RU2471200C1 - Method for passive detection and spatial localisation of mobile objects - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: method is realised by introducing new operations for processing received radio signals, which reduce interference of a powerful direct radio signal of an illumination transmitter via compression thereof and subsequent two-dimensional rejection in the frequency and time domain.

EFFECT: longer detection range and accuracy of spatial localisation of objects.

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Description

The invention relates to radio engineering and can be used in monitoring systems of ground and air space using direct and scattered objects of radio signals emitted by many uncontrolled and controlled transmitters of electronic systems for various purposes.

Achieving high detection efficiency, localization and identification of ground and air objects is limited by significant a priori uncertainty in size, spatial orientation, reflecting properties and parameters of the movement of objects, as well as the imperfection of known methods for detecting and tracking moving objects.

The technology of passive detection and tracking of moving objects, using natural radio illumination of targets, created at a variety of frequencies by radio emissions from transmitters for various purposes in the ranges of short, meter, decimeter and centimeter waves: broadcast (commercial FM broadcasting, high-definition television), information (communication) and measuring (control, navigation), has not yet received sufficient distribution, despite the fact that it can significantly increase the stealth and effectiveness of detection, spatial localization and identification of a wide class of moving objects.

The received radio signal, as a rule, includes powerful direct radio signals and the signal components of the selected target radio illumination transmitter scattered from the earth's infrastructure. In addition, it contains time-delayed and shifted by the frequency of the Doppler shift signals scattered by objects, as well as signals of other uncontrolled sources operating at a frequency that matches the frequency of reception. For effective detection and accurate spatial localization of a wide class of objects (cars, ships, planes and unmanned aerial vehicles, helicopters, rockets, descent vehicles), high-quality selection of weak radio signals scattered from objects against the background of a powerful direct signal of the selected radio backlight transmitter, as well as against the background of signals other unwanted sources. In most typical situations, the noise level is 40-60 dB higher than the level of scattered signals.

A known method of passive detection and spatial localization of moving objects [1], which consists in the fact that coherently receive radio signals by two spatially separated receiving channels, synchronously convert the received radio signals into complex digital signals, store digital signals from digital signals of a pair of channels for each expected direction of arrival the received radio signals form a complex two-dimensional cross-correlation function, depending on the time and frequency shifts of the received proxy signaling, isolated central portion of each complex cross-correlation function, convert each selected central part of the complex cross-correlation function of the complex cross spectral density function (FVSP) of complex form FVSP objects scattered signals, which operate the detection and spatial localization of moving objects.

This method has limited detection sensitivity and accuracy of spatial localization of moving objects due to the presence of only two coherent reception channels.

More effective is the method of passive detection and spatial localization of moving objects [2], free from this drawback and selected as a prototype.

According to this method, multipath radio signals coherently receive by spatially separated receiving channels, including a spread spectrum direct radio signal emitted from the backlight transmitter and radio signals of this transmitter scattered from objects, synchronously transform the ensemble of received radio signals into complex digital signals, synchronously register complex digital signals from digital signals of channel pairs form complex two-dimensional cross-correlation functions (DCF), which depend on both the time and and from the frequency shifts of the received signals, the complex DCFG of each channel pair is shifted in time by a value corresponding to each expected direction of arrival m of received direct and reflected radio signals from the objects, for each expected direction of arrival of m, the central two-dimensional parts of the shifted DCFFs are selected, and the averages selected for of the mth direction of arrival, the central two-dimensional parts of the shifted complex DKVFs, convert the averaged DKKF into a complex digital signal of the mth direction, form depending on of the belt and frequency shifts, the resulting complex DKVF between the direct digital signal of the transmitter and the digital signal of the mth direction, is determined by the maxima of the module of the resulting DKFV, the number of compressed signals of the mth direction and the time delay and absolute Doppler shift of each compressed signal are fixed, identify the corresponding individual the maximum module of the resulting DKFV components of the integrated DKFV as a time-frequency compressed signal of the m-th direction, the delay values by time are stored At the same time, the absolute Doppler shift and the azimuth-elevation direction of arrival of each compressed signal are detected and spatial coordinates of air objects are detected and determined by the values of delay and absolute Doppler shift and azimuth-elevation direction of arrival.

