KR20170104100A - System and Method For Ground Clutter Removing of WindProfiler - Google Patents

Abstract

The present invention eliminates the clutter generation of the wind profiler according to the terrain by preventing the waiting signal of the kitchen cabin from being buried by the strong terrain echo received at the main cabin, The present invention provides a wind profiler terrain clutter removal system and method therefor.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a wind profiler,

The present invention relates to a wind profiler terrain clutter removal system and method for removing a clutter occurrence of a wind profiler according to a terrain by removing a change of a waiting signal according to the terrain through a fast Fourier transform.

Wind Profiler Rader (WPR) is an important instrument used to observe the direction and magnitude of wind vectors in the atmosphere. It is widely used in meteorological studies and it can provide vertical structure of wind with time resolution of several minutes and spatial resolution of tens of meters. Due to this performance, it is widely used as a basic data for analyzing the risk weather and improving the prediction accuracy of the numerical forecasting model.

Wind Profiler uses the Doppler beam method to determine the vertical profile of the wind vector and transmits the electromagnetic pulse wave according to the fixed azimuth and elevation angles. Due to the characteristics of the atmospheric scattering process, the received signal has a phase difference due to the Doppler delay and determines the atmospheric wind vector component through the Doppler spectrum calculated by Fast Fourier Transform (FFT).

Since wind profiler data can be contaminated by various non-parametric signals such as ground echo, radio interference, Bird echo and complex echo during transmission and reception of pulsed waves, the removal of non-dominant signals in the Doppler spectrum And improvement should be preceded.

A beam that concentrates the radio waves in a specific direction on the antenna of the wind profiler and is emitted is called a main lobe. Further, the weak radio wave beam radiated to the periphery of the cabin is referred to as a side lobe.

The observed elevation of the wind profiler is determined by the time it takes for the wave transmitted from the cabin to be received again. If an object in the horizontal direction is also at a distance from the wind profiler, it is observed as a high signal corresponding to the distance. While the cabin of the wind profiler radiates toward the ceiling, the submarine is scattered at various elevation angles and azimuth angles, so it collides with various objects (buildings, cars, mountains, etc.) on the ground. Such a terrain echo of the wind profiler occurs when a strong terrestrial echo received from the submarine buries the waiting signal of the submarine.

The removal method of the terrain echo is a hardware method such as a clutter fence and a software method through data processing. The most traditional method of software is the direct current (DC) component removal method by Strauch (1982). The direct current component is a signal having a frequency of 0 Hz, or a signal having an average line speed of 0

Means that the visual speed is 0

Is referred to as a DC line. Also, because the terrestrial echo is a signal scattered by a stationary object, it appears as a DC component.

Since Korea is made up of complex mountainous terrain, wind profiler installed in Korea should pay more attention to topographical echoes due to mountainous terrain.

The terrain around the wind profiler of the Kangwon Provincial Meteorological Administration is located in a place where geographical geographical echoes are likely to occur due to the complex mountainous terrain in the west and south. Mountainous terrain below 200 m in height is distributed within 5 km radius, and mountainous terrain is 400 ~ 600 m above sea level in 5 ~ 10 km radius. Most of the mountainous terrain is more than 800m from a radius of 10km. The eastern and northern part of the site is composed of flat terrain less than 30m above sea level within a radius of 5km, and 5km outside the coast to the east. This corresponds to a very high possibility of terrestrial echo.

However, since most of the wind profiler in Korea including the wind profiler of Kangwon Provincial Meteorological Agency does not have a clutter fence installed, data processing must be done through a software method.

Korean Registered Patent No. 1,294,681 (Registered on Mar. 02, 2013) Korean Registered Patent Publication No. 1,255,736 (Registered on April 03, 2013)

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wind profiler terrain clutter removal system and method that prevents a waiting signal of a kitchen cabin from being buried by strong terrain echo received at a submarine.

In order to accomplish the above object, the present invention provides a Doppler spectrum acquisition module for collecting weather observation information through a Doppler spectrum in a wind profiler, a ground echo removal module for eliminating an atmospheric signal embedding phenomenon according to a terrain by fast Fourier transform, A signal determination module for determining the peak of the actual waiting signal, a velocity estimation module for estimating the visual velocity of the vertical beam and the oblique beam on the basis of the determined peak, the east-west component wind vector (U) And a calculation module for calculating a wind vector of the wind (W).

