Forest sample plot positioning method and device based on sky-ground integrated thermal infrared imaging

Abstract

The invention discloses a sky-ground integrated thermal infrared imaging forest sample plot positioning method and device, and the method comprises the steps: marking sample points at a to-be-investigated forest sample plot, recording the distance between the sample points, and enabling the sample points to be the vertexes or central points or edge designated points of the contour of the to-be-investigated forest sample plot; emitting a marker signal at the sample point, the marker signal being far infrared; the unmanned aerial vehicle acquires a sample point sending out the marking signal above the forest sample plot to be investigated, and records geographic coordinate information of the sample point, and the geographic coordinate information is longitude and latitude coordinate information. According to the method, longitude and latitude coordinate information is obtained based on the thermal infrared imaging technology, and the problems of position offset, drifting, large errors and the like existing in forest sample plot coordinate obtaining due to the multi-path effect of GPS signals in a forest, unstable satellite number and the like are fundamentally solved.

Description

Technical Field

[0001] This invention relates to the field of forest plot marking, specifically to a method and apparatus for locating forest plots using integrated sky-ground thermal infrared imaging. Background Technology

[0002] As the largest carbon sink in terrestrial ecosystems, forest management is crucial for consolidating and enhancing the carbon sequestration capacity of forest ecosystems and promoting carbon dioxide removal. In forest management carbon inclusion projects, whether it's the project designer determining forest age, verifying plot area, and defining emission reduction ownership, the project contractor carrying out forest tending, degraded forest restoration, pest control, and sustainable management, or the project approver verifying emission reductions, the primary step is to accurately determine the boundary coordinates of forest sample plots. However, due to environmental factors such as dense forest canopies and complex terrain, existing positioning technologies have significant limitations in practical applications, making it difficult to achieve accurate and efficient acquisition of sample plot coordinates.

[0003] Currently, the common methods for locating forest plots mainly include the following five: (1) Measurement-grade RTK GNSS receiver method This method involves receiving signals from at least 5-6 high-quality satellites and using a fixed solution to calculate coordinates. However, in forest environments, the dense canopy forms a "green umbrella"-like shielding layer, severely attenuating or even completely blocking the weak signals from low-elevation satellites. This often results in fewer than 3 receivable satellites, failing to meet the fixed solution requirement and causing coordinate distortion. Although RTK technology has differential correction capabilities, its effectiveness in eliminating errors caused by localized signal blockage is limited.

[0004] (2) Positioning method using handheld GPS or built-in GPS in mobile phone These types of devices struggle to stably track satellite signals in forest environments, resulting in drastic fluctuations in observations and inconsistent positioning results. Furthermore, the "multipath effect," caused by multiple reflections of satellite signals among leaves, branches, and trunks, leads to the receiver receiving delayed and distorted reflected signals instead of the direct signal. This effect is the most significant and persistent source of error in forest positioning, potentially causing positioning deviations of tens of centimeters to several meters.

[0005] (3) "Outside-forest benchmark, inside-forest attack" strategy This strategy requires deploying base stations in completely open areas outside the forest (such as mountaintops or open fields) to ensure signal quality. Once mobile stations (such as drones or personnel carrying equipment) enter the forest area, observation time needs to be extended (usually more than 10 minutes) to suppress some random errors and multipath effects through data averaging. Alternatively, operations can be conducted during the leaf fall period or at times with favorable satellite geometry (such as midday). However, this method requires additional open locations, extended operation times, or reliance on seasonal windows, significantly increasing survey costs and failing to meet the demands for real-time, current-readiness operations.

[0006] (4) Parameter extraction method based on point cloud and remote sensing data This method acquires point cloud data and remote sensing images of the sample plot, extracts information such as tree height and tree species, and uses a tree height-diameter-at-breast-thickness (DBH) regression model corresponding to the tree species to calculate DBH, thereby obtaining the forest structure parameters of the sample plot. Although this method helps improve the efficiency of acquiring parameters such as tree height and DBH, its focus is on forest parameter inversion and it does not elaborate on the accurate acquisition methods of sample plot boundary coordinates, thus failing to directly solve the coordinate positioning problem.

