A topographic map surveying method based on a UAV

Abstract

The present application relates to the technical field of surveying and mapping services, and specifically discloses a topographic map surveying and mapping method based on a UAV, comprising the following steps: deploying a laser emitter and a single-photon avalanche diode, causing the UAV to emit a laser pulse and record the emission time after reaching the survey area; capturing reflected photons and recording the time, and calculating the reflection duration; calculating a quality coefficient, and comparing the threshold to divide into weak, normal and strong echoes; up-regulating the energy of weak echoes, down-regulating the energy of strong echoes, and not adjusting normal echoes, and repeating until the signal is a normal echo; continuously collecting along a preset route until the laser pulse covers the entire survey area. The present application constructs a closed-loop adaptive energy regulation mechanism, introduces a comprehensive echo quality coefficient, divides the signal into three categories of strong, normal and weak, and dynamically adjusts the emission energy accordingly, so that the laser parameters and the reflection characteristics of the ground objects are matched in real time, and the uniformity, continuity and ranging accuracy of the point cloud data are ensured.

Description

Technical Field

[0001] This invention relates to the field of surveying and mapping service technology, and specifically to a topographic mapping method based on unmanned aerial vehicles (UAVs). Background Technology

[0002] In the field of topographic mapping, UAV-borne lidar measurement technology has become an important means of acquiring high-precision geospatial data due to its high mobility and operational efficiency. Traditional airborne lidar systems typically use linear mode detectors, whose operating principle relies on the intensity threshold triggering of the received echo signal. This often requires the emission of high-energy laser pulses, resulting in high system power consumption and limiting its integration and application on lightweight UAV platforms. Furthermore, when dealing with complex terrain cover, a single fixed-energy laser pulse is difficult to adapt to the varying reflection characteristics of ground features, easily leading to oversaturation or weak signal loss, affecting the integrity and accuracy of point cloud data.

[0003] To overcome the aforementioned shortcomings, single-photon detection technology has been introduced into the field of aerial mapping in recent years. Single-photon avalanche diodes possess extremely high sensitivity, capable of detecting extremely weak signals at the single-photon level, making elevation measurements possible at low laser energy levels and providing a new approach for lightweight system design. However, existing mapping methods based on single-photon detection still face challenges in practical applications due to insufficient adaptability. Because surface cover types exhibit significant differences in laser reflectivity and reflection characteristics, the quality of the acquired echo signal fluctuates drastically when the flight altitude and laser emission parameters are fixed. In low-reflectivity regions, the signal is too weak, resulting in insufficient effective photon counts, leading to ranging failures or a sharp drop in accuracy; while in high-reflectivity or specular reflection regions, echo saturation may occur, causing pulse broadening distortion, both of which severely degrade the quality of the final digital elevation model. Therefore, there is an urgent need for an UAV topographic mapping method capable of dynamically adjusting emission parameters based on real-time echo signal quality to improve the system's adaptability to different terrain environments. Summary of the Invention

[0004] The purpose of this invention is to provide a topographic mapping method based on unmanned aerial vehicles (UAVs) to solve the above-mentioned technical problems.

[0005] The objective of this invention can be achieved through the following technical solutions: A topographic mapping method based on unmanned aerial vehicles (UAVs) includes the following steps: A laser emitter and a single-photon avalanche diode are deployed on a drone. The drone's flight altitude H is preset. When the drone arrives at the starting point of the survey area, the drone is raised to altitude H, and the laser emitter emits a laser pulse with a preset energy value E. The time T1 when the laser pulse is emitted is recorded. When the single-photon avalanche diode captures the reflected photon signal, the time T2 is recorded. The echo quality coefficient X is calculated based on the photon signal data captured and reflected by a single-photon avalanche diode. The photon signal data includes the effective photon count N, the echo photon ratio B, and the echo pulse broadening C. The effective photon count represents the number of photons captured within a preset time window after the laser pulse is emitted. The echo photon ratio is the ratio of the effective photon count to the number of emitted photons. The echo pulse broadening refers to the duration of the photon signal captured and reflected by the single-photon avalanche diode on the time axis after the laser pulse is reflected. The captured photon signals are classified into strong echoes, normal echoes, and weak echoes according to the echo quality coefficient X. Adjust the energy value of the next laser pulse based on the photon signal division result, and repeat the above operation of adjusting the laser pulse energy value based on the echo quality coefficient until the captured photon signal is divided into a normal signal. Continue to collect data along the preset route in this way until the entire measurement area is covered.

