A method for measuring ground reflectance based on a rotor unmanned aerial vehicle

Abstract

The present application relates to satellite remote sensing calibration and authenticity inspection technical field, provide a kind of based on rotor unmanned aerial vehicle ground reflectivity measurement method, comprising: selecting octo-copter as ground reflectivity observation aerial platform, install SVC spectrometer optical fiber holder between the two rotor arms of octo-copter side;Formulate corresponding aerial flight scheme;Octo-copter is placed in the take-off point of flight route;Planning point and landing point are uploaded to octo-copter;Select polytetrafluoroethylene pressed white board as standard reference board;Before take-off and after landing, respectively measure and collect standard reference board data, complete one flight ground reflectivity measurement;According to each parameter, calculate time-corrected ground reflectivity, repeat the above steps until completing all flights ground reflectivity measurement task.The present application saves a lot of manpower and material resources, protects the field, improves calibration accuracy, effectively improves the measurement efficiency of ground reflectivity.

Description

Technical Field

[0001] This invention relates to the field of satellite remote sensing calibration and authenticity verification technology, and in particular to a method for measuring surface reflectance based on a rotary-wing unmanned aerial vehicle (UAV). Background Technology

[0002] Absolute radiometric calibration of on-orbit remote sensors is a primary means of monitoring their radiometric characteristics and a fundamental requirement for quantitative remote sensing applications. Utilizing the satellite-ground synchronous observation experiment of the radiometric correction field of China's remote sensing satellites to achieve absolute radiometric calibration of the solar reflection band of optical imaging payloads for various on-orbit satellites, including meteorological, oceanographic, land resource, environmental disaster reduction, mapping and seismic, high-resolution, and military satellites, is currently one of the important methods. Site calibration, on the other hand, involves selecting a uniform area on the ground as the radiometric calibration field, and then performing quasi-synchronous measurements from the ground or aircraft when the satellite passes overhead to achieve radiometric calibration of the on-orbit satellite remote sensors.

[0003] However, the traditional method of ground-to-satellite synchronous measurement of surface reflectance is based on vehicle-based observation, which not only consumes a lot of manpower and resources and is prone to damage to the site, but also introduces errors in measurement accuracy. Furthermore, the measurement data obtained lacks regional representativeness. Summary of the Invention

[0004] In view of this, the present invention provides a method for measuring surface reflectivity based on a rotary-wing UAV, in order to solve the technical problem of achieving maximum site protection and further improving the site calibration accuracy of the solar reflection band in the prior art.

[0005] This invention provides a method for measuring surface reflectance based on a rotary-wing unmanned aerial vehicle (UAV), comprising:

[0006] S1. Select an octopus drone as the aerial platform for observing surface reflectance, select an SVC spectrometer as the instrument for measuring surface reflectance, fix the instrument bracket carrying the SVC spectrometer to the bottom of the octopus drone, and install an SVC spectrometer fiber optic gimbal between the two rotor arms on the side of the octopus drone.

[0007] S2. Develop corresponding flight plans based on the requirements of different surface reflectance measurement tasks;

[0008] S3. Based on the corresponding aviation flight plan, place the octocopter UAV at the takeoff point of the flight path;

[0009] S4. Plan the flight path and landing point in the octopus UAV ground station and upload it to the octopus UAV;

[0010] S5. Select a polytetrafluoroethylene pressed white board as the standard reference board. Measure and collect the standard reference board data before takeoff and after landing to complete one sortie of octopus UAV surface reflectance measurement. The standard reference board data includes: observation time and latitude and longitude, solar zenith angle of the standard reference board at the time of observation calculated based on the recorded time and latitude and longitude, and standard reference board reflectance calculated based on the measured standard reference board spectral radiance and its own directional reflectance factor.

[0011] S6. Repeat S2-S5 until all air flights have completed the surface reflectance measurement task;

[0012] S7. Based on the standard reference plate data measured and collected before takeoff and after landing, and the variation law of the solar zenith angle, establish a time variation model of the standard reference plate reflectance radiance, and calculate the fitting coefficient of the time variation model of the standard reference plate reflectance radiance; simulate the standard reference plate reflectance radiance at the target observation time based on the target measurement time; simulate the standard reference plate reflectance radiance based on the target reflectance radiance at the target observation time and the time variation model of the standard reference plate reflectance radiance at the corresponding time, and calculate the time-corrected surface reflectance.

