An aircraft stereoscopic positioning method and system based on a spaceborne multi-spectral thermal infrared imager

Abstract

This invention discloses an aircraft stereo positioning method and system based on a spaceborne multi-band thermal infrared imager, comprising: (1) using machine learning algorithms to detect aircraft based on observation data from the spaceborne multi-band thermal infrared imager, and obtaining the latitude and longitude information of the aircraft target and the DN value of the aircraft target in the remote sensing image; (2) calculating the brightness temperature T1, T2, ..., T at the entrance pupil of the multi-band aircraft. n (3) Establish an aircraft radiation characteristic model to obtain the relationship between the aircraft's flight altitude and the brightness temperature at the entrance pupil; (4) Use multi-source observation data to obtain the environmental conditions at the aircraft's latitude and longitude location, and input them into the above aircraft radiation characteristic model to establish a flight altitude lookup table; (5) Obtain the flight altitude corresponding to the brightness temperature at the entrance pupil of the multi-spectral bands obtained in step (2) from the lookup table, calculate the average flight altitude, and obtain the inversion result. This invention has a wide detection range, does not rely on radio communication transmission media, and can realize all-day search and positioning of targets in a wide area.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of remote sensing and aviation safety, and particularly relates to a method and system for stereoscopic positioning of an aircraft based on a spaceborne multi-spectral thermal infrared imager. BACKGROUND

[0002] In the flight process of an aircraft or other aviation target, stereoscopic position information, including longitude, latitude and height, is of great importance. The flight height of an aircraft is mainly measured by ground radar and satellite communication. Air routes and airports use surveillance radars for detection and control. Secondary radars receive the number, height and direction information of an aircraft for traffic control. Automatic Dependent Surveillance-Broadcast (ADS-B) is currently the most important civil aviation aircraft monitoring technology, which determines the position of an aircraft through a satellite navigation system and broadcasts periodically, and the information is received by a traffic control ground station as a substitute for secondary radar. Due to the limited detection distance, ground radar systems cannot cover polar regions and ocean areas, and satellite communication systems rely on feedback information from aviation targets. These aircraft detection and information acquisition methods cannot meet the application requirements for detecting and searching unknown flying targets in a wide area.

[0003] Chinese patent document CN111879286A discloses a method for obtaining the flight height of an aircraft, which integrates the characteristics of different flight height measurement devices such as laser atmospheric data systems, global navigation satellite systems and wireless altimeters to perform data fusion to determine aircraft height information. The method needs to obtain information such as air pressure and temperature through sensors carried by the aircraft, and transmit the signals to a satellite or the ground.

[0004] In order to make the acquired data more accurate, those skilled in the art have also researched sensors, for example, Chinese patent document CN210689594U discloses a gas pressure sensor for real-time monitoring of aircraft flight height, which includes a gas pressure sensor body, and a flow resistance device is installed on the gas pressure sensor body to resist the airflow entering the gas pressure sensor body when the aircraft is flying. The utility model weakens the airflow when the aircraft is running at high speed, and the wind speed value during final detection is approximately equal to 0, which ensures the accuracy of the gas pressure sensor body without affecting the communication between the gas pressure sensor body and the outside world.

[0005] However, the above-mentioned methods for obtaining the flight height of an aircraft cannot realize the search and positioning of unknown targets. SUMMARY

[0006] The present application provides a method and system for stereoscopic positioning of an aircraft based on a spaceborne multi-spectral thermal infrared imager, which has a wide detection range and does not rely on radio communication transmission media, and uses space-based infrared detection means to realize all-weather search and positioning of targets in a wide area.

[0007] A method for stereoscopic positioning of an aircraft based on a spaceborne multi-spectral thermal infrared imager, comprising the following steps:

[0008] (1) Based on the observation data of the spaceborne multi-spectral thermal infrared imager, an aircraft detection is performed using a machine learning algorithm to obtain the longitude and latitude information of the aircraft target and the DN value of the aircraft target in the remote sensing image;

[0009] (2) The multi-spectral aircraft entrance pupil brightness temperature T1, T2, …, Tn is calculated n , n is the number of spectral bands;

[0010] (3) An aircraft radiation characteristic model is established to obtain the relationship between the aircraft flight height and the entrance pupil brightness temperature;

[0011] (4) The environmental conditions of the longitude and latitude position where the aircraft is located are obtained using multi-source observation data, including seasonal climate, ground temperature, and lighting conditions, which are brought into the above aircraft radiation characteristic model to establish a flight height lookup table;

[0012] (5) The flight height corresponding to the multi-spectral entrance pupil brightness temperature obtained in step (2) is obtained from the lookup table, the average flight height is calculated, and the inversion result is obtained.