[0006] As a further aspect of the present invention: the reflection time T of the photon signal is calculated as T = T2 - T1, and a pre-set waiting time threshold T is set. max When the reflection time T≥T max At that time, the drone's flight altitude is reduced by 10%. The drone then emits a laser pulse again after the altitude is reduced, and the reflection time is calculated. If the reflection time T ≥ T max This causes the drone's flight altitude to decrease by another 10% until the reflection time T < T. max The descent stopped.

[0007] As a further aspect of the present invention: a pre-set safety distance L is provided, and when the distance between the drone and the tree canopy is less than or equal to the safety distance L, the reflection time T is still greater than or equal to T. max At this point, the descent stops.

[0008] As a further aspect of the present invention: a method for calculating the echo quality coefficient X based on single-photon avalanche diode-captured reflected photon signal data: Calculate the echo quality factor Where λ1 represents the preset first coefficient, λ2 represents the preset second coefficient, and σ C C represents the preset tolerance for expansion. opt This represents the preset ideal pulse width.

[0009] As a further aspect of the present invention: classifying the captured photon signal into strong echo, normal echo, and weak echo based on the echo quality coefficient X includes the following steps: Preset quality coefficient threshold X min and the threshold X of the quality coefficient max When X < X min When X..., the captured photon signal is divided into weak echoes; when X... min ≤X<Xmax When X ≥ X, the captured photon signal is divided into normal echo; max At that time, the captured photon signal is divided into strong echoes.

[0010] As a further aspect of the present invention: adjusting the energy value of the next laser pulse based on the photon signal partitioning result specifically includes the following steps: If the photon signal is classified as a normal echo, no adjustment is performed; If the photon signal is classified as a weak echo, the energy value E of the laser emitter is increased by λ. If the photon signal is classified as a strong echo, the energy value E of the laser emitter is reduced by λ, where λ represents a preset adjustment coefficient, 0 < λ < 1.

[0011] As a further aspect of the present invention: when the single-photon avalanche diode fails to capture the reflected photon, the laser emitter is controlled to emit a laser pulse again with the same energy value E, and the maximum number of retransmissions I is set. If the laser emitter fails to capture the reflected photon in I consecutive laser pulses, the area is marked as an abnormal area and skipped. At the same time, the coordinates of the abnormal area are obtained, and the staff is notified that the terrain mapping at these coordinates is abnormal.

[0012] As a further aspect of the present invention: when the UAV arrives at the next test area, the initial energy value of the laser emitter in the next test area is made equal to the adjusted energy value in the previous test area.

[0013] The beneficial effects of this invention are as follows: By constructing a closed-loop adaptive energy regulation mechanism, this invention solves the signal quality mismatch problem caused by differences in surface reflection characteristics in traditional single-photon detection mapping systems, significantly improving the integrity and accuracy of mapping data in complex terrain environments. Specifically, this invention creatively introduces a comprehensive echo quality coefficient X that integrates effective photon count, echo photon ratio, and echo pulse broadening. This coefficient reflects the true state of the echo signal and scientifically classifies the signal into three categories: strong echo, normal echo, and weak echo. Based on this, the system adjusts the emission energy of the next laser pulse in real time and automatically according to the classification results. This collaborative control strategy of real-time evaluation, intelligent classification, and dynamic adjustment ensures that the laser emission parameters always maintain optimal matching with the current ground reflection characteristics of the survey area, thereby effectively guaranteeing the uniformity, continuity, and elevation ranging accuracy of the entire mapping point cloud data. Attached Figure Description

[0014] The present invention will now be further described with reference to the accompanying drawings.