[0013] Furthermore, the fiber optic input port of the SVC spectrometer fiber optic gimbal in S1 remains vertically downward throughout the flight of the octopus drone, where SVC is a spectral measurement device.

[0014] Furthermore, the standard reference plate has a reflectivity of 99%.

[0015] Furthermore, the aviation flight plan includes: flight route design, flight altitude design, and SVC spectrometer sampling interval design.

[0016] Furthermore, the S3

[0017] include:

[0018] S31. Based on the aforementioned flight plan, the SVC spectrometer is mounted on the octocopter UAV, and the optical fiber inlet is fixed.

[0019] S32. Set the fiber optic gimbal parameters and place the octocopter drone at the takeoff point of the flight path.

[0020] The parameters of the fiber optic PTZ include: the PTZ's orientation reference and the PTZ's sensitivity.

[0021] Further, S5 includes:

[0022] S51. Turn on the SVC spectrometer, place the SVC fiber optic inlet above the standard reference plate, and ensure that no shadows are projected onto the surface of the standard reference plate;

[0023] S52. Based on the surface of the standard reference plate, measure and collect the standard reference plate data before takeoff and after landing to complete one sortie of octopus UAV surface reflectance measurement.

[0024] Furthermore, the surface reflectance measurement of one octocopter UAV sortie in S52 includes:

[0025] The octocopter UAV takes off and completes its flight and landing according to the designed flight path.

[0026] Furthermore, in S51, the SVC spectrometer performs measurements in automatic measurement mode.

[0027] Furthermore, the octocopter UAV in S52 takes off by activating the automatic flight path mode.

[0028] Furthermore, S5 also includes:

[0029] After the octocopter UAV lands, the SVC fiber optic inlet is placed back above the standard reference plate, ensuring that no shadows are cast onto the surface of the standard reference plate.

[0030] The advantages of this invention compared to the prior art are:

[0031] 1. This invention greatly improves the spatial consistency and representativeness of surface reflectance measurement through a low-altitude measurement method for the surface reflectance of an octocopter UAV;

[0032] 2. This invention selects the SVC spectrometer, which has a relatively light overall weight, as the instrument for measuring surface reflectance, thus achieving a measurement effect with high integration and high measurement accuracy;

[0033] 3. This invention uses a polytetrafluoroethylene pressed white board as a standard reference board, which effectively ensures the measurement premise of high reflectivity reaching 99%, and provides a reliable guarantee for measurement accuracy;

[0034] 4. This invention utilizes the time of measurement of the standard reference plate before takeoff and after landing, combined with the variation law of the solar zenith angle during this period, to establish a time variation model of the standard reference plate radiance, to simulate the standard reference plate reflectance at each target observation time, and uses the target's measured spectral radiance and the corresponding simulated radiance of the standard reference plate to calculate the target reflectance, greatly improving the accuracy of reflectance measurement.

[0035] 5. This invention uses an octocopter drone, which successfully replaces the traditional method of on-site observation based on car track, greatly saving a lot of manpower and material resources, avoiding site damage caused by car running over the site and thus introducing errors to the measurement, and protecting the site to the greatest extent.

[0036] 6. This invention realizes the design and test flight of the entire process from route design, altitude selection, instrument parameter configuration, sampling strategy, and aviation data processing;

[0037] 7. The solution of the present invention obtains relative deviations of flight data of measurement results within 5%, which improves calibration accuracy and effectively improves the measurement efficiency of surface reflectivity. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in this invention, the accompanying drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a flowchart of a method for measuring surface reflectance based on a rotary-wing unmanned aerial vehicle (UAV) according to an embodiment of the present invention. Detailed Implementation

[0040] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0041] The following will describe in detail, with reference to the accompanying drawings, a method for measuring surface reflectance based on a rotary-wing unmanned aerial vehicle according to the present invention.

[0042] Figure 1 This is a flowchart of a method for measuring surface reflectance based on a rotary-wing unmanned aerial vehicle (UAV) according to an embodiment of the present invention.

