Method for reconstructing intertidal zone terrain based on multi-temporal remote sensing images combined with tidal height

Abstract

This invention discloses a method for reconstructing intertidal topography based on multi-temporal remote sensing images combined with tidal height data. The method includes: collecting multi-temporal remote sensing images of the study area and tidal height data at the imaging time; extracting tidal water level lines from each temporal remote sensing image; drawing baselines and tangents; extracting the planar coordinates of the intersection points of the tangents and tidal water level lines; obtaining the lengths of each tangent intercepted from adjacent water level lines and calculating the intertidal slope at each tangent point using the tidal height at the image imaging time; selecting a reference surface to calculate the elevation of each intersection point; and, based on the obtained elevations of each intersection point, using the minimum curvature interpolation method to grid the data and draw the intertidal topography. This invention achieves efficient, accurate, and low-cost reconstruction of intertidal topography, facilitating the monitoring of annual changes in intertidal topography.

Description

Technical Field

[0001] This invention belongs to the field of remote sensing technology, specifically relating to a method for reconstructing intertidal topography based on multi-temporal remote sensing images combined with tidal height. Background Technology

[0002] The intertidal zone has long played a vital role in global research on climate change and the marine environment. Worldwide, the intertidal zone is widely defined as the area between the average highest and lowest tide levels. As a region of interaction between land and sea, it is crucial for coastline stability, coastal wetland biodiversity, and the balance of marine ecosystems.

[0003] Due to the constant changes in tidal height, the intertidal zone is easily submerged by tides, making it a challenging task to measure its topography using RTK, airborne LiDAR, and remote sensing satellites. Furthermore, annually measuring the intertidal zone topography using these methods is not only costly in terms of manpower and resources, but also very slow.

[0004] In relevant studies both domestically and internationally, some scholars have assessed the erosion of the intertidal zone by extracting coastlines using DEM data and aerial imagery. Domestic scholars have combined DEM and mean high tide levels to determine the extent of the intertidal zone; however, the DEM data comes from oblique drone photography at low tide, a method that requires stopping during high tide, resulting in low efficiency. Generating tidal flat DEMs from airborne LiDAR data during low tide to infer tidal levels and thus determine the intertidal zone extent seems to have the same problem. Previously, some scholars have used remote sensing imagery and tidal data to infer intertidal slope, but they did not compare it with precise DEM data. In studies using remote sensing technology to acquire intertidal topography, some scholars have used remote sensing imagery from 22 years (1992-2013) to establish a probability model of tidal flat inundation to determine intertidal topography; however, this method ignores the interaction between the tidal flat and the seawater, as the tidal flat topography changes unpredictably over 22 years, making it unsuitable for monitoring annual changes in intertidal topography.

[0005] Therefore, in order to avoid the influence of factors such as tidal fluctuations and airspace control, and to effectively improve the efficiency of monitoring annual changes in intertidal topography, a new method needs to be designed for monitoring intertidal topography. Summary of the Invention

[0006] The purpose of this invention is to provide a method for reconstructing intertidal topography based on multi-temporal remote sensing images combined with tidal height, which can effectively improve the monitoring efficiency of annual changes in intertidal topography.

[0007] The technical solution to achieve the purpose of this invention is as follows: a method for reconstructing intertidal topography based on multi-temporal remote sensing images combined with tidal height, comprising the following steps:

[0008] The first step is to collect multi-temporal remote sensing images of the study area and tidal height data at the time of imaging;

[0009] The second step is to extract the tidal water level lines from the remote sensing images of each time phase.

[0010] The third step is to draw the baseline and tangent lines;

[0011] The fourth step is to extract the plane projection coordinates of the intersection point of the tangent and the tidal level line;

[0012] The fifth step is to obtain the length of each tangent intercepted from adjacent water level lines and calculate the intertidal slope at each tangent by combining it with the tidal height at the time of image imaging.

[0013] Step 6: Select a reference plane and calculate the elevation of each intersection point;

[0014] The seventh step is to grid the data using the minimum curvature interpolation method based on the obtained elevations of each intersection point and to draw the intertidal topography.

[0015] A computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the method described above.

[0016] A computer-readable storage medium having a computer program stored thereon that, when executed by a processor, implements the steps of the above-described method.

[0017] A computer program product includes a computer program that, when executed by a processor, implements the steps of the above-described method.

[0018] Compared with the prior art, the significant feature of the present invention is that the method proposed in the present invention has high working efficiency and low cost, and can simply and quickly realize the monitoring of intertidal topographic changes every year.

[0019] The invention will be further described in detail below with examples and accompanying drawings. Attached Figure Description

[0020] Figure 1 This is a flowchart of the method for reconstructing intertidal topography based on multi-temporal remote sensing images and tidal heights, according to the present invention.

