Unmanned aerial vehicle borne linear array hyperspectral BRDF fast construction method and system considering illumination

Abstract

The present application relates to a kind of unmanned aerial vehicle line array hyperspectral BRDF fast construction method and system considering illumination, mainly solve the technical problems, such as the BRDF data collected by existing BRDF acquisition method is not high in dimension richness, it is difficult to guarantee the continuity of data, and rarely consider the influence of illumination change on data, BRDF acquisition and construction efficiency is low for complex environment.The system includes hyperspectral imager, atmospheric downward irradiance measuring device and correction calibration component;The hyperspectral imager is used to be installed on unmanned aerial vehicle, obtains the BRDF data of target acquisition area;The atmospheric downward irradiance measuring device is used to be set on ground, obtains illumination data changing with time;The correction calibration component is set at target acquisition area, for collecting correction calibration data.

Description

Technical Field

[0001] This invention relates to a method and system for constructing a BRDF, specifically to a rapid method for constructing a UAV-borne linear array hyperspectral BRDF that takes into account changes in illumination, and a system for implementing this method. Background Technology

[0002] The bidirectional reflectance distribution function (BRDF) describes the distribution of incident light rays after reflection from a surface in various exit directions. When determining the incident and exit directions, it can be defined as the ratio of radiance in the exit direction to irradiance in the incident direction. BRDF is an important geocalibration parameter in low-altitude remote sensing, airborne remote sensing, and spaceborne remote sensing, and its accuracy directly affects calibration precision. Generally, BRDF data acquisition for a fixed target area requires shooting the target area at different zenith angles and fixed shooting heights at different azimuth intervals to acquire the corresponding spatial orientation parameters. Traditional acquisition methods require the use of multiple complex equipment to build an acquisition platform. The operating attitude and position parameters of the equipment itself have a significant impact on the acquired BRDF data. Furthermore, due to the complexity of the equipment, the selection of observation targets is easily affected by terrain and traffic, making BRDF acquisition work in complex terrains and environments very difficult. Traditional methods have significant limitations in terms of BRDF acquisition difficulty, cost, time, accuracy, and efficiency. Currently, drones and their onboard equipment are easy to operate, portable, and offer flexible data collection methods, providing new means for the collection and construction of BRDF.

[0003] The acquisition of BRDF (Brilliant Pathway Data Form) is highly dependent on the instruments and equipment onboard the UAV platform, flight plan planning, shooting environment conditions, and changes in spatial illumination. Currently used acquisition devices such as spectrometers and tracking cameras produce BRDF data with limited dimensionality. Fixed-position shooting methods struggle to ensure data continuity and rarely consider the impact of illumination variations, resulting in low efficiency in BRDF acquisition and construction in complex environments. Therefore, improving data dimensionality, optimizing UAV flight plans, and accelerating BRDF model construction while fully considering illumination conditions are urgent problems to be solved. Summary of the Invention

[0004] The purpose of this invention is to address the technical problems of existing BRDF acquisition methods, such as low dimensional richness of acquired BRDF data, difficulty in ensuring the continuity of BRDF data, and little consideration of the impact of illumination changes on BRDF data, resulting in low reliability of BRDF data and low efficiency in BRDF acquisition and construction in complex environments. The invention provides a rapid construction method and system for UAV-borne linear array hyperspectral BRDF that takes illumination into account.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A rapid construction method for UAV-borne linear array hyperspectral BRDF considering illumination, characterized by the following steps:

[0007] Step 1: Control the UAV to fly at an initial flight altitude H with a 0° zenith angle and start synchronously collecting data on the change of illumination over time, as well as BRDF data and calibration data of the target acquisition area;

[0008] Step 2: Control the drone at a zenith angle θ v Within the range from 0° to the preset maximum angle, the drone completes one flight at preset intervals along a preset flight trajectory; and after each flight, the zenith angle θ is used to determine the maximum angle. v The changes correspond to adjustments in flight altitude h and lateral movement distance s;

[0009] Zenith angle θ v The flight altitude h and lateral movement distance s satisfy the following relationship:

[0010] h = H * cosθ v ; s = H * sinθ v ;

[0011] During the drone's flight, BRDF data, calibration data, and data on changes in illumination over time were continuously collected.

[0012] Step 3: First, filter and classify the BRDF data according to the flight number of the UAV. Then, preprocess the BRDF data according to the calibration data. Finally, input the preprocessed BRDF data into the BRDF model to obtain the model parameters. Match the model parameters according to the time and illumination change data over time to obtain the BRDF distribution centered on the target acquisition area under different illumination conditions; complete the acquisition and construction of BRDF.

[0013] Furthermore, in step 2, the preset flight trajectory is:

[0014] The plane flies N times along a regular polygonal trajectory with side length L, where N > 1. The perpendicular bisectors of the corresponding sides of the N regular polygonal trajectories in the horizontal direction are set with preset angles according to the flight order.