[0007] (5) Method of combining drone photography with total station measurement This method utilizes drones to capture aerial images of the forest, while simultaneously using a total station to conduct multi-point measurements of the forest stand structure. The measurement data is then processed using office and data analysis software. However, total station measurements require visibility between measurement points and are only suitable for areas with sparse forest stand structures and gently undulating terrain. They are not applicable to mountainous forest plots with dense canopies and significant terrain curvature.

[0008] In summary, existing forest plot positioning technologies suffer from insufficient accuracy due to signal obstruction and multipath effects, or are hampered by harsh operating conditions, high costs, and poor timeliness, or focus solely on parameter extraction while neglecting coordinate acquisition. All these limitations prevent the accurate, rapid, and robust positioning of plot boundary coordinates in complex forest environments. Therefore, there is an urgent need to develop a new positioning technology and device that adapts to the complex forest environment and overcomes the shortcomings of existing technologies. Summary of the Invention

[0009] Therefore, in order to overcome the above-mentioned shortcomings, the present invention provides a method and device for locating forest plots using integrated sky-ground thermal infrared imaging. Based on thermal infrared imaging technology, it acquires latitude and longitude coordinate information, fundamentally solving the problems of "multipath effect" of "GPS" signals in forests and the instability of the number of satellites, which lead to "location offset, drift and large error" in the acquisition of forest plot coordinates.

[0010] On the one hand, the present invention provides a method for locating forest plots using integrated sky-ground thermal infrared imaging, comprising the following steps: Sampling points are marked in the forest plots to be investigated, and the distances between each sampling point are recorded. These sampling points are designated as vertices, center points, or edge points of the forest plot's outline. The forest plots to be investigated have diverse terrain conditions, especially areas with significant topographic relief within the forest plot area. This selection of forest plots is for the needs of the investigation. Because the carbon offset project investigates a single tree species, it is required to ensure the monotypicity of tree species within the plots. Therefore, the shape of the plots may not follow the contours of the mountain. However, to represent biodiversity, a rich variety of tree species is required, so the selection of plots may involve crossing ridges, etc.

[0011] A marker signal is emitted at the sampling point; this marker signal is far-infrared.

[0012] The drone acquires the sampling points that emit marker signals over the forest plot to be investigated, and records the geographic coordinates of the sampling points, which are longitude and latitude coordinates.

[0013] Optionally, the forest plot location method using integrated sky-ground thermal infrared imaging further includes: To correct the spacing between adjacent vertices with a slope, the correction method is as follows: ; in: D j It is the actual length that the measuring tape should show between two adjacent vertices on the slope, in meters; j These are the indexes of the side lengths between adjacent vertices that have a slope. j =1, 2, 3, 4; α i This represents the slope value at the apex of the forest plot. α i+1 for α i The slope values ​​of adjacent vertices, both in degrees, are given. α i+1 and α i The value ranges from 0 to 60°. i It is the vertex number; S This is the projected area of ​​the forest sample plot to be investigated, in square meters (m²).

[0014] In forest management carbon credit projects, it is required that the continuous land area of ​​a single forest plot be no less than 400 m². 2 The area here refers to the projected area, that is... Figure 3 The square enclosed by the dotted lines in the middle (a) ’ b ’ c ’ d ’The area of ​​the slope. Based on the projection of a square plot, the side length D of the terrain on the slope is calculated. j ≥20m.

[0015] The purpose of the correction steps described above is to ensure that the side length of the slope projected onto the plane is ≥20m, forming a square. Without correction, the obtained geographical coordinates of the sample plots will be inaccurate, and the shape of the plots may not be guaranteed to be square, with inaccurate side length values. This will lead to serious errors, not just minor mistakes, in subsequent calculations of biomass or carbon storage values ​​within the forest sample plots.