[0021] Figure 2 It is a false-color image of remote sensing data and a binary image of differential water index.

[0022] Figure 3 This is the first map showing the water level extraction results for the study area.

[0023] Figure 4 This is a map showing the water level extraction results for the second study area.

[0024] Figure 5 These are comparison images of the reconstructed terrain and the terrain generated by LiDAR. The top left image is the terrain map generated by LiDAR data for the first study area, the top right image is the terrain map reconstructed by the method of this invention for the first study area, the bottom left image is the terrain map generated by LiDAR data for the second study area, and the bottom right image is the terrain map reconstructed by the method of this invention for the second study area.

[0025] Figure 6 This is a correlation map between the elevations generated by LiDAR and the reconstructed terrain elevations. Detailed Implementation

[0026] This invention proposes a method for reconstructing intertidal topography based on multi-temporal remote sensing images combined with tidal height, comprising the following steps:

[0027] The first step is to collect multi-temporal remote sensing images of the study area and tidal height data at the time of imaging. The tidal height corresponding to the imaging time of the multi-temporal remote sensing images and the position of the tidal line in the images can reflect the topographic features of the intertidal zone. Multi-temporal remote sensing image data can be selected from Landsat series multispectral remote sensing images and Sentinel-2 multispectral remote sensing images. After atmospheric correction, registration, band fusion, and geometric correction preprocessing, the images can be used for tidal line extraction. Tidal height data can be obtained from tide gauge stations near the study area.

[0028] The second step is to extract the tidal water level lines from the remote sensing images of each time phase. The extraction method uses the Differential Water Index (MNDWI) to extract the water level lines from the preprocessed remote sensing images. The optical properties of liquid water are characterized by strong reflectivity in the green band and high absorption in the short-wave infrared band. Therefore, the water level lines can be identified from other features of the land, as shown in Equation (1):

[0029]

[0030] Green refers to the green light band, with a wavelength range of 0.525-0.600μm; SWIR refers to the short-wave infrared band, with a wavelength range of 1.560-1.660μm.

[0031] The third step is to draw the baseline and tangents. Draw a fixed baseline along the land-water boundary, maintaining a suitable distance from the water level. Along one end of the baseline, take sampling points at small intervals (this distance can be determined based on the resolution of the remote sensing image). At each sampling point, draw a tangent perpendicular to the baseline, ensuring the tangent intersects each water level line. Then, extract the coordinates of the intersection points of the tangent and the water level lines for slope calculation. If a tangent intersects a water level line at more than one point, discard the points closer to the land and retain those closer to the ocean. The baseline and tangent lines are drawn using the ArcGIS software platform.

[0032] The fourth step is to extract the planar projection coordinates of the intersection points of the tangent lines and the tidal level lines. Extracting planar projection coordinates instead of latitude and longitude is to facilitate the calculation of the intertidal slope at each tangent line. It is recommended to use ArcGIS software for this extraction.

[0033] The fifth step is to obtain the lengths of each tangent intercepted from adjacent water level lines and calculate the intertidal slope at each tangent line by combining this with the tidal height at the time of image imaging. The lengths of each tangent intercepted from adjacent water level lines are obtained using the following formula.

[0034] (n>1)

[0035] The length of the tangent line intercepted between the nth tidal level line and the (n-1)th tidal level line; Let x be the x-coordinate of the intersection point of the nth tidal level line and the i-th tangent line; Let x be the x-coordinate of the intersection point of the (n-1)th tidal level line and the ith tangent line; The ordinate of the intersection point of the nth tidal level line and the ith tangent line; The ordinate of the intersection point of the (n-1)th tidal level line and the ith tangent line is given.

[0036] After calculating the length of the tangent intercepted between each tidal level line, the corresponding tidal height is obtained based on the image imaging time, and the coastal slope at each tangent line is calculated using the following formula.

[0037]

[0038] Let be the tangent value of the slope between the (n-1)th and nth tidal water level lines on the i-th tangent line; The tidal height is the height of the nth tidal level. It represents the tidal height of the (n-1)th tidal level.

[0039] In practice, the number of tangents drawn is often large. To speed up the project, it is recommended to use a calculation program or write software to perform the calculation.

[0040] Step 6: Select a reference surface to calculate the elevation of each intersection point. After obtaining the intertidal slope at each tangent, select a suitable elevation reference surface and use the above formula to calculate the elevation value at each intersection point.

[0041] The seventh step involves using the obtained elevations of each intersection point to grid the data using the minimum curvature interpolation method, and then drawing the intertidal topography. Many software platforms are available for topographic mapping, such as Surfer, MapGIS, and ArcGIS.

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to examples and accompanying drawings.

