A Method for Extracting Urban Heat Island Footprints Based on Rotational Scanning

Abstract

The present invention discloses a method for extracting the footprint of urban heat island based on rotational scanning. First, based on multi-source remote sensing images, the single-window method and the dichotomy method are respectively used to invert the land surface temperature and extract the built-up area. Secondly, with the centroid of the built-up area as the center and the due north direction as the starting direction, the suburbs at a certain distance outside the city are scanned clockwise, and the building occupancy and water body occupancy within each 1° area are counted. A building occupancy threshold, a water body occupancy threshold, and a merging tolerance are set, and the suburbs for temperature curve fitting are selected according to these three parameters. Then, multiple buffer rings with an interval of 1 km are drawn for the selected area, the average temperature of each ring is counted, a temperature curve is drawn, and an exponential decay function is used to fit to obtain the extension distance of the heat island footprint and the background temperature. Finally, the heat island footprint is determined according to the footprint extension distance and the background temperature. This method minimizes the influence of the complexity of land use types around the city on the temperature curve, thereby obtaining a more accurate heat island footprint.

Description

Technical Field

[0001] The invention relates to a method for extracting urban heat island footprints based on rotation scanning, and belongs to the field of urban heat island footprint extraction methods. Background Art

[0002] Rapid urbanization has greatly changed the surface characteristics and the energy balance of cities, leading to various environmental problems. Urban heat island is one of the key issues. It is a phenomenon in which the temperature in urban areas is significantly higher than that in suburbs. This phenomenon has aggravated energy consumption and damaged the urban ecology. In addition, it also poses a huge threat to the health of residents, so it has received considerable attention. Some scholars have proposed the heat island footprint indicator to quantify the heat island effect, which comprehensively considers the intensity and spatial range of the heat island effect. At present, there are generally two methods for determining the heat island footprint. One method uses the Gaussian model to obtain the footprint. However, this method focuses more on describing the trajectory of the center of gravity of the heat island effect and cannot accurately represent the true spatial range of the heat island effect. The other method uses the exponential fitting method to obtain the footprint. In this method, the temperature curve is crucial. However, the temperature curve is greatly affected by factors such as land use type. Few studies have explored the accuracy of the temperature curve, resulting in rough footprint calculation. Therefore, it is necessary to design a method for extracting the urban heat island footprint to improve the accuracy of the temperature curve and thus improve the accuracy of the footprint. Summary of the invention

[0003] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for extracting urban heat island footprint based on rotation scanning, thereby solving the current problems of low accuracy of temperature curve and inaccurate heat island footprint.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: a method for extracting urban heat island footprint based on rotation scanning, comprising the following steps:

[0005] Step S1: Based on the nighttime light image data, the built-up area is extracted using the dichotomy method;

[0006] Step S2: Rotate and scan the suburbs at a certain distance outside the city, and count the proportion of buildings and water bodies within each 1° range;

[0007] Step S3: setting building ratio, water body ratio thresholds and merging tolerances, screening out suitable suburbs, and drawing their multi-ring buffer zones;

[0008] Step S4: Based on the remote sensing image data, the surface temperature is inverted using a single window algorithm;

[0009] Step S5: Count the average temperature of each ring, draw a temperature curve and perform exponential decay fitting;

[0010] Step S6: extracting the heat island footprint according to the fitted heat island extension distance and background temperature.

[0011] Further, the specific method of step S1 is as follows: Taking the built-up area statistical data as a reference, initially dichotomize the built-up area and the non-built-up area by setting an initial threshold, and compare and extract the difference between the area and the statistical data. Continuously adjust the threshold until the area is consistent with the statistical data, and select the built-up area with the largest area as the final urban area.

[0012] Further, the specific method of step S2 is as follows: Taking the urban center of gravity as the midpoint and the due north direction as the starting direction, scan the suburbs at a certain distance outside the city clockwise at a scanning angle of 1°, and count the building occupancy and water body occupancy within each 1° range.