[0043] like Figure 1 As shown, the method for measuring surface reflectance includes:

[0044] S1. Select an octopus drone as the aerial platform for observing surface reflectance, select an SVC spectrometer as the instrument for measuring surface reflectance, fix the instrument bracket carrying the SVC spectrometer to the bottom of the octopus drone, and install an SVC spectrometer fiber optic gimbal between the two rotor arms on the side of the octopus drone.

[0045] The reason for choosing an octocopter UAV for the surface reflectivity observation aerial platform is that it uses carbon fiber and aerospace aluminum materials, which are lightweight and strong; the whole aircraft is foldable, convenient for transportation, and has a quick-release structure; it is easy to operate and maintain; it has high safety, equipped with a parachute that can automatically deploy, and can return to home with one key in an emergency, and can hover automatically; it has a wind resistance of level 7 or above; it has a user-friendly black box function that automatically records flight data; the aircraft can autonomously complete flight missions according to preset routes; in addition to real-time monitoring of current value and battery consumption on ground station software, and providing power alarm prompts, it also has the advantages of long endurance, real-time image transmission, detection of high-risk areas, low cost, high resolution, and high maneuverability.

[0046] The fiber optic input port of the SVC spectrometer's fiber optic gimbal remains vertically downward throughout the flight of the octopus drone. Here, SVC is a spectral measurement device.

[0047] SVC stands for Spectra Vista Corporation, which specializes in spectral measurement equipment.

[0048] During flight, the SVC spectrometer is used to measure the spectral radiance of ground targets at fixed time intervals using a standard reference plate. The time and latitude / longitude of the target measurement are recorded. Based on the recorded time and latitude / longitude of the target measurement, the solar zenith angle at the time of the target measurement is calculated.

[0049] The octagonal drone is modified to accommodate an instrument bracket for an SVC spectrometer, which is fixed to the bottom of the drone. An SVC spectrometer fiber optic gimbal is installed between the two rotor arms on the side of the octagonal drone. Furthermore, the fiber optic inlet of the SVC spectrometer gimbal in step S2 remains vertically downward throughout the flight of the octagonal drone. This ensures no shadows are projected onto the reference plate surface, maximizing measurement accuracy. The invention chose an SVC spectrometer due to its high integration, high measurement accuracy, and relatively light weight.

[0050] For example, a standard reference plate is measured once before takeoff and once after landing, with each measurement repeated five times and the average value taken. During flight, only target observation is performed, with data measured every 10 seconds. The SVC spectrometer records the radiance and the surface reflectance calculated from the first standard reference plate data. For example, the radiance of the standard reference plate changes linearly over a 30-minute flight.

[0051] S2. Develop corresponding flight plans based on the requirements of different surface reflectance measurement tasks;

[0052] Since different surface reflectance measurement tasks have different measurement requirements, corresponding air flight plans should be developed based on the specific measurement task requirements.

[0053] The aviation flight plan includes: flight route design, flight altitude design, and SVC spectrometer sampling interval design.

[0054] An octocopter UAV was used instead of a runway for observation. To accurately assess the performance and endurance of the octocopter UAV, the experiment first conducted comprehensive tests on its endurance and stability using a weighted flight mode. Based on this, different flight paths were designed to meet the needs of ground reflectance spectral observation, including figure-eight, triangular, quadrilateral, and scanning flight paths, for flight measurements. Simultaneously, to analyze the impact of walkway measurements, different flight altitudes, and ground field of view on the measurement results, a hovering observation mode was also employed. For example, the UAV was hovered at different altitudes of 30m, 50m, 80m, 100m, 150m, 200m, 250m, and 300m, and the ground was observed using an SVC spectrometer. The diameter of the ground sampling area corresponds to the spectrometer diameter at different altitudes. For the measurement of the standard plate and the target, measurements of the standard reference plate were conducted before and after the sampling flight.

[0055] The sampling interval design of the SVC spectrometer is manually set according to different needs.

[0056] S3. Based on the corresponding aviation flight plan, place the octocopter UAV at the takeoff point of the flight path;

[0057] S31. Based on the aforementioned flight plan, the SVC spectrometer is mounted on the octocopter UAV, and the optical fiber inlet is fixed.

[0058] S32. Set the fiber optic gimbal parameters and place the octocopter drone at the takeoff point of the flight path.

