HYPERSPECTRAL IMAGING EQUIPMENT FOR UAVS WITH A BUILT-IN CALIBRATION UNIT FOR SPECTRAL AND RADIOMETRIC REFERENCE

Abstract

This utility model relates to optoelectronic surveillance systems, hyperspectral imaging, and remote sensing from unmanned aerial vehicles. The device can be used to obtain hyperspectral images of the earth's surface, vegetation, water bodies, engineering structures, road networks, infrastructure facilities, and other objects under observation, while simultaneously providing spectral and radiometric data referencing. The hyperspectral imaging equipment for an unmanned aerial vehicle comprises a housing, a lens, an entrance slit, a spectral unit with a dispersive element, a photoreceiver module, a control and data processing module, a memory unit, an interface for communication with the unmanned aerial vehicle's onboard system, and a mounting unit for the unmanned aerial vehicle.The imaging equipment is equipped with a built-in calibration unit, designed as a rotating standard holder containing a dark screen, a diffuse light standard, and a spectral standard with specified spectral lines. The standard holder is positioned in front of the entrance slit, allowing the dark screen, diffuse light standard, and spectral standard to be alternately fed into the optical path of the equipment.The data control and processing module is connected to the calibration unit, the photoreceiver module, the memory unit, and the communication interface with the onboard system of the unmanned aerial vehicle. It is configured to switch the equipment between shooting mode and calibration mode, control the position of the standard holder, receive calibration frames from the photoreceiver module, calculate calibration coefficients based on a dark screen, a diffuse light standard, and a spectral standard, and store these calibration coefficients along with a timestamp, equipment temperature, and exposure parameters. The technical result consists of increasing the reliability and comparability of hyperspectral data obtained from the UAV.

Description

[0001] This utility model relates to the field of optoelectronic surveillance systems, hyperspectral imaging, and remote sensing from unmanned aerial vehicles. The device can be used to obtain hyperspectral images of the earth's surface, vegetation, water bodies, engineering structures, road networks, infrastructure facilities, and other objects of observation, while simultaneously providing spectral and radiometric reference for the obtained data.

[0002] A hyperspectral camera is known from the prior art (patent for utility model RU No. 1 229 845), based on the Offner circuit, containing an objective, an electronics module, a slit diaphragm, a diffraction grating and a spectral unit, characterized in that the camera has a block structure and includes a cover unit with the cover itself, a lens unit with an objective and an electronics module, a slit diaphragm unit, a diffraction grating unit, a spectral unit, brackets for fastening to the device and a connector for connecting thermal and end sensors, wherein the diffraction grating unit contains a housing in which a cylinder with an external thread is installed by means of a threaded connection with the possibility of axial movement, forming a radial mount, and in turn a diffraction grating and a diffraction grating mirror are installed in it, a stepper motor with a gear transmission is also installed in this unit,wherein the cylinder with the external thread of the diffraction grating is connected to the mounting cylinder of the main mirror of the spectral unit by means of a threaded connection, the main mirror of the spectral unit itself is installed in the mounting cylinder of the spectral unit through a collar with an external thread, which is also installed with the possibility of axial movement due to a stepper motor with a gear transmission installed in the spectral unit, forming a radial mount, wherein the optical circuit of the device itself includes two main lenses installed in the front part of the objective, two small lenses, the main mirror and a small mirror installed in the rear part of the objective, a slit diaphragm, a mirror of the diffraction grating and the main mirror of the spectrometer.

[0003] Airborne hyperspectral cameras and imaging spectrometers are known to be mounted on aircraft, including unmanned aerial vehicles. Such devices typically comprise an objective lens, an entrance slit or slit aperture, a spectral unit with a dispersive element, a photodetector module, an electronics module, and a housing with mounting points for the carrier.

[0004] Current solutions allow the formation of hyperspectral images, which are a set of images of the same terrain in different spectral bands. However, the quality of subsequent processing of such data depends not only on the spatial resolution and number of spectral channels, but also on the accuracy of the radiometric and spectral calibration of the equipment.

[0005] When operating hyperspectral equipment on board a UAV, the survey results are affected by changes in illumination, cloudiness, viewing angle, flight altitude, body temperature, heating of the photoreceiving module, changes in exposure, dark signal drift, unevenness of pixel sensitivity, as well as possible shift in the position of the spectral channels relative to the photoreceiving matrix.