[0015] Figure 1 This is a schematic diagram of the structure of a topographic mapping method based on an unmanned aerial vehicle (UAV) according to the present invention; Figure 2This is a flowchart illustrating a topographic mapping method based on unmanned aerial vehicles (UAVs) according to the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Please see Figure 1 As shown, this invention is a topographic mapping method based on unmanned aerial vehicles (UAVs), comprising the following steps: A laser emitter and a single-photon avalanche diode are deployed on a drone. The drone's flight altitude H is preset. When the drone arrives at the starting point of the survey area, the drone is raised to altitude H, and the laser emitter emits a laser pulse with a preset energy value E. The time T1 when the laser pulse is emitted is recorded. When the single-photon avalanche diode captures the reflected photon signal, the time T2 is recorded. The echo quality coefficient X is calculated based on the photon signal data captured and reflected by a single-photon avalanche diode. The photon signal data includes the effective photon count N, the echo photon ratio B, and the echo pulse broadening C. The effective photon count represents the number of photons captured within a preset time window after the laser pulse is emitted. The echo photon ratio is the ratio of the effective photon count to the number of emitted photons. The echo pulse broadening refers to the duration of the photon signal captured and reflected by the single-photon avalanche diode on the time axis after the laser pulse is reflected. The captured photon signals are classified into strong echoes, normal echoes, and weak echoes according to the echo quality coefficient X. Adjust the energy value of the next laser pulse based on the photon signal division result, and repeat the above operation of adjusting the laser pulse energy value based on the echo quality coefficient until the captured photon signal is divided into a normal signal. Continue to collect data along the preset route in this way until the entire measurement area is covered.

[0018] It should be noted that a laser emitter and a single-photon avalanche diode are deployed on the UAV. The laser emitter emits laser pulses towards the ground target, while the single-photon avalanche diode acts as a receiver, capturing the photon signals reflected back from the ground. Before the operation begins, the UAV's flight altitude H is preset based on the terrain features of the survey area, weather conditions, and mapping accuracy requirements. This altitude must comprehensively consider the UAV's endurance, the atmospheric attenuation characteristics of the laser pulse, and the mapping resolution requirements. Simultaneously, the initial emission energy value E of the laser emitter is preset. This energy value is set to a moderate value, neither too high to cause echo saturation nor too low to result in insufficient effective photon count. When the UAV flies along the preset route and arrives at the starting point of the survey area, the flight control system issues a command to instruct the UAV to climb or descend to the preset flight altitude H and maintain a stable hovering or constant speed flight state. Subsequently, the laser emitter is controlled to emit a laser pulse towards the ground with the preset energy value E, while a high-precision timing module accurately records the moment T1 of the laser pulse emission.

[0019] After the laser pulse is reflected by the ground target, some photons return along the original path and are captured by a single-photon avalanche diode on the UAV. The single-photon avalanche diode operates in Geiger mode and can respond to a single incident photon, outputting an electrical pulse signal. When the single-photon avalanche diode successfully captures the reflected photon signal, the timing module records the time T2. Based on the transmission time T1 and the reception time T2, the flight time of the laser pulse, i.e., the reflection duration T = T2 - T1, can be calculated.

[0020] For successfully captured reflected photon signals, the echo quality coefficient X is calculated based on the photon signal data output by the single-photon avalanche diode. The photon signal data includes three core parameters: effective photon count N, echo photon ratio B, and echo pulse broadening C. The effective photon count N represents the total number of photons actually captured by the single-photon avalanche diode within a preset time window after the laser pulse is emitted; this value directly reflects the intensity of the echo signal. The echo photon ratio B is the ratio of the effective photon count to the total number of emitted photons contained in the emitted laser pulse. This ratio characterizes the overall reflection efficiency of the ground target to the laser, eliminating interference from changes in the absolute value of the emitted energy and more objectively reflecting the reflection characteristics of the ground object itself. The broadening C of the echo pulse refers to the overall duration of the reflected photon signal captured by the single-photon avalanche diode on the time axis after the laser pulse is reflected from the ground target. It is the width of the echo waveform and its magnitude is closely related to factors such as the roughness of the ground target, the tilt angle, and the penetration depth of vegetation. It is an important indicator for judging whether the echo signal is distorted.