[0059] The parameters of the fiber optic PTZ include: the PTZ's orientation reference and the PTZ's sensitivity.

[0060] S4. Plan the flight path and landing point in the octopus UAV ground station and upload it to the octopus UAV;

[0061] S5. Select a polytetrafluoroethylene pressed white board as the standard reference board. Measure and collect the standard reference board data before takeoff and after landing to complete one sortie of octopus UAV surface reflectance measurement. The standard reference board data includes: observation time and latitude and longitude, solar zenith angle of the standard reference board at the time of observation calculated based on the recorded time and latitude and longitude, and standard reference board reflectance calculated based on the measured standard reference board spectral radiance and its own directional reflectance factor.

[0062] The standard reference plate has a reflectivity of 99%.

[0063] The standard reference plate is made of polytetrafluoroethylene and has a geometric dimension of 400mm×400mm. Its small size effectively ensures the high reflectivity of the measurement and provides a reliable guarantee for measurement accuracy.

[0064] S51. Turn on the SVC spectrometer, place the SVC fiber optic inlet above the standard reference plate, and ensure that no shadows are projected onto the surface of the standard reference plate;

[0065] The SVC spectrometer in S51 performs measurements in automatic measurement mode.

[0066] The sampling interval of the SVC spectrometer is specified, and the measurement is performed using the SVC spectrometer.

[0067] S52. Based on the surface of the standard reference plate, measure and collect the standard reference plate data before takeoff and after landing to complete one sortie of octopus UAV surface reflectance measurement.

[0068] The surface reflectance measurement of an octagonal UAV in S52 includes: the octagonal UAV taking off, completing the flight and landing according to the flight path design.

[0069] The surface reflectance measurement of one sortie of the octocopter UAV in the S52 includes:

[0070] The octocopter UAV takes off and completes its flight and landing according to the designed flight path.

[0071] The S52 octocopter UAV takes off by activating the automatic flight path mode.

[0072] The formula for calculating the reflected radiance of the standard reference plate is as follows:

[0073]

[0074] In the formula Let θs be the incident direction. The reflected radiance of a standard reference plate with an emission direction of 0°. The radiance as observed vertically from the zenith. The directional reflectance factor is the spectral radiance of the standard reference plate.

[0075] BRF stands for bidirectional reflectance factor.

[0076] Following S5, the following is also included:

[0077] After the octocopter UAV lands, the SVC fiber optic inlet is placed back above the standard reference plate, ensuring that no shadows are cast onto the surface of the standard reference plate.

[0078] S6. Repeat S2-S5 until all air flights have completed the surface reflectance measurement task;

[0079] S7. Based on the standard reference plate data measured and collected before takeoff and after landing, and the variation law of the solar zenith angle, establish a time variation model of the standard reference plate reflectance radiance, and calculate the fitting coefficient of the time variation model of the standard reference plate reflectance radiance; simulate the standard reference plate reflectance radiance at the target observation time based on the target measurement time; simulate the standard reference plate reflectance radiance based on the target reflectance radiance at the target observation time and the time variation model of the standard reference plate reflectance radiance at the corresponding time, and calculate the time-corrected surface reflectance.

[0080] The standard reference plate reflectance is calculated based on the measured standard reference plate spectral radiance and its own directional reflectance factor, and the standard reference plate BRF correction of the measurement results is performed accordingly.

[0081] This invention modifies an octocopter UAV to carry an SVC spectrometer for measuring surface reflectance. By selecting the relatively lightweight SVC spectrometer as the surface reflectance measuring instrument, it achieves high integration and high measurement accuracy. Using a polytetrafluoroethylene (PTFE) pressed white board as a standard reference board effectively ensures a high reflectance of 99%, providing reliable assurance for measurement accuracy. This invention utilizes the time taken before takeoff and after landing to measure the standard reference board, combined with the variation of the solar altitude angle during this period, to establish a time-varying model of the reference board's radiance. This model simulates the reflected radiance of the standard reference board at each target observation moment, and uses the spectral radiance measured from the target... The target reflectivity is calculated by simulating radiance using a standard reference board at the corresponding time, greatly improving the accuracy of reflectivity measurement. By using an octocopter UAV to measure the surface reflectivity, it successfully replaces the traditional method of on-site observation based on a car track, greatly saving a lot of manpower and resources, avoiding site damage caused by vehicles and introducing errors into the measurement, and protecting the site to the greatest extent. This invention realizes the design and test flight of the entire chain from flight path design, flight altitude selection, instrument parameter configuration, sampling strategy, and aerial data processing. The relative deviation of the flight data obtained is within 5%, which improves the calibration accuracy and effectively improves the measurement efficiency of surface reflectivity.