The ground echo cancellation module includes an analysis point determination module that determines the FFT analysis points around the DC line.

The ground echo cancellation module includes an analysis point removal module that removes the determined FFT analysis points.

The ground echo canceling module includes an interpolation module that interpolates using two preserved adjacent FFT analysis points.

A Doppler spectrum acquisition step of collecting meteorological observation information through the Doppler spectrum in the wind profiler, a ground echo removal step of removing the atmospheric signal embedding phenomenon according to the terrain by the fast Fourier transform in the echo cancellation module, A velocity estimation step of estimating the visual velocity of the vertical beam and the oblique beam on the basis of the peak determined by the velocity estimation module, a calculation module for calculating the east-west component wind vector U, the north-south component wind vector V ) And a vertical component (W).

The ground echo removal step includes an analysis point determination step of determining an FFT analysis point around the DC line in the analysis point determination module.

The ground echo removal step includes an analysis point removal step of removing the FFT analysis point determined in the analysis point removal module.

The ground echo cancellation module includes an interpolation step of interpolating using two adjacent FFT analysis points preserved in the interpolation module.

The present invention provides a wind profiler terrain clutter removal system and method for preventing a phenomenon in which a waiting signal of a kitchen cabin is buried by powerful terrain echo received at a submarine, thereby improving the observation accuracy of the wind profiler .

1 is a conceptual diagram of a terrain clutter removal system for a wind profiler according to the present invention;
2 is a flowchart of a method of removing a terrain of a wind profiler according to the present invention;
3 is a Doppler spectrum before removing the ground echo in the low-level observation method.
FIG. 4 is a Doppler spectrum before removing the ground echo in the high-level observation method. FIG.
FIG. 5 is a wind vector comparison diagram of a wind profiler and a radio sonde before removing the ground echoes in the low and high rise observations.
6 is a Doppler spectrum after removing the ground echo in the low-level observation method.
FIG. 7 is a wind vector comparison of a wind profiler and a radio sonde after removing the ground echoes from the low-level observation method.
8 is a RMSE comparison of the wind profiler before and after the removal of the ground echo.
Figure 9 is a wind vector distribution of the wind profilers and radio sonde before and after removing the ground echo.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

It will be apparent to those skilled in the art that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know. Like reference numerals refer to like elements throughout.

1 is a conceptual diagram of a terrain clutter removal system for a wind profiler, in accordance with the present invention.

As shown in FIG. 1, the wind profiler's terrain clutter removal system according to the present invention includes a Doppler spectrum acquisition module 100 for collecting weather observation information through a Doppler spectrum in a wind profiler, The signal echo cancellation is accomplished through a fast Fourier transform, which is performed by a ground echo cancellation module 200, a signal determination module 300 for determining the peak of the actual wait signal, And a calculation module 500 for calculating a wind vector.

The Doppler spectrum acquisition module 100 receives a signal that a radio wave emitted upward from the wind profiler has a spatial fluctuation due to the refractive index of the atmosphere and a part thereof is scattered backward and returned to the antenna.

The ground echo removal module 200 includes an analysis point determination module 210 for determining an analysis point, an analysis point removal module 220 for removing the determined analysis point, and an interpolation module 230 for interpolating the preserved analysis point .

The analysis point determination module 210 may be a signal whose frequency is a direct current component of 0 Hz or whose average visual velocity is 0

A plurality of fast Fourier transform analysis points corresponding to the terrain echo, which is represented by a DC line, is determined.

The analysis point removal module 220 removes the value of the velocity component recorded in the fast Fourier transform analysis point determined in the analysis point determination module so that the waiting signal buried by the terrain echo is clearly displayed.

The interpolation module 230 uses the two adjacent fast Fourier transform analysis points stored outside the removed analysis point to determine whether the received signal is weakened due to compression, attenuation during transmission, discrimination in the receiving circuit, Interpret the signal to recover synchronously.

The signal determination module 300 determines the peak of the actual standby signal through the Doppler spectrum in which the terrain echo is removed.

The velocity estimation module 400 estimates the gaze velocity for one vertical beam and four oblique beams based on the determined peak signal.

The calculation module 500 calculates wind vectors of the east-west component wind vector U, the north-south component wind vector V and the vertical component W. [

2 is a flow chart of a method of removing a terrain clutter of a wind profiler, in accordance with the present invention.

