46 results about "Laser remote sensing" patented technology

An indoor fire hazard flashover risk prediction method based on a flame form and remote sensing data comprises the following steps: using fire hazard simulation software to simulate fire hazard data, and constructing a fire hazard data set; ignition is conducted, an indoor fire flame image is obtained through a high-definition camera, and the obtained image is processed; outputting the real-time heat release rate HRR of a fire point from the processed image through a residual network Resnet model; a methane laser remote sensing detector is used for monitoring and acquiring methane gas concentration data of an indoor flue gas layer at a specific height in real time; and building a fire hazard flashover risk prediction model based on the fire source heat release rate and the methane gas concentration, and predicting the flashover risk in advance. According to the invention, accurate identification and prediction of the flashover risk of the fire in the early stage of fire development are realized, and an early warning signal is sent when the fire is about to enter the flashover stage, so that casualties and property loss caused by the fire are reduced.

The invention discloses a laser radar attitude measurement positioning method and device for an aviation electromagnetic detection suspension system, and belongs to the technical field of aviation electromagnetic detection, attitude measurement and coordinate positioning. According to the invention, real-time space positioning information and attitude information of the aviation soft suspension flight pod subsystem are accurately obtained by adopting a non-contact laser remote sensing measurement mode, and attitude and positioning devices do not need to be fixedly installed on the suspension flight pod subsystem. Electromagnetic interference or dynamic stability of the attitude and positioning device and related auxiliary electronic equipment on the soft suspension flight pod subsystem is avoided, the accuracy of electromagnetic signals and data reliability in the detection process are ensured, and therefore the precision of aviation electromagnetic detection is improved.

The present invention relates to a method implementing measurements obtained with a LiDAR sensor (2) mounted on a wind turbine (1), and measurements obtained with at least one motion sensor (CAM), as well as a LiDAR measurement model (MOD M) and a wind model (MOD V). The method then implements an informative adaptive Kalman filter (KAL) to determine the wind speed (v) at some estimation points. At least one wind speed characteristic (CAR) can then be possibly deduced therefrom, in the rotor plane for example.

The invention provides a gas detection method based on galvanometer scanning, and the method comprises the following steps: obtaining a visible light image of a to-be-detected region collected by a visible light imaging module, processing the visible light image based on a pre-trained semantic segmentation model, and obtaining a background category matrix; acquiring gas concentration information of each scanning point obtained by scanning the to-be-detected area by the galvanometer laser telemetering assembly, wherein the galvanometer laser telemetering assembly is registered with the visible light imaging module in advance; and acquiring a background category corresponding to each scanning point according to the background category matrix, and correcting a gas concentration signal of the point based on a background correction coefficient associated with the background category. According to the gas detection method, the problems of false detection and the like caused by factors such as unknown background reflectors and unknown detection object types in the existing galvanometer scanning gas detection are effectively solved, and the accuracy of gas concentration detection is improved.

The invention discloses a light spot adjustable laser telemetering light machine system, and relates to the technical field of light spot adjustment. The light spot adjustable type laser telemetering light machine system comprises a laser emitting unit used for emitting laser beams, and a detection light lens adjusting unit used for receiving the laser beams emitted by the laser emitting unit and performing form control; the receiving lens is used for receiving an optical signal returned by telemetering after the laser beam subjected to form control by the detection light lens adjusting unit reaches a target, and focusing the optical signal; the detection unit is used for converting an optical signal focused by the receiving lens into an electric signal; the signal processing unit is used for receiving the electric signal output by the detection unit and analyzing and generating a regulation and control instruction, and the signal processing unit is used for intelligently regulating and controlling the laser emission unit, the detection light lens adjusting unit and the micro-displacement adjusting platform, so that the focal length is automatically adjusted, and the size of a light spot is further controlled; and the detection requirements of far and near distances are met, and the signal quality of the optical machine is automatically adjusted to be optimal.

