are difficult to obtain. Moreover, because remote sensing monitoring images are taken at a specific moment, the background temperature of images at different moments can vary greatly. This makes it difficult to select adjacent areas based on historical remote sensing image data using the adjacent region substitution method.

[0043] The Bay Average Temperature Method primarily uses the average temperature retrieved from remote sensing within the bay as the background temperature, after deducting the submerged discharge area. This method, known as the Bay Average Temperature Method, is significantly affected by the type of bay where the warm-water nuclear power plant is located. It is only applicable to semi-enclosed waters, with limited applicability. When the nuclear power plant is located in open waters or has a large bay estuary, determining the bay boundary is difficult.

[0044] The temperature at the outlet of warm wastewater is highest. As the warm wastewater diffuses, the surrounding temperature gradually decreases. A temperature gradient extends from the surrounding area toward the outlet, and the modulus of the gradient decreases with increasing distance from the outlet. When the modulus of the temperature gradient decreases to a certain level, it can be assumed that the temperature at that location is not affected by the warm wastewater and can be used as the background temperature. Based on this principle, the present invention provides a method for extracting the background temperature field from remote sensing images of warm wastewater from coastal nuclear power plants.

[0045] A method for extracting background temperature fields from remote sensing images of thermal drainage from coastal nuclear power plants, comprising:

[0046] Step S1: Invert the remote sensing image data to obtain the absolute temperature field data matrix.

[0047] Specifically, existing methods are used to invert remote sensing image data to obtain the absolute temperature field data matrix A(x,y). The processing steps include spatial cropping, geometric correction, absolute radiometric calibration, and land-water separation. The specific processing methods for each step are conventional techniques and are described in the "Technical Specifications for Satellite Remote Sensing Monitoring of Warm Discharge Water from Binhai Nuclear Power Plants (Trial)" (HJ 1213-2021). Based on the descriptions of this standard and conventional technical means, those skilled in the art can derive a unique technical solution. Therefore, the specific details of the specific steps are not repeated here.

[0048] Taking the warm water discharge area of Qinshan Nuclear Power Station in Zhejiang as an example, the remote sensing image data is inverted to obtain the absolute temperature field data. Figure 2 shown.

[0049] Step S2: Calculate the spatial gradient of the remote sensing inversion temperature field.

[0050] Specifically, the spatial gradient calculation method of the remote sensing inversion temperature field is:

[0051]

[0052] Where, is the spatial gradient of the remote sensing inversion temperature field; A is the temperature field obtained by remote sensing inversion; x and y are the spatial plane coordinates, and i and j are the unit vectors of the x and y coordinates respectively.

[0053] Since the gradient is a vector field, the temperature gradient of each point in space points to the direction of the fastest temperature increase. Therefore, the gradient of the remote sensing inversion temperature field is perpendicular to the isotherm and points from the low temperature area to the high temperature area. Taking the warm discharge water area of the Qinshan Nuclear Power Station in Zhejiang as an example, the spatial gradient vector field of the remote sensing inversion temperature field is as follows: Figure 3 shown.

[0054] Step S3: determine the critical spatial gradient and draw a contour map of the critical spatial gradient.

[0055] Specifically, according to the spatial gradient value of the remote sensing inversion temperature field calculated in step S2, the absolute value of the spatial gradient is plotted. The critical contour line map is used to determine the critical spatial gradient contour line. and draw the contour map of the critical spatial gradient accordingly.

[0056] Taking the warm water discharge area of Qinshan Nuclear Power Station in Zhejiang as an example, the contour map of critical spatial gradient is shown as follows: Figure 4 shown.

[0057] Step S4: Calculate the divergence value of the critical spatial gradient and draw the contour line with zero divergence value.

[0058] Specifically, the gradient field The formula for calculating the divergence value is:

[0059]

[0060] Where, 、 Gradient field exist and Directional component.

[0061] Divergence can be used to characterize the strength of a spatial vector field's divergence. Physically, divergence represents the active nature of a vector field. When the divergence value is greater than 0, it indicates a positive source emitting flux at that point; when the divergence value is less than 0, it indicates a negative source absorbing flux at that point.

[0062] For the divergence field of the critical spatial gradient, the temperature gradient near the drain outlet points to the drain outlet, which is the sink of the temperature gradient field, that is, the heat source of the temperature. Therefore, when the divergence value is less than 0, it means that there is a heat source at that point. Draw the contour line of the critical spatial gradient divergence of 0. The area where the critical spatial gradient divergence is less than 0 is the heat source. The contour line diagram of the critical spatial gradient divergence value of 0 is as follows Figure 5 shown.