As shown in FIG. 2, a method of removing a terrain clutter of a wind profiler according to the present invention includes a Doppler spectrum acquisition step (S1) of collecting weather observation information through a Doppler spectrum in a wind profiler, A ground echo removing step S2 for removing the atmospheric signal embedding phenomenon according to the terrain through fast Fourier transform, a signal determining step S3 for determining the peak of the actual waiting signal in the signal determining module, (S4) for estimating the line-of-sight velocity of the vertical beam and the oblique beam on the basis of the estimated velocity (S4) and the calculation step (S5) for calculating the wind vector.

In the Doppler spectral collection step (S1), a wave emitted from the wind profiler to the sky is subjected to spatial fluctuations due to the atmospheric refractive index, and a part thereof is scattered backward and received back to the antenna.

The terrestrial echo removal step S2 includes an analysis point determination step S2-1, an analysis point removal step S2-2, and an interpolation step S2-3.

In the analysis point determination step S2-1, the analysis point determination module 210 determines whether the DC point frequency is 0 Hz or the average line speed is 0

A plurality of fast Fourier transform analysis points corresponding to the terrain echo, which is represented by a DC line, is determined.

In the analysis point removal step S2-2, the value of the velocity component recorded in the fast Fourier transform analysis point determined in the analysis point determination step S2-1 is removed from the analysis point removal module 220 and buried by the terrain echo Make sure that the standby signal is clearly visible.

In the interpolation step S2-3, the received signal is compressed and attenuated during transmission using the two adjacent fast Fourier transform analysis points stored in the analysis point removal step S2-2. The interpolation module 230 interpolates the signal so as to synchronously recover the weakened or missing signal elements due to the discrimination action or the like.

The signal determination step S-3 determines the peak of the actual standby signal in the signal determination module 300 through the Doppler spectrum from which the terrain echo is removed.

The velocity estimation step S-4 estimates the gaze velocity for one vertical beam and four oblique beams in the velocity estimation module 400 based on the determined peak signal.

The calculation step S-5 calculates the wind vector of the east-west component wind vector U, the north-south component wind vector V and the east wind component vector W in the calculation module 500.

The wind vector calculated through this process is verified based on the wind vector of Radio Sonde (RS).

For the verification of the present invention, observation data of UHF Wind Profiler (PCL 1300) of Degreane of France installed at the Kangwon Provincial Meteorological Agency were used. The PCL 1300 is observed with a low-level observation method (high-mode) and a high-level observation method (high-mode). Such an observation method is distinguished by a variable setting of a pulse width (pulse width) of a radio wave radiated from a wind profiler and a pulse repetition frequency (PRF). The pulse width and pulse repetition frequency affect the wind profiler's spatial observation resolution and the effective observation altitude. The longer the pulse width, the lower the observation resolution, and the smaller the pulse repetition frequency, the higher the effective observation height. Due to this feature, the low-level observation method has high observation resolution and low effective observation height. In addition, the high-resolution observation method has low observation resolution and high observation height. The PCL 1300 used in the present invention collects a total of 71 altitude wind vectors. The observation resolution and effective observation altitude of the low-level observation system are 72 m and 9700 m, respectively, and high-rise observation systems are 164 m and 15000 m, respectively.

To improve the wind vector accuracy of the PCL 1300, we used data from low-level observations with high observational resolution, and data from high-rise observations were used to verify the impact of terrain clutter on the PCL 1300. For comparison and verification of wind profiler data collected at intervals of 10 minutes, Kangdong provincial municipal government has recruited Gardiozones 27 times. In addition, the radiosonde data was processed using the GRAWMET software developed by GRAW, using the DFM-06 model from Germany GRAW.

PCL 1300 of Kangwon Provincial Meteorological Administration is located in a position where geographical echoes are likely to occur due to the complex mountainous terrain in the west and south. In the Doppler spectrum of the wind profiler when the terrain echo occurs, DC components occur continuously at a certain altitude. This characteristic is evident in the PCL 1300 of the Kangwon Provincial Meteorological Administration.