[0006] The disadvantages of known technical solutions are:

[0007] 1. The need to perform pre-flight or post-flight calibration using external standards;

[0008] 2. Impossibility of promptly checking the radiometric stability of the equipment directly during the flight;

[0009] 3. The absence of a built-in unit that provides the input of dark, light and spectral standards into the optical path without dismantling the equipment;

[0010] 4. Reliability of hyperspectral data decreases when illumination changes during the route;

[0011] 5. Accumulation of errors during long-term shooting due to drift of the photoreceiving module and temperature changes;

[0012] 6. The need to increase the volume of subsequent software data correction, which complicates processing and reduces the efficiency of UAV use.

[0013] The technical objective of the utility model is to create hyperspectral imaging equipment for an unmanned aerial vehicle, providing built-in spectral and radiometric referencing of the images obtained directly during operation, without dismantling the equipment from the UAV and without the mandatory use of external ground standards during each imaging cycle.

[0014] The solution to the technical problem is achieved in that the hyperspectral imaging equipment for an unmanned aerial vehicle comprises a housing, a lens, an entrance slit, a spectral unit with a dispersing element, a photoreceiving module, a control and data processing module, a memory unit, an interface for exchanging with the on-board system of the unmanned aerial vehicle and a mounting unit to the unmanned aerial vehicle, characterized in that it is equipped with a built-in calibration unit made in the form of a rotary or linearly movable standard holder containing a dark screen, a diffuse light standard and a spectral standard with specified spectral lines or passbands, wherein the standard holder is placed in front of the entrance slit or in front of the lens with the possibility of alternately inputting the dark screen, the diffuse light standard and the spectral standard into the optical path of the equipment, and the control and data processing module is connected to the calibration unit, the photoreceiving module,a memory unit and an interface for communication with the on-board system of the unmanned aerial vehicle and is designed with the ability to switch the equipment between the shooting mode and the calibration mode, control the position of the standard holder, receive calibration frames from the photoreceiving module, calculate calibration coefficients using a dark screen, a diffuse light standard and a spectral standard and save the said calibration coefficients together with a time stamp, the temperature of the equipment and the exposure parameters.

[0015] The technical result consists in increasing the reliability and comparability of hyperspectral data obtained from onboard a UAV, due to the built-in calibration using dark, light and spectral standards, which provides compensation for the dark signal of the photoreceiving module, unevenness of pixel sensitivity, changes in illumination and possible shift of spectral channels.

[0016] The hyperspectral imaging equipment for UAVs contains a housing, a lens, an entrance slit, a spectral unit with a dispersing element, a photoreceiving module, a control and data processing module, a memory unit, an interface for communicating with the UAV's onboard system, and a mounting unit for the unmanned aerial vehicle.

[0017] The apparatus is additionally equipped with a built-in calibration unit, implemented as a rotating or linearly movable standard holder. This holder contains a dark screen, a diffuse light standard, and a spectral standard with specified spectral lines or bandwidths.

[0018] The calibration unit is located in front of the entrance slit or the objective lens, allowing for the sequential introduction of these standards into the optical path of the equipment. The control and data processing module is connected to the calibration unit, the photodetector module, the memory unit, the temperature sensor, and the communication interface with the UAV's onboard system.

[0019] The control module is designed with the ability to switch the equipment between the shooting mode and the calibration mode, control the position of the standard holder, receive signals from the photoreceiver module when each standard is introduced, calculate calibration coefficients and save the said coefficients together with the time stamp, equipment temperature, exposure parameters and the identifier of the shooting area.

[0020] The distinctive features of the claimed utility model are:

[0021] 1. The presence of a built-in calibration unit as part of the UAV hyperspectral equipment;

[0022] 2. Implementation of a calibration unit in the form of a rotary or linearly movable standard holder;

[0023] 3. Placing at least three reference elements on the holder: a dark screen, a diffuse light reference and a spectral reference;

[0024] 4. Possibility of sequential input of standards into the optical path of the equipment without dismantling the device from the UAV;

[0025] 5. Connecting the calibration unit to the control and data processing module;

[0026] 6. Implementation of the control module with the ability to automatically switch between shooting mode and calibration mode;

[0027] 7. Saving calibration coefficients together with the time stamp, equipment temperature and exposure parameters;

[0028] 8. Ability to perform calibration before shooting, after shooting, between route sections, or when temperature and illumination change above a set threshold.

[0029] The proposed utility model eliminates the shortcomings of known technical solutions as follows.