[0016] Optionally, the forest plot location method using integrated sky-ground thermal infrared imaging further includes: The latitude and longitude coordinates of the specified sample points are projected onto the remote sensing image of the area where the forest sample plot is located. The geometric shape projected onto the remote sensing image is a square. Verify the slope values ​​measured in the forest plots. α i To ensure accuracy, the slope at the same location was calculated using the known digital elevation model of the forest plot. Use this as a reference value, with an error accuracy within ±5°. That is, If the test fails, it indicates a large error, and the slope values ​​of the four vertices (or corners) of the forest plot need to be remeasured, or a new forest plot needs to be selected.

[0017] Preferably, when the forest plot to be investigated is a rectangular plot, the method for marking sample points in the forest plot and recording the distance between each sample point is as follows: The four vertices (or corners) and the center point of the square plot are used as sample points. The distance between adjacent vertices is measured and recorded using a tape measure. This distance is the side length of the square plot. The actual side length of the forest plot is obtained after correcting the side length using the correction method described above.

[0018] There are five designated sample points, which are the four vertices (or corners) and one center point of the square sample plot.

[0019] Optionally, the method of emitting marker signals at the sample points is: Workers wear far-infrared devices, such as heated helmets or clothing, at the marked points. The wavelength range of the far-infrared rays is 4-14 μm, which is also the spectral range that can be received by the thermal infrared sensors mounted on the drone.

[0020] On the other hand, the present invention also provides a forest plot positioning device for integrated sky-ground thermal infrared imaging, used to perform the forest plot positioning method for integrated sky-ground thermal infrared imaging, the device comprising: The sample point emission module is used to emit marker signals at sample points; The marker signal acquisition module is used to acquire sample points with marker signals over the forest sample plot and record the coordinate information of the sample points; The correction module is used to correct the outline size of the forest plots based on their slope. The processing module is used to draw and mark the boundary coordinates of forest plots based on the coordinate information of specified sample points and the corrected contour dimensions.

[0021] The present invention has the following advantages: This invention relates to a method and device for locating forest sample plots using integrated sky-ground thermal infrared imaging. Based on thermal infrared imaging technology, it acquires latitude and longitude coordinate information, fundamentally solving the problems of location offset, drift, and large errors in obtaining forest sample plot coordinates caused by the "multipath effect" of GPS signals in forests and the instability of the number of satellites. Furthermore, it is applicable to different forest ages and densities, different phenological periods, different survey times, and adaptable to complex terrain and mountain slopes. This invention, by combining "forest-based" positioning with thermal infrared detection, effectively overcomes the limitations of traditional methods in terms of forest cover, phenological changes, lighting conditions, and complex terrain, achieving a wider, more stable, and more flexible forest plot positioning. Attached Figure Description

[0022] Figure 1 This invention provides a method for locating square sample plots. Figure 2 This is another method for locating square plots according to the present invention. Figure 1 and Figure 2 In the diagram, the numbers 1, 2, 3, 4, 5, and 6 represent the numbers of the six measuring tapes. a , b , c , d These represent the coordinates of the four corner points of the forest plot, with o being the center point. Figure 3 This is a schematic diagram illustrating the calculation of the length after terrain correction according to the present invention (in the figure). D 1 ~ D 4 It is the length of the side. j =1, 2, 3, 4); Figure 4 This is a schematic diagram illustrating the acquisition of forest plot coordinates according to the present invention; Figure 5 It is the top of the forest plot cd A diagram showing two points that are not directly visible; in practical work, a measuring tape is used. cd The length of the segment is greater than ab The length of the segment; Figure 6 It is the top of the forest plot cd A diagram illustrating two points of sight; in practical work, a measuring tape is used. af The angle between the segment and the horizontal plane H α i and cf The angle between the segment and the horizontal plane H α i+1 Not equal, that is α i ≠α i+1 ;tape af The length of the segment and the measuring tape cf The lengths of the segments are also not equal, that is, af ≠ cd. Similarly, the measuring tape... be The angle between the segment and the horizontal plane H α i+2 and de The angle between the segment and the horizontal plane H α i+3 They are not equal either, that is, α i+2 ≠α i+3 ;tape be The length of the segment and the measuring tape de The lengths of the segments are also not equal, that is, be ≠ de. In special cases, there are also... α i ≠α i+1 ≠α i+2 ≠α i+3 , af ≠ cd ≠ be ≠ de .