FIG. 3 is a Doppler spectrum before removing the ground echo in the low-level observation method, FIG. 4 is a Doppler spectrum before removing the ground echo in the high-level observation method, FIG. 5 is a Doppler spectrum before removing the ground echo in the low- FIG. 6 is a Doppler spectrum after removing the ground echo from the low-level observation system, FIG. 7 is a wind vector comparison diagram between the wind profiler and the radio sonde after removing the ground echo from the low- 8 is the RMSE comparison of the wind profiler before and after the removal of the ground echo, and Fig. 9 is the wind vector distribution of the wind profilers and radio sonde before and after removing the echoes.

3 to 9, the Doppler spectrum of the west (270 °) tilted beam and the south (180 °) tilted beam of the PCL 1300 observed at 20 LST on June 17, 2013, The DC component can be confirmed over a wide area corresponding to the upper layer of 2 to 4.5 km. The Doppler spectra of opposing inclined beams are generally symmetrical in the atmospheric air, but no DC components are produced in the 270 ° tilted beam and the facing east (90 °) tilted beam. The Doppler spectra of the 270 ° tilted beam showed normal altitude distributions that are common in the atmospheric air. A 180 ° tilted beam and a north (360 °) tilted beam are similar in appearance to 270 ° tilted beams and 90 ° tilted beams. It can be seen that the DC components generated in the 270 ° and 180 ° tilted beams are not the waiting signals. In other words, the asymmetry between the inclined beams facing each other in the ambience is the basis for proving that the DC component is the topography echo.

DC component was generated in the upper and lower Doppler spectra of the low-level observation system, even though it is composed of low mountainous area of less than 100m above sea level within a radius of 5km centered on PCL 1300. The DC component in the upper layer of the low-level observation system is called UDC (Upper DC) and the DC component in the lower layer is called LDC (Lower DC). The UDC and LDC are considered to be caused by the high mountainous terrain outside the radius, which corresponds to the PCL 1300 valid observation altitude, rather than the low mountainous terrain within a radius of 5 km. The reason that the terrain can be observed farther than the effective observation altitude is due to the propagation distance folding phenomenon. The propagation distance folding means that the height of the scatterer, which is higher than the effective observation height of WPR, is calculated to be lower than the actual altitude. In general, by setting PRF to be long and setting the effective observation altitude to be high, the terrestrial echo that generates a strong signal even at a long distance can generate the propagation distance folding. The effective observation altitude is calculated through PRF as shown in Equation 1 below. Effective Observation Elevation by Low-Level Observation Method and High-Level Observation Method of PCL 1300 of Kangwon Provincial Meteorological Administration

) Are 9.7 km and 15 km respectively.

[Equation 1]

(

: Velocity of Light

The UDCs generated in the 270 ° tilted beam of FIG. 3 did not appear in the high-rise observing scheme of FIG. FIG. 5 shows the result of comparing the radiosonde wind vector observed in the case of FIGS. 3 and 4 with the wind vector of the PCL 1300. In the low - level observation method, the east - west component wind vector of the high degree of PCL 1300 at which the UDC appeared was underestimated compared to the radio sonde, while the high level observation method was in accord with the east - west component wind vector of radiosonded due to disappearance of UDC. This difference means that the terrestrial echoes of the subfamily from the low mountainous terrain within 10km radius are buried in the atmospheric signals observed from the mainframe, and the terrestrial echoes outside the effective observation altitude of 15km are the propagation distance folding height Is less than the waiting signal of the east-west component vector. UDC can be judged to be caused by the mountainous terrain within 600-1000m above sea level, which is 9.7km in radius, which is the valid observation altitude of low-level observation system. It is judged as a signal due to the terrain echo. In other words, the difference in the vertical distribution of the wind vector between the presence of the DC component generated in the low-level observing system and the high-level observing system and the radiosonde is the basis for proving that the DC component is the terrestrial echo. At the same time, it is the basis of secondary terrestrial echo due to propagation altitude folding phenomenon.

The UDCs generated in the 180 ° tilted beam of FIG. 3 also appear in the high-rise view of FIG. Within 10 km radius of PCL 1300, the southern terrain is more flat than the west and the mountainous terrain is less distributed. Nonetheless, UDCs are more prominent than the 270 ° tilted beam in high-rise observations because of the difference in the size of the east-west component wind vector and the north-south component wind vector. Since the east - west component wind vector is very strong compared to the north - south component wind vector, the Bragg scattering of the north - south component wind vector is weaker than the east - west component wind vector. Second order topographic echo, which did not appear in the strong atmospheric signal of the 270 ° tilted beam, appears to coincide with the waiting signal of the 180 ° tilted beam due to the weak Bragg scattering of the north-south component wind vector.