The most significant factor limiting the effectiveness of the prototype method is the lack of operations, suppression of the direct radio signal of the backlight transmitter, usually 40-60 dB higher than the level of radio signals scattered by objects.

In this regard, the main disadvantage of the prototype method (low detection sensitivity and limited accuracy of spatial localization of objects) can be eliminated by using the processing operations of the received radio signals that weaken the interfering effect of the powerful direct radio signal of the backlight transmitter, which is a coherent interference in the reception of weak scattered radio objects.

The technical result of the invention is to increase the detection range and accuracy of spatial localization of objects.

An increase in the detection range and the accuracy of spatial localization of objects is achieved by introducing new processing operations for the received radio signals, which reduce the interfering effect of the powerful direct radio signal of the backlight transmitter by compressing it and subsequent two-dimensional notch in the time-frequency domain.

The technical result is achieved by the fact that in the method of passive detection and spatial localization of moving objects, which consists in the fact that multi-beam radio signals including a spread spectrum direct signal emitted by the illumination transmitter and the radio signals of this transmitter scattered by the transmitter are coherently received by spatially separated reception channels, synchronously transform the ensemble of received radio signals into complex digital signals, synchronously register complex digital signals from The digital signals of the channel pairs form complex two-dimensional cross-correlation functions (DKVF), which depend on both the time and frequency shifts of the received signals, shift in time the complex DKKF of each channel pair by an amount corresponding to each expected direction m of arrival of received direct and scattered from objects of radio signals, allocate the central two-dimensional parts of the shifted DCFFs, average the central two-dimensional parts of the shifted complex DCFFs allocated for the m-th direction of arrival, according to the invention Averaged DCFV is converted into a complex digital signal of the mth direction, which is stored, identified for the integrated digital signal generated for the direction of the backlight transmitter and integrated as a direct complex digital signal, and for each mth direction, the resulting complex DVKF depending on time and frequency shifts between the direct digital signal of the transmitter and the digital signal of the m-th direction, the central part of the complex DCF is excluded and a signal of a modified comp Exact DCF, from the signal of the modified complex DCF and the direct complex digital signal, a modified diffuse complex digital signal is formed, a resultant complex DCF signal between the modified diffuse complex digital signal and the direct complex digital signal is dependent on the time and frequency shifts, and it is determined from the maxima of the module of the resulting signal of the complex DVKF the number of compressed scattered signals of the m-th direction and fix the delay values in time, abs Lute Doppler shift and azimuth-elevation direction of arrival of each compressed scattered signal, which operates the detection and determination of the spatial coordinates of air objects.

The operation of the method is illustrated in the drawing.

The method of passive detection and spatial localization of moving objects is as follows:

1) Multi-beam radio signals are coherently received by spatially separated receiving channels, including a direct spread radio signal emitted by the backlight transmitter and the radio signals of this transmitter scattered by objects.

As a result, an ensemble of radio signals x _n (t) is formed, depending on time t, where n = 1, ..., N is the number of the antenna of the receiving channel.

, где z - номер временного отсчета сигнала.2) Synchronously transform the ensemble of received radio signals x _n (t) into complex digital signals

where z is the time reference number of the signal.

.3) Synchronously register complex digital signals

.

, зависящие как от временного τ, так и от частотного F сдвигов принятых сигналов.4) Complex two-dimensional cross-correlation functions (DCF) are formed from digital signals of channel pairs

depending on both the time τ and the frequency F of the shifts of the received signals.

не несет дополнительной информации по сравнению с

, формирование выполняют только для пар каналов, номера которых удовлетворяют условию n<n', n=1, …, N, n'=1, …, N. Так, если n=1, то n'=2, 3, …, а если n=2, то n'=3, 4, … и т.д.Moreover, due to the fact that, for example,

does not carry additional information compared to

, the formation is performed only for pairs of channels whose numbers satisfy the condition n <n ', n = 1, ..., N, n' = 1, ..., N. So, if n = 1, then n '= 2, 3, ... , and if n = 2, then n '= 3, 4, ..., etc.

The formation of complex DCF is performed in the time or in the frequency domain by known methods [3, p. 95].

In the first case, the formation of complex DCF is performed according to the following formula:

n <n ',

означает комплексное сопряжение.Where

means complex pairing.