[0013] Further, the specific method of step S3 is as follows:

[0014] S31: Set the thresholds for building occupancy and water body occupancy. If the thresholds are exceeded, discard this area;

[0015] S32: Set the merging tolerance. If there are consecutive discarded area angles less than the merging tolerance, merge them into the adjacent reserved area;

[0016] S33: Draw buffer rings at intervals of 1 kilometer for the selected suburbs.

[0017] Further, the specific method of step S4 is as follows:

[0018] Based on Landsat remote sensing image data, using the single-window algorithm, calculate the land surface temperature through the linear relationship between the TOA brightness temperature and the land surface temperature. The calculation formula is:

[0019]

[0020] where LST is the land surface temperature, T b is the TOA brightness temperature in the TIR channel, ε is the surface emissivity of the same channel; the algorithm coefficients A i 、B i and C i are determined by the linear regression of the radiative transfer simulations performed on 10 types of total atmospheric column water vapor amounts (i = 1,..., 10).

[0021] Further, the specific method of step S5 is as follows:

[0022] S51: Statistically calculate the average temperature of each ring and plot it as a temperature curve;

[0023] S52: Fit the temperature curve using an exponential decay function. The fitting formula is as follows:

[0024]

[0025] Among them, y is the average surface temperature of each ring, A represents the heat island intensity, t is the exponential decay rate, d is the extension distance of the footprint, that is, the distance from the built-up area boundary to the buffer ring, and T0 is the fitted background temperature.

[0026] Furthermore, the specific manner of step S6 is as follows:

[0027] S61: Draw a buffer area according to the fitted footprint extension distance from the urban area boundary;

[0028] S62: Extract the area where the temperature is higher than the background temperature within the buffer area;

[0029] S63: Aggregate the extracted areas into a continuous range, that is, the final heat island footprint.

[0030] The beneficial effects of the present invention are as follows: Through the above-mentioned urban heat island footprint extraction method, the present invention can minimize the influence of uneven distribution of land use types outside the built-up area, improve the accuracy of the temperature curve, obtain a more accurate heat island footprint, and provide suggestions for urban heat environment research. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a flowchart of an embodiment of a method for extracting an urban heat island footprint based on rotational scanning according to the present invention;

[0032] Figure 2 It is a schematic diagram of rotational scanning according to the present invention;

[0033] Figure 3 It is a fitting diagram of the temperature curve according to the present invention;

[0034] Figure 4 It is a result diagram of heat island footprint extraction according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. However, it should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0037] A method for extracting an urban heat island footprint based on rotational scanning according to the present invention includes the following steps:

[0038] Step S1: Referring to the built-up area statistical data, initially dichotomize the built-up area and the non-built-up area by setting an initial threshold, and compare and extract the difference between the extracted area and the statistical data. Continuously adjust the threshold until the area is consistent with the statistical data. There may be multiple built-up areas in a city, and the built-up area with the largest area is selected as the final urban area.

[0039] Step S2: As shown in Figure 2 (a), taking the centroid of the built-up area as the midpoint and the due north direction as the starting direction, scan the suburbs at a certain distance outside the city clockwise at a scanning angle of 1°, and count the building occupancy and water body occupancy within each 1° range.

[0040] Step S3: Set the thresholds for building occupancy and water body occupancy. If the thresholds are exceeded, discard this area; set the merging tolerance. If there are consecutive discarded area angles less than the merging tolerance, merge them into the adjacent reserved area. Draw buffer rings at intervals of 1 km for the selected suburbs, as shown in Figure 2 (b).

[0041] Step S4: Based on Landsat remote sensing image data, calculate the land surface temperature using the single-window algorithm. The calculation formula is (T b is the TOA brightness temperature in the TIR channel, and ε is the surface emissivity in the same channel. The algorithm coefficients A i , B i and C i are determined by the linear regression of the radiative transfer simulations performed on 10 types of total atmospheric column water vapor amounts (i = 1,..., 10)) to calculate the land surface temperature.