The cause of LDC in the other inclined beams except for the 90 ° tilted beam is similar. Within 1 km radius of the PCL 1300, LDC occurred even though it consisted of flat terrain less than 30m above sea level. The visual speed of less than 1km is about 2

, Bragg scattering occurs weakly due to weak atmospheric motion. Attenuation due to weak Bragg scattering in the lower layer is caused by LDC due to secondary echoes buried in the atmospheric signal. Particularly, as the atmospheric motion becomes active at the altitude of 1 km at which the wind speed rapidly increases,

The near peak has disappeared.

The UDC and LDC in the Doppler spectrum of the Gangneung PCL 1300 at the Cheongcheon atmosphere were judged to be the second - order topographic echo caused by the propagation distance folding, and the accuracy of the PCL 1300 was improved. FIG. 6 is a re-computed Doppler spectrum obtained by removing the UDC and the LDC of FIG. The most significant feature is that the UDC and LDC are removed from all beams, so that the atmospheric signal buried by the secondary terrestrial echo is clearly visible. The asymmetry of the Doppler spectrum between opposing inclined beams, which appeared before the removal of the UDC and the LDC, disappeared and the symmetry was apparent at the altitude. The distinctive atmospheric signal after removing the DC component is the most obvious basis for proving that UDC and LDC are terrestrial echoes.

As shown in Fig. 7, the Doppler spectrum with the terrain echo removed shows that the east-west component wind vector, the north-south component wind vector, the wind speed and the wind direction are calculated and compared with the wind vector of the radiosonde. The east - west wind vector and the north - south wind vector of the PCL 1300, which were underestimated at the UDC altitude, were remarkably improved due to the removal of the terrain echo. Before removing the topography echoes, the east - west component wind vector was underestimated, and the northerly winds appeared, and the wind direction error was up to 90 °. However, as the underestimated east - west wind vector and north - south wind vector improved, the wind direction of the PCL 1300 was exactly the same as the radio sonde. The root mean square error (RMSE) for the wind speed before removing the topography echo is 3.6

, And after removal 1.5

, The wind speed of PCL 1300 was improved by more than 50%. At the altitude of the LDC,

The effect of improvement was not clear.

From the improvement process using proven terrain echo cancellation, we have selected cases where terrestrial echoes appeared on the PCL 1300 based on the time of the radiosondi reconnaissance, and the terrain echo cancellation through the RMSE on the wind speed before and after the PCL 1300 The results of this study are as follows. Up to 8.3 due to terrain echo

, And after the improvement, the maximum error was 2.6

Respectively. The case where the improvement effect was the largest was 86.6% error improvement. Since the wind speed error of the wind profiler due to the terrain echo is proportional to the actual wind speed, if the correct error is improved for the terrain echo, the improvement effect on the wind speed of the wind profiler is higher than that of the lower layer.

As shown in FIG. 8, the improvement effect of the PCL 1300 due to this characteristic is shown in FIG. 8 as the terrestrial echo is clearly generated at a wide altitude of the upper layer. In FIG. 6, the RMSE of the PCL 1300 is calculated for each altitude. Despite the occurrence of topographical echoes in the lower layer of less than 1 km,

. In the Doppler spectrum, not only the terrestrial echo but also the atmospheric signal was clearly received, and the improvement effect of PCL 1300 was not significant. Topography by eco 12

The error of the wind speed which occurred up to 2

Respectively. The error of wind direction due to topography echoes occurred up to about 50 °, but the error of wind direction due to removal of topography echoes was reduced to less than 5 °. The error of the lower wind direction was not different from before and after irrespective of the removal of the topography echo. The error of the lower wind direction is more affected by the sign than the size of the east-west component wind vector and the north-south component wind vector. The sign of the wind - vector and the inter - component wind - vector of the lower layer East - West component is stronger than that of the upper layer due to the influence of the earth 's surface. With this feature, the lower wind speed error is small, but the wind direction error is large. Also, when the wind speed of PCL 1300 was overestimated, it was not affected by the topography echo.