[0043] Example

[0044] like Figure 1 As shown, this embodiment provides a method for reconstructing intertidal topography based on multi-temporal remote sensing images combined with tidal height, including:

[0045] In the first step, the study areas selected for the examples in this invention are divided into two: the first study area covers approximately 4.4 square kilometers, and the second study area covers approximately 2.5 square kilometers, both located in a coastal wetland. The remote sensing images selected for the examples are Landsat series multispectral data, all imaged in the same year, as shown in Table 1. Tidal data are obtained from records at a tide gauge station.

[0046] Table 1. Tidal height information at the time of image imaging

[0047]

[0048] The second step is to extract water level lines at different tidal heights. The Modified Difference Water Index (MNDWI) is used to extract water level lines from the preprocessed Landsat 8 OLI image. The calculation method is as follows:

[0049]

[0050] Green is the green light band, the third band of the Landsat 8 OLI, with a wavelength range of 0.525-0.600μm; SWIR is the shortwave infrared band, the sixth band of the Landsat 8 OLI, with a wavelength range of 1.560-1.660μm.

[0051] Comparison of images before and after MNDWI processing Figure 2As shown, this invention only demonstrates the image processing results for one phase.

[0052] The third step is to draw the baseline and tangents. Using the ArcGIS software platform, the extracted tidal water level lines from each time phase image are imported. A fixed baseline is drawn along the land-water boundary line, maintaining a suitable distance from the water level lines. Sampling points are taken every 100 meters along one end of the baseline. At each sampling point, a tangent line perpendicular to the baseline is drawn, intersecting each water level line. Figure 3 and Figure 4 As shown.

[0053] The fourth step is to extract the coordinates of the intersection points of the tangent line and the water level line for slope calculation. If a tangent line intersects a water level line at more than one point, the points closer to the land should be discarded, and the points closer to the ocean should be retained.

[0054] Step 5: Elevation Calculation. Based on the coordinates of the intersection of the extracted tangent and the water level line, the length of the tangent intercepted between the tidal water levels at each moment can be calculated using the following formula:

[0055] (n>1)

[0056] in, The length of the tangent line intercepted between the nth tidal level line and the (n-1)th tidal level line; Let x be the x-coordinate of the intersection point of the nth tidal level line and the i-th tangent line; Let x be the x-coordinate of the intersection point of the (n-1)th tidal level line and the ith tangent line; The ordinate of the intersection point of the nth tidal level line and the ith tangent line; The ordinate of the intersection point of the (n-1)th tidal level line and the ith tangent line is given.

[0057] Step 6: After calculating the length of the tangent intercepted between each tidal level line, obtain the corresponding tidal height based on the image imaging time, and calculate the coastline slope at each tangent line using the following formula:

[0058]

[0059] Let be the tangent value of the slope between the (n-1)th and nth tidal water level lines on the i-th tangent line; The tidal height is the height of the nth tidal level. It represents the tidal height of the (n-1)th tidal level.

[0060] In this embodiment, the reference surface is established with the elevation of the intersection point of the water level line and each tangent line when the tide height is 268.5cm as 1 meter. The elevation values ​​of the intersection points of other water level lines and tangent lines can be obtained according to the above formula.

[0061] Step 7: After obtaining the elevations of each intersection point using the described method, the elevation data is gridded using the minimum curvature interpolation method. In this embodiment, the Surfer software platform is used to draw the topographic map. To illustrate the reliability of this invention, a topographic map drawn from LiDAR data is compared with that of this invention, such as... Figure 5 As shown.

[0062] according to Figure 5 The results show that although the topographic map reconstructed by the method proposed in this invention has a high degree of agreement with the topographic map drawn from LiDAR data, there is definitely a certain gap in accuracy. The reconstructed terrain and the terrain generated from LiDAR data are analyzed using relative error, and the analysis method follows the following formula:

[0063]

[0064] For error; Elevation at the i-th coordinate generated for LiDAR data; The elevation at the i-th coordinate calculated for TIE.

[0065] The elevation values ​​at the intersections of the tangent and the tidal water level lines at different times were obtained by minimum curvature gridding, resulting in a total of 7800 coordinate points. Points with the same coordinates were selected from the elevations generated from LiDAR data. The elevations generated from LiDAR data were taken as the true values, and the relative error was calculated using the above formula. The results are shown in Table 2.

[0066] Table 2. Error Statistics between LiDAR-generated elevations and reconstructed terrain elevations.

[0067]

[0068] 4114 coordinate points had a relative error of less than 5%, accounting for 52.74% of the total sample points. While this proportion is not high, it does not necessarily mean that the reconstructed terrain elevation map is unreliable. Therefore, a least-squares linear fit was performed between the two methods, and the results are as follows: Figure 6 As shown.