[0023] Figure 7 This is a flowchart illustrating the integrated thermal infrared imaging method for locating forest plots. Figure 8 This is a modular schematic diagram of an integrated thermal infrared imaging forest plot positioning device. Detailed Implementation

[0024] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0025] In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0026] As described in the background section, existing forest plot positioning technologies either suffer from insufficient positioning accuracy due to signal obstruction and multipath effects, or are hampered by harsh operating conditions, high costs, poor timeliness, or focus solely on parameter extraction while neglecting coordinate acquisition. None of these technologies can achieve accurate, rapid, and robust positioning of plot boundary coordinates in complex forest environments.

[0027] For the reasons mentioned above, this embodiment provides a forest plot location method using integrated sky-ground thermal infrared imaging, including the following steps: S100. Mark sample points in the forest plot to be investigated and record the distance of each sample point. The sample point is the vertex (or corner point), center point, or edge designated point of the outline of the forest plot to be investigated. S200: A marker signal is emitted at the sample point; the marker signal is far-infrared. S300. Correct the spacing between adjacent vertices with a slope. The correction method is as follows: To correct the spacing between adjacent vertices with a slope, the correction method is as follows: ; in: D j It is the actual length that the measuring tape should show between two adjacent vertices on the slope, in meters; j These are the indexes of the side lengths between adjacent vertices that have a slope. j=1、2、3、4 ; α i This represents the slope value at the apex of the forest plot. α i+1 for α i The slope values ​​of adjacent vertices, in degrees. i It is the vertex number; S This is the projected area of ​​the forest sample plot to be investigated, in m². 2 .

[0028] S400: The UAV acquires the sampling points that emit marker signals over the forest sample plot to be investigated, and records the geographic coordinate information of the sampling points, which is longitude and latitude coordinate information.

[0029] S500. Project the latitude and longitude coordinates of the specified sample points onto the remote sensing image of the area where the forest plot is located, and check that the geometric shape should be square. This is to verify the slope values ​​measured in the field within the forest plot. α i The accuracy can be determined by calculating the slope at the same location using the known digital elevation model of the forest plot. Use this as a reference value, with an error accuracy within ±5°. That is, If the test fails, it indicates a large error, and the slope values ​​of the four vertices (or corners) of the forest plot need to be remeasured, or a new forest plot needs to be selected.

[0030] For example, this embodiment will use a square plot of forest to be investigated as an example for illustration. The entire process and method are as follows: Staff member A, wearing a heated helmet that continuously emits far-infrared rays in the range of 4-14μm (made of materials such as iron powder, activated carbon, salt, water, and vermiculite), arrived at the forest plot to be investigated. This range of 4-14μm is also the spectral range that the drone equipped with a thermal infrared sensor can receive. Staff members B and C, in the forest plot, assisted staff member A, using six measuring tapes (such as...). Figure 1 and 2 In 1,2,3, 4,5,6 Locate the four corners of the sample plot (square sample plot). Figure 1 and Figure 2 The side length of the square sample plot ( ). ab = ah + bh, bd = be + de, dc = dg + cg and ca = af + cf The length of the sample plot is the actual length of the forest plot. D j It is necessary to adjust the slope according to the gradient on the slope. α i Slope correction is performed based on the size of the slope. Figure 3 The formula used for correction is... Perform calculations. D j The corrected side length of the square plot, with a length ≥ 20m, in meters; j The index of the side length j=1,2,3,4 ; α i Let be the angle between the side length and the projection plane. α i+1 and α i The value ranges from 0 to 60°. The projected area S of the forest plot to be investigated is a continuous land area of ​​not less than 400 m² for a single plot. 2 .