[0013] In step (2), the formula for calculating the multi-spectral aircraft entrance pupil brightness temperature is as follows:

[0014]

[0015] T i represents the brightness temperature of the i-th spectral band, i = 1, 2, …, n; k1 and k2 are coefficients for deriving the brightness temperature from the radiance; is the spectral radiance of the i-th spectral band calculated using the fitting coefficient and the signal response gray value.

[0016] The calculation formula of is as follows:

[0017]

[0018] where DN i is the value of the i-th spectral band signal converted to a digital number by an analog-to-digital converter, i.e., the gray value in the remote sensing image; a i and b i are the gain coefficient and bias coefficient of the i-th spectral band.

[0019] In step (3), the aircraft radiation characteristic model is established, and the specific process is as follows:

[0020] The aircraft entrance pupil radiance L airplane is represented as

[0021] L airplane(λ) = (L skin (λ) + L atm (λ)) · τ atm (λ) + L path (λ)

[0022] wherein, L skin is the radiance of the aircraft skin, L atm is the atmospheric reflected radiation, τ atm is the atmospheric transmittance, L pat is the path radiation, and λ is the wavelength; the atmospheric transmittance τ atm and the path radiation L path are related to the flight altitude of the aircraft, and are obtained by MODTRAN simulation.

[0023] The radiance of the aircraft skin L skin is expressed as

[0024]

[0025] wherein, ε skin is the infrared emissivity of the skin, T skin_ave is the average temperature of the aircraft skin, and M is the spectral radiance emittance, satisfying the Planck law;

[0026] The average temperature T skin_ave of the aircraft skin is expressed as

[0027]

[0028] wherein, T atm is the atmospheric temperature of the environment where the aircraft is located, β is the temperature recovery coefficient, and υ is the specific heat capacity ratio; C is a constant, Ma is the flight speed of the aircraft, and the unit is Mach number;

[0029] The atmospheric temperature T atm of the environment where the aircraft is located is related to the flight altitude of the aircraft, and the relationship is expressed as:

[0030] T atm = T L - α · H

[0031] wherein, T L is the ground air temperature, H is the flight altitude of the aircraft, and α is a coefficient. According to different climates and weathers, the range of the coefficient α is 0.58-0.65.

[0032] The radiance at the entrance pupil of the aircraft is converted into the brightness temperature T airplane at the entrance pupil, and the establishment of the aircraft radiation characteristic model is completed:

[0033]

[0034] Wherein, lambda1 and lambda2 are the start and end wavelengths of the spectral band respectively, c1 is the first radiation constant, and c2 is the second radiation constant.

[0035] In step (5), the multi-spectral entrance pupil brightness temperature corresponds to the flight height H1, H2, …, H n The condition should be met:

[0036] Based on the same inventive principle, the application also provides an aircraft stereoscopic positioning system based on a spaceborne multi-spectral thermal infrared imager, characterized by comprising a memory and one or more processors, the memory stores executable code, and the one or more processors execute the executable code to implement the above-mentioned aircraft stereoscopic positioning method.

[0037] Compared with the prior art, the application has the following beneficial effects:

[0038] 1. The method of the application does not require the target itself to provide feedback information, which is conducive to discovering unknown targets.

[0039] 2. The method of the application belongs to a passive detection means, which improves the concealment of obtaining target position information.

[0040] 3. The method of the application is suitable for day and night conditions. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 A flowchart of the aircraft stereoscopic positioning method based on the spaceborne multi-spectral thermal infrared imager of the application is shown in the figure.

[0042] Figure 2 The aircraft height inversion result in the embodiment of the application is shown in the figure. DETAILED DESCRIPTION

[0043] The application will be further described in detail below in combination with the drawings and embodiments, and it should be pointed out that the following embodiments are intended to facilitate the understanding of the application and do not limit the application in any way.