[0015] Furthermore, in step 2, the preset flight trajectory is:

[0016] The plane flies clockwise 3 times along a square trajectory with side length L. The perpendicular bisectors of the corresponding sides of the 3 square trajectories in the horizontal direction are set with a preset angle of 30° according to the flight order.

[0017] The side length L = 2*s;

[0018] The preset maximum angle is 50°;

[0019] The preset interval angle is 10°.

[0020] Furthermore, in step 3, the BRDF model is the Hapke model;

[0021] The calculation formula for the Hapke model is as follows:

[0022]

[0023] In the formula: r(μ0,u,g) is the model function, μ0 is the cosine of the incident angle, u is the cosine of the exit angle, g is the phase angle between the incident angle and the exit angle, ω is the single scattering albedo, B(g) is the backscattering function, p(g) is the phase function, and M(μ0,u) is the multiple scattering function.

[0024] Furthermore, the backscattering function B(g) satisfies the following relationship:

[0025]

[0026] In the formula: B0 is the amplitude of the hotspot effect, and k is the width of the hotspot effect;

[0027] The phase function p(g) satisfies the following relationship:

[0028]

[0029] In the formula: b and c are phase function parameters;

[0030] The multiple scattering function M(μ0,u) satisfies the following relationship:

[0031] M(μ0,u)=H(μ0)H(μ)-1;

[0032] In the formula: H(x) is the H function.

[0033] Meanwhile, the present invention also provides a rapid construction system for UAV-borne linear array hyperspectral BRDF considering illumination, which is used to realize a rapid acquisition and construction method for UAV-borne linear array hyperspectral BRDF, including a hyperspectral imager, an atmospheric down-current irradiance measurement device and a calibration component;

[0034] The hyperspectral imager is installed on the UAV to acquire BRDF data of the target acquisition area; the atmospheric down-current irradiance measurement device is set on the ground to acquire data on the change of illumination over time.

[0035] The calibration component is located in the target acquisition area and is used to acquire calibration data.

[0036] Furthermore, the calibration component includes a grayscale target and a whiteboard;

[0037] Both the grayscale target and the whiteboard are placed in the target acquisition area.

[0038] Furthermore, the atmospheric downward irradiance measuring device is mounted on the ground using a tripod.

[0039] Furthermore, the hyperspectral imager is used to be mounted on a drone via a stabilizing gimbal.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] 1. This invention utilizes a drone equipped with a hyperspectral imager to acquire BRDF data of the target acquisition area at different zenith and azimuth angles according to a preset flight trajectory, achieving multi-dimensional data acquisition. Preprocessing is performed using calibration data as a reference standard, followed by data fitting through a BRDF model to obtain model parameters. Finally, the acquired illumination variation data over time is matched to obtain the BRDF distribution centered on the target acquisition area under different illumination conditions. This invention effectively combines spatial, temporal, multi-angle, and spectral information to achieve rich, multi-dimensional data acquisition. The acquisition time is continuous and fully considers the influence of illumination variations, enabling rapid acquisition and construction of the BRDF of the target acquisition area.

[0042] 2. This invention controls the drone to fly in a square trajectory. The perpendicular bisector of the corresponding side of the square trajectory has a preset angle in the horizontal direction, which ensures that the target acquisition area is always in the center during the acquisition process, thereby ensuring the orientation consistency of the acquired data and realizing multi-dimensional acquisition. Attached Figure Description

[0043] Figure 1 This is a flowchart of an embodiment of the present invention, which considers illumination, for rapid construction of a UAV-borne linear array hyperspectral BRDF.

[0044] Figure 2 This invention relates to a method for rapid construction of a hyperspectral BRDF (Rapid Linear Array BRDF) on a UAV, taking into account illumination, with a zenith angle θ. v A schematic diagram showing the initial altitude H, flight altitude h, and lateral movement distance s;

[0045] Figure 3 This invention relates to a method for rapid construction of a hyperspectral BRDF (Rapid Linear Array BRDF) on a UAV, taking into account illumination, in an embodiment where the UAV is at a zenith angle θ. v Flight trajectory diagram at 10°, flight altitude h = 49.2m, and lateral movement distance s = 8.68m;

[0046] Figure 4This is an embodiment of the rapid construction method for a UAV-borne linear array hyperspectral BRDF considering illumination, in which the zenith angle θ is... v =20°, flight altitude h=46.9m, lateral movement distance s=17.1m. Detailed Implementation

[0047] To make the objectives, advantages, and features of this invention clearer, the following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a rapid construction method and system for UAV-borne linear array hyperspectral BRDF considering illumination. The advantages and features of this invention will become clearer according to the following specific embodiments. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise proportions, used only to facilitate and clarify the explanation of the embodiments of this invention; furthermore, the structures shown in the drawings are often part of the actual structure.