[0021] Subsequently, based on the calculated echo quality coefficient X, the captured photon signal was classified into three categories: strong echo, normal echo, and weak echo.

[0022] Based on the photon signal segmentation results, the system automatically adjusts the energy value of the next laser pulse emitted by the laser transmitter. If the photon signal is segmented as a normal echo, it indicates that the current emission energy value matches well with the reflection characteristics of the ground objects in the survey area, and no adjustment is needed; the energy value E remains unchanged. If the photon signal is segmented as a weak echo, it indicates that the current emission energy is insufficient to produce a sufficiently strong effective echo signal. In this case, the energy value E of the laser transmitter is increased to enhance the echo intensity and improve the effective photon count. If the photon signal is segmented as a strong echo, it indicates that the current emission energy is too high, causing the echo signal to saturate or the pulse to broaden excessively. In this case, the energy value E of the laser transmitter is decreased to reduce the emission power to avoid signal distortion and ensure that the echo waveform maintains an ideal shape.

[0023] After completing one energy adjustment, the system controls the laser emitter to emit laser pulses again with a new energy value, and repeats the above operations based on echo quality coefficient calculation and signal classification, re-capturing echo signals, recalculating X values, and re-classifying signals. If the newly captured photon signal is still not classified as a normal echo, the next round of energy adjustment continues based on the classification results. This cycle iterates until the captured photon signal is classified as a normal echo, at which point the laser emission parameters are considered to have reached an optimal match with the ground reflection characteristics of the current survey area. Using this adaptive closed-loop control method, the UAV continuously emits laser pulses and collects data along a preset planned route until the laser pulses cover the entire survey area, thereby acquiring high-quality data for the entire survey area.

[0024] In another preferred embodiment of the present invention, the reflection time T of the photon signal is calculated as T = T2 - T1, and a pre-set waiting time threshold T is set. max When the reflection time T≥T max At that time, the drone's flight altitude is reduced by 10%. The drone then emits a laser pulse again after the altitude is reduced, and the reflection time is calculated. If the reflection time T ≥ T max This causes the drone's flight altitude to decrease by another 10% until the reflection time T < T. max The descent stopped.

[0025] It is worth noting that by introducing a flight altitude adaptive adjustment mechanism based on the reflection duration T, a dual-coordinated approach is provided to ensure echo signal quality. This is especially important when extremely low surface reflectivity or severe atmospheric attenuation causes the reflection duration to exceed the threshold T. maxIn some cases, simply increasing the laser emission energy may not be enough to obtain a sufficiently strong effective echo signal. In such situations, actively lowering the UAV's flight altitude can effectively shorten the laser pulse propagation path and reduce atmospheric transmission loss, thereby physically enhancing the echo photon flux reaching the detector. Simultaneously, this scheme employs a 10% gradient decrease adjustment strategy, avoiding the flight safety risks associated with a single large descent while ensuring efficient convergence of the adjustment process. Setting a clear descent termination condition gives the altitude adjustment a clear target orientation and self-limiting nature, preventing excessive descent. Furthermore, maintaining a relatively high flight altitude while ensuring signal quality is beneficial for balancing surveying efficiency and UAV endurance, demonstrating the unity of safety and adaptability in the method. In another preferred embodiment of the present invention, a safety distance L is preset, and when the distance between the drone and the tree canopy is less than or equal to the safety distance L, the reflection time T is still greater than or equal to T. max At this point, the descent stops.

[0026] Understandably, by setting a safe distance L, a safety mechanism is introduced to ensure the drone's flight altitude adjustment. This is effective when the reflection time T is still greater than or equal to T. max While continuing to descend might improve echo signal quality, it could jeopardize flight safety. This solution assesses whether the drone has reached a safe distance from the tree canopy, making a rational trade-off between signal optimization needs and flight safety, and forcibly terminates the descent, effectively preventing a collision between the drone and the tree canopy.

[0027] In another preferred embodiment of the present invention, a method for calculating the echo quality coefficient X based on single-photon avalanche diode-captured reflected photon signal data is provided. Calculate the echo quality factor Where λ1 represents the preset first coefficient, λ2 represents the preset second coefficient, and σ C C represents the preset tolerance for expansion. opt This represents the preset ideal pulse width.