The invention relates to a photoelectric integrated double-frequency laser for coherent wind measurement, which comprises a first light source module, a second light source module, a first coupler module, a second coupler module, a third coupler module, a first beam splitter module, a second beam splitter module, a third beam splitter module and a first balanced photoelectric detector module, a second balance photoelectric detector module, a modulator module, an optical phase-locked loop module and a transceiver. Based on the silicon-based optoelectronic chip technology and the photoelectric hybrid packaging technology on the structural level, the coupler, the beam splitter and the photoelectric detector are integrated on the silicon optical chip, and the silicon optical chip, the DFB chip, the coupling optical path, the electrical module and the like are packaged together by utilizing the photoelectric hybrid packaging technology, so that high-density integration is realized; a heterodyne digital optical phase-locked loop technology is applied to a system level, so that a specific frequency difference exists between output signal light and reference light, and pulse light with a high extinction ratio is generated in a modulator cascading mode. Compared with a conventional single-light-source system scheme, the heterodyne Doppler wind measurement laser radar system can greatly improve the integration level, reduce the power consumption and the cost, and is beneficial to mass production, and compared with a homodyne detection mode, heterodyne detection is higher in measurement speed, simpler in scheme and better in stability. The system has extremely high expansibility, and can be applied to systems of optical fiber sensing, laser remote sensing and cold atomic clocks through operations of replacing a transmitting-receiving device, modifying a control program and the like.

The invention discloses a water body diffusion attenuation coefficient inversion method, system and device based on an underwater signal, and a storage medium, and belongs to the technical field of laser remote sensing. The method comprises the following steps: acquiring laser radar parameter data, laser radar actual measurement point cloud data of a target water area and target water area environment data; extracting a water bottom sounding point according to the point cloud data measured by the laser radar; calculating a water bottom photon counting rate based on the water bottom sounding point; water depth error correction is carried out on the water bottom sounding point, and the effective water depth and the included angle between the corrected water bottom sounding point and the light beam direction are calculated; and constructing a water bottom signal model based on the laser radar parameter data, the target water area environment data, the water bottom photon counting rate, the effective water depth and the corrected included angle between the water bottom sounding point and the light beam direction, and calculating a water body diffusion attenuation coefficient through the water bottom signal model. The diffusion attenuation coefficient of the water body is calculated through the water bottom sounding point, the anti-noise capability is high, and the monitoring precision of the water quality of the near-shore water area can be improved.

The application discloses a method for inverting marine aerosol optical depth by using spaceborne lidar noise, belongs to the technical field of laser remote sensing, and is used for quantitatively inverting aerosol optical depth. Under the premise that system hardware parameters of the spaceborne lidar and total background noise data detected by the spaceborne lidar, environmental parameters of a corresponding region and moment are given, a noise model of solar radiation items corresponding to water surface white froth diffuse reflection and water surface specular reflection, a water-leaving noise model (a noise model of solar radiation items of water body backscattering), and an atmospheric noise model (a noise model of solar radiation items of Rayleigh scattering of atmospheric molecules and Mie scattering of aerosol particles) are respectively constructed. Water surface noise, water-leaving noise and atmospheric Rayleigh scattering noise are removed from total noise rate of the atmosphere top detected by the lidar, and aerosol scattering noise results are obtained. Finally, marine aerosol optical depth of a satellite transit region and moment is quantitatively inverted by using the aerosol scattering noise results and the aerosol scattering noise model.

The invention relates to a space laser radar forest structure data correction method and system, and belongs to the technical field of space laser remote sensing and forest resource monitoring. Aiming at four kinds of errors of geometric positioning offset, slow distortion, terrain broadening effect and canopy structure influence of GEDI data, UAV control points are arranged by adopting a hierarchical arrangement strategy, a homonymy point relation is established through waveform registration, and weights are calculated; performing overall geometric correction based on the regular grid control points; carrying out local distortion correction based on the encryption control point; establishing a physical compensation model to compensate the terrain broadening effect; based on the canopy structure parameters and GEDI signal quality indexes, establishing a statistical regression model to correct a canopy height residual error; and finally, obtaining a high-precision canopy height convergence result through spatial smoothing processing, and outputting corrected data. The method achieves step-by-step precision improvement from the whole domain to the local domain and from the geometry to the height, and is low in cost, high in precision and wide in application range.

1. The name of the design product: the main body of the laser wind measuring instrument. 2. The use of the design product: the main body and the whole can be used as a laser remote sensing wind measuring device, installed at the top of the nacelle of a wind turbine generator. 3. The design points of the design product: in shape. 4. The picture or photo that best indicates the design points: perspective view 1. 5. Other circumstances that need to be explained: the solid line in the view defines the part claimed, and the dashed line defines the part not claimed.