[0048] This embodiment presents a rapid construction system for a UAV-borne linear array hyperspectral BRDF considering illumination, including a hyperspectral imager, an atmospheric down-current irradiance measurement device, and a calibration component.

[0049] The hyperspectral imager is mounted on the UAV to acquire BRDF data of the target acquisition area. Preferably, to improve the stability of the hyperspectral imager during acquisition, it is mounted on a stabilizing gimbal, which is then mounted on the UAV. The down-atmospheric irradiance measurement device is set on the ground via a tripod to ensure its directional accuracy in the direction perpendicular to the surface of the target acquisition area, acquiring data on illumination changes over time. The time synchronization between the hyperspectral imager and the down-atmospheric irradiance measurement device should be consistent. Specifically, the down-atmospheric irradiance measurement device consists of an analytical spectral device and a cosine corrector, both fixed on a tripod. The calibration component is set at the target acquisition area to acquire calibration data. The calibration component includes a grayscale target and a white board; both the grayscale target and the white board are laid out at the target acquisition area.

[0050] Based on the above-mentioned rapid construction system for UAV-borne linear array hyperspectral BRDF considering illumination, the following describes a rapid construction method for UAV-borne linear array hyperspectral BRDF considering illumination, specifically including the following steps:

[0051] Step 1: Control the UAV to fly at an initial flight altitude H with a 0° zenith angle, and start synchronously collecting BRDF data and calibration data of the target collection area, as well as data on the change of illumination over time; the initial flight altitude can be specifically set according to the range of the target collection area; in this embodiment, it is designed to be 50m, but in other embodiments of the present invention, it can also be designed to be 40m, 60m or 70m, etc.

[0052] Step 2: Control the drone at a zenith angle θ v The angle increases from 0° to a preset maximum angle. In this embodiment, the preset maximum angle is designed to be 50°. In other embodiments of the invention, the maximum angle can also be designed to be 40° or 60°, etc., as long as it can meet all the acquisition needs of the target acquisition area. A flight is completed with a preset flight trajectory at preset interval angles. In this embodiment, the preset interval angle is 10°. In other embodiments of the invention, depending on the accuracy requirements, it can also be designed to be 8° or 15°, etc. After each flight of the UAV, in order to ensure that the target acquisition area is always centered relative to the UAV's flight trajectory during the next flight, it is necessary to determine the zenith angle θ. v The changes correspond to adjustments in flight altitude h and lateral movement distance s; specifically, the zenith angle θ v The flight altitude h and lateral movement distance s satisfy the following relationship:

[0053] h = H * cosθ v ; s = H * sinθ v ;

[0054] Specifically, the drone's preset flight trajectory is as follows: it flies N times along a regular polygonal trajectory with side length L, where N > 1. The corresponding sides of the N regular polygonal trajectories have preset angles in the horizontal direction according to the flight order; side length L = 2*s. In this embodiment, the drone flies clockwise 3 times along a square trajectory with side length L. The perpendicular bisectors of the corresponding sides of the 3 square trajectories have preset angles of 30° in the horizontal direction according to the flight order. Figure 3 The image shows the drone at a zenith angle θ. v =10°, flight altitude h=49.2m, lateral movement distance s=8.68m, flight path Figure 4 At the zenith angle θ v The flight trajectory is shown in the table below, with a zenith angle θ = 20°, a flight altitude h = 46.9m, and a lateral movement distance s = 17.1m. This is the flight path in this embodiment. v Corresponding data to flight altitude h and lateral movement distance s:

[0055] Zenith angle, flight altitude, and lateral drift distance data table

[0056]

[0057] Furthermore, during the drone's flight, it continuously collects BRDF data and calibration data of the target acquisition area, as well as data on changes in illumination over time.

[0058] Step 3: First, filter and classify the BRDF data according to the flight number of the UAV. Then, preprocess the BRDF data according to the calibration data. Finally, input the preprocessed BRDF data into the BRDF model and obtain the model parameters by minimizing the error fitting. The error minimization method can be the least squares method, gradient descent method, Newton's method, Gauss-Newton method, etc.; preferably, in this embodiment, the Hapke model is selected as the BRDF model.

[0059] The calculation formula for the Hapke model is:

[0060]

[0061] In the formula: r(μ0,u,g) is the model function, μ0 is the cosine of the incident angle, u is the cosine of the exit angle, g is the phase angle between the incident angle and the exit angle, ω is the single scattering albedo, B(g) is the backscattering function, p(g) is the phase function, and M(μ0,u) is the multiple scattering function.

[0062] The backscattering function B(g) satisfies the following relationship:

[0063]

[0064] In the formula: B0 is the amplitude of the hotspot effect, and k is the width of the hotspot effect.