[0044] The embodiment of the application takes the TIS data carried by the SDGSAT-1 satellite as an example, as shown in the figure, an aircraft stereoscopic positioning method based on a spaceborne multi-spectral thermal infrared imager, comprising the following steps: Figure 1

[0045] Step 1, aircraft detection is performed using a machine learning model, combined with cloud detection to reduce false alarm rate, to obtain the DN value of the aircraft target in the space-based remote sensing image. At the same time, the longitude and latitude of the target are obtained according to the geographic information in the remote sensing image.

[0046] Step 2, aircraft multi-spectral entrance pupil brightness temperature calculation

[0047] ​The thermal infrared radiation imager carried by the SDGSAT-1 satellite has three spectral bands, 8-10.5 μm (B1), 10.3-11.3 μm (B2) and 11.5-12.5 μm (B3). The brightness temperature T i The calculation expression is:

[0048]

[0049] Where k1 and k2 are coefficients for deriving the brightness temperature from the radiance. The spectral radiance of the i-th spectral band is calculated using the fitting coefficients and the signal response gray value, and the calculation expression is:

[0050]

[0051] Where DN i is the value of the i-th spectral band signal converted into a digital number by the analog-to-digital converter, i.e., the gray value in the remote sensing image.a i and b i are the gain coefficient and the bias coefficient of the i-th spectral band.

[0052] As shown in Fig. 1(a), the longitude and latitude positions of the aircraft target in the image are E5.48 / N43.16, the three-spectral-band DN values are 1534 (B1), 1794 (B2) and 1244 (B3), and the converted entrance pupil brightness temperature is Figure 2 T1=264.27 K

[0053] T2=267.83 K

[0054] T3=266.60 K

[0055]

[0056] Step 3, aircraft radiation characteristic model establishment

[0057] The aircraft radiation signal reaching the entrance pupil includes the skin heat radiation generated by the aerodynamic heating of the aircraft in high-speed flight, the atmospheric reflection and the temperature rise caused by the sunlight on the aircraft, and the path radiation.

[0058] The entrance pupil radiance L airplane can be expressed as

[0059] L airplane (λ)=(L skin (λ)+L atm (λ))·τ atm (λ)+L path (λ)

[0060] Where L skin is the aircraft skin radiance, L atm is the atmospheric reflection radiation, and τ​atm is the atmospheric transmittance, L path is the path radiance, and λ is the wavelength. τ atm and L path Related to the flight altitude, which can be obtained by MODTRAN simulation.

[0061] The spectral infrared radiance L skun of the aircraft skin can be expressed as

[0062]

[0063] where ε skin is the infrared emissivity of the skin, T skin_ave is the average temperature of the skin, and M is the spectral radiance exitance, satisfying the Planck law.

[0064] The average temperature T skin_ave of the aircraft skin can be expressed as

[0065]

[0066] where T atm is the ambient atmospheric temperature of the aircraft, β is the temperature recovery coefficient, and υ is the specific heat capacity ratio. C is a constant, and Ma is the flight speed of the aircraft in Mach number.

[0067] The relationship between the ambient temperature T atm and the altitude can be expressed as

[0068] T atm = T L - α · H

[0069] where T L is the ground air temperature, H is the flight altitude of the aircraft, and α is a coefficient, which is usually in the range of 0.58-0.65 according to different climates and weather.

[0070] The radiance at the entrance pupil of the aircraft is converted into the brightness temperature T airplane at the entrance pupil, and the establishment of the aircraft radiation characteristic model is completed:

[0071]

[0072] where λ1 and λ2 are the start and end wavelengths of the spectral band, respectively, c1 is the first radiation constant, and c2 is the second radiation constant.

[0073] Step 4: According to the above model, combined with multi-source remote sensing information to obtain the local environmental conditions, an altitude lookup table is established as shown in (c) of Figure 2 . The inversion of the three spectral bands altitude is

[0074] H1 = 9.52 km

[0075] H2 = 9.65 km

[0076] H3 = 9.84 km

[0077] The height inversion result is 9.67 km, and the height difference of three spectrum inversion is 0.32 km, which meets the accuracy requirement (<1 km).

[0078] In summary, the scheme realizes the stereoscopic positioning of the aircraft by using the spaceborne multi-spectrum thermal infrared imager.

[0079] Based on the same inventive principle, the embodiment of the present application also provides a kind of aircraft stereoscopic positioning system based on spaceborne multi-spectrum thermal infrared imager, including memory and one or more processors, the executable code is stored in memory, when one or more processors execute the executable code, for realizing the aircraft stereoscopic positioning method mentioned in the above embodiment.