получают комплексные временные спектры

, где F_z{…} - оператор дискретного преобразования Фурье (ДПФ) по времени, как известно, эффективно вычисляемого на основе алгоритма быстрого преобразования Фурье, k=0, …, K-1 - номер частотного отсчета, а формирование комплексных ДВКФ выполняют по следующей формуле:In the second case, from the signals

receive complex time spectra

, where F _z {...} is the discrete Fourier transform (DFT) operator in time, which is known to be effectively calculated on the basis of the fast Fourier transform algorithm, k = 0, ..., K-1 is the number of the frequency reference, and the formation of complex DCFGs is performed by following formula:

 n <n ',

where ω _k is the frequency corresponding to the k-th frequency sample.

As a result of this operation, N (N-1) / 2 complex DVKF are obtained.

на величину

, соответствующую каждому ожидаемому направлению m=1, …, M прихода принятых прямого и рассеянных от объектов радиосигналов.5) Time-shifted complex DCF of each channel pair

by the amount

corresponding to each expected direction m = 1, ..., M of arrival of received direct and scattered radio signals from objects.

The shift is performed according to the following formulas:

,

,

,

,

, где

- оператор обратного ДПФ.

where

is the inverse DFT operator.

The values of time shifts corresponding to each expected direction of arrival of signals, for example, for an annular antenna array, are calculated by the following formula:

where R is the radius of the lattice, c is the speed of light, h = 0 ... H-1 is the current number of the grid node pointing the lattice in elevation.

As a result of the performance of the described operations, MN (N-1) / 2 shifted complex DVKFs are obtained

6) For each expected direction of arrival m perform the following actions:

сдвинутых ДВКФ- highlight the central two-dimensional parts

shifted DCF

The parameters Δ and Θ are selected based on the need to suppress noise and determine the level of mutual interference of the side peaks of the DCF.

Применение двухмерного окна к комплексной ДВКФ

эквивалентно двухмерной фильтрации комплексного цифрового сигнала, формируемого на последующих этапах. Эту фильтрацию можно также рассматривать как двухмерную фильтрацию комплексного цифрового сигнала в корреляционной области;This operation can be considered as the operation of applying a two-dimensional window having a square or rectangular support region to a complex DCF

Application of a two-dimensional window to a complex DCF

equivalent to two-dimensional filtering of a complex digital signal generated in the subsequent steps. This filtering can also be considered as two-dimensional filtering of a complex digital signal in the correlation region;

- average the central two-dimensional parts of the shifted complex DCFFs allocated for the mth direction of arrival

в комплексный цифровой сигнал m-го направления- convert the average DCF

into a complex digital signal of the m-th direction

запоминают.Integrated digital signal of the m-th direction

remember.

.As a result of the operations described, M complex digital signals are obtained.

.

Note that the direction of arrival of the direct radio signal from the backlight transmitter is generally a priori known, since the backlight transmitters are selected in advance based on the following criteria: known spatial location, type, frequency and power of the emitted radio signal; lack of mutual interference interference at the operating frequency of the transmitter.

Это может потребоваться в условиях многолучевого распространения радиоволн. Например, при использовании в качестве источника подсвета радиопередатчика KB диапазона, удаленного на расстояние 300-1000 км. На таких расстояниях радиосигнал передатчика распространяется ионосферной волной, направление прихода которой может отличаться от ожидаемого.If necessary, the direction of arrival of the direct radio signal can be clarified by comparing the digital signal modules obtained for directions adjacent to the a priori known direction m ', for example,

This may be required in multipath environments. For example, when using the KB range as a source of illumination, the range is remote at a distance of 300-1000 km. At such distances, the radio signal of the transmitter propagates by the ionospheric wave, the direction of arrival of which may differ from the expected one.

This operation can be considered as a generalization of the operation traditionally used in the one-dimensional case to search for the direction of arrival of the signal from the maximum radiation pattern of the antenna array.