[0028] In another preferred embodiment of the present invention, classifying the captured photon signal into strong echo, normal echo, and weak echo according to the echo quality coefficient X includes the following steps: Preset quality coefficient threshold X min and the threshold X of the quality coefficient max When X < X min When X..., the captured photon signal is divided into weak echoes; when X... min ≤X<X max When X ≥ X, the captured photon signal is divided into normal echo; max At that time, the captured photon signal is divided into strong echoes.

[0029] It should be noted that by presetting a lower and upper limit for the quality coefficient, a clear dual-threshold signal classification architecture is constructed, enabling refined hierarchical discrimination of echo signal quality. The lower threshold is used to identify weak echoes with insufficient signal energy, while the upper threshold is used to identify strong echoes with a risk of saturation. Together, they define the normal echo range that meets the requirements of surveying accuracy. This dual-threshold classification mechanism elevates signal quality assessment from qualitative judgment to quantitative grading, providing a clear and quantifiable control basis for subsequent differentiated energy adjustment strategies. Furthermore, the lower and upper limits of the quality coefficient can be flexibly preset according to different surveying scenarios and accuracy requirements, giving the method good scenario adaptability and scalability, ensuring the universality of this invention under different operating conditions.

[0030] In another preferred embodiment of the present invention, adjusting the energy value of the next laser pulse based on the photon signal partitioning result specifically includes the following steps: If the photon signal is classified as a normal echo, no adjustment is performed; If the photon signal is classified as a weak echo, the energy value E of the laser emitter is increased by λ. If the photon signal is classified as a strong echo, the energy value E of the laser emitter is reduced by λ, where λ represents a preset adjustment coefficient, 0 < λ < 1.

[0031] In another preferred embodiment of the present invention, when the single-photon avalanche diode fails to capture the reflected photon, the laser emitter is controlled to emit a laser pulse again with the same energy value E, and a maximum number of retransmissions I is set. If the laser emitter emits laser pulses for a continuous period of I without capturing the reflected photon, the area is recorded as an abnormal area and skipped. At the same time, the coordinates of the abnormal area are obtained, and the staff is notified that the terrain mapping at the coordinates is abnormal.

[0032] It is worth noting that an anomaly handling mechanism was constructed to address scenarios where signal loss occurs in single-photon detection due to strong absorption by ground objects, terrain obstruction, or extreme reflection conditions. By setting a maximum number of repetitions I, a reasonable balance is achieved between retransmission attempts and operational efficiency. This provides multiple opportunities for signal acquisition, avoiding data gaps caused by accidental single failures, while also preventing mapping stagnation due to endless retransmissions. When no echo is captured for I consecutive attempts, the system objectively determines that the area is a mapping anomaly and performs a skip operation. At the same time, it accurately records the coordinates of the anomaly area and alerts the staff. The acquisition of the anomaly coordinates also provides clear spatial guidance for subsequent manual re-surveys or alternative data collection.

[0033] In another preferred embodiment of the present invention, when the UAV arrives at the next test area, the initial energy value of the laser emitter in the next test area is set to be equal to the adjusted energy value in the previous test area.

[0034] It is worth noting that the energy parameter transfer mechanism between survey areas effectively improves the overall efficiency of continuous multi-survey-area mapping operations. When the UAV completes data acquisition in the current survey area and moves to the next survey area, adjacent survey areas typically have similar land cover types and reflection characteristics. Using the final converged and stable energy value of the previous survey area as the initial emission energy of the next survey area is equivalent to providing a near-optimal initial solution for the adaptive adjustment process of the next survey area. Compared to iterating from a fixed initial value in each new survey area, this scheme significantly reduces the number of convergence steps for energy adjustment, effectively reducing the time consumption caused by repeated laser pulse test firings. At the same time, fewer iterations also mean fewer laser emission times, which helps reduce system energy consumption and extend the single-operation endurance of the UAV.