[0031] Staff member D remotely controlled a drone equipped with a thermal infrared sensor to fly over the forest plot where staff member A was located in a low-lying open area (roadside, riverbank). The drone then captured five locations of staff member A and recorded their geographic coordinates, namely longitude and latitude. Figure 4 The five locations where staff member A is situated constitute forest plots. Figure 1 The four corner points (or vertices) in the diagram. a, b, c, d And the position of the center point o, e, f, g, h The points are the side lengths. bd, ca, dc and ab The midpoint of the line segment, o is the midpoint of the line segment. ef and gh The intersection point is also the center point of the forest plot. Figure 2 In the middle, there are 4 corner points (or vertices). a, b, c, d Let o be the coordinates of the corner (or vertex) of the forest plot. ad、bc The intersection point is also the center point of the forest plot.

[0032] Staff member D projected the recorded latitude and longitude coordinates of the five locations onto a remote sensing image of the forest plot area, confirming that the geometric shape should be square. This was to verify the slope values ​​measured in the field within the forest plot. α i The accuracy can be determined by calculating the slope at the same location using the known digital elevation model of the forest plot. Use this as a reference value, with an error accuracy within ±5°. That is, If the test fails, it indicates a large error. In this case, it is necessary to remeasure the slope values ​​of the four corner points (or apex) of the forest plot, or to select a new forest plot.

[0033] The above-mentioned technical features have the following advantages compared with the prior art: This invention is applicable to different forest ages and densities. Traditionally, obtaining the coordinates of forest plots primarily involves using GPS or RTK under the forest canopy to calculate latitude and longitude coordinates by receiving satellite signals. However, in dense middle-aged and mature forests, the "multipath effect" exists due to forest shading, meaning that under-forest GPS or RTK can only receive weak satellite signals or a small number of satellites (≤3), leading to discrepancies between the latitude and longitude coordinates obtained by workers and the coordinates projected onto the two-dimensional plane. In sparse young forests, due to the presence of "skylights," the accuracy of traditional under-forest GPS or RTK methods is less than that of this invention. This invention uses a drone equipped with a thermal infrared sensor to capture "thermal infrared images" of under-forest workers to obtain absolute location information. This location is actually a satellite signal "above the forest" that is not "shaded" by the forest.

[0034] This invention is applicable to different phenological stages. Traditional methods for obtaining stable GPS or RTK signals, aimed at reducing shading from tree canopy leaves, are only suitable during the leaf-fall period in forests (creating "skylights"), and are not applicable to evergreen broad-leaved forests. This invention, based on satellite signals "over the forest," is suitable for a longer phenological period (budding – leaf expansion – flowering – fruiting – leaf fall).

[0035] This invention is applicable to different survey times. Since this method is based on thermal infrared imaging technology, as long as worker A is wearing a "heated helmet" in the forest, a drone equipped with a thermal infrared sensor can capture (receive) the worker's thermal infrared image, thereby obtaining latitude and longitude coordinate information. Therefore, the survey time is not affected by sunlight, expanding the limitations of survey time.

[0036] This invention is applicable to mountain slopes of any curvature. Traditionally, obtaining forest plot coordinates using a total station is primarily done under conditions where visual communication between two points is guaranteed within the forest canopy. However, on relatively steep mountains, there are often situations where points c and d are not visually connected (…). Figure 4 The present invention acquires the marker signals of the sample points using a drone positioned above the forest sample area, which is unaffected by whether the two points are line-of-sight.

[0037] In another embodiment, a forest plot location device based on integrated sky-ground thermal infrared imaging is also provided for performing the forest plot location method based on integrated sky-ground thermal infrared imaging. The device includes: A sample point emission module for emitting marker signals at sample points; exemplified by, for example, a helmet or other wearable device capable of emitting infrared light.