[0065] The phase function p(g) satisfies the following relationship:

[0066]

[0067] In the formula: b and c are phase function parameters.

[0068] The multiple scattering function M(μ0,u) satisfies the following relationship:

[0069] M(μ0,u)=H(μ0)H(μ)-1;

[0070] In the formula: H(x) is the H function.

[0071] By matching the model parameters with data on the changes in time and illumination over time, the BRDF distribution centered on the target acquisition area can be obtained under different illumination conditions; thus completing the acquisition and construction of the BRDF.

Claims

1. A rapid construction method for a UAV-borne linear array hyperspectral BRDF considering illumination, characterized in that, Includes the following steps: Step 1: Control the UAV to fly at an initial flight altitude H with a 0° zenith angle and start synchronously collecting data on the change of illumination over time, as well as BRDF data and calibration data of the target acquisition area; Step 2: Control the drone at a zenith angle θ v Within the range from 0° to the preset maximum angle, the drone completes one flight at preset intervals along a preset flight trajectory; and after each flight, the zenith angle θ is used to determine the maximum angle. v The changes correspond to adjustments in flight altitude h and lateral movement distance s; Zenith angle θ v The flight altitude h and lateral movement distance s satisfy the following relationship: h=H*cosθ v ;s=H*sinθ v ; During the drone's flight, BRDF data, calibration data, and data on changes in illumination over time were continuously collected. Step 3: First, filter and classify the BRDF data according to the flight number of the UAV. Then, preprocess the BRDF data according to the calibration data. Finally, input the preprocessed BRDF data into the BRDF model to obtain the model parameters. Match the model parameters according to the time and illumination change data over time to obtain the BRDF distribution centered on the target acquisition area under different illumination conditions; complete the acquisition and construction of BRDF.

2. The rapid construction method for UAV-borne linear array hyperspectral BRDF considering illumination according to claim 1, characterized in that, In step 2, the preset flight trajectory is: The plane flies N times along a regular polygonal trajectory with side length L, where N > 1. The perpendicular bisectors of the corresponding sides of the N regular polygonal trajectories in the horizontal direction are set with preset angles according to the flight order.

3. The rapid construction method for UAV-borne linear array hyperspectral BRDF considering illumination according to claim 2, characterized in that, In step 2, the preset flight trajectory is: The plane flies clockwise 3 times along a square trajectory with side length L. The perpendicular bisectors of the corresponding sides of the 3 square trajectories in the horizontal direction are set with a preset angle of 30° according to the flight order. The side length L = 2*s; The preset maximum angle is 50°; The preset interval angle is 10°.

4. The rapid construction method for UAV-borne linear array hyperspectral BRDF considering illumination according to any one of claims 1-3, characterized in that: In step 3, the BRDF model is the Hapke model; The calculation formula for the Hapke model is as follows: In the formula: r(μ0,u,g) is the model function, μ0 is the cosine of the incident angle, u is the cosine of the exit angle, g is the phase angle between the incident angle and the exit angle, ω is the single scattering albedo, B(g) is the backscattering function, p(g) is the phase function, and M(μ0,u) is the multiple scattering function.

5. The rapid construction method for UAV-borne linear array hyperspectral BRDF considering illumination according to claim 4, characterized in that, The backscattering function B(g) satisfies the following relationship: In the formula: B0 is the amplitude of the hot spot effect, k is the width of the hot spot effect, and g is the phase angle between the incident angle and the exit angle; The phase function p(g) satisfies the following relationship: In the formula: b and c are phase function parameters; The multiple scattering function M(μ0,u) satisfies the following relationship: M(μ0,u)=H(μ0)H(μ)-1; In the formula: H(x) is the H function.

6. A rapid construction system for UAV-borne linear array hyperspectral BRDF considering illumination, used to implement the rapid construction method for UAV-borne linear array hyperspectral BRDF considering illumination as described in any one of claims 1-5, characterized in that: Includes a hyperspectral imager, an atmospheric downdraft irradiance measurement device, and calibration components; The hyperspectral imager is installed on the UAV to acquire BRDF data of the target acquisition area; the atmospheric down-current irradiance measurement device is set on the ground to acquire data on the change of illumination over time. The calibration component is located in the target acquisition area and is used to acquire calibration data.

7. The rapid construction system for UAV-borne linear array hyperspectral BRDF considering illumination according to claim 6, characterized in that: The calibration component includes a grayscale target and a whiteboard; Both the grayscale target and the whiteboard are placed in the target acquisition area.

8. The rapid construction system for UAV-borne linear array hyperspectral BRDF considering illumination according to claim 6 or 7, characterized in that: The atmospheric downward irradiance measuring device is set on the ground via a tripod.

9. The rapid construction system for UAV-borne linear array hyperspectral BRDF considering illumination according to claim 8, characterized in that: The hyperspectral imager is mounted on the drone via a stabilizing gimbal.

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