The method for quickly inverting aircraft wake vortex parameters based on mobile platform laser remote sensing comprises the following steps: a laser radar system scans a wake vortex influence area, and measurement data are subjected to quality control processing; a wake vortex core position and a vortex core radius are estimated; a wind speed of an arbitrary measurement point A located in the wake vortex range is subjected to vector decomposition, and the wind speed is expressed as a function of a wake vortex circulation parameter W 、 V 、 U A background wind speed and a laser radar motion speed are eliminated by using a non-wake vortex area measurement point; a difference between radial velocities of two measurement points in and out of a wake vortex influence range in the same laser emission direction is expressed as a function of a wake vortex circulation; and a turbulent disturbance is weakened by multiple measurements in the wake vortex influence range, and then a least square method is used to fit and solve the wake vortex circulation. The present application can accurately invert and correct aircraft wake vortex parameters by using less observation data. The calculation result is fast and accurate, and can provide scientific and reliable data support for aviation safety and aircraft cooperative operation.

The present application provides a method and device for determining the driving condition of a vehicle, which relates to the field of vehicle driving safety technology. In this method, the driving data and standard operating condition data of N vehicles traveling on a first road section within the same time range are obtained, and the road surface slipperiness of the first road section and / or the health of the braking system of the first vehicle are determined based on the driving data and standard operating condition data of the N vehicles, and the road surface slipperiness information of the first road section and / or the health of the braking system of the first vehicle are sent to the first vehicle. Among them, the standard operating condition data of the vehicle is the data collected when the vehicle is traveling on an ideal road surface when the braking system is healthy. These data do not need to be realized by setting up cameras on the road surface, laying sensors on the road surface, setting up laser remote sensing monitoring devices on the road surface, etc., and do not require a large amount of hardware cost and maintenance cost.

The invention discloses a laser remote sensing all-in-one machine, a data transmission method and a data processing method. The all-in-one machine comprises a first angle adjusting device, a preprocessing device, a remote sensing detection subsystem, a laser subsystem and a data processing device. The first angle adjusting device projects a remote sensing detection signal and a first laser signal to the preprocessing device; the preprocessing device transmits a first light path corresponding to the remote sensing detection signal to the remote sensing detection subsystem; a second light path corresponding to the first laser signal is transmitted to the laser subsystem; the remote sensing detection subsystem converts the first light path into a remote sensing image digital signal and sends the remote sensing image digital signal to the data processing device; the data processing device performs information extraction on the remote sensing image digital signal to obtain link establishment reference data; controlling a first angle adjustment device and a laser subsystem to perform chain establishment angle adjustment based on the chain establishment reference data; and the laser subsystem restores the second light path into the first laser signal and sends laser receiving data corresponding to the first laser signal to the data processing device.

The invention discloses a frequency discrimination curve calibration system, method and device, and relates to the technical field of laser remote sensing, the system locks the output laser frequency of a first laser on a low-concentration atom or molecule absorption peak to obtain an accurate frequency standard; the laser output by the second laser device and the laser output by the first laser device are subjected to beam combination beat frequency, a frequency difference is extracted from a beat frequency signal power spectrum to generate a tuning control signal of the second laser device, and the output laser frequency of the second laser device is locked at any preset frequency offset; the whole laser radar system utilizes an electric control optical switch to realize conversion between a calibration state and a detection state: in the calibration state, laser from the second laser is gated for frequency discrimination curve calibration; and in a detection state, gating the received atmospheric echo signal light for atmospheric remote sensing detection. Therefore, on the basis of ensuring the calibration precision and stability of the frequency discrimination curve, the calibration cost of the frequency discrimination curve is reduced, and the calibration efficiency of the frequency discrimination curve is improved.