с ожидаемым азимутально-угломестным направлением прихода (α, β) принятых прямых и отраженных радиосигналов, которые, в свою очередь, как отмечалось ранее, являются направлениями наведения антенной решетки;In this case, an unambiguous connection of the number M = 1, ..., M of complex digital signals is used

with the expected azimuthal elevation direction of arrival (α, β) of the received direct and reflected radio signals, which, in turn, as noted earlier, are the directions of pointing the antenna array;

как прямой комплексный цифровой сигнал

7) The complex digital signal generated for coinciding with the direction m 'to the backlight transmitter is identified

as a direct complex digital signal

8) For each expected direction of arrival m perform the following actions:

между прямым цифровым сигналом передатчика

и цифровым сигналом

m-го направления.- form the resulting complex DCFD depending on the time τ and frequency F shifts

between direct digital transmitter signal

and digital signal

m-th direction.

The formation is performed in temporary

или в частотной

or in frequency

областях.

areas.

следует, что физически данная операция эквивалентна свертке спектров сигналов

и

при фиксированном значении временного сдвига τ. В результате прямой сигнал от передатчика подсвета сжимается по спектру в одну гармоническую составляющую, концентрирующуюся в области нулевого частотного и временного сдвига;From the formula

it follows that physically this operation is equivalent to the convolution of signal spectra

and

at a fixed value of the time shift τ. As a result, the direct signal from the backlight transmitter is compressed over the spectrum into one harmonic component, concentrated in the region of zero frequency and time shift;

и получают сигнал модифицированной комплексной ДВКФ

- exclude the central part of the integrated FEFF

and receive the signal of the modified integrated DCF

The parameters Δ and Θ are selected based on the need to suppress the direct signal from the backlight transmitter, which is an obstacle to the subsequent selection of weak signals scattered from the targets.

. Эту операцию можно также рассматривать как двухмерную режекцию прямого цифрового сигнала передатчика в корреляционной области;This operation can be considered as the operation of applying a two-dimensional window to a complex DCF

. This operation can also be considered as a two-dimensional notch of the direct digital signal of the transmitter in the correlation region;

и прямого комплексного цифрового сигнала

формируют модифицированный рассеянный комплексный цифровой сигнал

- from the signal of the modified integrated DCF

and direct complex digital signal

form a modified scattered complex digital signal

выполняются следующие действия:When generating a modified scattered complex digital signal

The following actions are performed:

для получения сигнала

;a) summarize the signal values of the modified integrated DCF

to receive a signal

;

и получают сигнал

b) perform the inverse of the DFT signal

and receive a signal

умножают на комплексно сопряженный прямой цифровой сигнал

и получают модифицированный рассеянный комплексный цифровой сигнал

c) signal

multiplied by the complex conjugate direct digital signal

and receive a modified scattered complex digital signal

осуществляют по формуле

Another method is possible in which the formation of a modified scattered complex digital signal

carried out by the formula

This method provides higher resistance to amplitude fluctuations of signals;

The described operations are fundamental to increasing the detection sensitivity and accuracy of measurement of scattered signal parameters;

между модифицированным рассеянным комплексным цифровым сигналом

и прямым комплексным цифровым сигналом

- form the resulting signal of the integrated DCFF depending on the time τ and frequency F shifts

between the modified scattered complex digital signal

and direct complex digital signal

результирующего сигнала комплексной ДВКФ

число сжатых рассеянных сигналов m-го направления и фиксируют значения задержки по времени τ_pm, абсолютного доплеровского сдвига F_pm и азимутально-угломестное направление прихода (α_pm, β_pm) каждого p-го сжатого рассеянного сигнала, по которым выполняют обнаружение и определение пространственных координат воздушных объектов.- determined by the maxima of the module

the resulting signal of the integrated DVKF

the number of compressed scattered signals of the mth direction and fix the time delay τ _pm , the absolute Doppler shift F _pm and the azimuthal elevation direction of arrival (α _pm , β _pm ) of each pth compressed scattered signal, which detect and determine spatial coordinates of air objects.

A device in which the proposed method is implemented includes a series-connected antenna system 1, an N-channel frequency converter (RF) 2, an N-channel quadrature sampling device 3, a computer 4, and a display device 5.

In turn, the calculator 4 includes a generator of two-dimensional mutual correlation functions 4-1, a shift device 4-2, a device for compensating coherent interference 4-3, a device for detecting and determining spatial coordinates 4-4.

The generator of two-dimensional mutual correlation functions 4-1, a shift device 4-2, a device for compensating coherent interference 4-3, a device for detecting and determining spatial coordinates 4-4 can be performed in single-channel or multi-channel versions. Consider a multi-channel option that provides the highest possible detection performance and spatial localization of moving objects.