[0069] Figure 6The correlation between the two methods is extremely high, with a correlation coefficient of 0.91. This indicates that although the reconstructed terrain elevation differs from that of LiDAR, the difference lies in a ratio rather than in completely different terrain features. The elevations acquired by LiDAR data cover every part of the intertidal zone with centimeter-level accuracy, which is consistent with reality. The method proposed in this invention is perfectly capable of monitoring annual changes in intertidal terrain, and its efficiency is far superior to traditional surveying methods. Traditional surveying methods for LiDAR data acquisition are primarily used for high-precision topographic mapping. Considering tidal fluctuations, airspace control, and other factors, conducting traditional surveying in the intertidal zone annually using traditional methods is undoubtedly a slow and inefficient task for terrain monitoring.

[0070] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for reconstructing intertidal topography based on multi-temporal remote sensing imagery combined with tidal height, characterized in that, Includes the following steps: The first step is to collect multi-temporal remote sensing images of the study area and tidal height data at the time of imaging; The second step is to extract the tidal water level lines from the remote sensing images of each time phase. The third step is to draw the baseline and tangent lines; The fourth step is to extract the plane projection coordinates of the intersection point of the tangent and the tidal level line; The fifth step is to obtain the length of each tangent intercepted from adjacent water level lines and calculate the intertidal slope at each tangent by combining it with the tidal height at the time of image imaging. The lengths of each tangent intercepted from adjacent water level lines are obtained using equation (2); ，n>1 （2） in, The length of the tangent line intercepted between the nth tidal level line and the (n-1)th tidal level line; Let x be the x-coordinate of the intersection point of the nth tidal level line and the i-th tangent line; Let x be the x-coordinate of the intersection point of the (n-1)th tidal level line and the ith tangent line; The ordinate of the intersection point of the nth tidal level line and the ith tangent line; The ordinate of the intersection point of the (n-1)th tidal level line and the ith tangent line; After calculating the length of the tangent intercepted between each tidal level line, the corresponding tidal height is obtained according to the image imaging time, and the coastal slope at each tangent line is calculated respectively. The calculation method is as shown in equation (3): （3） in, Let be the tangent value of the slope between the (n-1)th and nth tidal water level lines on the i-th tangent line; The tidal height is the height of the nth tidal level. The tidal height of the (n-1)th tidal level line; Step 6: Select a reference plane and calculate the elevation of each intersection point; The seventh step is to grid the data using the minimum curvature interpolation method based on the obtained elevations of each intersection point and to draw the intertidal topography.

2. The method for reconstructing intertidal topography based on multi-temporal remote sensing images combined with tidal height as described in claim 1, characterized in that, The first step is to collect multi-temporal remote sensing images of the study area and tidal height data at the imaging time. The tidal height corresponding to the imaging time of the multi-temporal remote sensing images and the position of the tidal water level line in the images can reflect the topographic features of the intertidal zone. Historical remote sensing images are selected from Landsat series multispectral data or Sentinel-2 multispectral data.

3. The method for reconstructing intertidal topography based on multi-temporal remote sensing images combined with tidal height as described in claim 1, characterized in that, The second step is to extract the tidal water level lines from the remote sensing images of each time phase; the differential water index MNDWI is used to extract the water level lines from the preprocessed remote sensing images, as shown in equation (1): （1） Green refers to the green light band, with a wavelength range of 0.525-0.600μm; SWIR refers to the short-wave infrared band, with a wavelength range of 1.560-1.660μm.

4. The method for reconstructing intertidal topography based on multi-temporal remote sensing images combined with tidal height as described in claim 1, characterized in that, The third step is to draw the baseline and tangent. Draw a fixed baseline along the boundary between land and water, maintaining a set distance from the water level line. Take a sampling point at regular intervals along one end of the baseline, and draw a tangent perpendicular to the baseline at each sampling point so that the tangent intersects each water level line. Then extract the coordinates of the intersection points of the tangent and the water level line for slope calculation. If there is more than one intersection point of a tangent and a water level line, discard the points closer to the land and keep the points closer to the ocean.

5. The method for reconstructing intertidal topography based on multi-temporal remote sensing images combined with tidal height as described in claim 1, characterized in that, The fourth step is to extract the plane projection coordinates of the intersection of the tangent and the tidal level line. The purpose of extracting the plane projection coordinates instead of latitude and longitude is to calculate the intertidal slope at each tangent. The extraction method is completed using the ArcGIS software platform.

6. The method for reconstructing intertidal topography based on multi-temporal remote sensing images combined with tidal height as described in claim 1, characterized in that, The sixth step is to obtain the intertidal slope at each tangent, select the elevation reference surface, and use formula (3) to calculate the elevation value at each intersection point.

7. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the method described in any one of claims 1-6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method described in any one of claims 1-6.

9. A computer program product, comprising a computer program, characterized in that, When executed by a processor, the computer program implements the steps of the method described in any one of claims 1-6.

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