This observation system includes a laser beam guidance device (18) and a laser remote sensing device (8) configured to perform a range measurement on a range segment (12). The guidance device (18) is configured to redirect a laser beam emitted onto the range segment (12) and direct it along a plurality of directions from an observation plane of the observation system. The guidance device (18) includes at least one movable mirror (32) rotating about itself, configured to direct said laser beam along said plurality of directions. An axis of rotation of said movable mirror (32) and a longitudinal axis of said range segment are non-parallel and non-orthogonal. Figure for the abbreviation: Fig 6

A kind of indoor fire flashover risk prediction method based on flame shape and remote sensing data, steps include: using fire simulation simulation software to simulate fire data, construct fire data set;Ignition is carried out, the indoor fire flame image is obtained by high-definition camera, and the obtained image is processed;The real-time heat release rate HRR of ignition point is output by residual network Resnet model after processing image;Real-time monitoring and acquisition of indoor specific height smoke layer methane gas concentration data are carried out using methane laser remote sensing detector;Based on heat release rate and methane gas concentration, fire flashover risk prediction model is built, and flashover risk is predicted in advance.The present application realizes accurate identification and prediction of flashover risk of fire in early stage of fire development, and sends early warning signal when fire is about to enter flashover stage, reduces personnel casualties and property losses caused by fire.

The embodiment of the present invention discloses a coal mine gas inspection robot and inspection method based on laser remote sensing, including a laser remote sensing device with a ranging function, a longitudinal rotation device for controlling the longitudinal rotation of the laser remote sensing device, and a central processing unit; the laser remote sensing device synchronously collects gas concentration information and longitudinal distance information in the detection area, monitors the gas concentration information, and filters out the distance information from the top from the longitudinal distance information; the central processing unit uses the longitudinal distance information and the distance information from the top to obtain relative distance information through a trigonometric function relationship, and then uses the coordinates of the laser remote sensing device as the coordinate starting point, and obtains the acquisition position coordinates through coordinate conversion of the spatial coordinate system. The present invention obtains the spatial coordinate information of the acquisition point based on the coordinates of the acquisition point in the spatial coordinate system and the three-axis displacement vector, realizing the perfect integration of large-scale gas monitoring and spatial coordinate positioning. Since gas mostly floats on the top of the tunnel, the technology of the present invention can be better used.

The present invention relates to a method for inverting water body optical parameters of a satellite-borne single-photon laser radar, and belongs to the field of laser remote sensing technology. First, the effective signal of the satellite-borne single-photon laser radar when flying above the water surface and measuring is extracted, and the afterpulse effect of the single-photon laser radar is eliminated by a deconvolution algorithm. By establishing a theoretical model of water body backscattering, the water body backscattering coefficient and the diffuse attenuation coefficient are calculated by using the least squares fitting method and the water body backscattering laser pulse point cloud obtained after eliminating the afterpulse effect, and the water body backscattering coefficient is calculated according to the water body parameter backscattering model. The present invention can quickly and accurately calculate the main optical parameters of the seawater subsurface layer of the local water body through the point cloud data obtained when the satellite-borne single-photon laser radar flies over the ocean, which plays an important role in effectively monitoring water pollution, water eutrophication, water quality degradation, etc.

This invention discloses a blind-zone-free laser remote sensing system for stable boundary layer thermal material structures. The system includes a lateral scanning Raman scattering lidar receiving system with multiple lateral receiving systems, a lidar transmitting system, and a backscattering Raman scattering lidar receiving system. The lateral receiving system receives near-surface nitrogen and water vapor Raman signals and aerosol Mie-Rayleigh scattering signals, filling the detection blind zone of the backscattering lidar. The backscattering system detects signals in the upper atmosphere. The invention also discloses a blind-zone-free laser remote sensing method for stable boundary layer thermal material structures, which utilizes the lateral and backscattering systems for collaborative observation, respectively retrieving the water vapor mixing ratio, temperature, and aerosol extinction coefficient near the ground and in the upper atmosphere, and fusing them through a data stitching algorithm to obtain a blind-zone-free profile of the entire layer. This method enables refined detection of the entire layer from the ground to the upper atmosphere, continuously, with full parameters, and high spatiotemporal resolution.

Embodiments of the present application disclose a gas leakage risk simulation method and device based on laser remote sensing and a medium. The method comprises: dividing a region to be simulated into a plurality of two-dimensional geographic grids; using a laser remote sensing device to monitor the concentration of gas pollutants in a plurality of monitoring grids in the region to be simulated in real time, wherein the laser remote sensing device is arranged at a high position of a leakage risk region boundary in the region to be simulated, and a monitoring angle covers a leakage risk device and surrounding grids in the leakage risk region; monitoring grids with an instantaneous increment of pollutant concentration greater than a set positive threshold are identified as suspected leakage grids and added as leakage sources in an atmospheric diffusion simulation model, and a minute-level or higher time-precision simulation is performed on the pollutant leakage process of the leakage sources. The embodiments can capture leakage events in a larger range in real time and dynamically simulate diffusion paths.