[0063] Since smaller contour lines are usually caused by satellite remote sensing inversion errors, some smaller contour lines can be removed. In the embodiment of the present invention, contour lines with less than 10 pixels are removed to obtain a contour map with a divergence value of 0 for the optimized critical spatial gradient, as shown in FIG. Figure 6 shown.

[0064] Step S5: obtaining an envelope line including the outermost side of the warm water discharge outlet, and using the envelope line as a reference line for calculating the background temperature.

[0065] Specifically, the contour map of the critical spatial gradient obtained in the previous step is superimposed with the contour map of the optimized critical spatial gradient with a divergence value of 0 to obtain the outermost line containing the warm drainage outlet as the envelope line, and this envelope line is used as the reference line for calculating the background temperature, such as Figure 7 shown.

[0066] Step S6: Calculate the background temperature based on the inverted temperatures of all pixels within a set range on both sides of the background temperature reference line.

[0067] Specifically, according to the experience of those skilled in the art, the inverted temperatures of all pixels within 100m on both sides of the reference line are selected, and their average value is calculated as the background temperature. Figure 8 shown.

[0068] In the warm discharge waters of the Qinshan Nuclear Power Plant in Zhejiang Province, the average temperature within the area 100m away from the reference line is calculated, and the average temperature is 22.0℃. That is, the background temperature of the remote sensing image is 22.0℃. The temperature rise distribution in the warm discharge waters of the nuclear power plant can be obtained by subtracting the background temperature from the initial temperature field, as shown in the figure below: Figure 9 shown.

[0069] For ease of description, spatially relative terms such as "above", "above", "on the upper surface", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0070] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, tasks, devices, components and / or combinations thereof.

[0071] It should be noted that the terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0072] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for extracting the background temperature field of remote sensing images of coastal nuclear power plant thermal discharge, characterized in that: include: Invert remote sensing image data to obtain absolute temperature field data matrix; Calculate the spatial gradient of the temperature field retrieved from remote sensing; Determine the critical spatial gradient and draw the contour map of the critical spatial gradient; Calculate the divergence value of the critical spatial gradient and draw the contour line with zero divergence value; Obtain an envelope line including the outermost side of the warm water discharge outlet, and use this envelope line as a reference line for calculating the background temperature; Calculate the background temperature based on the inverted temperature of all pixels within the set range on both sides of the background temperature reference line; After calculating the divergence value of the critical spatial gradient and drawing the contour line with the divergence value of zero, the method further includes: optimizing the contour line with the critical spatial gradient divergence value of zero and drawing the contour line with the optimized critical spatial gradient divergence value of zero; The method of obtaining the outermost envelope line including the warm drainage outlet and using the envelope line as a reference line for calculating the background temperature includes: superimposing the obtained contour line map of the critical spatial gradient with the contour line with the optimized critical spatial gradient divergence value of zero to obtain the outermost envelope including the warm drainage outlet.

2. The method for extracting background temperature field of remote sensing images of coastal nuclear power plant thermal wastewater according to claim 1, characterized in that: The calculation method of the spatial gradient in the calculation of the spatial gradient of the remote sensing inversion temperature field is: ； in, is the spatial gradient; A is the temperature field obtained by remote sensing inversion; x and y are the spatial plane coordinates, and i and j are the unit vectors of x and y coordinates respectively.

3. The method for extracting background temperature field of remote sensing images of coastal nuclear power plant thermal wastewater according to claim 2, characterized in that: Determining the critical spatial gradient and drawing the contour map of the critical spatial gradient includes: drawing the critical contour map of the absolute value of the spatial gradient based on the calculated value of the spatial gradient of the remote sensing inversion temperature field; the critical contour map of the absolute value of the spatial gradient is between 0.004-0.006℃ / m.

4. The method for extracting background temperature field of remote sensing images of coastal nuclear power plant thermal wastewater according to claim 2, characterized in that: The divergence value of the critical spatial gradient is calculated, and the isoline with a divergence value of zero is drawn. The divergence value of the critical spatial gradient is calculated as follows: ； Where, 、 Gradient field exist and Directional component.

5. The method for extracting background temperature field of remote sensing images of coastal nuclear power plant thermal wastewater according to claim 1, characterized in that: In the calculation of the background temperature based on the inverted temperatures of all pixels within a set range on both sides of the background temperature reference line, the average inverted temperature of all pixels within 100m on both sides of the reference line is used as the background temperature.

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