[0042] Step S5: Statistically calculate the average land surface temperature of each ring, plot it as a temperature curve, and perform fitting according to the exponential decay formula (y is the average land surface temperature of each ring, A represents the heat island intensity, t is the exponential decay rate, d is the extension distance of the footprint, that is, the distance from the built-up area boundary to the buffer ring, and T0 is the fitted background temperature) for fitting. The fitting curve is as shown in Figure 3 .

[0043] Step S6: Draw a buffer ring from the built-up area boundary, and the buffer distance is the footprint extension distance. Within the buffer ring range, extract the areas where the temperature is higher than the background temperature and aggregate them into a continuous surface, which is the final heat island footprint, as shown in Figure 4 .

[0044] Through the above method for extracting the urban heat island footprint, the present invention can minimize the influence of the uneven distribution of land use types outside the built-up area, improve the accuracy of the temperature curve, and thus obtain a more accurate heat island footprint.

[0045] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for extracting the footprint of urban heat island based on rotational scanning, characterized in that, It includes the following steps: Step S1: Based on the night-time light image data, use the bisection method to extract the built-up area; Step S2: Rotate and scan the suburbs at a certain distance outside the city, and count the building occupancy and water body occupancy within each 1° range; Step S3: Set the thresholds for building occupancy, water body occupancy and the merging tolerance, select the appropriate suburbs, and draw their multi-ring buffers; Step S4: Based on the remote sensing image data, use the single-window algorithm to retrieve the land surface temperature; Step S5: Count the average temperature of each ring, draw the temperature curve and perform exponential decay fitting; Step S6: Extract the heat island footprint according to the heat island extension distance and background temperature obtained by fitting; The specific method of step S1 is as follows: Taking the built-up area statistical data as a reference, initially bisect the built-up area and non-built-up area by setting an initial threshold, and compare the difference between the extracted area and the statistical data. Continuously adjust the threshold until the area is consistent with the statistical data, and select the built-up area with the largest area as the final urban area; The specific method of step S2 is as follows: Taking the urban center of gravity as the midpoint and the due north direction as the starting direction, scan the suburbs at a certain distance outside the city clockwise at a scanning angle of 1°, and count the building occupancy and water body occupancy within each 1° range; The specific method of step S3 is as follows: S31: Set the thresholds for building occupancy and water body occupancy. If it exceeds the threshold, discard this area; S32: Set the merging tolerance. If there are consecutive discarded area angles less than the merging tolerance, merge them into the adjacent reserved area; S33: Draw buffer rings with an interval of 1 km for the selected suburbs; The specific method of step S4 is as follows: Based on the Landsat remote sensing image data, use the single-window algorithm to calculate the land surface temperature through the linear relationship between the TOA brightness temperature and the land surface temperature. The calculation formula is: where LST is the land surface temperature, T b is the TOA brightness temperature in the TIR channel, and ε is the surface emissivity in the same channel; the algorithm coefficients A i , B i and C i are determined by linear regression of radiative transfer simulations performed for 10 total atmospheric column water vapor amounts (i = 1, …, 10); The specific method of step S5 is as follows: S51: Count the average temperature of each ring and draw it into a temperature curve; S52: Fit the temperature curve using the exponential decay function. The fitting formula is as follows: Where y is the average land surface temperature of each ring, A represents the heat island intensity, t is the exponential decay rate, d is the extension distance of the footprint, that is, the distance from the built-up area boundary to the buffer ring, and T0 is the fitted background temperature; The specific method of step S6 is as follows: S61: Draw a buffer according to the footprint extension distance obtained by fitting from the urban area boundary; S62: Within the buffer range, extract the area where the temperature is higher than the background temperature; S63: Aggregate the extracted areas into a continuous range, which is the final heat island footprint.

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