The application discloses a laser remote sensing optical machine system with adjustable light spots and relates to the technical field of light spot adjustment. The laser remote sensing optical machine system with adjustable light spots comprises a laser emission unit for emitting a laser beam, a detection optical lens adjusting unit for receiving the laser beam emitted by the laser emission unit and performing shape control, a receiving lens for receiving the light signal returned by the laser beam after reaching a target after the shape control of the detection optical lens adjusting unit and performing focusing, a detection unit for converting the light signal focused by the receiving lens into an electric signal, and a signal processing unit for receiving the electric signal output by the detection unit and analyzing and generating a regulation and control instruction. The laser emission unit, the detection optical lens adjusting unit and the micro-displacement adjusting platform are intelligently regulated and controlled by the signal processing unit, so that the automatic adjustment of the focal length is realized, the size of the light spot is controlled, the detection requirements of different distances are adapted, and the optical machine signal quality is automatically adjusted to be optimal.

The application discloses a multi-channel laser sensor inter-channel angle error flight calibration method, device and equipment and a computer readable storage medium, and belongs to the technical field of unmanned aerial vehicle laser remote sensing. The method comprises the following steps: calibrating and splitting obtained point cloud data files to obtain channel point cloud data files; determining feature surface patches and reference surface patches based on channel point cloud data in the channel point cloud data files, wherein the reference surface patches are feature surface patches corresponding to middle channels; calculating channel angle errors of each channel according to distances from feature points on the feature surface patches to reference points on the reference surface patches, and determining angle error calibration results based on the channel angle errors and theoretical errors. In this way, angle error calibration is performed on each channel of the multi-channel laser sensor, and the precision of the multi-channel laser sensor is improved.

The invention relates to a composite toxic gas laser telemetering equipment performance test system and method, which is characterized in that a control center is arranged outside a composite toxic gas laser telemetering test environment, and a mobile gas measurement point and N gas measurement points are arranged in the composite toxic gas laser telemetering test environment, information data interaction between the movable gas measurement point locations and the gas measurement point locations is realized through wireless signals and the control center. According to the invention, by setting a plurality of gas measurement point locations, including a movable point location and N fixed points, and combining wireless communication and automatic control technologies, collection and transmission of composite toxic gas data can be completed without manual close-range operation, and information processing is carried out based on hardware characteristics of two types of measurement point locations, so that the measurement accuracy is improved. And data transmission reliability is introduced into model fusion weight calculation, so that the credibility of a fusion result is improved.

The invention relates to a laser sensor measurement error surveying and mapping calibration method which is suitable for the technical field of unmanned aerial vehicle laser remote sensing. The method comprises the following steps: determining the actual relative elevation of each ground control point relative to the unmanned aerial vehicle based on the three-dimensional coordinates of the unmanned aerial vehicle and the actual coordinate position of each ground control point; extracting data points corresponding to each ground control point in the ground surface point cloud data, and obtaining laser sensor attitude information when the laser sensor collects the data points corresponding to the ground control points; determining the measured relative elevation of each ground control point relative to the unmanned aerial vehicle based on the three-dimensional coordinates of the unmanned aerial vehicle and the data points corresponding to each ground control point; determining an elevation error corresponding to each ground control point based on the actual relative elevation and the measured relative elevation of each ground control point; obtaining an angle measurement regression fitting model based on the laser sensor attitude information and the elevation error corresponding to each ground control point; and calibrating the angle measurement error of the laser sensor based on the angle measurement regression fitting model.

The invention provides a laser remote sensing instrument and an intelligent response speed adjusting method thereof. The method comprises the steps that the detection distance between the laser remote sensing instrument and an inspection pipeline is measured; measuring the angular velocity of the laser telemeter in the inspection process; calculating the moving speed of the laser spot of the laser telemeter according to the detection distance and the angular speed; and according to the moving speed of the laser spot of the laser remote measuring instrument, the data refreshing speed of the laser remote measuring instrument is fed back and adjusted by adopting a segmentation method. The invention further provides a laser remote measuring instrument for realizing the process, the laser remote measuring instrument is provided with a laser ranging module, a front-end accelerometer and a rear-end accelerometer, and all the components are in signal connection with a main control module. According to the invention, intelligent adjustment of the response speed of the laser remote sensing instrument can be realized, the problem of deterioration of the spatial resolution of leakage detection caused by the change of the speed of the inspection light spot in the inspection process is avoided, the spatial resolution of leakage detection of the laser remote sensing instrument is ensured, and the data reliability of the laser remote sensing instrument is improved.