Antenna system 1 contains N antennas with numbers n = 1 ... N, combined in an array. The antenna array can be of any spatial configuration: flat rectangular, flat annular or three-dimensional, in particular, conformal.

The bandwidth of each channel of the multi-channel RFI 2 provides the simultaneous reception of many complex signals. In addition, multi-channel RFR 2 and device 3 are made with a common local oscillator, which provides coherent reception of radio signals. For periodic calibration of channels using an external signal source in order to eliminate their amplitude-phase non-identity, the RFI 2 provides the connection of one of the antennas, instead of all the antennas of the array. Calibration by internal signal source is possible. In this case, a noise generator can be used, the output of which can also be connected instead of all antennas for periodic calibration of channels. If the resolution and speed of the ADCs that are part of device 3 are sufficient for direct analog-to-digital conversion of the input signals, such as, for example, when constructing an image in the KB range, then a frequency-selective bandpass filter and amplifier can be used instead of the RFI 2. In other words, the analog part of the device that implements the proposed method can be built on the principle of direct amplification.

A device that implements the proposed method works as follows.

Multipath radio signals, including a spread spectrum direct signal emitted from the backlight transmitter and reflected from objects, the radio signals of this transmitter are coherently received by spatially separated receiving antennas of the array 1. The total radio signal x _n (t) received from each antenna array 1 is transmitted coherently to lower frequency.

комплексных ДВКФ

Полученные комплексные ДВКФ

поступают в устройство сдвига 4-2.The ensemble of received radio signals x _n (t) formed in RFI 2 is synchronously converted in device 3 into an ensemble of complex digital signals x _n (z). Complex digital signals x _n (z) are synchronously recorded at a given time interval in the DVKF 4-1 shaper. In addition, in the shaper 4-1 of the digital signals of pairs of channels simultaneously formed

integrated FEC

Received complex DVKF

enter the shear device 4-2.

сдвигается по времени на величину

соответствующую каждому ожидаемому направлению m=1, …, M прихода принятых прямого и отраженных от объектов радиосигналов.In device 4-2, an integrated DVKF of each channel pair

time shifted by

corresponding to each expected direction m = 1, ..., M of arrival of received direct and reflected from the objects radio signals.

сдвинутых комплексных ДВКФ

поступают в устройство компенсации когерентных помех 4-3.Received

shifted complex DCF

enter the coherent interference compensation device 4-3.

всех сдвинутых функций

Для каждого ожидаемого направления прихода m=1, …, M усредняются соответствующие центральные части

Полученное для m-го направления среднее значение

преобразуется в комплексный цифровой сигнал m-го направления

который запоминают.In the device 4-3, the central parts are simultaneously highlighted

all shifted functions

For each expected direction of arrival m = 1, ..., M, the corresponding central parts are averaged

The average value obtained for the mth direction

converted to a complex digital signal of the m-th direction

which is remembered.

поступают в устройство обнаружения и определения пространственных координат 4-4.Simultaneously received M complex digital signals

enter the device for detecting and determining spatial coordinates 4-4.

как прямой комплексный цифровой сигнал

.The device 4-4 identifies the complex digital signal generated for coinciding with the direction m 'to the backlight transmitter

as a direct complex digital signal

.

между прямым цифровым сигналом передатчика

и цифровым сигналом

m-го направления.In addition, in the device 4-4, (M-1) are simultaneously formed depending on the time m and frequency F shifts of the resulting complex DCFVs

between direct digital transmitter signal

and digital signal

m-th direction.

и получаются сигналы модифицированных комплексных ДВКФ

Из сигналов модифицированной комплексной ДВКФ

и прямого комплексного цифрового сигнала

формируют модифицированные рассеянные комплексные цифровые сигналы

The central part of each integrated FEFF is excluded

and get the signals of the modified complex DCF

From the signals of the modified integrated DCF

and direct complex digital signal

form modified scattered complex digital signals

между модифицированными рассеянными комплексными цифровыми сигналами

и прямым комплексным цифровым сигналом

Formed (M-1) depending on the time τ and frequency F shifts of the resulting signals of the integrated DCF