[0030] The presence of a built-in dark screen allows for the operational measurement of the dark signal of the photoreceiving module and takes into account its change when the equipment heats up during flight.

[0031] The presence of a diffuse light standard allows one to evaluate the unevenness of pixel sensitivity and changes in the overall radiometric characteristics of the equipment.

[0032] The presence of a spectral standard with specified spectral lines or bandwidths allows you to control the position of spectral channels and identify their shift caused by temperature or mechanical influences.

[0033] The ability to introduce standards into the optical path without dismantling the equipment eliminates the need for mandatory external calibration before each flight and reduces the dependence of the result on ground preparation conditions.

[0034] Storing calibration coefficients together with the timestamp, temperature and exposure parameters improves the comparability of data obtained at different points in time and simplifies subsequent processing of hyperspectral images.

[0035] Before the UAV's flight, the control and data processing module switches the hyperspectral equipment to initial calibration mode. The calibration unit sequentially introduces a dark screen, a diffuse light standard, and a spectral standard into the optical path. For each position of the standard holder, the photoreceiver module generates a corresponding calibration frame.

[0036] Using the dark screen image, the control module determines the dark signal of the photodetector module and its own noise level. Using the diffuse light standard image, it determines the unevenness of pixel sensitivity and the radiometric characteristics of the channels. Using the spectral standard image, it determines the position of spectral lines or bands on the photodetector matrix, after which the spectral referencing correction is calculated.

[0037] After completing the initial calibration, the reference holder is removed from the optical path, and the equipment switches to terrain survey mode. During survey, hyperspectral images are recorded in the memory unit along with exposure parameters, equipment temperature, timestamp, and data received from the UAV's onboard system.

[0038] During flight, the control module can repeatedly switch the equipment into calibration mode. Recalibration is performed at set intervals, between route segments, when the equipment temperature changes above a set threshold, when there is a sudden change in illumination, or upon a command from the UAV's onboard system.

[0039] After recalibration, the control module updates the calibration coefficients and associates them with the corresponding hyperspectral imagery segment. This allows each data fragment to be processed based on the actual state of the equipment at the time of acquisition.

[0040] Execution example

[0041] The hyperspectral equipment is mounted on a vibration-isolated mounting point at the bottom of the UAV body. The equipment's lens is oriented toward the Earth's surface. A miniature rotating reference holder is located in front of the entrance slit, containing three operating positions: a dark screen, a white diffuse reference, and a spectral reference.

[0042] Before the UAV's flight, the control module performs an initial calibration. First, a dark screen is introduced into the optical path, and the photoreceiver module generates a dark signal frame. Next, a diffuse light standard is introduced into the optical path, which is used to calculate the radiometric correction coefficients. After this, a spectral standard is introduced, which is used to determine the positions of the spectral channels.

[0043] After gaining altitude and entering the route, the calibration unit removes reference values ​​from the optical path, and the equipment performs hyperspectral imaging of the terrain. Every 10-15 minutes of flight, or if the equipment body temperature changes by more than a preset value, the control module briefly pauses the route imaging and repeats the calibration cycle. The resulting calibration coefficients are stored in the memory unit and used in processing the hyperspectral images.

[0044] As a result, the influence of photoreceiver module drift, temperature and illumination changes on the quality of hyperspectral data is reduced, and the accuracy of subsequent recognition and classification of objects based on spectral characteristics is increased.

Claims

A hyperspectral imaging apparatus for an unmanned aerial vehicle comprising a housing, a lens, an entrance slit, a spectral unit with a dispersing element, a photoreceiving module, a control and data processing module, a memory unit, an interface for communicating with the on-board system of the unmanned aerial vehicle and a mounting unit for the unmanned aerial vehicle, characterized in that it is equipped with a built-in calibration unit made in the form of a rotatable standard holder containing a dark screen, a diffuse light standard and a spectral standard with specified spectral lines, wherein the standard holder is located in front of the entrance slit with the possibility of alternately introducing the dark screen, the diffuse light standard and the spectral standard into the optical path of the apparatus, and the control and data processing module is connected to the calibration unit, the photoreceiving module,a memory unit and an interface for communication with the on-board system of the unmanned aerial vehicle and is designed with the ability to switch the equipment between the shooting mode and the calibration mode, control the position of the standard holder, receive calibration frames from the photoreceiving module, calculate calibration coefficients using a dark screen, a diffuse light standard and a spectral standard and save the said calibration coefficients together with a time stamp, the temperature of the equipment and the exposure parameters.