The application discloses a laser air speed tube device based on Rayleigh scattering laser radar and belongs to the field of laser remote sensing, which comprises an outgoing light path composed of a pulsed fiber laser, a first beam splitter, a beam expander and a launching barrel; a receiving light path comprising an arranged telescopic receiving system, a 2*1 polarization maintaining fiber coupler, a collimating lens, a narrowband interference filter, a polarization beam splitter prism and an F-P etalon, one output of the F-P etalon being provided with a first focusing lens, a second beam splitter and a first signal channel detector, and the other output of the F-P etalon being provided with a third focusing lens, a third beam splitter and a first signal channel detector; and a close-range signal detection light path comprising a common receiving section light path between the 2*1 polarization maintaining fiber coupler of the receiving light path and the second beam splitter and the third beam splitter; the first focusing lens is arranged between the first beam splitter beam splitting light path and the 2*1 polarization maintaining fiber coupler; and the first and second close-range signal detectors are arranged at the rear of the second and third beam splitting light paths respectively.

The application discloses a laser remote sensing type road surface state measuring system and a measuring method, the measuring system comprises an optical measuring module, the optical measuring module is used for emitting measuring light of a specific wavelength to irradiate a road surface target object and can receive reflected light reflected by the road surface target object; a weak signal detection module, the weak signal detection module is used for signal processing of an electric signal converted by the received reflected light reflected by the road surface target object; and a digital signal processing module, the digital signal processing module is used for processing of the electric signal after signal processing. The application obtains a road surface spectrum signal through the optical measuring module, and through signal processing of the weak signal detection module and the digital signal processing module, road surface states are recognized, and snow, ice or water film thickness of the road surface is measured.

The utility model discloses a binocular laser telemetering module, comprising a main body, the main body is provided with a first mounting hole and two second mounting holes located at two sides of the first mounting hole, the second mounting holes are inverted conical holes, the small hole end of each second mounting hole is provided with a receiver, and the receiver is provided with a camera. The large hole end of the second installation hole is provided with a light condensation assembly. A laser transmitter is mounted in the first mounting hole, a cover body is detachably mounted on the main body, and the cover body is used for covering the receiver and the laser transmitter; according to the invention, the structure of one-transmitting and two-receiving is realized, more and weaker optical signals can be superposed and received in a short time, the received weaker optical signals can be processed more accurately, further, concentration detection in a longer distance is realized, and the detection accuracy is improved.

The application discloses a kind of laser remote sensing two-dimensional scanning imaging device and method thereof, it is related to gas spectrum detection field.The concentration field measurement of scene is realized by two-dimensional intermittent scanning, can realize the quick leak diagnosis, evaluation and the quick positioning of leak point;During concentration measurement process, laser spot is static, and motion noise is not introduced, the accuracy of concentration measurement is improved;Intermittent movement of spot is realized using optical modulation, without complex intermittent motion mechanism, more economical in cost, longer service life;Without mechanical scanning device frequently start-stop in two-dimensional scanning process, reduce the time consumption brought by motion acceleration and deceleration process, improve the frame rate of system scanning, realize the quick scanning of high dynamic gas cloud.

This invention discloses a lidar attitude measurement and positioning method and device for an airborne electromagnetic detection suspension system, belonging to the fields of airborne electromagnetic detection technology, attitude measurement, and coordinate positioning technology. This invention accurately acquires real-time spatial positioning and attitude information of an airborne soft-suspension flight pod subsystem by employing a non-contact laser remote sensing measurement method, without the need to fix attitude and positioning devices on the suspension flight pod subsystem. This avoids electromagnetic interference or dynamic stability issues caused by attitude and positioning devices and related auxiliary electronic equipment to the soft-suspension flight pod subsystem, ensuring the accuracy of electromagnetic signals and data reliability during the detection process, thereby improving the precision of airborne electromagnetic detection.