[0038] The marker signal acquisition module is used to acquire sample points with marker signals over the forest sample plot and record the coordinate information of the sample points; for example, a drone equipped with a thermal infrared sensor.

[0039] A correction module is used to correct the outline dimensions of forest plots based on their slope; exemplified by existing computer software.

[0040] The processing module is used to draw and mark the boundary coordinates of forest plots based on the coordinate information of specified sample points and the corrected contour dimensions. An example is a computer.

[0041] The aforementioned technical features enable the forest plot location method using integrated sky-ground thermal infrared imaging. By combining "forest-based" location with thermal infrared detection, it effectively overcomes the limitations of traditional methods in terms of forest cover, phenological changes, lighting conditions, and complex terrain, achieving a wider, more stable, and more flexible forest plot location.

[0042] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for locating forest plots using integrated sky-ground thermal infrared imaging, characterized in that, Includes the following steps: Mark sample points in the forest plot to be investigated and record the distance of each sample point. The sample point is the vertex, center point or edge designated point of the outline of the forest plot to be investigated. A marker signal is emitted at the sampling point; the marker signal is far-infrared light. The drone acquires the sampling points that emit marker signals over the forest plot to be investigated, and records the geographic coordinates of the sampling points, which are longitude and latitude coordinates.

2. The forest plot location method using integrated sky-ground thermal infrared imaging according to claim 1, characterized in that, Also includes: To correct the spacing between adjacent vertices with a slope, the correction method is as follows: ； in: D j It is the actual length that the measuring tape should show between two adjacent vertices on the slope, in meters; j These are the indexes of the side lengths between adjacent vertices that have a slope. j=1、2、3、4 ; α i This represents the slope value at the apex of the forest plot. α i+1 for α i The slope value of adjacent vertices, in degrees. i It is the vertex number; S It is the projected area of ​​the forest sample plot to be investigated.

3. The forest plot location method using integrated sky-ground thermal infrared imaging according to claim 2, characterized in that, Also includes: The latitude and longitude coordinates of the specified sample points are projected onto the remote sensing image of the area where the forest sample plot is located. The geometric shape projected onto the remote sensing image is a square. Verify the slope values ​​measured in the forest plots. α i To ensure accuracy, the slope at the same location was calculated using the known digital elevation model of the forest plot. Use this as a reference value, with an error accuracy within ±5°.

4. The forest plot location method using integrated sky-ground thermal infrared imaging according to claim 3, characterized in that, When the forest plot to be investigated is a rectangular plot, the method for marking sample points in the forest plot and recording the distance between each sample point is as follows: The four vertices and the center point of the square plot are used as sample points. The distance between adjacent vertices is measured and recorded using a tape measure. This distance is the side length of the square plot. The actual side length of the forest plot is obtained after correcting the side length using the correction method described above.

5. The forest plot location method based on integrated sky-ground thermal infrared imaging according to claim 4, characterized in that, There are five designated sample points in total, consisting of four vertices and one center point.

6. The forest plot location method using integrated sky-ground thermal infrared imaging according to claim 1, characterized in that, The method for emitting marker signals at the sample points is as follows: Staff members wear far-infrared devices, such as heated helmets or clothing, at the marked points.

7. The forest plot location method based on integrated sky-ground thermal infrared imaging according to claim 1 or 6, characterized in that, The wavelength range of the far-infrared rays is 4-14μm.

8. A forest plot positioning device using integrated sky-ground thermal infrared imaging, characterized in that, The apparatus for performing the forest plot location method for integrated sky-ground thermal infrared imaging as described in any one of claims 1-7 comprises: The sample point emission module is used to emit marker signals at sample points; The marker signal acquisition module is used to acquire sample points with marker signals over the forest sample plot and record the coordinate information of the sample points; The correction module is used to correct the outline size of the forest plots based on their slope. The processing module is used to draw and mark the boundary coordinates of forest plots based on the coordinate information of specified sample points and the corrected contour dimensions.

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