between modified scattered complex digital signals

and direct complex digital signal

результирующего сигнала комплексной ДВКФ число сжатых рассеянных сигналов m-го направления и фиксируется значение задержки по времени τ_pm, абсолютного доплеровского сдвига F_pm и азимутально-угломестного направления прихода (α_pm, β_pm) каждого p-го сжатого рассеянного сигнала. По значениям задержки по времени τ_pm, абсолютного доплеровского сдвига F_pm и азимутально-угломестного направления прихода (α_pm, β_pm) каждого p-го сжатого рассеянного сигнала выполняется обнаружение и определение пространственных координат воздушных объектов.Determined by module maxima

the resultant signal of the complex DCIF is the number of compressed scattered signals of the mth direction and the time delay τ _pm , the absolute Doppler shift F _pm and the azimuthal elevation direction of arrival (α _pm , β _pm ) of each pth compressed scattered signal are fixed. Using the values of the time delay τ _pm , the absolute Doppler shift F _pm and the azimuthal elevation direction of arrival (α _pm , β _pm ) of each pth compressed scattered signal, the spatial coordinates of airborne objects are detected and determined.

The following actions are performed:

- the absolute Doppler shift F _pm and the elevation direction of arrival (β _pm ) of the rth compressed scattered signal are compared with the threshold, and when the threshold is exceeded, a decision is made to detect a moving object in the direction α _pm .

The threshold is selected based on minimizing the probability of missing an object;

- the absolute distance of the signal τ _pm determines the apparent distance to the object D _pm = τ _pm c, where c is the speed of light;

- the spatial coordinates of the detected object are determined by the apparent range D _pm and the values of the arrival direction α _{pm of the} scattered signals.

Moreover, for the pair “detection device - transmitter”, an ellipsoid of equal apparent distances corresponding to the geometrical location of points in space is constructed, the sum of the distances to which (from the transmitter to the object and from the object to the detection device) is equal to the found value of the apparent range D _pm . The geographic coordinates of the detected object are determined by the intersection of the ellipsoid of equal apparent distances and the value of the azimuthal elevation direction of arrival (α _pm , β _pm ) of the scattered signals.

The device 5 displays the results of the detection and spatial localization of objects.

Thus, by reducing the interfering effect of the powerful direct radio signal of the backlight transmitter by compressing it and subsequent two-dimensional rejection in the time-frequency domain, it is possible to solve the problem with achieving a technical result.

INFORMATION SOURCES

1 RU, patent, 2316018, cl. G01S 5/04, 2008

2 RU, patent, 2319976, cl. G01S 5/04, 2008

3 Shirman Y.D., Manzhos V.N. The theory and technique of processing radar information against the background of interference. - M: Radio and communications, 1981.

Claims (1)

The method of passive detection and spatial localization of moving objects, which consists in the fact that multipath radio signals including a spread spectrum direct signal emitted by the illumination transmitter and the radio signals of this transmitter emitted by the illumination transmitter are coherently received by the spatially separated receiving channels, synchronously transform the ensemble of received radio signals into complex digital signals, register complex digital signals, from digital signals of pairs of channels form a set Two-dimensional cross-correlation functions (DCF), which depend on both the time and frequency shifts of the received signals, shift in time the complex DCF of each channel pair by an amount corresponding to each expected direction m of arrival of the received direct and scattered radio signals from the objects, and the central two-dimensional parts of the shifted DCFFs average the central two-dimensional parts of the shifted complex DCFFs selected for the mth direction of arrival, characterized in that they convert the averaged DCFF to complex the th digital signal of the mth direction, which is memorized, identifies the complex digital signal generated for matching the direction of the backlight transmitter as a direct complex digital signal, for each mth direction, the resulting complex DKVF between the direct digital signal of the transmitter is formed depending on the time and frequency shifts and a digital signal of the mth direction, exclude the central part of the complex DCF and receive the signal of the modified complex DCF from the signal of the modified comp the LEFF DCF and the direct complex digital signal generate a modified scattered complex digital signal, form the resultant complex DKFF signal depending on the time and frequency shifts between the modified scattered complex digital signal and the direct complex digital signal, and determine the number of compressed scattered signals m from the maxima of the resultant signal module of the complex DKF m -th direction and fix the values of time delay, absolute Doppler shift and azimuth lomestnoe direction of arrival of each compressed scattered signal, which operates the detection and determination of the spatial coordinates of air objects.

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