[0080] The above-mentioned embodiments have been described in detail for the technical solutions and beneficial effects of the present application. It should be understood that the above-mentioned is only a specific embodiment of the present application, and is not used to limit the present application. Any modification, supplement and equivalent replacement made within the principle range of the present application shall be included in the protection scope of the present application.

Claims

1. A method for three-dimensional positioning of an aircraft based on a spaceborne multi-band thermal infrared imager, characterized in that, Includes the following steps: (1) Based on the observation data of the spaceborne multi-band thermal infrared imager, the machine learning algorithm is used to detect aircraft and obtain the latitude and longitude information of the aircraft target and the DN value of the aircraft target in the remote sensing image. (2) Calculate the brightness temperatures T1, T2, ..., T at the entrance pupil of a multi-spectral aircraft. n Where n is the number of spectral segments; the formula is as follows: T i Let k1 and k2 represent the brightness temperature of the i-th spectral band, where i = 1, 2, ..., n; k1 and k2 are coefficients derived from the radiance to determine the brightness temperature. It is the spectral radiance of the i-th spectral band calculated using the fitting coefficients and the gray value of the signal response; The calculation formula is as follows: Among them, DN i The i-th spectral band signal is converted into a digital value by an analog-to-digital converter, which is the gray value in the remote sensing image; a i and b i These are the gain coefficient and bias coefficient for the i-th spectral band; (3) Establish an aircraft radiation characteristic model to obtain the relationship between the aircraft's flight altitude and the brightness temperature at the entrance pupil; the specific process is as follows: Radiance L at the entrance pupil of the aircraft airplane Represented as L airplane (λ)=(L skin (λ)+L atm (l))·t atm (λ)+L path (l) Among them, L skin For aircraft skin radiance, L atm For atmospheric reflected radiation, τ atm For atmospheric transmittance, L path For path radiation, λ is the wavelength; Aircraft skin radiance L skin Represented as Where, ε skin T represents the infrared emissivity of the skin. skin_ave Let M be the average temperature of the aircraft skin, and M be the spectral radiative exitance, which satisfies Planck's law. The average temperature T of aircraft skin skin_ave Represented as Among them, T atm ν is the ambient atmospheric temperature where the aircraft is located, β is the temperature recovery coefficient, υ is the specific heat ratio, C is a constant, and Ma is the aircraft's flight speed in Mach number. Atmospheric temperature T in the aircraft's environment atm The relationship with the aircraft's flight altitude is expressed as follows: T atm =T L -α·H Among them, T L α represents the surface temperature, H represents the aircraft's flight altitude, and α is a coefficient. Convert the radiance at the aircraft's entrance pupil into the luminance-temperature T at the entrance pupil. airplane Complete the establishment of the aircraft radiation characteristic model: Where λ1 and λ2 are the start and end wavelengths of the spectral band, respectively, c1 is the first radiation constant, and c2 is the second radiation constant; (4) Use multi-source observation data to obtain the environmental conditions of the aircraft's latitude and longitude location, including seasonal climate, surface temperature and light conditions, and input them into the above-mentioned aircraft radiation characteristic model to establish a flight altitude lookup table. (5) Obtain the flight altitude corresponding to the brightness temperature at the entrance pupil of the multi-band obtained in step (2) from the lookup table, calculate the average flight altitude, and obtain the inversion result.

2. The aircraft stereo positioning method based on a spaceborne multi-band thermal infrared imager according to claim 1, characterized in that, Atmospheric transmittance τ atm and path radiation L path It is related to the aircraft's flight altitude and is obtained through MODTRAN simulation.

3. The aircraft stereo positioning method based on a spaceborne multi-band thermal infrared imager according to claim 1, characterized in that, Depending on the climate and weather, the coefficient α ranges from 0.58 to 0.

65.

4. The aircraft stereo positioning method based on a spaceborne multi-band thermal infrared imager according to claim 1, characterized in that, In step (5), the flight altitudes H1, H2, ..., H corresponding to the brightness temperature at the multi-spectral entrance pupil are... n Conditions to be met:

5. An aircraft stereo positioning system based on a spaceborne multi-band thermal infrared imager, characterized in that, The system includes a memory and one or more processors, wherein the memory stores executable code, and the one or more processors execute the executable code to implement the aircraft stereo positioning method according to any one of claims 1-4.

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