[0082] All of the above-mentioned optional technical solutions can be combined in any way to form the optional embodiments of this application, and will not be described in detail here.

[0083] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this disclosure.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for measuring surface reflectance based on a rotary-wing unmanned aerial vehicle (UAV), characterized in that, include: S1. Select an octopus drone as the aerial platform for observing surface reflectance, select an SVC spectrometer as the instrument for measuring surface reflectance, fix the instrument bracket carrying the SVC spectrometer to the bottom of the octopus drone, and install an SVC spectrometer fiber optic gimbal between the two rotor arms on the side of the octopus drone. S2. Develop corresponding flight plans based on the requirements of different surface reflectance measurement tasks; S3. Based on the corresponding aviation flight plan, place the octocopter UAV at the takeoff point of the flight path; The aviation flight plan includes: flight route design, flight altitude design, and SVC spectrometer sampling interval design. S4. Plan the flight path and landing point in the octopus UAV ground station and upload it to the octopus UAV; S5. Select a polytetrafluoroethylene pressed white board as the standard reference board. Measure and collect the standard reference board data before takeoff and after landing to complete one sortie of octopus UAV surface reflectance measurement. The standard reference board data includes: observation time and latitude and longitude, solar zenith angle of the standard reference board at the time of observation calculated based on the recorded time and latitude and longitude, and standard reference board reflectance calculated based on the measured standard reference board spectral radiance and its own directional reflectance factor. S6. Repeat S2-S5 until all air flights have completed the surface reflectance measurement task; S7. Based on the standard reference plate data measured and collected before takeoff and after landing, and the variation law of the solar zenith angle, establish a time variation model of the standard reference plate reflective radiance, and calculate the fitting coefficient of the time variation model of the standard reference plate reflective radiance; simulate the standard reference plate reflective radiance at the target observation time based on the target measurement time; simulate the standard reference plate reflective radiance based on the target reflective radiance at the target observation time and the time variation model of the standard reference plate reflective radiance at the corresponding time, and calculate the time-corrected surface reflectivity; Wherein, S5 includes: S51. Turn on the SVC spectrometer, place the SVC fiber optic inlet above the standard reference plate, and ensure that no shadows are projected onto the surface of the standard reference plate; S52. Based on the surface of the standard reference plate, measure and collect the standard reference plate data before takeoff and after landing respectively; the octopus drone takes off and completes the flight and landing according to the flight path design, thereby completing one sortie of octopus drone surface reflectance measurement.

2. The method for measuring surface reflectance according to claim 1, characterized in that, The fiber optic input port of the SVC spectrometer gimbal in S1 remains vertically downward throughout the flight of the octopus drone. Here, SVC is a spectral measurement device.

3. The method for measuring surface reflectance according to claim 1, characterized in that, The standard reference plate has a reflectivity of 99%.

4. The method for measuring surface reflectance according to claim 1, characterized in that, S3 includes: S31. Based on the aforementioned flight plan, the SVC spectrometer is mounted on the octocopter UAV, and the optical fiber inlet is fixed. S32. Set the fiber optic gimbal parameters and place the octocopter drone at the takeoff point of the flight path. The parameters of the fiber optic PTZ include: the PTZ's orientation reference and the PTZ's sensitivity.

5. The method for measuring surface reflectance according to claim 1, characterized in that, The SVC spectrometer in S51 performs measurements in automatic measurement mode.

6. The method for measuring surface reflectance according to claim 1, characterized in that, The S52 octocopter UAV takes off by activating the automatic flight path mode.

7. The method for measuring surface reflectance according to claim 1, characterized in that, The S5 also includes: After the octocopter UAV lands, the SVC fiber optic inlet is placed back above the standard reference plate, ensuring that no shadows are cast onto the surface of the standard reference plate.

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