[0035] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A topographic mapping method based on unmanned aerial vehicles (UAVs), characterized in that, Includes the following steps: A laser emitter and a single-photon avalanche diode are deployed on a drone. The drone's flight altitude H is preset. When the drone arrives at the starting point of the survey area, the drone is raised to altitude H, and the laser emitter emits a laser pulse with a preset energy value E. The time T1 when the laser pulse is emitted is recorded. When the single-photon avalanche diode captures the reflected photon signal, the time T2 is recorded. The echo quality coefficient X is calculated based on the photon signal data captured and reflected by a single-photon avalanche diode. The photon signal data includes the effective photon count N, the echo photon ratio B, and the echo pulse broadening C. The effective photon count represents the number of photons captured within a preset time window after the laser pulse is emitted. The echo photon ratio is the ratio of the effective photon count to the number of emitted photons. The echo pulse broadening refers to the duration of the photon signal captured and reflected by the single-photon avalanche diode on the time axis after the laser pulse is reflected. The captured photon signals are classified into strong echoes, normal echoes, and weak echoes according to the echo quality coefficient X. Adjust the energy value of the next laser pulse based on the photon signal division result, and repeat the above operation of adjusting the laser pulse energy value based on the echo quality coefficient until the captured photon signal is divided into a normal signal. Continue to collect data along the preset route in this way until the entire measurement area is covered.

2. The topographic mapping method based on unmanned aerial vehicles (UAVs) according to claim 1, characterized in that, Calculate the reflection time of the photon signal T = T2 - T1, and preset the waiting time threshold T. max When the reflection duration T ≥ T max At that time, the drone's flight altitude is reduced by 10%. The drone then emits a laser pulse again after the altitude is reduced, and the reflection time is calculated. If the reflection time T ≥ T max This causes the drone's flight altitude to decrease by another 10% until the reflection time T < T. max The descent stopped at that time.

3. The topographic mapping method based on unmanned aerial vehicles (UAVs) according to claim 2, characterized in that, A pre-set safe distance L is ensured that when the drone is less than or equal to the tree canopy, the reflection time T remains greater than or equal to T. max At this point, the descent stops.

4. The topographic mapping method based on unmanned aerial vehicles (UAVs) according to claim 1, characterized in that, A method for calculating the echo quality coefficient X based on single-photon avalanche diode-captured reflected photon signal data: Calculate the echo quality factor Where λ1 represents the preset first coefficient, λ2 represents the preset second coefficient, and σ C C represents the preset tolerance for expansion. opt This represents the preset ideal pulse width.

5. The topographic mapping method based on unmanned aerial vehicles (UAVs) according to claim 1, characterized in that, Classifying captured photon signals into strong echo, normal echo, and weak echo based on the echo quality coefficient X includes the following steps: Presetting a threshold value X for the quality coefficient. min and the threshold X of the quality coefficient max When X < X min When X..., the captured photon signal is divided into weak echoes; when X... min ≤X<X max When X ≥ X, the captured photon signal is divided into normal echo; max At that time, the captured photon signal is divided into strong echoes.

6. The topographic mapping method based on unmanned aerial vehicles (UAVs) according to claim 1, characterized in that, Adjusting the energy value of the next laser pulse based on the photon signal division results specifically includes the following steps: If the photon signal is classified as a normal echo, no adjustment is performed; If the photon signal is classified as a weak echo, the energy value E of the laser emitter is increased by λ. If the photon signal is classified as a strong echo, the energy value E of the laser emitter is reduced by λ, where λ represents a preset adjustment coefficient, 0 < λ < 1.

7. The topographic mapping method based on unmanned aerial vehicles (UAVs) according to claim 1, characterized in that, When the single-photon avalanche diode fails to capture the reflected photon, the laser emitter is controlled to emit a laser pulse again with the same energy value E, and the maximum number of retransmissions I is set. If the laser emitter fails to capture the reflected photon in I consecutive laser pulses, the area is marked as an abnormal area and skipped. At the same time, the coordinates of the abnormal area are obtained, and the staff is notified that the terrain mapping at these coordinates is abnormal.

8. The topographic mapping method based on unmanned aerial vehicles (UAVs) according to claim 1, characterized in that, When the UAV arrives at the next test area, the initial energy value of the laser emitter in the next test area is set to be equal to the adjusted energy value in the previous test area.

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