As a result, the wind speed of the PCL 1300 was improved by 68.4%, and the correlation with the radiosonde wind speed was improved from 0.58 to 0.97. 9A, the wind speed of the PCL 1300 before the improvement is 15

The radial sonde 's wind speed and linear distribution. 15-25

In Fig. 9 (b), the terrestrial echo cancellation results in a coincidence with the wind speed of the radio sonde. The east - west wind vector of PCL 1300 was improved by 69.4%, and the correlation with radio - sonde was improved from 0.62 to 0.98. The east - west wind vector of PCL 1300 showed similar characteristics to wind speed. 12

Of the total radiosonde and 12 ~ 25

Of the total. The overestimation of PCL 1300 for east - west component wind vectors has been improved significantly by topographic echo cancellation. The inter - component wind vector of PCL 1300 improved by 32.2%, and the correlation with radio - sonde improved from 0.85 to 0.94. The north - south component wind vector of PCL 1300 was smaller than the east - west component wind vector.

Based on the results of this study, the hardware observation accuracy of PCL 1300 of Kangwon Provincial Meteorological Administration is about 2.0

Respectively. Weak 6.0 before improvement

It is difficult to judge the observation error by the hardware error of the wind profiler. The upper wind vector is underestimated due to the contamination of the data by terrain echo in the signal processing stage. The PCL 1300 is not receiving a wait signal, but is mistaken for a terrain echo as a wait signal. In other words, in order to objectively evaluate the hardware observation accuracy of the PCL 1300, it is necessary to use an atmospheric signal with no environmental factors such as terrestrial echo, and a signal processing process is required in order to use it correctly in a numerical model or musical instrument observation.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention as defined in the appended claims. You will understand.

100: Doppler spectrum acquisition module
200: Ground Echo Cancellation Module
210: Analytical Point Determination Module
220: Analytical Point Removal Module
230: Interpolation module
300: signal determination module
400: Speed measurement module
500: Calculation module
S1: Doppler spectral collection step
S2: Ground echo cancellation phase
S2-1: Analysis point determination step
S2-2: Analysis point removal step
S2-3: interpolation step
S3: signal determination step
S4: Speed estimation step
S5: Calculation step

Claims (8)

A Doppler spectrum acquisition module for collecting weather observation information through a Doppler spectrum in a wind profiler;
A ground echo cancellation module for removing an atmospheric signal embedding phenomenon according to a terrain of the collected weather observation information through a fast Fourier transform;
A signal determining module for determining an actual waiting signal peak of the weather observation information from which the ground echo is removed;
A velocity estimation module for estimating a visual velocity of the vertical beam and the oblique beam based on the determined peak;
And a calculation module for calculating a wind vector of the east-west component (U), the north-south component (V) and the vertical component (W) according to the gaze speed. The method according to claim 1,
Wherein the terrestrial echo cancellation module includes an analysis point determination module for determining a fast Fourier transform analysis point around a DC line having a frequency or an average visual velocity of zero. 3. The method of claim 2,
Wherein the terrestrial echo cancellation module includes an analysis point removal module for removing the determined fast Fourier transform analysis point. The method of claim 3,
Wherein the terrestrial echo cancellation module comprises an interpolation module that interpolates using two conserved fast Fourier transform analysis points. A Doppler spectrum acquisition step of collecting weather observation information through a Doppler spectrum in a wind profiler;
A ground echo cancellation step of eliminating the atmospheric signal embedding phenomenon according to the terrain in the echo cancellation module through a fast Fourier transform;
A signal determination step of determining a peak of an actual standby signal in the signal determination module;
A velocity estimation step of estimating a line-of-sight velocity of the vertical beam and the oblique beam on the basis of the peak determined by the velocity estimation module;
Calculating a wind vector of the east-west component (U), the north-south component (V) and the vertical component (W) in the calculation module. 6. The method of claim 5,
Wherein the terrestrial echo cancellation step includes an analysis point determination step of determining a fast Fourier transform analysis point around a DC line having a frequency or an average visual velocity of zero in the analysis point determination module. Way. The method according to claim 6,
Wherein the terrestrial echo removing step includes an analyzing point removing step of removing the fast Fourier transform analysis point determined by the analysis point removing module. 8. The method of claim 7,
Wherein the terrestrial echo cancellation module comprises an interpolation step of interpolating using two adjacent fast Fourier transform analysis points stored in the interpolation module.

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